DK2246454T3

DK2246454T3 - Opkulningsresistent metal material

Info

Publication number: DK2246454T3
Application number: DK09715929.7T
Authority: DK
Inventors: Yoshitaka Nishiyama; Takahiro Osuki; Satoshi Matsumoto
Original assignee: Nippon Steel & Sumitomo Metal Corp
Priority date: 2008-02-27
Filing date: 2009-02-23
Publication date: 2015-10-05
Also published as: KR101210113B1; JP4329883B1; CN101946016B; CN101946016A; CA2711415A1; JPWO2009107585A1; WO2009107585A1; EP2246454A1; KR20100092498A; ES2545488T3; EP2246454B1; EP2246454A4; US20100034690A1; CA2711415C

Description

jcourar i iuin ?chnical Field 1001] The present invention relates to a metal material that has excellent high-temperature strength and superior corrosion ssistance, and in particular is used in a carburizing gas atmosphere containing hydrocarbon gas and CO gas. More particularly, relates to a metal material having excellent weldability and metal dusting resistance, which is suitable as a raw material for acking furnaces, reforming furnaces, heating furnaces, heat exchangers, etc. in petroleum refining, petrochemical plants, and ie like. ackground Art 1002] Demand for clean energy fuels such as hydrogen, methanol, liquid fuels (GTL: Gas to Liquids), and dimethyl ether (DME) expected to significantly increase in the future. Therefore, a reforming apparatus for producing such a synthetic gas tends to 3 large in size, and an apparatus that achieves higher thermal efficiency and is suitable for mass production is demanded. Also, 3at exchange for recovering exhaust is often used to enhance energy efficiency in reforming apparatuses in the conventional 3troleum refining, petrochemical plants, and the like, and ammonia manufacturing apparatuses, hydrogen manufacturing Dparatuses, and the like, in which raw materials such as petroleum are used. 1003] To effectively use the heat of such a high-temperature gas, heat exchange in a temperature range of 400 to 800°C, which relatively low, has become important, and corrosion caused by carburization of a high Cr - high Ni - Fe alloy based metal aterial used for reaction tubes, heat exchangers, and the like in this temperature range poses a problem. 1004] Usually, a synthetic gas reformed in the above-described reactors, that is, a gas containing H2, CO, CO2, H2O, and /drocarbon such as methane comes into contact with the metal material of a reaction tube and the like at a temperature of about 300°C or higher. In this temperature range, on the surface of the metal material, elements such as Cr and Si, which have higher <idation tendency than Fe or Ni or the like, are oxidized selectively, and a dense film of chromium oxide or silicon oxide or the like formed, by which corrosion is restrained. In a portion such as a heat exchange part in which the temperature is relatively low, Dwever, the diffusion of element from the inside to the surface of metal material is insufficient. Therefore, the formation of oxide m, which achieves a corrosion restraining effect, delays, and additionally, such a gas having a composition containing /drocarbon comes to have carburizing properties, so that carbon intrudes into the metal material through the surface thereof, id carburization occurs. 1005] In an ethylene cracking furnace tube and the like, if carburization proceeds and a carburized layer comprising carbide of r or Fe or the like is formed, the volume of that portion increases. As a result, fine cracks are liable to develop, and in the worst ase, the tube in use is broken. Also, if the metal surface is exposed, carbon precipitation (coking) in which metal serves as a atalyst occurs on the surface, so that the flow path area of the tube decreases and the heat-transfer characteristics degrade. 1006] In a heating furnace tube and the like for a catalytic cracking furnace for increasing the octane value of naphtha obtained / distillation of crude oil as well, a heavily carburizing environment consisting of hydrocarbon and hydrogen is created, so that arburization and metal dusting occur. 1007] On the other hand, in an environment in which the carburizing properties of gas in the reforming furnace tube, heat <changer, and the like are severer, the carbide is supersaturated, and thereafter graphite precipitates directly. Therefore, a ase material metal is exfoliated away and the thickness of base material decreases, that is, corrosion loss called metal dusting oceeds. Further, coking occurs with the exfoliated metal powder serving as a catalyst. 1008] If the cracks, loss, and in-tube closure increase, an apparatus failure or the like occurs. As a result, operation may be jspended. Therefore, careful consideration must be given to the selection of material used for an apparatus member. 1009] To prevent the aforementioned carburization and the corrosion caused by metal dusting, various countermeasures have anventionally been studied. 1010] For example, Patent Document 1 proposes an Fe-based alloy or a Ni-based alloy containing 11 to 60% (mass%, the 1 ame snail apply nereinaner; οι i^r concerning me meiai ousung resistance in an aimospnenc gas οι *tuu ιο /uu c, containing M2, O, CO2 and H2O. Specifically, it is shown that the invention of an Fe-based alloy containing 24% or more of Cr and 35% or more : N, a Ni-based alloy containing 20% or more of Cr and 60% or more of Ni, and an alloy material in which Nb is further added to lese alloys is excellent. However, even if a Cr or Ni content in the Fe-based alloy or the Ni-based alloy is merely increased, a jfficient carburization restraining effect cannot be achieved, so that a metal material having higher metal dusting resistance has een demanded. 1011] Also, in a method disclosed in Patent Document 2, to prevent corrosion caused by metal dusting of a high-temperature loy containing iron, nickel, and chromium, one or more kinds of metals of the VIII group, the IB group, the IV group, and the V 'oup of the element periodic table and a mixture thereof are adhered to the surface by the ordinary physical or chemical means, id the alloy is annealed in an inert atmosphere to form a thin layer having a thickness of 0.01 to 10 pm, by which the alloy jrface is protected. In this case, Sn, Pb, Bi, and the like are especially effective. Although effective at the early stage, this ethod may lose effectiveness in that the thin layer is exfoliated in long-term use. 1012] Patent Document 3 relates to the metal dusting resistance of a metal material in an atmospheric gas of 400 to 700°C intaining H2, CO, CO2 and H2O. As the result of an investigation of the interaction with carbon made from the viewpoint of solute ement in iron, Patent Document 3 discloses that the addition of an element producing stable carbide in the metal material, such 5 Ti, Nb, V and Mo, or the alloying element in which the interaction co-factor Q represents a positive value, such as Si, Al, Ni, Cu id Co is effective in restraining metal dusting in addition to enhancing the protecting properties of oxide film. However, the crease of Si, Al and the like sometimes leads to the decrease in hot workability and weldability. Therefore, considering the anufacturing stability and plant working, this metal material leaves room for improvement. 1013] Next, to break off the contact of carburizing gas with the metal surface, there have been disclosed a method for oxidizing a etal material in advance and a method for performing surface treatment. 1014] For example, Patent Document 4 and Patent Document 5 disclose a method for pre-oxidizing a low Si-based 25Cr-20Ni K40) heat resistant steel or a low Si-based 25Cr-35Ni heat-resisting steel at a temperature near 1000°C for 100 hours or nger in the air. Also, Patent Document 6 discloses a method for pre-oxidizing an austenitic heat-resisting steel containing 20 to 5% of Cr in the air. Further, Patent Document 7 proposes a method for improving the carburization resistance by heating a high i-Cr alloy in a vacuum and by forming a scale film. 1015] Patent Document 8 proposes an austenitic alloy whose contents of Si, Cr and Ni satisfy the formula of Si < (Cr + 0.15Ni -3)/10; thereby a Cr-based oxide film having high adhesiveness even in an environment, in which the alloy is subjected to a sating/cooling cycle, is formed to provide the alloy with excellent carburization resistance even in an environment in which the loy is exposed to a corrosive gas at high temperatures. Patent Document 9 proposes an austenitic stainless steel having <cellent scale exfoliation resistance even in an environment in which the steel is subjected to a heating/cooling cycle, which is Oduced by containing Cu and a rare earth element (Y and Ln group) therein and thereby forming a uniform oxide film having gh Cr concentration in the film. Also, Patent Document 10 proposes a method for improving the carburization resistance by irming a concentrated layer of Si or Cr by performing surface treatment. Unfortunately, all of these prior arts require special heat eatment or surface treatment, and therefore they are inferior in economy. Also, since scale restoration (scale recycling) after the •e-oxidized scale or the surface treatment layer has exfoliated away is not considered, if the material surface is damaged once, ie subsequent effect cannot be anticipated. 1016] Patent Document 11 proposes a stainless steel pipe having excellent carburization resistance and containing 20 to 55% : Cr, which is produced by forming a Cr-deficient layer, which has a Cr concentration of 10% or higher and lower than the Cr incentration of the base material, on the surface of steel pipe. In this patent document, however, the improvement of weldability, hich is an issue of the Cu-containing steel, has not been studied. 1017] Besides, a method for adding H2S into the atmospheric gas has been thought of. However, the application of this method restricted because H2S may remarkably decrease the activity of a catalyst used for reforming. 1018] Patent Document 12 and Patent Document 13 propose a metal material in which the gas dissociative adsorption las/metal surface reaction) is restrained by containing a proper amount of one kind or two or more kinds of P, S, Sb and Bi. ince these elements segregate on the metal surface, even if the elements are not added excessively, the elements can restrain arburization and metal dusting corrosion significantly. However, since these elements segregate not only on the metal surface jt also at the grain boundary of metal grainy, a problem associated with hot workability and weldability remains to be solved. 2 puivj lecnmques ior ennanung corrosion resistance anu crevice corrosion resistance uy auumg cu nave aiso oeen proposeu. atent Document 14 describes a technique for enhancing corrosion resistance by containing Cu, and on the other hand, for creasing the hot workability improving effect due to B by reducing S and 0 as far as possible. Patent Document 15 describes a chnique for improving corrosion resistance and crevice corrosion resistance excellent in sulfuric acid and sulfate environments 1 setting the G.l. value (General Corrosion Index) represented by ”-Cr + 3.6Ni + 4.7Mo + 11.5Cu," at 60 to 90 and by setting the .I. value (Crevice Corrosion Index) represented by "Cr + 0.4M + 2.7Mo + Cu + 18.7N" at 35 to 50. Patent Document 16 ascribes a technique for improving hot workability by adding B exceeding 0.0015% while increasing a Cu content and by keeping i oxygen content low. In all of these techniques, the upper limit of a C content is restricted to a low level to avoid the decrease in xrosion resistance. Therefore, the solid-solution strengthening of C cannot be anticipated, and a sufficient high-temperature rength cannot be obtained. For this reason, these techniques are unsuitable for a metal material used at high temperatures. 1020]

’atent Document 1] JP9-78204A ’atent Document 2] JP11-172473A ’atent Document 3] JP2003-73763A ’atent Document 4] JP53-66832A ’atent Document 5] JP53-66835A ’atent Document 6] JP57-43989A ’atent Document 7] JP11-29776A ’atent Document 8] JP2002-256398A ’atent Document 9] JP2006-291290A ’atent Document 10] JP2000-509105A ’atent Document 11] JP2005-48284A ’atent Document 12] JP2007-186727A ’atent Document 13] JP2007-186728A ’atent Document 14] JP1-21038A ’atent Document 15] JP2-170946A ’atent Document 16] JP4-346638A 1021] Zhang et al., "Effect on copper on metal dusting of austenitic stainless steels", Corrosion Science, Oxford, GB, vol. 49, no. 5 December 2006, pages 1450-1467, XP005793496, ISSN: 0010-938X, D0l:10.1016/J.CORSCI.2006.06.032, discloses three eels, 304SS, 31 OSS and 800H, which were alloyed with 5%, 10%, and 20% (by weight) copper, and then exposed to 68%CO-1%H2-1%H20 gas at 680 °C under thermal cycling conditions. Kinetic measurements showed that copper-free alloys all dusted, ith 304SS experiencing the greatest metal wastage. Copper additions did not have any effect on metal wastage of 304SS, but sduced the attack on 31 OSS and 800H markedly at levels of 5% and 10%. isclosure of the Invention roblems to be Solved by the Invention 1022] As described above, various techniques for enhancing the metal dusting resistance, the carburization resistance, and the iking resistance of metal material have been proposed conventionally. However, all of these techniques require special heat 3 eaimem ana sunace ireaimeni, so mai cost ana laoor are neeaea. miso, inese lecnniques nave no luncuon ot scale resioranon scale recycling) after the pre-oxidized scale or the surface treatment layer has exfoliated away. Therefore, if the material surface damaged once, the subsequent metal dusting cannot be restrained. Also, these techniques have a problem associated with eldability of metal material. 1023] Also, there is a method for restraining metal dusting by adding H2S into the atmospheric gas in the tube of a reforming Dparatus and manufacturing apparatus for synthetic gas as described above, not by improving the metal material itself, owever, since H2S may remarkably decrease the activity of a catalyst used for reforming hydrocarbon, the technique for «training metal dusting by adjusting the components of atmospheric gas is merely applied limitedly. 1024] The present invention has been made in view of the present situation, and accordingly an object thereof is to provide a etal material that has metal dusting resistance, carburization resistance, and coking resistance, and further has improved eldability due to the restraint of reaction between carburizing gas and the metal surface in an ethylene plant cracking furnace ibe, a heating furnace tube of catalytic reforming furnace, a synthetic gas reforming furnace tube, and the like. eans for Solving the Problems 1025] The solution is given in the claims. 1026] The inventors analyzed a phenomenon that carbon intrudes into a metal in a molecular state, and revealed that this lenomenon progresses in an elementary process consisting of the following items (a) to (c). 1. (a) Gas molecules consisting of C compounds such as hydrocarbon and CO approach the metal surface. 2. (b) The approaching gas molecules are dissociatively adsorbed onto the metal surface. 3. (c) The dissociated atomic carbon intrudes into the metal and diffuses. 1027] As the result of various studies on methods for restraining the aforementioned phenomenon, it was found that the illowing methods (d) and (e) are effective. I) Oxide scale is formed positively on the metal surface during the use of metal material, by wfnich the contact with the metal of ie gas molecules consisting of C compounds is broken off. i) The dissociative adsorption of the gas molecules consisting of C compounds is restrained on the metal surface. 1028] As the result that the study on oxide scale having a breaking-off effect as in the item (d) was conducted, it was revealed lat oxide scale consisting of Cr and Si acts effectively. In particular, in a carburizing gas environment such as an ethylene plant acking furnace tube, a heating furnace tube of catalytic reforming furnace, and a synthetic gas reforming furnace tube, the artial pressure of oxygen in gas is low. Therefore, it was revealed that oxide scale consisting mainly of Cr can be formed on the as side and oxide scale consisting mainly of Si can be formed on the metal side by containing proper amounts of Cr and Si. 1029] On the other hand, as the result that the study was conducted from the viewpoint of dissociative adsorption as in the item s), it was revealed that if proper amounts of noble metal elements such as Cu, Ag and Pt and elements of the VA group and the IA group in the periodic table are added, an effect of restraining the dissociative adsorption of gas molecules consisting of C impounds is achieved. In particular, Cu is low in cost among the noble metal elements, and additionally less problems occur in elting and solidification when Cu is contained in an Fe-Ni-Cr based metal material. Therefore, the use of Cu is preferable. 1030] It was revealed that according to the methods (d) and (e), the intrusion of carbon into the metal in the above-described ementary process of items (a) to (c) can be restrained effectively, and by applying the methods (d) and (e) simultaneously, the etal dusting resistance, the carburization resistance, and the coking resistance can be improved dramatically. 1031] However, if an element such as Si and Cu is added, the corrosion resistance can be improved; on the other hand, the eldability is deteriorated. In particular, in a region subjected to an influence of heat cycle of rapid heating/rapid cooling caused i welding, that is in a welding heat affected zone (hereinafter, referred to as "HAZ'), cracks caused by grain boundary melting e liable to develop. Specifically, if Si, Cu or the like element segregates at the crystal grain boundary of the base material, the 4 elting point ot grain boundary lowers. At this time, when the grain boundary is subjected to welding heat cycle and is heated to a imperature just below the melting point, the grain boundary melts and is torn off by the thermal stress at the time of welding, hich develops a crack. This is a HAZ crack. Therefore, in the case where the metal material is used for a welded structure, weld acks of this kind must be restrained. 1032] The inventors studied various methods capable of restraining HAZ cracks at the time of welding while improving the Drrosion resistance by adding a considerable amount of Si or Cu. As a result, the inventors came to obtain a knowledge that the AZ cracks can be restrained by the following methods (f) and (g). ) Cr-based carbides are precipitated at the crystal grain boundary of the base material by increasing the C content, by which the elting point of grain boundary is raised. l) The grain coarsening in the HAZ at the time when the welding heat cycle occurs is restrained by the precipitation of Cr arbides of high melting point, by which the surface area of grain boundary is increased, and thereby the segregation of Si, Cu or e like at the grain boundary is decreased. 1033] Based on this knowledge, in a metal material containing 18 to 30% of Cr or preferably 22 to 30% of Cr, the contents, i.e. , Si and Cu, were changed variously, by which the HAZ crack susceptibility was studied. As a result, it was revealed that the wer limit of C content capable of preventing HAZ cracks changes according to the Si, Cu and Cr contents. Specifically, it was ivealed that as the Si and Cu contents lowering the melting point of grain boundary increase, the allowable lower limit of C intent is raised, and as the Cr content constituting the carbides raising the melting point of grain boundary increases, the lowable lower limit of C content is lowered. 1034] From the results of systematical experiments in which components were changed variously, a relational expression stween the C content capable of preventing HAZ cracks and the Si, Cu and Cr contents was estimated experimentally. As a »sult, the inventors obtained a knowledge that by satisfying Expression (1), both of excellent metal dusting resistance and <cellent HAZ crack susceptibility resistance can be obtained. C > 0.062xSi + 0.033xCu - 0.004xCr + 0.043 ... (1) which the symbol of element in Expression (1) represents the content of that element in mass%. )035] The present invention is given by the claims and has been completed based on the above-described knowledge, and the sts of the present invention are as described in the following items (1) to (3). Hereunder, the gists are called invention (1) to vention (3), and are sometimes generally named the present invention. 1. (1) A carburization resistant metal material characterized by consisting of, by mass%, C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn: 0.05 to 2.5%, P: 0.04% or less, S: 0.015% or less, Cr: 22 to 30%, Ni: 20% or higher and less than 30%, Cu: 0.5 to 10.0%, Al: 0.01 to 1%, Ti: 0.01 to 1%, N: 0.15% or less, and O (oxygen): 0.02% or less , the balance being Fe and impurities, and satisfying Expression (1). [ C > 0.062xSi + 0.033xCu - 0.004xCr + 0.043 ... (1) in which the symbol of element in Expression (1) represents the content of that element in mass%. 2. (2) A carburization resistant metal material characterized by consisting of, by mass%, C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn: 0.05 to 2.5%, P: 0.04% or less, S: 0.015% or less, Cr: 18 to 30%, Ni: 20% or higher and less than 30%, Cu: 0.5 to 10.0%, Al: 0.01 to 1%, Ti: 0.01 to 1%, N: 0.15% or less, and O (oxygen): 0.02% or less , the balance being Fe and impurities, and satisfying Expression (1). C > 0.062xSi + 0.033xCu - 0.004xCr + 0.043 ... (1) in which the symbol of element in Expression (1) represents the content of that element in mass%. 3. (3) The carburization resistant metal material described in item (1) or (2) above, characterized by further containing, by mass%, at least one kind of a component selected from at least one group of the first group to the fifth group described below: first group: Co: 10% or less, second group: Mo: 2.5% or less and W: 5% or less, 5 third group: B: 0.1% or less, V: 0.5% or less, Zr: 0.1% or less, Nb: 2% or less, and Hf: 0.5% or less, fourth group: Mg: 0.1 % or less and Ca: 0.1% or less, fifth group: Y: 0.15% or less, La: 0.15% or less, Ce: 0.15% or less, and Nd: 0.15% or less, dvantages of the Invention 1036] The metal material in accordance with the present invention has an effect of restraining reaction between carburizing gas id the metal surface, and has excellent metal dusting resistance, carburization resistance, and coking resistance. Further, since ie weldability is improved, the metal material can be used for welded structure members of cracking furnaces, reforming irnaces, heating furnaces, heat exchangers, etc. in petroleum refining, petrochemical plants, and the like, and can significantly iprove the durability and operation efficiency of apparatus. 1037] In particular, the metal material in accordance with the present invention is suitable as a metal material used for reaction ibes and heat exchangers used for heat exchange in a temperature range (400 to 800°C) lower than the conventional imperature range, so that metal dusting, which poses a problem in this temperature range, can be restrained effectively. est Mode for Carrying Out the Invention 1038] The reason why the composition range of metal material is restricted according to the invention is as described below. In ie explanation below, the "%" representation of the content of each element means "mass%". : 0.08 to 0.4% 1039] C (carbon) is one of important elements in the present invention. Carbon not only enhances the strength at high mperatures but also achieves an effect of improving the weldability in combination with chromium to form carbides. In particular, ie effect is remarkable in the metal material in accordance with the present invention that has high Si and Cu contents. To jfficiently achieve this effect, 0.08% or more of C must be contained. However, if C content exceeds 0.4%, the toughness of alloy wers extremely, so that the upper limit of C content is set at 0.4%. The C content is preferably in the range of higher than 0.1% id 0.35% or less, further preferably in the range of higher than 0.15% and 0.25% or less. i: 0.6 to 2.0% 1040] Si (silicon) is one of important elements in the present invention. Since silicon has a strong affinity with oxygen, it forms Si-ased oxide scale in the lower layer of a protective oxide scale layer such as (>203, and isolates carburizing gas. This action is ought about when the Si content is 0.6% or higher. However, if the Si content exceeds 2.0%, the weldability decreases (markably, so that the upper limit of Si content is set at 2.0%. The Si content is preferably in the range of 0.7 to 2.0%, further -eferably in the range of 0.8 to 1.5%. n: 0.05 to 2.5% 1041] Mn (manganese) has deoxidizing ability and also improves the workability and weldability, so that 0.05% or more of Mn is Ided. Also, since manganese is an austenite-generating element, some of Ni can be replaced with Mn. However, excessive Edition of Mn harms the carburizing gas isolating properties of protective oxide scale layer, so that the upper limit of Mn content set at 2.5%. The Mn content is preferably in the range of 0.1 to 2.0%, further preferably in the range of 0.7 to 1.6%. : 0.04%or less 6 1042] P (phosphorus) decreases the hot workability and weldability, so that the upper limit of P content is set at 0.04%. In articular, when the Si and Cu contents are high, this effect is important. The upper limit of P content is preferably 0.03%, further -eferably 0.025%. However, since phosphorus acts to restrain the dissociative adsorption reaction on the metal surface of arburizing gas, it may be contained when the decrease in weldability can be permitted. : 0.015%or less 1043] S (sulfur) decreases the hot workability and weldability like phosphorus, so that the upper limit of S content is set at 015%. In particular, when the Si and Cu contents are high, this effect is important. The upper limit of S content is preferably 01 %, further preferably 0.003%. However, like phosphorus, since sulfur acts to restrain the dissociative adsorption reaction on ie metal surface of carburizing gas, it may be contained when the decrease in weldability can be permitted. r: 18 to 30%or preferably 22 to 30% 1044] Cr (chromium) forms oxide scale such as Cr2C>3 stably, and has an effect of isolating carburizing gas. Therefore, even in severe carburizing gas environment, chromium provides sufficient carburization resistance, metal dusting resistance, and coking ssistance. Also, chromium improves the weldability because it combines with carbon to form carbides. In particular, when the Si id Cu contents are high, this effect is important. To sufficiently achieve this effect, 18% or more of Cr must be contained, owever, since excessive addition decreases not only the workability but also the structural stability, the upper limit of Cr is set at 3%. The lower limit of Cr content is preferably 19%, further preferably 22%, and still further preferably 23%. Also, the upper limit : Cr content is preferably 28%, further preferably 27%. i: 20%or higher and less than 30% 1045] Ni (nickel) is an element necessary for obtaining a stable austenitic micro-structure according to the Cr content, and lerefore 20% or more of Ni must be contained. Also, when carbon intrudes into the metal material, nickel has a function of iducing the intrusion rate. Further, nickel acts to secure the high-temperature strength of the metal micro-structure. However, ie nickel content higher than necessary may lead to cost increase and manufacturing difficulties, and may also accelerate coking id metal dusting especially in a gas environment that contains hydrocarbon. Therefore, the upper limit of Ni content is restricted i less than 30%. Preferably, the content of Ni is 22.5% or higher and less than 30%. Further preferably, the content of Ni is gher than 25% and 29.5% or less. u: 0.5 to 10.0% 1046] Cu (copper) is one of important elements in the present invention. Copper restrains reaction between carburizing gas and ie metal surface, and greatly improves the metal dusting resistance and the like. Also, since copper is an austenite-generating ement, some of Ni can be replaced with Cu. To achieve the metal dusting resistance improving effect, 0.5% or more of Cu must 3 contained. However, if Cu exceeding 10.0% is contained, the weldability decreases, so that the upper limit of Cu content is set : 10.0%. The Cu content is preferably 1.0 to 6.0%, further preferably 2.1 to 4.0%. I: 0.01 to 1% 1047] A1 (aluminum) is an element effective in improving the high-temperature strength. Also, aluminum has an effect as a soxidizer because it has a high affinity with oxygen. In addition, aluminum serves as one of the constituent elements of oxide ;ale, and enhances the gas isolating properties. This effect can be anticipated especially in an environment in which the arburizing properties are strong. To achieve this effect, it is effective to contain 0.01 % or more of Al. On the other hand, if the Al intent exceeds 1%, the weldability is impaired. Therefore, the Al content is set in the range of 0.01 to 1%. The Al content is 'eferably in the range of 0.12 to 0.8%, further preferably in the range of 0.2 to 0.6%. : 0.01 to 1% 7 1048] Ti (titanium) is an element effective in improving the high-temperature strength. Also, since titanium has an affinity with <ygen, it serves as one of the constituent elements of oxide scale, and enhances the gas isolating properties. This effect can be iticipated especially in an environment in which the carburizing properties are strong. Therefore, titanium is contained positively. 5 achieve this effect, it is effective to contain 0.01% or more of Ti. However, if titanium is contained excessively, the workability id weldability decrease, so that the upper limit of Ti content is set at 1%. The Ti content is preferably in the range of 0.12 to 8%, further preferably in the range of 0.2 to 0.6%. : 0.15%or less 1049] N (nitrogen) need not necessarily be contained. If nitrogen is contained, it acts to enhance the high-temperature strength : metal material. However, if the N content exceeds 0.15%, the workability is impaired. Therefore, the upper limit of N content is it at 0.15%. The preferred upper limit thereof is 0.05%. To achieve the effect of enhancing the high-temperature strength of etal material, preferably 0.0005% or more, further preferably 0.001 % or more, of N is contained. : 0.02%or less 1050] O (oxygen) is an impurity element mingled from a raw material or the like when the metal material is melted . If the O intent exceeds 0.02%, large amounts of oxide inclusions exist in the metal material, so that the workability decreases, and also a aw may occur on the surface of metal material. Therefore, the upper limit of O content is set at 0.02%. 1051] Next, in addition to the method of invention (1) or invention (2), invention (3) relating to a metal material whose strength, jctility, and toughness are improved is explained. 1052] Invention (3) relates to a carburization resistant metal material characterized by further containing, by mass%, at least one nd of a component selected from at least one group of the first group to the fifth group described below in a metal material lecified in invention (1) or (2): st group: Co: 10% or less, icond group: Mo: 2.5% or less and W: 5% or less, lird group: B: 0.1 % or less, V: 0.5% or less, Zr: 0.1 % or less, Nb: 2% or less, and Hf: 0.5% or less, iurth group: Mg: 0.1 % or less and Ca: 0.1 % or less, th group: Y: 0.15% or less, La: 0.15% or less, Ce: 0.15% or less, and Nd: 0.15% or less. 1053] Next, these optionally added elements are explained, irst group (Co: 10%or less, by mass°/<) 1054] Co (cobalt) acts to stabilize the austenite phase, so that it can replace some of Ni component. Therefore, cobalt may be intained as necessary. However, if the Co content exceeds 10%, cobalt deteriorates the hot workability. Therefore, when cobalt contained, the content is 10% or less. From the viewpoint of hot workability, the Co content is preferably in the range of 0.01 to Vo, further preferably in the range of 0.01 to 3%. econd group (Mo: 2.5%or less and W: 5%or less, by mass°/<) 1055] Mo (molybdenum) and W (tungsten) are solid-solution strengthening elements, so that either one or both of them may be intained as necessary. However, when molybdenum is contained, molybdenum deteriorates the workability and impairs the 8 ruciurai siøDNiiy it ΐπθ coniøni exceeds z.o/ο. i nereiore, wnen muiyuuenurn is cunidinecj, ine cuniem is ^.o/o ui iess. i ne ινιυ intent is preferably 0.01 to 2.3%. Also, when tungsten is contained, tungsten deteriorates the workability and impairs the ructural stability if the content exceeds 5%. Therefore, when tungsten is contained, the content is 5% or less. The W content is eferably 0.01 to 2.3%. •rird group (B: 0.1%or less, V: 0.5%or less, Zr: 0.1%or less, Nb: 2%or less, and Hf: 0.5%or less, by mass0/!) 1056] B (boron), V (vanadium), Zr (zirconium), Nb (niobium) and Hf (hafnium) are elements effective in improving the high-imperature strength characteristics, so that one kind or two or more kinds of these elements may be contained. However, when iron is contained, boron deteriorates the weldability if the content exceeds 0.1 %. Therefore, when boron is contained, the Dntent is 0.1% or less. The B content is preferably 0.001 to 0.05%. When vanadium is contained, vanadium deteriorates the eldability if the content exceeds 0.5%. Therefore, when vanadium is contained, the content is 0.5% or less. The V content is •eferably 0.001 to 0.1%. When zirconium is contained, zirconium deteriorates the weldability if the content exceeds 0.1%. herefore, when zirconium is contained, the content is 0.1% or less. The Zr content is preferably 0.001 to 0.05%. When niobium contained, niobium deteriorates the weldability if the content exceeds 2%. Therefore, when niobium is contained, the content is !o or less. The Nb content is preferably 0.001 to 0.1%. Also, when hafinium is contained, hafnium deteriorates the weldability if e content exceeds 0.5%. Therefore, when hafnium is contained, the content is 0.5% or less. The Hf content is preferably 0.001 i 0.1%. ourth group (Mg: 0.1 %or less and Ca: 0.1 %or less, by mass°/<) 1057] Mg (magnesium) and Ca (calcium) have an effect of improving the hot workability, so that one kind or two or more kinds of ese elements may be contained as necessary. However, when magnesium is contained, magnesium deteriorates the weldability the content exceeds 0.1%. Therefore, when magnesium is contained, the content is 0.1% or less. The Mg content is preferably 0005 to 0.1%. Also, when calcium is contained, calcium deteriorates the weldability if the content exceeds 0.1%. Therefore, hen calcium is contained, the content is 0.1 % or less. The Ca content is preferably 0.0005 to 0.1%. ifth group (Y: 0.15%or less, La: 0.15%or less, Ce: 0.15%or less, and Nd: 0.15%or less, by mass0/) 1058] Y (yttrium), La (lanthanum), Ce (cerium) and Nd (neodymium) have an effect of improving the oxidation resistance, so that ie kind or two or more kinds of these elements may be contained as necessary. However, when these elements are contained, ese elements deteriorate the workability if the content of any one element thereof exceeds 0.15%. Therefore, when these ements are contained, the content of any one element thereof is 0.15% or less. The content is preferably 0.0005 to 0.15%. 1059] The metal material in accordance with the present invention having a function of restraining the reaction between arburizing gas and the metal surface has only to satisfy the requirements specified in the above-described items (f) and (g) scause the metal material has problems of metal dusting, carburization, and coking. 1060] The metal material in accordance with the present invention may be formed into a required shape such as a thick plate, leet, seamless tube, welded tube, forged product, and wire rod by means of melting, casting, hot working, cold rolling, welding, id the like. Also, the metal material may be formed into a required shape by means of powder metallurgy, centrifugal casting, id the like. The surface of the metal material having been subjected to final heat treatment may be subjected to surface eatment such as pickling, shotblasting, shotpeening, mechanical cutting, grinding, and electropolishing. Also, on the surface of e metal material in accordance with the present invention, one or two or more irregular shapes such as protruding shapes may 3 formed. Also, the metal material in accordance with the present invention may be combined with various kinds of carbon steels, ainless steels, Ni-based alloys, Co-based alloys, Cu-based alloys, and the like to be formed into a required shape. In this case, e joining method of the metal material in accordance with the present invention to the various kinds of steels and alloys is not jbject to any restriction. For example, mechanical joining such as pressure welding and "staking" and thermal joining such as elding and diffusion treatment can be performed. 1061] Next, the present invention is explained in more detail with reference to examples. The present invention is not limited to ese examples.

Example 1] 9 1062] A metal material having a chemical composition given in Table 1 was melted by using a high-frequency heating vacuum irnace, and a metal plate having a plate thickness of 6 mm was manufactured by hot forging and hot rolling. The metal plate was jbjected to solid-solution heat treatment at 1160 to 1230°C for 5 minutes, a part of which was cut to produce a test piece . 1063] From the metal material described in Table 1, a test piece measuring 15 mm wide and 20 mm long was cut. This test ece was isothermally maintained at 650°C in a 45%C0-42.5%H2-6.5%CC>2-6%H20 (percent by volume) gas atmosphere. The ist piece was taken out after 200 hours had elapsed, and the presence of a pit formed on the surface of test piece was omined by visual observation and by optical microscope observation. The results are summarized in Table 2. 1064] [Table 1] able 1 r'.homiral rnmnncitinn imasc0/» helenee heinn Fe and imnuritiesl Rinht hand side 1

10

Chemical composition (mass%, balance being Fe and impurities) Right hand side)

ΊυΐΡ. IVICII r\ I I IVJ I υΐ IMP W I LI Iti f«»l ILIIIVtillLIV-MI. { 1065] [Table 2] able 2

.................................................................................................................................................................................................................................................1 11 650°C, 200h, in 45%CCM2.5%H2-6.5%C02-| 650°C, 10h, in 30%C3He- j

33 Present___j_ Present j 0/10 j 1066] Table 2 indicates that, among Nos. 24 to 33 metal materials in which the chemical composition deviates from the condition Decified in the present invention, Nos. 24, 26, 28, 32 and 33 metal materials had a pit formed after 200 hours had elapsed, herefore, the metal dusting resistance is poor in a synthetic gas environment containing CO. On the other hand, in all of the etal materials specified in the present invention, no pit is formed, and therefore, these metal materials have excellent metal jsting resistance.

Example 2] 1067] A metal material having a chemical composition given in Table 1 was melted by using a high-frequency heating vacuum irnace, and a metal plate having a plate thickness of 6 mm was manufactured by hot forging and hot rolling. The metal plate was jbjected to solid-solution heat treatment at 1160 to 1230°C for 5 minutes, a part of which was cut to produce a test piece. From ie metal material described in Table 1, a test piece measuring 15 mm wide and 20 mm long was cut. This test piece was othermally maintained at 650°C in a 30%C3H8-70%H2 (percent by volume) gas atmosphere. The test piece was taken out after 3 hours had elapsed, and the presence of a pit formed on the surface of test piece was examined by visual observation and by Dtical microscope observation. The results are summarized in Table 2. 1068] Table 2 indicates that, among Nos. 24 to 33 metal materials in which the chemical composition deviates from the condition )ecified in the present invention, Nos. 24, 26 to 28, and 31 to 33 metal materials had a pit formed in the 10-hour test. Therefore, ie metal dusting resistance is poor in a hydrocarbon gas environment. On the other hand, in all of the metal materials specified the present invention, no pit is formed, and therefore, these metal materials have excellent metal dusting resistance.

Example 3] 1069] A metal material having a chemical composition given in Table 1 was melted by using a high-frequency heating vacuum irnace, and two metal plates each having a plate thickness of 12 mm, a width of 50 mm, and a length of 100 mm was anufactured from each metal material by hot forging and hot rolling. The metal plates were subjected to solid-solution heat eatment at 1200°C for 5 minutes, a part of which was cut to produce a test piece. 1070] Then, on one side in the lengthwise direction of the test piece, a V-type edge having an angle of 30 degrees and a root lickness of 1.0 mm was prepared. Thereafter, the periphery of the test pieces was restraint-welded onto a commercially available etal plate of SM400C specified in JIS G3106(2004) measuring 25 mm thick, 150 mm wide, and 150 mm long by using a covered ectrode of DNiCrMo-3 specified in JIS Z3224(1999). Subsequently, multi-layer welds were made by TIG welding under a Dndition of heat input of 6 kJ/cm by using a TIG welding wire of YNiCrMo-3 specified in JIS Z3334(1999). After the orementioned welding, ten test pieces for observing the sectional microstructure of joint were cut from each test piece, and the 12 cress sections inereui were mirror ponsneu anu corroaea. i nereuy, me presence 01 cracKS in me i-imz. was ODservea Dy an optical microscope at x500 magnification. The results are summarized in Table 2.

[0071] Table 2 indicates that in No. 24 metal material in which the C content deviates from the condition specified in the present invention and No. 25 metal material that does not satisfy Expression (1), HAZ cracks are recognized. Also, it is indicated that for Nos. 28 to 31 metal materials in which the Cu, Si and S contents deviate from the condition specified in the present invention though the C content meets the specified condition, the HAZ crack restraining effect is small. On the other hand, in all of the metal materials specified in the present invention, HAZ cracks are not generated. Therefore, the weldability thereof is excellent.

Industrial Applicability [0072] There is provided a metal material that has an effect of restraining reaction between carburizing gas and the metal surface, has excellent metal dusting resistance, carburization resistance, and coking resistance, and further has improved weldability. This metal material can be used for welded structure members of cracking furnaces, reforming furnaces, heating furnaces, heat exchangers, etc. in petroleum refining, petrochemical plants, and the like, and can significantly improve the durability and operation efficiency of apparatus.

REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description • JF9078204.A [0020] • JP2003073763A [0020] • JP53066832A iQQ2Qf • JP57Q43988A [0020] • JP11029776A [0020Ί • JP2002256398A [0020] • JP2006291290A f00201 • JP2000509105A Γ00201 • .JP2005048284A [0020] • JP2007186727A Γ00201 • JP2007186728A [0020] • 3P1021038A fS02Dt • JP2170946A Γ00201 • JP4346633A f0020i

Non-patent literature cited in the description • ZHANG et al.Effect on copper on metal dusting of austenitic stainless steelsCorrosion Science, 2006, vol. 49, 30010-938X1450-1467 [0021] 13

Claims

1

1. Coating-resistant metal material, characterized in that it consists in mass percent of C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn: 0.05 to 2.5%, P: 0.04% or less, S: 0.015% or less, Cr: 18 to 30%, Ni: 20% or more and less than 30%, Cu: 0.5 to 10.0%, Al: 0, 01 to 1%, Ti: 0.01 to 1%, N: 0.15% or less, and O (oxygen): 0.02% or less, optionally at least one type of component selected from at least one group of the first to fifth groups described below, wherein the remaining amount is Fe and impurities and satisfies the expression (1); C> 0.062 x Si + 0.033 x Cu - 0.004 x Cr + 0.043 ... (1) where the element symbol in the expression (1) represents the content of that element in mass percent; first group: Co: 10% or less, second group: Mo: 2.5% or less and W: 5% or less, third group: B: 0.1% or less, V: 0.5% or less, Zr: 0.1% or less, Nb: 2% or less and Hf: 0.5% or less, fourth group: Mg: 0.1% or less and Ca: 0.1% or less and fifth group: Y : 0.15% or less, La: 0.15% or less, Ce: 0.15% or less and Nd: 0.15% or less.

Coating-resistant metal material according to claim 1, characterized in that it contains Cr: 22 to 30%.