JP2018066064A - Austenitic stainless steel for fuel reformer excellent in adhesion of oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an austenitic stainless steel sheet for a fuel reformer combining economical efficiency with such a durability that adhesion of an oxide film is not impaired even when a heating and cooling cycle of activation and stop is repeated under a modified gas environment without depending on addition of rare earth elements or Ni.SOLUTION: The austenitic stainless steel sheet for a fuel reformer excellent in adhesion of an oxide film is provided that includes, by mass%, Cr:15 to 25%, C:0.1% or less, Si:5% or less, Mn:3% or less, P:0.05% or less, S:0.01% or less, Ni:8 to 18%, Cu:3% or less, Mo;3% or less, N:0.3% and further one or two or more kind of Nb:0.01 to 0.5%, Ti:0.01 to 0.5%, V:0.01 to 0.5%, Al:0.01 to 0.5%, B:0.005% or less and Mg:0.005% or less. It is preferred that a Cr-based oxide layer including Si and/or Mn is formed on the surface of the austenitic stainless steel sheet and that two or more kinds of Si oxide, Mn oxide, Nb oxide, Ti oxide and Al oxide are present between the Cr-based oxide layer and a base material.SELECTED DRAWING: None

Description

  The present invention is suitable for high-temperature members of fuel cells such as reformers and heat exchangers used when reforming hydrocarbon fuels such as city gas, methane, natural gas, propane, kerosene, and gasoline into hydrogen. The present invention relates to an austenitic stainless steel and a method for producing the same.

Recently, the spread of new systems replacing conventional power generation systems is accelerating due to problems such as depletion of fossil fuels such as petroleum and global warming due to CO ₂ emissions. As one of them, “fuel cell”, which has high practical value as a distributed power source and a power source for automobiles, is attracting attention. There are several types of fuel cells. Among them, polymer electrolyte fuel cells (PEFC) and solid oxide fuel cells (SOFC) have high energy efficiency, and are expected to expand in the future.

  A fuel cell is a device that generates electric power through a reaction process opposite to that of water electrolysis, and requires hydrogen. Hydrogen is produced by a reforming reaction of hydrocarbon fuels such as city gas (LNG), methane, natural gas, propane, kerosene, and gasoline in the presence of a catalyst. Above all, a fuel cell using city gas as a raw fuel has an advantage that hydrogen can be produced in an area where city gas piping is provided.

  The fuel reformer is usually operated at a high temperature of 200 to 900 ° C. in order to ensure the amount of heat necessary for the hydrogen reforming reaction. Further, under such a high temperature operation, it is exposed to an oxidizing atmosphere containing a large amount of water vapor, carbon dioxide, carbon monoxide and the like, and the heating / cooling cycle by starting and stopping is repeated according to the demand for hydrogen. Hitherto, high-alloy stainless steel represented by SUS310S (25Cr-20Ni) has been used as a practical material having sufficient durability under such a severe environment. In the future, cost reduction is indispensable for the spread of fuel cell systems, and reduction of alloy costs by optimizing the materials used is an important issue.

In Patent Document 1, Cr: 15 to 25%, Ni: 7 to 15%, C: 0.02 to 0.1%, Si: 1 to 4%, Mn: 2% or less, S: 0.008% Petroleum-based fuel reforms containing one or more of N: 0.05 to 0.20%, Mo: 1.0 to 3.0%, Nb: 0.05 to 0.50% An austenitic stainless steel for a quality organ is disclosed. These stainless steels are characterized in that 30% by mass or more of Cr ₂ O ₃ is contained in an oxide film after heating for 100 hours at a temperature of 900 ° C. in an atmosphere of 50% by volume H ₂ O + 20% by volume CO _2. Yes.

In Patent Document 2, Cr: 15 to 25%, Ni: 7 to 15%, C: 0.01 to 0.1%, Si: 2.56 to 4%, Mn: 2% or less, S: 0.00. An austenitic stainless steel for alcohol-based fuel reformers containing 008% or less and further including one or two of N: 0.05 to 0.20% and Mo: 0.1 to 3.0% is disclosed. Yes. These stainless steels are characterized by being excellent in steam oxidation resistance and red scale resistance in an atmosphere of 50% by volume H ₂ O + 20% by volume CO ₂ .

The austenitic stainless steels of Patent Documents 1 and 2 are aimed at improving the oxidation resistance in an environment of 50% by volume H ₂ O + 20% by volume CO _2, promoting the formation of a Cr-based oxide film by adding Si, REM, Ca, Al The technical idea is to strengthen the oxide film by dissolving it in a Cr-based oxide. The reformed gas of fuel cells using city gas as raw fuel is characterized by containing a large amount of hydrogen in addition to water vapor / carbon dioxide / carbon monoxide, and the oxidation characteristics under such reformed gas environment Is unknown. Furthermore, the main technical problem when applying austenitic stainless steel to a fuel reformer is that the oxide film produced by the difference in thermal expansion coefficient between the steel and the oxide film formed on the surface in the heating / cooling cycle accompanying start / stop It is in peeling. No mention is made of the effectiveness of the austenitic stainless steels of Patent Documents 1 and 2 with respect to the adhesion of the oxide film based on the oxidation characteristics in the reformed gas environment containing a large amount of hydrogen described above. In other words, the austenitic stainless steel that has both oxide film adhesion and economy, which is an index of durability under the reformed gas environment, has not yet appeared.

Japanese Patent No. 3886786 Japanese Patent No. 3886787

  The present invention has been devised to solve the above-described problems, and has durability and economy that does not impair the adhesion of the oxide film even when the heating / cooling cycle of start / stop is repeated in a reformed gas environment. The present invention provides an austenitic stainless steel sheet for a fuel reformer having both properties.

(1) In mass%, Cr: 15-25%, C: 0.1% or less, Si: 5% or less, Mn: 3% or less, P: 0.05% or less, S: 0.01% or less Ni: 8-18%, Cu: 3% or less, Mo: 3% or less, N: 0.3% or less, Nb: 0.01-0.5%, Ti: 0.01-0. 5%, V: 0.01 to 0.5%, Al: 0.01 to 0.5%, B: 0.005% or less, Mg: 0.005% or less, including one or more, An austenitic stainless steel for a fuel reformer having excellent oxide film adhesion, wherein the balance is Fe and inevitable impurities.
(2) The steel is further mass%, Sn: 0.5% or less, Sb: 0.5% or less, Co: 0.5% or less, W: 0.5% or less, Ca: 0.005 % Or less, Zr: 0.5% or less, La: 0.1% or less, Ce: 0.1%, Y: 0.1% or less, Hf: 0.1% or less, REM: 0.1% or less The austenitic stainless steel for fuel reformers having excellent oxide film adhesion as described in (1), wherein the austenitic stainless steel contains one or more.
(3) A Cr-based oxide layer containing Si or Mn is formed on the surface, and between the Cr-based oxide layer and the base material, Si oxide, Mn oxide, Nb oxide, Ti oxide, Al The austenitic stainless steel for fuel reformer having excellent adhesion of the oxide film according to (1) or (2), wherein two or more kinds of oxides are mixed.
(4) The oxide film according to (1) or (2), wherein an oxide film is formed on a stainless steel surface by heat treatment in an atmosphere containing water vapor and hydrogen in a range of 300 to 1000 ° C. For producing austenitic stainless steel for fuel reformer with excellent adhesion.

  Hereinafter, the inventions related to the steels (1), (2), and (3) are referred to as the present invention. The inventions (1) to (4) may be collectively referred to as the present invention.

  In order to solve the above-mentioned problems, the present inventors have affected Si and Mn on the adhesion of an oxide film formed on the surface of an austenitic stainless steel in a steam oxidation atmosphere containing a large amount of hydrogen assuming a reformed gas environment. In addition, the present invention was completed by intensive experiments and studies on the effects of the trace elements Nb, Ti, Al, V, B, Mg, and N. The knowledge obtained by the present invention will be described below.

(A) In a reformed gas environment where hydrogen is present, the growth and internal oxidation of the Cr-based oxide film tend to be promoted as compared with the atmosphere and a conventional steam oxidation environment. Although many of these oxidation promotion mechanisms are still unclear, it is presumed that hydrogen or water vapor promotes defect formation in the oxide film.
(B) Under the above-described reformed gas environment, Si and Mn were dissolved in the Cr-based oxide film, and new findings were obtained that contribute to the growth of the Cr-based oxide film and the suppression of internal oxidation. Furthermore, Si or Mn also concentrates immediately under the Cr-based oxide film (forms an internal oxide), thereby delaying accelerated oxidation by hydrogen or water vapor.
(C) In order to further improve the adhesion of the Cr-based oxide film, it is effective to add a small amount of Nb, Ti, or Al. The improvement in the adhesion of the Cr-based oxide film by the addition of these trace elements is due to the formation of internal oxides of Nb, Ti, and Al. From this, it was found that the adhesion of the Cr-based oxide film in the heating / cooling cycle up to 900 ° C. was improved.
(D) Furthermore, it has been found that the addition of trace elements of V, B, and Mg is also effective for improving the adhesion of the Cr-based oxide film. The addition of a small amount of V, B, and Mg improves the adhesion of the oxide film by suppressing grain boundary oxidation.

  As described above, in the reformed gas environment, the soundness of the Cr-based oxide film is enhanced by Si or Mn, and depending on the addition of rare earth elements or Ni by adding a small amount of Nb, Ti, Al, V, B, or Mg. Thus, a completely novel finding that can impart oxidation resistance and adhesion of the oxide film was obtained. The present inventions (1) to (4) have been completed based on the above-described examination results.

  Hereinafter, each requirement of the present invention will be described in detail. In addition, "%" display of the content of each element means "mass%".

  The reasons for limiting the components will be described below.

  In addition to corrosion resistance, Cr is a basic constituent element for securing the target oxidation resistance of the present invention. In the present invention, if it is less than 15%, the target basic characteristics cannot be sufficiently ensured. Therefore, the lower limit is 15%. However, excessive addition facilitates the formation of the σ phase, which is an embrittlement phase, when exposed to a high temperature atmosphere, and also makes it difficult to ensure the stability of the γ phase. Furthermore, the upper limit is set to 25% in order to reduce the alloy cost that is the target of the present invention. A preferable range is 17 to 22% from the viewpoint of basic characteristics, oxidation resistance, and cost.

  C becomes a Cr-based carbide and consumes an amount of Cr effective for the oxidation resistance targeted by the present invention. Precipitation of Cr-based carbides reduces high temperature strength and γ phase stability. Therefore, the upper limit of the C content is 0.1%. However, since the high-temperature strength and structural stability of the γ phase are reduced as the amount of C is reduced, the content is preferably 0.02% or more.

  Si is an important element in securing the oxidation resistance targeted by the present invention. It dissolves in Cr-based oxide film in a reformed gas environment and improves the soundness of Cr-based oxide film. These effects become significant from 1%. Si also delays accelerated oxidation by hydrogen or water vapor by concentrating (forming an internal oxide) just below the Cr-based oxide film. On the other hand, excessive addition causes a decrease in workability and weldability of the steel, so the upper limit is made 5%. From the viewpoint of oxidation resistance and basic characteristics, a preferable range is 2 to 4%, and a more preferable range is 2.5 to 3.5%.

  Mn is an element that is effective in enhancing the stability of the γ phase and being effective as an alternative component of Ni, as well as ensuring the oxidation resistance of the present invention. Under the reformed gas environment, it dissolves together with Si in the Cr-based oxide film, improving the soundness of the Cr-based oxide film. These effects become significant from 0.5%. On the other hand, excessive addition leads to a decrease in the corrosion resistance and oxidation resistance of the steel, so the upper limit is made 3%. From the viewpoint of oxidation resistance and basic characteristics, the preferred range is 0.5 to 2.5%, more preferably 0.8 to 1.5%. In a more preferable range of Mn, concentration (internal oxide formation) is easy even immediately below the Cr-based oxide film, and accelerated oxidation by hydrogen or water vapor is delayed. In order for one or both of Si and Mn to dissolve in the Cr-based oxide film and contribute to the growth of the Cr-based oxide film and the suppression of internal oxidation, one or both of Si and Mn in the steel is the lower limit in the above What is necessary is just the above content.

  P is an unavoidable impurity element contained in the steel, and causes a reduction in the oxidation resistance targeted by the present invention. Therefore, the upper limit is 0.05%. However, excessive reduction leads to an increase in refining costs. Therefore, the lower limit is preferably 0.01%. From the viewpoint of oxidation resistance and manufacturability, the preferred range is 0.02 to 0.03%.

  S is an unavoidable impurity element contained in the steel and lowers the target oxidation resistance of the present invention. In particular, the presence of Mn-based inclusions and solute S acts as a starting point for destroying the Cr-based oxide film when used at high temperatures for a long time. Therefore, the lower the amount of S, the better. However, excessive reduction leads to an increase in raw materials and refining costs. Therefore, the upper limit is made 0.01%. From the viewpoint of oxidation resistance and manufacturability, the preferred range is 0.0005 to 0.002%.

  Ni is an indispensable element for maintaining the γ phase. In order to maintain the structural stability and high temperature strength of the γ phase even in the heating / cooling cycle of the reformer, the lower limit is 8%. However, an excessive addition exceeding 18% causes an increase in the alloy cost targeted by the present invention and a decrease in manufacturability due to stabilization of the γ phase. From the viewpoint of basic characteristics and manufacturability / cost, the preferable range is 9 to 15%, and the more preferable range is 11 to 14%.

  Cu is an element that increases the stability of the γ phase and is effective as an alternative component of Ni, and is effective in improving corrosion resistance and high-temperature strength. However, excessive addition leads to deterioration of hot workability and weldability, so the upper limit is made 3%. From the viewpoint of basic characteristics and manufacturability, the preferred range is 0.1 to 2.5%, more preferably 0.5 to 2.0%.

  Mo is an element that is effective for remarkably enhancing the corrosion resistance and increasing the high-temperature strength like Ni and Cu. However, excessive addition leads to an increase in alloy costs and a decrease in manufacturability, so the upper limit is made 3%. From the viewpoint of basic characteristics, manufacturability and cost, the preferred range is 0.1 to 2.5%, more preferably 0.5 to 1.0%.

  N, like Ni, Cu, and Mn, is an element that is effective in enhancing the structural stability and high temperature strength of the γ phase. However, excessive addition consumes an amount of Cr effective for the target oxidation resistance of the present invention. The precipitation of Cr-based nitride decreases the high temperature strength and the stability of the γ phase. Therefore, the upper limit is made 0.3%. An excessive reduction in the amount of N inhibits manufacturability. Therefore, the lower limit is preferably 0.01%. From the viewpoint of oxidation resistance, the preferable range is 0.01 to less than 0.05%, and when the Cr amount exceeds 20%, the addition of N ensures the structural stability of the γ phase without depending on excessive Ni addition. It works effectively. Thus, when adding actively, it becomes like this. Preferably it is 0.18-0.3, and a more preferable range is more than 0.2%-0.25%.

  Nb, Ti, V, Al, B, and Mg are trace elements that are effective in enhancing the oxidation resistance under the reformed gas environment of the present invention. Concentrated directly under the Cr-based oxide film, Nb, Ti, and Al form an oxide (internal oxide) between the Cr-based oxide layer and the base material. In the cooling cycle, the adhesion of the Cr-based oxide film is improved. V, B, and Mg improve the adhesion of the oxide film by suppressing grain boundary oxidation. In order to obtain the above effects, one or more of Nb, Ti, V, Al, B, and Mg are added. When adding, Nb, Ti, V, and Al are 0.01 to 0.5%, and a preferable range is 0.05 to 0.3%. In the case of B and Mg, the content is 0.005% or less, and a preferable range is 0.0003 to 0.0015.

  Furthermore, it is preferable to contain the following elements as required.

  Sn, Sb, Co, and W are elements effective for solid solution strengthening and corrosion resistance similar to Mo, but excessive addition has an effect of inhibiting productivity by precipitation or segregation. When added, the upper limit is preferably 0.5%, and the lower limit is preferably 0.01%.

  Ca has an effect of improving hot workability and can be selectively added. When added, the upper limit is preferably 0.005%, and the lower limit is preferably 0.0001%.

  Zr, La, Ce, Y, Hf, and REM may be selectively added since they have an effect of significantly improving the adhesion of the Cr-based oxide film. When these elements are added, the internal oxide defined in the present invention may be formed of only one type. The upper limit in the case of adding is Zr: 0.5% or less, La: 0.1% or less, Ce: 0.1%, Y: 0.1% or less, Hf: 0.1% or less, REM: 0.00. 1%. Since these elements are extremely expensive, the total amount is preferably 0.01 to 0.05% from the viewpoint of cost effectiveness.

  The austenitic stainless steel for fuel reformer of the present invention contains the above components, thereby forming a Cr-based oxide layer containing Si or Mn on the surface, and between the Cr-based oxide layer and the base material. It is preferable that two or more of Si oxide, Mn oxide, Nb oxide, Ti oxide, and Al oxide are mixed. Thereby, it can be set as the austenitic stainless steel for fuel reformers excellent in the adhesiveness of an oxide film. Regarding the presence or absence of Si and Mn in the Cr-based oxide layer, 1 mass of Si and Mn is contained in an oxide film in which Cr is detected together with O by 50 mass% or more by glow discharge mass spectrometry (GDS analysis). It can be determined by whether or not more than% is detected. In addition, regarding the presence or absence of an oxide (internal oxide) between the Cr-based oxide layer and the base material, the cross section of the oxide film is subjected to FE-SEM observation and EDS elemental analysis, and Si, Mn is directly under the Cr-based oxide film. Nb, Ti, Al can be determined based on whether or not it is detected together with O.

  The steel sheet using the austenitic stainless steel of the present invention is mainly cold-rolled annealing in which hot-rolled steel strip is subjected to cold rolling after descaling without annealing or annealing, followed by finish annealing and descaling. The board is the target. In some cases, a hot-rolled annealed plate that is not subjected to cold rolling may be used. Furthermore, for gas piping, a welding rod manufactured from a steel plate is also included. The pipe is not limited to a weld rod, and may be a seamless rod manufactured by hot working. The above-described finish annealing of the steel is preferably performed at 900 to 1150 ° C. If it is less than 900 ° C., softening and recrystallization of the steel become insufficient, and predetermined material characteristics may not be obtained. On the other hand, if it exceeds 1150 ° C., it becomes coarse and may impair the toughness and ductility of the steel.

  Furthermore, the durability assumed for long-term use is a dense oxide film in which Cr, Si, and Mn are concentrated in the initial operation of the system by performing preliminary oxidation before using the austenitic stainless steel for fuel reformers. It is effective to uniformly form on the steel plate surface. By forming a dense oxide film on the surface in advance before the operation of the fuel reformer, the uniformity and barrier properties of the oxide film formed in the initial stage are improved compared to the state of the metal surface, and long-term acid resistance And the adhesion of the oxide film can be further improved. Pre-oxidation conditions are preferably 300 to 1000 ° C. and 24 hours or less. The pre-oxidation can be performed in an atmosphere containing water vapor and hydrogen.

  Examples of the present invention will be described below.

Various austenitic stainless steels whose ingredients are listed in Table 1 are melted, hot rolled, annealed pickling,
A cold-rolled annealed material having a plate thickness of 1.0 mm was manufactured through cold rolling and finish annealing.

A test piece was cut out from each austenitic stainless steel, and the cold-rolled annealed plate was subjected to an oxidation test. The oxidation test assumes an atmosphere in which the steel material is exposed in a reformed gas environment, and is an atmosphere of 26 volume% H ₂ O + 7 volume% CO ₂ + 7% volume% CO-60% H ₂ , heated to 850 ° C. and 1000 h After continuing, it was cooled to room temperature. The surface oxide film of the austenitic stainless steel plate after the oxidation test was measured for thickness and oxide concentration by glow discharge mass spectrometry (GDS analysis). In the oxide film in which Cr and O were detected by 50% by mass or more together with O by GDS analysis, it was determined that 1% by mass or more of Si or Mn was detected as being dissolved in the Cr-based oxide film. “◯” was entered in the “Si” and “Mn” columns of “Cr-based oxide film”. Otherwise, it was “−”. Also, FE-SEM observation and EDS elemental analysis were performed on the cross section of the oxide film prepared with a cross-section polisher. It was determined that there was an oxide (internal oxide) between the oxide layer and the base material, “◯” was displayed in the “Internal oxide” column of Table 2, and the detected element was entered.

Furthermore, the adhesion of the surface oxide film produced in the modified gas environment was evaluated by repeated oxidation tests in the air. The heating temperature was 800 ° C., 850 ° C., and 900 ° C., and one cycle was heated for 25 minutes and air-cooled for 5 minutes until 400 cycles. The appearance of the surface was observed and the change in weight was measured. From the appearance observation, the oxide film was peeled off and the weight change was poor, and the adhesion evaluation was “x”. The oxide film was not peeled off and the weight change was plus 3 mg / cm ² or less. The evaluation was “◯”. For the adhesion of the oxide film targeted by the present invention, an evaluation at a heating temperature of 850 ° C. or higher is “◯”.

The obtained results are shown in Table 2. No. 1 to 9 have the components specified in the present invention, produce a sound Cr-based oxide film by an oxidation test assuming a reformed gas environment, and satisfy the adhesion of the oxide film targeted by the present invention It is. Furthermore, no. 3 to 5 are cases where trace elements were added with respect to the more preferable amounts of Si and Mn, and the adhesion of the Cr-based oxide film was good even at a heating temperature of 900 ° C. No. 8 shows the case where a rare earth element was added, although the formation of the internal oxide was one, and it had good Cr-based oxide film adhesion even at a heating temperature of 900 ° C. No. No. 9 No. 1 and the same steel were pre-oxidized in 25% H ₂ O-8% CO ₂ -8% CO-59% H ₂ at 600 ° C. for 100 h to improve the adhesion of the Cr-based oxide film. The evaluation was “◯” even at a temperature of 900 ° C.

  Steel No. Nos. 10 to 12 are not included in the steel components defined in the present invention, and do not include trace elements that are features of the present invention. These steels had an adhesion evaluation of “x” at a heating temperature of 850 ° C. or higher.

  According to the present invention, in the reformed gas environment, the soundness of the Cr-based oxide film is enhanced by Si and Mn, and further, by adding a small amount of Nb, Ti, Al, V, B, and Mg, An austenitic stainless steel for fuel reformers that combines durability and economy without adding a large amount of rare earth elements or Ni without losing the adhesion of the oxide film even after repeated heating and cooling cycles of start and stop Can be provided. The austenitic stainless steel of the present invention can be industrially produced regardless of a special production method.

(1) In mass%, Cr: 15 to 22 %, C: 0.1% or less, Si: 0.4 to 5%, Mn: 0.8 to 1.5 %, P: 0.05% or less , S: 0.01% or less, Ni: 8 to 18%, Cu: 2.0 % or less, Mo; 3% or less, N: 0.3% or less, and V: 0.01 to 0.5 An austenitic stainless steel for a fuel reformer excellent in adhesion of an oxide film, wherein the balance is made of Fe and inevitable impurities.
(2) The steel is further in mass%, Nb: 0.01 to 0.5%, Ti: 0.01 to 0.5%, Al: 0.01 to 0.5%, 1 type or 2 Containing more than seeds, and in mass%, Sn: 0.5% or less, Sb: 0.5% or less, Co: 0.5% or less, W: 0.5% or less , Zr: 0.5% or less La: 0.1% or less, Ce: 0.1%, Y: 0.1% or less, Hf: 0.1% or less, REM: 0.1% or less, and the balance is one or more. The austenitic stainless steel for fuel reformer having excellent oxide film adhesion as described in (1), characterized by comprising Fe and inevitable impurities .
(3) For the fuel reformer with excellent adhesion of the oxide film according to (1) or (2), wherein the steel further contains Ca: 0.005% or less by mass%. Austenitic stainless steel.
(4) (1) to (3) characterized in that the steel further contains one or two of B: 0.005% or less and Mg: 0.005% or less in terms of mass%. Austenitic stainless steel for fuel reformer excellent in the adhesion of the oxide film described in any one of the above.
(5) A Cr-based oxide layer containing Si or Mn is formed on the surface of the austenitic stainless steel for a fuel reformer according to any one of (1) to (4), and the Cr-based oxidation between the object layer and the base material, Si oxide, Mn oxide, Nb oxide, Ti oxide, two or more of Al oxide has excellent adhesion to the oxide film you characterized by mixed Austenitic stainless steel for fuel reformers.
(6) In an atmosphere containing water vapor and hydrogen, an oxide film is formed on the surface of the stainless steel by heat treatment in the range of 300 to 1000 ° C. The adhesion of the oxide film according to ( 5 ) An excellent method for producing austenitic stainless steel for fuel reformers.

Hereinafter, the inventions related to the steels (1), (2), (3) , (4), and (5) are referred to as the present invention. The inventions (1) to ( 6 ) may be collectively referred to as the present invention.

Claims (4)

  In mass%, Cr: 15-25%, C: 0.1% or less, Si: 5% or less, Mn: 3% or less, P: 0.05% or less, S: 0.01% or less, Ni: 8-18%, Cu: 3% or less, Mo; 3% or less, N: 0.3% or less, Nb: 0.01-0.5%, Ti: 0.01-0.5%, V: 0.01 to 0.5%, Al: 0.01 to 0.5%, B: 0.005% or less, Mg: 0.005% or less, including one or more, the balance being Fe And an austenitic stainless steel for a fuel reformer excellent in adhesion of an oxide film, characterized by comprising inevitable impurities.   The steel is further in mass%, Sn: 0.5% or less, Sb: 0.5% or less, Co: 0.5% or less, W: 0.5% or less, Ca: 0.005% or less, One of Zr: 0.5% or less, La: 0.1% or less, Ce: 0.1%, Y: 0.1% or less, Hf: 0.1% or less, REM: 0.1% or less The austenitic stainless steel for a fuel reformer excellent in the adhesion of the oxide film according to claim 1, wherein two or more types are contained.   A Cr-based oxide layer containing Si or Mn is formed on the surface, and Si oxide, Mn oxide, Nb oxide, Ti oxide, Al oxide are formed between the Cr-based oxide layer and the base material. The austenitic stainless steel for a fuel reformer having excellent oxide film adhesion according to claim 1 or 2, wherein two or more kinds are mixed.   The oxide film according to claim 1 or 2, wherein an oxide film is formed on the stainless steel surface by heat treatment in a range of 300 to 1000 ° C in an atmosphere containing water vapor and hydrogen. A method for producing austenitic stainless steel for fuel reformers.