Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
  • B21K1/00—Making machine elements
  • B21K1/06—Making machine elements axles or shafts
  • B21K1/063—Making machine elements axles or shafts hollow
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
  • B21K1/00—Making machine elements
  • B21K1/06—Making machine elements axles or shafts
  • B21K1/10—Making machine elements axles or shafts of cylindrical form
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/058—Alloys based on nickel or cobalt based on nickel with chromium without Mo and W
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C30/00—Alloys containing less than 50% by weight of each constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal

Definitions

• synthesis gases produced in such a reaction apparatus as mentioned above namely gases containing H 2 , CO, CO 2 , H 2 O and hydrocarbons such as methane, are in contact with a metal material constituting reactor tubes whose temperature is around 1000° C. or higher.
• a metal material constituting reactor tubes whose temperature is around 1000° C. or higher.
• Cr and Si have a higher oxidation tendency than Fe and Ni, Cr and Si are selectively oxidized on the metal surface to form dense oxide layers having Cr oxide and Si oxide thereon, which result in suppressing corrosion.
• the metal of the reforming furnace pipes or heat exchanger pipes in an environment where the carburizing effect of the gases is more serious is supersaturated with carbides. Then the graphite deposits and the corrosive wear, called metal dusting proceeds, and the base metal exfoliates and falls off reducing the base metals thickness. Furthermore, the metal powder formed upon exfoliation acts as a catalyst, which causes coking.
• Patent Document 1 proposes a Fe-based alloy or Ni-based alloy containing 11-60% of Cr. More specifically, it is shown that an invention relating to a Fe-based alloy containing at least 24% of Cr and at least 35% of Ni, a Ni-based alloy containing at least 20% of Cr and at least 60% of Ni and alloy s resulting from the further addition of Nb to those alloys, produces excellent effects. However, no sufficient effect for suppressing carburization can be obtained by merely increasing the contents of Cr or Ni in Fe-based alloys or Ni-based alloys; a metal material more resistant to metal dusting is demanded.
• Patent Document 2 The method disclosed in Patent Document 2 is to protect the surface of a high-temperature alloy containing iron, nickel and chromium against corrosion due to metal dusting by causing one or more metals selected from among the metals of the groups VIII, IB, IV and V of the periodic table of the elements, either solely or in admixture, to adhere to the surface by a conventional physical or chemical means, followed by annealing in an inert atmosphere to form a thin layer which has a thickness of 0.01 to 10 ⁇ m. It is alleged that Sn, Pb and Bi are especially effective in this case. However, while this method may be effective in the initial stage but, during a long period of use, the thin layer may possibly spall and accordingly, the effect may possibly be lost.
• Patent Document 3 it is disclosed that, as a result of investigations concerning the interaction with C, from the viewpoint of solute elements in iron in relation to the metal dusting resistance of metal materials in a gaseous atmosphere, containing H 2 , CO, CO 2 and H 2 O at 400 to 700° C., the addition of an element or elements forming stable carbides in the metal, such as Ti, Nb, V and Mo, or the addition of an alloying element or elements whose interaction auxiliary coefficient ⁇ shows a positive value, such as Si, Al, Ni, Cu and Co, was found to be effective in suppressing metal dusting in addition to the enhanced protective effect of the oxide layers.
• an element or elements forming stable carbides in the metal such as Ti, Nb, V and Mo
• an alloying element or elements whose interaction auxiliary coefficient ⁇ shows a positive value such as Si, Al, Ni, Cu and Co
• Patent Document 4 and Patent Document 5 disclose a method comprising subjecting a low Si-25% Cr-20% Ni (HK40) heat-resisting steel or a low Si-25% Cr-35Ni heat-resisting steel species to preliminary oxidation in the air at a temperature in the vicinity of 1000° C. for at least 100 hours
• Patent Document 6 discloses a method comprising carrying out preliminary oxidation of an austenitic heat-resisting steel species containing 20 to 35% Cr in the air.
• Patent Document 7 proposes a method of improving the carburization resistance by heating a high Ni—Cr alloy under vacuum to cause the formation of a scale layer.
• Patent Document 8 proposes a method of improving the carburization resistance by forming a Si- or Cr-enriched layer by surface treatment.
• a method of suppressing metal dusting comprises adding H 2 S to the gaseous atmosphere in pipes of an apparatus for reforming or producing synthesis gas, without improving the metal material itself.
• a method of suppressing metal dusting which comprises adding H 2 S to the gaseous atmosphere in the pipes of an apparatus for reforming or producing synthesis gas, without improving the metal material itself.
• H 2 S markedly reduces the activity of the catalyst used in reforming hydrocarbons; therefore, the technique of suppressing metal dusting by adjusting the composition of the gaseous atmosphere is applied to only to a limited extent.
• the present inventors made various investigations in an attempt to find a method of suppressing metal dusting from occurring and, as a result, obtained the following findings (a) to (i).
• the occurrence of metal dusting is influenced by the protective effect of the oxide layer formed on the surface and the development of the carburized layer formed inside the oxide layer.
• C penetrates from the surface site into the metal material and forms a carburized layer and, on that occasion, metal dusting occurs as a result of a change in the volume or a formation and decomposition of the carbides.
• adding an element or elements such as Ti, Nb, V and Mo that forms stable carbides in the metal material in addition to the enhancement of the protective effect of the oxide layer, can lead to suppressing the penetration of C into the metal material and also reducing the rate of the penetration of C, which result in suppressing the growth of the carburized layer formed inside the oxide layer.
• an element or elements such as Si, Al and Ni that have little affinity for carbon in addition to enhancement of the protective effect of the oxide layer, can lead to suppressing the growth of the carburized layer formed inside the oxide layer.
• the elements that have little affinity for carbon may be an element effective in increasing the activity of C solutable in Fe, in other words, an alloying element such as Co, Cu, Ag, As, P, S and N whose interaction auxiliary coefficient ⁇ shows a positive value.
• Co and Cu when contained as alloy elements in the metal material, are effective in improving the metal dusting resistance since they will not deteriorate such properties of the metal material as hot workability and toughness and they can also be used within the content range acceptable from the cost viewpoint.
• Ag from the cost viewpoint and As from the toxicity viewpoint
• P, S and N as alloy elements since they deteriorate such properties of the metal material as hot workability and toughness.
• P, S, Sb and Bi are elements segregating along grain boundaries in the metal structure, it is expected that they may also segregate on the metal surface and, therefore, it is estimated that they can efficiently suppress the surface reactions between carburizing gases and the metal. Therefore, it is considered that there is no need for intentionally adding P, S, Sb and/or Bi in an excessive amount.
• P and S have already been mentioned in Patent Document 3 as elements having little affinity for carbon, and which, when added, can suppress the carburized layer formed inside the oxide layer from growing. Since S and P are elements segregating along grain boundaries and deteriorate such properties of the metal material as hot workability, it is considered difficult to add them as alloy elements. P and S have so far been regarded as detrimental elements which deteriorate the hot workability of metal, promoting the exfoliation of oxide scales and adversely affecting welding; therefore, it has been attempted to reduce these impurities as far as possible in the refining process and, further, to fix the trace amounts of P and S in metal material grains by adding an element capable of fixing P and S.
• the present invention has been completed based on such findings.
• the gist of the present invention is shown in the following described under (1) to (3).
• the followings (1) to (3) are referred to as the inventions (1) to (3), respectively.
• the gist of the invention is sometimes collectively referred to as the present invention.
• a metal material having excellent metal dusting resistance characterized in comprising, by mass %, C, 0.01 to 0.4%, Si: 0.01 to 2.5%, Mn: 0.01 to 2.5%, Cr: 15 to 35%, Ni: 20 to 65%, Cu: 0.05 to 20%, S: not more than 0.1%, N: not more than 0.25% and O (oxygen): not more than 0.02% and the balance Fe and impurities, and also containing, by mass %, one or more selected among the elements of P: more than 0.05% and not more than 0.3%, Sb: 0.001 to 1% and Bi: 0.001 to 0.5.
• First group by mass %, Co: not more than 10%; Second group: by mass %, Mo: not more than 3% and W: not more than 6%; Third group: by mass %, Ti: not more than 1% and Nb: not more than 2%; Fourth group: by mass %, B: not more than 0.1%, Zr: not more than 1.2% and Hf not more than 0.5%; Fifth group: by mass %, Mg: not more than 0.1%, Ca: not more than 0.1% and Al: not more than 0.8%; Sixth group: by mass %, Y: not more than 0.15%, La: not more than 0.15% and Ce: not more than 0.15%.
• the metal material according to the present invention has an effect of suppressing the surface reactions between carburizing gases and the metal and is excellent in metal dusting resistance and therefore can be used for constructing cracking furnaces, reforming furnaces, heating furnaces, heat exchangers in petroleum refining or petrochemical plants and can markedly improve the durability of apparatus and the operation efficiency.
• a C content of 0.01% is necessary for securing the strength at elevated temperatures. However, at levels exceeding 0.4%, the toughness of the metal markedly deteriorates, so that the upper limit is set at 0.4%.
• a preferred range is 0.03 to 0.35%, and a more preferred range is 0.03 to 0.3%.
• Si has strong affinity for oxygen and encourages uniform formation of protective layers of oxide scales such as Cr 2 O 3 . Further, it forms Si-based oxide scales under the Cr 2 O 3 layer, which shuts off carburizing gases. This effect is produced at content levels not lower than 0.01%. At levels exceeding 2.5%, however, the toughness decreases, so that the upper limit is set at 2.5%. A preferred range is 0.1 to 2.5%, and a more preferred range is 0.3 to 2%.
• Mn is necessary for deoxidation and improvement in workability and a content level of not lower than 0.01% is necessary to obtain such effects. Since Mn is an austenite-forming element, it is also possible to replace part of Ni with Mn. However, an excessive content of Mn impairs the carburizing gas shut-off performance of the protective layer of oxide scale, so that the upper limit is set at 2.5%. A preferred Mn content range is 0.1 to 2%.
• Cr stably forms oxide scales such as Cr 2 O 3 and therefore it is effective in shutting off carburizing gases.
• a content of not lower than 15% is necessary. Since an excessive content deteriorates the workability and also deteriorates the structural stability, the upper limit to the content thereof is set at 35%.
• a preferred range is 18 to 33%, and a more preferred range is 23 to 33%.
• Ni is an element necessary for obtaining a stable austenitic structure depending on the Cr content. When C penetrates into metal, it reduces the rate of penetration. Further, it also functions in securing the strength at elevated temperatures of the metal structure. However, unnecessarily high content levels result in an increased cost and difficulty in production, therefore an appropriate content range is 20 to 65%. A preferred range is 25 to 65%, and a more preferred range is 28 to 50%.
• Cu is one of the important elements in the practice of the present invention. Cu suppresses the surface reactions between carburizing gases and the metal and also markedly improves the metal dusting resistance. Further, since it is an austenite-forming element, it is also possible to replace part of Ni with Cu. In order to improve the metal dusting resistance, a content level not lower than 0.05% is necessary. Since, however, levels exceeding 20% tend to cause marked decreases in weldability, the upper limit is set at 20%. A preferred content range is 0.2 to 15%, and a more preferred content range is 0.5 to 10%.
• S is effective in suppressing the reactions between the carburizing gases and the metal.
• an excessive content markedly impairs the hot workability and weldability and, therefore, it is necessary to set the upper limit to the content thereof at 0.1%.
• the content thereof in the case of a catalyst being used in the concerned plant, is desirably as low as possible; therefore, the upper limit to the S content is preferably set at 0.015%.
• the upper limit of the S content is 0.1% and, if a catalyst is being used in the plant, the upper limit to the S content is preferably set at 0.015%. Therefore, the use of S alone may become insufficient to produce the effect of suppressing the reactions between carburizing gases and the metal in certain cases. Thus, in order to suppress the reactions between carburizing gases and the metal, it is necessary to add one or more of P, Sb and Bi, as described below.
• N can be contained. When contained, it is effective in increasing the strength at elevated temperatures of the metal material. If content levels exceed 0.25%, however, it significantly impairs the workability. Therefore, the upper limit to the N content is set at 0.25%. A preferred upper limit thereto is 0.2%. For obtaining the effect of enhancing the strength at elevated temperatures of the metal material, a content of at least 0.001% is preferred.
• O oxygen
• the O content allowable in the practice of the present invention is up to 0.02%.
• P is one of the most important elements in the present invention. These elements all are active in suppressing the reactions between carburizing gases and the metal. These elements produce that effect when contained either solely or when contained in combination.
• the P content be in excess of 0.05%. Since, at excessive content levels, P markedly impairs the hot workability and weldability, it is necessary to set the upper limit of the P content to 0.3%.
• a preferred P content range is 0.06 to 0.25%, and a more preferred P content range is 0.085 to 0.2%.
• Sb is one of the most important elements in the present invention. These elements all are active in suppressing the reactions between carburizing gases and the metal. These elements produce that effect when contained solely or when contained in combination.
• the Sb content be not lower than 0.001%. Since, at excessive content levels, Sb markedly impairs the hot workability and weldability, it is necessary to set the upper limit of the Sb content to 1%.
• a preferred Sb content range is 0.005 to 0.8%, and a more preferred Sb content range is 0.01 to 0.7%.
• Bi is one of the most important elements in the practice of the present invention. These elements all are active in suppressing the reactions between carburizing gases and the metal. These elements produce that effect when contained either solely or when contained in combination.
• the Bi content be not lower than 0.001%. Since, at excessive content levels, Bi markedly impairs the hot workability and weldability, it is necessary to set the upper limit of the Bi content to 0.5%.
• a preferred Bi content range is 0.005 to 0.3%, and a more preferred Bi content range is 0.01 to 0.2%.
• the invention (1) relating to a metal material having excellent metal dusting resistance by adding one or more of P, Sb and Bi have been described hereinabove.
• the invention (2) provides a metal material having excellent metal dusting resistance which is characterized in that it is provided with workability as well by further adding Nd, as described below.
• Nd is an element optionally added when it is desired that the workability of the above-mentioned metal material having excellent metal dusting resistance, be secured. For marked improvements in metal dusting resistance, it is necessary to cause one or more of P: more than 0.05% and not more than 0.3%, Sb: 0.001 to 1% and Bi: 0.001 to 0.5% to be contained, as mentioned above, whereas Nd is effective in suppressing the reduction in hot workability as resulting from the addition of these elements or further from the content of S. For producing the effect of suppressing such reduction in workability, it is necessary that the Nd content be not lower than 0.001%.
• Nd combines with O (oxygen) to form inclusions abundantly, which cause not only reductions in workability but also cause defects on the metal surface. Therefore, it is necessary to set the upper limit to the Nd content at 0.15%.
• the Nd content is preferably 0.005 to 0.12%, more preferably 0.01 to 0.10%.
• the invention (3) which relates to a metal material improved in strength, ductility and toughness in addition to the techniques according to the inventions (1) and (2).
• the invention (3) relates to a metal material having excellent metal dusting resistance, which is characterized in further comprising at least one element selected from at least one group among the following first to sixth groups in the metal material defined in the invention (1) or invention (2).
• First group by mass %, Co: not more than 10%
• Second group by mass %
• Mo not more than 3%
• W not more than 6%
• Third group by mass %
• Ti not more than 1% and Nb: not more than 2%
• Fourth group by mass %
• B not more than 0.1%
• Zr not more than 1.2%
• Hf not more than 0.5%
• Fifth group by mass %
• Mg not more than 0.1%
• Ca not more than 0.1% and Al: not more than 0.8%
• Sixth group by mass %
• Y not more than 0.15%
• La not more than 0.15% and Ce: not more than 0.15%.
• Co is effective in stabilizing the austenitic phase, so that it can substitute for part of the Ni element; thus, the metal material may contain it if necessary. At content levels exceeding 10%, however, it lowers the hot workability; therefore, when Co is added, the content thereof should be not more than 10%. From the hot workability viewpoint, a preferred range is 0.01 to 5%, and a more preferred range is 0.01 to 3%.
• Second group Mo: not more than 3% and W: not more than 6%
• Both Mo and W are solid solution strengthening elements, so that one or both may be added if necessary.
• Mo When Mo is added, Mo, at content levels exceeding 3%, causes a decrease in workability and also threatens the structural stability; therefore, when Mo is added, the content level thereof should be not more than 3%.
• the Mo content is preferably 0.01 to 2.5%.
• W When W is added, W, at content levels exceeding 6%, causes a decrease in workability and also threatens the structural stability; therefore, when W is added, the content thereof should not be more than 6%.
• the W content is preferably 0.01 to 2.5%.
• Both Ti and Nb at very low content levels, improve the strength at elevated temperatures as well as ductility and toughness and, when P, S or Bi coexists, they improve the creep strength and, therefore, one or both of them may be added if necessary.
• Ti When Ti is added, Ti, at content levels exceeding 1%, causes a decrease in workability and weldability; therefore, when Ti is added, the content thereof should be not more than 1%.
• the Ti content is preferably 0.01 to 1%.
• Nb Nb, at content levels exceeding 2%, causes a decrease in workability and weldability; therefore, when Nb is added, the content thereof should be not more than 2%.
• the Nb content is preferably 0.01 to 2%.
• B, Zr and Hf all strengthen grain boundaries and show the effects of improving the hot workability and high-temperature strength characteristics and, therefore, one or more of them may be added if necessary.
• B when B is added, B, at content levels exceeding 0.1%, causes a decrease in weldability; therefore, when B is added, the content thereof should be not more than 0.1%.
• the B content is preferably 0.001 to 0.1%.
• Zr Zr, at content levels exceeding 1.2%, causes a decrease in weldability; therefore, when Zr is added, the content thereof should be not more than 1.2%.
• the Zr content is preferably 0.001 to 1.0%.
• Hf When Hf is added, Hf, at content levels exceeding 0.5%, causes a decrease in weldability; therefore, when Hf is added, the content thereof should be not more than 0.5%.
• the Hf content is preferably 0.001 to 0.5%.
• Mg, Ca and Al all have the effects of improving the hot workability and, therefore, one or more of these may be added if necessary.
• Mg Mg, at content levels exceeding 0.1%, causes a decrease in weldability; therefore, when Mg is added, the content thereof should be not more than 0.1%.
• the Mg content is preferably 0.0005 to 0.1%.
• Ca Ca, at content levels exceeding 0.1%, causes a decrease in weldability; therefore, when Ca is added, the content thereof should be not more than 0.1%.
• the Ca content is preferably 0.0005 to 0.1%.
• Al Al, at content levels exceeding 0.8%, causes a decrease in weldability; therefore, when Al is added, the content thereof should be not more than 0.8%.
• the Al content is preferably 0.001 to 0.8%.
• Y, La and Ce all have the effects of improving the oxidation resistance and, therefore, one or more of these may be added if necessary.
• these elements are added at respective content levels exceeding 0.15%, they cause decreases in workability; therefore, when they are added, the content of each of them should be not more than 0.15%.
• the content is preferably 0.0005 to 0.15%.
• the metal material according to the present invention is excellent in metal dusting resistance, in particular in atmospheres containing 1% or more, by volume, of hydrocarbons and carbon monoxide, either solely or in total or even 25% or more, by volume, of hydrocarbons, carbon monoxide and hydrogen either solely or in combination, at a temperature not higher than 1000° C. Therefore, when weld joints made of this metal material are applied in such parts as reactor pipes or peripheral devices in heat exchanger-type hydrocarbon reformers, an exhaust heat recovering apparatus in petroleum refining, the weldability, durability and safety of the apparatus can be markedly improved.
• the metal material according to the present invention can be molded into the required shapes such as plates, sheets, seamless pipes, welded pipes, forgings and wires by such means as melting, casting, hot working, cold working and welding. It can be formed into required shapes also by such means as powder metallurgy and centrifugal casting. Further, the metal surface after final heat treatment can be subjected to a surface processing treatment such as pickling, shot blasting, shot peening, mechanical grinding, grinder buffing and electrolytic grinding. The metal material according to the present invention can also be molded into irregular profiles having one or more projections on the surface.
• the metal material according to the present invention can be made into multi-layer or composite s in combination with various carbon steel, stainless steel, Ni-based alloy, Co-based alloy and Cu-based alloy species; the shaped articles manufactured from that metal material are not particularly restricted in shape or form.
• the method of joining the metal material according to the present invention to various steel or alloy species is not particularly restricted but includes mechanical joining such as pressure welding or caulking; it is also possible to give the metal material such shapes suited for thermal joining such as welding or diffusion treatment.
• Metal materials which have the respective chemical compositions shown in Table 1 and Table 2 were prepared by melting, using a high-frequency induction vacuum furnace and made into billets, which were subjected to hot forging and cold rolling to give the metal pipes with an outside diameter of 56 mm and a wall thickness of 6 mm.
• the metal pipes were subjected to a solution treatment under the conditions given below, and test specimens were prepared by cutting a part of each metal pipe.
• the solution heat treatment was carried out under the conditions of 1160 to 1230° C. for 10 minutes.
• Some of the metals according to the present invention were pressure-welded to the alloy 800H to produce clad materials, and test specimens were prepared in the same manner.
• Test specimens with a width of 15 mm and a length of 20 mm were cut out from each of the metal materials described in Table 1 and Table 2.
• the test specimens were maintained in a gas atmosphere containing, on the % by volume basis, 60% CO-26% H 2 -11.5% CO 2 -2.5% H 2 O at a constant temperature of 620° C. for a maximum of 1000 hours.
• the test specimens were taken out at timed intervals and the specimen surfaces were observed; the point of time at which pitting of a test specimen was confirmed was regarded as the pitting time of the test specimen.
• the results thus obtained are summarized in Table 3 and Table 4.
• the metal materials in Test Nos. 21 to 24 which failed to satisfy the chemical composition requirements specified herein gave pitting times as short as 500 hours at the longest and thus were inferior in metal dusting resistance.
• the metal materials according to the present invention in Test Nos. 1 to 20 and 25 to 44 all showed pitting times longer than 1000 hours and were excellent in metal dusting resistance, as seen in Table 3 and Table 4.
• Metal materials having the respective chemical compositions shown in Table 5 were prepared by melting using a high-frequency induction vacuum furnace and made into billets, which were subjected to hot forging and cold rolling to produce metal plates with a thickness of 12 mm.
• the metal plates were subjected to solution heat treatment under the conditions given below, and test specimens were prepared by cutting a part of each metal plate.
• the solution heat treatment was carried out under the conditions of 1160 to 1230° C. for 10 minutes.
• test specimens with a width of 15 mm and a length of 20 mm were cut out from each metal material described in Table 5.
• the test specimens were maintained in a gas atmosphere containing, on the % by volume basis, 60% CO-26% H 2 -11.5% CO 2 -2.5% H 2 O at a constant temperature of 620° C. for a maximum of 1000 hours, the test specimens were taken out at timed intervals and the specimen surfaces were observed; the point of time at which pitting of a test specimen was confirmed was regarded as the pitting time of the test specimen.
• the results thus obtained are shown in Table 6.
• Test specimen Nos. 45 to 58 show the present invention, and Nos. 59 to 61 the comparative.
• the metal materials according to the present invention in Test Nos. 45 to 58 showed percent reductions in the area at 900° C. of not smaller than 60%, hence satisfied the hot workability requirement and, in addition, all showed pitting times longer than 1000 hours and were excellent in metal dusting resistance.
• the metal materials in Test Nos. 59 and 60 which failed to satisfy the chemical composition requirements specified herein gave pitting times longer than 1000 hours and thus were excellent in metal dusting resistance but showed percent reductions in area at 900° C. of lower than 60% and were therefore inferior in hot workability. Further, the metal material in Test No. 61 which also failed to satisfy the chemical composition requirements specified herein was excellent in hot workability but gave a pitting time as short as 200 hours and thus was inferior in metal dusting resistance.
• the metal material of the present invention has the effect of suppressing the surface reactions between carburizing gases and the metal and is excellent in metal dusting resistance and therefore can be utilized for cracking furnaces, reforming furnaces, heating furnaces, heat exchangers in petroleum refining and petrochemical plants to markedly improve the durability of apparatus and the operation efficiency.

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• 2007
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