WO2015064739A1 - 燃料改質器用フェライト系ステンレス鋼およびその製造方法 - Google Patents
燃料改質器用フェライト系ステンレス鋼およびその製造方法 Download PDFInfo
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
- C23C8/16—Oxidising using oxygen-containing compounds, e.g. water, carbon dioxide
- C23C8/18—Oxidising of ferrous surfaces
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
- H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
- H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
- H01M8/0618—Reforming processes, e.g. autothermal, partial oxidation or steam reforming
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- 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 a ferritic stainless steel and a method for producing the same.
- fuel cell which has high practical value as a distributed power source and a power source for automobiles, is attracting attention.
- fuel cells 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.
- PEFC polymer electrolyte fuel cells
- SOFC solid oxide fuel cells
- 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.
- hydrocarbon fuels such as city gas (LNG), methane, natural gas, propane, kerosene, and gasoline in the presence of a catalyst.
- the fuel reformer is usually operated at a high temperature of 200 to 900 ° C. 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.
- austenitic stainless steel represented by SUS310S 25Cr-20Ni
- 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.
- Patent Document 1 Cr: 8 to 35%, C: 0.03% or less, N: 0.03% or less, Mn: 1.5% or less, Si: 0.8 to 2.5%, and / or Al: 0.6 to 6.0%, Nb: 0.05 to 0.80%, Ti: 0.03 to 0.50%, Mo: 0.1 to 4%, Cu: 0.1
- a ferritic stainless steel for a petroleum fuel reformer is disclosed that contains one or more of ⁇ 4% and has a composition in which the total amount of Si and Al is adjusted to 1.5% or more. These stainless steels are characterized by a small increase in oxidation during heating / cooling to 900 ° C. in an atmosphere of 50% by volume H 2 O + 20% by volume CO 2 .
- Patent Document 2 Cr: 12 to 20%, C: 0.03% or less, N: 0.03% or less, Si: 0.1 to 1.5%, Mn: 0.95 to 1.5% Carbonization including Al: 1.5% or less, Nb: 0.10 to 0.80%, Mo: 0.1 to 4%, Cu: 0.1 to 4% Ferritic stainless steel for hydrogen fuel reformers is disclosed. These stainless steels are characterized in that the increase in oxidation after heating and cooling to 700 ° C. 500 times in an atmosphere of 50 vol% H 2 O + 20 vol% CO 2 is 2.0 mg / cm 2 or less.
- Patent Document 3 Cr: 8 to 25%, C: 0.03% or less, N: 0.03% or less, Si: 0.1 to 2.5%, Mn: 1.5% or less, Al: Including 0.1 to 4%, Nb: 0.05 to 0.80%, Ti: 0.03 to 0.5%, Mo: 0.1 to 4%, Cu: 0.1 to 4% Ferritic stainless steel for alcohol-based fuel reformers containing one or more types is disclosed. These stainless steels are characterized in that the increase in oxidation after repeated heating and cooling to 600 ° C. 500 times in an atmosphere of 50 vol% H 2 O + 20 vol% CO 2 is 2.0 mg / cm 2 or less.
- Patent Document 4 Cr: 11 to 22%, C: 0.03% or less, N: 0.03% or less, Si: 2% or less, Mn: 1.5% or less, Al: 1 to 6%
- a ferritic stainless steel suitable for a power generation system satisfying Cr + 5Si + 6Al ⁇ 30 is disclosed. These stainless steels are characterized by good oxidation resistance in a 50 volume% H 2 O atmosphere (remaining air).
- Patent Document 5 Cr: 11 to 21%, C: 0.03% or less, N: 0.03% or less, Si: 3% or less, Mn: 1.0% or less, Al: 6% or less, Cu : 0.01 to 0.5%, Mo: 0.01 to 0.5%, Nb: 0.1% or less, Ti: 0.005 to 0.5%, Sn: 0.001 to 0.1% , O: 0.002% or less, H: 0.00005% or less, and Pb: 0.01% or less, a ferritic stainless steel suitable for a high-temperature reformer for a fuel cell is disclosed. These stainless steels are characterized by good oxidation resistance in a 10% by volume H 2 O atmosphere (remaining air).
- Patent Documents 1 to 3 are directed to improving the oxidation resistance in an environment of 50% by volume H 2 O + 20% by volume CO 2 , adding 2.5% or less of Si and 0.01% or more of Al.
- the technical idea is to promote the formation of an oxide film mainly composed of Cr-based oxides by addition and to strengthen the oxide film by solid solution of Y, REM, Ca, and Al in Cr-based oxides.
- Patent Documents 4 and 5 aim to improve oxidation resistance in an environment containing 10 to 50% by volume H 2 O (remaining air), the former being 1% or more Al-containing ferritic stainless steel, and the latter being substantially Is limited to 18Cr-1.9 to 3.3Al ferritic stainless steel containing 0.5% or less of Si.
- the reformed gas of the fuel cell uses the above-mentioned city gas as a raw fuel, and is characterized by containing a large amount of hydrogen in addition to water vapor / carbon dioxide / carbon monoxide.
- an oxide film mainly composed of a Cr-based oxide as compared with the atmosphere or a conventional high-temperature steam environment. (Hereinafter also referred to as “Cr-based oxide film”) is difficult to form, and oxidation of the internal steel structure, internal oxidation as a so-called FeCr-based oxide, and abnormal oxidation that is rapid growth of the Fe-based oxide It tends to be encouraged.
- Patent Document 6 discloses a ferritic stainless steel sheet for a separator for a solid oxide fuel cell that can form an oxide film by heat treatment before use or heat during operation of the solid oxide fuel cell.
- the heat treatment is not performed in a reformed gas environment in which a large amount of water vapor and hydrogen coexist, and it is unclear how much the oxide film is promoted in the reformed gas environment of the fuel cell.
- Patent Document 7 discloses a ferritic stainless steel having an oxide layer formed by ion bombardment mainly composed of Cr on the surface and excellent in oxidation resistance used in a high temperature environment of 400 ° C. or higher. .
- Patent Document 8 discloses a heat transfer material based on a ferritic stainless steel, which is used for collecting heat from a high-temperature gas in a steam environment of 800 ° C. level.
- Patent Document 9 discloses a high-temperature corrosion resistance, no significant carburization even when exposed to corrosive gas at high temperature, and substantially no oxide film peeling under a heating / cooling cycle.
- An alloy is disclosed.
- Patent Documents 1 to 9 have an effect of suppressing internal oxidation in a high temperature atmosphere in which a large amount of water vapor and hydrogen coexist.
- the reformed gas contains a large amount of water vapor and hydrogen, and hydrogen is considered to be a factor that promotes internal oxidation.
- Patent Documents 1 to 9 do not focus on the problem of promotion of internal oxidation of stainless steel by hydrogen in the reformed gas, and oxidation resistance in a high-temperature atmosphere in which a large amount of hydrogen is present in addition to a large amount of water vapor. Sex has not been fully studied.
- the present invention provides a ferritic stainless steel sheet for a fuel reformer that is excellent in durability of a Cr-based oxide film and is economical without causing abnormal oxidation in a reformed gas environment in which a large amount of water vapor and hydrogen coexist. It is to provide.
- Si and Mn are concentrated by forming an oxide directly under the Cr-based oxide film, delaying the progress of internal oxidation by hydrogen and water vapor, and accompanying the formation of an oxide film mainly composed of Fe-based oxide Suppresses abnormal oxidation. Due to such effects, the durability of the Cr-based oxide film can be enhanced.
- Nb is concentrated by forming an oxide immediately below the Cr-based oxide film, thereby suppressing internal oxidation and grain boundary oxidation, thereby improving the durability of the Cr-based oxide film.
- a ferritic stainless steel for a fuel reformer comprising any of the above, the balance being composed of Fe and inevitable impurities, and having a composition satisfying the formula (i).
- the element symbol in a formula means the content mass% in the steel of the said element.
- the surface of the ferritic stainless steel of the present invention is mainly composed of a Cr-based oxide by exposing it to an atmosphere of a reformed gas environment containing a large amount of hydrogen in addition to water vapor / carbon dioxide / carbon monoxide.
- a Cr-based oxide film is formed, and the Cr-based oxide contains at least one element of Si and Mn in an amount of 0.5% by mass or more.
- the “Cr-based oxide” is an oxide in which Cr is detected together with O and 50 mass% or more is detected by glow discharge mass spectrometry (GDS analysis). “Mainly” means that the ratio of the volume of the Cr-based oxide in the entire oxide film to the volume of the entire oxide film is 50% or more.
- the Cr-based oxide film of the ferritic stainless steel of the present invention may contain MnCr 2 O 4 , SiO 2 , Al 2 O 3 and the like in addition to the Cr-based oxide.
- Mn is less than 0.95%.
- the stainless steel is further, in mass%, Ni: 1% or less, Cu: 1% or less, Mo: 2% or less, Sn: 1% or less, W: 1% or less, Co: 0.5%
- V 0.5% or less
- Ti 0.3% or less
- B 0.005% or less
- Ca 0.005% or less
- Mg 0.005% or less
- Zr 0.5% or less
- the stainless steel having the composition according to any one of (1) to (5) is 300% in an atmosphere containing 10 to 50% by volume of water and 10 to 70% by volume of hydrogen. By performing heat treatment in the range of ⁇ 1000 ° C., an oxide containing 0.5% by mass or more of at least one of Si and Mn and 50% by mass or more of Cr occupies the surface of the stainless steel material.
- the surface contains either 0.5% by mass or more of any element of Si and Mn, and the content of both Cr and O is 50
- the element symbol in a formula means the content mass% in the steel of the said element.
- Ni 1% or less
- Cu 1% or less
- Mo 2% or less
- Sn 1% or less
- W 1% or less
- Co 0.5% or less
- V 0 0.5% or less
- Ti 0.3% or less
- B 0.005% or less
- Ca 0.005% or less
- Mg 0.005% or less
- Zr 0.5% or less
- La 0.1 % Or less
- Y 0.1% or less
- Hf 0.1% or less
- REM 0.1% or less
- a ferritic stainless steel for a fuel reformer according to any one of the above.
- the inventions related to the steels (1) to (13) are referred to as the present invention.
- the inventions (1) to (13) may be collectively referred to as the present invention.
- Invention Example No. 2 in Table 2 3 is a result of GDS analysis of the composition of an oxide film after an oxidation test for 1000 hours at 850 ° C. assuming a reformed gas environment, and is a diagram showing each element profile in the depth direction.
- Invention Example No. 2 in Table 2 1 to 14 and Comparative Example No. For 19, 20, 22, 23, 25, 27, 30, 35, and 36, the effect on the evaluation at the heating temperature of 900 ° C. of the atmospheric repeated oxidation test is assumed assuming the formula (i) and the reformed gas environment of the present invention. It is the figure which showed the influence of the higher value of Si and Mn contained in Cr type oxide in the Cr type oxide film after a test.
- the oxide film mainly composed of a Cr-based oxide containing Si and Mn as described above uses a ferritic stainless steel having a component defined in the present invention described in (I) below, and a fuel described in (III) below. It is formed on the surface of stainless steel in the reforming gas environment of the reformer. Some component systems of the present invention are formed on the surface of stainless steel in the reformed gas environment of the fuel reformer after performing the predetermined pre-oxidation described in (IV) below.
- Cr is a basic constituent element for the Cr-based oxide film to have target durability in addition to corrosion resistance.
- the target oxidation resistance is not sufficiently ensured. Therefore, the lower limit is 12%.
- excessive addition when exposed to a high temperature atmosphere, promotes the formation of the ⁇ phase, which is an embrittlement phase, and increases the alloy cost.
- the upper limit is 24% from the viewpoint of basic characteristics and alloy costs. From the viewpoint of basic characteristics, oxidation resistance and cost, the preferred range is 14.5 to 22.5%. A more preferable range is 17.5 to 20%.
- C inhibits the target oxidation resistance of the present invention by forming a solid solution or Cr carbide in the ferrite phase. For this reason, the smaller the amount of C, the better.
- the upper limit is made 0.03%. However, excessive reduction leads to an increase in refining costs, so the lower limit is preferably 0.001%. From the viewpoint of oxidation resistance and manufacturability, the preferred range is 0.002 to 0.02%.
- Mn improves the durability of the film by dissolving in a Cr-based oxide together with Si in a reformed gas environment. These effects are obtained from more than 0.1%. On the other hand, excessive addition leads to a decrease in corrosion resistance and oxidation resistance of the steel, so the upper limit is made 2%. From the viewpoint of oxidation resistance and basic characteristics, the preferred range is 0.2 to 1.5%. In a preferable range of Mn, Mn is concentrated by forming an oxide directly under the Cr-based oxide film, and the progress of internal oxidation by hydrogen or water vapor is delayed.
- the Mn content in the Cr-based oxide is set to 0.00 when used in the reformed gas environment of the fuel reformer described in (III) below. It can be 5 mass% or more. However, even if the Mn content in the steel is more than 0.1%, the following (III) explains that the Si content described later is 2.5% or less and the Al content is more than 0.5%. There is a possibility that the Mn content in the Cr-based oxide cannot be made 0.5 mass% or more only by using it in the reformed gas environment of the fuel reformer.
- the Cr-based oxide is stably formed in the reformed gas environment of the subsequent fuel reformer.
- the Mn content in the medium can be 0.5% by mass or more.
- the oxide film formed on the surface is (Cr, Mn) -based only when used in the reformed gas environment of the fuel reformer described in (III) below.
- the oxide is mainly used and the Cr-based oxide of the present invention is not formed. Therefore, the Mn content is preferably less than 0.95%. Therefore, in order to actively utilize the effects of Si and Mn, the upper limit is more preferably less than 0.95%, and an even more preferable range is 0.2% to 0.8%.
- the fuel reformer can stably operate in the reformed gas environment of the subsequent fuel reformer.
- a Cr-based oxide is formed on the surface of the stainless steel.
- the upper limit is made 0.05%.
- the lower limit is preferably 0.003%. From the viewpoint of manufacturability and weldability, the preferred range is 0.005 to 0.04%, more preferably 0.01 to 0.03%.
- the oxidation resistance targeted by the present invention is an inevitable impurity element contained in the steel, and lowers the oxidation resistance targeted by the present invention.
- the presence of Mn-based inclusions and solute S acts as a starting point for destroying the Cr-based oxide film when used at a high temperature for a long time. Therefore, the lower the amount of S, the better. Therefore, the upper limit is made 0.01%.
- the lower limit is made 0.0001%. From the viewpoint of manufacturability and oxidation resistance, the preferred range is 0.0001 to 0.002%, more preferably 0.0002 to 0.001%.
- N like C, inhibits the target oxidation resistance of the present invention. For this reason, the smaller the amount of N, the better.
- the upper limit is made 0.03%. However, excessive reduction leads to an increase in refining costs, so the lower limit is preferably 0.002%. From the viewpoint of oxidation resistance and manufacturability, the preferred range is 0.005 to 0.02%.
- Nb is enriched by forming an oxide directly under the Cr-based oxide film, in addition to improving oxidation resistance through high purity of steel by the action of a stabilizing element that fixes C and N, By suppressing the progress of internal oxidation and grain boundary oxidation under a reformed gas environment, it has the effect of enhancing the durability of the Cr-based oxide film targeted by the present invention.
- These Nb addition effects can be obtained from 0.01% or more.
- excessive addition leads to a decrease in manufacturability accompanying an increase in alloy costs and a recrystallization temperature, so the upper limit is made 1%.
- a preferable range is 0.1 to 0.6%, and a more preferable range is 0.2 to 0.4%.
- Si is an important element in securing the oxidation resistance targeted by the present invention. It dissolves in Cr-based oxides in a reformed gas environment and enhances the durability of Cr-based oxide films. These effects are obtained from 0.3% and become prominent over 2.5%. On the other hand, excessive addition causes deterioration of workability and weldability of steel, so the upper limit is made 4%. From the viewpoint of oxidation resistance and basic characteristics, the preferred range is 0.4 to 3.5%. Within a preferable range of Si, Si is concentrated by forming an oxide immediately below the Cr-based oxide film, and the progress of internal oxidation by hydrogen or water vapor is delayed.
- the Si in the steel is 0.3% or more and the Mn is 0.00. It is preferable that the content satisfies at least one of more than 1%. Further, in order to actively utilize the effects of Si and Mn, the lower limit of Si is more preferably more than 2.50%, and still more preferably the range is more than 2.50% to 3.5%. .
- the Si content in the Cr-based oxide is 0.5 mass when used in the reformed gas environment of the fuel reformer described in (III) below. % Or more. If the Si content is 0.3% or more and the following Al content is 0.5% or less, Cr-based oxidation will occur when used in the reformed gas environment of the fuel reformer described in (III) below. Si content in a thing can be 0.5 mass% or more. When the Si content is 0.3% or more and the Al content is more than 0.5%, the Cr-based oxide is only used in the reformed gas environment of the fuel reformer described in (III) below. There is a possibility that the Si content in it cannot be made 0.5 mass% or more.
- the steel components can be used stably in the reformed gas environment of the fuel reformer described in (III) below.
- Si content in Cr type oxide film can be 0.5 mass% or more.
- Al is an effective element that improves deoxidation and oxidation resistance, and is preferably contained in an amount of 0.001% or more.
- the upper limit is made 4%.
- the upper limit is preferably 2%.
- the addition of a large amount of Al leads to the deterioration of the durability of the Cr-based oxide film targeted by the present invention by promoting the progress of internal oxidation and grain boundary oxidation in the reformed gas environment.
- the upper limit is more preferably 0.5%. From the viewpoint of oxidation resistance and deacidification, a more preferable range is 0.002 to 0.2%, and an even more preferable range is 0.01 to 0.08%.
- the value of the formula (i) is preferably 25 or more, and more preferably 30 or more.
- the upper limit of the value of the formula (i) is not particularly specified, but is preferably set to 40 in consideration of the influence on the manufacturability of steel by the addition of Cr and Si.
- the coefficient concerning each element of the formula (i) uses steel materials containing various components, the effect of modified Si containing a large amount of water vapor and hydrogen is five times that of Cr, and the effect of contained Nb is Cr This is because the effect of the contained Mn was found to be equivalent to that of Cr.
- the ferritic stainless steel of the present invention satisfies the conditions of Mn: less than 0.95%, Si: more than 2.50% and / or Al: 0.5% or less, as described in the above section of Mn and Si. , It is not necessary to perform the predetermined pre-oxidation described in (IV) below, and when used in the reformed gas environment of the fuel reformer described in (III) below, Si and / Or since Mn content can be 0.5 mass% or more, it is preferable.
- the ferritic stainless steel of the present invention may further comprise Ni: 1% or less, Cu: 1% or less, Mo: 2% or less, Sn: 1% or less, W: 1% or less, Co: 0 as required. 0.5% or less, V: 0.5% or less, Ti: 0.3% or less, B: 0.005% or less, Ca: 0.005% or less, Mg: 0.005% or less, Zr: 0.5 % Or less, La: 0.1% or less, Y: 0.1% or less, Hf: 0.1% or less, REM: 0.1% or less. Also good.
- Ni, Cu, Mo, Sn, W, and Co are effective elements for increasing the oxidation resistance and high-temperature strength in the reformed gas environment, and are added as necessary.
- the upper limit of Ni, Cu, Sn and W is 1%.
- Mo is an element that reduces the thermal expansion coefficient of the ferritic stainless steel of the present invention and is also effective in suppressing high-temperature deformation
- the upper limit of the amount of Mo added is 2%, more preferably 0.5. %.
- the lower limit of the more preferable content of any element is 0.1%.
- V, B, and Mg are elements that promote the effect of improving oxidation resistance due to the addition of Nb, and are added as necessary.
- the upper limit of V is 0.5% and the upper limits of B and Mg are 0.005%.
- the lower limit of the more preferable content of V is 0.05%, and the more preferable lower limit of B and Mg is 0.0002%.
- the element symbol in a formula means the content mass% in the steel of the said element.
- Ti is an element that improves oxidation resistance through the purification of steel by the action of a stabilizing element that fixes C and N, and is added as necessary.
- a stabilizing element that fixes C and N, and is added as necessary.
- excessive addition leads to the progress of internal oxidation and grain boundary oxidation under the reformed gas environment and leads to the deterioration of the durability of the Cr-based oxide film targeted by the present invention. It is limited to 0.3% or less. From the viewpoint of oxidation resistance, the lower limit of the preferable content is 0.01%.
- Ca is an element that improves hot workability and secondary workability, and is added as necessary. However, since excessive addition leads to the inhibition of manufacturability, the upper limit is made 0.005%. A preferred lower limit is 0.0001%.
- Zr, La, Y, Hf, and REM are effective elements for improving hot workability and steel cleanliness and improving oxidation resistance of the present invention. Also good. However, from the technical idea of the present invention and the reduction of the alloy cost, it does not depend on the effect of adding these elements.
- the upper limit of Zr is 0.5%, and the upper limits of La, Y, Hf, and REM are each 0.1%.
- a more preferable lower limit of Zr is 0.01%, and a preferable lower limit of La, Y, Hf, and REM is 0.001%.
- REM is an element belonging to atomic numbers 57 to 71, such as Ce, Pr, and Nd.
- the steel sheet using the ferritic stainless steel of the present invention is mainly cold-rolled annealing in which a hot-rolled steel strip is cold-rolled after descaling without annealing or annealing, followed by finish annealing and descaling.
- the board is the target.
- a hot-rolled annealed plate that is not subjected to cold rolling may be used.
- 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 700 to 1100 ° C.
- the temperature is lower than 700 ° C., softening and recrystallization of the steel become insufficient, and predetermined material characteristics may not be obtained. On the other hand, if it exceeds 1100 ° C., it becomes coarse and may impair the toughness and ductility of the steel.
- the oxide film mainly comprising a Cr-based oxide containing 0.5% by mass or more of Si and / or Mn on the surface of the ferritic stainless steel of the present invention is a ferritic stainless steel having the above-mentioned composition defined in the present invention. Is formed on the surface of the stainless steel by exposing it to the reformed gas environment of the fuel reformer.
- the reformed gas environment means an environment exposed to a high temperature of 200 to 900 ° C. in an atmosphere containing a large amount of water vapor, hydrogen, carbon dioxide, carbon monoxide and the like.
- Some of the steel components of the present invention described above are mainly composed of a Cr-based oxide containing 0.5 mass% or more of Si and / or Mn on the surface of the stainless steel in the reformed gas environment of the fuel reformer.
- a dense oxide film enriched with Cr, Si and Mn is formed on the surface of the steel sheet. It is effective to form it uniformly.
- 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.
- the pre-oxidation atmosphere is an atmosphere containing water vapor and hydrogen, and the pre-oxidation temperature is 300 to 1000 ° C. Under such conditions, it is possible to form a highly durable oxide film by dissolving Si or Mn in the Cr-based oxide and concentrating it directly under the film.
- the lower limit is 300 ° C., preferably 400 ° C.
- the pre-oxidation temperature is high, the oxide film contains a large amount of Fe and lowers the durability, so the upper limit is 1000 ° C., preferably less than 850 ° C.
- the upper limit of the pre-oxidation time is not particularly specified but is preferably 200 hours or less. Furthermore, in order to form a Cr-based oxide film having high durability even in a short time of 100 hours or less, it is preferable that the water vapor and hydrogen in the pre-oxidation atmosphere be 10% by volume or more, respectively. When the water vapor is less than 10% by volume, the oxidation property is low and the growth of the oxide film is slow, so the lower limit of the pre-oxidation time is preferably set to more than 100 hours. When hydrogen is less than 10% by volume, since the solid solution of Si or Mn in the Cr-based oxide tends not to proceed, it is preferable to set the lower limit of the pre-oxidation time to more than 100 hours.
- the upper limit of water vapor and hydrogen is not particularly specified, but the upper limit of water vapor is preferably 50% by volume and the upper limit of hydrogen is preferably 70% by volume.
- the pre-oxidation atmosphere may contain other gases such as nitrogen, carbon dioxide, carbon monoxide, and hydrocarbon gases.
- gases such as nitrogen, carbon dioxide, carbon monoxide, and hydrocarbon gases.
- the range of other gases is not particularly specified, but the upper limit is preferably 30% by volume.
- the total of hydrogen and carbon monoxide, which is a reducing gas is 50% by volume or more, the oxidation is low and the growth of the oxide film is slow, so the total amount of water vapor and carbon dioxide which are oxidizing gases is 20 volumes. % Or more, and more preferably more than 32% by volume.
- the thickness of the Cr-based oxide film obtained by the preliminary oxidation is preferably set to 0.01 ⁇ m or more in order to maintain durability in a high temperature reformed gas environment.
- the upper limit of the film thickness is not particularly specified, but is preferably 5 ⁇ m in consideration of the pre-oxidation efficiency.
- the ratio of the volume or thickness of the Cr-based oxide in the oxide film obtained by pre-oxidation is 50% or more, and MnCr 2 O 4 , SiO 2 , Al 2 O exhibiting durability in the modified gas environment. 3 etc. may be included.
- the ferritic stainless steel for fuel reformer of the present invention forms an oxide film mainly composed of Cr-based oxide containing Si and / or Mn on the surface, and Si, Mn is formed between the oxide film and the base material. , Nb is preferably concentrated. As a result, a Cr-based oxide film having excellent durability can be formed.
- the presence of Si and Mn in the Cr-based oxide is detected by glow discharge mass spectrometry (GDS analysis) in the oxide in which Cr is detected together with O, and Cr is detected by 50 mass% or more. It can be determined by whether or not Mn is detected by 0.5 mass% or more.
- Concentration of Si, Mn, and Nb between the Cr-based oxide film and the base material is performed by FE-SEM observation and EDS elemental analysis of the cross section of the oxide film, and Si, Mn, Nb immediately below the Cr-based oxide film. Can be determined based on whether or not is detected higher than the base material concentration.
- the pre-oxidation may be performed before the fuel reformer is operated, and may be performed before the ferritic stainless steel having the composition of the present invention described above is formed into a component of the fuel reformer. Alternatively, the pre-oxidation may be performed after the ferritic stainless steel having the above-described composition of the present invention is formed into the component parts of the fuel reformer.
- the preliminary oxidation is not limited to one time but may be performed a plurality of times. Alternatively, preliminary oxidation for less than 100 hours may be performed a plurality of times, and preliminary oxidation may be performed so that the total preliminary oxidation time exceeds 100 hours. Alternatively, a plurality of preliminary oxidations may be performed under the same or different conditions until an oxide film mainly composed of Cr-based oxide containing 0.5 mass% or more of Si and / or Mn is formed on the surface of ferritic stainless steel. You may go round.
- the reformed gas is applied to the ferritic stainless steel of the present invention for the purpose of evaluating the Cr-based oxide film formed on the ferritic stainless steel surface.
- Heat treatment simulating the environment may be performed.
- the simulated heat treatment for evaluating the surface structure of the ferritic stainless steel of the present invention for example, the following heat treatment can be exemplified. Needless to say, the simulated heat treatment applicable to the ferritic stainless steel of the present invention is not limited to these simulated heat treatment conditions.
- an oxide film mainly composed of a Cr-based oxide containing 0.5% by mass or more of Si and / or Mn can be formed on the surface of stainless steel.
- ferritic stainless steel having the component composition defined in the present invention is subjected to a treatment that simulates preliminary oxidation, and then before the fuel reformer is used in the reformed gas environment, You may evaluate that the said ferritic stainless steel is stainless steel which has the Cr type oxide film of this invention by performing the heat processing which simulated the reformed gas environment.
- the ferritic stainless steel subjected to the above-described simulated heat treatment is further, in mass%, Ni: 1% or less, Cu: 1% or less, Mo: 2% or less, Sn: 1% or less, W: 1% or less.
- composition of the atmosphere of the above-mentioned simulated reformed gas environment may cause an error of about ⁇ 3% by volume, but this error is allowed because the evaluation of the oxide film is not so changed.
- a test piece was cut out from each ferritic 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, is an atmosphere of 26 volume% H 2 O + 7 volume% CO 2 + 7% volume% CO + 60 volume% H 2 , is heated to 850 ° C., and 850 After holding at 1000C for 1000 hours, it was cooled to room temperature.
- the composition of the surface oxide film produced in the modified gas environment was evaluated by the GDS analysis method.
- Si and Mn in the Cr-based oxide in which Cr was detected with O in an amount of 50% by mass or more were set to the values of Si and Mn at the same depth position as the depth position where Cr had the highest concentration.
- the durability of the surface oxide film produced in the modified gas environment was evaluated by repeated oxidation tests in the atmosphere.
- the temperature corresponding to the start and stop of the fuel reformer is increased or decreased, and the temperature of the fuel reformer is increased or decreased to examine the destruction of the oxide film and the accompanying abnormal oxidation.
- the post-oxidation test piece of the above reformed gas environment not subjected to GDS analysis is used as a test material, heating temperatures are 800 ° C., 900 ° C., 1000 ° C., and one cycle is heated for 25 minutes and air cooled for up to 400 cycles.
- the durability of the Cr-based oxide film targeted by the present invention is “ ⁇ ” at a heating temperature of 900 ° C. or higher.
- the oxidation test of the reformed gas environment as described above the GDS analysis of the surface oxide film generated in the environmental reformed gas environment, A repeated oxidation test was conducted in the air after the oxidation test of the reformed gas environment.
- % in the atmosphere display of the preliminary oxidation test shown in Table 2 means volume%.
- the pre-oxidation atmospheres a to e shown in Table 2 define a gas environment having the following composition.
- Atmosphere a 20% H 2 O-15% CO 2 -5% CO-30% H 2 -30% N 2 Atmosphere b: 25% H 2 O-8% CO 2 -8% CO-59% H 2 Atmosphere c: 16% H 2 O-43% H 2 -41% N 2 Atmosphere d: 3% H 2 O-9% CO 2 -16% CO-32% H 2 -40% N 2 Atmosphere e: 24% H 2 O-19% CO 2 -5% H 2 -52% N 2 In addition, a test piece with any of asterisks “*”, “**”, and “***” in the “steel” column of Table 2 indicates that a pre-oxidation treatment has been performed.
- the (Fe, Cr) -based film means that Fe and Cr are detected together with O by GDS analysis, Fe is 10 mass% or more, Cr is 10 mass% or more, and the total of Fe and Cr is 50
- the (Cr, Mn) -based film detects Cr and Mn together with O by GDS analysis, and Cr is 10
- the film is detected by GDS analysis with Fe, Cr and Mn together with O, Fe is 5 mass% or more, Cr is 5 mass% or more, Mn is 5 mass% or more, and the total of Fe, Cr and Mn is 50 mass % Or more detected (Fe, Cr, Mn) It means an oxide film mainly composed of product.
- No. Nos. 1 to 8 are components of each element specified in the present invention and steels A to H satisfying the formula (i), and after an oxidation test assuming a reformed gas environment, Si and / or Mn is 0.5 mass% or more.
- a highly durable Cr-based oxide film mainly composed of a Cr-based oxide is produced, and both are evaluated as “ ⁇ ” at the heating temperatures of 800 ° C. and 900 ° C. in the repeated atmospheric oxidation test.
- No. The result of 3 is shown in FIG.
- No. Nos. 4, 6, and 8 are those in which the value of the formula (i) is 25 or more and the durability of the Cr-based oxide film is improved, and the evaluation is “ ⁇ ” at a heating temperature of 1000 ° C.
- No. Nos. 3 and 5 contain Si in excess of 2.5% and Al in an amount of 0.50% or less, and the value of the formula (i) is 30 or more, and the durability of the Cr-based oxide film is remarkably improved.
- the evaluation was “ ⁇ ” even at a heating temperature of 1000 ° C.
- No. No. 7 The durability of the Cr-based oxide film was remarkably improved by the combined addition of B, V, and Mg to the steel No. 2 and the evaluation was “ ⁇ ” even at a heating temperature of 1000 ° C.
- No. Nos. 9 and 14 are Nos.
- the same steel A as in No. 1 was pre-oxidized to improve the durability of the Cr-based oxide film, and the evaluation was improved to “ ⁇ ” even at a heating temperature of 1000 ° C.
- No. 17, 19, 20, and 23 satisfy the components (i) and the components of each element defined in the present invention, but all of them are mainly composed of Cr-based oxides containing 0.5 mass% or more of Si and / or Mn. It does not have an oxide film.
- No. Each of 17, 19, 20, and 23 has a composition in which any of the components of Mn, Si, and Al is out of the preferable component range. Specifically, no. Steel K of No. 17 has a Mn content exceeding 0.95%. Steel No. 19 has an Si content of less than 2.50% and an Al content of more than 0.5%. No. Steel No. 20 has a Mn content of over 0.95%, a Si content of less than 2.50%, and an Al content of over 0.5%. No. Steel No.
- No. Nos. 17, 19, 20, and 23 are tests that do not contain Mn, Si, and Al to such an extent that the above-described effects of Si and Mn are positively utilized, and in which pre-oxidation is not performed. It is a piece. After the oxidation test assuming a reformed gas environment, No. 17 produces an oxide film mainly composed of (Cr, Mn) oxide. Nos. 19, 20 and 23 produce Cr-based oxide films, but Si and Mn in the Cr-based oxides are less than 0.5% by mass, and the evaluation is “x” or “ ⁇ ”.
- No. 10, 11, 12, and 13 are No. This is a pre-oxidized steel having the same composition as 17, 19, 20, and 23. Pre-oxidation improves the durability of the oxide film, and after oxidation tests assuming a reformed gas environment, highly durable Cr mainly composed of Cr-based oxides containing 0.5% by mass or more of Si and / or Mn A system oxide film is formed. No. In all of Nos. 10 to 13, the evaluation at the heating temperatures of 800 ° C. and 900 ° C. in the atmospheric repeated oxidation test is improved to “ ⁇ ”.
- No. No. 16 (i) is outside the lower limit of the appropriate range of the present invention, and after an oxidation test assuming a reformed gas environment, an oxide film mainly composed of (Fe, Cr, Mn) oxide is generated.
- the evaluation is “x” at a heating temperature of 900 ° C. in the atmospheric repeated oxidation test.
- No. No. 15 Nb is outside the lower limit of the appropriate range of the present invention.
- No. 18 has Cr outside the lower limit of the appropriate range of the present invention.
- Mn is outside the upper limit of the present invention.
- Al and Ti are outside the upper limit of the proper range of the present invention.
- Nos. 15, 18, and 24 are (Fe, Cr) -based oxides.
- No. 21 generates an oxide film mainly composed of a (Cr, Mn) -based oxide, and the evaluation is “x” at a heating temperature of 900 ° C. in a repeated atmospheric oxidation test.
- No. No. 22 produces a Cr-based oxide film mainly composed of a Cr-based oxide containing 0.5% by mass or more of Mn after an oxidation test assuming a reformed gas environment.
- the lower limit of the range is exceeded, and the evaluation is “x” at a heating temperature of 900 ° C. in the atmospheric repeated oxidation test.
- Si and Mn are out of the preferred lower limit of the present invention, and a Cr-based oxide film is formed, but Si and Mn in the Cr-based oxide are less than 0.5% by mass, and heating in an atmospheric repeated oxidation test The evaluation is “x” at a temperature of 900 ° C.
- No. Nos. 26, 28, 29, and 31 are steel Nos. Defined in the present invention or No. (i) out of the proper range. Although the steel was pre-oxidized with 15, 18, 21, and 24, there was no improvement in the oxide film, and all evaluations were “x” at a heating temperature of 900 ° C. in the atmospheric repeated oxidation test, and there was no improvement.
- No. Nos. 27 and 30 are No. 27 in which the formula (i) defined in the present invention is outside the appropriate range. 16 and 22 are pre-oxidized to improve the durability of the oxide film, and the evaluation has been improved from “ ⁇ ” or “ ⁇ ” to “ ⁇ ” at a heating temperature of 800 ° C. in the atmospheric repeated oxidation test. In both cases, the evaluation is “x” at the heating temperature of 900 ° C. and there is no improvement.
- No. Nos. 32 and 36 are Nos. In which Si and Mn are outside the preferred lower limit of the present invention.
- Steel S of 25 and the same steel were pre-oxidized, but there was no improvement in the oxide film, and there was no improvement with an evaluation “x” at a heating temperature of 900 ° C. in the atmospheric repeated oxidation test.
- No. Nos. 33 and 35 are No.s that satisfy the above-described components of the respective elements and the formula (i) defined in the present invention. 17 and 23 are pre-oxidized. However, no. No. 33 has water vapor in the pre-oxidation atmosphere of less than 10% and a pre-oxidation time of less than 100 hours. No. 35 has less than 10% of hydrogen in the pre-oxidation atmosphere and a pre-oxidation time of less than 100 hours. In these comparative examples, there is no improvement of the oxide film, and in all cases, the evaluation is “x” at the heating temperature of 900 ° C. in the atmospheric repeated oxidation test, and there is no improvement.
- No. No. 34 is a No. 34 satisfying the above-mentioned components of each element and the formula (i) defined in the present invention. 1 is pre-oxidized. However, since the pre-oxidation temperature is higher than 1000 ° C, the durability of the oxide film deteriorates, and after the oxidation test assuming a reformed gas environment, an oxide film mainly composed of Fe-based oxide is formed, and heating in the atmospheric repeated oxidation test is performed. Evaluation deteriorated to “x” at temperatures of 800 ° C. and 900 ° C.
- the horizontal axis represents the formula (i) defined in the present invention
- the vertical axis represents Si in the Cr-based oxide after the oxidation test assuming a reformed gas environment.
- Steel A used for the preparation of test piece No. 1 in Table 2 does not contain elements B and Mg, and the evaluation is “x” at a heating temperature of 1000 ° C. in a repeated atmospheric oxidation test.
- test pieces No. 101 to No. 106 in which the total amount of addition of elements B and Mg is 0.0002% or more, good results are obtained at a heating temperature of 1000 ° C. in a repeated atmospheric oxidation test. ing.
- the steel satisfies the elements (i) and the components of each element defined in the present invention, and the surface after the oxidation test assuming a reformed gas environment has 0.5 mass of Si and / or Mn.
- the steel having a Cr-based oxide film mainly composed of Cr-based oxide containing at least 50% is superior to the comparative example in the evaluation at a heating temperature of 900 ° C. in the repeated atmospheric oxidation test. It was revealed that the generated oxide film was excellent in durability.
- the steel that satisfies the pre-oxidation conditions specified in the present invention for the steel satisfying the formula (i) and the components of each element specified in the present invention has 0 Si and / or Mn in the reformed gas environment.
- a Cr-based oxide film mainly composed of a Cr-based oxide containing 5% by mass or more is produced.
- a steel that does not satisfy the components of each element defined in the present invention has a Si and / or Mn content of 0.5 mass in a reformed gas environment, regardless of the presence or absence of the pre-oxidation conditions defined in the present invention. It can be seen that a Cr-based oxide film mainly composed of a Cr-based oxide containing at least% is not generated. Further, the steel that does not satisfy the formula (i) defined in the present invention has a Cr-based oxide film mainly composed of a Cr-based oxide containing 0.5 mass% or more of Si and / or Mn in a reformed gas environment.
- the solid solution of Si and Mn in the Cr-based oxide and the oxide of Si, Mn, and Nb just under the Cr-based oxide film are not formed, and the Cr-based oxidation is caused by the concentration of Si, Mn, and Nb.
- the improvement of the durability of the film is generally insufficient, the evaluation at the heating temperature of 900 ° C. in the atmospheric repeated oxidation test is inferior, and the durability of the oxide film generated in the reformed gas environment is insufficient I understand that.
- the amount of Si, Mn, Nb is optimized, and by adding a small amount of V, B, Mg, etc. and the amount of Al, Ti added, It is possible to provide a ferritic stainless steel for a fuel reformer that has both excellent oxidation resistance and economy without depending on a large amount of addition.
- the ferritic stainless steel of the present invention can be industrially produced regardless of a special production method.
Abstract
Description
従って、フェライト系ステンレス鋼を燃料改質器に適用する際、その表面に形成されるCr系酸化皮膜の耐久性を高め、異常酸化を抑制することが技術的課題となる。
(a)多量の水蒸気と水素が共存する改質ガス環境下において、Si及びMnは、Cr系酸化物へ固溶して、Cr系酸化皮膜の成長と内部酸化の抑制に寄与する新規な知見が得られた。更に、SiやMnはCr系酸化皮膜の直下に酸化物を形成することにより濃化して、水素や水蒸気による内部酸化の進行を遅延させ、Fe系酸化物を主体とする酸化皮膜の形成に伴う異常酸化を抑制する。このような作用効果により、Cr系酸化皮膜の耐久性を高めることができる。
(b)前記したCr系酸化皮膜の耐久性を更に高めるには、Nbの微量添加が有効であることを知見した。Nbは、Cr系酸化皮膜の直下に酸化物を形成することにより濃化して、内部酸化ならびに粒界酸化を抑制することによって、Cr系酸化皮膜の耐久性を改善する。
(c)V、B、Mgの微量添加もNbと同様な効果を発現することが分かった。これら元素の微量添加によって、Nb添加の効果が重畳する。
(d)一方、Al、TiはCr系酸化物への固溶や界面への濃化によって酸化皮膜を強化する作用もあるものの、当該改質ガス環境下では添加量によっては内部酸化ならびに粒界酸化の進行を助長してCr系酸化皮膜の耐久性を損なう作用もあることが分かった。
(e)水蒸気及び水素を含む雰囲気中において、雰囲気、温度及び処理時間の条件が特定された予備酸化処理を実施することで、前記Cr系酸化物中のSi及びMnを濃化して、Cr系酸化皮膜の耐久性を高めることができることが分った。
以下の(1)~(13)の本発明は、上述した検討結果に基づいて完成されたものである。
Cr+5Si+Mn+2Nb≧22 ・・・(i)
但し、式中の元素記号は、当該元素の鋼中における含有質量%を意味する。
上記した組成により、本発明のフェライト系ステンレス鋼の表面を、水蒸気/二酸化炭素/一酸化炭素に加えて多量の水素を含む改質ガス環境の雰囲気に晒すことによって、Cr系酸化物を主体とした酸化皮膜であるCr系酸化皮膜が形成され、前記Cr系酸化物中にはSi及びMnのうち少なくともいずれかの元素が0.5質量%以上含有される。
Cr系酸化物中に、Si及びMnのうち少なくともいずれかの元素を0.5質量%以上含むことにより、Cr系酸化皮膜の成長と内部酸化の抑制に寄与することができ、改質ガス環境下において十分な耐久性を得ることができる。
尚、「Cr系酸化物」とはグロー放電質量分析法(GDS分析法)により、CrがOとともに検出され、且つ、Crが50質量%以上検出される酸化物である。また「主体とする」とは、酸化皮膜全体に占めるCr系酸化物の体積の酸化皮膜全体の体積に対する比率が50%以上であることを意味する。本発明のフェライト系ステンレス鋼のCr系酸化皮膜には、Cr系酸化物以外にMnCr2O4、SiO2、Al2O3などを含んでいてもよい。
(2)Mnが0.95%未満であることを特徴とする(1)に記載の燃料改質器用フェライト系ステンレス鋼。
(3)Siが2.50%超であることを特徴とする(1)または(2)に記載の燃料改質器用フェライト系ステンレス鋼。
(4)Alが0.5%以下であることを特徴とする(1)~(3)のうちいずれかに記載の燃料改質器用フェライト系ステンレス鋼。
(5)前記ステンレス鋼が、さらに質量%にて、Ni:1%以下、Cu:1%以下、Mo:2%以下、Sn:1%以下、W:1%以下、Co:0.5%以下、V:0.5%以下、Ti:0.3%以下、B:0.005%以下、Ca:0.005%以下、Mg:0.005%以下、Zr:0.5%以下、La:0.1%以下、Y:0.1%以下、Hf:0.1%以下、REM:0.1%以下の1種または2種以上含有していることを特徴とする(1)~(4)のうちいずれかに記載の燃料改質器用フェライト系ステンレス鋼。
(6)ステンレス鋼の表面に酸化皮膜を有し、酸化皮膜の成分として、Si及びMnのうち少なくともいずれかの元素を0.5質量%以上と、Crを50質量%以上含有する酸化物が酸化皮膜に占める体積の比率が50%以上であることを特徴とする(1)~(5)のうちいずれかに記載の燃料改質器用フェライト系ステンレス鋼。
(7)(1)~(5)のいずれかに記載の組成を有するステンレス鋼を、水分を10体積%以上50体積%以下及び水素を10体積%以上70体積%以下含む雰囲気中において、300~1000℃の範囲で熱処理することにより、前記ステンレス鋼材の表面に、Si及びMnのうち少なくともいずれかの元素を0.5質量%以上と、Crを50質量%以上を含有する酸化物が占める体積の比率が50%以上である酸化皮膜を形成することを特徴とする燃料改質器用フェライト系ステンレス鋼の製造方法。
(8)質量%にて、Cr:12以上24%以下、C:0.001%以上0.03%以下、Al:0.002%以上4%以下、P:0.05%以下、S:0.01%以下、N:0.03%以下、Nb:0.011%以上1%以下を含み、更にSi:0.3%以上4%以下及びMn:0.1%超2%以下の少なくともいずれかを含み、残部がFeおよび不可避的不純物からなり、かつ(i)式を満たす組成を有し、26体積%H2O+7体積%CO2+7%体積%CO+60体積%H2の雰囲気で850℃にて1000時間保持した後で室温まで冷却したとき、その表面にSi及びMnのうちいずれかの元素を0.5質量%以上と、Cr及びOの両者の含有量を合算して50質量%以上とを含有する酸化皮膜が形成されていることを特徴とする燃料改質器用フェライト系ステンレス鋼。
Cr+5Si+Mn+2Nb≧22 ・・・(i)
但し、式中の元素記号は、当該元素の鋼中における含有質量%を意味する。
(9)質量%にて、Cr:12以上24%以下、C:0.001%以上0.03%以下、Al:0.002%以上4%以下、P:0.05%以下、S:0.01%以下、N:0.03%以下、Nb:0.011%以上1%以下を含み、更にSi:0.3%以上4%以下及びMn:0.1%超2%以下の少なくともいずれかを含み、残部がFeおよび不可避的不純物からなり、かつ(i)式を満たす組成を有し、20体積%H2O+15体積%CO2+5%体積%CO+30体積%H2+30体積%N2の雰囲気で650℃にて100時間保持する熱処理を施した後に、26体積%H2O+7体積%CO2+7%体積%CO+60体積%H2の雰囲気で850℃にて1000時間保持した後で室温まで冷却したとき、その表面にSi及びMnのうちいずれかの元素を0.5質量%以上と、Cr及びOの両者の含有量を合算して50質量%以上とを含有する酸化皮膜が形成されていることを特徴とする燃料改質器用フェライト系ステンレス鋼。
Cr+5Si+Mn+2Nb≧22 ・・・(i)
但し、式中の元素記号は、当該元素の鋼中における含有質量%を意味する。
(10)Mnが0.95%未満であることを特徴とする(8)または(9)に記載の燃料改質器用フェライト系ステンレス鋼。
(11)Siが2.50超であることを特徴とする(8)~(10)のうちいずれかに記載の燃料改質器用フェライト系ステンレス鋼。
(12)Alが0.5%以下であることを特徴とする(8)~(11)のうちいずれかに記載の燃料改質器用フェライト系ステンレス鋼。
(13)さらに質量%にて、Ni:1%以下、Cu:1%以下、Mo:2%以下、Sn:1%以下、W:1%以下、Co:0.5%以下、V:0.5%以下、Ti:0.3%以下、B:0.005%以下、Ca:0.005%以下、Mg:0.005%以下、Zr:0.5%以下、La:0.1%以下、Y:0.1%以下、Hf:0.1%以下、REM:0.1%以下の1種または2種以上含有していることを特徴とする(8)~(12)のうちいずれかに記載の燃料改質器用フェライト系ステンレス鋼。
尚、B及びMgのそれぞれの添加量が前記下限に満たない場合であっても、これらの添加量が下記の式(ii)を充足する場合、耐酸化性向上効果が促進される。
B+Mg≧0.0002%・・・(ii)
但し、式中の元素記号は、当該元素の鋼中における含有質量%を意味する。
酸化試験は、改質ガス環境下で鋼材が曝される雰囲気を想定し、26体積%H2O+7体積%CO2+7%体積%CO+60体積%H2の雰囲気とし、850℃に加熱し、850℃にて1000時間保持した後で室温まで冷却した。
雰囲気a:20%H2O-15%CO2-5%CO-30%H2-30%N2
雰囲気b:25%H2O-8%CO2-8%CO-59%H2
雰囲気c:16%H2O-43%H2-41%N2
雰囲気d:3%H2O-9%CO2-16%CO-32%H2-40%N2
雰囲気e:24%H2O-19%CO2-5%H2-52%N2
また、表2の「鋼」欄にアスタリスク“*”、“**”及び“***”のいずれかが付された試験片は、予備酸化処理が実施されていることを示す。
元素B及びMg間の相互扶助的な耐酸化性向上効果を確認すべく、表3に成分を示す各種フェライト系ステンレス鋼T~Uを溶製し、熱間圧延、焼鈍酸洗、冷間圧延、仕上げ焼鈍を経て板厚1.0mmの冷延焼鈍材を製造した。次いで、各フェライト系ステンレス鋼から試験片No.101~No.106を切り出し、表2の試験片No.1~36と同様の条件にて大気中繰り返し酸化試験により、これらの試験片の耐久性を評価した。試験片No.101~No.106の耐久性の評価結果を表4に示す。
表5に成分を示す各種フェライト系ステンレス鋼W及びXを溶製し、熱間圧延、焼鈍酸洗、冷間圧延、仕上げ焼鈍を経て板厚1.0mmの冷延焼鈍材を製造した。次いで、各フェライト系ステンレス鋼から試験片No.201~No.204を切り出し、表2の試験片No.1~36と同様の条件にて大気中繰り返し酸化試験により、これらの試験片の耐久性を評価した。試験片No.101~No.106の耐久性の評価結果を表6に示す。
一方、本発明で規定する各元素の成分を満たしていない鋼は、本発明で規定する予備酸化条件の実施の有無に係わらず、改質ガス環境下でSi及び/又はMnが0.5質量%以上含むCr系酸化物を主体とするCr系酸化皮膜を生成しないことがわかる。また、本発明で規定する(i)式を満たしていない鋼は、改質ガス環境下でSi及び/又はMnが0.5質量%以上含むCr系酸化物を主体とするCr系酸化皮膜を生成する場合もある。しかし、Cr系酸化物へのSi、Mnの固溶とCr系酸化皮膜の直下へのSi、Mn、Nbの酸化物が十分に形成されず、Si、Mn、Nbの濃化によるCr系酸化皮膜の耐久性の改善が総合的に不十分であり、大気繰り返し酸化試験の加熱温度900℃における評価が劣位であり、改質ガス環境下に生成される酸化皮膜の耐久性が不十分であることがわかる。
Claims (13)
- 質量%にて、Cr:12以上24%以下、C:0.001%以上0.03%以下、Al:0.002%以上4%以下、P:0.05%以下、S:0.01%以下、N:0.03%以下、Nb:0.01以上1%以下を含み、更にSi:0.3%以上4%以下及びMn:0.1%超2%以下の少なくともいずれかを含み、残部がFeおよび不可避的不純物からなり、かつ(i)式を満たす組成を有することを特徴とする燃料改質器用フェライト系ステンレス鋼。
Cr+5Si+Mn+2Nb≧22 ・・・(i)
但し、式中の元素記号は、当該元素の鋼中における含有質量%を意味する。
- Mnが0.95%未満であることを特徴とする請求項1に記載の燃料改質器用フェライト系ステンレス鋼。
- Siが2.50超であることを特徴とする請求項1または2に記載の燃料改質器用フェライト系ステンレス鋼。
- Alが0.5%以下であることを特徴とする請求項1~3のうちいずれか1項に記載の燃料改質器用フェライト系ステンレス鋼。
- 前記ステンレス鋼が、さらに質量%にて、Ni:1%以下、Cu:1%以下、Mo:2%以下、Sn:1%以下、W:1%以下、Co:0.5%以下、V:0.5%以下、Ti:0.3%以下、B:0.005%以下、Ca:0.005%以下、Mg:0.005%以下、Zr:0.5%以下、La:0.1%以下、Y:0.1%以下、Hf:0.1%以下、REM:0.1%以下の1種または2種以上含有していることを特徴とする請求項1~4のうちいずれか1項に記載の燃料改質器用フェライト系ステンレス鋼。
- 前記ステンレス鋼の表面に酸化皮膜を有し、該酸化皮膜の成分として、Si及びMnのうち少なくともいずれかの元素を0.5質量%以上と、Crを50質量%以上含有する酸化物が前記酸化皮膜に占める体積の比率が50%以上であることを特徴とする請求項1~5のうちいずれか1項に記載の燃料改質器用フェライト系ステンレス鋼。
- 請求項1~5のいずれか1項に記載の組成を有するステンレス鋼材を、水分を10体積%以上50体積%以下及び水素を10体積%以上70体積%以下含む雰囲気中において、300~1000℃の範囲で熱処理することにより、前記ステンレス鋼材の表面に、Si及びMnのうち少なくともいずれかの元素を0.5質量%以上と、Crを50質量%以上含有する酸化物が占める体積の比率が50%以上である酸化皮膜を形成することを特徴とする燃料改質器用フェライト系ステンレス鋼の製造方法。
- 質量%にて、Cr:12以上24%以下、C:0.001%以上0.03%以下、Al:0.002%以上4%以下、P:0.05%以下、S:0.01%以下、N:0.03%以下、Nb:0.01以上1%以下を含み、更にSi:0.3%以上4%以下及びMn:0.1%超2%以下の少なくともいずれかを含み、残部がFeおよび不可避的不純物からなり、かつ(i)式を満たす組成を有し、
26体積%H2O+7体積%CO2+7%体積%CO+60体積%H2の雰囲気で850℃にて1000時間保持した後で室温まで冷却したとき、その表面にSi及びMnのうちいずれかの元素を単独で0.5質量%以上或いはSi及びMnの両方の元素をそれぞれ0.5質量%以上と、Crを50質量%以上含有する酸化物が占める体積の比率が50%以上である酸化皮膜が形成されていることを特徴とする燃料改質器用フェライト系ステンレス鋼。
Cr+5Si+Mn+2Nb≧22 ・・・(i)
但し、式中の元素記号は、当該元素の鋼中における含有質量%を意味する。
- 質量%にて、Cr:12以上24%以下、C:0.001%以上0.03%以下、Al:0.002%以上4%以下、P:0.05%以下、S:0.01%以下、N:0.03%以下、Nb:0.01以上1%以下を含み、更にSi:0.3%以上4%以下及びMn:0.1%超2%以下の少なくともいずれかと、残部がFeおよび不可避的不純物からなり、かつ(i)式を満たす組成を有し、
20体積%H2O+15体積%CO2+5%体積%CO+30体積%H2+30体積%N2の雰囲気で650℃にて100時間保持する熱処理を施した後に、
26体積%H2O+7体積%CO2+7%体積%CO+60体積%H2の雰囲気で850℃にて1000時間保持した後で室温まで冷却したとき、その表面にSi及びMnのうちいずれかの元素を単独で0.5質量%以上或いはSi及びMnの両方の元素をそれぞれ0.5質量%以上と、Crを50質量%以上含有する酸化物が占める体積の比率が50%以上である酸化皮膜が形成されていることを特徴とする燃料改質器用フェライト系ステンレス鋼。
Cr+5Si+Mn+2Nb≧22 ・・・(i)
但し、式中の元素記号は、当該元素の鋼中における含有質量%を意味する。
- Mnが0.95%未満であることを特徴とする請求項8または9に記載の燃料改質器用フェライト系ステンレス鋼。
- Siが2.50超であることを特徴とする請求項8~10のうちいずれか1項に記載の燃料改質器用フェライト系ステンレス鋼。
- Alが0.5%以下であることを特徴とする請求項8~11のうちいずれか1項に記載の燃料改質器用フェライト系ステンレス鋼。
- さらに質量%にて、Ni:1%以下、Cu:1%以下、Mo:2%以下、Sn:1%以下、W:1%以下、Co:0.5%以下、V:0.5%以下、Ti:0.3%以下、B:0.005%以下、Ca:0.005%以下、Mg:0.005%以下、Zr:0.5%以下、La:0.1%以下、Y:0.1%以下、Hf:0.1%以下、REM:0.1%以下の1種または2種以上含有していることを特徴とする請求項8~12のうちいずれか1項に記載の燃料改質器用フェライト系ステンレス鋼。
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JP7233195B2 (ja) | 2018-10-26 | 2023-03-06 | 日鉄ステンレス株式会社 | フェライト系ステンレス鋼及びその製造方法、並びに燃料電池用部材 |
KR20240007212A (ko) | 2021-10-07 | 2024-01-16 | 닛테츠 스테인레스 가부시키가이샤 | 페라이트계 스테인리스 강관 및 그 제조 방법, 그리고 연료 전지 |
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EP3064606A1 (en) | 2016-09-07 |
JP6067134B2 (ja) | 2017-02-01 |
EP3064606B1 (en) | 2022-03-02 |
JPWO2015064739A1 (ja) | 2017-03-09 |
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