Solid oxide fuel cell components

Abstract

The present invention provides a solid oxide fuel cell member having excellent electrical conductivity and excellent resistance to Cr poisoning. A ferritic stainless steel having a composition of 14.0-32.0% Cr and 2.50-7.00% Al, by mass, is used as the substrate, and the surface of the substrate is coated with precious metal particles, with the precious metal particles having an average particle size of 1 μm to 10 μm, a coating thickness of 0.5 μm to 10 μm, and a surface coverage of 1.0% or more.

Description

[Technical field]

[0001] The present invention relates to a member for a solid oxide fuel cell having excellent electrical conductivity and chromium poisoning resistance. [Background technology]

[0002] Fuel cells emit little harmful gas and have high power generation efficiency, so they are expected to be used in a wide range of power generation systems, including large-scale power generation, cogeneration systems, and automotive power sources.

[0003] Among them, solid oxide fuel cells (also called SOFCs) have the advantages of operating at high temperatures of 500 to 900°C, not requiring a catalyst for the electrode reaction, and being able to use a variety of fuel gases. For these reasons, solid oxide fuel cells are attracting attention as a next-generation energy source.

[0004] Among the components of solid oxide fuel cells, the interconnector (sometimes called a separator or bipolar plate) serves to form a gas flow path and connect adjacent cells in a fuel cell stack. The interconnector also serves to pass electric current. Therefore, the interconnector is required to have electrical conductivity. Various metal materials have been proposed as materials for use in the interconnectors of such solid oxide fuel cells.

[0005] For example, Patent Document 1 states: "A ferritic stainless steel for solid oxide fuel cell components, characterized in that it contains, in mass%, C: 0.03% or less, Mn: 2.0% or less, Ni: 0.6% or less, N: 0.03% or less, Cr: 10.0 to 32.0%, and at least one of Si: 2.0% or less and Al: 6.0% or less in a total amount of 1.5% or more, with the remainder essentially consisting of Fe." has been disclosed.

[0006] In Patent Document 2, "A ferritic stainless steel having, by mass%, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.045% or less, S: 0.0030% or less, Cr: 20.025.0%, Mo: 0.32.0%, N: 0.040% or less, Al: 0.50% or less, V: 0.20% or less, Nb: 0.0010.500% and / or Ti: 0.0010.50%, with the balance being Fe and unavoidable impurities." has been disclosed.

[0007] Patent Document 3 states: "A method usable in an electrode for an electrochemical device, comprising coating a top surface of a corrosion-resistant metal substrate with a noble metal." has been disclosed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2003-187828 A [Patent Document 2] International Publication No. 2018 / 008658 [Patent Document 3] U.S. Patent No. 9,765,421 Summary of the Invention

[0009] The metallic material disclosed in Patent Document 1 contains a large amount of Si and / or Al in its component composition. However, when a large amount of Si and Al is contained, oxides with low electrical conductivity such as silica and alumina are formed on the surface of the metallic material in the high-temperature environment in which a solid oxide fuel cell is used. Therefore, when the metallic material disclosed in Patent Document 1 is used for an interconnector of a solid oxide fuel cell, electrical resistance increases and the performance of the cell decreases.

[0010] Moreover, the metallic material disclosed in Patent Document 2 contains a certain amount of Cr in its composition, and an oxide film mainly composed of Cr-based oxides such as Cr2O3 is formed on the surface of the metallic material. However, in a high-temperature environment in which a solid oxide fuel cell is used, the Cr-based oxides volatilize and adhere to the electrodes, which can easily cause deterioration in the performance of the electrodes (hereinafter also referred to as "Cr poisoning"). In fact, Patent Document 2 does not take into consideration the suppression of Cr poisoning. Therefore, when the metallic material disclosed in Patent Document 2 is used for solid oxide fuel cell members, particularly for interconnectors, there is a concern that the performance of the electrodes may deteriorate due to Cr poisoning.

[0011] Similarly, in Patent Document 3, no consideration is given to suppressing Cr poisoning. Therefore, when the metal material disclosed in Patent Document 3 is used for solid oxide fuel cell components, particularly interconnectors, there is concern about deterioration of electrode performance due to Cr poisoning.

[0012] The present invention has been developed in view of the above-mentioned current situation, and has an object to provide a solid oxide fuel cell member having excellent electrical conductivity and excellent resistance to Cr poisoning.

[0013] The inventors have conducted extensive research in order to achieve the above object. the result, (1) A ferritic stainless steel having a Cr content of 14.0 to 32.0 mass% and an Al content of 2.50 to 7.00 mass% in the composition is used as the base material, and (2) The surface of the substrate is coated with precious metal particles. Average particle size of precious metal particles: 1 μm to 10 μm Coating thickness of precious metal particles on a substrate (hereinafter also referred to simply as coating thickness): 0.5 μm or more and 10 μm or less, and Surface coverage rate of precious metal particles to the substrate (hereinafter also referred to simply as surface coverage rate): 1.0% or more; It has been found that the above object can be achieved by

[0014] The inventors consider the reason for this to be as follows. That is, in a high-temperature environment in which a solid oxide fuel cell is used, in a ferritic stainless steel having a composition with a Cr content of 14.0 to 32.0 mass% and an Al content of 2.50 to 7.00 mass%, an alumina surface layer is formed on the surface, preventing the formation of Cr-based oxides. As a result, the volatilization of Cr-based oxides is suppressed, and Cr poisoning of the electrode is prevented. However, alumina has low electrical conductivity, and if alumina is formed on the surface of the substrate, the desired electrical conductivity cannot be obtained. In order to overcome this point, when the precious metal particles are coated and the precious metal particles are fused with the surface of the Al-containing ferritic stainless steel, a current path is generated through the alumina surface layer. Then, by controlling the average particle size and coating thickness of the precious metal particles to the above range, the precious metal particles continue to exist in a state of protruding from the alumina formed on the surface of the substrate, and the current path is maintained. In addition, if the surface coverage rate of the precious metal particles is equal to or higher than a certain level, a sufficient current path is secured, and good electrical conductivity is obtained. For these reasons, the inventors believe that by simultaneously satisfying the above requirements (1) and (2), it is possible to achieve both excellent electrical conductivity and excellent resistance to Cr poisoning. The present invention was completed based on the above findings and through further investigation.

[0015] That is, the gist and configuration of the present invention are as follows. 1. A solid oxide fuel cell member having a substrate and precious metal particles on a surface of the substrate, The substrate is, in mass %, C: 0.025% or less, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 14.0-32.0%, Al: 2.50-7.00%, Ni: 0.01 to 1.00% and N: 0.025% or less and the balance being Fe and unavoidable impurities. The average particle size of the precious metal particles is 1 μm or more and 10 μm or less, The coating thickness of the precious metal particles on the substrate is 0.5 μm or more and 10 μm or less, A solid oxide fuel cell member, wherein the surface coverage of the substrate with the noble metal particles is 1.0% or more.

[0016] 2. The solid oxide fuel cell member according to 1 above, wherein the precious metal particles contain one or more elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru and Os, and alloy particles of these elements.

[0017] 3. The composition of the ferritic stainless steel further comprises, in mass%, Mo: 3.00% or less, Cu: 0.50% or less, Co: 1.00% or less, W: 3.00% or less, Ti: 0.30% or less, Nb: 1.00% or less, V: 0.50% or less, Zr: 0.50% or less, B: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0100% or less and REM: 0.20% or less 2. The solid oxide fuel cell member according to 1 above, comprising one or more selected from the following:

[0018] 4. The composition of the ferritic stainless steel further comprises, in mass%, Mo: 3.00% or less, Cu: 0.50% or less, Co: 1.00% or less, W: 3.00% or less, Ti: 0.30% or less, Nb: 1.00% or less, V: 0.50% or less, Zr: 0.50% or less, B: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0100% or less and REM: 0.20% or less 3. The solid oxide fuel cell member according to 2 above, comprising one or more selected from the following:

[0019] According to the present invention, it is possible to obtain a solid oxide fuel cell member having excellent electrical conductivity and resistance to Cr poisoning. [Brief description of the drawings]

[0020] [Figure 1] 1 is an example of a SEM photograph of No. A3 in an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will be described based on the following embodiments.

[0022] (1) Base material First, the composition of the ferritic stainless steel (hereinafter also referred to as the base ferritic stainless steel) that serves as the base material of the solid oxide fuel cell member according to one embodiment of the present invention will be described. Note that the unit of the composition is always "mass %", and hereinafter, unless otherwise specified, it will be simply represented as "%".

[0023] C: 0.025% or less C has the effect of increasing the high-temperature strength of steel. To obtain such an effect, the C content is preferably 0.001% or more. However, if the C content exceeds 0.025%, the toughness and workability of the steel decrease. For this reason, the C content is set to 0.025% or less. The C content is preferably 0.010% or less.

[0024] Silicon: 0.05 to 1.00% Silicon has the effect of improving the oxidation resistance of steel. To obtain this effect, the silicon content is set to 0.05% or more. However, if the silicon content exceeds 1.00%, silica with low electrical conductivity is formed at the interface between the oxide film formed at high temperatures and the base material, lowering electrical conductivity. For this reason, the silicon content is set to 1.00% or less. The silicon content is preferably 0.20% or less.

[0025] Mn: 0.05 to 1.00% Mn has the effect of increasing the peeling resistance of the oxide film formed at high temperatures. To obtain this effect, the Mn content is set to 0.05% or more. However, if the Mn content exceeds 1.00%, the oxide film may grow abnormally, decreasing the oxidation resistance. In addition, the oxide film may become thick, decreasing the electrical conductivity. For this reason, the Mn content is set to 1.00% or less. The Mn content is preferably 0.20% or less.

[0026] P:0.050% or less P is a harmful element that reduces the toughness of steel. Therefore, it is desirable to reduce P as much as possible. Therefore, the P content is set to 0.050% or less. The P content is preferably 0.030% or less. There is no particular lower limit for the P content. However, since excessive de-P leads to an increase in costs, the P content is preferably 0.010% or more.

[0027] S: 0.010% or less S is a harmful element that adversely affects the workability and oxidation resistance of steel. Therefore, it is desirable to reduce S as much as possible. Therefore, the S content is set to 0.010% or less. The S content is preferably 0.005% or less. There is no particular lower limit for the S content. However, since excessive de-S leads to increased costs, the S content is preferably 0.0001% or more.

[0028] Cr: 14.0~32.0% Cr is an important element that assists the formation of alumina on the surface of the base ferritic stainless steel. To obtain this effect, the Cr content is set to 14.0% or more. The Cr content is preferably set to 18.0% or more. However, if the Cr content exceeds 32.0%, the toughness and workability of the steel decrease. Therefore, the Cr content is set to 32.0% or less. The Cr content is preferably set to 22.0% or less.

[0029] Al: 2.50-7.00% Al is an important element that forms alumina on the surface of the base ferritic stainless steel and suppresses the generation of Cr-based oxides. That is, Al has the effect of suppressing the volatilization of Cr and preventing Cr poisoning of the electrode. To obtain such an effect, the Al content is set to 2.50% or more. The Al content is preferably 5.00% or more, more preferably 5.50% or more. On the other hand, if the Al content exceeds 7.00%, the toughness of the steel decreases and manufacturing becomes difficult. Therefore, the Al content is set to 7.00% or less. The Al content is preferably 6.5% or less.

[0030] Ni: 0.01 to 1.00% Ni has the effect of improving the toughness and oxidation resistance of steel. To obtain such an effect, the Ni content is set to 0.01% or more. On the other hand, if the Ni content exceeds 1.00%, a γ phase is generated at high temperatures, and the oxidation resistance decreases. Therefore, the Ni content is set to 1.00% or less. The Ni content is preferably less than 0.20%.

[0031] N: 0.025% or less N is an element that reduces the toughness and workability of steel, and is preferably reduced as much as possible. In particular, if the N content exceeds 0.025%, toughness and workability may be significantly reduced. Therefore, the N content is set to 0.025% or less. The N content is preferably less than 0.010%. There is no particular lower limit for the N content. However, since excessive denitrification leads to an increase in costs, the N content is preferably 0.001% or more.

[0032] The composition of the ferritic stainless steel substrate of the solid oxide fuel cell member according to one embodiment of the present invention further includes: Mo: 3.00% or less, Cu: 0.50% or less, Co: 1.00% or less, W: 3.00% or less, Ti: 0.30% or less, Nb: 1.00% or less, V: 0.50% or less, Zr: 0.50% or less, B: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0100% or less and REM: 0.20% or less One or more selected from the following may be optionally contained.

[0033] Mo: 3.00% or less Mo has the effect of improving the high-temperature strength and oxidation resistance of steel. To obtain such an effect, the Mo content is preferably 0.01% or more. The Mo content is more preferably 1.20% or more. On the other hand, if the Mo content exceeds 3.00%, the steel becomes hard and the manufacturability decreases. Therefore, when Mo is contained, the Mo content is set to 3.00% or less. The Mo content is preferably 2.30% or less.

[0034] Cu: 0.50% or less Cu has the effect of precipitating in steel and improving the high-temperature strength of the steel. To obtain such an effect, the Cu content is preferably 0.01% or more. However, if the Cu content exceeds 0.50%, the toughness decreases and the manufacturability decreases. Therefore, when Cu is contained, the Cu content is set to 0.50% or less.

[0035] Co: 1.00% or less Co has the effect of improving the toughness of steel. To obtain such an effect, the Co content is preferably 0.01% or more. On the other hand, if the Co content exceeds 1.00%, the workability of the steel decreases. Therefore, when Co is contained, the Co content is set to 1.00% or less. The Co content is preferably 0.30% or less.

[0036] W:3.00% or less W has the effect of improving the high-temperature strength of steel. To obtain such an effect, the W content is preferably 0.01% or more. On the other hand, if the W content exceeds 3.00%, the steel becomes hard and manufacturing becomes difficult. Therefore, when W is contained, the W content is 3.00% or less. The W content is preferably 1.00% or less.

[0037] Ti: 0.30% or less Ti has the effect of improving the workability of steel. To obtain such an effect, the Ti content is preferably 0.01% or more. However, if the Ti content exceeds 0.30%, coarse Ti(C,N) precipitates are generated, and the toughness of the steel is reduced. Furthermore, the oxidation resistance is reduced. Therefore, when Ti is contained, the Ti content is set to 0.30% or less. The Ti content is preferably 0.15% or less, and more preferably 0.05% or less.

[0038] Nb: 1.00% or less Nb has the effect of increasing the high-temperature strength of steel. To obtain such an effect, the Nb content is preferably 0.01% or more. However, if the Nb content exceeds 1.00%, the steel becomes hard and the manufacturability decreases. Therefore, when Nb is contained, the Nb content is set to 1.00% or less. The Nb content is preferably 0.40% or less.

[0039] V: 0.50% or less V has the effect of improving the workability and oxidation resistance of steel. To obtain such an effect, the V content is preferably 0.01% or more. However, if the V content exceeds 0.50%, coarse V(C,N) precipitates are generated, and the toughness of the steel decreases. Therefore, when V is contained, the V content is set to 0.50% or less. The V content is preferably 0.10% or less.

[0040] Zr: 0.50% or less Zr has the effect of improving oxidation resistance. To obtain such an effect, the Zr content is preferably 0.01% or more. However, if the Zr content exceeds 0.50%, Zr intermetallic compounds precipitate, and the toughness of the steel decreases. Therefore, when Zr is contained, the Zr content is set to 0.50% or less. The Zr content is preferably 0.10% or less.

[0041] B: 0.0050% or less B has the effect of improving the toughness of steel. To obtain such an effect, the B content is preferably 0.0002% or more. On the other hand, if the B content exceeds 0.0050%, BN is generated and the workability of the steel decreases. Therefore, when B is contained, the B content is set to 0.0050% or less. The B content is preferably 0.0010% or less.

[0042] Ca: 0.0050% or less Ca has the effect of improving oxidation resistance. To obtain such an effect, the Ca content is preferably 0.0002% or more. However, if the Ca content exceeds 0.0050%, the steel is more likely to have surface defects. Therefore, when Ca is contained, the Ca content is set to 0.0050% or less. The Ca content is preferably 0.0020% or less.

[0043] Mg: 0.0100% or less Mg has the effect of improving oxidation resistance. To obtain such an effect, the Mg content is 0.0002% or more. However, if the Mg content exceeds 0.0100%, the steel is prone to surface defects. Therefore, when Mg is contained, the Mg content is set to 0.0100% or less. The Mg content is preferably 0.0025% or less.

[0044] REM: 0.20% or less REM is a general term for Sc, Y, La, Ce, Pr, Nd, Pm, Sm, and Hf. REM has the effect of improving the adhesion of alumina on the surface of the base ferritic stainless steel and improving oxidation resistance. To obtain such an effect, the REM content is preferably 0.01% or more, more preferably 0.06% or more. On the other hand, if the REM content exceeds 0.20%, surface defects tend to occur in the steel. Therefore, when REM is contained, the REM content is set to 0.20% or less. The REM content is preferably 0.10% or less.

[0045] The balance of the components other than those mentioned above is Fe and unavoidable impurities.

[0046] The base ferritic stainless steel preferably has a ferrite phase volume fraction of 95% or more. The remaining structure volume fraction is preferably 5% or less. Examples of the remaining structure include an austenite phase and a martensite phase. The base ferritic stainless steel may have a single-phase ferrite structure (volume fraction: 100%).

[0047] Here, the identification of the structure (calculation of the volume fraction of the ferrite phase) is performed as follows. That is, a test piece for cross-sectional observation is prepared from the base ferritic stainless steel, and is etched with a picric acid saturated hydrochloric acid solution. Next, the test piece for cross-sectional observation is observed with an optical microscope at 100x magnification in 10 fields of view, and the ferrite phase is identified from the structure shape and etching strength. Next, the volume fraction of the ferrite phase is determined for each field of view by image processing, and the average value is calculated. The volume fraction of the ferrite phase is calculated excluding intermetallic compounds, precipitates, and inclusions. The volume fraction of the remaining structure is calculated by subtracting the volume fraction of the ferrite phase from 100%.

[0048] In addition, the solid oxide fuel cell component according to one embodiment of the present invention includes not only those processed into the shape of parts such as interconnectors, but also materials (e.g., plate-shaped materials) before being processed into the shape of parts.

[0049] The shape of the base ferritic stainless steel may be, for example, a plate (steel plate) or a part. The thickness of the base ferritic stainless steel in the plate (steel plate) or part shape is not particularly limited. However, from the viewpoint of Cr poisoning resistance and workability, the thickness of the base ferritic stainless steel is preferably 0.01 to 10.0 mm. The thickness of the base ferritic stainless steel is preferably 0.03 mm or more. The thickness of the base ferritic stainless steel is preferably 8.0 mm or less, more preferably 2.0 mm or less.

[0050] (2) Precious metal particles Next, the noble metal particles that are coated on the surface of the above-mentioned base ferritic stainless steel will be described.

[0051] The noble metal particles are particles of Au, Ag, Pt, Pd, Rh, Ir, Ru and Os, and alloy particles of these elements. Among them, it is preferable to contain a noble metal with a high melting point (>1500°C) such as Pt, Ir, Rh, Pd, Os and Ru, and it is particularly preferable to contain Ru. The noble metal with a high melting point ensures long-term operational stability at the high temperature at which the SOFC operates. The noble metal particles may be composed of one of the above elements, or may be composed of two or more of the above elements. In the latter case, for example, the particles may be a mixture of two or more of the above elements, or an alloy particle of two or more of the above elements.

[0052] The precious metal particles coated on the surface of the above-mentioned ferritic stainless steel substrate are present on the surface in the form of isolated islands. Here, the island form is referred to as "particles". By maintaining the island form of the precious metal coating instead of the conventional continuous layered coating, a) the amount of precious metal used can be reduced, and b) stress between the coating layer and the substrate due to mismatch in thermal expansion coefficients can be minimized. In high-temperature SOFC applications, it is necessary to avoid peeling of the coating layer by the above b).

[0053] As described above, it is extremely important to simultaneously control the average particle size, coating thickness and surface coverage of the precious metal particles coated on the surface of the base ferritic stainless steel, each within the following ranges.

[0054] Average particle size of precious metal particles: 1μm to 10μm If the average particle size of the precious metal particles is less than 1 μm, it becomes difficult to reliably adhere (or fuse) the precious metal particles to the base ferritic stainless steel. On the other hand, if the average particle size of the precious metal particles exceeds 10 μm, the precious metal particles may peel off from the base ferritic stainless steel due to stress between the precious metal particles and the base material caused by mismatch in thermal expansion coefficients. If the precious metal particles peel off, the electrical path is lost and good electrical conductivity cannot be obtained. Therefore, the average particle size of the precious metal particles is set to be 1 μm or more and 10 μm or less.

[0055] Here, the average particle size of the precious metal particles is the average value of the circle-equivalent diameter calculated from the area of ​​each precious metal particle observed on the surface of the substrate. Specifically, it is measured by the method described in the Examples below. The average particle size of the precious metal particles is calculated excluding particles with a circle-equivalent diameter of less than 0.1 μm that do not substantially contribute to ensuring the current path. In addition, the coating thickness and surface coverage rate of the precious metal particles described below are also calculated excluding particles with a circle-equivalent diameter of less than 0.1 μm.

[0056] Precious metal particle coating thickness: 0.5 μm to 10 μm If the coating thickness of the precious metal particles is less than 0.5 μm, a thick layer of alumina will be formed on the surface of the base ferritic stainless steel in the high-temperature environment in which the solid oxide fuel cell is used, covering the precious metal particles. As a result, the electrical path will be lost and good electrical conductivity will not be obtained. On the other hand, if the coating thickness of the precious metal particles exceeds 10 μm, the precious metal particles will be easily peeled off from the surface of the base ferritic stainless steel. If the precious metal particles peel off, the electrical path will be lost and good electrical conductivity will not be obtained. Therefore, the coating thickness of the precious metal particles is set to be 0.5 μm or more and 10 μm or less.

[0057] Here, the coating thickness of the precious metal particles is the average value of the maximum length of the precious metal particles in the direction perpendicular to the surface of the substrate (hereinafter also referred to as the direction perpendicular to the substrate surface). More specifically, it is measured by the method described in the examples below.

[0058] Surface coverage of precious metal particles: 1.0% or more If the surface coverage of the precious metal particles is less than 1.0%, the current path is insufficient and good electrical conductivity cannot be obtained. Therefore, the surface coverage of the precious metal particles is set to 1.0% or more. The surface coverage of the precious metal particles is preferably 5.0% or more. There is no particular upper limit to the surface coverage of the precious metal particles. The upper limit of the surface coverage of the precious metal particles may be 95%. However, a high surface coverage of the precious metal particles leads to an increase in costs. Therefore, the surface coverage of the precious metal particles is preferably less than 80%.

[0059] Here, the surface coverage of the precious metal particles is the surface coverage of the precious metal particles relative to the surface of the base material, and is calculated by the following formula. [Surface coverage rate of precious metal particles (%)] = [Area of ​​the region where precious metal particles cover the surface of the substrate (mm 2 )]÷[Substrate surface area (mm 2 )] x 100

[0060] (3) Manufacturing method Next, an example of a method for producing a solid oxide fuel cell member according to one embodiment of the present invention will be described.

[0061] First, a ferritic stainless steel substrate to be used as the substrate is prepared. For example, molten steel is produced in a melting furnace such as a converter or an electric furnace. The molten steel is then subjected to secondary refining by ladle refining or vacuum refining to adjust the composition to the above-mentioned composition. The molten steel is then made into a slab by a continuous casting method or an ingot casting-blooming rolling method. From the viewpoints of productivity and quality, the continuous casting method is preferred. The slab is then hot-rolled to produce a hot-rolled steel sheet. The hot-rolled steel sheet may be further subjected to hot-rolled sheet annealing and / or pickling. Hereinafter, when simply referring to hot-rolled steel sheet, it includes not only as-hot-rolled steel sheet (including steel sheet obtained by subjecting as-hot-rolled steel sheet to pickling or the like), but also so-called hot-rolled annealed sheet (including steel sheet obtained by subjecting as-hot-rolled steel sheet to hot-rolled sheet annealing, and steel sheet obtained by further subjecting the steel sheet obtained by subjecting the hot-rolled sheet annealing to pickling or the like). Depending on the application, it is also possible to use the hot-rolled steel sheet as it is as a product (hereinafter also referred to as a hot-rolled product) without performing cold rolling or the like. For example, when manufacturing a housing for a solid oxide fuel cell, the hot-rolled steel sheet can be used as it is as a substrate.

[0062] Next, the hot-rolled steel sheet is cold-rolled to obtain a cold-rolled steel sheet. Next, the cold-rolled steel sheet is subjected to various processes such as finish annealing (cold-rolled sheet annealing) and pickling to obtain a product such as a cold-rolled annealed sheet (hereinafter also referred to as a cold-rolled product). The cold-rolled annealed sheet includes a steel sheet obtained by subjecting an as-cold-rolled steel sheet to finish annealing (cold-rolled sheet annealing), and a steel sheet obtained by further subjecting the steel sheet obtained by subjecting the finish annealing (cold-rolled sheet annealing) to pickling or the like. The atmosphere for the cold-rolled sheet annealing is not particularly limited, and BA (bright) annealing in a reducing atmosphere such as hydrogen may be performed, and pickling may be omitted. Note that before pickling, scale may be removed by shot blasting, mechanical descaling, or the like.

[0063] In the manner described above, a base ferritic stainless steel can be prepared.

[0064] Here, the conditions of each of the above steps may be in accordance with the usual method. For example, when the steel slab is heated before hot rolling, the temperature is preferably 1050 to 1250°C. The hot-rolled sheet annealing is preferably performed in a temperature range of 800 to 1150°C by continuous annealing. The cold rolling may be performed once or two or more times with intermediate annealing in between. From the viewpoint of productivity and required quality, it is preferable to perform two or more times of cold rolling with intermediate annealing in between. In addition, the total reduction rate of the cold rolling is preferably 50% or more, more preferably 60% or more. The finish annealing (cold-rolled sheet annealing) is preferably performed in a temperature range of 850 to 1100°C by continuous annealing. A more preferable temperature range is 900 to 1050°C. Furthermore, depending on the application, after the finish annealing, skin pass rolling or the like may be performed to adjust the shape, surface roughness and material of the steel sheet.

[0065] The surface of the prepared base ferritic stainless steel is then coated with the above-mentioned noble metal particles. For example, a thermal spraying method can be used as the coating method. A noble metal salt solution or a metal particle suspension can be used as the thermal spray material. These can be heated by flame, plasma or electric arc, and sprayed with gas to coat.

[0066] After coating, in order to improve the adhesion between the precious metal particles and the base ferritic stainless steel, a heat treatment may be performed at a temperature of 100 to 500° C. for a time of 1 second to 10 hours.

[0067] In addition, the base ferritic stainless steel may be optionally cut, bent, stretched, drawn, or otherwise processed before or after coating to form it into a desired shape, such as the shape of an interconnector, etc. The coating can be performed before or after forming, or both before and after forming. EXAMPLES

[0068] Steel having the composition shown in Table 1 (the balance being Fe and unavoidable impurities) was melted in a vacuum melting furnace and cast into a 30 kg steel ingot. This steel ingot was heated to 1250°C, and then hot-rolled into a sheet bar having a thickness of 30 mm. This sheet bar was heated to 1150°C, and then hot-rolled to obtain a hot-rolled steel sheet. This hot-rolled steel sheet was hot-rolled at a temperature of 850 to 1100°C, and then ground to obtain a hot-rolled annealed sheet having a thickness of 4.0 mm. Next, the hot-rolled annealed sheet was cold-rolled to obtain a cold-rolled steel sheet. Next, this cold-rolled steel sheet was finish-annealed at a temperature of 850 to 1100°C to obtain a cold-rolled annealed sheet having a thickness of 1.0 mm. Next, the front and back surfaces of the cold-rolled annealed sheet were polished with #800 emery paper, and then degreased with acetone. In addition, test pieces for cross-sectional optical microscope observation were prepared from each cold-rolled annealed sheet, etched with a picric acid saturated hydrochloric acid solution, and observed with an optical microscope at a magnification of 100 times to identify the structure of each cold-rolled annealed sheet. As a result, it was confirmed that each sheet had a ferrite single phase structure (volume fraction of ferrite phase: 100%).

[0069] The cold-rolled annealed sheet thus obtained was used as a substrate and coated with ruthenium metal particles by a flame spraying method to produce samples No. A1 to A5 and No. B2 to B3 in Table 2. For comparison, samples No. B1 and No. B4 in Table 2 were produced as cold-rolled annealed sheets without being coated with precious metal particles.

[0070] Next, the average particle size, coating thickness and surface coverage of the precious metal particles of these samples were measured in the following manner. The results are shown in Table 2.

[0071] That is, 10 random positions on the surface of each sample were observed at a magnification of 1000 times by scanning electron microscopy (hereinafter also referred to as SEM). Next, in the photograph taken by SEM (hereinafter also referred to as SEM photograph), the precious metal particles coated on the surface of the substrate were identified by image analysis, and the area of ​​each precious metal particle was measured. Then, the circle equivalent diameter calculated from the area of ​​each precious metal particle was obtained. The average value of these was taken as the average particle size of the precious metal particles. For reference, the SEM photograph of No. A3 is shown in Figure 1.

[0072] The total area of ​​the precious metal particles in the SEM photograph is calculated as the area (mm 2 The total area of ​​the precious metal particles in the SEM photograph was divided by the total area of ​​the observation region in the SEM photograph to obtain the surface coverage rate of the precious metal particles.

[0073] The coating thickness of the precious metal particles was measured by scraping the precious metal particles and the substrate in the direction perpendicular to the substrate surface using a focused ion beam system (hereinafter also referred to as FIB) using Ga ions, preparing a cross-sectional observation sample of the precious metal particles, and observing the cross-section (observation surface) with an SEM at a magnification of 10,000 times. That is, a cross-sectional observation test piece was taken from each sample so that any five precious metal particles were included as the observation target, and the observation surface was photographed with an SEM to determine the maximum length of the five precious metal particles in the direction perpendicular to the substrate surface (the distance between the upper and lower ends of the precious metal particles in the observation surface in the direction perpendicular to the substrate surface. Note that, in the direction perpendicular to the substrate surface, the end of the precious metal particle close to the surface of the substrate is the lower end, and the end of the precious metal particle opposite to this is the upper end). The average value of these was determined as the coating thickness of the precious metal particles.

[0074] Furthermore, these samples were evaluated for Cr poisoning resistance and electrical conductivity as follows, and the results are shown in Table 2.

[0075] <Evaluation of electrical conductivity> The above sample was cut into a size of 1.0 mm x 20 mm x 20 mm, and the cut sample was subjected to an oxidation treatment in air at 700°C for 2000 hours. Pt paste of 5 mm x 5 mm was applied to the front and back sides of the sample after the oxidation treatment, and the sample was dried by holding it at 700°C for 30 minutes. Next, a Pt mesh (10 mm x 10 mm) to which a Pt wire for applying current and a Pt wire for measuring voltage were spot-welded was placed on each of the front and back sides of the sample where the Pt paste was applied. The sample was then subjected to a 0.1 kgf / cm 2 The specimen was held in a heating furnace heated to 700°C for 30 minutes under a load of 0.5 A / cm. 2 A current was passed through the sample so that the voltage was measured to determine the electrical resistance (contact resistance). The electrical resistance was then determined for each sample (n=3, n = 3) (each sample was measured for electrical resistance three times), and the electrical conductivity was evaluated based on the average value according to the following criteria. Good: The average electrical resistance is 0.1 Ω cm 2 below Poor: The average electrical resistance is 0.1 Ω cm 2 Super

[0076] <Cr toxicity resistance> The above sample was cut to 1.0 mm x 20 mm x 20 mm, and the cut sample was loaded into a quartz sample holder in a quartz tubular furnace. The sample holder was placed in the center of the tubular furnace. Quartz wool was placed downstream of the sample holder to collect Cr evaporated from the sample. Then, the temperature in the tubular furnace was set to 700°C while flowing 15 vol.% H2O + air into the tubular furnace, and the temperature was held at 700°C for 100 hours. After the holding, the total amount of Cr attached to the sample holder and the quartz wool was dissolved in an acid solution, and the Cr concentration in the acid solution was measured by ICP-MS (inductively coupled plasma mass spectrometry). Then, the amount of Cr contained in the acid solution was calculated from the Cr concentration and the amount of acid solution. Then, the amount of Cr evaporated from the sample was calculated by dividing the amount of Cr contained in the acid solution by the surface area of ​​the sample. Then, the Cr poisoning resistance was evaluated according to the following criteria. Good: Cr evaporation amount is 1.0mg / cm2 below Defective: Cr evaporation amount is 1.0mg / cm 2 Super

[0077] [Table 1]

[0078] [Table 2]

[0079] As shown in Table 2, all of the examples of the invention were excellent in electrical conductivity and resistance to Cr poisoning. On the other hand, in the comparative example No. B1, the surface of the substrate was not coated with precious metal particles, and therefore sufficient electrical conductivity was not obtained. In No. B2, the surface coverage of the precious metal particles was below the appropriate range, so sufficient electrical conductivity was not obtained. In No. B3, the Al content of the base ferritic stainless steel was below the appropriate range, so sufficient resistance to Cr poisoning was not obtained. In No. B4, the Al content of the base ferritic stainless steel was below the appropriate range, so sufficient resistance to Cr poisoning was not obtained.

[0080] The above examples are provided merely for illustration and should not be construed as limiting in any way. While various embodiments have been referred to, the terms used herein are terms of description and illustration, rather than terms of limitation. Moreover, although specific means, materials, and embodiments have been referred to, there is no limitation to the subject matter disclosed herein. Rather, the embodiments are intended to cover all functionally equivalent structures, methods, and uses, as falling within the scope of the appended claims. [Industrial Applicability]

[0081] The solid oxide fuel cell member of the present invention can be particularly suitably used as an interconnector, and can also be suitably used as a solid oxide electrolysis cell (also called SOEC) and a solid oxide reversible cell (also called SORC) member.

Claims

1. A solid oxide fuel cell member having a substrate and precious metal particles on a surface of the substrate, The substrate comprises, in mass %, C: 0.025% or less, Si: 0.05-1.00%, Mn: 0.05-1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 14.0-32.0%, Al: 2.50-7.00%, Ni: 0.01 to 1.00% and N: 0.025% or less and the balance being Fe and unavoidable impurities, The average particle size of the precious metal particles is 1 μm or more and 10 μm or less, The coating thickness of the precious metal particles on the substrate is 0.5 μm or more and 10 μm or less, A solid oxide fuel cell member, wherein the surface coverage of the substrate with the noble metal particles is 1.0% or more.

2. 2. The solid oxide fuel cell member according to claim 1, wherein the precious metal particles contain one or more selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru and Os, and alloy particles of these elements.

3. The composition of the ferritic stainless steel further comprises, in mass%, Mo: 3.00% or less, Cu: 0.50% or less, Co: 1.00% or less, W: 3.00% or less, Ti: 0.30% or less, Nb: 1.00% or less, V: 0.50% or less, Zr: 0.50% or less, B: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0100% or less; REM: 0.20% or less 2. The solid oxide fuel cell member according to claim 1, comprising one or more selected from the following:

4. The composition of the ferritic stainless steel further comprises, in mass%, Mo: 3.00% or less, Cu: 0.50% or less, Co: 1.00% or less, W: 3.00% or less, Ti: 0.30% or less, Nb: 1.00% or less, V: 0.50% or less, Zr: 0.50% or less, B: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0100% or less; REM: 0.20% or less 3. The solid oxide fuel cell member according to claim 2, comprising one or more selected from the following:

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