US3389991A - Stainless steel and method - Google Patents

Description

United States Patent Wee ABSTRACT OF THE DISCLOSURE Heat-hardenable stainless steel which, in addition to chromium and carbon, essentially contains nitrogen and columbium-tantalum in particular amount, and in which any molybdenum and/or tungsten is maintained in critically low amount. More particularly, the steel essentially consists of about .01% to about .25% carbon, about .01% to 3% manganese, about .01% to about 2% silicon, about 10% to about 16% chromium, any molybdenum not exceeding .3% and any tungsten not exceeding .5% and with molybdenum and tungsten together not exceeding about .5% in total, about..04% to about .2% nitrogen, about .03% to about .75% columbium-tantalum, up to about .75% vanadium, and remainder substantially all iron. The steel is particularly produced in the form of bar stock from which various products are fashioned, especially turbine blading and the like.

My invention relates to the straight chromium grades of stainless steel, more particularly the A.I.S.I. (American Iron & Steel Institute) 400 series of compositions generally indicated below.

One of the objects of the invention is the provision of a high temperature stainless steel which is hardenable by heat-treatment, to give high tensile strength and high yield strength at room temperatures and at high temperature as well, and which, moreover, is tough, ductile and of good impact strength.

A further object is the provision of such a steel which works well in the hot-mill, as in the production of plate, sheet and strip as well as bar, rod and wire and which lends itself to a variety of working and forming operations such as machining, cutting, blanking, threading, and the like, as well as forging, and which in addition readily lends itself to soldering, brazing and welding as in the production of a variety of articles and products of ultimate use suited to high temperature applications, that is, applications where there are reached temperatures up to about -1100 F. 7

Another object is the provision of a stainless steel and method of heat-treating the same wherein the response to heat-treatment is uniform throughout the metal and which stainless steel exhibits great resistance to tempering and to creep.

Other objects of my invention in part will be obvious and in part more particularly pointed to in the description which follows.

My invention, in general, is considered to reside in the combination of chemical elements, in the composition of ingredients and in the relation of each of the same with one or more of the others as described herein, and in the sequence of operational steps and interrelation between them as also described, the scope of the application of all of which is set out in the claims made at the end of this specification.

Background of the invention As an aid to a better understanding of certain features of my invention, it is to be noted at this point that the straight chromium grades of stainless steel which are hardena-ble by heat-treatment, that is, the A.I.S.I. 400

Patented June 25, 1968 series from 403 up to 440, are of a martensitic structure. This embraces Type 403 (11.5% to 13% chromium, 1.00% max. manganese, 0.50% max. silicon, 0.15% max. carbon, and remainder iron), Type 410 (11.5% to 13.5% chromium, 1.00% max. manganese, 1.00% max. silicon, 0.15 max. carbon, and remainder iron), Type 414 (11.5% to 13.5% chromium, 1.25% to 2.50% nickel, 1.00% max. manganese, 1.00% max. silicon, 0.15% max. carbon, and remainder iron), Type 416 (12% to 14% chromium, 1.25% manganese, 1.00% max. silicon, 0.15% min. sulphur, with molybdenum and zirconium each up to 0.60% max, 0.15% max. carbon, and remainder iron), Type 420 (12% to 14% chromium, 1.00% max. manganese, 1.00% max. silicon, over .15 carbon, and remainder iron), Type 431 (15% to 17% chromium, 1.25% to 2.50% nickel, 1.00% maxpmanganese, 1.00% max. silicon, 0.20% max. carbon, and remainder iron), and Type 440 (16% to 18% chromium, 1.00% max. manganese, 1.00% max. silicon, with molybdenum to 0.75% max., 0.60% to 1.20% carbon for different varieties of the Type 440, and remainder iron).

While, as suggested above, the heat-hardenable stainless steels of the 400 series are possessed of many favorable properties and lend themselves to a variety of applications, I find that they are deficient in a number of respects and are not truly suited to certain applications. Thus these prior art steels are subject to severe segregation effects, rather inadequate toughness, limited machinability and a susceptibility to stress-corrosion cracking. More particularly, these steels are inclined to sulfer from non-uniformity in texture and weakness in mechanical strength due to segregation of massive carbides. And the steels are susceptible to quench cracking.

Although the straight chromium grades of stainless steel in recent years have been modified through the addition of one or more further ingredients such as molybdenum, tungsten, vanadium and colubiu-m, still a desired combination of strength, both at room temperatures and at high temperatures, and toughness, is not fully achieved. Reference is made to the modifications introduced over the years to the 12% chromium grade of stainless steel. Initially this steel, identified as Type 410, as noted above, analyzed 11.5% to 13.5% chromium, up to 1.00% max. each of manganese and silicon, 0.15 max. carbon, and remainder substantially all iron. The steel was subsequently modified and identified as Type 422 through the introduction of small amounts of the ingredients nickel, molybdenum, tungsten and vanadium, the steel typically analyzing 13.0% chromium, .75% nickel, 1.0% molybdenum, 1.0% tungsten, .34% vanadium, 22% carbon, and remainder iron. A further modified steel, generally referred to as 12 Cr-Ni-Mo-V typically analyzes 11.5 chromium, .70% nickel, 1.0% molybdenum, .25% vanadium, .17% carbon, and remainder iron. Another, referred to as 12-2W, analyzes 12.0% chromium, 2.0% nickel, 3.0% tungsten, .18% carbon, and remainder iron. .But I find that these various modified steels also lack the desired combination of strength and toughness. They lack the combination of room temperature strength along with high temperature strength; when one is satisfac tory the other is deficient. And they lack toughness; the impact strength is inadequate and so, too, the resistance to stress-corrosion cracking. They are notch-sensitive. Moreover, with substantial additions of nickel, molybdenum and tungsten, they are expensive.

Perhaps the most recent modified Type 410 stainless steel which has been made available is that described and claimed in my prior U.S. Letters Patent 3,000,729 of Sept. 19, 1961. That steel, in addition to some 10.0% to 14.0% chromium and .07% to .14% carbon, contains columbium-tantalum in the amount of .05% to r I v I. i s .35 with or without vanadium-in amounts up to The remainder of the composition, of course, is substantially all iron. While this-steel possesses many of the charaoteristicstnow -sought,it is;lacking.in strength both at roomtemperatures and atelevated temperatures. .And I find that the desired :strengthis not ..achieved..merely by adding more ofthe columbium-tantalurn and Nanadiumingredients. Y

There is the further steel, this being :that describedv and claimed in the U.S. LetterseP-atent --3,1 39,37- issued to Boyle et-al. on June. 30, 1964. Butrhere again,r the tens sile strength isinadequate.- And .moreover, Kthe irnpact strength is deficient. Additionally, the steel like several of those referred to abovenisaobjectionably expensive becauseof the kind and" quantity of alloying-ingredients employed.

Accordingly, one of the objects.of-myuinvention is the provision of a-steel that overcomes-the deficiencieszof the steels of the prior art, which is a comparativelyinexpensive modified.;.grade of heat-hardenable straight chromium stainless steel; which, moreover, lends itself to hardening and tempering to give a steel which is strong, tough and resistant to stress-corrosion cracking both at room temperatures and at high temperatures as well; which readily may be machined and fabricated as 'by cuttingyblanking, threading, .and the like and brazed or welded as desired in the production of a variety of arti effect is had in the so-called straight chromium steels, this over and beyond the hardening had with carbon, by way of an addition of nitrogen and columbium-tantalum. Apparently there isa reaction between nitrogen and columbiumiantalum which isrnost beneficial in achieving a fine grain structurefwith nitrides finely dispersed throughout .themetal which. strengthens the matrix-There results fan increase inahardness and strength-not only at room temperatures but at elevated temperatures, as Well. This is" had in'abse'nceof massive carbides for I find that the presence of 'columbiumdantalum minimizes the formation of the..massive..chromium carbides; the chromiumcarbides which do form are small and well dispersed throughout the steel. And ductility and toughness directlyb'enefit. .1 v

= Forbest results, since theecarbon reaction seems .to take precedence over the nitrogen reactiornalarge amount of carbon: is not desirable but .ratherthere is employed only just sufiicient' carbonto achieve desired ,quench hardness; Greater amounts of-carbon merely tie up or combine with one of the columbiumdantalum, chromium and others of the alloy ingredients present. There direct- .7 1y results a loss in their effectiveness. And the carbides cles of ultimate use; and which may be heat-treated in simple and direct fashion with uniform and consistent results.

Summary of the invention Referring now more particularly to the practice of my invention, I find that in the steels of the prior art strength andh'ardness' are developed by virtue of the substantial carbon content. The steels, when hardened, of course are martensitic. With the prior art steels, massive ledeburitic carbides are formed in the ingot. These carbides remain as segregates which are not readily dispered in the steel matrix, either by working or by thermal treatment. On the contrary, they remain as clusters or as stringers (extended fibres) following conversion of the ingot to semifinished sections or in the final product. As a consequence, the metal is weakened, particularly in transverse direction, that is, transverse to the direction of rolling or drawing.

And while in certain steels of the prior art greater strength is had as a result of additions of molybdenum formed serve as undesirable inclusions which lower ductility'and toughness. 1

Nitrogen is. used in amount sufiicient to achieve the desired final hardness and retain that hardness upon tempering, With the nitrogen addition hardness and strength arehad and subsequently :retained at elevated temperatures. There seems to be had some. molecular locking rather than the interference effect noted with massive carbides found in the steels of the prior art. But here again, irrespective of theory, in my steel there is had and/or tungsten, I findthat the addition of either one or both of these ingredients definitely decreases the solubility for carbon; that it becomes difficult to get the carbon into solution and difficult to achieve a desired quench-hardness which hardness is retained following a tempering treatment. Moreover, as in the case of chromium carbides, the molybdenum carbides and tungsten carbides which form are inclined to coalesce or enlarge, giving massive carbides dispersed throughout the metal. I feel that these massive carbides, while providing a block to the flow of the metal under stress, and in a sense strengthening the metal, necessarily detract from the duetility and toughness. The action is not a true hardening and strengthening effect, but rather is in the nature of an impediment to flow which is purposely introduced. And particularly increases in high temperature hardness and strength are not fully had through further increases of carbon, molybdenum and tungsten because of even greater clifliculty in taking the carbon into solution with the larger carbides. In addition, with increases in, carban the metal becomes more difficult to process in the mill.

Regardless of theory, however, I find that the steels of the prior art employing molybdenum and/or tungsten or even chromium with substantial quantities of carbon, do not enjoy a combination of ductility and toughness along with tensile strength.

Now it is my discovery that a secondary hardening ductility and toughness along with hardness and strength. Hardness and strength, withoutloss in ductility'and toughness, are'further heightened by an: addition of vanadium, this in controlled amount as appears more fully below.

In accordance with the teachings of my invention, I provide a stainless steel essentially consisting of about .0l% to about :.25%' carbon, about 10% to about 16% chromium, about 0.4% to about .2% nitrogen, about .03% to about .75% columbium-tantalum, and remainder substantially all iron. In the steel of my invention manganesernay' be present in theamount of about .01% to about 3% and silicon in the amount of about .01% to about 2%. So, too, nickel may be present in amounts up to 2% as a maximum. The ingredients phosphorus and sulphur, commonly presentin all stainless steels, are maintained in amounts each not exceeding .050% as :a maximum. And any molybdenum which may be present is maintained ata value not exceeding 3% and preferably not exceeding-about .2% because of the ferritizing tendency, as more particularly pointed to below. Similarly,

any tungsten which-rnaybe present is maintained at a value not exceeding about .5%and preferably not exceeding about 2% for best results; The combined molybdenum and tungsten is maintained at a figure-not exceeding about 5%, preferably not exceeding about 2% for best ductility andtoughness' for steel of minimum cost. Actually, molybdenum and tungsten seldom exceed .05% to .'08% for the molybdenum and about .l()% for the tungsten.

Vanadium, this in amount up'to about .75%, preferably is included in'the composition as appears more fully hereinafter. customarily, vanadium amounts to some .03% to about preferably about .03% to about .35%, or more preferably about .10% to about 35% for the best combination of hardness, strength and toughness. 1 1

- Now in the steel of my invention the ingredients car bon, chromium,nitrogen' and colirmbium-tantalum are in every sense critical. Thus the chromium content must be at least about 10% for otherwise there' is a sharp loss in corrosion resistance and an undesired devclopment of heat-scale in service at elevated temperatures. Moreover,

there is a loss in the solubility for-nitrogen, an ingredient essential to my steel. On the other hand, the chromium content should not exceed about 16% because chromium in excess of this figure is inclined to give a steel which is excessively ferritic with attendant loss of mechanical properties. For a steel of minimum cost the preferred chromium content amounts to about 11% to 12%, or even about to about 13%. For a steel of greater strength and toughness as well as greater corrosion resistance, the chromium content amounts to about 13% to about 15%, more especially, about 15%.

The carbon content of my stainless steel is maintained at a value of at least .01% since little purpose and little benefit is achieved by a lesser amount. Carbon, how ever, must not exceed about .25%, because I find that any further amount of carbon develops an excessive number of segregates which adversely affect the toughness of the metal. A preferred carbon content amounts to about .15 to about .25 more preferably about .1% to about .2%, for certain applications, for example, turbine blading and blades for compressors. In some applications as for steels of general utility, I prefer a carbon content of about .05% to about .15% for the steels of the higher chromium contents. In still others, as where greater hardness is required, a carbon content of about .10% to about .20% is preferable.

The ingredient nitrogen, as indicated above, is essential, this in the amount of about .04% toabout .2%. A nitrogen content less than about .04% I find to be of no particular benefit. And with a nitrogen content exceeding about .2% even with a chromium content as high as about 16%, there is a possibility of gassiness with the result that unsound metal is had. In general, I prefer a nitrogen content of about 0.06% to about .16%, although in some embodiments, as noted below, the nitrogen content amounts to about .04% to about .2%.

Columbium-tantalum, as noted above, is in the amount of about .03% to about .75 At least'.03% columbium tantalum is required in order to give any benefit either in grain size control or in reaction with the nitrogen present. And columbium-tantalum in excess of .35%

merely tiesup carbon, thereby lowering .the amount.

which may be taken into solution, with the result that both the quench hardness and the temper hardness suffer. Moreover, an excess quantity of columbium-tantalum gives rise to massive segregates which impair the ductility and toughness of the metal. For most steels, the preferred columbium-tantalum content is on the order of about .1% to about 3%, or even about .1% to about .2% or, more particularly .O8% to .15 depending upon the proportioning of the other ingredients, as more fully noted below. a

Vanadium, where employed, is in the amount of at least .O3%, any lesser amount offering little or no benefit. The vanadium, however, should not exceed about .75 because, like an excess of columbium-tantalum, the excess merely ties up carbon, thereby decreasing the amount which may be taken into solution and both quench hardness and temper hardness are adversely affected. As well, massive segregates appear causing a loss of yield strength, ductility, toughness and impact resistance. With both columbium-tantalum and vanadium present in the steel. it appears that the columbium-tantalnm reacts with the carbon present, leaving the vanadium to act with the nitrogen content to best increase hardness and strength. The

presence of both gives the steel its best mechanical properties.

In my steel, as noted above, there are present the ingredients manganese, silicon, phosphorus and sulphur, ingredients which commonly are present in all stainless steels. The manganese and silicon contents are each in the amount of at least .01%, this being a practical lower limit for these ingredients, on up to about 1% or even about 2% for the silicon as noted above and on up to about 1% for the manganese. Actually, as also noted above the manganese may be employedbeneficially in amounts up to about 3%, this serving principally as a means of stabilizing the high temperature austenite of the steel. An excess, however, would be inclined to make the metal sluggish in transforming to martensite in quench hardening. The manganese additionally has the benefit of serving as a convenient vehicle for introducing a substantial part of the nitrogen required; the nitrogen generally being added by way of a nitrided electrolytic manganese. The silicon employed serves to impart a resistance to heatscale in high temperature applications. But silicon in an amount exceeding 2% induces segregates, in this respect acting very much like an excess of carbon. Moreover, the excess silicon is inclined to make the metal objectionably ferritic.

The phosphorus and sulphur contents each should not exceed .-05% as a maximum because they are inclined to introduce hot-working difficulties. And, mon'eover, with the higher sulphur contents the impact strength of the metal drastically suffers.

The nickel content of my steel should not exceed 2% as indicated above, for nickel is an austenite stabilizer and with the higher nickel content there is difliculty in annealing the metal. Moreover, nickel is an expensive ingredient. In my steel I prefer a nickel content not exceeding 1% as a maximum, and more preferably a maximum of .5

As an important feature, the steel of my invention is made virtually free of the ingredients molybdenum and tungsten, ingredients which commonly are present in substantial quantity in the high temperature straight chromium stainless steels of the prior art. For I find that these two ingredients incline toward the development of a hyper-eutectoid steel and the production of massive segregates. While both molybdenum and tungsten long have been recognized as strong carbide forming elements and to lend strength at high temperatures, I find that the carbides of these two ingredients, possibly because of the tendency toward the production of massive carbide segregates, definitely impair ductility, toughness and impact resistance. This impairment I attribute to an impeding of plastic flow. Regardless of theory, however, I find that massive carbides do exist. And in the steel of my invention I purposely limit the amount of any molybdenum to a figure not exceeding about .3%, preferably not exceeding about .2%, and an tungsten present in the metal to a level not exceeding about .5 and preferably not exceeding about 3%, with the sum of the two not exceeding about .5 and preferably not exceeding about .2% in total.

Description 07 the preferred embodiments A preferred steel acording to my invention essentially consists of about .01%, or even about .05%, on up to about .25% carbon, about .0l% to about 1% manganese, about 10% to about 13% chromium, about .04% to about .1'6%, or even to about .2% nitrogen, about 03% to about .75 or more preferably about .1% to about .3% columbium-tantalum, up to about .75 and preferably about .03% to about .75 vanadium, with the sum of any molybdenum and tungsten not exceeding about .5 preferably not exceeding about .2% as a maximum, and remainder substantially all iron. Another esentially consists of about .01% to about .2% carbon, about 11% to about 12% chromium, about .04% to about .16% nitrogen, about .1% to about .75 or more preferably about .1% to about 3% columbium-tantalum, about 0% to about .60% vanadium, the vanadium content perferably amounting to about .2% to about .4%, with any molybdenum and tungsten not exceeding about .5 in total, preferably not exceeding .2% in total, and remainder substantially all iron. A further steel, particularly suited to petroleum and chemical applications where strength, toughness and resistance to softening at high temperature is required, essentially consists of about .1% to about 2% carbon, about 13% to about 15% chrois presented the chemical compositions of some five 12- mium, about .04% to about 2% nitrogen, about 1% to chromium grades of stainless steel, one according to the about .3% columbium-tantalum, to .6% and prefer present invention containing the ingredients columbiumably about .2% to about .6% vanadium, with the sum of tantalum and nitrogen in combination, another according any molybdenum and tungsten not exceeding about'.5% to the invention in which vanadium, alsois present, and and preferably not exceeding .2%, with remainder snbthree othersfthese departing from the steels'of thepresstantially all iron. ent inventionin the absence of one or both of the ingredi- The stainless steel of my invention conveniently may ents columbium-tantalum andnitrogcn'. And 'in Table II be melted in the electric arc furnace. Or, as desired, it below there are presented the Rockwell hardness values may be melted in the induction furnace. Of course, it of these various steels, following heating and quenching may also be vacuum-melted, i.e., melted in the electric from difierent temperatures and also following a temperarc furnace under vacuum conditions. Or there may be ing treatment'of the several hardened steels.

TABLE I.-OHEMICAL COMPOSITION OF FIVE l2-CHROMIUMSTAINLESS STEELS 0 Mn P S St Cr Ni Mo N Cb? V Heat- No R4982-1 049 74 015 017 33 12. 25 13 04 058 005 01 34982-2 1 049 74 015 017 33 12 25 13 04 058 11 01 34282-3 l 049 74 015 017 33 12. 25 13 04 058 11 21 12CR-Cb 12 .30 .015 016 28 12.00 15 04 027 15 01 12Cr-Cb-V 13 43 011 019 11. 67 16 i 08 026 10 11 1 Steel of invention. Z Columbium-tantalum, reported as Columbium.

NOTE-The remainder of the composition is substantially all iron.

employed a double melting process, i.e., melting in the The steels of Table I were variously solution-treated at electric arc furnace or induction furnace followed by l700 R, 1800? F. and 1900" F. and quenched in oil and remelting under vacuum conditions. But, in general, in subsequently tempered at 1200 F. for 4 hours and airorder to produce a satisfactory steel, this at minimum cooled. The Rockwell hardness figures were taken for all cost, electric arc furnace melting is found to be entirely samples in quenched and in tempered conditions, the

satisfactory. hardness figures being reported in Table II below:

TABLE IL-ROCKWELL HARDNESS FIGURES FOR THE STEELS OF TABLE I IN THE HARDENED AND IN THE HARDENED AND TEMPERED CONDITION 7 1,700F., 1,800F., 1,900F., 1,700" 0 800 F., o.

O.Q. O.Q. O.Q. 4

F, .Q. 1, ,O.Q. +1,200 F., 411 +1,200 F., 4 hrs.,

- A.0. A.C. no.

039 C38 C38 B95 B95 B05 03s (:38 C37 C22 024 C28 C37 C38 C36 C26 C27 C29 C42 044 044 C23 C24 025 IZCr-Cb-V C43 C44 C44 C23 C25 C25 1 Steel of invention.

The steel, however melted, conveniently is cast in the Of the several steels whose chemical compositions are form of ingots from which it is converted into slabs, 45 set out in Table I, it will be noted that the steels desigblooms or billets, from which it is further converted into natedlZCr-Cb and IZCr-Cb-V, while deficient in nitrogen,

plate, sheet, strip, bars and wire through conventional respectively contain columbium, tantalum and columbihot-rolling operation. The metal readily may be forged um-tantalum+vanadium. And the steel designated R4982- as in the production of a variety of rough-fashioned 1, while containing the ingredient nitrogen, is deficient in articles and then machined to specification. both columbiu-m and vanadium. It is the steels R4982-2 My steel is particularly suited to the production of and R4982-3, steels of the present invention, which consteam turbine blades as well as the compressor blades for tain the ingredients nitrogen and columbium-tantalurn, jet propulsion engines. Because of its greater yield with the steel R4982-3 containing the further ingredient strength my steel permits the construction and use of vanadium. larger blades, and thereby increased efficiency in turbine In the quench-hardened condition, as may be seen from and compressor operation. the data presented in Table II, all five steels exhibited The stainless steel and articles of my invention ar substantial hardness, the hardness figures ranging between quench-hardened as by heating at a temperature of about Rockwell C36'-and RockwellC44. It is the steels lZCr-Cb 1700 t a u for time P 0 about 4 hours and 12Cr-Cb-V which exhibit maximum hardness, both or more an h n q n h in water or the like. so amounting to about RockwellC44, quenched from 1800 FOHQWiIlg the quench-hardening the metal y then be to 1900 F., this hardness being attributed to the signifisubjected to a tempering treatment, this to relieve stresses cant carbon content, that is, a carbon content of about and impart a desired temper. Here the metal is reheated 12% to b t 13% Th th t l 1149824, R4932 2 to a temperature of 313913900 to 1300 and Cooled, and R4982-3, in quench-hardened condition, display as desired. With this tr atm more fully indicated hardnesses amounting to about Rockwell (336-38 when below, there is had an excellent combination of yield quenched from 1800to 1900 F., this being attributed strength, ductility and toughness. There ar a iev d in to the substantially lower carbon content, a carbon conth h and tempered Steel of 3 invention Yield tent of 049%, although there is a nitrogen content of Stfcntgths 125,000 P- and e. valong with a PY .058%, with the sum ofthe carbon and nitrogencon- V-notch impact str ngth of a lea 18 10 0 tents in'these three steels amounting to .l07%.

In the stainless steel of my invention the surprising When tempered, the two steels IZCr-Cb and HG- properties had with the combination of columbium-tanta- Cb-V ufier a substantial loss of hardness, the hardness lum and nitrogen, with and without vanadium, is perhaps falling to Rockwell 023-25, a loss of some 20 points for best illustrated by comparison with steels in which one or each of these steels for the several different hardening more of these ingredients is absent.InTableIbelow there temperatures. The steel 1(49824, a steel free of both columbium-tantalum and vanadium but containing nitrogen, sufiers an even greater loss in tempering, the hardness there dropping to Rockwell B95.

While substantial hardness is retained in the steel-bearing both nitrogen and columbium-tantalum, the steel R4982-2, the final'hardness had varies substantially, depending upon the temperature of hardening, this ranging from Rockwell C22 -for the 1700 F. treatment to C28 for the hardening from 1900 F. It is only in the steel R4982-3 containing all three of nitrogen, columbiumtantalum and vanadium in which best retained hardness is had, this irrespective of variations in the temperature of heat hardening. Note that while the steel hardened from 1800 F. and oilquenched and then tempered has a hardness of Rockwell C27, that heat-hardened at 1900 F. and tempered has a hardness of RockwellC29.

As further illustrative of the steel of my invention, this ascompared to certain of the better steels of the prior art, I give below in Table'III the chemical composition of five steels and in Table IV their comparative mechanical properties.

10 of molybdenum, while the other, 12Cr-Ni-Mo-W-V, in addition to the vanadium and molybdenum, also contains a large amount of tungsten. As distinguished from these steels of the prior art, thepreferred steel of the present invention, while free of the ingredients molybdenum and tungsten, essentially contains columbium, tantalum and nitrogen, as well as vanadium.

Now the hardened and tempered steel of my invention (Heat 033089), as shown in Table IV above, has a tensile strength of 151,000 p.s.i. with a yield strength of 133,000 p.s.i., while the 12Cr-Cb and 12Cr-Cb-V steels of the prior art, respectively have tensile strengths of 132,000 and 133,000 p.s.i., and 0.2% yield strengths of only 116,000 and 117,000 p.s.i. The prior art steel 12Cr-Ni-Mo-V is but little better than the other two prior art steels noted, this steel having a tensile strength of 140,000 p.s.i. and a yield strength of 119,000 p.s.i. Thus, the superior strength of my preferred steel as compared to that of three of the prior art steels is at once apparent.

While the further prior art steel IZCr-Ni-Mo-W-V is TABLE III.CHEMIOAL COMPOSITION OF FIVE IZ-CHROMIUM STAINLESS STEELS Heat No. 0 Mn P s Si Cr N1 M0 N on V w 033089 .12 .85 .014 .019 .23 11.58 .14 .03 .072 .16 .25 12Cr=Ni=Mo=V .17 .69 .016 .014 .43 11.71 .46 1.03 .032 .19

1 Steel of invention.

Columbium-tantalum, reported as columbium.

Norm-The remainder of the composition is substantially all iron.

The several steels of Table III were forged into test possessed of about the same tensile strength and yield bars, machined to specification and suitably heat-treated, strength of my preferred steel, a tensile strength of 154,000 i.e., solution-treated and quenched, followed by temperp.s.i. and a yield strength of 130,000 p.s.i. as compared ing. Samples of all five of the steels'were solution-treated to the 151,000 p.s.i. and 133,000 p.s.i. of the present steel, at 1900 F. for minutes and oil-quenched, following it is noted that that prior art steel falls far short of the which they weregiven a tempering treatment at, 1150" ductility and toughness had in the steel of interest. While F. for 4 hours, and brought .to room temperature. Furthe present steel has an elongation of 16% with reduction ther. samples. of my steel (Heat. 033089) and the best of in area of 60% and a Charpy V-notch impact strength of the prior art steels (Heat- 12Cr.-Ni-Mo-.W-V) were solu- 25 ft. lbs., the prior art steel has an elongation of 17% tion-treated at 2000 F. for 30 minutes and oil-quenched, with a reduction in area of only 50% and a Charpy V- followed by tempering at 1150 F. for 4 hours and notch impact strength of 12 ft. lbs. And this difference in brought to room temperaturejThe mechanical properties ductility and strength becomes even more pronounced of the various steels, i.e., the ultimate tensile strength, where there is employed a higher temperature for soluthe 0.2% yield strength, the percent elongation, the per tion-treatment. Thus, as seen from Table IV above, while cent reduction in area, and the Charpy V-notch impact the best steel of the prior art (the 12Cr-Ni-M0-W-V steel) strength, were run and reported, these results being given has an elongation of 14% with a reduction in area of in Table IV below: only 32% and a Charpy V-notch impact strength of only TABLE IV.-MECHANICAL PROPERTIES OF THE STEELS OF TABLE III IN HARDENED AND TEMPERED CONDITION In 2" Area Charpy Heat No. Condition U.T.S., 0.2% Y.S., V-Notch p.s.i. p.s.i. Percent El. Percent Red. Impact,

ft./lbs.

.Q. plus 1,150 F., Temp 151, 000 133, 000 16 25 .Q. plus l,150 F., Temp 140, 000 119, 000 15 45 20 .Q. plus 1,150 F., Temp 132, 000 116, 000 19 64 .Q. plus 1,150 F., Temp 133, 000 117,000 19 62 .Q. plus 1,150" F., Temp-.. 154, 000 130, 000 17 50 12 .Q. plus 1,150 F., Temp..- 155, 000 138,000 16 58 18 153, 500 130, 000 14 32 9 It will be seen from the chemical analyses presented in 65 9ft. lbs. when oil-quenched from 2000 F. and then tem- Table III above that of thefour steels of the prior art, one (steel designated 12Cr-Cb) in addition to chromium and carbon, essentially contains columbium butis virtually free of vanadium and nitrogen, while another of virtually the same composition (the steel designated 12Cr-Cb-V) does contain the further ingredient vanadium but not nitrogen. Two others of the prior art steels, notably the one designated IZCr-Ni-Mo-V, although free of columbium and nitrogen, does contain vanadium but pered at 1150 F., the steel of the present invention when identically treated has an elongation of 16% With a reduction in area of 58% and a Charpy V-notch impact strength of 18 ft. lbs. And with the higher solution-treatment the steel of the present invention is superior in tensile strength and yield strength as well. In short, then, the steel of the present invention is at least equal in tensile strength and superior in yield strength, ductility and impact strength, this latter by a great margin, to the best of even greater consequence, it contains alarge quantity steels of the prior art.

A further specific example of the preferred steel accordmium content, is of the following composition: about .1% ing to my invention, Heat 3809-2, analyzes as follows: to .2% carbon, about 15% chromium, about .1% to Carbon .l6%, manganese 02%, phosphorus 017%, sulabout 2% nitrogen, about .1% to about 3%, or more phur .016%, silicon .10%, chromium 11.18%, nickel preferably about .2% columbium-tantalum, about .2% .l9%, molybdenum .03%, nitrogen .12%, columbiumto .6%, more preferably about .3% to .4% vanadium,

tantalum 09%, vanadium 39%, and remainder iron. and remainder substantially all iron. The phosphorus, sul- This steel, hardened by heating at 1800" 'F. for 30 minphur, silicon and molybdenum-tungsten.contents are low. utes and oil-quenching, followed by tempering at 1200 Four specific examples of this steel, with differing carbon F. 1014 hours and air-cooling, has an ultimate tensile and chromium contents, are set out below. The chemical strength of 129,800 p.s.i., a 0.2% yield strength of 95,500

a analyses of the steels are given'in Table 'VI' and their p.s.i., an elongation i112" of 16.7%, a reduction in area correspoding mechanical properties in Table VII.

TABLE VI.-FOUR Cr STAINLESS STEELS CONTAINING Cb, V AND N Heat No. 0 Mn P s s1 Cr Ni' N' Cb V of 53.6%, and a Rockwell hardness of C27. Improvement The mechanical properties of the steels of Table VI is had in all of these mechanical propertles where the in hardened and tempered condition (2000 F. 30 mins.,

steel is hardened by heating at the higher temperature of and oil quench, followed by 1150" F. 4 hrs. and air cool, 1900 F. for 30 minutes and oil-quenching, followed by also like hardening but subsequent tempering at 1200 F. tempering at 1200" F. for 4 hours and air-cooling. The for 4 hrs. and air cool) are given below in Table VII.

steel, so treated, has an ultimate tensile strength of 141,900 TABLE VIL MECHANICAL PROPERTIES OF HARDENED p.s.i., a yield strength of 102,700 p.s.i., an elongation in AND TEMPEREDlti Cr STAINLESS STEELS 0F TABLE IV 2" of 17.3%, a reduction in area of 56.2%, and a hard- Imus" 02% Y5 Yemen, Yemen 11685 01 Rockwell C305. Heat No. Condition p.s.i. p.s.i. El. in Red.

A still further specific preferred steel of my invention, Jmrea this in the form of 3" square billets and in the form of 153,800 125,500 13 33 v 1" square bars, was subjected to mechanical test. The ig 'ggg igg'ggg 2? chemical composition of the steel is as follows: Carbon, 1111200 1401900 0 1s .12%, chromium 12.0%, nickel .15 molybdenum 6,; 3 88 gg'gg if g 06%, columbium-tantalum .15 vanadium .25 nitro- 152, 700 1271300 13 41 gen 070%, and remainder substantially all iron. The 157,600 132,100 15 49 mechanical properties of this steel, made into standard 2,000 F., mars. oil quench plus 1,1s0 F.,4hrs. an 0001. test bars from a square billet and other test bars from 2,000" F., 30 mins. oil quench plus 1,200 F., 4 hrs. air cool. a 1" square bar under diifering conditions of hardening, Comparison of the mechanical properties of the 15% quenching from 1800 F., 1900 F. and 2000 F. with chromium steel as given in Table VII (Heats R5304-2 tempering treatments at 1150 and 1200 F., are reported and R5305-2) with those of the 12% chromium steel of in Table V below: like carbon content as given in Table V reveals the signifi- TABLE V.MECHANICAL PROPERTIES OF HARDENED TIQEMPERED 12G: STAINLESS STEELS CONTAINING Ob, V

U.T.S., 0.2% Y.S., Percent E1. Gharpy Section Conditions, Degrees F. p.s.i. p.s.l. in 2' Percent R/A gon H. 1,800, '1, 1,150 147,000 131,000 17 58 20/22 H, 1,800, T, 1,200 139, 000 123,000 16 59 34/4 H, 1,900, '1, 1,150 151, 000 133, 000 16 59 22/22 H, 1,900, T, 1,200 145, 000 128, 000 16 60 25/30 R, 2,000, '1, 1,130 150, 000 138, 000 10 58 18/18 H, 2,000, T, 1,200 150, 000 13 15 58 21/25 H, 1,800, '1, 1,100.- 160, 000 140,000 10 58 22/29 H, 1,800, T, 1,150-- 153, 000 135, 000 16 18/22 H, 1,900, 'r, 1, 0-- 103, 000 141, 000 16 58 11/17 Do H, 1,900, T, 1,150 151,000 132,000 17 18/18 Nora-H =Qucnch hardened from temperature indicated in F. T=Tempered from temperature indicated in F.

In comparing the mechanical properties of the sample cant improvement in tensile and yield strength had with prepared from a 3" square billet and those from a 1" 60 the 15% chromium steel, this, however, at some sacrifice square bar, it seems that there is very little diiference. in ductility. The main advantage had with the higher Thus, the sample from a 3 square billet quench-hardened chromium steel, however, is an improved corrosion refrom 1 800" -F. and tempered at 1150" F., While somesistance. 1

what lower in strength than the sample prepared from a 1" square bar and similarly quench-hardened and tem- Coachman pered, has somewhat better ductility and impact strength, It will be seen that I provide in my invention a quencha matter of some 20/22 ft. lbs., as compared to 18/22. hardeuable stainless steel in which the various objects At the somewhat higher quench-hardening temperature hereinbefore set forth together with many practical adof 1900 F. with tempering at 1150 F., the mechanical vantages are successfully achieved. The steel is comparaproperties are virtually identical, except for the impact tively inexpensive in that it employs 'a minimum of costly strength, this being in favor of the sample taken from alloying ingredients, but nevertheless enjoys a combinathe 3" square billet, an impact strength of about 22 ft. tionofgood tensile strength, yield "strength andtoughlbs. as compared to 18 ft. lbs. for the sample taken from ness. The steel works well in the mill and readily lends the 1" square bar. itself to fabrication into a variety of articles of ultimate Another preferred steel, this of somewhat higher chrouse invarious forming, machiningbraziug andwelding techniques. The steel and articles fashioned of the same are suited to useful application in the quench-hardened or quench-hardened and tempered condition.

Since many embodiments may be made of my invention and since various changes or modifications may be made in the embodiments set forth above, it will be understood that all matter described herein is intended by way of illustration and not by way of limitation.

I claim as my invention:

1. A heat-hardenable stainless steel essentially consisting of about .0l% to about .25% carbon, about .01% to 3% manganese, about .01% to about 2% silicon, about 10% to about 16% chromium, any molybdenum not exceeding 3% and any tungsten not exceeding .5% and with molybdenum and tungsten together not exceeding about .5% in total, about .04% to about .2% nitrogen, about .03% to about .75 columbium-tantalum, up to about .75 vanadium, and remainder substantially all iron.

2. A heat-hardenable stainless steel essentially consisting of about 01% to about 25% carbon, about 01% to about 1% manganese, about 01% to about 1% silicon, about 10% to about 16% chromium, any molybdenum and tungsten together not exceeding about .2% in total, about .06% to about .16% nitrogen, about .03% to about .75 columbium-tantalum, up to about .75 vanadium, and remainder substantially all iron.

3. A heat-hardeuable stainless steel essentially consisting of about .01% to about .25 carbon, about 10% to about 16% chromium, any molybdenum not exceeding .3% and any tungsten not exceeding .5 and with molybdenum and tungsten together not exceeding about .5 in total, about .04% to about .16% nitrogen, about .03% to about .75 columbium-tantalurn, about .03% to about .35% vanadium, and remainder substantially all iron.

4. A heat-hardenable stainless steel essentially consisting of about .05% to about .25% carbon, about 10% to about 13% chromium, any molybdenum not exceeding .3% and any tungsten not exceeding .5 and with molybdenum and tungsten together not exceeding about .5 in total, about .04% to about .16% nitrogen, about .1% to about .75 columbium-tantalum, about .2% to about .4% vanadium, and remainder substantially all iron.

5. A heat-hardenable stainless steel essentially consisting of about .1% to about .2% carbon, about 11% to about 12% chromium, any molybdenum and tungsten together not exceeding about .2% in total, about .1% to about .16% nitrogen, about .1% to about .3% columbium-tantalum, about .1% to about .4% vanadium, and remainder substantially all iron.

6. A heat-hardenable stainless steel essentially consisting of about .1% to about .2% carbon, about 13% to about 15% chromium, any molybdenum not exceeding .3% and any tungsten not exceeding .5 and with molybdenum and tungsten together not exceeding about .5% in total, about .04% to about .2% nitrogen, about .1% to about .3% columbium-tantalum, 0% to about .6% vanadium, and remainder substantially all iron.

7. A heat-hardenable stainless steel essentially consisting of about .1% to about .2% carbon, about 15% chromium, molybdenum and tungsten together not exceeding about .5% in total, about .1% to about .2% nitrogen, about .l% to about .3% columbium-tantalum, about .2% to .6% vanadium, and remainder substantially all iron.

8. Stainless steel bar stock essentially consisting of about .01% to about .25% carbon, about 10% to about 16% chromium, any molybdenum and tungsten together not exceeding about .15% in total, about .04% to about .2% nitrogen, about .03% to about .75% columbiumtantalum, about .03% to about .75 vanadium, and remainder substantially all iron.

9. Blading for turbines, compressors and the like essentially consisting of about .01% to about 25% carbon, about .01% to about 3% manganese, about .01% to about 2% silicon, about 10% to about 13% chromium, any molybdenum not exceeding .3% and any tungsten not exceeding .5% and with molybdenum and tungsten together not exceeding about .5 in total, about .04% to about .16% nitrogen, about .03% to about .75 columbium-tantalum, up to about .75 vanadium, and remainder substantially all iron.

References Cited UNITED STATES PATENTS 2,513,935 7/1950 Harris 75l26 2,793,113 5/1957 Rait 75l26 X 3,000,729 9/1961 Tanczyn 75l26 X 3,069,257 12/1962 Clarke 75l26 3,139,337 6/1964 Boyle 148-37 X I) HYLAND BIZOT, Primary Examiner.

DAVID L. RECK, Examiner.

P. WEINSTEIN, Assistant Examiner.