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 that has excellent electrical conductivity and chromium poisoning resistance. [Background technology]

[0002] Fuel cells emit few harmful gases and have high power generation efficiency, which is why they are expected to be applied to a wide range of power generation systems, including large-scale power generation, cogeneration systems, and automotive power sources.

[0003] Among these, solid oxide fuel cells (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, interconnectors (sometimes called separators or bipolar plates) serve to form gas flow paths and connect adjacent cells in a fuel cell stack. Interconnectors also serve to conduct electric current. Therefore, interconnectors are required to have electrical conductivity. Various metal materials have been proposed as materials for use in 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 by containing, by 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 substantially consisting of Fe." has been disclosed.

[0006] Patent Document 2 states: "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%, and the balance consisting of 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] Japanese Patent Application Laid-Open No. 2003-187828 [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 in an interconnector for a solid oxide fuel cell, electrical resistance increases, resulting in a decrease in cell performance.

[0010] Furthermore, 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 the high-temperature environment in which solid oxide fuel cells are used, the Cr-based oxides volatilize and adhere to the electrodes, which can easily cause deterioration in electrode performance (hereinafter also referred to as "Cr poisoning"). In fact, Patent Document 2 does not consider the prevention of Cr poisoning. Therefore, when the metallic material disclosed in Patent Document 2 is used in solid oxide fuel cell components, particularly interconnectors, there is a concern that the performance of the electrodes may deteriorate due to Cr poisoning.

[0011] Similarly, Patent Document 3 does not consider the prevention of Cr poisoning. Therefore, when the metal material disclosed in Patent Document 3 is used for a solid oxide fuel cell component, particularly an interconnector, there is a concern that the performance of the electrode may be deteriorated due to Cr poisoning.

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

[0013] The inventors have conducted extensive research to achieve the above object. the result, (1) A ferritic stainless steel is used as the base material, in which the Cr content of the component composition is controlled to the range of 14.0 to 32.0 mass% and the Al content is controlled to the range of 2.50 to 7.00 mass%, and (2) The surface of the substrate is coated with precious metal particles. Average particle size of precious metal particles: 1 μm or more and 10 μm or less, The coating thickness of the precious metal particles on the substrate (hereinafter also referred to simply as the coating thickness): 0.5 μm or more and 10 μm or less, and Surface coverage rate of precious metal particles to the substrate (hereinafter simply referred to 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. Specifically, in the high-temperature environment in which solid oxide fuel cells are used, a ferritic stainless steel with a composition containing 14.0 to 32.0 mass% Cr and 2.50 to 7.00 mass% Al generates an alumina surface layer on the surface, preventing the formation of Cr-based oxides. As a result, the volatilization of Cr-based oxides is suppressed, preventing Cr poisoning of the electrodes. However, alumina has low electrical conductivity, and if alumina forms on the surface of the substrate, the desired electrical conductivity cannot be achieved. To overcome this issue, a coating of precious metal particles is applied. When the precious metal particles fuse with the surface of the Al-containing ferritic stainless steel, a current path is formed through the alumina surface layer. By controlling the average particle size and coating thickness of these precious metal particles within the above ranges, the precious metal particles continue to protrude from the alumina formed on the surface of the substrate, maintaining the current path. Furthermore, a surface coverage of the precious metal particles above a certain level ensures sufficient current path, resulting in good electrical conductivity. From the above, the inventors believe that by simultaneously satisfying the above (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 further investigations.

[0015] That is, the gist and configuration of the present invention are as follows. 1. A solid oxide fuel cell component having a substrate and precious metal particles on the 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 noble metal particles is 1 μm or more and 10 μm or less, The coating thickness of the noble 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 item 1 above, wherein the noble 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 is further, 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 is further, 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, which contains one or more selected from the following:

[0019] According to the present invention, a member for a solid oxide fuel cell having excellent electrical conductivity and resistance to Cr poisoning can be obtained. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is an example of an SEM photograph of Example No. A3. DETAILED DESCRIPTION OF THE INVENTION

[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 for a solid oxide fuel cell component according to one embodiment of the present invention will be described. Note that the unit of the composition is "% by 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 achieve this 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] Si: 0.05 to 1.00% Si has the effect of improving the oxidation resistance of steel. To achieve this effect, the Si content is set to 0.05% or more. However, if the Si 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, reducing electrical conductivity. For this reason, the Si content is set to 1.00% or less. The Si 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 achieve 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, reducing oxidation resistance. Furthermore, an increase in the thickness of the oxide film may reduce 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 the P content 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 dephosphorization increases 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 desulfurization increases costs, the S content is preferably 0.0001% or more.

[0028] Cr: 14.0 to 32.0% Cr is an important element that assists the formation of alumina on the surface of the base ferritic stainless steel. To achieve this effect, the Cr content is set to 14.0% or more. The Cr content is preferably 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 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 Cr volatilization and preventing Cr poisoning of the electrode. To achieve this 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, making manufacturing 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 this 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 formed at high temperatures, reducing oxidation resistance. 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 Nitrogen (N) is an element that reduces the toughness and workability of steel, and is therefore 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 increases 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 achieve this 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 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 precipitates in steel and has the effect of improving the high-temperature strength of the steel. To achieve this effect, the Cu content is preferably 0.01% or more. However, if the Cu content exceeds 0.50%, the toughness decreases and manufacturability decreases. Therefore, if 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 this 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 this 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 set to 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 achieve this effect, the Ti content is preferably 0.01% or more. However, if the Ti content exceeds 0.30%, coarse Ti(C,N) precipitates are formed, reducing the toughness of the steel. Also, 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 this effect, the Nb content is preferably 0.01% or more. However, if the Nb content exceeds 1.00%, the steel becomes hard and 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 this effect, the V content is preferably 0.01% or more. However, if the V content exceeds 0.50%, coarse V(C,N) precipitates are formed, reducing the toughness of the steel. 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 this effect, the Zr content is preferably 0.01% or more. However, if the Zr content exceeds 0.50%, Zr intermetallic compounds precipitate, reducing the toughness of the steel. Therefore, if Zr is contained, the Zr content should be 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 this effect, the B content is preferably 0.0002% or more. On the other hand, if the B content exceeds 0.0050%, BN is formed, which reduces the workability of the steel. 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 this effect, the Ca content is preferably 0.0002% or more. However, if the Ca content exceeds 0.0050%, surface defects tend to occur in the steel. 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 this effect, the Mg content must be 0.0002% or more. However, if the Mg content exceeds 0.0100%, surface defects tend to occur in the steel. Therefore, if Mg is added, the Mg content must be 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 achieve this 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. However, the base ferritic stainless steel may have a single ferrite phase (volume fraction: 100%).

[0047] Here, the structure is identified (the volume fraction of the ferrite phase is calculated) as follows. Specifically, a test piece for cross-sectional observation is prepared from the base ferritic stainless steel and etched using a picric acid saturated hydrochloric acid solution. Next, the test piece for cross-sectional observation is observed using 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, image processing is used to determine the volume fraction of the ferrite phase for each field of view, 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] Note that the solid oxide fuel cell component according to one embodiment of the present invention includes not only components processed into the shape of components such as interconnectors, but also materials (e.g., plate-shaped materials) before being processed into the shape of components.

[0049] The shape of the base ferritic stainless steel may be, for example, a plate (steel plate) or part. The thickness of the base ferritic stainless steel in the form of a plate (steel plate) or part is not particularly limited. However, from the viewpoints 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 include particles of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os, as well as alloy particles of these elements. Among these, it is preferable to contain noble metals with high melting points (>1500°C), such as Pt, Ir, Rh, Pd, Os, and Ru, and it is particularly preferable to contain Ru. The high-melting-point noble metal ensures long-term operational stability at the high temperatures at which SOFCs operate. The noble metal particles may be composed of one of the above elements, or 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 of two or more of the above elements.

[0052] The precious metal particles coated on the surface of the ferritic stainless steel substrate are present on the surface in the form of discrete islands. Here, the island-like morphology is referred to as "particles." Maintaining the island-like morphology of the precious metal coating, instead of the conventional continuous layer-like coating, allows a) a reduction in the amount of precious metal used and b) minimization of stress between the coating layer and the substrate due to mismatch in thermal expansion coefficients. For high-temperature SOFC applications, it is necessary to avoid peeling of the coating layer by taking advantage of the above b).

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

[0054] Average particle size of precious metal particles: 1 μm to 10 μm 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 stress between the precious metal particles and the base material caused by the mismatch in thermal expansion coefficients may cause the precious metal particles to peel off from the base ferritic stainless steel. If the precious metal particles peel off, the electrical conduction path will be lost and good electrical conductivity will not 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 a current-carrying path. In addition, the coating thickness and surface coverage 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 form on the surface of the ferritic stainless steel substrate in the high-temperature environment in which solid oxide fuel cells are used, covering the precious metal particles. As a result, the electrical conduction 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 prone to peeling off from the surface of the ferritic stainless steel substrate. If the precious metal particles peel off, the electrical conduction 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%, there will be insufficient electrical conduction paths and good electrical conductivity will not 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 will result in 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 noble metal particles is the surface coverage of the noble metal particles relative to the surface of the substrate, 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 )] × 100

[0060] (3) Manufacturing method Next, an example of a method for manufacturing 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 range. The molten steel is then formed 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 form 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 a hot-rolled steel sheet, it includes not only an as-hot-rolled steel sheet (including a steel sheet obtained by subjecting an as-hot-rolled steel sheet to pickling or the like) but also a so-called hot-rolled annealed sheet (including a steel sheet obtained by subjecting an as-hot-rolled steel sheet to hot-rolled annealing, and a steel sheet obtained by further subjecting the steel sheet obtained by the hot-rolled annealing to pickling or the like). Depending on the application, the hot-rolled steel sheet can be used as a product (hereinafter also referred to as a hot-rolled product) without undergoing 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 a substrate as is.

[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 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). Note that 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 above finish annealing (cold-rolled sheet annealing) to pickling or the like. The atmosphere for 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 for each of the above-mentioned steps may be conventional. For example, when a steel slab is heated before hot rolling, the temperature is preferably 1050 to 1250°C. Hot-rolled sheet annealing is preferably performed by continuous annealing in a temperature range of 800 to 1150°C. Cold rolling may be performed once or in two or more passes with intermediate annealing in between. From the standpoint of productivity and required quality, two or more passes with intermediate annealing in between are preferred. Furthermore, the total reduction rate of cold rolling is preferably 50% or more, more preferably 60% or more. Finish annealing (cold-rolled sheet annealing) is preferably performed by continuous annealing in a temperature range of 850 to 1100°C. A more preferred temperature range is 900 to 1050°C. Furthermore, depending on the application, skin-pass rolling or the like may be performed after finish annealing to adjust the shape, surface roughness, and material properties of the steel sheet.

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

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

[0067] Optionally, the ferritic stainless steel substrate before or after coating may be subjected to processing such as cutting, bending, stretching, drawing, etc. to form it into a desired shape, for example, the shape of an interconnector, etc. The coating can be performed before or after forming, or both before and after forming. [Example]

[0068] A steel having the chemical 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 with a thickness of 30 mm. This sheet bar was heated to 1150°C and then hot-rolled to form a hot-rolled steel sheet. This hot-rolled steel sheet was subjected to hot-rolled annealing at a temperature of 850 to 1100°C and then ground to obtain a hot-rolled annealed sheet with a thickness of 4.0 mm. Next, this hot-rolled annealed sheet was cold-rolled to form a cold-rolled steel sheet. Next, this cold-rolled steel sheet was subjected to finish annealing at a temperature of 850 to 1100°C to obtain a cold-rolled annealed sheet with 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. Test specimens for cross-sectional optical microscope observation were prepared from each cold-rolled and annealed sheet, etched with a picric acid saturated hydrochloric acid solution, and observed with an optical microscope at a magnification of 100x to identify the structure of each cold-rolled and 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 steel sheet thus obtained was used as a substrate and coated with ruthenium metal particles by flame spraying to produce samples Nos. A1 to A5 and B2 to B3 in Table 2. For comparison, samples Nos. B1 and B4 in Table 2 were prepared as cold-rolled annealed steel 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 also shown in Table 2.

[0071] Specifically, 10 randomly selected positions on the surface of each sample were observed at 1000x magnification using scanning electron microscopy (hereinafter also referred to as SEM). Next, the precious metal particles coated on the surface of the substrate were identified using image analysis of the SEM photographs (hereinafter also referred to as SEM photographs), and the area of ​​each precious metal particle was measured. The equivalent circle diameter was calculated from the area of ​​each precious metal particle. The average of these values ​​was used 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 noble metal particles in the SEM photograph was calculated as the area (mm 2 The total area of ​​the noble metal particles in the SEM photograph was divided by the total area of ​​the observation region in the SEM photograph, and the resulting value was taken as the surface coverage rate of the noble metal particles.

[0073] The coating thickness of the precious metal particles was measured by scraping the precious metal particles and the substrate in a direction perpendicular to the substrate surface using a focused ion beam system (hereinafter also referred to as FIB) using Ga ions to create cross-sectional observation samples of the precious metal particles, and observing the cross-sections (observation surfaces) with an SEM at 10,000x magnification. Specifically, cross-sectional observation specimens were taken from each sample so that five selected precious metal particles were included as the observation targets. The observation surfaces were then photographed with the 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 closest to the substrate surface is considered the lower end, and the end of the precious metal particle opposite this is considered the upper end). The average of these measurements was then used 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. After the oxidation treatment, a 5 mm x 5 mm Pt paste was applied to the front and back surfaces of the sample, and the sample was dried 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 areas on the front and back surfaces of the sample where the Pt paste had been applied. The sample was then subjected to a pressure of 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 three times), and the electrical conductivity was evaluated using the average value according to the following criteria. Good: 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 into a 1.0 mm × 20 mm × 20 mm size and loaded onto a quartz sample holder in a quartz tubular furnace. The sample holder was located in the center of the furnace. A quartz wool filter was placed downstream of the sample holder to capture Cr evaporating from the sample. Next, the furnace was heated to 700°C and maintained for 100 hours while a 15 vol.% H2O + air mixture was flowed through the furnace. After this period, the Cr adhering to the sample holder and quartz wool was dissolved in an acid solution, and the Cr concentration in the acid solution was measured using an inductively coupled plasma mass spectrometer (ICP-MS). The amount of Cr in the acid solution was calculated from the Cr concentration and the volume of the acid solution. The amount of Cr evaporated from the sample was calculated by dividing the amount of Cr in the acid solution by the surface area of ​​the sample. The Cr poisoning resistance was evaluated according to the following criteria. Good: Cr evaporation amount 1.0mg / cm2 below Poor: Cr evaporation amount 1.0 mg / cm 2 Super

[0077] [Table 1]

[0078] [Table 2]

[0079] As shown in Table 2, all of the inventive examples 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 illustrative purposes and should not be construed as limiting in any way. While reference has been made to various embodiments, the terms used herein are terms of description and illustration, rather than of limitation. Moreover, while reference has been made to particular means, materials, and embodiments, 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 fall 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 member for a solid oxide electrolysis cell (also called SOEC) and a solid oxide reversible cell (also called SORC).

Claims

1. A solid oxide fuel cell component having a substrate and precious metal particles on a surface of the substrate, The substrate is, in mass %, C: 0.025% or less, Si: 0.05-1.00%, 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 noble metal particles is 1 μm or more and 10 μm or less, a coating thickness of the noble metal particles on the substrate is 0.5 μm or more and 10 μm or less; the surface coverage of the noble metal particles with respect to the substrate is 1.0% or more; The solid oxide fuel cell member, wherein the noble metal particles are Ru.

2. 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 claim 1, comprising one or more selected from the following:

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