JP7413867B2 - Coated steel material for solid oxide fuel cell components, solid oxide fuel cell components and manufacturing method thereof - Google Patents

Description

The present invention relates to a coated steel material for solid oxide fuel cell members, a solid oxide fuel cell member, and a method for manufacturing the same.

Solid oxide fuel cells have excellent features such as high power generation efficiency, low generation of SOx, NOx, and _CO2 , good responsiveness to load fluctuations, and compact size. It is expected to be applied to a wide range of power generation systems, including large-scale centralized power generation as an alternative to thermal power generation, distributed power generation in urban areas, and private power generation. In recent years, solid oxide fuel cells that operate at medium to high temperatures of around 700 to 900°C have been developed, and parts for solid oxide fuel cells such as separators, interconnectors, and current collectors are made of solid oxide fuel cells. Properties such as oxidation resistance at high temperatures, electrical conductivity, thermal expansion coefficient close to that of electrolytes and electrodes, low cost, and ease of processing are required. For this reason, a metal base material made of ferritic stainless steel, such as a Fe--Cr alloy, is preferably used as the material. The applicant of the present application has also proposed ferritic stainless steel with excellent oxidation resistance in Japanese Patent Application Publication No. 2007-16297 (Patent Document 1), International Publication No. 2012/144600 (Patent Document 2), and the like.

When Fe-Cr alloys are used for separators, interconnectors, current collectors, etc., oxidation progresses on the metal surface due to the high-temperature oxidizing atmosphere that occurs during the operation of solid oxide fuel cells, resulting in the formation of Cr. An oxide film mainly composed of ₂ O ₃ is formed, and this acts as a protective film to ensure oxidation resistance. However, on the other hand, Cr or Cr compound (hereinafter abbreviated as Cr) volatilizes from the oxide film mainly composed of Cr ₂ O ₃ and redeposit on the electrode, gradually deteriorating the electrode characteristics, which is called Cr poisoning. There is a problem.
To solve this problem, separators, interconnectors, and current collectors are made of a metal base material with a coating having both oxidation resistance and conductivity on the surface.

For example, Patent Document 3 discloses a solid oxide fuel cell that includes as a component a separator whose surface is coated with a Ni--Co alloy. When a Ni-Co alloy coated with a predetermined ratio is subjected to surface treatment (oxidation treatment) for a certain period of time, an oxide (NiCr ₂ O ₄ ) having a spinel structure with excellent conductivity is generated on the surface. Furthermore, it is stated that by coating with the Ni-Co alloy, a chromium oxide (Cr ₂ O ₃ ) oxide film forms a double oxide layer inside the coating, and that the evaporation of chromium can be prevented by the nickel-cobalt coating layer. has been done.

Further, Patent Document 4 discloses a method for manufacturing a fuel cell interconnector in which a film mainly composed of Co oxide is formed on a base material mainly composed of stainless steel. After performing Co plating on the base material, an oxidation process is performed to oxidize the Co plating layer in an oxidizing atmosphere to convert the metal Co plating layer into a Co oxide coating. It is stated that Cr evaporation can be suppressed when a Co oxide film is provided on the surface. On the other hand, if the reaction of metal Co to diffuse into the base material occurs preferentially, the oxidation resistance of the base material will decrease, so the surface roughness (Ra) of the base material should be reduced to 1.2 μm before Co plating. By performing the following polishing process, the oxidation resistance of the base material is made difficult to deteriorate. Co oxide described in Patent Document 7 is generally known to have a spinel structure.

Japanese Patent Application Publication No. 2007-16297 International Publication No. 2012/144600 Japanese Patent Application Publication No. 2012-119126 Japanese Patent Application Publication No. 2011-192546

As described above, spinel-based oxidation is achieved by coating the surface of a metal base material made of an Fe-Cr alloy with metallic Co or Ni-Co alloy and intentionally performing preliminary oxidation treatment to oxidize the surface. It is known to form Co films or Ni--Co oxide films and use them as separators, interconnectors, and current collectors.

When a metal film containing austenite stabilizing elements such as Ni and Mn is coated on a metal base material, such as the Ni-Co alloy described in Patent Document 3, Ni, Mn, etc. diffuse into the metal base material side. This destabilizes the ferrite structure on the surface of the metal base material and stabilizes the austenite structure. When austenite is formed on the surface of a metal base material, the coefficient of thermal expansion increases significantly, which may cause delamination between the metal base material and the coating, or the difference in thermal expansion between the electrodes and electrolyte that make up the cell will increase, resulting in cell damage. There is a risk of causing Furthermore, it is necessary to perform surface treatment (oxidation treatment) for a certain period of time in order to form a Ni--Co oxide film.

The technology disclosed in Patent Document 4 is an interconnector that improves the oxidation resistance of the metal base material of the interconnector and prevents adverse effects on members connected to the interconnector, such as volatilization of chromium components. This is a manufacturing method that reduces the surface roughness of the metal base material and performs preliminary oxidation treatment to form a Co oxide film on the surface so that the Co in the Co plating layer does not diffuse into the metal base material. . That is, the Co oxide film is made of pure Co oxide, and is characterized in that it does not allow Co to diffuse into the metal base material or alloy elements from the metal base material to diffuse into the Co plating layer. However, the denseness of the oxide film of the Co oxide film is not sufficient, and there is a possibility that the oxide film will peel off, and a sufficient effect of suppressing Cr poisoning may not be obtained. Further, it is necessary to perform preliminary oxidation treatment to form a Co oxide film.

As described above, an object of the present invention is to provide a solid oxide fuel cell member that has excellent oxidation resistance and suppresses Cr poisoning. Another object of the present invention is to provide a solid oxide fuel cell member and a method for manufacturing the same.

For the above purpose, the present inventors investigated the composition of a metal base material to which a Co coating is applied. As a result, in a metal base material made of a Fe-Cr-based ferrite alloy with excellent oxidation resistance containing appropriate amounts of Mn and Cu, the metal base material The diffusion of Mn and Cu from the material to the Co coating forms a spinel-type oxide layer of (Co, Mn, Cu) ₃ O ₄ containing Mn and Cu, which suppresses Cr evaporation. A chromia-based oxide layer is formed at the boundary of the (Co, Mn, Cu) ₃ O ₄ spinel-type oxide layer, and a two-layer oxide layer consisting of a spinel-type oxide layer and a chromia-based oxide layer is formed. The present invention was achieved by discovering that the oxidation resistance is improved by the layer and that the metal substrate maintains a ferrite structure even after long-term oxidation.

That is, one aspect of the present invention is a coated steel material for a solid oxide fuel cell member having a metal coating on the surface layer of a metal base material, wherein the metal base material has C: more than 0% by mass % of 0.1 % or less, Al: 0.2% or less, Si: 0.2% or less, Mn: 0.1% or more and 1.0% or less, Cr: 20.0% or more and 26.0% or less, Ni: 0.1 % or more and 1.0% or less, Cu: 0.3% or more and %4.0% or less, W: 1.0% or more and 3.0% or less, La: 0.02% or more and 0.12% or less, Zr: 0.01% or more and 0.5% or less, La+Zr: 0.03% or more and 0.52% or less, the remainder being Fe and unavoidable impurities, and the metal coating has a Co content of 0.5 μm or more and 5.0 μm or less in thickness. This is a coated steel material for a solid oxide fuel cell member, characterized by comprising a layer.
Preferably, the Mn and Cu in the metal base material are Mn: 0.1% or more and 0.5% or less, and Cu: 0.3% or more and 2.0% or less.
Preferably, the metal base material has a plate shape with a thickness of 1.5 mm or less.

Another aspect of the present invention is a solid oxide fuel cell member using the above-described coated steel material for solid oxide fuel cell members, the solid oxide fuel cell member comprising the metal The surface layer of the base material has an oxide film, and the oxide film includes a layer A which is a chromia-based oxide layer, and a spinel type oxide layer formed directly on the layer A and containing Co, Mn, and Cu. This is a member for a solid oxide fuel cell, characterized in that it is comprised of a B layer, which is

Another aspect of the present invention is to apply the above-mentioned coated steel material for solid oxide fuel cell members to a solid oxide fuel cell, and to apply the above-mentioned coated steel material for solid oxide fuel cell members to The metal coating formed on the coated steel material for oxide fuel cell components is changed into an oxide coating to produce a solid oxide fuel cell component, and the oxide coating is a layer A which is a chromia-based oxide layer. and a layer B, which is a spinel type oxide layer containing Co, Mn, and Cu, and is formed directly on the layer A.

According to the present invention, there is provided a highly reliable solid oxide fuel cell member that does not require special preliminary oxidation treatment, has excellent current collection characteristics over a long period of time, and suppresses Cr poisoning, and a method for manufacturing the same. can be obtained. Then, a coated steel material for solid oxide fuel cell members suitable for these purposes can be obtained.

1 is a cross-sectional micrograph of a coated steel material for a solid oxide fuel cell when it is not in use. It is a cross-sectional micrograph of a coated steel material for a solid oxide fuel cell after being heated at 850° C. for 4000 hours. (a) It is an electron diffraction image of [001] incidence obtained from a metal coating region of a coated steel material for a solid oxide fuel cell when it is not in use. (b) It is an electron diffraction simulation image of [001] incidence in a dense hexagonal structure. (a) It is an electron diffraction image of [111] incidence obtained from a metal base material region of a coated steel material for a solid oxide fuel cell after being heated at 850° C. for 4000 hours. (b) It is an electron diffraction simulation image of [111] incidence of ferrite. (a) [110] incident electrons obtained from the upper oxide layer region of the two oxide layers after heating the coated steel material for solid oxide fuel cells at 850°C for 4000 hours This is a diffraction image. (b) An electron diffraction simulation image of [110] incidence in a spinel structure. (a) It is a backscattered electron image of a cross section of a coated steel material for a solid oxide fuel cell after being heated at 850° C. for 4000 hours. (b) It is a surface analysis result of Co by an electron beam microanalyzer. (c) It is a surface analysis result of Mn by an electron beam microanalyzer. (d) It is a surface analysis result of Cu by an electron beam microanalyzer.

The metal base material in the coated steel material for solid oxide fuel cell members of the present invention will be explained. The metal base material is C: more than 0% and 0.1% or less, Al: 0.2% or less, Si: 0.2% or less, Mn: 0.1% or more and 1.0% or less, Cr: 20.0% or more and 26.0% or less, Ni: 0.1% or more and 1.0% or less, Cu: 0.3% or more and 4.0% or less, W: 1.0% or more and 3.0% or less , La: 0.02 or more and 0.12% or less, Zr: 0.01 or more and 0.5% or less, La + Zr: 0.03% or more and 0.5% or less, and the balance is Fe and inevitable impurities. .
The Fe-Cr alloy with this composition is a ferrite alloy, and when it has a Co film on the surface of the metal base material, at the operating temperature of the solid oxide fuel cell, Mn and Cu diffuse into the metal film ( By forming a Co, Mn, Cu) ₃ O ₄ spinel type oxide layer, it is possible to suppress evaporation of Cr, improve oxidation resistance, and suppress deterioration in fuel cell performance.
The reason for specifying the content of each element is as follows. Note that the content of each element is expressed as mass %.

<C: More than 0% but not more than 0.1%>
C is an element that reduces the amount of Cr in the base material by bonding with Cr and reduces the oxidation resistance. Therefore, in order to improve oxidation resistance, it is effective to reduce C as much as possible, and in the present invention, it is limited to a range of 0.1% or less. A preferable upper limit of C is 0.04%.
However, in the case of the coated steel material for solid oxide fuel cell components of the present invention containing Zr, C forms Zr carbide (Zr carbonitride when N is also present), but if C is too low, Zr carbide forms. Even if Zr that does not form a solid solution is dissolved in the ferrite base, surplus Zr may still remain. Excess Zr reacts with Fe to form an intermetallic compound such as a Laves phase and precipitates, reducing oxidation resistance. Therefore, C needs to exceed 0%. The preferable lower limit of C is 0.001%.

<Al: 0.2% or less>
Al forms Al ₂ O ₃ in the form of particles and needles in the metal structure near the chromia-based oxide at the operating temperature of the solid oxide fuel cell. Note that the chromia-based oxide refers to an oxide mainly composed of chromia. This makes the outward diffusion of Cr non-uniform and prevents the formation of a stable chromia-based oxide layer, thereby deteriorating the oxidation resistance. Therefore, in the present invention, the content is limited to a range of 0.2% or less (including 0%).

<Si: 0.2% or less>
Si forms an SiO ₂ film near the interface between the chromia-based oxide layer and the base material at the operating temperature of the solid oxide fuel cell. Since the electrical resistivity of SiO ₂ is higher than that of the chromia-based oxide layer, electrical conductivity is reduced. Furthermore, similarly to the formation of Al ₂ O ₃ described above, oxidation resistance is deteriorated by preventing the formation of a stable chromia-based oxide layer. Therefore, in the present invention, the content is limited to a range of 0.2% or less (including 0%).

<Mn: 0.1% or more and 1.0% or less>
Mn is an element that diffuses from the metal base material into the Co film together with Cu to form a spinel-type oxide at an operating temperature of about 700° C. to 900° C. when the metal base material has a Co film on its surface. A spinel-type oxide layer containing Co and Mn is formed on the outside (surface side) of the chromia-based oxide layer. In this spinel type oxide layer, Cr, which forms a composite oxide that is deposited on ceramic parts such as electrolytes and electrodes of solid oxide fuel cells and deteriorates the performance of the fuel cell, is removed from the steel for solid oxide fuel cells. It has a protective effect that prevents evaporation. Therefore, a minimum content of 0.1% is required.
On the other hand, if it is added excessively, the Mn content in the spinel oxide layer will increase, the oxide film will become thicker, and oxidation resistance and conductivity may deteriorate. Therefore, the upper limit of Mn is 1.0%. A preferable upper limit of Mn is 0.5%.

<Cr: 20.0% or more and 26.0% or less>
Cr is an element necessary to maintain the ferrite structure of the metal base material and to achieve excellent oxidation resistance by forming a dense chromia-based oxide layer at the operating temperature of solid oxide fuel cells. It is. A minimum content of 20.0% is required to obtain good oxidation resistance and electrical conductivity. A preferable lower limit of Cr is 22.0%, and a more preferable lower limit of Cr is 23.0%.
However, excessive addition is not only not very effective in improving oxidation resistance but also causes deterioration of workability, so the upper limit is limited to 26.0%. A preferable upper limit of Cr is 25.0%.

<Ni: 0.1% or more and 1.0% or less>
Adding a small amount of Ni is effective in improving toughness. Further, since it has the effect of improving the hot workability of steel containing Cu, a minimum content of 0.1% is required. On the other hand, Ni is an austenite-forming element, and when it is contained in an excessive amount, it tends to form a ferrite-austenite two-phase structure and increases the coefficient of thermal expansion. Further, when producing ferritic stainless steel like the one of the present invention, for example, if a melted raw material of recycled material is used, it may be unavoidably mixed. If the content of Ni is too large, there is a concern that the bondability will be lowered or the ceramic parts will be damaged due to the difference in thermal expansion with the ceramic parts, so it is not preferable to add or mix a large amount of Ni. Therefore, in the present invention, the upper limit of Ni is set to 1.0%.

<Cu: 0.3% or more and %4.0% or less>
When the metal base material has a Co film on its surface, Cu diffuses from the metal base material into the Co film at an operating temperature of about 700°C to 900°C, and forms Co and Mn on the chromia-based oxide layer. densify spinel-type oxides containing This spinel-type oxide has the effect of suppressing evaporation of Cr from the chromia-based oxide layer. Therefore, a minimum content of 0.3% is required. On the other hand, if Cu is added excessively, the Cu phase will precipitate in the matrix, making it difficult to form a dense chromia-based oxide layer where the Cu phase exists, resulting in decreased oxidation resistance and poor hot workability. The upper limit of Cu was set at 4.0% because there is a possibility that the ferrite structure may decrease or the ferrite structure may become unstable. The preferable upper limit of Cu is 2.0% or less.

<La: 0.02% or more and 0.12% or less>
When added in a small amount, La densifies the oxide film mainly containing Cr and improves adhesion, thereby exhibiting good oxidation resistance, and its addition is indispensable. If La is added less than 0.02%, it will have little effect on improving the density and adhesion of the oxide film, while if it is added more than 0.12%, inclusions such as oxides containing La will increase, making hot processing difficult. Since there is a risk of deterioration in properties, La is set to 0.02% or more and 0.12% or less.

<Zr: 0.01% or more and 0.5% or less>
Zr also has the effect of significantly improving oxidation resistance and electrical conductivity of the oxide film by making the oxide film dense and improving the adhesion of the oxide film when added in a small amount. If Zr is less than 0.01%, it will have little effect on improving the density and adhesion of the oxide film, while if it is added more than 0.5%, many coarse compounds containing Zr will be formed, resulting in poor hot workability and Cold workability may deteriorate. Further, since Zr reacts with Fe to form an intermetallic compound such as a Laves phase and precipitates, reducing oxidation resistance, Zr is set at 0.01% or more and 0.5% or less.

<La+Zr: 0.03% or more and 0.52% or less>
In the present invention, the above-mentioned La and Zr are preferably added in combination because they both have an excellent effect of improving oxidation resistance at high temperatures, but in that case, the total amount of La and Zr is less than 0.03%. On the other hand, if it is added in excess of 0.52%, a large amount of compounds containing La and Zr will be produced, leading to concerns about deterioration of hot workability and cold workability. Therefore, the total content of La and Zr is 0.03% or more and 0.52% or less.

<W: 1.0% or more and 3.0% or less>
Generally, Mo is known as an element that exhibits the same effects as W on solid solution strengthening and the like. However, compared to Mo, W has the effect of moderately suppressing the outward diffusion of Cr in the metal base material of the Fe-Cr ferrite alloy when oxidized at the operating temperature of the solid oxide fuel cell. It is effective in suppressing the excessive growth of a dense chromia-based oxide layer and maintaining a stable protective effect for a long time. Therefore, in the present invention, W alone is essential.
By appropriately suppressing the outward diffusion of Cr in the metal base material of the Fe-Cr-based ferrite alloy by adding W, it is possible to suppress the decrease in the amount of Cr inside the alloy after the formation of the chromia-based oxide layer. . As a result, a dense chromia-based oxide layer is maintained for a long time, thereby preventing abnormal oxidation of the alloy and maintaining excellent oxidation resistance for a long time. In order to exhibit this effect, a minimum content of 1.0% is required. However, if W is added in an amount exceeding 3.0%, hot workability deteriorates, so the upper limit of W is set at 3.0.

In the present invention, elements other than those mentioned above are Fe and inevitable impurities. Typical impurities and their preferred upper limits are listed below. In addition, since it is an impurity element, the preferable lower limit of each element is 0%.
<Mo: 0.2% or less>
Mo is not actively added because it lowers the oxidation resistance, but the content is limited to 0.2% or less since it does not significantly affect the oxidation properties.
<S: 0.015% or less>
S forms sulfide-based inclusions with rare earth elements, lowering the effective amount of rare earth elements that have an effect on oxidation resistance, and not only reducing oxidation resistance but also improving hot workability and surface texture. To avoid deterioration, it is preferable to keep the content to 0.015% or less. Preferably, it is 0.008% or less.
<P: 0.04% or less>
P is an element that is more easily oxidized than Cr, which forms an oxide film, and degrades oxidation resistance, so it is preferably limited to 0.04% or less. The content is preferably 0.03% or less, more preferably 0.02% or less, and even more preferably 0.01% or less.
<B: 0.003% or less>
B increases the growth rate of the oxide film at high temperatures of about 700° C. or higher and deteriorates the oxidation resistance. Furthermore, contact resistance is degraded by increasing the surface roughness of the oxide film and reducing the contact area between the oxide film and the electrode. Therefore, B is preferably limited to 0.003% or less, and preferably reduced to 0% as much as possible. The upper limit is preferably 0.002% or less, more preferably less than 0.001%.
<H: 0.0003% or less>
If H is present in excess in the Fe-Cr-based ferrite matrix, it tends to gather in defective areas such as grain boundaries, which may cause hydrogen embrittlement and cause cracks during manufacturing. It is best to limit it to less than %. More preferably, it is 0.0002% or less.

Next, the metal coating formed on the surface layer of the metal base material in the coated steel material for solid oxide fuel cell members of the present invention will be explained.
The metal coating of the present invention includes a Co layer, and the Co layer consists of Co and other inevitable impurities. The coated steel material for solid oxide fuel cells of the present invention having this metal coating forms a spinel-type oxide layer containing Co, Mn, and Cu at an operating temperature of about 700°C to 900°C, and forms a spinel-type oxide layer containing Co, Mn, and Cu. Contributes to Cr poisoning resistance and oxidation resistance.
Among the inevitable impurities, when Ni, which is an austenite stabilizing element, diffuses into the metal base material, an austenite phase is formed near the surface of the metal base material, the thermal expansion coefficient increases, and the metal base material and oxide It is a harmful element because it causes delamination of the coating. Therefore, Ni is preferably 0.2% or less, more preferably 0.1% or less. Mn is also an austenite stabilizing element, but it has a smaller influence than Ni, and its inclusion in small amounts can be tolerated. Although it is also effective in forming spinel-type oxides containing Co and Mn, Mn is not present in the metal base material. When containing Mn, it is not necessary to contain Mn in the Co film, and since a Co film that does not contain Mn has better manufacturability, Mn is preferably 0.5% or less, more preferably 0.1%. % or less is better.

As the method for forming the metal coating, any method that forms a dense coating with excellent adhesion to the metal base material can be selected. Preferred film forming methods include electroplating and electroless plating, since a thin film can be formed relatively easily.

In an unused state as a coated steel material for solid oxide fuel cells, the thickness of the metal coating is preferably 0.5 to 5.0 μm. If it is less than 0.5 μm, the spinel type oxide film becomes thin and the effect of suppressing Cr evaporation becomes insufficient. Therefore, the lower limit is set to 0.5 μm. A preferable lower limit of the metal coating thickness is 1.0 μm, and a more preferable lower limit of the metal coating thickness is 1.5 μm. On the other hand, if it exceeds 5.0 μm, the oxide film becomes thick and the conductivity decreases, and there is a risk that the oxide layer may peel off due to thermal cycles during repeated operations of the solid oxide fuel cell. Therefore, the upper limit is set to 5.0 μm. A more preferable upper limit of the thickness of the metal coating is 4.5 μm.

Since atoms diffuse at grain boundaries faster than within grains, diffusion of Mn and Cu in the metal substrate into the metal coating is promoted at the operating temperature of the solid oxide fuel cell. Therefore, it is preferable that the crystal grains of the metal coating have crystal grain boundaries in an orientation close to perpendicular to the surface of the metal base material in an unused state as a coated steel material for a solid oxide fuel cell. At this time, "having grain boundaries in an orientation close to perpendicular to the surface of the metal base material" means that the boundary between the metal base material and the metal coating in coated steel is magnified using an electron microscope, as shown in Figure 1. This means that the grain boundaries observed in the metal coating are at an angle of 0° to 45° with respect to the vertical direction of the interface between the metal base material and the metal coating.

After the metal coating is formed, when it is unused as a coated steel material for solid oxide fuel cells, the Co metal coating has a close-packed hexagonal crystal structure at room temperature, and the lattice constant of the (001) plane is It is known to be about 0.25 nm. On the other hand, the closest atomic distance of the (110) plane of the Fe-Cr-based ferrite alloy with a body-centered cubic structure, which is the metal base material, is about 0.25 nm, which is very close to the lattice constant of Co, making it a good choice. Film formation is possible with orientational relationships. This is also advantageous for film adhesion and crystal orientation control. If a Co film contains many impurity elements or alloying elements, the lattice constant will change, and there is a concern that the adhesion to the metal substrate will change. Therefore, the Co film has a close-packed hexagonal crystal structure. It is preferable that you do so.

Next, the reason for defining the range of plate thickness in the metal base material of the coated steel material for solid oxide fuel cell components of the present invention will be described.
The metal base material of the present invention is provided by rolling, and its thickness is preferably 1.5 mm or less. It is generally known that the oxidation resistance of alloys used in high-temperature environments decreases as the plate thickness becomes thinner, and that it more significantly reflects the properties of the alloy material. The present invention can improve the oxidation resistance particularly in thin plates by achieving the above-mentioned alloy composition. Therefore, the preferable upper limit of the plate thickness of the coated steel material for solid oxide fuel cells of the present invention was set to 1.5 mm. It goes without saying that even when the plate thickness is over 1.5 mm, the oxidation resistance of the coated steel material for solid oxide fuel cells can be improved by achieving the alloy composition of the present invention.

By using the coated steel material for solid oxide fuel cell members of the present invention, Mn and Cu in the metal base material can be A spinel type oxide layer containing Co, Mn and Cu is formed by diffusing to the coating side. Furthermore, a chromia-based oxide layer is formed at the boundary between the metal base material and the spinel-type oxide layer. This two-layer oxide film structure provides excellent oxidation resistance and suppresses Cr poisoning. In other words, by using the coated steel material for solid oxide fuel cell components of the present invention, as shown in FIG. A solid oxide fuel cell member that suppresses poisoning can be obtained. At this time, the oxide film is composed of layer A, which is a chromia-based oxide layer, and layer B, which is a spinel-type oxide layer that is formed directly on layer A and contains Co, Mn, and Cu.
The B layer, which is a spinel type oxide layer and is formed directly above the A layer, which is a chromia-based oxide layer, is an oxide layer containing Co as a main component. A spinel-type oxide layer made only of Co does not have sufficient density or stability of the oxide film, and if the thickness exceeds about 1 μm, there is a concern that peeling may occur. A spinel type oxide layer containing Co, Mn and Cu is formed by diffusion and oxidation of Mn and Cu from a metal base material made of a Fe-Cr based ferrite alloy containing Mn and Cu defined in the present invention into a Co metal film. When formed directly on layer A, the adhesion, density, and stability of the spinel oxide layer improve, and it becomes difficult to peel off even when the thickness increases. The conductivity of the material also improves.

As a result of the above, a solid oxide fuel cell member having an oxide film on the surface layer of a metal base material, wherein the metal base material has C: more than 0% and 0.1% or less in mass %, Al : 0.2% or less, Si: 0.2% or less, Mn: 0.1% or more and 1.0% or less, Cr: 20.0% or more and 26.0% or less, Ni: 0.1% or more1. 0% or less, Cu: 0.3% or more and 4.0% or less, W: 1.0% or more and 3.0% or less, La: 0.02% or more and 0.12% or less, Zr: 0.01% 0.5% or less, La+Zr: 0.03% or more and 0.52% or less, and the balance is Fe and unavoidable impurities. and a layer B, which is a spinel-type oxide layer containing Co, Mn, and Cu, formed directly above the solid oxide fuel cell member.
Preferably, the above-mentioned Mn and Cu are Mn: 0.1% or more and 0.5% or less, and Cu: 0.3% or more and 2.0% or less, in terms of mass %. Preferably, the metal base material is in the form of a plate with a thickness of 1.5 mm or less.

The present invention will be explained in more detail in the following Examples, but the present invention is not limited by these Examples.
A steel ingot was produced from the metal base material of the present invention using a vacuum induction furnace or a vacuum refining furnace. During vacuum melting or vacuum refining, melting was performed while controlling the operating conditions in order to keep C, Si, Al, and impurity elements low within the specified range. The operating conditions referred to here are, for example, operating conditions that include careful selection of raw materials, high vacuum atmosphere in the furnace, Ar bubbling, etc., either singly or in combination.
The obtained steel ingot had a mass percentage of C: 0.02%, Al: 0.053%, Si: 0.08%, Mn: 0.27%, Cr: 24.05%, Ni: 0. 59%, Cu: 0.9%, W: 2.02%, Zr: 0.21%, La: 0.06%, the balance being Fe and unavoidable impurities. Among the unavoidable impurities, Mo, P, B and H were in the ranges of Mo≦0.2%, P≦0.04%, B<0.001%, and H≦0.0003%, respectively.
Thereafter, the steel ingot was processed into a size of 1 mm thick by plastic working such as hot forging, hot rolling, and cold rolling, and then annealed at 950° C. for several minutes to obtain an annealed material.

A plate-shaped test piece of 10 mm (w) x 10 mm (l) x 1 mm (t) was cut out from the above annealed material, and the surface of the plate-shaped test piece was polished to #1000 using sandpaper. Thereafter, Co coatings having thicknesses of 0.5 μm, 1.0 μm, and 4.0 μm were plated on the surface of the plate-shaped test piece to obtain coated steel materials shown in Table 1. At this time, a plate-shaped test piece without Co plating was prepared as a comparative example.

Various tests were conducted using the above plate-shaped test piece.
First, a plate-shaped test piece was heat-treated at 850° C. for 500 to 5000 hours in the atmosphere, and then its weight before and after oxidation was measured. In addition, the presence or absence of peeling of the oxide film was visually observed for the test pieces heated at 850° C. for 5000 hours.
Next, regarding the test pieces shown in Table 1, the degree of suppression of Cr evaporation was confirmed using the following test method. An alumina ring was placed on the test piece, and La ₁ -xSrxMnO ₃ (hereinafter referred to as LSM) powder, which is suitably used for the air electrode of solid oxide fuel cells, was placed inside the alumina ring, and the absolute humidity was 10%. Heating was carried out for 30 hours in an atmosphere controlled at a heating temperature of 850°C. Thereafter, the amount of Cr contained in the LSM powder was measured by ICP analysis. Table 2 shows the weight gain by oxidation, the presence or absence of peeling of the oxide film, and the amount of Cr evaporated in the above measurements.

No. defined in the present invention. The coated steel materials for solid oxide fuel cell components Nos. 1 to 3 are Comparative Example No. 1 to 3. Compared to No. 4, the weight gain due to oxidation at 500 hours is large. This is because the Co film of the coated steel material changes into a spinel type oxide film at the initial stage of oxidation, which includes an oxidation increase in weight. When discussing the oxidation resistance of steel materials that are exposed to a high-temperature oxidizing atmosphere for long periods of time in solid oxide fuel cells, it is appropriate to ignore this oxidation increase in weight during the initial stage of oxidation. Therefore, based on the weight at 500 hours, and looking at the weight increase by oxidation up to 5000 hours, No. The coated steel materials for solid oxide fuel cells of Nos. 1 to 3 are Comparative Example No. It can be seen that the weight increase due to oxidation is smaller than that of Sample No. 4, and the oxidation resistance is improved. Furthermore, no peeling of the oxide film was observed in any of the test pieces after the heat treatment. However, No. Among the coated steel materials 1 to 3, No. The Co-coated steel material of No. 2 with a thickness of 1.0 μm has the largest oxidation weight increase after 5000 hours based on the 500 hour time point. This is No. Since the 0.5 μm Co-coated steel material of No. 1 has a thin Co coating layer, the increase in Co oxidation amount is small; The 4.0 μm Co-coated steel in No. 3 has a thick Co coating layer, so a spinel-type oxide layer with a stable thickness is initially formed, and the growth rate is slow, resulting in a low oxidation weight gain. No. Although a slightly thicker spinel-type oxide layer was formed on the 1.0 μm Co-coated steel material in No. 2, the thickness was insufficient to sufficiently reduce the growth rate, resulting in a large oxidation increase. it is conceivable that.

From Table 2, No. defined in the present invention. The coated steel materials for solid oxide fuel cells of Nos. 1 to 3 are Comparative Example No. 4, it is clear that the amount of chromium evaporation is significantly suppressed at the initial stage of oxidation and after high-temperature, long-term oxidation. However, the thinnest 0.5 μm Co-coated steel material No. In No. 1, Cr evaporation was detected, albeit slightly. Among the coated steel materials No. 1 to 3, the results were slightly inferior in terms of suppressing Cr evaporation.
From the above results, in order to achieve both high levels of oxidation resistance and suppression of Cr evaporation, the Co coating thickness is preferably 1.5 μm or more.

No. of Table 1 Regarding the test piece No. 3, the metal base material and metal coating were observed using a transmission electron microscope. The obtained photograph is shown in Figure 1. The metal coating has grain boundaries in a direction perpendicular to the metal substrate. Further, FIG. 3 is an electron diffraction image of [001] incidence obtained from the metal coating region, and from the coincidence with the electron diffraction simulation image, it can be seen that the metal coating has a dense hexagonal structure.

No. of Table 1 Regarding the test piece No. 3, the metal base material and oxide film after heating at 850° C. for 4000 hours were observed with a transmission electron microscope. The obtained photograph is shown in Figure 2. By heating in the atmosphere, a two-layer oxide film is formed, which is a chromia-based oxide layer and a spinel-type oxide layer in this order from the metal substrate side. At this time, FIG. 4 is an electron diffraction image of the [111] incident on the metal base material, which is the region 5 in FIG. I can see that you are holding it. Further, an electron diffraction image of [110] incidence obtained from the region 3 in FIG. 2 is shown in FIG. 5, and it can be confirmed from the coincidence with the electron diffraction simulation image that it has a spinel type structure.

No. of Table 1 After heating the test piece No. 3 at 850°C for 4000 hours, Ni plating was applied to prevent the oxide layer from peeling off due to processing, and the metal base material and oxide film were observed using a scanning electron microscope and Co, Mn using an electron beam microanalyzer. , conducted a surface analysis of Cu. The obtained photograph is shown in FIG. By comparing the backscattered electron image and the surface analysis of each element, it can be confirmed that the region of the spinel type oxide layer contains Mn and Cu in addition to Co.

1 Metal coating 2 Metal base material 3 Spinel type oxide layer 4 Chromia type oxide layer 5 Metal base material 6 Ni plating

Claims (4)

A coated steel material for solid oxide fuel cell components having a metal coating on the surface layer of a metal base material, wherein the metal base material has C: more than 0% and 0.1% or less, Al: 0.2% by mass. % or less, Si: 0.2% or less, Mn: 0.1% or more and 1.0% or less, Cr: 20.0% or more and 26.0% or less, Ni: 0.1% or more and 1.0% or less, Cu: 0.3% to 4.0%, W: 1.0% to 3.0%, La: 0.02% to 0.12%, Zr: 0.01% to 0.0%. 5% or less, La+Zr: 0.03% or more and 0.52% or less, the remainder being Fe and unavoidable impurities, and the metal coating is characterized by comprising a Co layer with a thickness of 0.5 μm or more and 5.0 μm or less. Coated steel materials for solid oxide fuel cell components. The solid oxide according to claim 1, wherein the Mn and Cu are 0.1% or more and 0.5% or less, and Cu: 0.3% or more and 2.0% or less in mass %. Coated steel material for fuel cell parts. The coated steel material for a solid oxide fuel cell member according to claim 1 or 2, wherein the metal base material has a plate shape with a thickness of 1.5 mm or less . Applying the coated steel material for solid oxide fuel cell members according to claims 1 to 3 to a solid oxide fuel cell,
Under the operating environment of the solid oxide fuel cell, the metal coating formed on the coated steel material for solid oxide fuel cell members is changed into an oxide film to form a solid oxide fuel cell member;
The oxide film includes a layer A which is a chromia-based oxide layer,
A method for manufacturing a solid oxide fuel cell member, comprising: a layer B, which is a spinel type oxide layer containing Co, Mn, and Cu, and is formed directly above the layer A.