HK1196023B

HK1196023B - Austenitic stainless steel

Info

Publication number: HK1196023B
Application number: HK14109436.7A
Authority: HK
Inventors: 塞西尔．弗农．罗斯科
Original assignee: 新加坡商．联合管线亚太有限公司
Priority date: 2011-05-26
Filing date: 2012-05-24
Publication date: 2017-04-28

Description

Austenitic stainless steel

Background and technical field

The present invention relates to austenitic stainless steels.

Traditionally, 300 series austenitic stainless steels such as uns 30403 (304L) and uns 30453 (304 LN) have specified chemical compositions in weight percent as shown in table 1 herein:

TABLE 1

The above-mentioned conventional austenitic stainless steels have some drawbacks associated with their specific specification ranges. This can potentially lead to a lack of proper control of the chemical analysis during the melting stage, which is necessary to optimize the alloy properties to provide a good combination of mechanical strength properties and good corrosion resistance.

The mechanical properties obtained with alloys such as UNSS30403 and UNSS30453 are not optimized and are relatively low compared to other common stainless steel types such as 22Cr duplex stainless steels, 25Cr duplex and 25Cr super duplex stainless steels. This is shown in table 2, which compares the performance of these conventional austenitic stainless steels with typical grades of 22Cr duplex, 25Cr duplex and 25Cr super duplex stainless steels.

TABLE 2

Mechanical properties of austenitic stainless steels

Mechanical properties of 22Cr duplex stainless steel

Mechanical properties of 25Cr duplex and 25Cr super duplex stainless steel

Note 2: the cited hardness values apply to the solution annealed state.

It is an object of the present invention to provide an austenitic stainless steel which alleviates at least one of the disadvantages of the prior art and/or to provide the public with a useful choice.

Disclosure of Invention

According to a first aspect of the present invention there is provided an austenitic stainless steel as claimed in claim 1.

Further preferred features can be found in the dependent claims.

It can be appreciated from the described embodiments that austenitic stainless steel (Cr-Ni-Mo-N) alloys include high levels of nitrogen with a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. In particular, the described embodiments also address the problem of relatively low mechanical strength properties of conventional 300 series austenitic stainless steels, such as UNSS30403 and UNSS30453, when compared to 22Cr duplex stainless steels and 25Cr duplex and 25Cr super duplex stainless steels.

Detailed Description

304LM4N

For ease of illustration, the first embodiment of the present invention is referred to as 304LM 4N. In general, the 304LM4N is a high strength austenitic stainless steel (Cr-Ni-Mo-N) alloy that includes a high level of nitrogen and is formulated to achieve a minimum specified (specified) pitting resistance equivalent (PittingResistenceEquivalent) PRE _N≧ 25, and preferably PRE_NNot less than 30. Root of herbaceous plantCalculate PRE according to the formula_N：

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

304LM4N high strength austenitic stainless steel has a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance.

The chemical composition of the 304LM4N high strength austenitic stainless steel is selective and characterized by an alloy of the following chemical elements in weight (wt%) percentages: 0.030wt% C (carbon) max, 2.00wt% Mn (manganese) max, 0.030wt% P (phosphorus) max, 0.010wt% S (sulfur) max, 0.75wt% Si (silicon) max, 17.50wt% Cr (chromium) -20.00 wt% Cr, 8.00wt% Ni (nickel) -12.00 wt% Ni, 2.00wt% Mo (molybdenum) max, and 0.40wt% N (nitrogen) -0.70 wt% N.

The 304LM4N stainless steel also includes primarily Fe (iron) as the remainder, and may also contain very small amounts of other elements, such as 0.010wt% B (boron) max, 0.10wt% Ce (cerium) max, 0.050wt% Al (aluminum) max, 0.01wt% Ca (calcium) max and/or 0.01wt% Mg (magnesium) max, as well as other impurities typically present at residual levels.

The chemical composition of 304LM4N stainless steel is optimized during the melting phase to primarily ensure that the base material has an austenitic microstructure after solution heat treatment, which is typically performed in the range of 1100 degrees celsius to 1250 degrees celsius, followed by water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. Thus, 304LM4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures, while achieving excellent toughness at ambient and low temperatures. The chemical composition of the high strength austenitic stainless steel is adjusted to reach PRE in view of 304LM4N _NNot less than 25, but preferably PRE_NThe fact that it is not less than 30,this ensures that the material has good general corrosion resistance and local corrosion (pitting and crevice corrosion) resistance also in a wide range of processing environments. The 304LM4N stainless steel also has improved stress corrosion cracking resistance compared to conventional austenitic stainless steels such as UNSS30403 and UNSS30453 in chloride containing environments.

It has been determined that the optimal chemical composition range for 304LM4N stainless steel is carefully selected to include the following weight percentages of chemical elements based on the first embodiment:

carbon (C)

The carbon content of the 304LM4N stainless steel is ≦ 0.030wt% C (i.e., 0.030wt% C maximum). Preferably, the carbon content should be ≥ 0.020wt% C and ≤ 0.030wt% C and more preferably ≤ 0.025wt% C.

Manganese (Mn)

The 304LM4N stainless steel of the first embodiment may have two variations: low manganese or high manganese.

For low manganese alloys, the manganese content of the 304LM4N stainless steel is less than or equal to 2.0wt% Mn. Preferably, the range is 1.0wt% or more and 2.0wt% or less of Mn, and more preferably 1.20wt% or more and 1.50wt% or less of Mn. By this composition, an optimum ratio of Mn to N of ≦ 5.0 is achieved, and preferably ≧ 1.42 and ≦ 5.0. More preferably, the ratio is ≧ 1.42 and ≦ 3.75.

For high manganese alloys, the manganese content of the 304LM4N stainless steel is less than or equal to 4.0wt% Mn. Preferably, the manganese content is ≥ 2.0 wt.% Mn and ≤ 4.0 wt.% Mn, and more preferably the upper limit is ≤ 3.0 wt.% Mn. Even more preferably, the upper limit is 2.50 wt.% Mn. With this selected range, a Mn to N ratio of ≦ 10.0 is achieved, and preferably ≦ 2.85 and ≦ 10.0. More preferably, for high manganese alloys, the ratio of Mn to N is ≧ 2.85 and ≦ 7.50, and more preferably ≧ 2.85 and ≦ 6.25.

Phosphorus (P)

The phosphorus content of the 304LM4N stainless steel is controlled to be less than or equal to 0.030wt% P. Preferably, the 304LM4N alloy has ≦ 0.025wt% P and more preferably ≦ 0.020wt% P. Even more preferably, the alloy has ≦ 0.015wt% P and even further more preferably ≦ 0.010wt% P.

Sulfur (S)

The 304LM4N stainless steel of the first embodiment includes a sulfur content of 0.010wt% S or less. Preferably, the 304LM4N has 0.005wt% S or less and more preferably 0.003wt% S or less and even more preferably 0.001wt% S or less.

Oxygen (O)

The oxygen content of the 304LM4N stainless steel is controlled to be as low as possible, and in the first embodiment, the 304LM4N has ≦ 0.070wt% O. Preferably, the 304LM4N alloy has 0.050wt% O or less and more preferably 0.030wt% O or less. Even more preferably, the alloy has 0.010 wt.% O or less and even further more preferably 0.005 wt.% O or less.

Silicon (Si)

The silicon content of the 304LM4N stainless steel is less than or equal to 0.75wt% Si. Preferably, the alloy has ≥ 0.25wt% Si and ≤ 0.75wt% Si. More preferably, the range is 0.40wt% Si or more and 0.60wt% Si or less. However, for certain higher temperature applications where improved oxidation resistance is desired, the silicon content may be 0.75 wt.% Si or more and 2.00 wt.% Si or less.

Chromium (Cr)

The chromium content of the 304LM4N stainless steel of the first embodiment is more than or equal to 17.50wt% Cr and less than or equal to 20.00wt% Cr. Preferably, the alloy has ≧ 18.25wt% Cr.

Nickel (Ni)

The nickel content of the 304LM4N stainless steel is more than or equal to 8.00wt% of Ni and less than or equal to 12.00wt% of Ni. Preferably, the upper limit of Ni of the alloy is 11wt% Ni or less and more preferably 10wt% Ni or less.

Molybdenum (Mo)

The molybdenum content of the 304LM4N stainless steel alloy is 2.00wt% Mo or less, but preferably 0.50wt% Mo or more and 2.00wt% Mo or less. More preferably, the lower limit of Mo is 1.0wt% or more.

Nitrogen (N)

The nitrogen content of the 304LM4N stainless steel is 0.70wt% N or less, but is preferably 0.40wt% N or more and 0.70wt% N or less. More preferably, the 304LM4N alloy has ≥ 0.40wt% N and ≤ 0.60wt% N, and even more preferably ≥ 0.45wt% N and ≤ 0.55wt% N.

PRE _N

Pitting Resistance Equivalent (PRE)_N) Using this formula to calculate:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

the 304LM4N stainless steel is formulated to have the following composition:

(i) The chromium content is more than or equal to 17.50wt% Cr and less than or equal to 20.00wt% Cr, but preferably more than or equal to 18.25wt% Cr;

(ii) the molybdenum content is 2.00wt% or less, but preferably 0.50wt% or more and 2.00wt% or less, and more preferably 1.0wt% or more;

(iii) the nitrogen content is 0.70wt% N or less, but preferably 0.40wt% N or more and 0.70wt% N or less, and more preferably 0.40wt% N or more and 0.60wt% N or less, and even more preferably 0.45wt% N or more and 0.55wt% N or less.

The 304LM4N stainless steel achieves PRE by high levels of nitrogen_N≧ 25, and preferably PRE_NNot less than 30. This ensures that the alloy has good general corrosion resistance and localized corrosion (pitting and crevice corrosion) resistance in a wide range of processing environments. The 304LM4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS30403 and UNSS30453 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 304LM4N stainless steel was optimized during the melting phase to ensure the properties according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of the equivalent weights is in the range of > 0.40 and < 1.05Preferably, however, > 0.45 and < 0.95, in order to obtain mainly an austenitic microstructure of the base material after solution heat treatment, which is typically carried out in the range 1100-1250 deg.c, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

304LM4N stainless steel also has a majority of iron (Fe) as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium, and/or magnesium, in the following weight percentages:

boron (B)

304LM4N stainless steel may not have boron intentionally added to the alloy, so for mills that are unwilling to intentionally add boron to heats, the boron level is typically ≧ 0.0001wt% B and ≦ 0.0006wt% B. Alternatively, 304LM4N stainless steel can be made to explicitly include ≦ 0.010wt% B. Preferably, the boron is in the range ≥ 0.001wt% B and ≤ 0.010wt% B, more preferably ≥ 0.0015wt% B and ≤ 0.0035wt% B. In other words, boron is added exclusively during stainless steel production, but is controlled to achieve this level.

Cerium (Ce)

The 304LM4N stainless steel of the first embodiment may also include 0.10 wt.% Ce, but is preferably 0.01 wt.% Ce and 0.10 wt.% Ce. More preferably, the amount of cerium is 0.03 wt.% or more and 0.08 wt.% or less of Ce. If the stainless steel contains cerium, it may also contain other rare metals (REM) such as lanthanum, as REM is typically supplied to stainless steel manufacturers as Mischmetal (Mischmetal). It should be noted that the rare earth metals can be utilized alone, or together as mischmetal, which provides a total amount of REM that meets the Ce levels specified herein.

Aluminum (Al)

The 304LM4N stainless steel of the first embodiment may also include 0.050 wt.% Al or less, but is preferably 0.005 wt.% Al and 0.050 wt.% Al or less, and more preferably 0.010 wt.% Al and 0.030 wt.% Al or less.

Calcium (Ca)/magnesium (Mg)

The 304LM4N stainless steel may also include 0.010wt% Ca and/or Mg. Preferably, the stainless steel may have ≥ 0.001wt% Ca and/or Mg, and ≤ 0.010wt% Ca and/or Mg, and more preferably ≥ 0.001wt% Ca and/or Mg, and ≤ 0.005wt% Ca and/or Mg, and other impurities typically present at residual levels.

In accordance with the above characteristics, 304LM4N stainless steel has a minimum yield strength of 55ksi or 380MPa for the forged plate. More preferably, a minimum yield strength of 62ksi or 430MPa can be achieved for the forged plate. The cast plate had a minimum yield strength of 41ksi or 280 MPa. More preferably a minimum yield strength of 48ksi or 330MPa for the cast plate can be achieved. Based on the preferred strength values, the forging mechanical strength properties of 304LM4N stainless steel compared to the forging mechanical strength properties of UNSS30403 of table 2, indicate that the minimum yield strength of 304LM4N stainless steel is likely to be 2.5 times higher than the minimum yield strength specified for UNSS 30403. Similarly, the forging mechanical strength properties of the novel and innovative 304LM4N stainless steel compared to those of uns 30453 in table 2 indicate that the minimum yield strength of 304LM4N stainless steel is likely to be 2.1 times higher than the minimum yield strength specified for uns 30453.

The 304LM4N stainless steel of the first embodiment had a minimum tensile strength of 102ksi or 700MPa for the forged plate. More preferably, a minimum tensile strength of 109ksi or 750MPa can be achieved for the forged plate. The cast plate had a minimum tensile strength of 95ksi or 650 MPa. More preferably, a minimum tensile strength of 102ksi or 700MPa can be achieved for the cast plate. Based on preferred values, the forging mechanical strength properties of the novel and innovative 304LM4N stainless steel compared to the forging mechanical strength properties of uns 30403 in table 2, show that the minimum tensile strength of 304LM4N stainless steel is more than 1.5 times higher than the minimum tensile strength specified for uns 30403. Likewise, the forging mechanical strength properties of the novel and innovative 304LM4N austenitic stainless steel compared to those of UNSS30453 in table 2 indicate that the minimum tensile strength of the 304LM4N stainless steel may be 1.45 times higher than the minimum tensile strength specified for uns 30453. Indeed, if the forging mechanical strength properties of the novel and innovative 304LM4N stainless steel are compared to the forging mechanical strength properties of the 22Cr duplex stainless steel in table 2, it can be shown that the minimum tensile strength of the 304LM4N stainless steel is around 1.2 times higher than the minimum tensile strength specified for S31803, and is similar to the minimum tensile strength specified for the 25Cr super duplex stainless steel. Thus, the minimum mechanical strength properties of the 304LM4N stainless steel have been significantly improved compared to conventional austenitic stainless steels, such as UNSS30403 and UNSS30453, and the tensile strength properties are superior to those specified for 22Cr duplex stainless steels and similar to those specified for 25Cr super duplex stainless steels.

This means that applications using forged 304LM4N stainless steel can often be designed with reduced wall thickness, thus, when specifying 304LM4N stainless steel, significant weight savings will result due to the potentially significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as UNSS30403 and UNSS 30453. In fact, the minimum allowable design stress for forged 304LM4N stainless steel may be higher than the minimum allowable design stress for 22Cr duplex stainless steel, and similar to 25Cr super duplex stainless steel.

For certain applications, other variants of 304LM4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 304LM4N stainless steel is selective and characterized by an alloy of chemical composition in weight percent:

copper (Cu)

The copper content of the 304LM4N stainless steel is ≦ 1.50wt% Cu, but preferably ≦ 0.50wt% Cu and ≦ 1.50wt% Cu, and more preferably ≦ 1.00wt% Cu for the lower copper range alloys. For higher copper range alloys, the copper content may include ≦ 3.50wt% Cu, but preferably ≦ 1.50wt% Cu and ≦ 3.50wt% Cu and more preferably ≦ 2.50wt% Cu.

Copper may be added alone or in conjunction with tungsten, vanadium, titanium and/or niobium plus tantalum, in all various combinations of these elements, to further enhance the overall corrosion performance of the alloy. Copper is expensive and therefore is purposefully limited to optimize the economics of the alloy while at the same time optimizing the ductility, toughness and corrosion performance of the alloy.

Tungsten (W)

The tungsten content of the 304LM4N stainless steel is ≦ 2.00wt% W, but preferably ≦ 0.50wt% W and ≦ 1.00wt% W, and more preferably ≦ 0.75wt% W. For the 304LM4N stainless steel tungsten containing variant, the pitting resistance equivalent weight was calculated using the formula:

PRE_NW=%Cr+[3.3×%(Mo+W)]+(16×%N)。

this tungsten-containing variant of 304LM4N stainless steel was specifically formulated to have the following composition:

(iii) the nitrogen content is 0.70wt% N or less, but preferably 0.40wt% N or more and 0.70wt% N or less, and more preferably 0.40wt% N or more and 0.60wt% N or less, and even more preferably 0.45wt% N or more and 0.55wt% N or less; and

(iv) the tungsten content is ≦ 2.00wt% W, but preferably ≦ 0.50wt% W and ≦ 1.00wt% W and more preferably ≦ 0.75wt% W.

The tungsten containing variant of 304LM4N stainless steel has a high specified level of nitrogen and PRE_NWNot less than 27, but preferably PRE_NWIs more than or equal to 32. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion. Tungsten can beEither alone or in combination with the elements copper, vanadium, titanium and/or niobium plus tantalum, in all of the various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is extremely expensive and is therefore purposefully limited to optimize the economics of the alloy while at the same time optimizing the ductility, toughness and corrosion performance of the alloy.

Vanadium (V)

The vanadium content of the 304LM4N stainless steel is ≦ 0.50wt% V, but preferably ≦ 0.10wt% V and ≦ 0.50wt% V and more preferably ≦ 0.30wt% V. Vanadium may be added alone or in combination with copper, tungsten, titanium and/or niobium plus tantalum, in all of various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is expensive and is therefore purposefully limited to optimize the economics of the alloy while at the same time optimizing the ductility, toughness and corrosion performance of the alloy.

Carbon (C)

For certain applications, other variants of 304LM4N high strength austenitic stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. Specifically, the carbon content of the 304LM4N stainless steel may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C. These particular variants of 304LM4N high strength austenitic stainless steel may be considered as 304HM4N or 304M4N versions, respectively.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilized variants of 304HM4N or 304M4N stainless steel are desirable, which have been specifically formulated to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C, or ≥ 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They include a stabilized version of titanium called 304HM4NTi or 304M4NTi, in contrast to the typical 304LM4N stainless steel version.

The titanium content was controlled according to the following formula:

respectively Ti4 xc minimum, 0.70wt% Ti maximum, or Ti5 xc minimum, 0.70wt% Ti maximum, to form a titanium stabilized derivative of the alloy.

(ii) There are also niobium stabilized versions of 304HM4NNb or 304M4NNb, where the niobium content is controlled according to the following formula:

nb8 xc minimum, 1.0wt% Nb maximum, or Nb10 xc minimum, 1.0wt% Nb maximum, respectively, to form niobium stabilizing derivatives of the alloy.

(iii) In addition, other variations of the alloy can also be made to include niobium plus tantalum stabilized versions of 304HM4NNbTa or 304M4NNbTa, where the niobium plus tantalum content is controlled according to the following formula: nb + Ta8 XC minimum, 1.0wt% Nb + Ta maximum, 0.10wt% Ta maximum, or Nb + Ta10 XC minimum, 1.0wt% Nb + Ta maximum, 0.10wt% Ta maximum.

Variations of titanium stabilization, niobium stabilization, and niobium plus tantalum stabilization of the alloy may be subjected to a stabilization heat treatment at a temperature below the initial solution heat treatment temperature. Titanium and/or niobium plus tantalum may be added alone or in combination with the elements copper, tungsten and vanadium, in all of the various combinations, to optimize the alloy for certain applications requiring higher carbon content. These alloying elements may be utilized alone or in all of the various combinations of these elements to tailor the stainless steel for a particular application and to further enhance the overall corrosion performance of the alloy.

Forged and cast plates of 304LM4N stainless steel, as well as other variations and embodiments discussed herein, are typically provided under solution annealed conditions. However, welds of manufactured parts, assemblies, and structures are typically provided in as-welded conditions, provided that appropriate welding process assessments (weldprodurequalifications) have passed prequalification in accordance with respective standards and specifications. Forged plates for particular applications may also be provided in cold worked conditions.

Proposed effects of alloying elements and their compositions

One of the most important properties of stainless steels is generally their corrosion resistance, not corrosion resistance, which they may find little industrial application, since in many instances their mechanical properties may be opposed by lower cost materials.

Changes in the alloying element content are desirable to establish attractive corrosion resistance characteristics, which can have a significant impact on the metallurgy of stainless steels. This can therefore affect the physical and mechanical characteristics that can be used in practice. The establishment of certain desirable properties such as high strength, ductility and toughness relies on microstructure control, which may limit the achievable corrosion resistance. Alloying elements in solid solution, manganese sulfide inclusions and phase regions that can precipitate and give depleted zones of chromium and molybdenum around the precipitates can have a significant impact on the microstructure, mechanical properties of the alloy and the maintenance or destruction of passivity.

Therefore, it is very challenging to obtain an optimal composition of elements in the alloy such that the alloy has good mechanical strength properties, excellent ductility and toughness, as well as good weldability and resistance to general and localized corrosion. This is particularly true given the complex array of metallurgical variables that make up the alloy composition and how each variable affects the passivity, microstructure, and mechanical properties. It is also necessary to incorporate this knowledge into new alloy development projects, manufacturing and heat treatment plans. In the following paragraphs, it is discussed how the individual elements of the alloy are optimized to achieve the above properties.

Action of chromium

Stainless steels derive their passivating properties from chromium-containing alloys. The chromium-containing alloyed iron shifts the initial passivation potential in the positive (noble) direction. This in turn leads to an expansion of the passivation potential range and a reduction of the passivation current density i_pass. Increasing chromium content of stainless steel in chloride solution increases pittingBit E_pThereby extending the passivation potential range. Chromium thus increases the resistance to local corrosion (pitting and crevice corrosion) as well as general corrosion. The increase in the ferrite forming element chromium may be balanced by the addition of nickel and other austenite forming elements such as nitrogen, carbon and manganese to maintain primarily the austenite microstructure. However, it has been found that chromium together with molybdenum and silicon may increase the tendency of intermetallic phases and unwanted precipitates to precipitate. Thus, in practice, the level of chromium may be increased to a maximum without increasing the rate of formation of intermetallic phases in thick portions, which in turn may lead to a reduction in the ductility, toughness and corrosion properties of the alloy. The 304LM4N stainless steel has been specially formulated to have a chromium content of greater than or equal to 17.50wt% Cr and less than or equal to 20.00wt% Cr to achieve optimal results. Preferably, the chromium content is 18.25wt% or more Cr.

Action of Nickel

It has been found that nickel causes pitting potential E_pMoving in the positive direction, thus enlarging the passivation potential range and also reducing the passivation current density i_pass. The nickel thus increases the localized corrosion resistance and general corrosion resistance of the austenitic stainless steel. Nickel is the austenite forming element and the levels of nickel, manganese, carbon and nitrogen are optimized in the first embodiment to balance the ferrite forming elements such as chromium, molybdenum and silicon to maintain primarily the austenite microstructure. Nickel is extremely expensive and therefore purposely limited to optimize the economics of the alloy, while optimizing the ductility, toughness and corrosion properties of the alloy. The 304LM4N stainless steel has been specially formulated to have a nickel content of 8.00wt% Ni and 12.00wt% Ni, but preferably 11.00wt% Ni and more preferably 10.00wt% Ni.

Action of molybdenum

At certain levels of chromium content, molybdenum has been found to have a strong beneficial effect on the passivation of austenitic stainless steels. The addition of molybdenum shifts the pitting potential in the positive direction, thus expanding the passivation potential range. Increasing the molybdenum content also decreases i_maxThus, molybdenum improves the general corrosion resistance and the local corrosion resistance (pitting and crevice corrosion) in a chloride environment. Molybdenum is also mentioned Resistance to chloride stress corrosion cracking in chloride-containing environments is increased. Molybdenum is a ferrite forming element and the level of molybdenum is optimized along with the levels of chromium and silicon to balance austenite forming elements such as nickel, manganese, carbon and nitrogen to primarily maintain the austenite microstructure. However, molybdenum, along with chromium and silicon, may increase the tendency of intermetallic phases and unwanted precipitates to precipitate. At higher levels of molybdenum, it is possible to undergo macro-segregation, especially in castings and primary products, which may further increase the kinetics of such intermetallic phases and detrimental precipitates. Sometimes other elements such as tungsten may be introduced into the hot mass to reduce the relative amount of molybdenum required for the alloy. Thus, in particular, without increasing the rate of formation of intermetallic phases in thick portions, the level of molybdenum can be increased to a maximum, which in turn can lead to a reduction in the ductility, toughness and corrosion properties of the alloy. The 304LM4N stainless steel has been specially formulated to have a molybdenum content of 2.00wt% Mo or less, but preferably 0.05wt% Mo or more and 2.00wt% Mo or less and more preferably 1.0wt% Mo or more.

Action of Nitrogen

In the first (and subsequent examples), one of the most significant increases in the localized corrosion performance of austenitic stainless steels was obtained by increasing the level of nitrogen. Nitrogen raises pitting potential E _pThereby extending the passivation potential range. The nitrogen modifies the passivation protection film to improve protection against passivation damage. Have reported that¹High nitrogen concentrations were found on the metal side of the metal-passivation film interface using auger electron spectroscopy. Nitrogen and carbon are extremely strong austenite forming elements. Likewise, manganese and nickel are also austenite forming elements, although to a lesser extent. Austenite forming elements such as nitrogen and carbon, and manganese and nickel are all optimized in these embodiments to balance the ferrite forming elements such as chromium, molybdenum and silicon to primarily maintain the austenite microstructure. Thus, nitrogen indirectly limits the tendency to form intermetallic phases due to the relatively slow diffusion rate in austenite. Thus reducing the kinetics of intermetallic phase formation. Also, considering the fact that austenite has good nitrogen solubility, this means that during the welding cycleDuring which harmful deposits such as M are formed in the weld metal and heat affected zone of the weld₂X (carbonitride, nitride, boride, boronitride or borocarbide) and M₂₃C₆The probability of carbides decreases. The nitrogen in solid solution is primarily responsible for improving the mechanical strength properties of 304LM4N stainless steel while ensuring the austenitic microstructure to optimize the ductility, toughness and corrosion properties of the alloy. However, nitrogen has limited solubility in both the melting stage and in solid solution. 304LM4N stainless steel has been specially formulated to have a nitrogen content of 0.70wt% N or less, but preferably 0.40wt% N or more and 0.70wt% N or less, more preferably 0.40wt% N or more and 0.60wt% N or less, more preferably 0.45wt% N or more and 0.55wt% N or less.

Action of manganese

Manganese is an austenite forming element and the levels of manganese, nickel, carbon and nitrogen in the examples are all optimized to balance ferrite forming elements such as chromium, molybdenum and silicon to maintain primarily the austenite microstructure. Thus, higher levels of manganese indirectly allow for higher solubility of both carbon and nitrogen in both the melting stage and solid solution to reduce harmful precipitates such as M₂X (carbonitride, nitride, boride, boronitride or borocarbide) and M₂₃C₆The risk of carbides. Thus, increasing the concentration of manganese to a certain level to increase the solid solubility of nitrogen results in increased localized corrosion performance of the austenitic stainless steel. Manganese is also a more cost-effective element than nickel and can be used to a certain level to limit the amount of nickel utilized in the alloy. However, there are limits to the levels of manganese that can be successfully used, since manganese levels can lead to the formation of manganese sulfide inclusions, which are a favorable site for the onset of pitting corrosion, and thus have a detrimental effect on the local corrosion performance of austenitic stainless steels. Manganese also increases the tendency of intermetallic phases and harmful precipitates to precipitate. Thus, in particular, without increasing the rate of formation of intermetallic phases in thick portions, the level of violence can be increased to a maximum, which in turn can lead to a reduction in the ductility, toughness and corrosion properties of the alloy. The 304LM4N stainless steel has been specially formulated to have a manganese content of Mn not less than 1.00wt% and not more than 2.00wt% M n, but preferably has a manganese content of 1.20 wt.% Mn and 1.50 wt.% Mn. The manganese content may be controlled to ensure that the ratio of manganese to nitrogen is ≦ 5.0, but is preferably ≧ 1.42 and ≦ 5.0. More preferably, for alloys in the low manganese range, the ratio is ≧ 1.42 and ≦ 3.75. The manganese content may be characterized by: the alloy contains 2.0wt% or more and 4.0wt% or less Mn, but preferably 3.0wt% or less and more preferably 2.50wt% or less Mn, wherein the Mn to N ratio is 10.0 or less, but preferably 2.85 or more and 10.0 or less. More preferably the ratio is ≥ 2.85 and ≤ 7.50, even more preferably ≥ 2.85 and ≤ 6.25 for alloys in the high manganese range.

Action of Sulfur, oxygen and phosphorus

Impurities such as sulfur, oxygen and phosphorus may have a negative effect on the mechanical properties and the resistance to local corrosion (pitting and crevice corrosion) and general corrosion of austenitic stainless steels. This is because sulfur at a particular level, along with manganese, promotes the formation of manganese sulfide inclusions. In addition, oxygen at a particular level in conjunction with aluminum or silicon promotes oxide inclusions such as Al₂O₃Or SiO₂Is performed. These inclusions are favorable sites for the initiation of pitting and thus have a detrimental effect on the local corrosion performance, ductility and toughness of the austenitic stainless steel. Likewise, phosphorus promotes the formation of harmful precipitates, which are favorable sites for the onset of pitting corrosion, which have an adverse effect on the pitting and crevice corrosion resistance of the alloy, as well as its ductility and toughness. In addition, sulfur, oxygen and phosphorus have a detrimental effect on hot workability as well as sensitivity to hot and cold cracks (especially in castings and weld metals of weldments of austenitic stainless steels) in forged austenitic stainless steels. Oxygen at certain levels also causes porosity in austenitic stainless steel castings. This can create potential crack initiation sites within cast components that experience high cyclic loading. Thus, modern melting techniques such as arc melting, induction melting and vacuum oxygen decarburization or argon oxygen decarburization along with other secondary remelting techniques such as electroslag remelting or vacuum arc remelting and other refining techniques are utilized to ensure extremely low sulfur, oxygen and phosphorus contents, thereby improving hot workability of forged stainless steel and reducing hot cracking And sensitivity to cold cracking and reduction of porosity particularly in castings and in weld metals of weldments. Modern melting techniques also result in reduced levels of inclusions. This improves the cleanliness and hence the ductility and toughness and the overall corrosion performance of the austenitic stainless steel. Such 304LM4N stainless steels have been specially formulated to have a sulfur content of 0.010wt% S or less, but preferably have a sulfur content of 0.005wt% S or less and more preferably 0.003wt% S or less and even more preferably 0.001wt% S or less. The oxygen content is as low as possible and is controlled to 0.070 wt.% O, but preferably 0.050 wt.% O, and more preferably 0.030 wt.% O, and even more preferably 0.010 wt.% O, and even further more preferably 0.005 wt.% O. The phosphorus content is controlled to 0.030 wt.% P or less, but preferably 0.025 wt.% P or less, and more preferably 0.020 wt.% P or less, and even more preferably 0.015 wt.% P or less, and even further more preferably 0.010 wt.% P or less.

Action of silicon

Silicon shifts the pitting potential in the positive direction, thus expanding the passivation potential range. Silicon also improves the fluidity of the melt during the manufacture of stainless steel. As such, silicon improves the fluidity of the hot weld metal during the welding cycle. Silicon is a ferrite forming element and the level of silicon along with the levels of chromium and molybdenum are optimized to balance austenite forming elements such as nickel, manganese, carbon and nitrogen to primarily maintain the austenite microstructure. Silicon content in the range of 0.75wt% Si and 2.00wt% Si may improve oxidation resistance for higher temperature applications. However, silicon contents in excess of about 1.0wt% Si, along with chromium and molybdenum, can increase the tendency of intermetallic phases and unwanted precipitates to precipitate. Thus, in particular, without increasing the rate of formation of intermetallic phases in thick portions, it is possible to increase the level of silicon, which is at a maximum, which in turn may lead to a reduction in the ductility, toughness and corrosion properties of the alloy. This 304LM4N stainless steel has been specially formulated to have a silicon content ≦ 0.75wt% Si, but preferably ≦ 0.25wt% Si and ≦ 0.75wt% Si, and more preferably ≦ 0.40wt% Si and ≦ 0.60wt% Si. The silicon content may be characterized by: for special higher temperature applications where increased oxidation resistance is desired, the alloy contains 0.75 wt.% Si and 2.00 wt.% Si.

Action of carbon

Carbon and nitrogen are extremely strong austenite forming elements. Similarly, manganese and nickel are also austenite forming elements, although to a lesser extent. The levels of austenite forming elements such as carbon and nitrogen, and manganese and nickel are optimized to balance the ferrite forming elements such as chromium, molybdenum and silicon to primarily maintain the austenite microstructure. Thus, carbon indirectly limits the tendency to form intermetallic phases due to the relatively low diffusion rate in austenite. Thus, the kinetics of intermetallic phase formation are reduced. Likewise, in view of the fact that austenite has good solubility for carbon, this means that harmful precipitates such as M form in the weld metal and heat affected zone of the weld during the welding cycle₂X (carbonitride, nitride, boride, boronitride or borocarbide) and M₂₃C₆The probability of carbides decreases. Carbon and nitrogen in solid solution are primarily responsible for improving the mechanical strength properties of 304LM4N stainless steel while ensuring the austenitic microstructure to optimize ductility, toughness and corrosion performance of the alloy. The carbon content is generally limited to a maximum of 0.030wt% C to optimize performance, but also to ensure good hot workability of the forged austenitic stainless steel. This 304LM4N stainless steel has been specially formulated to have a carbon content ≦ 0.030wt% Cmax, but preferably ≦ 0.020wt% C and ≦ 0.030wt% C and more preferably ≦ 0.025wt% C. In certain applications, where the higher carbon content is ≧ 0.040wt% C and < 0.10wt% C, but preferably ≦ 0.050wt% C or > 0.030wt% C and ≦ 0.08wt% C, but preferably < 0.040wt% C, these applications are satisfactory, the particular variant of 304LM4N stainless steel, i.e., 304HM4N or 304M4N, respectively, has also been formulated purposefully.

Effects of boron, cerium, aluminum, calcium and magnesium

The hot workability of stainless steel is improved by introducing discrete amounts of other elements such as boron or cerium. If the stainless steel contains cerium, it may also contain other rare metals (REM) such as lanthanum, as REM is usually supplied to stainless steel manufacturers as Mischmetal (Mischmetal). In general, for those who are unwilling to intentionally add boron to hot materialsThe typical residual level of boron present in stainless steel is 0.0001 wt.% B or more and 0.0006 wt.% B or less. The 304LM4N stainless steel can be manufactured without adding boron. Alternatively, the 304LM4N stainless steel can be made to explicitly have a boron content ≧ 0.001wt% B and ≦ 0.010wt% B, but preferably ≧ 0.0015wt% B and ≦ 0.0035wt% B. The beneficial effect of boron on hot workability results from ensuring that boron remains in solid solution. Therefore, it is necessary to ensure that harmful precipitates such as M₂X (boride, boronitride, or borocarbide) does not precipitate in the microstructure at the grain boundaries of the matrix material during the manufacturing and heat treatment cycles or in the as-welded weld metal and heat affected zone of the weld during the welding cycle.

The 304LM4N stainless steel can be made to specifically have a cerium content of 0.10 wt.% Ce, but preferably 0.01 wt.% Ce and 0.10 wt.% Ce, and more preferably 0.03 wt.% Ce and 0.08 wt.% Ce. Cerium forms cerium oxysulfides in stainless steel to improve hot workability, but at a certain level, this does not adversely affect the corrosion resistance of the material. In certain applications, higher carbon contents of ≥ 0.04 wt.% C and ≤ 0.10 wt.% C, but preferably ≤ 0.050 wt.% C, or ≥ 0.030 wt.% C and ≤ 0.08 wt.% C, but preferably ≤ 0.040 wt.% C are desirable, for which applications variants of the 304LM4N stainless steel can also be manufactured with a boron content ≤ 0.010 wt.% B, but preferably ≥ 0.001 wt.% B and ≤ 0.010 wt.% B, and more preferably ≥ 0.0015 wt.% B and ≤ 0.0035 wt.% B, or a cerium content ≤ 0.10 wt.% Ce, but preferably ≥ 0.01 wt.% Ce and ≤ 0.10 wt.% Ce, and more preferably ≥ 0.03 wt.% Ce and ≤ 0.08 wt.% Ce. It should be noted that the rare earth metals can be utilized alone or as mischmetal providing a total amount of REM that meets the Ce levels specified herein. The 304LM4N stainless steel may be manufactured to specifically contain aluminum, calcium, and/or magnesium. These elements may be added to the deoxidized and/or desulfurized stainless steel to improve the cleanliness and hot workability of the material. In the relevant case, the aluminum content is generally controlled to have an aluminum content of 0.050 wt.% Al or less, but preferably 0.005 wt.% Al and 0.050 wt.% Al or less, and more preferably 0.010 wt.% Al and 0.030 wt.% Al or less to suppress precipitation of nitrides. Similarly, the calcium and/or magnesium content is typically controlled to have a Ca and/or Mg content of 0.010wt% Ca and/or Mg or less, but preferably 0.001wt% Ca and/or Mg and 0.010wt% Ca and/or Mg or less, and more preferably 0.001wt% Ca and/or Mg and 0.005wt% Ca and/or Mg or less to limit the amount of slag formation in the melt.

Other variants

For certain applications, other variants of 304LM4N stainless steel may be formulated to be manufactured to include specific levels of other alloying elements such as copper, tungsten, and vanadium. Similarly, in certain applications, where higher carbon contents of ≧ 0.040 wt.% C and < 0.10 wt.% C, but preferably ≦ 0.050 wt.% C or > 0.030 wt.% C and ≦ 0.08 wt.% C, but preferably < 0.040 wt.% C are desirable, particular variants of 304LM4N stainless steel, i.e., 304HM4N or 304M4N, respectively, have been intentionally formulated. Furthermore, in certain applications where higher carbon content ≧ 0.040 wt.% C and < 0.10 wt.% C, but preferably ≦ 0.050 wt.% C or > 0.030 wt.% C and ≦ 0.08 wt.% C, but preferably < 0.040 wt.% C is desirable, particular variations of 304HM4N or 304M4N stainless steel, i.e., titanium stabilized 304HM4NTi or 304M4NTi, niobium stabilized 304HM4NNb or 304M4NNb, and niobium plus tantalum stabilized 304HM4NNbTa or 304M4NNbTa, have also been intentionally formulated. Variations of titanium stabilization, niobium stabilization, and niobium plus tantalum stabilization of the alloy may be subjected to a stabilization heat treatment at a temperature below the initial solution heat treatment temperature. Titanium and/or niobium plus tantalum may be added alone or in combination with the elements copper, tungsten and vanadium, in all of the various combinations, to optimize the alloy for certain applications where higher carbon content is desired. These alloying elements may be utilized alone or in all of the various combinations of these elements to tailor the stainless steel for a particular application and to further enhance the overall corrosion performance of the alloy.

Action of copper

The beneficial effect of copper addition on the corrosion resistance of stainless steel in non-oxidizing media is well known. If about 0.50wt% copper is added, both the active dissolution rate in boiling hydrochloric acid and the crevice corrosion loss in chloride solution are reduced. It has been found that with the addition of copper to 1.50wt% Cu, the general corrosion resistance in sulfuric acid is also improved². Copper as well as nickel, manganese, carbon and nitrogen are austenite forming elements. Thus, copper can improve the local corrosion and general corrosion performance of stainless steel. The levels of copper and other austenite forming elements are optimized to balance the ferrite forming elements such as chromium, molybdenum and silicon to primarily maintain the austenite microstructure. Thus, the 304LM4N stainless steel variant has been specifically selected to have a copper content ≦ 1.50wt% Cu, but preferably ≦ 0.50wt% Cu and ≦ 1.50wt% Cu, and more preferably ≦ 1.00wt% Cu for the lower copper range alloys. The copper content of 304LM4N may be characterized by: the alloy includes ≦ 3.50wt% Cu, but preferably ≦ 1.50wt% Cu and ≦ 3.50wt% Cu, and more preferably ≦ 2.50wt% Cu for the higher copper range alloys.

Copper may be added alone or in combination with the elements tungsten, vanadium, titanium and/or niobium plus tantalum, in all of the various combinations, to further enhance the overall corrosion performance of the alloy. Copper is expensive and is therefore purposely limited to optimize the economics of the alloy while at the same time optimizing the ductility, toughness and corrosion performance of the alloy.

Effect of tungsten

Tungsten and molybdenum occupy similar positions in the periodic table and have similar effectiveness and impact against localized corrosion (pitting and crevice corrosion) properties. At certain levels of chromium and molybdenum content, tungsten has a strong beneficial effect on the passivation of austenitic stainless steels. The addition of tungsten shifts the pitting potential in the more positive direction, thus expanding the passivation potential range. Increasing the tungsten content also reduces the passivation current density i_pass. Tungsten is present in the passivation layer and is adsorbed in the absence of the oxidation state modification³. In acidic chloride solutions, tungsten may pass directly from the metal to the passive film, through interaction with water and form insoluble WO₃Rather than by desorption followed by adsorption. The beneficial effect of tungsten in neutral chloride solution is explained by WO₃Interact with other oxides resulting in improved stability and improved bonding of the oxide layer to the base material.Tungsten improves the general corrosion resistance and the local corrosion resistance (pitting and crevice corrosion) in a chloride environment. Tungsten also improves resistance to chloride stress corrosion cracking in chloride-containing environments. Tungsten is a ferrite forming element and the levels of tungsten as well as chromium, molybdenum and silicon are optimized to balance austenite forming elements such as nickel, manganese, carbon and nitrogen to primarily maintain the austenite microstructure. However, tungsten, as well as chromium, molybdenum and silicon, may increase the tendency of intermetallic phases and unwanted precipitates to precipitate out. Thus, in practice, without increasing the rate of formation of intermetallic phases in thick portions, there is an increase in the maximum level of tungsten which in turn may lead to a decrease in the ductility, toughness and corrosion properties of the alloy. Thus, variants of 304LM4N stainless steel have been specifically formulated to have a tungsten content ≦ 2.00wt% W, but preferably ≦ 0.05wt% W and ≦ 1.00wt% W and more preferably ≦ 0.75wt% W. Tungsten may be added alone or together with copper, vanadium, titanium and/or niobium plus tantalum, in all of various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is extremely expensive and therefore purposefully limited to optimize the economics of the alloy, as well as the ductility, toughness and corrosion properties of the alloy.

Effect of vanadium

At certain levels of chromium and molybdenum content, vanadium has a strong beneficial effect on the passivation of austenitic stainless steels. The addition of vanadium shifts the pitting potential in the more positive direction, thus expanding the passivation potential range. Increasing the vanadium content also decreases i_maxVanadium and molybdenum thus improve the resistance to general corrosion and to local corrosion (pitting and crevice corrosion) in a chloride environment. Vanadium as well as molybdenum may also improve resistance to chloride stress corrosion cracking in chloride-containing environments. However, vanadium, as well as chromium, molybdenum and silicon, may increase the tendency of intermetallic phases and unwanted precipitates to precipitate out. Vanadium has the effect of forming harmful precipitates such as M₂X (carbonitride, nitride, boride, or borocarbide) and M₂₃C₆The strong tendency of carbides. Thus, in practice, there is a maximum of vanadium without increasing the rate of formation of intermetallic phases in thick portionsThe level may be increased. Vanadium also increases the tendency of such deleterious precipitates to form in the weld metal and heat affected zone of the weld during the welding cycle. Such intermetallic phases and deleterious precipitates may in turn lead to a reduction in the ductility, toughness and corrosion properties of the alloy. Thus, variants of 304LM4N stainless steel have been specially formulated to have a vanadium content ≦ 0.50wt% V, but preferably ≦ 0.10wt% V and ≦ 0.50wt% V and more preferably ≦ 0.30wt% V. Vanadium may be added alone or together with copper, tungsten, titanium and/or niobium plus tantalum, in all of various combinations, to further enhance the overall corrosion performance of the alloy. Vanadium is expensive and therefore purposely limited to optimize the economics of the alloy, as well as the ductility, toughness and corrosion properties of the alloy.

Effect of titanium, niobium and niobium plus tantalum

In certain applications, where higher carbon content ≧ 0.040wt% C and < 0.10wt% C, but preferably ≦ 0.050wt% C, or > 0.030wt% C and ≦ 0.08wt% C, but preferably < 0.040wt% C is desirable, a particular variant of 304HM4N or 304M4N stainless steel, i.e., 304HM4NTi or 304M4Nti, has been purposefully formulated to have a titanium content according to the following formula: respectively Ti4 xc min, 0.70wt% Ti max or Ti5 xc min, 0.70wt% Ti max, to have a titanium stabilizing derivative of the alloy. The titanium stabilized variant of the alloy may be given a stabilizing heat treatment at a temperature below the initial solution heat treatment temperature. Titanium may be added alone or in combination with copper, tungsten, vanadium and/or niobium plus tantalum in all of the various combinations to optimize ductility, toughness and corrosion performance of the alloy.

Likewise, in certain applications where higher carbon content ≧ 0.040wt% C and < 0.10wt% C, but preferably ≦ 0.050wt% C, or > 0.030wt% C and ≦ 0.08wt% C, but preferably < 0.040wt% C is desirable, particular variants of 304HM4N or 304M4N stainless steels have been purposefully formulated to have niobium content according to the following formula: nb8 xc min, 1.0wt% Nb max, or Nb10 xc min, 1.0wt% Nb max, respectively, to have a niobium stabilizing derivative of the alloy. In addition, other variations of the alloy were also made to include niobium plus tantalum stabilized versions of 304HM4NNbTa or 304M4NNbTa, where the niobium plus tantalum content was controlled according to the following formula: nb + Ta8 XCmin, 1.0wt% Nb + Ta max, 0.10wt% Ta max, or Nb + Ta10 XCmin, 1.0wt% Nb + Ta max, 0.10wt% Ta max. The niobium stabilized and niobium plus tantalum stabilized variants of the alloy may be given a stabilizing heat treatment at a temperature below the initial solution heat treatment temperature. Niobium and/or niobium plus tantalum may be added alone or in combination with the elements copper, tungsten, vanadium and/or titanium, in all of the various combinations, to optimize the ductility, toughness and corrosion properties of the alloy.

Pitting resistance equivalent

It is apparent from the foregoing that a plurality of alloying elements in stainless steel shift the pitting potential in the direction. These benefits are complex, interactive, and many attempts have been made to use empirical relationships of compositionally derived pitting resistance indicators. The most commonly accepted formula for calculating pitting resistance equivalent is:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

it is generally recognized that PREs of such alloys are described herein_NValues less than 40 may be classified as "austenitic" stainless steels. PRE of such alloys as described herein_NValues greater than or equal to 40 may be classified as "superaustenitic" stainless steels, reflecting their superior general and local corrosion resistance. This 304LM4N stainless steel has been specially formulated to have the following composition:

(i) the chromium content is more than or equal to 17.50wt% Cr and less than or equal to 20.00wt% Cr, but preferably more than or equal to 18.25wt% Cr,

(ii) the molybdenum content is 2.00wt% or less Mo, but preferably 0.50wt% or more Mo and 2.00wt% or less Mo and more preferably 1.0wt% or more Mo

The 304LM4N stainless steel has a high specified level of nitrogen and PRE _NNot less than 25, but preferably PRE_NNot less than 30. Thus, the 304LM4N stainless steel has a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. There is some preservation with respect to utilizing this formula in full isolation. The formula does not take into account the beneficial effects of other elements that improve pitting performance, such as tungsten. For the 304LM4N stainless steel variant containing tungsten, the pitting resistance equivalent weight was calculated using the formula: PRE_NW=%Cr+[3.3×%(Mo+W)]+ (16X% N). It is generally recognized that PREs of such alloys are described herein_NWValues less than 40 may be classified as "austenitic" stainless steels. And PRE as described herein_NWAlloys of the type having a value of 40 or greater may be classified as "superaustenitic" stainless steels, reflecting their superior general and localized corrosion resistance. This tungsten-containing variant of 304LM4N stainless steel has been specifically formulated to have the following composition:

(ii) the molybdenum content is 2.00wt% or less Mo, but preferably 0.50wt% or more Mo and 2.00wt% or less Mo and more preferably 1.0wt% or more Mo,

(iii) the nitrogen content is 0.70wt% N or less, but preferably 0.40wt% N or more and 0.70wt% N or less, more preferably 0.40wt% N or more and 0.60wt% N or less, and even more preferably 0.45wt% N or more and 0.55wt% N or less

The tungsten containing variant of 304LM4N stainless steel has a high specified level of nitrogen and PRE_NWNot less than 27, but preferably PRE_NWIs more than or equal to 32. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

Austenitic microstructure

The chemical composition of the 304LM4N stainless steel of the first embodiment is optimized during the melting phase to primarily ensure that the base material has an austenitic microstructure after solution heat treatment, typically in the range of 1100 to 1250 degrees celsius, followed by water quenching.

The microstructure of the 304LM4N base material under solution heat treatment conditions, as well as the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements, as described above, to primarily ensure that the alloy is austenitic.

The relative effectiveness of the elements to stabilize the ferrite and austenite phases may be based on their [ Cr ] s]And [ Ni]The equivalent weight. Schaeffler has been used⁴The proposed method for predicting the structure of a weld metal illustrates the use of [ Cr ]]And [ Ni ]Combined effects of equivalents. Schaeffler⁴The diagram applies strictly only to rapid casting and cooling of alloys such as welds or chilled castings (chillcasting). However, Schaeffler⁴The chart may also give an indication of the phase balance of the "parent" material. According to their [ Cr ]]And [ Ni]Their chemical composition, Schaeffler, expressed as equivalents⁴The structure of the stainless steel weld metal formed by rapid cooling is predicted. Schaeffler⁴The chart uses [ Cr ] according to the following formula]And [ Ni]Equivalent weight:

[ Cr ] equivalent = wt% Cr + wt% Mo +1.5 × wt% Si +0.5 × wt% Nb (1)

[ Ni ] equivalent = wt% Ni +30 × wt% C +0.5 × wt% Mn (2)

However, Schaeffler⁴The graph does not take into account the significant effect of nitrogen in stabilizing austenite. Thus, Schaeffler⁴Chart has been published by Delong⁵Modified to incorporate the important effects of nitrogen as an austenite forming element. Delong⁵Chart usage and Schaeffler⁴The same [ Cr ] used in the formula (1)]And (4) an equivalent formula. However, [ Ni ]]The equivalent weight has been corrected according to the following formula:

[ Ni ] equivalent = wt% Ni +30 × wt% (C + N) +0.5 × wt% Mn (3)

This Delong⁵The graph shows the ferrite content and the number of ferrites (ferritenember) of the Welding Research Committee (WRC) determined from the ferrite content determined from the magnetism. The difference between the ferrite number and the ferrite percentage (i.e. > 6% ferrite value) is related to the WRC calibration procedure and calibration curve used in the magnetic measurements. Schaeffler ⁴Chart and Delong⁵Modified Schaeffler⁴Comparison of the graphs shows that for a given [ Cr ]]Equivalent sum of [ Ni ]]Equivalent weight, Delong⁵The graph predicts a higher ferrite content (i.e., about 5% higher).

Schaeffler⁴Charts and DeLong⁵The graphs were developed primarily for welds and therefore are not strictly applied to "parent" materials. However, they do provide a good indication of the phases that may be present and give valuable information on the relative effects of different alloying elements.

Schoefer⁶It has been shown that Schaeffler can be used⁴The revised version of the chart describes the ferrite number in the casting. This has been achieved by transforming Schaeffler⁴The coordinate of the graph is converted to horizontal axis with ferrite number or ferrite volume percentage as ASTM A800/A800M-10⁷As used herein. The vertical axis is represented by [ Cr ]]Equivalent weight divided by [ Ni ]]Ratio of equivalents. Schoefer⁶Also corrects [ Cr ] according to the following formula]Equivalent factor and [ Ni]Equivalent factor:

[ Cr ] equivalent = wt% Cr +1.5 × wt% Si +1.4 × wt% Mo + wt% Nb-4.99 (4)

[ Ni ] equivalent = wt% Ni +30 × wt% C +0.5 × wt% Mn +26 × wt% (N-0.02) +2.77(5)

This also indicates that other elements as ferrite stabilizers may also influence [ Cr]Equivalent factor to that in Schoefer⁶The change (variation) is given in this equation employed. They include the following elements, which have been assigned respective ones [Cr]The equivalent factor, which may be related to the variants comprised in the alloys herein:

it has likewise been shown that other elements as austenite stabilizers may also influence [ Ni]Equivalent factor to that in Schoefer⁶The change is given in the equation employed. This includes the next element, which has been assigned the respective [ Ni ]]The equivalent factor, which may be related to the variants comprised in the alloys herein:

element [ Ni ] equivalent factor

Copper 0.44

However, ASTMA800/A800M-10⁷Specifying Schoefer⁶The graph applies only to stainless steel alloys containing alloying elements in weight percentages according to the following specified ranges:

CMnSiCrNiMoNbN

minimum 17.004.00

Maximum 0.202.002.0028.0013.004.001.000.20

From the foregoing, it can be concluded that the nitrogen content in 304LM4N stainless steel is 0.70wt% N or less, but preferably 0.40wt% N or more and 0.70wt% N or less, and more preferably 0.40wt% N or more and 0.60wt% N or less, and even more preferably 0.45wt% N or more and 0.55wt% N or less. This exceeds, for example, ASTMA800/A800M-10⁷Adopted Schoefer⁶Maximum limit of the graph. Nevertheless, Schoefer, where appropriate⁶The graph will give a relative comparison of the number of ferrites or the volume percent of ferrites present in the austenitic stainless steel with the higher nitrogen content.

Nitrogen and copper are extremely strong austenite forming elements. Similarly, manganese and nickel are also austenite forming elements, although to a lesser extent. The levels of austenite forming elements such as nitrogen and carbon, and manganese and nickel are optimized to balance the ferrite formElements such as chromium, molybdenum and silicon to maintain primarily an austenitic microstructure. Thus, nitrogen indirectly limits the tendency to form intermetallic phases, since the diffusion rate in austenite is relatively slow. Thus, the kinetics of intermetallic phase formation are reduced. Also, in view of the fact that austenite has good nitrogen solubility, this means that during the welding cycle, in the weld metal and heat affected zone of the weld, harmful precipitates such as M are formed₂X (carbonitride, nitride, boride, boronitride or borocarbide) and M₂₃C₆The probability of carbides decreases. As already discussed, other variations of stainless steel may also include elements such as tungsten, vanadium, titanium, tantalum, aluminum, and copper.

Thus, 304LM4N stainless steel has been specifically developed to primarily ensure that the microstructure of the base material under solution heat treated conditions and in the as-welded weld metal and heat affected zone of the weld is austenitic. This is controlled by optimizing the balance between austenite forming elements and ferrite forming elements. Thus, the chemical analysis of 304LM4N stainless steel was optimized during the melting phase to ensure that according to Schoefer ⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably ≧ 0.45 and < 0.95.

Thus, the 304LM4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures, while at the same time ensuring excellent toughness at ambient and low temperatures. In addition, the alloy can be manufactured and provided in a non-magnetic state.

Optimum chemical composition

In view of the foregoing, it has been determined that the optimal chemical composition range for 304LM4N stainless steel is selective and comprises, in weight percent:

(i) 0.030wt% C max, but preferably ≥ 0.020wt% C and ≤ 0.030wt% C and more preferably ≤ 0.025wt% C;

(ii) 2.0 wt.% Mn, but preferably 1.0 wt.% Mn and 2.0 wt.% Mn, and more preferably 1.20 wt.% Mn and 1.50 wt.% Mn, wherein the ratio of Mn to N is 5.0 and preferably 1.42 and 5.0 but more preferably 1.42 and 3.75 for lower manganese range alloys;

(iii) 0.030wt% P, but preferably 0.025wt% P and more preferably 0.020wt% P and even more preferably 0.015wt% P and even further more preferably 0.010wt% P;

(iv) 0.010wt% S or less, but preferably 0.005wt% S or less and more preferably 0.003wt% S or less, and even more preferably 0.001wt% S or less;

(v) 0.070wt% O, but preferably 0.050wt% O, but more preferably 0.030wt% O, and even more preferably 0.010wt% O, and even more preferably 0.005wt% O;

(vi) 0.75wt% or less of Si, but preferably 0.25wt% or more and 0.75wt% or less of Si, but more preferably 0.40wt% or more and 0.60wt% or less of Si;

(vii) 17.50wt% or more and 20.00wt% or less of Cr, but preferably 18.25wt% or more of Cr;

(viii) 8.00wt% or more and 12.00wt% or less of Ni, but preferably 11wt% or less and more preferably 10wt% or less of Ni;

(ix) 2.00wt% or less of Mo, but preferably 0.50wt% or more and 2.00wt% or less of Mo and more preferably 1.0wt% or more of Mo;

(x) 0.70wt% N or less, but preferably 0.40wt% N or more and 0.70wt% N or less and more preferably 0.40wt% N or more and 0.60wt% N or less and even more preferably 0.45wt% N or more and 0.55wt% N or less.

304LM4N stainless steel has a high specified level of nitrogen and PRE_NNot less than 25, but preferably PRE_NNot less than 30. The chemical composition of 304LM4N stainless steel was optimized during the melting phase to ensure the properties according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably ≧ 0.45 and < 0.95.

The 304LM4N stainless steel also contains primarily Fe as the remainder and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium, and/or magnesium and other impurities that may be present at residual levels. 304LM4N stainless steel can be manufactured without boron additions, with boron residual levels typically being 0.0001wt% B and 0.0006wt% B for plants that are not willing to intentionally add boron to the hot mass. Alternatively, the 304LM4N stainless steel can be made to explicitly have a boron content ≧ 0.001wt% B and ≦ 0.010wt% B, but preferably ≧ 0.0015wt% B and ≦ 0.0035wt% B. Cerium may be added with a cerium content of 0.10 wt.% or less, but preferably 0.01 wt.% or more and 0.10 wt.% or less, and more preferably 0.03 wt.% or more and 0.08 wt.% or less. If the stainless steel contains cerium, it may also contain other Rare Earth Metals (REM) such as lanthanum, as REM is usually supplied to stainless steel manufacturers as Mischmetal (Mischmetal). It should be noted that the rare earth metals can be utilized alone, or together as mischmetal, which provides a total amount of REM that meets the Ce levels specified herein. Aluminum may be added with an aluminum content of 0.050wt% Al or less, but is preferably 0.005wt% Al or more and 0.050wt% Al or less, and more preferably 0.010wt% Al or more and 0.030wt% Al or less. Calcium and/or magnesium may be added with a Ca and/or Mg content of 0.001 and 0.01wt% Ca and/or Mg but preferably 0.005wt% Ca and/or Mg.

From the foregoing, applications using forged 304LM4N stainless steel can often be designed with reduced wall thickness, and therefore, when specifying 304LM4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as UNSS30403 and UNSS 30453. In fact, the minimum allowable design stress for forged 304LM4N stainless steel is higher than the minimum allowable design stress for 22Cr duplex stainless steel and is similar to 25Cr super duplex stainless steel.

It should also be appreciated that if forged 304LM4N stainless steel were specified and utilized, this may result in an overall savings in manufacturing and construction costs, as thinner walled components may be designed that are easier to handle and require less manufacturing time. Thus, 304LM4N stainless steel may be utilized in a wide range of industrial applications requiring structural integrity and corrosion resistance, particularly for offshore and onshore oil and gas applications.

Forged 304LM4N stainless steel, which is widely used in various markets and industrial fields, such as for the upper pipe systems and welded (fabricated) modules of ships for Floating Liquefied Natural Gas (FLNG) offshore, is desirable, which in turn results in significant cost savings due to the significant weight savings and manufacturing time savings that can be achieved. Given the high mechanical strength properties and ductility of 304LM4N stainless steel, and its excellent toughness at ambient and low temperatures, they can also be specified and can be used in piping systems used in offshore and onshore applications, such as in marine FLNG vessels and onshore LNG plants.

In addition to 304LM4N austenitic stainless steel, this specification also presents a second embodiment referred to as 316LM 4N.

316LM4N

316LM4N high strength austenitic stainless steel contains high levels of nitrogen and specifies a pitting resistance equivalent PRE_NNot less than 30, but preferably PRE_NNot less than 35. Referred to as PRE_NThe pitting resistance equivalent weight of (c) is calculated according to the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

316LM4N stainless steel has been formulated to have a unique combination of high mechanical strength properties and excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. The chemical composition of 316LM4N stainless steel is selective and is characterized by an alloy of the following chemical elements in weight (wt) percentages: 0.030wt% Cmax, 2.00wt% Mn max, 0.030wt% Pmax, 0.010wt% Smax, 0.75wt% Si max, 16.00wt% Cr-18.00 wt% Cr, 10.00wt% Ni-14.00 wt% Ni, 2.00wt% Mo-4.00 wt% Mo, 0.40wt% N-0.70 wt% N.

316LM4N stainless steel also includes primarily Fe as the remainder, and may also contain very small amounts of other elements, such as 0.010wt% B max, 0.10wt% Ce max, 0.050wt% Al max, 0.01wt% Ca max, and/or 0.01wt% Al maxMaximum% Mg and other impurities typically present at residual levels. The chemical composition of 316LM4N stainless steel is optimized during the melting phase to primarily ensure that the base material has an austenitic microstructure after solution heat treatment, typically in the range of 1100 degrees celsius to 1250 degrees celsius, followed by water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. Thus, 316LM4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures while ensuring excellent toughness at ambient and low temperatures. Chemical analysis in view of 316LM4N stainless steel was adjusted to ensure PRE _NNot less than 30, but preferably PRE_NThe fact of ≧ 35 ensures that the material also has good general corrosion resistance and local corrosion resistance (pitting and crevice corrosion) in a wide range of processing environments. 316LM4N stainless steel also has improved resistance to stress corrosion cracking in chloride containing environments compared to conventional austenitic stainless steels such as uns 31603 and uns 31653.

It has been determined that the optimal chemical composition range for 316LM4N stainless steel is carefully selected to include the following weight percentages of chemical elements based on the second embodiment:

carbon (C)

The carbon content of 316LM4N stainless steel is 0.030wt% Cmax, but is preferably 0.020wt% C and 0.030wt% C and more preferably 0.025wt% C.

Manganese (Mn)

The 316LM4N stainless steel of the second embodiment can have two variations: low manganese or high manganese.

For low manganese alloys, the manganese content of the 316LM4N stainless steel is 2.0 wt.% Mn, but preferably 1.0 wt.% Mn and 2.0 wt.% Mn, and more preferably 1.20 wt.% Mn and 1.50 wt.% Mn. By this composition, an optimum ratio of Mn to N of ≦ 5.0 is achieved, and preferably ≧ 1.42 and ≦ 5.0. More preferably, the ratio is ≧ 1.42 and ≦ 3.75.

For high manganese alloys, the manganese content of 316LM4N is 4.0wt% Mn or less. Preferably, the manganese content is ≥ 2.0 wt.% Mn and ≤ 4.0 wt.% Mn, and more preferably the upper limit is ≤ 3.0 wt.% Mn. Even more preferably, the upper limit is 2.50 wt.% Mn. With these selected ranges, a Mn to N ratio of ≦ 10.0 is achieved, and preferably ≦ 2.85 and ≦ 10.0. More preferably, for high manganese alloys, the ratio of Mn to N is ≧ 2.85 and ≦ 7.50, and more preferably ≧ 2.85 and ≦ 6.25.

Phosphorus (P)

The phosphorus content of 316LM4N stainless steel is controlled to be less than or equal to 0.030wt% P. Preferably, the 316LM4N alloy has ≦ 0.025wt% P and more preferably ≦ 0.020wt% P. Even more preferably, the alloy has ≦ 0.015wt% P and even further more preferably ≦ 0.010wt% P.

Sulfur (S)

The sulfur content of the 316LM4N stainless steel is less than or equal to 0.010wt% S. Preferably, the 316LM4N has 0.005wt% S or less and more preferably 0.003wt% S or less and even more preferably 0.001wt% S or less.

Oxygen (O)

The oxygen content of the 316LM4N stainless steel is controlled to be as low as possible, and in a second embodiment, the 316LM4N has ≦ 0.070wt% O. Preferably, the 316LM4N has 0.050wt% O or less and more preferably 0.030wt% O or less. Even more preferably, the alloy has 0.010 wt.% O or less and even further more preferably 0.005 wt.% O or less.

Silicon (Si)

The silicon content of the 316LM4N stainless steel has 0.75wt% Si or less. Preferably, the alloy has ≥ 0.25wt% Si and ≤ 0.75wt% Si. More preferably, the range is 0.40wt% Si or more and 0.60wt% Si or less. However, for higher temperature applications where improved oxidation resistance is desired, the silicon content may be 0.75 wt.% Si or more and 2.00 wt.% Si or less.

Chromium (Cr)

The chromium content of the 316LM4N stainless steel of the first embodiment is more than or equal to 16.00wt% Cr and less than or equal to 18.00wt% Cr. Preferably, the alloy has ≧ 17.25wt% Cr.

Nickel (Ni)

The nickel content of the 316LM4N stainless steel is more than or equal to 10.00wt% of Ni and less than or equal to 14.00wt% of Ni. Preferably, the upper limit of Ni of the alloy is 13.00wt% Ni or less and more preferably 12.00wt% Ni or less.

Molybdenum (Mo)

The molybdenum content of the 316LM4N stainless steel is more than or equal to 2.00wt% of Mo and less than or equal to 4.00wt% of Mo. Preferably, the lower limit is 3.0wt% or more of Mo.

Nitrogen (N)

The nitrogen content of the 316LM4N stainless steel is 0.70wt% N or less, but is preferably 0.40wt% N or more and 0.70wt% N or less. More preferably, the 316LM4N has ≥ 0.40wt% N and ≤ 0.60wt% N, and even more preferably ≥ 0.45wt% N and ≤ 0.55wt% N.

PRE _N

Pitting Resistance Equivalent (PRE)_N) Using this formula to calculate:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

the 316LM4N stainless steel has been formulated to have the following composition:

(i) the chromium content is more than or equal to 16.00wt% Cr and less than or equal to 18.00wt% Cr, but preferably more than or equal to 17.25wt% Cr,

(ii) the molybdenum content is more than or equal to 2.00wt% Mo and less than or equal to 4.00wt% Mo, but preferably more than or equal to 3.0wt% Mo,

The 316LM4N stainless steel achieves PRE by high levels of nitrogen_NNot less than 30, but preferably PRE_NNot less than 35. This ensures that the alloy has good general corrosion resistance and localized corrosion (pitting and crevice corrosion) resistance in a wide range of processing environments. The 316LM4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as uns 31603 and uns 31653 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 316LM4N stainless steel was optimized in the melting phase to ensure the properties according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

316LM4N stainless steel also has a majority of Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium and/or magnesium, measured in weight percent, and the composition of these elements is the same as in 304LM 4N. In other words, the paragraphs on these elements of 304LM4N apply here as well.

The 316LM4N stainless steel according to the second embodiment had a minimum yield strength of 55ksi or 380MPa for the forged plate. More preferably, a minimum yield strength of 62ksi or 430MPa can be achieved for the forged plate. The cast plate had a minimum yield strength of 41ksi or 280 MPa. More preferably, a minimum yield strength of 48ksi or 330MPa can be achieved for the cast plate. Based on the preferred levels, the wrought mechanical strength properties of 316LM4N stainless steel compared to those of uns 31603 indicate that the minimum yield strength of 316LM4N stainless steel is likely to be 2.5 times higher than the minimum yield strength specified for uns 31603. Similarly, the forging mechanical strength properties of the novel and inventive 316LM4N stainless steel compared to the forging mechanical strength properties of uns 31653 may indicate that the minimum yield strength of 316LM4N stainless steel is 2.1 times higher than the minimum yield strength specified for uns 31653.

Stainless steel according to second embodiment 316LM4N has a minimum tensile strength of 102ksi or 700MPa for a forged plate. More preferably, a minimum tensile strength of 109ksi or 750MPa can be achieved for the forged plate. The cast plate had a minimum tensile strength of 95ksi or 650 MPa. More preferably, a minimum tensile strength of 102ksi or 700MPa can be achieved for the cast plate. Based on the preferred values, the forging mechanical strength properties of 316LM4N stainless steel compared to the forging mechanical strength properties of uns 31603 may indicate that the minimum tensile strength of 316LM4N stainless steel is more than 1.5 times higher than the minimum tensile strength specified for uns 31603. Similarly, the forging mechanical strength properties of 316LM4N stainless steel compared to the forging mechanical strength properties of uns 31653 may indicate that the minimum tensile strength of 316LM4N stainless steel may be 1.45 times higher than the minimum tensile strength specified for uns 31653. Indeed, if the forging mechanical strength properties of the novel and innovative 316LM4N stainless steel were compared to the forging mechanical strength properties of 22Cr duplex stainless steel, it could be shown that the minimum tensile strength of 316LM4N stainless steel may be around 1.2 times higher than the minimum tensile strength specified for S31803, and similar to the minimum tensile strength specified for 25Cr super duplex stainless steel. Thus, the minimum mechanical strength properties of 316LM4N stainless steel have been significantly improved compared to conventional austenitic stainless steels such as uns 31603 and uns 31653, and the tensile strength properties are superior to those specified for 22Cr duplex stainless steels and similar to those specified for 25Cr super duplex stainless steels.

This means that applications using forged 316LM4N stainless steel can often be designed with reduced wall thickness, thus, when specifying 316LM4N stainless steel, will result in significant weight savings due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as uns 31603 and uns 31653. In fact, the minimum allowable design stress for forged 316LM4N stainless steel may be higher than the minimum allowable design stress for 22Cr duplex stainless steel, and similar to 25Cr super duplex stainless steel.

For certain applications, other variants of 316LM4N stainless steel have been purposely formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 316LM4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 304LM 4N. In other words, the paragraphs regarding these elements of 304LM4N apply here also to 316LM 4N.

Tungsten (W)

The tungsten content of the 316LM4N stainless steel is ≦ 2.00wt% W, but preferably ≦ 0.50wt% W and ≦ 1.00wt% W and more preferably ≦ 0.75wt% W. For the tungsten containing variant of 316LM4N stainless steel, the pitting resistance equivalent weight was calculated using the formula:

PRE_NW=%Cr+[3.3×%(Mo+W)]+(16×%N)。

This tungsten-containing variant of 316LM4N stainless steel has been specifically formulated to have the following composition:

(i) the chromium content is more than or equal to 16.00wt% Cr and less than or equal to 18.00wt% Cr, but preferably more than or equal to 17.25wt% Cr;

(ii) the molybdenum content is more than or equal to 2.00wt% Mo and less than or equal to 4.00wt% Mo, but preferably more than or equal to 3.0wt% Mo;

(iii) the nitrogen content is 0.70wt% N or less, but preferably 0.40wt% N or more and 0.70wt% N or less, and preferably 0.40wt% N or more and 0.60wt% N or less, and even more preferably 0.45wt% N or more and 0.55wt% N or less; and

The tungsten containing variant of 316LM4N stainless steel has a high specified level of nitrogen and PRE_NW32 or more, but preferably PRE_NWNot less than 37. It should be emphasized that these equations ignore microstructural factors versus pitting or crevicesThe effects of corrosion induced passive destruction. Tungsten may be added alone or in combination with the elements copper, vanadium, titanium and/or niobium plus tantalum, in all various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is extremely expensive and therefore is purposefully limited to optimize the economics of the alloy, as well as the ductility, toughness and corrosion properties of the alloy.

Carbon (C)

For certain applications, other variants of 316LM4N stainless steel are desirable, which have been specifically formulated to include higher levels of carbon. In particular, the carbon content of the 316LM4N stainless steel may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C. These particular variants of 316LM4N stainless steel may be considered as the 316HM4N or 316M4N versions, respectively.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilized variants of 316HM4N or 316M4N stainless steel are desirable, which have been specifically formulated to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They include a stabilized version of titanium called 316HM4NTi or 316M4NTi to contrast with the typical 316LM4N stainless steel version. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized versions of 316HM4NNb or 316M4NNb, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include niobium plus tantalum stabilized versions of 316HM4NNbTa or 316M4NNbTa, where the niobium plus tantalum content is controlled according to the following formula:

nb + Ta8 XC minimum, 1.0wt% Nb + Ta maximum, 0.10wt% Ta maximum, or Nb + Ta10 XC minimum, 1.0wt% Nb + Ta maximum, 0.10wt% Ta maximum.

Forged and cast plates of 316LM4N stainless steel, as well as other variations and embodiments discussed herein, are typically provided under solution annealed conditions. However, weldments to make parts, assemblies and structures are typically provided in as-welded conditions, provided that the proper welding process assessment has passed prequalification in accordance with respective standards and specifications. Forged plates for particular applications may also be provided in cold worked conditions.

It should be understood that the various elements as discussed with respect to 304LM4N and the effects of their compositions also apply to 316LM4N (and the various embodiments discussed below) to understand how to obtain the optimal chemical composition of 316LM4N stainless steel (and the remaining various embodiments).

In addition to the 304LM4N and 316LM4N austenitic stainless steels, a further variant is proposed, appropriately referred to as 317L57M4N, and this forms a third embodiment of the invention.

[317L57M4N]

The 317L57M4N high strength austenitic stainless steel has a high level of nitrogen and specifies a pitting corrosion resistance equivalent PRE_NNot less than 40, but preferably PRE_NNot less than 45. Referred to as PRE_NThe pitting resistance equivalent weight of (c) is calculated according to the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

317L57M4N stainless steel has been formulated to have a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. The chemical composition of the 317L57M4N stainless steel is selective and is characterized by an alloy of the following chemical elements in weight (wt%) percent: 0.030wt% Cmax, 2.00wt% Mn max, 0.030wt% Pmax, 0.010wt% Smax, 0.75wt% Si max, 18.00wt% Cr-20.00 wt% Cr, 11.00wt% Ni-15.00 wt% Ni, 5.00wt% Mo-7.00 wt% Mo, 0.40wt% N-0.70 wt% N.

The 317L57M4N stainless steel also includes primarily Fe as the remainder and may also contain very small amounts of other elements such as 0.010wt% B max, 0.10wt% Ce max, 0.050wt% Al max, 0.01wt% Ca max and/or 0.01wt% Mg max and other impurities typically present at residual levels.

The chemical composition of the 317L57M4N stainless steel is optimized during the melting phase to primarily ensure that the base material has an austenitic microstructure after solution heat treatment, typically in the range of 1100-1250 degrees celsius, followed by water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. Thus, the 317L57M4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures, while achieving excellent toughness at both ambient and low temperatures. Chemical analysis of stainless steel was adjusted to reach PRE in view of 317L57M4N_NNot less than 40, but preferably PRE_NThe fact of being > 45 ensures that the material has good general corrosion resistance and local corrosion resistance (pitting and crevice corrosion) also in a wide range of processing environments. The 317L57M4N stainless steel also has improved stress corrosion cracking resistance compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments.

It has been determined that the optimal chemical composition range for the 317L57M4N stainless steel is carefully selected to include the following weight percentages of chemical elements based on the third example:

carbon (C)

The carbon content of the 317L57M4N stainless steel is less than or equal to 0.030wt% C maximum. Preferably, the carbon content should be ≥ 0.020wt% C and ≤ 0.030wt% C and more preferably ≤ 0.025wt% C.

Manganese (Mn)

The 317L57M4N stainless steel of the third embodiment may have two variations: low manganese or high manganese.

For low manganese alloys, the manganese content of the 317L57M4N stainless steel is 2.0wt% Mn or less. Preferably, the range is 1.0wt% or more and 2.0wt% or less of Mn, and more preferably 1.20wt% or more and 1.50wt% or less of Mn. By this composition, an optimum ratio of Mn to N of ≦ 5.0 is achieved, and preferably ≧ 1.42 and ≦ 5.0. More preferably, the ratio is ≧ 1.42 and ≦ 3.75.

For high manganese alloys, the manganese content of 317L57M4N is 4.0wt% Mn or less. Preferably, the manganese content is ≥ 2.0 wt.% Mn and ≤ 4.0 wt.% Mn, and more preferably, the upper limit is ≤ 3.0 wt.% Mn. Even more preferably, the upper limit is 2.50 wt.% Mn. With these selected ranges, a Mn to N ratio of ≦ 10.0 is achieved, and preferably ≦ 2.85 and ≦ 10.0. More preferably, for high manganese alloys, the ratio of Mn to N is ≧ 2.85 and ≦ 7.50, and more preferably ≧ 2.85 and ≦ 6.25.

Phosphorus (P)

The phosphorous content of the 317L57M4N stainless steel is controlled to be less than or equal to 0.030wt% P. Preferably, the 317L57M4N alloy has ≦ 0.025wt% P and more preferably ≦ 0.020wt% P. Even more preferably, the alloy has ≦ 0.015wt% P and even further more preferably ≦ 0.010wt% P.

Sulfur (S)

The sulfur content of the 317L57M4N stainless steel of the third embodiment includes ≦ 0.010wt% S. Preferably, the 317L57M4N has 0.005wt% S or less and more preferably 0.003wt% S or less and even more preferably 0.001wt% S or less.

Oxygen (O)

The oxygen content of the 317L57M4N stainless steel is controlled to be as low as possible, and in the third embodiment, the 317L57M4N also has ≦ 0.070wt% O. Preferably, the 317L57M4N alloy has 0.050wt% O or less and more preferably 0.030wt% O or less. Even more preferably, the alloy has 0.010 wt.% O or less and even further more preferably 0.005 wt.% O or less.

Silicon (Si)

The silicon content of the 317L57M4N stainless steel is less than or equal to 0.75wt% Si. Preferably, the alloy has ≥ 0.25wt% Si and ≤ 0.75wt% Si. More preferably, the range is 0.40wt% Si or more and 0.60wt% Si or less. However, for certain higher temperature applications where improved oxidation resistance is desired, the silicon content may be 0.75 wt.% Si or more and 2.00 wt.% Si or less.

Chromium (Cr)

The chromium content of the 317L57M4N stainless steel is more than or equal to 18.00wt% of Cr and less than or equal to 20.00wt% of Cr. Preferably, the alloy has 19.00wt% Cr or more.

Nickel (Ni)

The nickel content of the 317L57M4N stainless steel is more than or equal to 11.00wt% of Ni and less than or equal to 15.00wt% of Ni. Preferably, for alloys in the lower nickel range, the upper limit of Ni for the alloy is 14.00wt% Ni or less and more preferably 13.00wt% Ni or less.

For alloys in the higher nickel range, the nickel content of the 317L57M4N stainless steel may have 13.50wt% Ni or more and 17.50wt% Ni or less. Preferably, for higher nickel range alloys, the upper limit of Ni is 16.50wt% Ni or less and more preferably 15.50wt% Ni or less.

Molybdenum (Mo)

The molybdenum content of the 317L57M4N stainless steel alloy is 5.00wt% Mo or more and 7.00wt% Mo or less, but preferably 6.00wt% Mo or more. In other words, molybdenum has a maximum of 7.00wt% Mo.

Nitrogen (N)

The nitrogen content of the 317L57M4N stainless steel is 0.70wt% N or less, but is preferably 0.40wt% N or more and 0.70wt% N or less. More preferably, the 317L57M4N has 0.40wt% N and 0.60wt% N, and even more preferably 0.45wt% N and 0.55wt% N.

PRE _N

The pitting resistance equivalent weight is calculated using the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

the 317L57M4N stainless steel has been formulated to have the following composition:

(i) the chromium content is more than or equal to 18.00wt% Cr and less than or equal to 20.00wt% Cr, but preferably more than or equal to 19.00wt% Cr;

(ii) The molybdenum content is more than or equal to 5.00wt% Mo and less than or equal to 7.00wt% Mo, but preferably more than or equal to 6.00wt% Mo;

The 317L57M4N stainless steel reached PRE by high levels of nitrogen_N≧ 40, and preferably PRE_NNot less than 45. This ensures that the alloy has good general corrosion resistance and localized corrosion (pitting and crevice corrosion) resistance in a wide range of processing environments. The 317L57M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. Should be strongIt is recalled that these equations neglect the influence of microstructural factors on the passive destruction caused by pitting or crevice corrosion.

The chemical composition of the 317L57M4N stainless steel was optimized during the melting phase to ensure that the alloy was able to withstand Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

The 317L57M4N stainless steel also has predominantly Fe as the remainder and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium and/or magnesium, measured in weight percent, and the composition of these elements is the same as that of 304LM 4N. In other words, the paragraphs on these elements of 304LM4N apply here as well.

According to a third embodiment, 317L57M4N stainless steel has a minimum yield strength of 55ksi or 380MPa for forged plates. More preferably, a minimum yield strength of 62ksi or 430MPa can be achieved for the forged plate. The cast plate had a minimum yield strength of 41ksi or 280 MPa. More preferably, a minimum yield strength of 48ksi or 330MPa can be achieved for the cast plate. Based on the preferred values, the forging mechanical strength properties of the novel and innovative 317L57M4N stainless steel are compared to the forging mechanical strength properties of UNSS31703, indicating that the minimum yield strength of the 317L57M4N stainless steel may be 2.1 times higher than the minimum yield strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 317L57M4N stainless steel compared to the forging mechanical strength properties of UNSS31753 indicate that the minimum yield strength of 317L57M4N stainless steel is likely to be 1.79 times higher than the minimum yield strength specified for UNSS 31753.

According to the third embodiment, 317L57M4N stainless steel has a minimum tensile strength of 102ksi or 700MPa for a wrought plate. More preferably, a minimum tensile strength of 109ksi or 750MPa can be achieved for the forged plate. The cast plate had a minimum tensile strength of 95ksi or 650 MPa. More preferably, a minimum tensile strength of 102ksi or 700MPa can be achieved for the cast plate. Based on the preferred values, the wrought mechanical strength properties of the 317L57M4N stainless steel are compared to those of UNSS31703, indicating that the minimum tensile strength of the 317L57M4N stainless steel is more than 1.45 times higher than the minimum tensile strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of the novel and innovative 317L57M4N austenitic stainless steel are compared to the forging mechanical strength properties of UNSS31753, indicating that the minimum tensile strength of the 317L57M4N stainless steel is likely to be 1.36 times higher than the minimum tensile strength specified for UNSS 31753. Indeed, if the forging mechanical strength properties of the 317L57M4N stainless steel are compared to the forging mechanical strength properties of the 22Cr duplex stainless steel in table 2, it can be shown that the minimum tensile strength of the 317L57M4N stainless steel is about 1.2 times higher than the minimum tensile strength specified for S31803, and is similar to the minimum tensile strength specified for the 25Cr super duplex stainless steel. Thus, the minimum mechanical strength properties of the 317L57M4N stainless steel have been significantly improved compared to conventional austenitic stainless steels such as uns 31703 and uns 31753, and the tensile strength properties are superior to those specified for 22Cr duplex stainless steels and similar to those specified for 25Cr super duplex stainless steels.

This means that applications using forged 317L57M4N stainless steel can often be designed with reduced wall thickness, thus, when specifying 317L57M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as UNSS31703 and UNSS 31753. In fact, the minimum allowable design stress of the forged 317L57M4N stainless steel may be higher than the minimum allowable design stress of the 22Cr duplex stainless steel, and is similar to the 25Cr super duplex stainless steel.

For certain applications, other variants of the 317L57M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of the 317L57M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 304LM 4N. In other words, the paragraphs regarding these elements of 304LM4N apply here also to 317L57M 4N.

Tungsten (W)

The tungsten content of the 317L57M4N stainless steel is ≦ 2.00wt% W, but preferably ≦ 0.50wt% W and ≦ 1.00wt% W and more preferably ≦ 0.75wt% W. For the tungsten containing variant of the 317L57M4N stainless steel, the pitting resistance equivalent weight is calculated using the formula:

PRE_NW=%Cr+[3.3×%(Mo+W)]+(16×%N)。

This tungsten-containing variant of 317L57M4N stainless steel has been specifically formulated to have the following composition:

(ii) the molybdenum content is more than or equal to 5.0wt% Mo and less than or equal to 7.00wt% Mo, but preferably more than or equal to 6.00wt% Mo,

The tungsten containing variant of the 317L57M4N stainless steel has a high specified level of nitrogen and PRE_NW≧ 42, but preferably PRE_NWNot less than 47. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion. Tungsten may be added alone or in combination with the elements copper, vanadium, titanium and/or niobium plus tantalum, in all various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is very highExpensive and therefore purposefully limits tungsten to optimize the economics of the alloy while optimizing the ductility, toughness and corrosion performance of the alloy.

Carbon (C)

For certain applications, other variants of the 317L57M4N stainless steel are desirable, which have been specifically formulated to contain higher levels of carbon. In particular, the carbon content of the 317L57M4N stainless steel may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C. These particular variants of 317L57M4N stainless steel are the 317H57M4N or 31757M4N versions, respectively.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of the 317H57M4N or 31757M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They included a titanium stabilized version known as 317H57M4NTi or 31757M4NTi, in contrast to the general 317L574N stainless steel version. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized 317H57M4NNb or 31757M4NNb versions where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include the niobium plus tantalum stabilized 317H57M4NNbTa or 31757M4NNbTa versions, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast plates of 317L57M4N stainless steel and other variations are generally provided in the same manner as in the previous examples.

Further, another variation is proposed, suitably referred to as 317L35M4N high strength austenitic stainless steel, which is a fourth embodiment of the present invention. The 317L35M4N stainless steel has virtually the same chemical composition as the 317L57M4N stainless steel except for the molybdenum content. Therefore, only the differences are described herein, and the description of the various chemical compositions is not repeated.

[317L35M4N]

As mentioned above, 317L35M4N has exactly the same wt% carbon, manganese, phosphorus, sulfur, oxygen, silicon, chromium, nickel and nitrogen content as the third example 317L57M4N stainless steel, except for the molybdenum content. In 317L57M4N stainless steel, the molybdenum level was between 5.00wt% and 7.00wt% Mo. In contrast, the molybdenum content of the 317L35M4N stainless steel was between 3.00wt% and 5.00wt% Mo. In other words, 317L35M4N can be considered a low molybdenum content version of 317L57M4N stainless steel.

It will be appreciated that, in addition to the molybdenum content, the paragraph on 317L57M4N applies here as well.

Molybdenum (Mo)

The molybdenum content of the 317L35M4N stainless steel may be 3.00wt% Mo or more and 5.00wt% Mo or less, but is preferably 4.00wt% Mo or more. In other words, the molybdenum content of 317L35M4N has a maximum of 5.00wt% Mo.

PRE _N

The pitting resistance equivalent of 317L35M4N was calculated using the same formula as 317L57M4N, but due to the different molybdenum content, the PRE was calculated_NIs ≧ 35, but preferably PRE_NNot less than 40. This ensures that the material has good general corrosion resistance and local corrosion (pitting and crevice corrosion) resistance also in a wide range of processing environments. The 317L35M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of the 317L35M4N stainless steel was optimized in the melting phase to ensure the chemical composition according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. Thus, the 317L35M4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures while ensuring excellent toughness at ambient and low temperatures. The alloy can thus be manufactured and provided in a non-magnetic state.

Like the 317L57M4N embodiment, the 317L35M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium and/or magnesium, measured in weight percent, and the composition of these elements is the same as that of 317L57M4N, and thus 304LM 4N.

The 317L35M4N stainless steel of the fourth embodiment has a minimum yield strength and minimum tensile strength that is equivalent or similar to the minimum yield strength and minimum tensile strength of the 317L57M4N stainless steel. Similarly, the strength properties of the forged and cast plates of 317L35M4N were also equivalent to those of the forged and cast plates of 317L57M 4N. Thus, the specific intensity values are not repeated here and reference is made to the preceding 317L57M4N paragraph. Comparison of forging mechanical strength properties between 317L35M4N and conventional austenitic stainless steel uns 31703, and between 317L35M4N and uns 31753, demonstrated higher magnitudes of yield and tensile strengths, similar to those found at 317L57M 4N. Similar comparisons of tensile properties of 317L35M4N show that they are superior to the tensile properties specified for 22Cr duplex stainless steel and similar to the tensile properties specified for 25Cr super duplex stainless steel, just like 317L57M 4N.

This means that applications using forged 317L35M4N stainless steel can often be designed with reduced wall thickness, thus, when specifying 317L35M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as UNSS31703 and UNSS 31753. In fact, the minimum allowable design stress of the forged 317L35M4N stainless steel is higher than the minimum allowable design stress of the 22Cr duplex stainless steel, and is similar to the 25Cr super duplex stainless steel.

For certain applications, other variants of the 317L35M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of the 317L35M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 317L57M4N and that of 304LM 4N. In other words, the paragraphs regarding these elements of 304LM4N apply here also to 317L35M 4N.

Tungsten (W)

The tungsten content of the 317L35M4N stainless steel was similar to that of 317L57M4N, and the pitting resistance equivalent, PRE, of 317L35M4N was calculated using the formula used for 317L57M4N mentioned above _NWIs not less than 37, but preferably PRE_NW42 or more, which is caused by the difference of the content of molybdenum. It should be apparent that the paragraph regarding the use and action of molybdenum in 317L57M4N also applies to 317L35M 4N.

Further, 317L35M4N may have a higher level of carbon, referred to as 317H35M4N and 31735M4N, corresponding to 317H57M4N and 31757M4N, respectively, discussed previously, and the carbon wt% ranges discussed previously are also applicable to 317H35M4N and 31735M 4N.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 317H35M4N or 31735M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C, or ≥ 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They included titanium stabilized versions referred to as 317H35M4NTi or 31735M4NTi, to contrast with the general 317L35M 4N. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized 317H35M4NNb or 31735M4NNb versions, where the niobium content is controlled according to the following formula:

(iii) Additionally, other variations of the alloy can also be made to include the niobium plus tantalum stabilized 317H35M4NNbTa or 31735M4NNbTa versions, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast plates of 317L35M4N stainless steel and other variations are generally provided in the same manner as in the previous examples.

Further, another variation is proposed, appropriately referred to in this specification as 312L35M4N, which is a fifth embodiment of the present invention.

[312L35M4N]

The 312L35M4N high strength austenitic stainless steel has a high level of nitrogen and is resistant to pitting equivalent PRE_NNot less than 37, but preferably PRE_NIs more than or equal to 42. Referred to as PRE_NThe pitting resistance equivalent weight of (c) is calculated according to the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

312L35M4N stainless steel has been formulated to have a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. The chemical composition of 312L35M4N stainless steel is selective and is characterized by the following chemically analyzed alloy in weight (wt%) percent: 0.030wt% Cmax, 2.00wt% Mn max, 0.030wt% Pmax, 0.010wt% Smax, 0.75wt% Si max, 20.00wt% Cr-22.00 wt% Cr, 15.00wt% Ni-19.00 wt% Ni, 3.00wt% Mo-5.00 wt% Mo, 0.40wt% N-0.70 wt% N.

The 312L35M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements, such as 0.010wt% B max, 0.10wt% Ce max, 0.050wt% Al max, 0.01wt% Ca max, and/or 0.01wt% Mg max, as well as other impurities that are typically present at residual levels.

The chemical composition of the 312L35M4N stainless steel is optimized during the melting phase to primarily ensure that the base material has an austenitic microstructure after solution heat treatment, typically in the range of 1100-1250 degrees celsius, followed by water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure that the alloy is primarily austenitic. Thus, the 312L35M4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures while ensuring excellent toughness at ambient and low temperatures. The chemical composition of stainless steel is adjusted to reach PRE in view of 312L35M4N stainless steel_NNot less than 37, but preferably PRE_NThe fact of being > 42 ensures that the material has good general corrosion resistance and local corrosion resistance (pitting and crevice corrosion) also in a wide range of processing environments. The 312L35M4N stainless steel also has improved stress corrosion cracking resistance compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments.

It has been determined that the optimal chemical composition range for the 312L35M4N stainless steel is carefully selected to include the following weight percentages of chemical elements based on the fifth embodiment:

Carbon (C)

The carbon content of the 312L35M4N stainless steel is less than or equal to 0.030wt% C maximum. Preferably, the carbon content should be ≥ 0.020wt% C and ≤ 0.030wt% C and more preferably ≤ 0.025wt% C.

Manganese (Mn)

The 312L35M4N stainless steel of the fifth embodiment may have two variations: low manganese or high manganese.

For low manganese alloys, the manganese content of the 312L35M4N stainless steel is less than or equal to 2.0wt% Mn. Preferably, the range is 1.0wt% or more and 2.0wt% or less of Mn, and more preferably 1.20wt% or more and 1.50wt% or less of Mn. By this composition, an optimum ratio of Mn to N of ≦ 5.0 is achieved, and preferably ≦ 1.42 and ≦ 5.0. More preferably, the ratio is ≧ 1.42 and ≦ 3.75.

For high manganese alloys, the manganese content of 312L35M4N is 4.0wt% Mn or less. Preferably, the manganese content is ≥ 2.0 wt.% Mn and ≤ 4.0 wt.% Mn, and more preferably, the upper limit is ≤ 3.0 wt.% Mn. Even more preferably, the upper limit is 2.50 wt.% Mn. With these selected ranges, a Mn to N ratio of ≦ 10.0 is achieved, and preferably ≦ 2.85 and ≦ 10.0. More preferably, for high manganese alloys, the ratio of Mn to N is ≧ 2.85 and ≦ 7.50, and more preferably ≧ 2.85 and ≦ 6.25.

Phosphorus (P)

The phosphorus content of the 312L35M4N stainless steel is controlled to be less than or equal to 0.030wt% P. Preferably, the 312L35M4N alloy has ≦ 0.025wt% P and more preferably ≦ 0.020wt% P. Even more preferably, the alloy has ≦ 0.015wt% P and even further more preferably ≦ 0.010wt% P.

Sulfur (S)

The sulfur content of the 312L35M4N stainless steel of the fifth embodiment includes ≦ 0.010wt% S. Preferably, the 312L35M4N has 0.005wt% S or less and more preferably 0.003wt% S or less and even more preferably 0.001wt% S or less.

Oxygen (O)

The oxygen content of the 312L35M4N stainless steel is controlled to be as low as possible, and in a fifth embodiment, the 312L35M4N has ≦ 0.070wt% O. Preferably, the 312L35M4N has 0.050wt% O or less and more preferably 0.030wt% O or less. Even more preferably, the alloy has 0.010 wt.% O or less and even further more preferably 0.005 wt.% O or less.

Silicon (Si)

The silicon content of the 312L35M4N stainless steel is less than or equal to 0.75wt% Si. Preferably, the alloy has ≥ 0.25wt% Si and ≤ 0.75wt% Si. More preferably, the range is 0.40wt% Si or more and 0.60wt% Si or less. However, for certain higher temperature applications where improved oxidation resistance is desired, the silicon content may be 0.75 wt.% Si or more and 2.00 wt.% Si or less.

Chromium (Cr)

The chromium content of the 312L35M4N stainless steel is more than or equal to 20.00wt% of Cr and less than or equal to 22.00wt% of Cr. Preferably, the alloy has ≧ 21.00wt% Cr.

Nickel (Ni)

The nickel content of the 312L35M4N stainless steel is more than or equal to 15.00wt% of Ni and less than or equal to 19.00wt% of Ni. Preferably, the upper limit of Ni of the alloy is 18wt% Ni or less and more preferably 17wt% Ni or less.

Molybdenum (Mo)

The molybdenum content of the 312L35M4N stainless steel alloy is 3.00wt% Mo or more and 5.00wt% Mo or less, but preferably 4.00wt% Mo or more. In other words, the molybdenum content of this example has a maximum of 5.00wt% Mo.

Nitrogen (N)

The nitrogen content of the 312L35M4N stainless steel is 0.70wt% N or less, but is preferably 0.40wt% N or more and 0.70wt% N or less. More preferably, the 312L35M4N has ≥ 0.40wt% N and ≤ 0.60wt% N, and even more preferably ≥ 0.45wt% N and ≤ 0.55wt% N.

PRE _N

The pitting resistance equivalent weight is calculated using the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

the 312L35M4N stainless steel has been specifically formulated to have the following composition:

(i) the chromium content is more than or equal to 20.00wt% Cr and less than or equal to 22.00wt% Cr, but preferably more than or equal to 21.00wt% Cr;

(ii) the molybdenum content is more than or equal to 3.00wt% Mo and less than or equal to 5.00wt% Mo, but preferably more than or equal to 4.00wt% Mo;

The 312L35M4N stainless steel reached PRE by high levels of nitrogen_N≧ 37, and preferably PRE_NIs more than or equal to 42. This ensures that the alloy has good general corrosion resistance and localized corrosion (pitting and crevice corrosion) resistance in a wide range of processing environments. The 312L35M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 312L35M4N stainless steel was optimized during the melting phase to ensure the properties according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

The 312L35M4N stainless steel also has primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium and/or magnesium, measured in weight percent, and the composition of these elements is the same as that in 304LM 4N. In other words, the paragraphs on these elements of 304LM4N apply here as well.

According to the fifth embodiment, the 312L35M4N stainless steel has a minimum yield strength of 55ksi or 380MPa for forged plates. More preferably, a minimum yield strength of 62ksi or 430MPa can be achieved for the forged plate. The cast plate had a minimum yield strength of 41ksi or 280 MPa. More preferably a minimum yield strength of 48ksi or 330MPa for the cast plate can be achieved. Based on the preferred values, the forging mechanical strength properties of the novel and innovative 312L35M4N stainless steel are compared to the forging mechanical strength properties of UNSS31703, indicating that the minimum yield strength of the 312L35M4N stainless steel may be 2.1 times higher than the minimum yield strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 312L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31753, indicate that the minimum yield strength of 312L35M4N stainless steel is likely to be 1.79 times greater than the minimum yield strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 312L35M4N stainless steel compared to those of UNSS31254 indicate that the minimum yield strength of 312L35M4N stainless steel may be 1.38 times greater than the minimum yield strength specified for UNSS 31254.

According to the fifth embodiment, the 312L35M4N stainless steel has a minimum tensile strength of 102ksi or 700MPa for forged plates. More preferably, a minimum tensile strength of 109ksi or 750MPa can be achieved for the forged plate. The cast plate had a minimum tensile strength of 95ksi or 650 MPa. More preferably, a minimum tensile strength of 102ksi or 700MPa can be achieved for the cast plate. Based on the preferred values, the forging mechanical strength properties of 312L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31703 indicate that the minimum tensile strength of 312L35M4N stainless steel may be more than 1.45 times greater than the minimum tensile strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 312L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31753 indicate that the minimum tensile strength of 312L35M4N stainless steel is likely to be 1.36 times higher than the minimum tensile strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 312L35M4N stainless steel compared to those of UNSS31254 indicate that the minimum tensile strength of 312L35M4N stainless steel may be 1.14 times greater than the minimum tensile strength specified for UNSS 31254. Indeed, if the wrought mechanical strength properties of 312L35M4N stainless steel are compared to the wrought mechanical strength properties of 22Cr duplex stainless steel, then it can be shown that the minimum tensile strength of the 312L35M4N stainless steel is about 1.2 times higher than the minimum tensile strength specified for S31803, and is similar to the minimum tensile strength specified for 25Cr super duplex stainless steel. Thus, the minimum mechanical strength properties of the 312L35M4N stainless steel have been significantly improved compared to conventional austenitic stainless steels such as uns 31703, uns 31753 and uns 31254, and the tensile strength properties are superior to those specified for 22Cr duplex stainless steels and similar to those specified for 25Cr super duplex stainless steels.

This means that applications using forged 312L35M4N stainless steel can often be designed with reduced wall thickness, thus, when specifying 312L35M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as uns 31703, uns 31753, and uns 31254. In fact, the minimum allowable design stress of forged 312L35M4N stainless steel is higher than the minimum allowable design stress of 22Cr duplex stainless steel, and is similar to 25Cr super duplex stainless steel.

For certain applications, other variants of 312L35M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 312L35M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 304LM 4N. In other words, the paragraphs for these elements of 304LM4N also apply to 312L35M 4N.

Tungsten (W)

The tungsten content of the 312L35M4N stainless steel is ≦ 2.00wt% W, but preferably ≦ 0.50wt% W and ≦ 1.00wt% W, and more preferably ≦ 0.75wt% W. For the 312L35M4N stainless steel tungsten containing variant, the pitting resistance equivalent weight is calculated using the formula:

PRE_NW=%Cr+[3.3×%(Mo+W)]+(16×%N)。

This tungsten-containing variant of 312L35M4N stainless steel has been specifically formulated to have the following composition:

(ii) the molybdenum content is greater than or equal to 3.00wt% Mo and less than or equal to 5.00wt% Mo, but more preferably greater than or equal to 4.00wt% Mo;

The tungsten containing variant of 312L35M4N stainless steel has a high specified level of nitrogen and PRE_NWNot less than 39, but preferably PRE_NWIs more than or equal to 44. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion. Tungsten may be added alone or in combination with the elements copper, vanadium, titanium and/or niobium plus tantalum, in all various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is extremely expensive and therefore is purposefully limited to optimize the economics of the alloy, as well as the ductility, toughness and corrosion properties of the alloy.

Carbon (C)

For certain applications, other variants of 312L35M4N stainless steel are desirable, which have been specifically formulated to contain higher levels of carbon. In particular, the carbon content of the 312L35M4N stainless steel may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C. These particular variants of 312L35M4N stainless steel are considered to be 312H35M4N or 31235M4N versions, respectively.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 312H35M4N or 31235M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They include a stabilized version of titanium called 312H35M4NTi or 31235M4NTi for comparison with a typical 312L35M4N stainless steel version. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized versions of 312H35M4NNb or 31235M4NNb, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include niobium plus tantalum stabilized 312H35M4NNbTa or 31235M4NNbTa versions, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast plates of 312L35M4N stainless steel, and other variations, are generally provided in the same manner as the previous examples.

Further, another variation is proposed, suitably referred to as 312L57M4N high strength austenitic stainless steel, which is a sixth embodiment of the present invention. The 312L57M4N stainless steel has virtually the same chemical composition as the 312L35M4N stainless steel except for the molybdenum content. Therefore, only the differences are described herein, and the description of the various chemical compositions is not repeated.

[312L57M4N]

As mentioned above, the 312L57M4N and fifth example 312L35M4N stainless steels have exactly the same wt% carbon, manganese, phosphorus, sulfur, oxygen, silicon, chromium, nickel, and nitrogen contents, except for the molybdenum content. In 312L35M4N, the molybdenum content was between 3.00wt% and 5.00 wt%. In contrast, the molybdenum content of the 312L57M4N stainless steel is between 5.00wt% and 7.00 wt%. In other words, 312L57M4N can be considered a higher molybdenum content version of 312L35M4N stainless steel.

It will be appreciated that, in addition to the molybdenum content, the paragraph on 312L35M4N applies here as well.

Molybdenum (Mo)

The molybdenum content of the 312L57M4N stainless steel may be 5.00wt% Mo or more and 7.00wt% Mo or less, but is preferably 6.00wt% Mo or more. In other words, the molybdenum content of 312L57M4N has a maximum of 7.00wt% Mo.

PRE _N

The pitting resistance equivalent of 312L57M4N was calculated using the same formula as 312L35M4N, but due to the different molybdenum content, the PRE was calculated_NIs 43 or more, but preferably PRE_NIs more than or equal to 48. This ensures that the timberThe material also has good general corrosion resistance and local corrosion resistance (pitting corrosion and crevice corrosion) under a wide range of processing environments. The 312L57M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 312L57M4N stainless steel was optimized during the melting phase to ensure the properties according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

Like the 312L35M4N embodiment, the 312L57M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium, and/or magnesium, measured in weight percent, and the composition of these elements is the same as that of 312L35M4N, and thus 304LM 4N.

The 312L57M4N stainless steel of the sixth embodiment has a minimum yield strength and minimum tensile strength that is equivalent or similar to the minimum yield strength and minimum tensile strength of the 312L35M4N stainless steel. Similarly, the strength properties of the forged and cast plates of 312L57M4N were also equivalent to the strength properties of the forged and cast plates of 312L35M 4N. Thus, the specific intensity values are not repeated here, and reference is made to the previous paragraph of 312L35M 4N. Comparison of forging mechanical strength properties between 312L57M4N and conventional austenitic stainless steel uns 31703, and between 312L57M4N and uns 31753/uns 31254, indicates higher magnitude yield and tensile strengths, similar to those found at 312L35M 4N. Similarly, a comparison of the tensile properties of 312L57M4N shows that they are superior to the tensile properties specified for 22Cr duplex stainless steel and similar to the tensile properties specified for 25Cr super duplex stainless steel, just like 312L35M 4N.

This means that applications using forged 312L57M4N stainless steel can often be designed with reduced wall thickness, and therefore, when specifying 312L57M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as UNSS31703, S31753, and S31254. In fact, the minimum allowable design stress of forged 312L57M4N stainless steel is higher than the minimum allowable design stress of 22Cr duplex stainless steel, and is similar to 25Cr super duplex stainless steel.

For some applications, other variants of 312L57M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 312L57M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 312L35M4N and that of 304LM 4N. In other words, the paragraphs for these elements of 304LM4N also apply here to 312L57M 4N.

Tungsten (W)

The tungsten content of the 312L57M4N stainless steel is similar to the tungsten content of the 312L35M4N, and the pitting resistance equivalent, PRE, of the 312L57M4N_NWCalculated using the formula used in 312L35M4N, and the pitting resistance equivalent weight is PRE _NW≧ 45, but preferably PRE_NW> 50, due to the difference in molybdenum content. It should be apparent that the paragraph on the use and effect of molybdenum in 312L35M4N also applies to 312L57M 4N.

Further, 312L57M4N may have a higher level of carbon, referred to as 312H57M4N or 31257M4N, corresponding to 312H35M4N and 31235M4N, respectively, discussed previously, and the carbon wt% ranges discussed previously also apply to 312H57M4N and 31257M 4N.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 312H57M4N or 31257M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They include a stabilized version of titanium called 312H57M4NTi or 31257M4NTi, for comparison with the typical 312L57M4N stainless steel version. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized versions of 312H57M4NNb or 31257M4NNb, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include niobium plus tantalum stabilized 312H57M4NNbTa or 31257M4NNbTa versions, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast plates of 312L57M4N stainless steel, as well as other variations, are generally provided in the same manner as the previous embodiments.

Further, another variant is proposed, appropriately referred to in this specification as 320L35M4N, which is a seventh embodiment of the invention.

[320L35M4N]

The 320L35M4N high strength austenitic stainless steel has a high level of nitrogen and a specific pitting resistance equivalent PRE_NNot less than 39, but preferably PRE_NIs more than or equal to 44. Referred to as PRE_NThe pitting resistance equivalent weight of (c) is calculated according to the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

320L35M4N stainless steel has been formulated to have a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. The chemical composition of 320L35M4N stainless steel is selective and is characterized by an alloy of chemical elements in the following weight (wt%) percentages: 0.030wt% Cmax, 2.00wt% Mn max, 0.030wt% Pmax, 0.010wt% Smax, 0.75wt% Si max, 22.00wt% Cr-24.00 wt% Cr, 17.00wt% Ni-21.00 wt% Ni, 3.00wt% Mo-5.00 wt% Mo, 0.40wt% N-0.70 wt% N.

The 320L35M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements, such as 0.010wt% B max, 0.10wt% Ce max, 0.050wt% Al max, 0.01wt% Ca max, and/or 0.01wt% Mg max, as well as other impurities that are typically present at residual levels.

The chemical composition of 320L35M4N stainless steel is optimized during the melting stageTo ensure mainly that the matrix material has an austenitic microstructure after solution heat treatment, which is typically performed in the range 1100-1250 deg.c, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure that the alloy is primarily austenitic. Thus, 320L35M4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures while ensuring excellent toughness at ambient and low temperatures. The chemical composition of stainless steel is adjusted to reach PRE in view of 320L35M4N stainless steel_NNot less than 39, but preferably PRE_NThe fact of ≧ 44 ensures that the material also has good general corrosion resistance and local corrosion resistance (pitting and crevice corrosion) in a wide range of processing environments. The 320L35M4N stainless steel also has improved stress corrosion cracking resistance compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments.

It has been determined that the optimal chemical composition range for 320L35M4N stainless steel is carefully selected to include the following weight percentages of chemical elements based on the seventh embodiment:

Carbon (C)

The carbon content of the 320L35M4N stainless steel is less than or equal to 0.030wt% C maximum. Preferably, the carbon content should be ≥ 0.020wt% C and ≤ 0.030wt% C and more preferably ≤ 0.025wt% C.

Manganese (Mn)

The 320L35M4N stainless steel of the seventh embodiment may have two variations: low manganese or high manganese.

For low manganese alloys, the manganese content of 320L35M4N stainless steel is 2.0wt% Mn or less. Preferably, the range is 1.0wt% or more and 2.0wt% or less of Mn, and more preferably 1.20wt% or more and 1.50wt% or less of Mn. By this composition, an optimum ratio of Mn to N of ≦ 5.0 is achieved, and preferably ≦ 1.42 and ≦ 5.0. More preferably, the ratio is ≧ 1.42 and ≦ 3.75.

For high manganese alloys, the manganese content of 320L35M4N was 4.0wt% Mn or less. Preferably, the manganese content is ≥ 2.0 wt.% Mn and ≤ 4.0 wt.% Mn, and more preferably, the upper limit is ≤ 3.0 wt.% Mn. Even more preferably, the upper limit is 2.50 wt.% Mn. With these selected ranges, a Mn to N ratio of ≦ 10.0 is achieved, and preferably ≦ 2.85 and ≦ 10.0. More preferably, for high manganese alloys, the ratio of Mn to N is ≧ 2.85 and ≦ 7.50, and more preferably ≧ 2.85 and ≦ 6.25.

Phosphorus (P)

The phosphorus content of 320L35M4N stainless steel is controlled to be less than or equal to 0.030wt% P. Preferably, the 320L35M4N alloy has ≦ 0.025wt% P and more preferably ≦ 0.020wt% P. Even more preferably, the alloy has ≦ 0.015wt% P and even further more preferably ≦ 0.010wt% P.

Sulfur (S)

The sulfur content of the 320L35M4N stainless steel of the seventh embodiment includes 0.010wt% S or less. Preferably, the 320L35M4N has 0.005wt% S or less and more preferably 0.003wt% S or less and even more preferably 0.001wt% S or less.

Oxygen (O)

The oxygen content of 320L35M4N stainless steel is controlled to be as low as possible, and in a seventh embodiment, the 320L35M4N has ≦ 0.070wt% O. Preferably, the 320L35M4N has 0.050wt% O or less and more preferably 0.030wt% O or less. Even more preferably, the alloy has 0.010 wt.% O or less and even further more preferably 0.005 wt.% O or less.

Silicon (Si)

The silicon content of the 320L35M4N stainless steel is less than or equal to 0.75wt% of Si. Preferably, the alloy has ≥ 0.25wt% Si and ≤ 0.75wt% Si. More preferably, the range is 0.40wt% Si or more and 0.60wt% Si or less. However, for certain higher temperature applications where improved oxidation resistance is desired, the silicon content may be 0.75 wt.% Si or more and 2.00 wt.% Si or less.

Chromium (Cr)

The chromium content of the 320L35M4N stainless steel is more than or equal to 22.00wt% of Cr and less than or equal to 24.00wt% of Cr. Preferably, the alloy has ≧ 23.00wt% Cr.

Nickel (Ni)

The nickel content of the 320L35M4N stainless steel is more than or equal to 17.00wt% of Ni and less than or equal to 21.00wt% of Ni. Preferably, the upper limit of Ni of the alloy is 20.00wt% Ni or less and more preferably 19.00wt% Ni or less.

Molybdenum (Mo)

The molybdenum content of the 320L35M4N stainless steel alloy is 3.00wt% Mo or more and 5.00wt% Mo or less, but preferably 4.00wt% Mo or more.

Nitrogen (N)

The nitrogen content of the 320L35M4N stainless steel is 0.70wt% N or less, but is preferably 0.40wt% N or more and 0.70wt% N or less. More preferably, the 320L35M4N has ≥ 0.40wt% N and ≤ 0.60wt% N, and even more preferably ≥ 0.45wt% N and ≤ 0.55wt% N.

PRE _N

The pitting resistance equivalent weight is calculated using the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

the 320L35M4N stainless steel has been formulated to have the following composition:

(i) the chromium content is more than or equal to 22.00wt% Cr and less than or equal to 24.00wt% Cr, but preferably more than or equal to 23.00wt% Cr;

(ii) the molybdenum content is more than or equal to 3.00wt% Mo and less than or equal to 5.00wt% Mo, but preferably more than or equal to 4.00wt% Mo,

The 320L35M4N stainless steel reached PRE by high levels of nitrogen_N≧ 39, and preferably PRE_NIs more than or equal to 44. This ensures thatGold has good general corrosion resistance and localized corrosion (pitting and crevice corrosion) resistance in a wide range of processing environments. The 320L35M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 320L35M4N stainless steel was optimized during the melting phase to ensure the properties according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

The 320L35M4N stainless steel also has a majority of Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium and/or magnesium, measured in weight percent, and the composition of these elements is the same as that in 304LM 4N. In other words, the paragraphs on these elements of 304LM4N apply here as well.

According to the seventh embodiment, 320L35M4N stainless steel has a minimum yield strength of 55ksi or 380MPa for forged plates. More preferably, a minimum yield strength of 62ksi or 430MPa can be achieved for the forged plate. The cast plate had a minimum yield strength of 41ksi or 280 MPa. More preferably, a minimum yield strength of 48ksi or 330MPa can be achieved for the cast plate. Based on the preferred values, the wrought mechanical strength properties of 320L35M4N stainless steel are compared to those of UNSS31703, indicating that the minimum yield strength of 320L35M4N stainless steel is likely to be 2.1 times higher than the minimum yield strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 320L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31753, indicate that the minimum yield strength of 320L35M4N stainless steel is likely to be 1.79 times higher than the minimum yield strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 320L35M4N stainless steel compared to those of UNSS32053 indicate that the minimum yield strength of 320L35M4N stainless steel may be 1.45 times higher than the minimum yield strength specified for UNSS 32053.

According to the seventh embodiment, 320L35M4N stainless steel has a minimum tensile strength of 102ksi or 700MPa for a forged plate. More preferably, a minimum tensile strength of 109ksi or 750MPa can be achieved for the forged plate. The cast plate had a minimum tensile strength of 95ksi or 650 MPa. More preferably, a minimum tensile strength of 102ksi or 700MPa can be achieved for the cast plate. Based on the preferred values, the wrought mechanical strength properties of 320L35M4N stainless steel are compared to those of UNSS31703, indicating that the minimum tensile strength of 320L35M4N stainless steel may be more than 1.45 times higher than the minimum tensile strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 320L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31753 indicate that the minimum tensile strength of 320L35M4N stainless steel is likely to be 1.36 times higher than the minimum tensile strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 320L35M4N stainless steel compared to the forging mechanical strength properties of UNSS32053 indicate that the minimum tensile strength of 320L35M4N stainless steel may be 1.17 times higher than the minimum tensile strength specified for UNSS 32053. Indeed, if the wrought mechanical strength properties of 320L35M4N stainless steel are compared to those of 22Cr duplex stainless steel, then it can be shown that the minimum tensile strength of 320L35M4N stainless steel is about 1.2 times higher than the minimum tensile strength specified for S31803, and is similar to that specified for 25Cr super duplex stainless steel. Thus, the minimum mechanical strength properties of the novel and innovative 320L35M4N stainless steel have been significantly improved compared to conventional austenitic stainless steels such as uns 31703, uns 31753 and uns 32053, and the tensile strength properties are superior to those specified for 22Cr duplex stainless steels and similar to those specified for 25Cr super duplex stainless steels.

This means that applications using forged 320L35M4N stainless steel can often be designed with reduced wall thickness, thus, when specifying 320L35M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as uns 31703, uns 31753, and uns 32053. In fact, the minimum allowable design stress for forged 320L35M4N stainless steel is higher than the minimum allowable design stress for 22Cr duplex stainless steel, and is similar to 25Cr super duplex stainless steel.

For some applications, other variants of 320L35M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 320L35M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 304LM 4N. In other words, the paragraphs for these elements of 304LM4N also apply to 320L35M 4N.

Tungsten (W)

The tungsten content of the 320L35M4N stainless steel is ≤ 2.00wt% W, but preferably ≥ 0.50wt% W and ≤ 1.00wt% W, and more preferably ≥ 0.75wt% W. For the 320L35M4N stainless steel tungsten containing variant, the pitting resistance equivalent weight was calculated using the formula:

PRE_NW=%Cr+[3.3×%(Mo+W)]+(16×%N)。

This tungsten-containing variant of 320L35M4N stainless steel has been specifically formulated to have the following composition:

The tungsten containing variant of 320L35M4N stainless steel has a high specified level of nitrogen and PRE_NW≧ 41, but preferably PRE_NWIs more than or equal to 46. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion. Tungsten may be added alone or in combination with the elements copper, vanadium, titanium and/or niobium plus tantalum, in all various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is extremely expensive and therefore is purposefully limited to optimize the economics of the alloy, as well as the ductility, toughness and corrosion properties of the alloy.

Carbon (C)

For certain applications, other variants of 320L35M4N stainless steel are desirable, which have been specifically formulated to contain higher levels of carbon. In particular, the carbon content of the 320L35M4N stainless steel may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C. These particular variants of 320L35M4N stainless steel are considered to be 320H35M4N or 32035M4N versions, respectively.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 320H35M4N or 32035M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They included a titanium stabilized version called 320H35M4NTi or 32035M4NTi, in contrast to the general 320L35M4N version. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized versions of 320H35M4NNb or 32035M4NNb, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include niobium plus tantalum stabilized versions of 320H35M4NNbTa or 32035M4NNbTa, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast plates of 320L35M4N stainless steel, and other variations, are generally provided in the same manner as the previous examples.

Further, another variant, suitably referred to as 320L57M4N high strength austenitic stainless steel, is proposed, which is an eighth embodiment of the invention. The 320L57M4N stainless steel has virtually the same chemical composition as 320L35M4N, except for the molybdenum content. Therefore, only the differences are described, and the description of the various chemical compositions is not repeated.

[320L57M4N]

As mentioned above, the 320L57M4N stainless steel and the seventh embodiment 320L35M4N stainless steel have exactly the same wt% carbon, manganese, phosphorus, sulfur, oxygen, silicon, chromium, nickel, and nitrogen content, except for the molybdenum content. In 320L35M4N, the molybdenum content was between 3.00wt% and 5.00 wt%. In contrast, the molybdenum content of 320L57M4N stainless steel is between 5.00wt% and 7.00wt% Mo. In other words, 320L57M4N can be considered a higher molybdenum content version of 320L35M4N stainless steel.

It should be understood that, in addition to the molybdenum content, the paragraph on 320L35M4N applies here as well.

Molybdenum (Mo)

The molybdenum content of the 320L57M4N stainless steel may be 5.00wt% Mo or more and 7.00wt% Mo or less, but is preferably 6.00wt% Mo or more. In other words, the molybdenum content of 320L57M4N has a maximum of 7.00wt% Mo.

PRE _N

The pitting resistance equivalent of 320L57M4N was calculated using the same formula as 320L35M4N, but the PRE was calculated due to the different molybdenum content_NIs 45 or more, but preferably PRE_NMore than or equal to 50. This ensures that the material has good general corrosion resistance and local corrosion (pitting and crevice corrosion) resistance also in a wide range of processing environments. The 320L57M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 320L57M4N stainless steel was optimized during the melting phase to ensure the properties according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, so that the base material obtains mainly an austenitic microstructure after solution heat treatment, typically at 1100-125 degrees celsius, followed by water quenchingIn the range of 0 degrees celsius. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

Like the 320L35M4N embodiment, the 320L57M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium, and/or magnesium, measured in weight percent, and the composition of these elements is the same as that of 320L35M4N, and thus also as that of 304LM 4N.

The 320L57M4N stainless steel of the eighth embodiment has a minimum yield strength and minimum tensile strength that is equivalent or similar to the minimum yield strength and minimum tensile strength of 320L35M4N stainless steel. Similarly, the strength properties of the forged and cast plates of 320L57M4N were also equivalent to the strength properties of the forged and cast plates of 320L35M 4N. Thus, the specific intensity values are not repeated here, and reference is made to the preceding paragraph 320L35M 4N. Comparison of forging mechanical strength properties between 320L57M4N and conventional austenitic stainless steel uns 31703, and between 320L57M4N and uns 31753/uns 32053, indicates higher magnitudes of yield and tensile strengths, similar to those found at 320L35M 4N. Similarly, a comparison of the tensile properties of 320L57M4N shows that they are superior to the tensile properties specified for 22Cr duplex stainless steel and similar to the tensile properties specified for 25Cr super duplex stainless steel, just like 320L35M 4N.

This means that applications using forged 320L57M4N stainless steel can often be designed with reduced wall thickness, and therefore, when 320L57M4N stainless steel is specified, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as UNSS31703, S31753, and S32053. In fact, the minimum allowable design stress for forged 320L57M4N stainless steel is higher than the minimum allowable design stress for 22Cr duplex stainless steel, and is similar to 25Cr super duplex stainless steel.

For some applications, other variants of 320L57M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 320L57M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 320L35M4N and that of 304LM 4N. In other words, the paragraphs for these elements of 304LM4N also apply to 320L57M4N herein.

Tungsten (W)

The tungsten content of 320L57M4N stainless steel is similar to the tungsten content of 320L35M4N, and the pitting resistance equivalent, PRE, of 320L57M4N_NWCalculated using the formula used for 320L35M4N mentioned above, and the pitting resistance equivalent weight is PRE _NW≧ 47, but preferably PRE_NWIs greater than or equal to 52, which is caused by the different content of molybdenum. It should be apparent that the paragraphs concerning the use and effect of molybdenum in 320L35M4N also apply to 320L57M 4N.

Further, 320L57M4N may have a higher level of carbon, referred to as 320H57M4N or 32057M4N, corresponding to 320H35M4N and 32035M4N, respectively, discussed previously, and the carbon wt% ranges discussed previously also apply to 320H57M4N and 32057M 4N.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 320H57M4N or 32057M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They include a titanium stabilized version called 320H57M4NTi or 32057M4NTi, in contrast to the general 320L57M 4N. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized 320H57M4NNb or 32057M4NNb versions, where the niobium content is controlled according to the following formula:

nb8 xc minimum 1.0wt% Nb maximum, or Nb10 xc minimum 1.0wt% Nb maximum, respectively, to form niobium stabilizing derivatives of the alloy.

(iii) In addition, other variations of the alloy can also be made to include niobium plus tantalum stabilized versions of 320H57M4NNbTa or 32057M4NNbTa, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast plates of 320L57M4N stainless steel, and other variations, are generally provided in the same manner as the previous embodiments.

Further, another variation is proposed, appropriately referred to in this specification as 326L35M4N, which is a ninth embodiment of the invention.

[326L35M4N]

326L35M4N high strength austenitic stainless steels have high levels of nitrogen and are particularly resistant to pitting corrosionEquivalent PRE_N≧ 42, but preferably PRE_NNot less than 47. Referred to as PRE_NThe pitting resistance equivalent weight of (c) is calculated according to the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

326L35M4N stainless steel has been formulated to have a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. The chemical composition of 326L35M4N stainless steel is selective and is characterized by an alloy of the following chemical elements in weight percent (wt): 0.030wt% Cmax, 2.00wt% Mn max, 0.030wt% Pmax, 0.010wt% Smax, 0.75wt% Si max, 24.00wt% Cr-26.00 wt% Cr, 19.00wt% Ni-23.00 wt% Ni, 3.00wt% Mo-5.00 wt% Mo, 0.40wt% N-0.70 wt% N.

The 326L35M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements, such as 0.010wt% B max, 0.10wt% Ce max, 0.050wt% Al max, 0.01wt% Ca max and/or 0.01wt% Mg max, as well as other impurities typically present at residual levels.

The chemical composition of 326L35M4N stainless steel is optimized during the melting phase to primarily ensure that the base material has an austenitic microstructure after solution heat treatment, typically in the range of 1100-1250 degrees celsius, followed by water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure that the alloy is primarily austenitic. Thus, 326L35M4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures while ensuring excellent toughness at ambient and low temperatures. Whereas the chemical composition of 326L35M4N stainless steel is adjusted to reach PRE_NNot less than 42, but preferably PRE_NThe fact that this ensures good general corrosion resistance and local corrosion resistance (pitting and pitting) of the material also in a wide range of working environmentsCrevice corrosion) properties. The 326L35M4N stainless steel also has improved resistance to stress corrosion cracking in chloride containing environments compared to conventional austenitic stainless steels such as uns 31703 and uns 31753.

It has been determined that the optimal chemical composition range for the 326L35M4N stainless steel is carefully selected to include the following weight percentages of chemical elements based on the ninth embodiment:

Carbon (C)

The carbon content of the 326L35M4N stainless steel is less than or equal to 0.030wt% Cmax. Preferably, the carbon content should be ≥ 0.020wt% C and ≤ 0.030wt% C and more preferably ≤ 0.025wt% C.

Manganese (Mn)

The 326L35M4N stainless steel of the ninth embodiment may have two variations: low manganese or high manganese.

For low manganese alloys, the manganese content of the 326L35M4N stainless steel is 2.0wt% Mn or less. Preferably, the range is 1.0wt% or more and 2.0wt% or less of Mn, and more preferably 1.20wt% or more and 1.50wt% or less of Mn. By this composition, an optimum ratio of Mn to N of ≦ 5.0 is achieved, and preferably ≦ 1.42 and ≦ 5.0. More preferably, the ratio is ≧ 1.42 and ≦ 3.75.

For high manganese alloys, the manganese content of 326L35M4N is 4.0wt% Mn or less. Preferably, the manganese content is ≥ 2.0 wt.% Mn and ≤ 4.0 wt.% Mn, and more preferably, the upper limit is ≤ 3.0 wt.% Mn. Even more preferably, the upper limit is 2.50 wt.% Mn. With these selected ranges, a Mn to N ratio of ≦ 10.0 is achieved, and preferably ≦ 2.85 and ≦ 10.0. More preferably, the ratio of Mn to N is ≧ 2.85 and ≦ 7.50 for high-manganese alloys, and more preferably ≧ 2.85 and ≦ 6.25 for higher-manganese range alloys.

Phosphorus (P)

The phosphorus content of the 326L35M4N stainless steel is controlled to be less than or equal to 0.030wt% P. Preferably, the 326L35M4N alloy has ≦ 0.025wt% P and more preferably ≦ 0.020wt% P. Even more preferably, the alloy has ≦ 0.015wt% P and even further more preferably ≦ 0.010wt% P.

Sulfur (S)

The sulfur content of the 326L35M4N stainless steel of the ninth embodiment includes ≦ 0.010wt% S. Preferably, the 326L35M4N has 0.005wt% S or less and more preferably 0.003wt% S or less and even more preferably 0.001wt% S or less.

Oxygen (O)

The oxygen content of the 326L35M4N stainless steel is controlled to be as low as possible, and in the ninth embodiment, the 326L35M4N has ≦ 0.070wt% O. Preferably, the 326L35M4N has 0.050wt% O or less and more preferably 0.030wt% O or less. Even more preferably, the alloy has 0.010 wt.% O or less and even further more preferably 0.005 wt.% O or less.

Silicon (Si)

The silicon content of the 326L35M4N stainless steel is less than or equal to 0.75wt% Si. Preferably, the alloy has ≥ 0.25wt% Si and ≤ 0.75wt% Si. More preferably, the range is 0.40wt% Si or more and 0.60wt% Si or less. However, for certain higher temperature applications where improved oxidation resistance is desired, the silicon content may be 0.75 wt.% Si or more and 2.00 wt.% Si or less.

Chromium (Cr)

The chromium content of the 326L35M4N stainless steel is more than or equal to 24.00wt% of Cr and less than or equal to 26.00wt% of Cr. Preferably, the alloy has ≧ 25.00wt% Cr.

Nickel (Ni)

The nickel content of the 326L35M4N stainless steel is more than or equal to 19.00wt% of Ni and less than or equal to 23.00wt% of Ni. Preferably, the upper limit of Ni of the alloy is 22.00wt% Ni or less and more preferably 21.00wt% Ni or less.

Molybdenum (Mo)

The molybdenum content of the 326L35M4N stainless steel alloy is 3.00wt% Mo or more and 5.00wt% Mo or less, but preferably 4.00wt% Mo or more.

Nitrogen (N)

The nitrogen content of the 326L35M4N stainless steel is 0.70wt% N or less, but is preferably 0.40wt% N or more and 0.70wt% N or less. More preferably, the 326L35M4N has 0.40wt% N and 0.60wt% N, and even more preferably 0.45wt% N and 0.55wt% N.

PRE _N

The pitting resistance equivalent weight is calculated using the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

the 326L35M4N stainless steel has been formulated to have the following composition:

(i) the chromium content is more than or equal to 24.00wt% Cr and less than or equal to 26.00wt% Cr, but preferably more than or equal to 25.00wt% Cr;

The 326L35M4N stainless steel reached PRE by high levels of nitrogen_N≧ 42, but preferably PRE_NNot less than 47. This ensures that the alloy has good general corrosion resistance and localized corrosion (pitting and crevice corrosion) resistance in a wide range of processing environments. The 326L35M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 326L35M4N stainless steel was optimized during the melting phase to ensure the chemical composition according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, so that the base material obtains mainly an austenitic microstructure after solution heat treatment, typically at 1100 degrees celsius-1250 degrees celsius. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

The 326L35M4N stainless steel also has primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium and/or magnesium, measured in weight percent, and the composition of these elements is the same as that in 304LM 4N. In other words, the paragraphs on these elements in 304LM4N apply here as well.

According to the ninth embodiment, 326L35M4N stainless steel has a minimum yield strength of 55ksi or 380MPa for forged plates. More preferably, a minimum yield strength of 62ksi or 430MPa can be achieved for the forged plate. The cast plate had a minimum yield strength of 41ksi or 280 MPa. More preferably, a minimum yield strength of 48ksi or 330MPa can be achieved for the cast plate. Based on the preferred values, the wrought mechanical strength properties of 326L35M4N stainless steel are compared to those of UNSS31703, indicating that the minimum yield strength of 326L35M4N stainless steel is likely to be 2.1 times higher than the minimum yield strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 326L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31753, indicate that the minimum yield strength of 326L35M4N stainless steel is likely to be 1.79 times higher than the minimum yield strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 326L35M4N stainless steel compared to those of uns 32615 indicate that the minimum yield strength of 326L35M4N stainless steel is likely to be 1.95 times higher than the minimum yield strength specified for uns 32615.

According to the ninth embodiment, 326L35M4N stainless steel has a minimum tensile strength of 102ksi or 700MPa for a wrought plate. More preferably, a minimum tensile strength of 109ksi or 750MPa can be achieved for the forged plate. The cast plate had a minimum tensile strength of 95ksi or 650 MPa. More preferably, a minimum tensile strength of 102ksi or 700MPa can be achieved for the cast plate. Based on the preferred values, the forging mechanical strength properties of 326L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31703 indicate that the minimum tensile strength of 326L35M4N stainless steel may be more than 1.45 times higher than the minimum tensile strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 326L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31753, indicate that the minimum tensile strength of 326L35M4N stainless steel is likely to be 1.36 times higher than the minimum tensile strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 326L35M4N stainless steel compared to the forging mechanical strength properties of uns 32615 indicate that the minimum tensile strength of 326L35M4N stainless steel may be 1.36 times higher than the minimum tensile strength specified for uns 32615. Indeed, if the forging mechanical strength properties of 326L35M4N stainless steel were compared to those of 22Cr duplex stainless steel, it could be shown that the minimum tensile strength of 326L35M4N stainless steel is about 1.2 times higher than the minimum tensile strength specified for S31803, and is similar to the minimum tensile strength specified for 25Cr super duplex stainless steel. Thus, the minimum mechanical strength properties of the 326L35M4N stainless steel have been significantly improved compared to conventional austenitic stainless steels such as uns 31703, uns 31753 and uns 32615, and the tensile strength properties are superior to and similar to those specified for 22Cr duplex stainless steels.

This means that applications using forged 326L35M4N stainless steel can often be designed with reduced wall thickness, thus, when 326L35M4N stainless steel is specified, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as uns 31703, uns 31753, and uns 32615. In fact, the minimum allowable design stress of the forged 326L35M4N stainless steel is higher than the minimum allowable design stress of the 22Cr duplex stainless steel, and is similar to the 25Cr super duplex stainless steel.

For certain applications, other variants of 326L35M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 326L35M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 304LM 4N. In other words, the paragraphs for these elements of 304LM4N also apply to 320L35M 4N.

Tungsten (W)

The tungsten content of the 326L35M4N stainless steel is ≦ 2.00wt% W, but preferably ≦ 0.50wt% W and ≦ 1.00wt% W, and more preferably ≦ 0.75wt% W. For the 326L35M4N stainless steel tungsten containing variant, the pitting resistance equivalent weight is calculated using the formula:

PRE_NW=%Cr+[3.3×%(Mo+W)]+(16×%N)。

This tungsten-containing variant of 326L35M4N stainless steel has been specifically formulated to have the following composition:

The tungsten containing variant of 326L35M4N stainless steel has a high specified level of nitrogen and PRE_NW≧ 44, but preferably PRE_NWIs more than or equal to 49. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion. Tungsten may be added alone or in combination with the elements copper, vanadium, titanium and/or niobium plus tantalum, in all various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is extremely expensive and therefore purposefully limited to optimize the economics of the alloy, while optimizing the ductility, toughness and corrosivity of the alloy Can be used.

Carbon (C)

For certain applications, other variants of 326L35M4N stainless steel are desirable, which have been specifically formulated to contain higher levels of carbon. In particular, the carbon content of the 320L35M4N stainless steel may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C. These particular variants of 326L35M4N stainless steel are considered versions of 326H35M4N or 32635M4N, respectively.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 326H35M4N or 32635M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They included a titanium stabilized version known as 326H35M4NTi or 32635M4NTi, in contrast to the general 326L35M4N version. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized 326H35M4NNb or 32635M4NNb versions, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include the niobium plus tantalum stabilized 326H35M4NNbTa or 32635M4NNbTa versions, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast plates of 326L35M4N stainless steel, and other variations, are generally provided in the same manner as the previous examples.

Further, another variant, appropriately referred to as 326L57M4N high strength austenitic stainless steel, is proposed, which is a tenth embodiment of the invention. The 326L57M4N stainless steel has virtually the same chemical composition as the 326L35M4N stainless steel except for the molybdenum content. Therefore, only the differences are described, and the description of the various chemical compositions is not repeated.

[326L57M4N]

As mentioned above, the 326L57M4N and ninth embodiment 326L35M4N stainless steels have exactly the same wt% carbon, manganese, phosphorus, sulfur, oxygen, silicon, chromium, nickel, and nitrogen contents, except for the molybdenum content. In 326L35M4N, the molybdenum content was between 3.00wt% and 5.00 wt%. In contrast, the molybdenum content of 326L57M4N stainless steel is between 5.00wt% and 7.00wt% Mo. In other words, 326L57M4N can be considered a higher molybdenum content version of 326L35M4N stainless steel.

It will be appreciated that, in addition to the molybdenum content, the paragraph on 326L35M4N applies here as well.

Molybdenum (Mo)

The molybdenum content of the 326L57M4N stainless steel may be 5.00wt% Mo or more and 7.00wt% Mo or less, but is preferably 6.00wt% Mo or more and 7.00wt% Mo or less, and more preferably 6.50wt% Mo or more. In other words, the molybdenum content of 326L57M4N has a maximum of 7.00wt% Mo.

PRE _N

The pitting resistance equivalent of 326L57M4N was calculated using the same formula as 326L35M4N, but due to the molybdenum content, the PRE was calculated_NIs 48.5 or more, but preferably PRE_NNot less than 53.5. This ensures that the material has good general corrosion resistance and local corrosion (pitting and crevice corrosion) resistance also in a wide range of processing environments. The 326L57M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 326L57M4N stainless steel was optimized during the melting phase to ensure the chemical composition according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

Like the 326L35M4N embodiment, the 326L57M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium, and/or magnesium, measured in weight percent, and the composition of these elements is the same as that of 326L35M4N, and thus 304LM 4N.

The 326L57M4N stainless steel of the tenth embodiment has a minimum yield strength and minimum tensile strength that is equivalent or similar to the minimum yield strength and minimum tensile strength of 326L35M4N stainless steel. Similarly, the strength properties of the forged and cast plates of 326L57M4N were also equivalent to the strength properties of the forged and cast plates of 326L35M 4N. Thus, the specific intensity values are not repeated here, and reference is made to the preceding 326L35M4N paragraph. Comparison of forging mechanical strength properties between 326L57M4N and conventional austenitic stainless steel uns 31703, and between 326L57M4N and uns 31753/uns 32615, indicated higher magnitudes of yield and tensile strengths, similar to those found at 326L35M 4N. Similarly, a comparison of the tensile properties of 326L57M4N shows that they are superior to the tensile properties specified for 22Cr duplex stainless steel and similar to the tensile properties specified for 25Cr super duplex stainless steel, just like 326L35M 4N.

This means that applications using forged 326L57M4N stainless steel can often be designed with reduced wall thickness, and therefore, when 326L57M4N stainless steel is specified, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as uns 31703, S31753, and S32615. In fact, the minimum allowable design stress of the forged 326L57M4N stainless steel is higher than the minimum allowable design stress of the 22Cr duplex stainless steel, and is similar to the 25Cr super duplex stainless steel.

For some applications, other variants of 326L57M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 326L57M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 326L35M4N and that of 304LM 4N. In other words, the paragraphs for these elements of 304LM4N also apply to 326L57M4N herein.

Tungsten (W)

The tungsten content of 326L57M4N stainless steel is similar to the tungsten content of 326L35M4N, and the 326L57M4N is resistant to pitting corrosionQuantity, PRE_NWCalculated using the formula used for 326L35M4N mentioned above and the pitting resistance equivalent weight is PRE _NWNot less than 50.5, but preferably PRE_NWIs greater than or equal to 55.5, which is caused by the different content of molybdenum. It should be apparent that the paragraphs concerning the use and effect of molybdenum in 326L35M4N also apply to 326L57M 4N.

Further, 326L57M4N may have a higher level of carbon, referred to as 326H57M4N or 32657M4N, corresponding to 326H35M4N and 32635M4N, respectively, discussed previously, and the carbon wt% ranges discussed previously also apply to 326H57M4N and 32657M 4N.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 326H57M4N or 32657M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They include a titanium stabilized version known as 326H57M4NTi or 32657M4NTi, to contrast with the general 326L57M 4N. The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized 326H57M4NNb or 32657M4NNb versions, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include niobium plus tantalum stabilized 326H57M4NNbTa or 32657M4NNbTa versions, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast plates of 326L57M4N stainless steel, as well as other variations, are generally provided in the same manner as the previous embodiments.

Further, another variation is proposed, appropriately referred to in this specification as 351L35M4N, which is an eleventh embodiment of the invention.

[351L35M4N]

351L35M4N stainless steel has a high level of nitrogen and a specific pitting resistance equivalent PRE_N≧ 44, but preferably PRE_NIs more than or equal to 49. Referred to as PRE_NThe pitting resistance equivalent weight of (c) is calculated according to the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

351L35M4N stainless steel has been formulated to have a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. The chemical composition of 351L35M4N stainless steel is selective and is characterized by an alloy of the following chemical elements in weight percent (wt): 0.030wt% Cmax, 2.00wt% Mn max, 0.030wt% Pmax, 0.010wt% Smax, 0.75wt% Si max, 26.00wt% Cr-28.00 wt% Cr, 21.00wt% Ni-25.00 wt% Ni, 3.00wt% Mo-5.00 wt% Mo, 0.40wt% N-0.70 wt% N.

351L35M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements, such as 0.010wt% B max, 0.10wt% Ce max, 0.050wt% Al max, 0.01wt% Ca max and/or 0.01wt% Mg max, as well as other impurities that are typically present at residual levels.

The chemical composition of 351L35M4N stainless steel is optimized during the melting stage to primarily ensure that the base material has an austenitic microstructure after solution heat treatment, typically in the range of 1100-1250 degrees celsius, followed by water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure that the alloy is primarily austenitic. Thus, 351L35M4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures, while ensuring excellent toughness at ambient and low temperatures. Whereas the chemical composition of 351L35M4N stainless steel is adjusted to reach PRE_N44 or more, but preferably PRE_NThe fact of > 49 ensures that the material has good general corrosion resistance and local corrosion resistance (pitting and crevice corrosion) also in a wide range of processing environments. The 351L35M4N stainless steel also has improved resistance to stress corrosion cracking in chloride containing environments compared to conventional austenitic stainless steels such as uns 31703 and uns 31753.

It has been determined that the optimal chemical composition range for the 351L35M4N stainless steel is carefully selected to include the following weight percentages of chemical elements based on the eleventh example:

Carbon (C)

The carbon content of 351L35M4N stainless steel is less than or equal to 0.030wt% Cmax. Preferably, the carbon content should be ≥ 0.020wt% C and ≤ 0.030wt% C and more preferably ≤ 0.025wt% C.

Manganese (Mn)

The 351L35M4N stainless steel of the eleventh embodiment can have two variations: low manganese or high manganese.

For low manganese alloys, the manganese content of the 351L35M4N stainless steel is less than or equal to 2.0wt% Mn. Preferably, the range is 1.0wt% or more and 2.0wt% or less of Mn, and more preferably 1.20wt% or more and 1.50wt% or less of Mn. By this composition, an optimum ratio of Mn to N of ≦ 5.0 is achieved, and preferably ≦ 1.42 and ≦ 5.0. More preferably, the ratio is ≧ 1.42 and ≦ 3.75.

For high manganese alloys, the manganese content of 351L35M4N is 4.0wt% Mn or less. Preferably, the manganese content is ≥ 2.0 wt.% Mn and ≤ 4.0 wt.% Mn, and more preferably, the upper limit is ≤ 3.0 wt.% Mn. Even more preferably, the upper limit is 2.50 wt.% Mn. With these selected ranges, a Mn to N ratio of ≦ 10.0 is achieved, and preferably ≦ 2.85 and ≦ 10.0. More preferably, for high manganese alloys, the ratio of Mn to N is ≧ 2.85 and ≦ 7.50, and more preferably ≧ 2.85 and ≦ 6.25.

Phosphorus (P)

The phosphorus content of 351L35M4N stainless steel is controlled to be less than or equal to 0.030wt% P. Preferably, the 351L35M4N alloy has ≦ 0.025wt% P and more preferably ≦ 0.020wt% P. Even more preferably, the alloy has ≦ 0.015wt% P and even further more preferably ≦ 0.010wt% P.

Sulfur (S)

The sulfur content of the 351L35M4N stainless steel of the eleventh embodiment includes ≦ 0.010wt% S. Preferably, the 351L35M4N has 0.005wt% S or less and more preferably 0.003wt% S or less and even more preferably 0.001wt% S or less.

Oxygen (O)

The oxygen content of 351L35M4N stainless steel is controlled to be as low as possible, and in the eleventh embodiment, the 351L35M4N has ≦ 0.070wt% O. Preferably, the 351L35M4N has 0.050wt% O or less and more preferably 0.030wt% O or less. Even more preferably, the alloy has 0.010 wt.% O or less and even further more preferably 0.005 wt.% O or less.

Silicon (Si)

The silicon content of 351L35M4N stainless steel is less than or equal to 0.75wt% Si. Preferably, the alloy has ≥ 0.25wt% Si and ≤ 0.75wt% Si. More preferably, the range is 0.40wt% Si or more and 0.60wt% Si or less. However, for certain higher temperature applications where improved oxidation resistance is desired, the silicon content may be 0.75 wt.% Si or more and 2.00 wt.% Si or less.

Chromium (Cr)

The chromium content of the 351L35M4N stainless steel is more than or equal to 26.00wt% of Cr and less than or equal to 28.00wt% of Cr. Preferably, the alloy has 27.00wt% Cr or more.

Nickel (Ni)

The nickel content of the 351L35M4N stainless steel is more than or equal to 21.00wt% of Ni and less than or equal to 25.00wt% of Ni. Preferably, the upper limit of Ni of the alloy is 24.00wt% Ni or less and more preferably 23.00wt% Ni or less.

Molybdenum (Mo)

The molybdenum content of the 351L35M4N stainless steel is more than or equal to 3.00wt% Mo and less than or equal to 5.00wt% Mo, but is preferably more than or equal to 4.00wt% Mo.

Nitrogen (N)

The nitrogen content of 351L35M4N stainless steel is 0.70wt% N or less, but is preferably 0.40wt% N or more and 0.70wt% N or less. More preferably, the 351L35M4N has 0.40wt% N and 0.60wt% N, and even more preferably 0.45wt% N and 0.55wt% N.

PRE _N

The pitting resistance equivalent weight is calculated using the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

the 351L35M4N stainless steel has been specifically formulated to have the following composition:

(i) the chromium content is more than or equal to 26.00wt% Cr and less than or equal to 28.00wt% Cr, but preferably more than or equal to 27.00wt% Cr;

The 351L35M4N stainless steel achieves PRE with high levels of nitrogen_N≧ 44, but preferably PRE_NIs more than or equal to 49. This ensures that the alloy has good general corrosion resistance and localized corrosion (pitting and crevice corrosion) resistance in a wide range of processing environments. The 351L35M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 351L35M4N stainless steel was optimized during the melting phase to ensure the chemical composition according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

351L35M4N stainless steel also has primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium and/or magnesium, measured in weight percent, and the composition of these elements is the same as that in 304LM 4N. In other words, the paragraphs on these elements in 304LM4N apply here as well.

According to the eleventh embodiment, 351L35M4N stainless steel has a minimum yield strength of 55ksi or 380MPa for a forged plate. More preferably, a minimum yield strength of 62ksi or 430MPa can be achieved for the forged plate. The cast plate had a minimum yield strength of 41ksi or 280 MPa. More preferably, a minimum yield strength of 48ksi or 330MPa can be achieved for the cast plate. Based on the preferred values, the forging mechanical strength properties of 351L35M4N stainless steel are compared to those of UNSS31703, indicating that the minimum yield strength of 351L35M4N stainless steel is likely to be 2.1 times higher than the minimum yield strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 351L35M4N stainless steel were compared to those of UNSS31753, indicating that the minimum yield strength of 351L35M4N stainless steel is likely to be 1.79 times greater than the minimum yield strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 351L35M4N stainless steel were compared to those of UNSS35115, indicating that the minimum yield strength of 351L35M4N stainless steel may be 1.56 times higher than the minimum yield strength specified for UNSS 35115.

According to the eleventh embodiment, 351L35M4N stainless steel has a minimum tensile strength of 102ksi or 700MPa for a forged plate. More preferably, a minimum tensile strength of 109ksi or 750MPa can be achieved for the forged plate. The cast plate had a minimum tensile strength of 95ksi or 650 MPa. More preferably, a minimum tensile strength of 102ksi or 700MPa can be achieved for the cast plate. Based on the preferred values, the forging mechanical strength properties of 351L35M4N stainless steel are compared to those of UNSS31703, indicating that the minimum tensile strength of 351L35M4N stainless steel may be more than 1.45 times higher than the minimum tensile strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 351L35M4N stainless steel compared to those of UNSS31753 indicate that the minimum tensile strength of 351L35M4N stainless steel is likely to be 1.36 times higher than the minimum tensile strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 351L35M4N stainless steel compared to those of UNSS35115 indicate that the minimum tensile strength of 351L35M4N stainless steel is likely to be 1.28 times higher than the minimum tensile strength specified for UNSS 35115. Indeed, if the forging mechanical strength properties of 351L35M4N stainless steel are compared to those of 22Cr duplex stainless steel, it can be shown that the minimum tensile strength of 351L35M4N stainless steel is about 1.2 times higher than that specified for S31803, and is similar to that specified for 25Cr super duplex stainless steel. Thus, the minimum mechanical strength properties of the 351L35M4N stainless steel have been significantly improved compared to conventional austenitic stainless steels such as uns 31703, uns 31753 and uns 35115, and the tensile strength properties are superior to those specified for 22Cr duplex stainless steels and similar to those specified for 25Cr super duplex stainless steels.

This means that applications using forged 351L35M4N stainless steel can often be designed with reduced wall thickness, and therefore, when specifying 351L35M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as uns 31703, S31753, and S35115. In fact, the minimum allowable design stress for forged 351L35M4N stainless steel is higher than the minimum allowable design stress for 22Cr duplex stainless steel, and is similar to 25Cr super duplex stainless steel.

For some applications, other variants of 351L35M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 351L35M4N stainless steel is selective, and that the copper and vanadium composition is the same as that of 304LM 4N. In other words, the paragraphs for these elements of 304LM4N also apply to 351L35M 4N.

Tungsten (W)

351L35M4N stainless steel has a tungsten content of ≤ 2.00wt% W, but preferably ≥ 0.50wt% W and ≤ 1.00wt% W, and more preferably ≥ 0.75wt% W. For the 351L35M4N stainless steel tungsten containing variant, the pitting resistance equivalent weight was calculated using the formula:

PRE_NW=%Cr+[3.3×%(Mo+W)]+(16×%N)。

This tungsten-containing variant of 351L35M4N stainless steel has been specifically formulated to have the following composition:

The tungsten containing variant of 351L35M4N stainless steel has a high specified level of nitrogen and PRE_NW≧ 46, but preferably PRE_NWNot less than 51. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion. Tungsten may be added alone or in combination with the elements copper, vanadium, titanium and/or niobium plus tantalum, in all various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is extremely expensive and therefore is purposefully limited to optimize the economics of the alloy, as well as the ductility, toughness and corrosion properties of the alloy.

Carbon (C)

For certain applications, other variants of 351L35M4N stainless steel are desirable, which have been specifically formulated to contain higher levels of carbon. Specifically, the carbon content of the 351L35M4N stainless steel may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C. These particular variants of 351L35M4N stainless steel are considered to be 351H35M4N or 35135M4N versions, respectively.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 351H35M4N or 35135M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They included a titanium stabilized version called 351H35M4NTi or 35135M4NTi, in contrast to the general 351L35M4N version.

The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized versions of 351H35M4NNb or 35135M4NNb, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include the niobium plus tantalum stabilized 351H35M4NNbTa or 35135M4NNbTa versions, where the niobium plus tantalum content is controlled according to the following formula:

Forged and cast versions of 351L35M4N stainless steel, as well as other variations, are generally provided in the same manner as the previous embodiments.

Further, another variation, properly called 351L57M4N high strength austenitic stainless steel, is proposed, which is a twelfth embodiment of the invention. The 351L57M4N stainless steel has virtually the same chemical composition as the 351L35M4N stainless steel, except for the molybdenum content. Therefore, only the differences are described, and the description of the various chemical compositions is not repeated.

[351L57M4N]

As mentioned above, the 351L57M4N and eleventh embodiment 351L35M4N stainless steels have exactly the same wt% carbon, manganese, phosphorus, sulfur, oxygen, silicon, chromium, nickel, and nitrogen contents, except for the molybdenum content. In 351L35M4N, the molybdenum content is between 3.00wt% and 5.00wt% Mo. In contrast, the molybdenum content of 351L57M4N stainless steel is between 5.00wt% and 7.00wt% Mo. In other words, 351L57M4N can be considered a higher molybdenum content version of 351L35M4N stainless steel.

It will be appreciated that, in addition to the molybdenum content, the paragraph on 351L35M4N applies here as well.

Molybdenum (Mo)

The molybdenum content of the 351L57M4N stainless steel may be 5.00wt% Mo or more and 7.00wt% Mo or less, but is preferably 5.50wt% Mo or more and 6.50wt% Mo or less, and more preferably 6.00wt% Mo or more. In other words, the molybdenum content of 351L57M4N has a maximum of 7.00wt% Mo.

PRE _N

The pitting resistance equivalent of 351L57M4N was calculated using the same formula as 351L35M4N, but due to the molybdenum content, the PRE was calculated_NIs ≧ 50.5, but PRE is preferred_NIs more than or equal to 55.5. This ensures that the material has good general corrosion resistance and local corrosion (pitting and crevice corrosion) resistance also in a wide range of processing environments. In a chloride-containing environment when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753The 351L57M4N stainless steel also improved stress corrosion cracking resistance. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

351L57M4N stainless steel is optimized in the melting stage to ensure a chemical composition according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

Like the 351L35M4N embodiment, the 351L57M4N stainless steel also includes primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium, and/or magnesium, measured in weight percent, and the composition of these elements is the same as that of the 351L35M4N, and thus also as that of the 304LM 4N.

The 351L57M4N stainless steel of the twelfth embodiment has a minimum yield strength and minimum tensile strength that are equivalent or similar to the minimum yield strength and minimum tensile strength of the 351L35M4N stainless steel. Similarly, the strength properties of the 351L57M4N forged and cast plates were also equivalent to the 351L35M4N forged and cast plates. Thus, the specific intensity values are not repeated here, and reference is made to the preceding paragraph 351L35M 4N. Comparison of forging mechanical strength properties between 351L57M4N and conventional austenitic stainless steel uns 31703, and between 351L57M4N and uns 31753/uns 35115, indicates higher magnitudes of yield and tensile strengths, similar to those found at 351L35M 4N. Similarly, a comparison of the tensile properties of 351L57M4N shows that they are superior to the tensile properties specified for 22Cr duplex stainless steel and similar to the tensile properties specified for 25Cr super duplex stainless steel, just like 351L35M 4N.

This means that applications using forged 351L57M4N stainless steel can often be designed with reduced wall thickness, and therefore, when specifying 351L57M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as uns 31703, S31753, and S35115. In fact, the minimum allowable design stress for forged 351L57M4N stainless steel is higher than the minimum allowable design stress for 22Cr duplex stainless steel, and is similar to 25Cr super duplex stainless steel.

For some applications, other variants of 351L57M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 351L57M4N stainless steel is selective, and that the copper and vanadium compositions are the same as the 351L35M4N copper and vanadium compositions and the 304LM4N copper and vanadium compositions. In other words, the paragraphs on these elements of 304LM4N also apply to 351L57M4N herein.

Tungsten (W)

The tungsten content of 351L57M4N stainless steel is similar to that of 351L35M4N, and the pitting resistance equivalent, PRE, of 351L57M4N_NWCalculated using the formula used for 351L35M4N mentioned above, and the pitting corrosion resistance equivalent is PRE _NW≧ 52.5, but preferably PRE_NW57.5, which is caused by the difference in the molybdenum content. It should be apparent that the paragraphs concerning the use and effect of molybdenum in 351L35M4N also apply to 351L57M 4N.

Further, 351L57M4N may have a higher level of carbon, referred to as 351H57M4N or 35157M4N, corresponding to 351H35M4N and 35135M4N, respectively, discussed previously, and the carbon wt% ranges discussed previously also apply to 351H57M4N and 35157M 4N.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 351H57M4N or 35157M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They included titanium stabilized versions referred to as 351H57M4NTi or 35157M4NTi, to contrast with the generic 351L57M 4N.

The titanium content was controlled according to the following formula:

(ii) There are also niobium stabilized versions of 351H57M4NNb or 35157M4NNb, where the niobium content is controlled according to the following formula:

nb8 xc minimum, 1.0wt% Nb maximum or Nb10 xc minimum, 1.0wt% Nb maximum, respectively, to form niobium stabilizing derivatives of the alloy.

(iii) In addition, other variations of the alloy can also be made to include the niobium plus tantalum stabilized 351H57M4NNbTa or 35157M4NNbTa versions, where the niobium plus tantalum content is controlled according to the following formula:

351L57M4N stainless steel forged and cast plates, as well as other variations, are generally provided in the same manner as the previous embodiments.

Further, another variation is proposed, appropriately referred to in this specification as 353L35M4N, which is a thirteenth embodiment of the invention.

[353L35M4N]

353L35M4N stainless steel has a high level of nitrogen and a specific pitting resistance equivalent PRE_N≧ 46, but preferably PRE_NNot less than 51. Referred to as PRE_NThe pitting resistance equivalent weight of (c) is calculated according to the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

353L35M4N stainless steel has been formulated to have a unique combination of high mechanical strength properties with excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. The chemical composition of 353L35M4N stainless steel is selective and is characterized by an alloy of the following chemical elements in weight (wt%): 0.030wt% Cmax, 2.00wt% Mn max, 0.030wt% Pmax, 0.010wt% Smax, 0.75wt% Si max, 28.00wt% Cr-30.00 wt% Cr, 23.00wt% Ni-27.00 wt% Ni, 3.00wt% Mo-5.00 wt% Mo, 0.40wt% N-0.70 wt% N.

The 353L35M4N stainless steel also contains primarily Fe as the remainder, and may also contain very small amounts of other elements, such as 0.010wt% B max, 0.10wt% Ce max, 0.050wt% Al max, 0.01wt% Ca max and/or 0.01wt% Mg max, as well as other impurities typically present at residual levels.

The chemical composition of 353L35M4N stainless steel is optimized during the melting phase to primarily ensure that the base material has an austenitic microstructure after solution heat treatment, typically in the range of 1100-1250 degrees celsius, followed by water quenching.The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure that the alloy is primarily austenitic. Thus, 353L35M4N stainless steel exhibits a unique combination of high strength and ductility at ambient temperatures while ensuring excellent toughness at ambient and low temperatures. Chemical analysis was adjusted to reach PRE in view of 353L35M4N stainless steel_N≧ 46, but preferably PRE_NThe fact that this ensures good general corrosion resistance and local corrosion resistance (pitting and crevice corrosion) of the material also in a wide range of processing environments. The 353L35M4N stainless steel also has improved stress corrosion cracking resistance compared to conventional austenitic stainless steels such as uns 31703 and uns 31753 in chloride containing environments.

It has been determined that the optimal chemical composition range for 353L35M4N stainless steel is carefully selected to include the following weight percentages of chemical elements based on the thirteenth embodiment:

Carbon (C)

The carbon content of 353L35M4N stainless steel is less than or equal to 0.030wt% C maximum. Preferably, the carbon content should be ≥ 0.020wt% C and ≤ 0.030wt% C and more preferably ≤ 0.025wt% C.

Manganese (Mn)

The 353L35M4N stainless steel of the thirteenth embodiment can have two variations: low manganese or high manganese.

For low manganese alloys, the manganese content of 353L35M4N stainless steel is less than or equal to 2.0wt% Mn. Preferably, the range is 1.0wt% or more and 2.0wt% or less of Mn, and more preferably 1.20wt% or more and 1.50wt% or less of Mn. By this composition, an optimum ratio of Mn to N of ≦ 5.0 is achieved, and preferably ≦ 1.42 and ≦ 5.0. More preferably, the ratio is ≧ 1.42 and ≦ 3.75.

For high manganese alloys, the manganese content of 353L35M4N was 4.0wt% Mn or less. Preferably, the manganese content is ≥ 2.0 wt.% Mn and ≤ 4.0 wt.% Mn, and more preferably, the upper limit is ≤ 3.0 wt.% Mn. Even more preferably, the upper limit is 2.50 wt.% Mn. With these selected ranges, a Mn to N ratio of ≦ 10.0 is achieved, and preferably ≦ 2.85 and ≦ 10.0. More preferably, the high manganese alloy has a Mn to N ratio of ≥ 2.85 and ≤ 7.50, and more preferably ≥ 2.85 and ≤ 6.25.

Phosphorus (P)

The phosphorous content of 353L35M4N stainless steel is controlled to be less than or equal to 0.030wt% P. Preferably, the 353L35M4N alloy has ≦ 0.025wt% P and more preferably ≦ 0.020wt% P. Even more preferably, the alloy has ≦ 0.015wt% P and even further more preferably ≦ 0.010wt% P.

Sulfur (S)

The sulfur content of the 353L35M4N stainless steel of the thirteenth embodiment includes 0.010wt% S or less. Preferably, the 353L35M4N has ≦ 0.005wt% S and more preferably ≦ 0.003wt% S, and even more preferably ≦ 0.001wt% S.

Oxygen (O)

The oxygen content of 353L35M4N stainless steel is controlled to be as low as possible, and in the thirteenth embodiment, the 353L35M4N has ≦ 0.070wt% O. Preferably, the 353L35M4N has 0.050wt% O or less and more preferably 0.030wt% O or less. Even more preferably, the alloy has 0.010 wt.% O or less and even further more preferably 0.005 wt.% O or less.

Silicon (Si)

The silicon content of 353L35M4N stainless steel is less than or equal to 0.75wt% Si. Preferably, the alloy has ≥ 0.25wt% Si and ≤ 0.75wt% Si. More preferably, the range is 0.40wt% Si or more and 0.60wt% Si or less. However, for certain higher temperature applications where improved oxidation resistance is desired, the silicon content may be 0.75 wt.% Si or more and 2.00 wt.% Si or less.

Chromium (Cr)

The chromium content of the 353L35M4N stainless steel is more than or equal to 28.00wt% of Cr and less than or equal to 30.00wt% of Cr. Preferably, the alloy has ≧ 29.00wt% Cr.

Nickel (Ni)

The nickel content of the 353L35M4N stainless steel is more than or equal to 23.00wt% of Ni and less than or equal to 27.00wt% of Ni. Preferably, the upper limit of Ni of the alloy is 26.00wt% Ni or less and more preferably 25.00wt% Ni or less.

Molybdenum (Mo)

The molybdenum content of the 353L35M4N stainless steel is more than or equal to 3.00wt% Mo and less than or equal to 5.00wt% Mo, but is preferably more than or equal to 4.00wt% Mo.

Nitrogen (N)

The nitrogen content of the 353L35M4N stainless steel is 0.70wt% N or less, but is preferably 0.40wt% N or more and 0.70wt% N or less. More preferably, the 353L35M4N has 0.40wt% N and 0.60wt% N, and even more preferably 0.45wt% N and 0.55wt% N.

PRE _N

The pitting resistance equivalent weight is calculated using the formula:

PRE_N=%Cr+(3.3×%Mo)+(16×%N)。

the 353L35M4N stainless steel has been specifically formulated to have:

(i) the chromium content is more than or equal to 28.00wt% Cr and less than or equal to 30.00wt% Cr, but preferably more than or equal to 29.00wt% Cr;

The 353L35M4N stainless steel reached PRE by high levels of nitrogen_N≧ 46, but preferably PRE_NNot less than 51. This ensures that the material has good general corrosion resistance and local corrosion (pitting and crevice corrosion) resistance also in a wide range of processing environments. When used with conventional austenitic stainless steels such as UNSS31703 and UNSS31 in chloride-containing environments753 the 353L35M4N stainless steel also exhibits improved resistance to stress corrosion cracking. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 353L35M4N stainless steel was optimized during the melting phase to ensure that the alloy was compatible with Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

The 353L35M4N stainless steel also has primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium, and/or magnesium, measured in weight percent, and the composition of these elements is the same as that in 304LM 4N. In other words, the paragraphs on these elements in 304LM4N apply here as well.

According to the thirteenth embodiment, 353L35M4N stainless steel has a minimum yield strength of 55ksi or 380MPa for a forged plate. More preferably, a minimum yield strength of 62ksi or 430MPa can be achieved for the forged plate. The cast plate had a minimum yield strength of 41ksi or 280 MPa. More preferably, a minimum yield strength of 48ksi or 330MPa can be achieved for the cast plate. Based on the preferred values, the wrought mechanical strength properties of 353L35M4N stainless steel were compared to those of UNSS31703, indicating that the minimum yield strength of 353L35M4N stainless steel may be 2.1 times higher than the minimum yield strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 353L35M4N stainless steel compared to those of UNSS31753 indicate that the minimum yield strength of 353L35M4N stainless steel is likely to be 1.79 times greater than the minimum yield strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 353L35M4N stainless steel compared to those of UNSS35315 indicate that the minimum yield strength of 353L35M4N stainless steel is likely to be 1.59 times greater than the minimum yield strength specified for UNSS 35315.

According to the thirteenth embodiment, 353L35M4N stainless steel has a minimum tensile strength of 102ksi or 700MPa for a forged plate. More preferably, a minimum tensile strength of 109ksi or 750MPa can be achieved for the forged plate. The cast plate had a minimum tensile strength of 95ksi or 650 MPa. More preferably, a minimum tensile strength of 102ksi or 700MPa can be achieved for the cast plate. Based on the preferred values, the forging mechanical strength properties of 353L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31703 indicate that the minimum tensile strength of 353L35M4N stainless steel may be more than 1.45 times greater than the minimum tensile strength specified for UNSS 31703. Similarly, the forging mechanical strength properties of 353L35M4N stainless steel compared to the forging mechanical strength properties of UNSS31753 indicate that the minimum tensile strength of 353L35M4N stainless steel is likely to be 1.36 times higher than the minimum tensile strength specified for UNSS 31753. Likewise, the forging mechanical strength properties of 353L35M4N stainless steel compared to those of UNSS35315 indicate that the minimum tensile strength of 353L35M4N stainless steel may be 1.15 times greater than the minimum tensile strength specified for UNSS 35315. Indeed, if the wrought mechanical strength properties of 353L35M4N stainless steel are compared to those of 22Cr duplex stainless steel, then it can be shown that the minimum tensile strength of 353L35M4N stainless steel is about 1.2 times higher than the minimum tensile strength specified for S31803, and is similar to the minimum tensile strength specified for 25Cr super duplex stainless steel. Thus, the minimum mechanical strength properties of 353L35M4N stainless steel have been significantly improved compared to conventional austenitic stainless steels such as uns 31703, uns 31753 and uns 35315, and the tensile strength properties are superior to those specified for 22Cr duplex stainless steels and similar to those specified for 25Cr super duplex stainless steels.

This means that applications using forged 353L35M4N stainless steel can often be designed with reduced wall thickness, thus, when specifying 353L35M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as UNSS31703, S31753, and S35315. In fact, the minimum allowable design stress for forging 353L35M4N stainless steel is higher than the minimum allowable design stress for 22Cr duplex stainless steel, and is similar to 25Cr super duplex stainless steel.

For certain applications, other variants of 353L35M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 353L35M4N stainless steel according to claim 1 is selective and the copper and vanadium composition is the same as that of 304LM 4N. In other words, the paragraph for these elements of 304LM4N also applies to 353L35M 4N.

Tungsten (W)

The tungsten content of the 353L35M4N stainless steel is ≤ 2.00wt% W, but preferably ≥ 0.50wt% W and ≤ 1.00wt% W, and more preferably ≥ 0.75wt% W. For the 353L35M4N stainless steel tungsten containing variant, the pitting resistance equivalent weight was calculated using the formula:

PRE_NW=%Cr+[3.3×%(Mo+W)]+(16×%N)。

This tungsten-containing variant of 353L35M4N stainless steel has been specifically formulated to have the following composition:

The tungsten containing variant of 353L35M4N stainless steel has a high specified level of nitrogen and PRE_NW48, but preferably PRE_NWIs more than or equal to 53. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion. Tungsten may be added alone or in combination with the elements copper, vanadium, titanium and/or niobium plus tantalum, in all various combinations, to further enhance the overall corrosion performance of the alloy. Tungsten is extremely expensive and therefore is purposefully limited to optimize the economics of the alloy, as well as the ductility, toughness and corrosion properties of the alloy.

Carbon (C)

For certain applications, other variants of 353L35M4N stainless steel are desirable, which have been specifically formulated to contain higher levels of carbon. Specifically, the carbon content of 353L35M4N can be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C. These particular variants of 353L35M4N stainless steel are considered versions of 353H35M4N or 35335M4N, respectively.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 353H35M4N or 35335M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon content may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They included a titanium stabilized version called 353H35M4NTi or 35335M4NTi, in contrast to the typical 353L35M4N version.

The titanium content was controlled according to the following formula:

(ii) There are also versions of 353H35M4NNb or 35335M4NNb for niobium stabilization, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include the 353H35M4NNbTa or 35335M4NNbTa versions of niobium plus tantalum stabilized with the niobium plus tantalum content controlled according to the following formula:

353L35M4N stainless steel forged and cast plates and other variations are generally provided in the same manner as the previous examples.

Further, another variation, properly called 353L57M4N high strength austenitic stainless steel, is proposed, which is a fourteenth embodiment of the invention. The 353L57M4N stainless steel had virtually the same chemical composition as the 353L35M4N stainless steel except for the molybdenum content. Therefore, only the differences are described, and the description of the various chemical compositions is not repeated.

[353L57M4N]

As mentioned above, the 353L57M4N and thirteenth embodiment 353L35M4N stainless steels have exactly the same wt% carbon, manganese, phosphorus, sulfur, oxygen, silicon, chromium, nickel, and nitrogen contents, except for the molybdenum content. In 353L35M4N, the molybdenum content was between 3.00wt% and 5.00wt% Mo. In contrast, the molybdenum content of 353L57M4N stainless steel is between 5.00wt% and 7.00wt% Mo. In other words, 353L57M4N may be considered a higher molybdenum content version of 353L35M4N stainless steel.

It should be understood that, in addition to the molybdenum content, the paragraph on 353L35M4N applies here as well.

Molybdenum (Mo)

The molybdenum content of the 353L57M4N stainless steel may be 5.00wt% Mo or more and 7.00wt% Mo or less, but is preferably 5.50wt% Mo or more and 6.50wt% Mo or less, and is more preferably 6.00wt% Mo or more. In other words, the molybdenum content of 353L57M4N had a maximum of 7.00wt% Mo.

PRE _N

The pitting resistance equivalent of 353L57M4N was calculated using the same formula as 353L35M4N, but due to the molybdenum content, the PRE was calculated_NIs 52.5 or more, but preferably PRE_NNot less than 57.5. This ensures that the material has good general corrosion resistance and local corrosion (pitting and crevice corrosion) resistance also in a wide range of processing environments. The 353L57M4N stainless steel also has improved stress corrosion cracking resistance when compared to conventional austenitic stainless steels such as UNSS31703 and UNSS31753 in chloride containing environments. It should be emphasized that these equations ignore the effect of microstructural factors on passive destruction by pitting or crevice corrosion.

The chemical composition of 353L57M4N stainless steel was optimized during the melting phase to ensure that the alloy was compatible with Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, but preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. Micro-size of base material under solution heat treatmentThe microstructure, as well as the microstructure of the as-welded weld metal and the heat-affected zone of the weld, is controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state.

Like 353L35M4N, 353L57M4N stainless steel also includes primarily Fe as the remainder, and may also contain very small amounts of other elements such as boron, cerium, aluminum, calcium, and/or magnesium, measured in weight percent, and which have the same composition as 353L35M4N, and thus 304LM 4N.

The 353L57M4N stainless steel of the fourteenth embodiment has a minimum yield strength and minimum tensile strength that is equivalent or similar to the minimum yield strength and minimum tensile strength of 353L35M4N stainless steel. Similarly, the strength properties of the 353L57M4N forged and cast plates were also equivalent to the strength properties of the 353L35M4N forged and cast plates. Thus, the specific intensity values are not repeated here and reference is made to the preceding paragraph of 353L35M 4N. Comparison of forging mechanical strength properties between 353L57M4N and conventional austenitic stainless steel uns 31703, and between 353L57M4N and uns 31753/uns 35315, indicates higher magnitudes of yield and tensile strengths, similar to those found at 353L35M 4N. Similarly, a comparison of the tensile properties of 353L57M4N shows that they are superior to the tensile properties specified for 22Cr duplex stainless steel and similar to the tensile properties specified for 25Cr super duplex stainless steel, just like 353L35M 4N.

This means that applications using forged 353L57M4N stainless steel can often be designed with reduced wall thickness, thus, when specifying 353L57M4N stainless steel, significant weight savings will result due to the significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as UNSS31703, S31753, and S35315. In fact, the minimum allowable design stress for forging 353L57M4N stainless steel is higher than the minimum allowable design stress for 22Cr duplex stainless steel, and is similar to 25Cr super duplex stainless steel.

For some applications, other variants of 353L57M4N stainless steel have been purposefully formulated for manufacturing, including specified levels of other alloying elements such as copper, tungsten, and vanadium. It has been determined that the optimal chemical composition range for other variants of 353L57M4N stainless steel is selective, and that the copper and vanadium compositions are the same as the 353L35M4N copper and vanadium compositions and 304LM4N copper and vanadium compositions. In other words, the paragraphs on these elements of 304LM4N also apply to 351L57M4N herein.

Tungsten (W)

The tungsten content of 353L57M4N stainless steel is similar to that of 353L35M4N, and the pitting resistance equivalent, PRE, of 353L57M4N_NWCalculated using the formula used for 353L35M4N mentioned above, and the pitting corrosion resistance equivalent is PRE _NW≧ 54.5, but preferably PRE_NW59.5, which is caused by the difference of the molybdenum content. It should be apparent that the paragraph regarding the use and effect of molybdenum in 353L35M4N also applies to 353L57M 4N.

Further, 353L57M4N may have a higher level of carbon, referred to as 353H57M4N or 35357M4N, corresponding to 353H35M4N and 35335M4N, respectively, discussed previously, and the carbon wt% ranges discussed previously apply to 353H57M4N and 35357M 4N.

Titanium (Ti)/niobium (Nb) plus tantalum (Ta)

Furthermore, for certain applications, other stabilizing variants of 353H57M4N or 35357M4N stainless steel are desirable, which have been specifically formulated to be manufactured to contain higher levels of carbon. In particular, the carbon may be ≥ 0.040wt% C and < 0.10wt% C, but preferably ≤ 0.050wt% C or > 0.030wt% C and ≤ 0.08wt% C, but preferably < 0.040wt% C.

(i) They included titanium stabilized versions referred to as 353H57M4NTi or 35357M4NTi to contrast with the generic 353L57M 4N. The titanium content was controlled according to the following formula:

(ii) There are also versions of 353H57M4NNb or 35357M4NNb for niobium stabilization, where the niobium content is controlled according to the following formula:

(iii) In addition, other variations of the alloy can also be made to include the 353H57M4NNbTa or 35357M4NNbTa versions of niobium plus tantalum stabilized with the niobium plus tantalum content controlled according to the following formula:

353L57M4N stainless steel forged and cast plates and other variations are generally provided in the same manner as the previous embodiments.

The described embodiments should not be construed as limiting, and other embodiments may be formulated in addition to those described herein. For example, all of the different types of alloy compositions of the above-described embodiments or austenitic stainless steel series, as well as variations thereof, may be produced with tailored chemistries for specified applications. One example is the use of higher Mn contents of > 2.00 wt.% Mn and ≦ 4.00 wt.% Mn to facilitate the passage ofAccording to Schoefer⁶The proportional amount of the proposed equation reduces the nickel content level. This will reduce the overall cost of the alloy, since nickel is extremely expensive. Thus, the nickel content can be purposefully limited to optimize the economics of the alloy.

The described embodiments may also be controlled to meet other criteria that have been defined herein. For example, the control examples have a specified ratio of manganese to carbon + nitrogen in addition to the ratio of manganese to nitrogen.

For "LM 4N", the type of low manganese range alloy, this achieves an optimum ratio of Mn to C + N ≦ 4.76, and preferably ≧ 1.37 and ≦ 4.76. More preferably, the ratio of Mn to C + N is ≥ 1.37 and ≤ 3.57. For "LM 4N", the type of high manganese range alloy, this achieves an optimal Mn to C + N ratio ≦ 9.52, and preferably ≦ 2.74 and ≦ 9.52. More preferably, for these "LM 4N" high manganese alloy types, the ratio of Mn to C + N is ≧ 2.74 and ≦ 7.14, and even more preferably the ratio of Mn to C + N is ≧ 2.74 and ≦ 5.95. The current embodiment includes the following: alloys of the type 304LM4N, 316LM4N, 317L35M4N, 317L57M4N, 312L35M4N, 312L57M4N, 320L35M4N, 320L57M4N, 326L35M4N and 326L57M4N, 351L35M4N, 351L57M4N, 353L35M4N, 353L57M4N, and variations thereof, which may include a maximum of up to 0.030wt% carbon.

For "HM 4N", the type of low manganese range alloy, this achieves an optimum ratio of Mn to C + N ≦ 4.55, and preferably ≧ 1.25 and ≦ 4.55. More preferably, the ratio of Mn to C + N is ≥ 1.25 and ≤ 3.41. For "HM 4N", the type of high manganese range alloy, this achieves an optimum ratio of Mn to C + N ≦ 9.10, and preferably ≧ 2.50 and ≦ 9.10. More preferably, for these "HM 4N", high manganese alloy types, the ratio of Mn to C + N is ≧ 2.50 and ≦ 6.82, and even more preferably the ratio of Mn to C + N is ≧ 2.50 and ≦ 5.68. The current embodiment includes the following: 304HM4N, 316HM4N, 317H57M4N, 317H35M4N, 312H35M4N, 312H57M4N, 320H35M4N, 320H57M4N, 326H35M4N, 326H57M4N, 351H35M4N, 351H57M4N, 353H35M4N and 353H57M4N types of alloys and their variants, which may include from 0.040wt% carbon up to 0.10wt% carbon, and

for "M4N", the type of low manganese range alloy, this achieves an optimum ratio of Mn to C + N ≦ 4.64, and preferably ≧ 1.28 and ≦ 4.64. More preferably, the ratio of Mn to C + N is ≥ 1.28 and ≤ 3.48. For "M4N", the type of high manganese range alloy, this achieves an optimum ratio of Mn to C + N ≦ 9.28, and preferably ≧ 2.56 and ≦ 9.28. More preferably, for these types of "M4N" high manganese alloys, the ratio of Mn to C + N is ≧ 2.56 and ≦ 6.96, and even more preferably the ratio of Mn to C + N is ≧ 2.56 and ≦ 5.80. The current embodiment includes the following: 304M4N, 316M4N, 31757M4N, 31735M4N, 31235M4N, 31257M4N, 32035M4N, 32057M4N, 32635M4N, 32657M4N, 35135M4N, 35157M4N, 35335M4N, and 35357M4N type alloys and their variants, which may include from more than 0.030wt% carbon up to 0.080wt% carbon.

N′GENIUS^TMHigh strength austenitic series and superaustenitic stainless steels include alloys of the "LM 4N", "HM 4N", and "M4N" types, as well as other variations discussed herein, may be specified and utilized as a range of products and product packaging for complete systems.

It should be apparent that the chemical compositional ranges for a particular one of the elements (e.g., chromium, nickel, molybdenum, carbon, nitrogen, etc.) in a particular alloy composition type and their variants may also apply to the elements in other alloy composition types and their variants.

Products, markets, industrial sectors and applications

Proposed N' GENIUS^TMThe series of high strength austenitic and super austenitic stainless steels may be specified as international standards and specifications and, in view of their high mechanical strength properties at ambient and low temperatures, excellent ductility and toughness, as well as good weldability and good general and local corrosion resistance, they are useful for a range of applications both offshore and onshore.

Product(s)

Products include, but are not limited to, primary and secondary products such as ingots, billets, rolled pipe, blooms, small and medium parisons, bars, flat bars, profiles, bars, wires, welding materials, plates, sheets, strips and coils, forgings, static castings, die castings, centrifugal casting castings, powder metallurgy products, hot isostatic pressing, seamless line pipes, seamless pipes, drill pipes, petroleum industry pipes, casings, pipes for condensers and heat exchangers, welded pipes, welded steel pipes, tubular products, induction heated elbows, butt welded joints, seamless fittings, fasteners, bolts, screws and studs, cold and cold rolled steel bars, bar and wire, cold and cold rolled pipes, flanges, compact flanges, snap-in connectors, forged joints, pumps, valves, separators, ships, and accessories. The primary and secondary products described above are also associated with metallurgical composite products (e.g. thermo-mechanical bonding, hot roll bonding, explosive bonding, etc.), weld overlay composite products, mechanical or hydraulic lining products or CRA lining products.

As can be appreciated from the number of alternative alloy compositions discussed above, the proposed N' GENEUS^TMHigh strength austenitic and superaustenitic stainless steels may be specified and used in various markets and industrial sectors in a wide range of applications. When utilizing these alloys, significant weight savings and manufacturing time savings can be achieved, which in turn results in significant cost savings in overall construction costs.

Market, industrial sector and applications

Upstream and downstream oil and gas industries (onshore and offshore, where offshore includes shallow, deep and ultra-deep water technologies)

Applications for the manufactured article may include, but are not limited to, the following:

onshore and offshore pipelines comprising: external field and production lines (InterfieldPipelines and Flowlines), internal field and production lines (InfieldPipelines and Flowlines), spring dampers (BuckleArrestors),High Pressure High Temperature (HPHT) pipeline (for multiphase fluids such as oil, natural gas and containing chlorides, CO)₂And H₂S and other components of condensate), seawater injection and formation water injection pipelines, subsea production system equipment, manifolds, jumpers, joints (Tie-in), spools (Spool), pigingloops (pigingloops), pipe fittings, petroleum specialty tubing (OCTG) and casing, steel catenary risers, structural splash zone risers, river and waterway junctions (cross), valves, pumps, separators, ships (vessels), filtration systems, forgings, fasteners, and all related ancillary products and equipment.

Pipe packing system (pinegpackagesystem): such as processing and utility systems, seawater cooling systems, and fire protection systems, which can be used for all types of onshore and offshore applications. Offshore applications include, but are not limited to, fixed platforms, floating platforms, spa and hulls (Hull) such as processing platforms (ProcessPlatform), utility platforms, wellheads, riser platforms, compression platforms (CompressionPlatform), floating storage and offloading (FPSO 'S), floating storage and offloading (FSO' S), spa and Hull infrastructure, structures, structure modules, and all related ancillary products and equipment.

Tubular packaging system (TubingPackageSystem): such as supply pipes (ubtilical), condensers, heat exchangers, desalination, desulfurization and all the associated auxiliary products and equipment.

Liquefied natural gas industry (LNGIndstreasures)

Applications for the manufactured article may include, but are not limited to, the following: pipeline and pipeline packaging system infrastructures, constructions, construction modules, valves, ships, pumps, filtration systems, forgings, fasteners and all related ancillary products and equipment for offshore Floating Liquefied Natural Gas (FLNG) vessels, Floating Storage Regasification Units (FSRU) or onshore Liquefied Natural Gas (LNG) plants, ships and terminals for processing, storing and transporting LNG at cryogenic temperatures.

Chemical, petrochemical, GTL (gas to oil) and refining industries

for processing and transporting corrosive fluids from chemical, petrochemical, gas-to-oil and refining industries, as well as acids, bases and other corrosive fluids (including chemicals typically found in vacuum columns, atmospheric columns and hydrotreaters): pipeline and pipe packaging systems, infrastructure, constructions, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment, including railway and highway chemical ships.

Environmental protection industry

for pollution control (e.g. steam recovery systems, CO) from chemical and refining industries₂Insulation and flue gas desulfurization) of waste products and wet toxic gases: pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Iron and steel industry

for steel making and processing: pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Mining and mineral industry

for mining and mineral extraction and for corrosive slurries and drainage transport over mines: pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Electric power industry

for power generation and for the transport of corrosive media associated with power generation (i.e. fossil fuels, gas, nuclear fuels, geothermal energy, hydroelectric power and all other forms of power generation): pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Pulp and paper industry

for use in the pulp and paper industry and for the transport of corrosive fluids in bleaching plants: pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Seawater desalination industry

used in the desalination industry and for the transport of seawater and brine used in desalination plants: pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Maritime, navy and defense industries

for the maritime, naval and defense industries and for the transport of corrosive media and for the public pipe systems of chemical ships, shipbuilding and submarines: pipeline and duct packaging systems, constructions, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners, and all related ancillary products and equipment.

Water and wastewater industries

in the water and wastewater industry (including casings for wells, utility distribution networks, sewer networks and irrigation systems): pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Construction, engineering and construction industries

structural integrity and decorative applications for use in the construction, civil and mechanical engineering and construction industries: pipes, tubes, infrastructure, constructions, forgings and fasteners and all associated ancillary products and equipment.

Food and wine industry

in the food and beverage industry and related consumer products: pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Pharmaceutical, biochemical, health and medical industries

in the pharmaceutical, biochemical, health and medical industries, and related consumer product: pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

Automobile industry

For use in the automotive industry (including automotive manufacturing for highways and railways, and surface and underground public passenger transport system management): pipeline and duct packaging systems, infrastructure, constructions, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners, assemblies, and all related ancillary products and equipment.

Expert research and industry development

used in expert research and industry development: pipeline and duct packaging systems, infrastructure, construction modules, valves, pumps, ships, filtration systems, forgings, fasteners and all related ancillary products and equipment.

The present invention relates to austenitic stainless steels that include a high level of nitrogen and a minimum specified pitting resistance equivalent for each specified type of alloy. Referred to as PRE_NThe pitting resistance equivalent weight of (c) is calculated according to the formula:

PRE_N= Cr + (3.3 × Mo) + (16 × N); and/or

PRE_NW=%Cr+[3.3×%(Mo+W)]+ (16 x% N), where applicable to each specified type of alloy, as discussed above.

For different embodiments or types of austenitic stainless steels and/or superaustenitic stainless steels, the low carbon range alloys are referred to as 304LM4N, 316LM4N, 317L35M4N, 317L57M4N, 312L35M4N, 312L57M4N, 320L35M4N, 320L57M4N, 326L35M4N, 326L57M4N, 351L35M4N, 351L57M4N, 353L35M4N, and 353L57M4N, as well as these other variations that have been disclosed. As described herein In embodiments of (a), the austenitic stainless steel and/or the superaustenitic stainless steel comprises 16.00wt% chromium to 30.00wt% chromium; from 8.00wt% nickel to 27.00wt% nickel; no more than 7.00wt% molybdenum and no more than 0.70wt% nitrogen, but preferably from 0.40wt% nitrogen to 0.70wt% nitrogen. For lower carbon range alloys, these include no more than 0.030wt% carbon. For lower manganese range alloys, these include no more than 2.00wt% manganese and the manganese to nitrogen ratio is controlled to be less than or equal to 5.0, and preferably at least 1.42 and less than or equal to 5.0, or more preferably at least 1.42 and less than or equal to 3.75. For higher manganese range alloys, these include no more than 4.00wt% manganese, and the ratio of manganese to nitrogen is controlled to be less than or equal to 10.0, and preferably at least 2.85 and less than or equal to 10.0, or more preferably at least 2.85 and less than or equal to 7.50, or even more preferably at least 2.85 and less than or equal to 6.25, or even more preferably at least 2.85 and less than or equal to 5.0, or even more preferably at least 2.85 and less than or equal to 3.75. The phosphorus value is not more than 0.030wt% phosphorus and is controlled as low as possible so that it may be less than or equal to 0.010wt% phosphorus. The value of sulfur does not exceed 0.010wt% sulfur and is controlled as low as possible so that it can be less than or equal to 0.001wt% sulfur. The level of oxygen in the alloy does not exceed 0.070wt% oxygen and is critically controlled to be as low as possible so that it may be less than or equal to 0.005wt% oxygen. The silicon in the alloy does not exceed 0.75wt% silicon, and unless it is a particular higher temperature application that requires increased oxidation resistance, in which case the silicon content may range from 0.75wt% silicon to 2.00wt% silicon. For certain applications, other variants of stainless steels and superaustenitic stainless steels have been purposefully formulated to contain specified levels of other alloying elements, such as copper, not more than 1.50 wt.% copper for the lower copper range alloys, not more than 3.50 wt.% copper for the higher copper range alloys, tungsten, not more than 2.00 wt.% tungsten, and vanadium, not more than 0.50 wt.% vanadium. Austenitic stainless steels and super austenitic stainless steels, also contain primarily Fe as the remainder, and may also contain very small amounts of other elements, such as boron, not exceeding 0.010wt% boron; cerium, no more than 0.10wt% cerium; aluminum, no more than 0.050wt% aluminum; and calcium and/or magnesium, not more than 0.010w t% of calcium and/or magnesium. Austenitic stainless steels and superaustenitic stainless steels have been formulated to have a unique combination of high mechanical strength properties and excellent ductility and toughness, as well as good weldability and good general and localized corrosion resistance. Chemical analysis of stainless steels and superaustenitic stainless steels is characterized in that it is optimized in the melting phase to ensure the properties according to Schoefer⁶，[Cr]Equivalent weight divided by [ Ni ]]The ratio of equivalents is in the range > 0.40 and < 1.05, or preferably > 0.45 and < 0.95, in order to obtain a mainly austenitic microstructure of the base material after solution heat treatment, typically in the range 1100-1250 degrees celsius, and subsequent water quenching. The microstructure of the base material under solution heat treatment conditions, as well as the microstructure of the as-welded weld metal and heat affected zone of the weld, are controlled by optimizing the balance between austenite forming elements and ferrite forming elements to ensure primarily that the alloy is austenitic. The alloy can thus be manufactured and provided in a non-magnetic state. The minimum specified mechanical strength properties of the novel and innovative stainless steels and super austenitic stainless steels have been significantly improved compared to their respective counterparts, including austenitic stainless steels such as UNSS30403, UNSS30453, UNSS31603, UNSS31703, UNSS31753, UNSS31254, UNSS32053, UNSS32615, UNSS35115, and UNSS 35315. Furthermore, the minimum specified tensile strength performance can be better than that specified for 22Cr duplex stainless steel (uns 31803) and similar to that specified for 25Cr super duplex stainless steel (uns 32760). This means that system components for different applications using forged stainless steel can be characterized in that the alloy can often be designed with reduced wall thickness, thus resulting in significant weight savings when specifying stainless steel due to significantly higher minimum allowable design stresses compared to conventional austenitic stainless steels such as those detailed herein. In fact, the minimum allowable design stress of a forged austenitic stainless steel is higher than the minimum allowable design stress of a 22Cr duplex stainless steel, and is similar to the minimum allowable design stress specified for a 25Cr super duplex stainless steel.

For certain applications, other variants of austenitic stainless steels and super austenitic stainless steels have been specifically formulated to be manufactured to contain levels of carbon above that previously defined herein. The higher carbon range of alloys of different types of austenitic and superaustenitic stainless steels is referred to as 304HM4N, 316HM4N, 317H35M4N, 317H57M4N, 312H35M4N, 312H57M4N, 320H35M4N, 320H57M4N, 326H35M4N, 326H57M4N, 351H35M4N, 351H57M4N, 353H35M4N, and 353H57M4N, and these types of alloys include from 0.040wt% carbon up to less than 0.10wt% carbon. However, alloys of the 304M4N, 316M4N, 31735M4N, 31757M4N, 31235M4N, 31257M4N, 32035M4N, 32057M4N, 32635M4N, 32657M4N, 35135M4N, 35157M4N, 35335M4N and 35357M4N types include from greater than 0.030wt% carbon up to 0.080wt% carbon.

Furthermore, for certain applications, other variants of higher carbon range alloys of austenitic and superaustenitic stainless steels are desirable, which have been specifically formulated to make stabilized versions. Specific variants of these austenitic and superaustenitic stainless steels are alloys of the titanium-stabilized "HM 4 NTi" or "M4 NTi" type, in which the titanium content is controlled according to the following formula: respectively Ti4 xc minimum, 0.70wt% Ti maximum, or Ti5 xc minimum, 0.70wt% Ti maximum, to form a titanium stabilized derivative of the alloy. Similarly, there are niobium stabilized alloys of the "HM 4 NNb" or "M4 NNb" type, in which the niobium content is controlled according to the following formula: nb8 xc minimum, 1.0wt% Nb maximum, or Nb10 xc minimum, 1.0wt% Nb maximum, respectively, to form niobium stabilizing derivatives of the alloy. In addition, other variations of the alloy can also be made to include niobium plus tantalum stabilized "HM 4 NNbTa" or "M4 NNbTa" type alloys, where the niobium content is controlled according to the following formula: nb + Ta8 XC minimum, 1.0wt% Nb + Ta maximum, 0.10wt% Ta maximum, or Nb + Ta10 XC minimum, 1.0wt% Nb + Ta maximum, 0.10wt% Ta maximum. Variations of titanium stabilization, niobium stabilization, and niobium plus tantalum stabilization of the alloy may be subjected to a stabilization heat treatment at a temperature below the initial solution heat treatment temperature. Titanium and/or niobium plus tantalum may be added alone or in combination with the elements copper, tungsten and vanadium, in all of the various combinations, to optimize the alloy for certain applications requiring higher carbon content. These alloying elements may be utilized alone or in all of the various combinations of these elements to make austenitic stainless steels for specific applications and to further optimize the overall corrosion performance of the alloy.

Reference to the literature

1.A.J.Sedriks,StainlessSteels’84,ProceedingsofG?teborgConference,BookNo320.TheInstituteofMetals,1CarltonHouseTerrace,LondonSW1Y5DB,p.125,1985.

2.P.GuhaandC.A.Clark,DuplexStainlessSteelConferenceProceedings,ASMMetals/MaterialsTechnologySeries,Paper(8201–018)p.355,1982.

3.N.Bui,A.Irhzo,F.DabosiandY.Limouzin-Maire,CorrosionNACE,Vol.39,p.491,1983.

4.A.L.Schaeffler,MetalProgress,Vol.56,p.680,1949.

5.C.L.LongandW.T.DeLong,WeldingJournal,Vol.52,p.281s,1973.

6.E.A.Schoefer,WeldingJournal,Vol.53,p.10s,1974.

7.ASTMA800/A800M–10

Claims

1. Austenitic stainless steel, characterized by a non-magnetic austenitic microstructure, comprising: 16.00 wt% chromium to 30.00 wt% chromium (Cr); 8.00 wt% nickel to 27.00 wt% nickel (Ni); less than 7.00 wt% molybdenum (Mo); 0.40 wt% nitrogen to 0.70 wt% nitrogen (N), 1.0 wt% manganese to 4.00 wt% manganese (Mn), no more than 1.0 wt% niobium (Nb), less than 0.10 wt% carbon (C), < 0.070 wt% oxygen, no more than 2.00 wt% silicon (Si), and the balance iron and unavoidable impurities,

wherein the ratio of the manganese (Mn) to the nitrogen (N) is controlled to be less than or equal to 10.0; and

wherein the ratio of chromium equivalent [ Cr ] to nickel equivalent [ Ni ] is determined and controlled to exceed 0.40 and be less than 1.05; and

wherein the chromium equivalent is determined and controlled according to a first formula as: [ Cr ] ═ (wt% Cr) + (1.5 × wt% Si) + (1.4 × wt% Mo) + (wt% Nb) -4.99; and

wherein the nickel equivalent is determined according to a second formula and controlled as: [ Ni ] ═ wt% Ni) + (30X wt% C) + (0.5X wt% Mn) + ((26X wt% (N-0.02)) +2.77, and wherein

The stainless steel is solution heat treated at a temperature between 1100 ℃ and 1250 ℃ and subsequently water quenched to form a nonmagnetic austenitic microstructure.

2. The austenitic stainless steel of claim 1, wherein the chromium is 17.50 wt% to 20.00 wt% Cr.

3. Austenitic stainless steel according to claim 1 or 2, characterized in that the chromium is ≥ 18.25 wt% Cr.

4. The austenitic stainless steel of claim 1, wherein the nickel is 8.00 wt% to 12.00 wt% Ni.

5. The austenitic stainless steel of claim 4, wherein the nickel is ≦ 11.00 wt% Ni.

6. The austenitic stainless steel of claim 4, wherein the nickel is ≦ 10.00 wt% Ni.

7. The austenitic stainless steel of claim 1 or 2, wherein the molybdenum is no more than 2.00 wt% Mo.

8. The austenitic stainless steel of claim 1 or 2, wherein the molybdenum is 0.50 wt% or more and 2.00 wt% or less Mo.

9. Austenitic stainless steel according to claim 1 or 2, characterized in that the molybdenum is more than or equal to 1.00 wt% Mo.

10. The austenitic stainless steel of claim 1, wherein the chromium is 16.00 wt% to 18.00 wt% Cr.

11. The austenitic stainless steel of claim 1, wherein the chromium is ≥ 17.25 wt% Cr.

12. The austenitic stainless steel of claim 1, wherein the nickel is 10.00 wt% to 14.00 wt% Ni.

13. The austenitic stainless steel of claim 1, wherein the nickel is ≦ 13 wt% Ni.

14. The austenitic stainless steel of claim 1, wherein the nickel is ≦ 12 wt% Ni.

15. The austenitic stainless steel of claim 1, wherein the molybdenum is greater than or equal to 2.00 wt% to less than or equal to 4.00 wt% Mo.

16. The austenitic stainless steel of any of claims 1, 10-15, wherein the molybdenum is ≥ 3.00 wt% Mo.

17. The austenitic stainless steel of claim 1, wherein the chromium is 18.00 wt% to 20.00 wt% Cr.

18. The austenitic stainless steel of claim 1, wherein the chromium is 19.00 wt% or more Cr.

19. The austenitic stainless steel of claim 1, wherein the nickel is 11.00 wt% to 15.00 wt% Ni.

20. The austenitic stainless steel of claim 1, wherein the nickel is ≦ 14.00 wt% Ni.

21. The austenitic stainless steel of claim 18, wherein the nickel is ≤ 13.00 wt% Ni.

22. The austenitic stainless steel of claim 1, wherein the nickel is 13.50 wt% to 17.50 wt% Ni.

23. The austenitic stainless steel of claim 22, wherein the nickel is 16.50 wt% Ni or less.

24. The austenitic stainless steel of claim 22, wherein the nickel is ≤ 15.50 wt% Ni.

25. The austenitic stainless steel of any of claims 1, 17 through 24, wherein the molybdenum is ≥ 3.00 wt% and ≤ 5.00 wt% Mo.

26. The austenitic stainless steel of any of claims 1, 17-24, wherein the molybdenum is 4.00 wt% Mo or more.

27. The austenitic stainless steel of any of claims 1, 17-24, wherein the molybdenum is ≥ 5.00 wt% and less than 7.00 wt% Mo.

28. The austenitic stainless steel of any of claims 1, 17-24, wherein the molybdenum is ≥ 6.00 wt% Mo.

29. The austenitic stainless steel of claim 1, wherein the chromium is 20.00 wt% to 22.00 wt% Cr.

30. The austenitic stainless steel of claims 1 or 29, wherein the chromium is ≥ 21.00 wt% Cr.

31. The austenitic stainless steel of claims 1 or 29, wherein the nickel is 15.00 wt% to 19.00 wt% Ni.

32. The austenitic stainless steel of claims 1 or 29, wherein the nickel is ≤ 18.00 wt% Ni.

33. The austenitic stainless steel of claims 1 or 29, wherein the nickel is ≤ 17.00 wt% Ni.

34. The austenitic stainless steel of claim 29, wherein the molybdenum is greater than or equal to 5.00 wt% and less than 7.00 wt% Mo.

35. The austenitic stainless steel of claim 29, wherein the molybdenum is greater than or equal to 6.00 wt% Mo.

36. The austenitic stainless steel of claim 29, wherein the molybdenum is greater than or equal to 3.00 wt% and less than or equal to 5.00 wt% Mo.

37. The austenitic stainless steel of claim 36, wherein the molybdenum is 4.00 wt% Mo or more.

38. The austenitic stainless steel of claim 1, wherein the chromium is 22.00 wt% to 24.00 wt% Cr.

39. The austenitic stainless steel of claim 38, wherein the chromium is ≥ 23.00 wt% Cr.

40. The austenitic stainless steel of claims 1 or 38, wherein the nickel is 17.00 wt% to 21.00 wt% Ni.

41. The austenitic stainless steel of claims 1 or 38, wherein the nickel is ≤ 20.00 wt% Ni.

42. The austenitic stainless steel of claims 1 or 38, wherein the nickel is ≤ 19.00 wt% Ni.

43. The austenitic stainless steel of claim 38, wherein the molybdenum is greater than or equal to 5.00 wt% and less than 7.00 wt% Mo.

44. The austenitic stainless steel of claim 43, wherein the molybdenum is greater than or equal to 6.00 wt% Mo.

45. The austenitic stainless steel of claim 38, wherein the molybdenum is greater than or equal to 3.00 wt% and less than or equal to 5.00 wt% Mo.

46. The austenitic stainless steel of claim 45, wherein the molybdenum is greater than or equal to 4.00 wt% Mo.

47. The austenitic stainless steel of claim 1, wherein the chromium is 24.00 wt% to 26.00 wt% Cr.

48. The austenitic stainless steel of claim 47, wherein the chromium is greater than or equal to 25.00 wt% Cr.

49. The austenitic stainless steel of claims 1 or 47, wherein the nickel is 19.00 wt% to 23.00 wt% Ni.

50. The austenitic stainless steel of claims 1 or 47, wherein the nickel is ≤ 22.00 wt% Ni.

51. The austenitic stainless steel of claims 1 or 47, wherein the nickel is ≤ 21.00 wt% Ni.

52. The austenitic stainless steel of claim 47, wherein the molybdenum is greater than or equal to 5.00 wt% Mo and less than 7.00 wt% Mo.

53. The austenitic stainless steel of claims 1 or 47, wherein the molybdenum is ≥ 6.00 wt% and less than 7.00 wt% Mo.

54. The austenitic stainless steel of claims 1 or 47, wherein the molybdenum is ≥ 6.50 wt% Mo.

55. The austenitic stainless steel of claim 47, wherein the molybdenum is greater than or equal to 3.00 wt% and less than or equal to 5.00 wt% Mo.

56. The austenitic stainless steel of claim 55, wherein the molybdenum is greater than or equal to 4.00 wt% Mo.

57. The austenitic stainless steel of claim 1, wherein the chromium is 26.00 wt% to 28.00 wt% Cr.

58. The austenitic stainless steel of claim 57, wherein the chromium is greater than or equal to 27.00 wt% Cr.

59. The austenitic stainless steel of claims 1 or 57, wherein the nickel is 21.00 wt% to 25.00 wt% Ni.

60. The austenitic stainless steel of claims 1 or 57, wherein the nickel is ≤ 24.00 wt% Ni.

61. The austenitic stainless steel of claims 1 or 57, wherein the nickel is ≤ 23.00 wt% Ni.

62. The austenitic stainless steel of claim 57, wherein the molybdenum is greater than or equal to 5.00 wt% Mo and less than 7.00 wt% Mo.

63. The austenitic stainless steel of claims 1 or 57, wherein the molybdenum is ≥ 5.50 wt% and ≤ 6.50 wt% Mo.

64. The austenitic stainless steel of claim 63, wherein the molybdenum is greater than or equal to 6.00 wt% Mo.

65. The austenitic stainless steel of claim 57, wherein the molybdenum is greater than or equal to 3.00 wt% and less than or equal to 5.00 wt% Mo.

66. The austenitic stainless steel of claim 65, wherein the molybdenum is greater than or equal to 4.00 wt% Mo.

67. The austenitic stainless steel of claim 1, wherein the chromium is 28.00 wt% to 30.00 wt% Cr.

68. The austenitic stainless steel of claim 67, wherein the chromium is greater than or equal to 29.00 wt% Cr.

69. The austenitic stainless steel of claims 1 or 67, wherein the nickel is 23.00 wt% to 27.00 wt% Ni.

70. The austenitic stainless steel of claims 1 or 67, wherein the nickel is ≤ 26.00 wt% Ni.

71. The austenitic stainless steel of claims 1 or 67, wherein the nickel is ≤ 25.00 wt% Ni.

72. The austenitic stainless steel of claim 67, wherein the molybdenum is greater than or equal to 5.00 wt% Mo and less than 7.00 wt% Mo.

73. The austenitic stainless steel of claim 67, wherein the molybdenum is greater than or equal to 5.50 wt% and less than or equal to 6.50 wt% Mo.

74. The austenitic stainless steel of claim 67, wherein the molybdenum is greater than or equal to 6.00 wt% Mo.

75. The austenitic stainless steel of claim 67, wherein the molybdenum is greater than or equal to 3.00 wt% and less than or equal to 5.00 wt% Mo.

76. The austenitic stainless steel of claim 75, wherein the molybdenum is 4.00 wt% Mo or more.

77. The austenitic stainless steel of claim 1, wherein the nitrogen is 0.40 wt.% or more and 0.60 wt.% or less N.

78. The austenitic stainless steel of claim 1, wherein the nitrogen is 0.45 wt% or more and 0.55 wt% or less N.

79. The austenitic stainless steel of claim 1, further comprising 0.030 wt.% or less carbon.

80. The austenitic stainless steel of claim 1, further comprising 0.020 wt% to 0.030 wt% carbon.

81. The austenitic stainless steel of claim 1, wherein the carbon is ≦ 0.025 wt% C.

82. The austenitic stainless steel of claim 1, further comprising no more than 2.0 wt.% Mn.

83. The austenitic stainless steel of claim 1, further comprising 1.0 wt% manganese to 2.0 wt% manganese.

84. The austenitic stainless steel of claim 1, wherein the manganese is ≥ 1.20 wt.% and ≤ 1.50 wt.% manganese.

85. The austenitic stainless steel of claim 1, wherein the ratio of manganese to nitrogen is controlled to be less than or equal to 5.0.

86. The austenitic stainless steel of claim 1, wherein the ratio of manganese to nitrogen is controlled to be less than or equal to 3.75.

87. The austenitic stainless steel of claim 1, further comprising 2.0 wt% manganese to 4.0 wt% manganese.

88. The austenitic stainless steel of claim 87, wherein the manganese is ≦ 3.0 wt% manganese.

89. The austenitic stainless steel of claim 87, wherein the manganese is ≦ 2.50 wt% manganese.

90. The austenitic stainless steel of claims 1 or 87, wherein the ratio of manganese to nitrogen is controlled to be less than or equal to 7.50.

91. The austenitic stainless steel of claims 1 or 87, wherein the ratio of manganese to nitrogen is controlled to be less than or equal to 6.25.

92. The austenitic stainless steel of claim 1, further comprising 0.030 wt% or less phosphorous.

93. The austenitic stainless steel of claim 1, further comprising 0.025 wt.% or less phosphorous.

94. The austenitic stainless steel of claim 1, further comprising 0.020 wt.% or less phosphorous.

95. The austenitic stainless steel of claim 1, further comprising 0.015 wt.% or less phosphorous.

96. The austenitic stainless steel of claim 1, further comprising 0.010 wt.% or less phosphorous.

97. The austenitic stainless steel of claim 1, further comprising 0.010 wt.% sulfur.

98. The austenitic stainless steel of claim 1, further comprising 0.005 wt.% sulfur.

99. The austenitic stainless steel of claim 1, further comprising 0.003 wt.% sulfur.

100. The austenitic stainless steel of claim 1, further comprising 0.001 wt.% or less of sulfur.

101. The austenitic stainless steel of claim 21, wherein the oxygen is 0.050 wt.% or less oxygen.

102. The austenitic stainless steel of claim 1, wherein the oxygen is 0.030 wt% oxygen or less.

103. The austenitic stainless steel of claim 1, wherein the oxygen is ≤ 0.010 wt% oxygen.

104. The austenitic stainless steel of claim 1, wherein the oxygen is ≤ 0.005 wt% oxygen.

105. The austenitic stainless steel of claim 1, further comprising no more than 0.75 wt% silicon.

106. The austenitic stainless steel of claim 1, wherein the silicon is 0.25 wt.% or more and 0.75 wt.% or less.

107. The austenitic stainless steel of claim 1, wherein the silicon is 0.40 wt.% or more and 0.60 wt.% or less.

108. The austenitic stainless steel of claim 1, wherein the silicon is 0.75 wt.% Si or more and 2.00 wt.% silicon or less.

109. The austenitic stainless steel of claim 1, further comprising at least one member selected from the group consisting of boron, cerium, aluminum, calcium, magnesium, copper, tungsten, vanadium, titanium, and/or niobium plus tantalum.

110. The austenitic stainless steel of claim 1, further comprising 0.010 wt% or less boron.

111. The austenitic stainless steel of claim 1, further comprising 0.001 wt.% or more and 0.010 wt.% or less boron.

112. The austenitic stainless steel of claim 1, further comprising 0.0015 wt% boron and 0.0035 wt% boron.

113. The austenitic stainless steel of claim 1, further comprising 0.0001 wt.% or more and 0.0006 wt.% or less boron.

114. The austenitic stainless steel of claim 1, further comprising ≤ 0.10 wt.% cerium.

115. The austenitic stainless steel of claim 1, further comprising 0.01 wt.% or more and 0.10 wt.% or less cerium.

116. The austenitic stainless steel of claims 114 or 115, wherein the cerium is 0.03 wt.% or more and 0.08 wt.% or less cerium.

117. The austenitic stainless steel of claim 1, further comprising 0.050 wt.% or less aluminum.

118. The austenitic stainless steel of claim 1, further comprising 0.005 wt.% or more aluminum and 0.050 wt.% or less aluminum.

119. The austenitic stainless steel of claim 1, further comprising 0.010 wt.% or more and 0.030 wt.% or less aluminum.

120. The austenitic stainless steel of claim 1, further comprising ≤ 0.010 wt% calcium.

121. The austenitic stainless steel of claim 1, further comprising 0.001 wt% or more calcium and 0.010 wt% or less calcium.

122. The austenitic stainless steel of claim 121, wherein the calcium is greater than or equal to 0.001 wt% calcium and less than or equal to 0.005 wt% calcium.

123. The austenitic stainless steel of claim 1, further comprising ≦ 0.010 wt% magnesium.

124. The austenitic stainless steel of claim 123, further comprising 0.001 wt.% or more magnesium and 0.010 wt.% or less magnesium.

125. The austenitic stainless steel of claim 124, wherein the magnesium is 0.001 wt.% or more and 0.005 wt.% or less magnesium.

126. The austenitic stainless steel of claim 1, further comprising ≦ 1.50 wt% copper.

127. The austenitic stainless steel of claim 1, further comprising 0.50 wt.% or more copper and 1.50 wt.% or less copper.

128. The austenitic stainless steel of claim 127, wherein the copper is ≦ 1.00 wt% copper.

129. The austenitic stainless steel of claim 1, further comprising ≦ 3.50 wt% copper.

130. The austenitic stainless steel of claim 129, further comprising ≥ 1.50 wt.% copper and ≤ 3.50 wt.% copper.

131. The austenitic stainless steel of claim 130, wherein the copper is ≦ 2.50 wt% copper.

132. The austenitic stainless steel of claim 1, further comprising ≦ 2.00 wt% tungsten.

133. The austenitic stainless steel of claim 1, further comprising 0.50 wt.% or more and 1.00 wt.% or less tungsten.

134. The austenitic stainless steel of claim 133, wherein the tungsten is 0.75 wt% or more tungsten.

135. The austenitic stainless steel of claim 1, further comprising 0.50 wt.% or less vanadium.

136. The austenitic stainless steel of claim 1, further comprising 0.10 wt.% or more vanadium and 0.50 wt.% or less vanadium.

137. The austenitic stainless steel of claim 135, wherein the vanadium is ≦ 0.30 wt% vanadium.

138. The austenitic stainless steel of claim 1, further comprising 0.040 wt% carbon to less than 0.10 wt% carbon.

139. The austenitic stainless steel of claim 1, further comprising 0.040 wt% carbon to 0.050 wt% carbon.

140. The austenitic stainless steel of claim 138, wherein the carbon is > 0.030 wt% carbon and ≦ 0.08 wt% carbon.

141. The austenitic stainless steel of claim 140, wherein the carbon is > 0.030 wt% carbon and < 0.040 wt% carbon.

142. The austenitic stainless steel of claim 138, further comprising no more than 0.70 wt% titanium.

143. The austenitic stainless steel of claim 142, wherein the titanium exceeds Ti_{Minimum value}(ii) a Wherein the content of the first and second substances,

Ti_{minimum value}From 4 XC_{Minimum value}Calculating; and wherein

C_{Minimum value}Is the minimum amount of carbon.

144. The austenitic stainless steel of claim 140, further comprising no more than 0.70 wt% titanium, wherein the titanium exceeds Ti_{Minimum value}(ii) a Wherein the content of the first and second substances,

Ti_{minimum value}From 5 XC_{Minimum value}Calculating; and wherein

C_{Minimum value}Is the minimum amount of carbon.

145. The austenitic stainless steel of claim 138, wherein the niobium exceeds Nb_{Minimum value}(ii) a Wherein the content of the first and second substances,

Nb_{minimum value}From 8 XC_{Minimum value}Calculating; wherein

C_{Minimum value}Is the minimum amount of carbon.

146. The austenitic stainless steel of claim 140, wherein the niobium exceeds Nb _{Minimum value}(ii) a Wherein the content of the first and second substances,

Nb_{minimum value}From 10 XC_{Minimum value}Calculating; wherein

C_{Minimum value}Is the minimum amount of carbon.

147. The austenitic stainless steel of claim 145, further comprising no more than 1.0wt niobium plus tantalum, and up to 0.10wt tantalum.

148. The austenitic stainless steel of claim 147, wherein the niobium plus tantalum exceeds Nb + Ta_{Minimum value}(ii) a Wherein the content of the first and second substances,

Nb+Ta_{minimum value}From 8 XC_{Minimum value}Calculating; wherein

C_{Minimum value}A minimum amount of carbon of 0.10 wt% Ta_{Maximum value}。

149. The austenitic stainless steel of claim 140, further comprising no more than 1.0 wt% niobium plus tantalum, and up to 0.10 wt% tantalum, wherein the niobium plus tantalum exceeds Nb + Ta_{Minimum value}(ii) a Wherein the content of the first and second substances,

Nb+Ta_{minimum value}From 10 XC_{Minimum value}Calculating; wherein

C_{Minimum value}A minimum amount of carbon of 0.10 wt% Ta_{Maximum value}。

150. Austenitic stainless steel, characterized in that it has a non-magnetic austenitic microstructure, comprising 0.40 to 0.70 wt% of nitrogen and a defined pitting corrosion resistance equivalent (PRE)_N) Alloy composition of not less than 25; wherein

PRE_NChromium + (3.3 × wt% molybdenum) + (16 × wt% nitrogen),

wherein the alloy composition further comprises from 16.00 wt% chromium to 30.00 wt% chromium (Cr); 8.00 wt% nickel to 27.00 wt% nickel (Ni); less than 7.00 wt% molybdenum (Mo); 1.0 wt% manganese to 4.00 wt% manganese (Mn), not more than 1.0 wt% niobium (Nb), less than 0.10 wt% carbon (C), < 0.070 wt% oxygen, not more than 2.00 wt% silicon (Si), and the balance iron and unavoidable impurities,

Wherein the ratio of manganese (Mn) to nitrogen (N) is controlled to be less than or equal to 10.0; and

wherein the nickel equivalent is determined according to a second formula and controlled as: [ Ni ] ═ (wt% Ni) + (30X wt% C) + (0.5X wt% Mn) + ((26X wt% (N-0.02)) +2.77, and

wherein the stainless steel is solution heat treated at a temperature between 1100 ℃ and 1250 ℃ and subsequently water quenched to form a nonmagnetic austenitic microstructure.

151. Austenitic stainless steel, characterized in that it has a non-magnetic austenitic microstructure comprising 0.40 to 0.60 wt% nitrogen and a defined pitting corrosion resistance equivalent (PRE)_N) Alloy composition of not less than 25; wherein

PRE_NChromium + (3.3 × wt% molybdenum) + (16 × wt% nitrogen ═ wt%

Wherein the alloy composition further comprises from 16.00 wt% chromium to 30.00 wt% chromium (chromium); 8.00 wt% nickel to 27.00 wt% nickel (Ni); less than 7.00 wt% molybdenum (Mo); 1.0 wt% manganese to 4.00 wt% manganese (Mn), not more than 1.0 wt% niobium (Nb), less than 0.10 wt% carbon (C), < 0.070 wt% oxygen, not more than 2.00 wt% silicon (Si), and the balance iron and unavoidable impurities,

wherein the chromium equivalent is determined and controlled according to a first formula, [ Cr ] ═ wt% Cr) + (1.5 × wt% Si) + (1.4 × wt% Mo) + (wt% Nb) -4.99; and

wherein the nickel equivalent is determined and controlled according to a second formula, [ Ni ] ═ wt% Ni) + (30 × wt% C) + (0.5 × wt% Mn) + ((26 × wt% (N-0.02)) +2.77, and

152. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 30.

153. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 35.

154. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 40.

155. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 45.

156. The austenitic stainless steel of claims 150 or 151, wherein the PRE _NIs not less than 37.

157. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs not less than 42.

158. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs not less than 43.

159. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs not less than 48.

160. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs not less than 39.

161. The method of claim 150The austenitic stainless steel of claim 151, wherein the PRE_NIs not less than 44.

162. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 50.

163. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs not less than 47.

164. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 48.5.

165. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs not less than 53.5.

166. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs not less than 49.

167. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 50.5.

168. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 55.5.

169. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs not less than 46.

170. The austenitic stainless steel of claim 150 or 151, wherein the austenitic stainless steel isPRE_NIs more than or equal to 51.

171. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 52.5.

172. The austenitic stainless steel of claims 150 or 151, wherein the PRE_NIs more than or equal to 57.5.

173. Austenitic stainless steel, characterized in that it has a non-magnetic austenitic microstructure, comprising 0.50 to 1.00 wt% of tungsten, 0.40 to 0.70 wt% of nitrogen, and a defined Pitting Resistance Equivalent (PRE)_NW) Alloy composition of not less than 27; wherein

PRE_NWWt% chromium + [ (3.3 × wt% (molybdenum + tungsten)]+ (16X wt% Nitrogen)

174. Austenitic stainless steel, characterized in that it has a non-magnetic austenitic microstructure comprising 0.40 to 0.60 wt% of nitrogen, 0.50 to 1.00 wt% of tungsten and a defined Pitting Resistance Equivalent (PRE)_NW) Alloy composition of not less than 27; wherein

PRE_NWWt% chromium + [ (3.3 × wt% (molybdenum + tungsten)]+ (16X wt% Nitrogen)

175. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 32.

176. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs not less than 37.

177. According to the claims173 or 174, wherein the PRE is an austenitic stainless steel_NWIs not less than 42.

178. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs not less than 47.

179. The austenitic stainless steel of claims 173 or 174, wherein the PRE is _NWIs not less than 39.

180. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs not less than 44.

181. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 45.

182. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 50.

183. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 41.

184. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs not less than 46.

185. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs not less than 52.

186. The austenitic stainless steel of claims 173 or 174,the PRE_NWIs not less than 49.

187. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 50.5.

188. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 55.5.

189. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 51.

190. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 52.5.

191. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 57.5.

192. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs not less than 48.

193. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs not less than 53.

194. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 54.5.

195. The austenitic stainless steel of claims 173 or 174, wherein the PRE is_NWIs more than or equal to 59.5.

196. The austenitic stainless steel of claim 1, 150, 151, 173, or 174, wherein the ratio of chromium equivalents to nickel equivalents is in the range of more than 0.45 and less than 0.95.

197. A wrought steel, comprising the austenitic stainless steel of claims 1, 150, 151, 173, or 174.

198. A cast steel comprising the austenitic stainless steel of any of claims 1, 150, 151, 173, or 174.

199. The austenitic stainless steel of claim 1, claim 150, or claim 151, claim 173, or claim 174, wherein [ Cr ] and [ Ni ] are further defined as:

Chromium equivalent, [ Cr ] ═ Cr) + (1.5 × wt% Si) + (1.4 × wt% Mo) + (wt% Nb) + (0.72 × wt% W) + (2.27 × wt% V) + (2.20 × wt% Ti) + (0.21 × wt% Ta) + (2.48 × wt% Al) -4.99; and

nickel equivalent, [ Ni ] ═ Ni (wt% Ni) + (30 × wt% C) + (0.5 × wt% Mn) + ((26 × wt% (N-0.02)) + (0.44% × wt% Cu) +2.77, where

The wt% of Nb, W, V, Ti, Ta, Al and Cu are all nonzero values; and

wherein

Nb ═ niobium

W ═ tungsten;

v is vanadium;

ti ═ titanium;

ta ═ tantalum;

al ═ aluminum; and

cu ═ copper.