Method for producing a stainless steel substrate and its use

Abstract

Use of a stainless steel substrate for a fuel cell separator, wherein stainless steel means steel containing 1.2 wt% or less C and 10.5 wt% or more Cr, wherein the stainless steel substrate contains Nb in a solid solution state, the stainless steel substrate contains Nb in a range of 0.05 to 0.50 wt%, and the number of precipitates of Nb-containing intermetallic compounds having a particle diameter of 2 µm or more, determined in an image of size 50 µm long × 50 µm wide by examining the stainless steel substrate using EPMA, is five or fewer.

Description

BACKGROUND Technical area

[0001] The present disclosure relates to a stainless steel substrate for use as a fuel cell separator. The present disclosure also relates to a fuel cell separator. Furthermore, the present disclosure relates to a fuel cell. Finally, the present disclosure relates to a method for producing a stainless steel substrate for use as a fuel cell separator. State of the art

[0002] A cell of a polymer electrolyte fuel cell comprises a membrane electrode assembly (MEA), which includes an ion-permeable electrolyte membrane, an anode-side catalyst layer (electrode layer), and a cathode-side catalyst layer (electrode layer) sandwiching the electrolyte membrane. Gas diffusion layers (GDLs) for supplying a fuel gas or an oxidizing gas and collecting electricity generated by an electrochemical reaction are formed on both sides of the membrane electrode assembly. The membrane electrode assembly, which has the GDLs arranged on both sides, is called a MEGA (membrane electrode and gas diffusion layer assembly), and the MEGA is sandwiched between or embedded by a pair of separators.The MEGA is the power generation section of the fuel cell, and if no gas diffusion layers are present, the membrane electrode assembly is the power generation section of the fuel cell.

[0003] As a stainless steel used in a polymer electrolyte fuel cell, JP 2010-205443 A discloses stainless steel for a polymer electrolyte fuel cell separator with a small amount of ions dissolved at high voltage, containing: C: 0.03% or less, N: 0.03% or less, Si: 0.01 to 2.0%, Mn: 0.01 to 2.0%, Al: 0.001 to 0.3%, Cr: 20 to 35%, Mo: 4.0% or less, and Nb: 0.2 to 2.0% by mass, the remainder being Fe and unavoidable impurities, and furthermore the amount of Cr, the amount of Nb, and the amount of Mo comply with the relationship of a predetermined formula. Furthermore, JP 2010-205443 A describes that Nb is an effective element for fixing C and N in steel as a carbonitride to improve corrosion resistance and press formability.

[0004] Furthermore, International Publication No. WO 2016 / 052622 discloses a ferritic stainless steel material having a predetermined chemical composition in which a value calculated by a predetermined formula is 20 to 45%, and boride-based metallic precipitates or precipitates of the M2B type are dispersed in a parent phase containing only a ferrite phase and are exposed to the surface. International Publication No. WO 2016 / 052622 also describes that Nb is an optionally added element in the invention of International Publication No. WO 2016 / 052622, but is an element for stabilizing C and N in steel. SUMMARY

[0005] As described above, it is known that Nb is added as a sensitization inhibitor to a stainless steel substrate used as a fuel cell separator. Sensitization here is a phenomenon in which the chromium concentration decreases along the grain boundaries in a metal, and chromium-deficient or chromium-deficient regions (sections with low chromium concentration) are formed. Sensitization is caused by the fact that carbon, present as an impurity around the grain boundaries, forms metal carbides (Cr₂₃C₆ and similar compounds) with chromium, accumulating chromium around the grain boundaries.

[0006] Even when a stainless steel substrate, whose corrosion resistance is improved by the inclusion of Nb as a sensitization inhibitor, is used as a fuel cell separator, corrosion can still occur in a corrosive environment. This is especially true when a polymer electrolyte fuel cell separator is placed in a harsh, corrosive environment for stainless steel, including the solution of F - -ions from the solid polymer membrane, the entry of Cl - -ions from the outside air, and a low pH due to the concentration of H + When -ions are introduced into the generated water, the aforementioned problem becomes clearly apparent. Therefore, a stainless steel substrate, as used in a fuel cell separator, is required to exhibit better corrosion resistance.

[0007] Accordingly, the present disclosure provides a stainless steel substrate used for a fuel cell, which contains Nb and is excellent in terms of corrosion resistance.

[0008] The present inventors have carefully investigated and discovered for the first time that intermetallic compounds containing Nb, i.e., Nb-containing intermetallic compounds, are precipitated in an Nb-containing stainless steel substrate, that the precipitates or precipitates of these Nb-containing intermetallic compounds dissolve as metal ions in a corrosive environment, and that pitting corrosion occurs in the stainless steel substrate with these dissolved particles, which represent starting points.

[0009] In particular, for example, precipitates or precipitates of Nb-containing intermetallic compounds are present in a commercially available, Nb-containing stainless steel substrate (e.g., SUS447J1L), as seen in the TEM photography of Fig. Figure 1 shows that the precipitates of Nb-containing intermetallic compounds are particularly prevalent around or at the grain boundaries. As shown in Fig. As shown in Figure 2, when these precipitates of Nb-containing intermetallic compounds are introduced into the corrosive environment of a fuel cell, which contains acid, fluoride ions, chloride ions, and similar substances, the precipitates dissolve as metal ions. Subsequently, corrosion progresses with these dissolved particles, which represent the starting points, and pitting corrosion occurs in the stainless steel substrate. In particular, this shows Fig.2(A) a state in which a precipitation of an Nb-containing intermetallic compound exists in a stainless steel substrate. Next, as in Fig. As shown in Figure 2(B), this precipitation of the Nb-containing intermetallic compound dissolves in the generated water, which contains an acid, fluoride ions, chloride ions, and the like. In particular, a voltage is applied during the operation of a fuel cell, and therefore the dissolution of the precipitation likely continues. Next, as shown in Figure 2(B), the following occurs: Fig. Figure 2(C) shows pitting corrosion with a hole formed by the dissolution of the precipitate as a starting point.

[0010] The present inventors obtained a stainless steel substrate, in which essentially no precipitates of Nb-containing intermetallic compounds are present, by heating a stainless steel substrate to dissolve precipitates of Nb-containing intermetallic compounds and subsequently quenching the stainless steel substrate. The present inventors then discovered that this stainless steel substrate, which essentially contains no precipitates of Nb-containing intermetallic compounds, is a fuel cell separator with excellent corrosion resistance and arrived at the embodiments.

[0011] Examples of aspects of the embodiments are described below. (1) A stainless steel substrate used for a fuel cell separator, containing Nb in a mixed crystal state or a solid solution state, and containing essentially no precipitation of an Nb-containing intermetallic compound. (2) The stainless steel substrate according to point ( 1 ), which contains Nb in a range of 0.05 to 0.50 mass %. (3) A fuel cell separator containing a stainless steel substrate, wherein the stainless steel substrate contains Nb in a state of solid solution, and essentially contains no precipitation of an Nb-containing intermetallic compound. (4) The fuel cell separator according to point ( 3 ), wherein the stainless steel substrate contains Nb in a range of 0.05 to 0.50 wt%. (5) A fuel cell comprising: the fuel cell separator according to point ( 3 ) or ( 4 ); and a solid electrolyte membrane. (6) The fuel cell according to point ( 5 ), wherein the solid electrolyte membrane contains a fluorine-based electrolyte resin. (7) A method for producing a stainless steel substrate for use as a fuel cell separator, comprising: Heating a stainless steel substrate containing a precipitate of an Nb-containing intermetallic compound in an inert atmosphere to dissolve the Nb-containing intermetallic compound; and Quenching the stainless steel substrate after heat treatment. (8) The method for producing a stainless steel substrate according to point ( 7 ), comprising the production of the stainless steel substrate containing the precipitation of the Nb-containing intermetallic compound, by means of the steps comprising Melting a raw material made of stainless steel, which contains at least Nb, Casting a stainless steel substrate from the molten raw material, Hot rolling of the cast stainless steel substrate, Cold rolling of the hot-rolled stainless steel substrate, and Pickling of the cold-rolled stainless steel substrate. Advantageous effect of the invention

[0012] The present disclosure can provide a stainless steel substrate which is used for a fuel cell separator containing Nb and exhibiting excellent corrosion resistance. List of characters Fig. Figure 1 is a TEM image of a stainless steel substrate; Fig. Figure 2 is a schematic diagram to explain a flow in which pitting corrosion occurs with a hole formed by the dissolution of a precipitate of an Nb-containing intermetallic compound, which is a starting point; Fig.Figure 3 is a schematic diagram showing examples of the arrangements or configurations of devices or apparatus used in a heat treatment step and a quenching step in a process for producing a stainless steel substrate according to the embodiments; Fig. Figure 4 is a schematic cross-sectional view to explain an example of the arrangement of a fuel cell according to the embodiments; Fig. Figure 5 is a diagram showing the temperature profiles of the heat treatment and quenching steps in the examples or comparison examples; Fig. Figure 6 is a schematic cross-sectional view to explain the arrangement of a gap-forming element used in a pitting corrosion resistance test in the examples; Fig. Figure 7 is a diagram showing an EPMA photograph of a stainless steel substrate. E1shows which was obtained in Example 1 (950 °C, quenching); Fig. Figure 8 is a diagram which shows an EPMA photograph of a stainless steel substrate. E4 shows which was obtained in Example 4 (1150 °C, quenching); Fig. Figure 9 is a diagram which shows an EPMA photograph of a stainless steel substrate. C2 shows which in comparison example 2 (1150 °C, air cooling) was obtained; and Fig. Figure 10 is a diagram which shows an EPMA photograph of a stainless steel substrate. C3 shows which in comparison example 3 (SUS447J1L) was obtained. DETAILED DESCRIPTION

[0013] Aspects of the embodiments are described below. (stainless steel substrate)

[0014] One aspect of the embodiments relates to a stainless steel substrate used for a fuel cell separator, which contains Nb in a state of solid solution or mixed crystal and essentially contains no precipitates of Nb-containing intermetallic compounds.

[0015] The stainless steel substrate according to the embodiments contains Nb, and therefore sensitization is suppressed. Furthermore, in the stainless steel substrate according to the embodiments, Nb is mainly present in a solid solution state within the substrate, and the stainless steel substrate according to the embodiments contains essentially no precipitates of Nb-containing intermetallic compounds. Therefore, there are essentially no particles that can detach and serve as starting points for corrosion in a corrosive environment. Consequently, the occurrence of corrosion can be suppressed in the stainless steel substrate according to the embodiments, even in a corrosive environment such as a fuel cell, particularly in the highly corrosive environment of a polymer electrolyte fuel cell or similar device.

[0016] As used here, “contains essentially no precipitates of Nb-containing intermetallic compounds” means that the stainless steel substrate according to the embodiments contains no precipitates of Nb-containing intermetallic compounds at all, or that precipitates of Nb-containing intermetallic compounds are present only to such an extent that the effectiveness of the embodiments is not impeded, even if they are present. In other words, “contains essentially no precipitates of Nb-containing intermetallic compounds” means that the stainless steel substrate according to the embodiments may contain precipitates of Nb-containing intermetallic compounds to such an extent that the effectiveness of the embodiments is not impeded.As used here, precipitations of Nb-containing intermetallic compounds refer to precipitations containing Nb at a concentration of 0.5 wt% or more.

[0017] As used here, stainless steel means steel which contains 1.2 wt% or less C and 10.5 wt% or more Cr, as defined in the Japanese Industrial Standards (JIS).

[0018] In some embodiments, the Nb content in the stainless steel substrate is 0.05 wt% or more and 0.50 wt% or less. At Nb content of 0.05 wt% or more, the function of Nb as a sensitization inhibitor can be demonstrated effectively. At Nb content of 0.50 wt% or less, the formation of precipitates of Nb-containing intermetallic compounds can be effectively suppressed. In some embodiments, the Nb content in the stainless steel substrate is 0.10 wt% or more. In some embodiments, the Nb content in the stainless steel substrate is 0.40 wt% or less, or 0.30 wt% or less.

[0019] In some embodiments, "contains substantially no precipitates of Nb-containing intermetallic compounds" means that the number of precipitates of Nb-containing intermetallic compounds having a particle diameter of 2 µm or more is five or fewer (for example, three or fewer) in an image (size: 50 µm long × 50 µm wide) obtained by examining the stainless steel substrate using EPMA (magnification: 1000). The particle diameter means the diameter of a circle with the same area as a precipitate of an Nb-containing intermetallic compound (equivalent circle diameter) in the image. The particle diameter can be calculated, for example, using commercially available software. Examples of such software may include WinRoof.

[0020] In some embodiments, the stainless steel substrate contains Fe as the main component, and contains 18 to 30 wt% Cr, 0 to 2.0 wt% Mo, 0 to 0.02 wt% C, and 0 to 0.02 wt% N, 0 to 0.1 wt% Cu, 0 to 0.05 wt% Al, 0 to 0.4 wt% Si, 0 to 0.001 wt% S, 0 to 0.03 wt% P, 0 to 0.1 wt% Mn, and 0.05 to 0.50 wt% Nb.

[0021] The stainless steel substrate is not particularly limited and can be, for example, austenitic, ferritic, or duplex austenitic-ferritic.

[0022] The shape of the stainless steel substrate is not particularly limited, and is, for example, a plate shape.

[0023] The stainless steel substrate can have a protective film, such as a metal oxide film, on its surface, which differs from an oxide film that forms naturally on the surface of the stainless steel substrate. The metal oxide film can be formed, for example, by a physical vapor deposition (PVD) process using sputtering, vacuum deposition, ion deposition, ion plating, or similar methods. Examples of metal oxide films include tin oxide, which has high electrical conductivity. (Method for producing a stainless steel substrate)

[0024] One aspect of the embodiments is a method for producing a stainless steel substrate for use as a fuel cell separator, comprising a heat treatment step of heating a stainless steel substrate containing precipitates of Nb-containing intermetallic compounds under an inert gas atmosphere to dissolve the Nb-containing intermetallic compounds; and a quenching step of quenching the stainless steel substrate after the heat treatment step. By means of the embodiments, a stainless steel substrate containing Nb in a solid solution state and substantially free of precipitates of Nb-containing intermetallic compounds can be obtained.

[0025] In the heat treatment step, a stainless steel substrate containing precipitates of nitrogen-containing intermetallic compounds is heated under an inert gas atmosphere to dissolve the nitrogen-containing intermetallic compounds. Heating the stainless steel substrate under an inert gas atmosphere suppresses oxidation on the surface of the stainless steel.

[0026] The stainless steel substrate to be treated can be produced from a stainless steel raw material. In particular, the stainless steel substrate to be treated can be produced by means of steps comprising a raw material melting step, a casting step, a hot rolling step, a cold rolling step, and a pickling step. In other words, in one embodiment, the stainless steel substrate containing precipitates of Nb-containing intermetallic compounds is produced by means of a step comprising a melting step of melting a stainless steel raw material containing at least Nb, a casting step of casting a stainless steel substrate from the molten raw material, a hot rolling step of hot rolling the cast stainless steel substrate, a cold rolling step of cold rolling the hot-rolled stainless steel substrate, and a pickling step of subjecting the cold-rolled stainless steel substrate to a pickling treatment.

[0027] Stainless steel powder, for example, can be used as the raw material. In some embodiments, the stainless steel powder contains, for example, iron as the main component, and contains 18 to 30 wt% chromium and 0.05 to 0.50 wt% nitrogen.

[0028] The stainless steel substrate to be treated is a stainless steel substrate containing precipitates of Nb-containing intermetallic compounds, and a commercially available stainless steel substrate can be used, for example. Examples of such stainless steel substrates include SUS447J1L, SUS444, SUS429, and SUS430J1L.

[0029] Examples of precipitates of Nb-containing intermetallic compounds include NbFe2, NbMo, and NbCr. The presence of these precipitates can be confirmed, for example, by TEM, EPMA, or a residue extraction method.

[0030] The compositions of Nb-containing intermetallic compounds can be determined, for example, using EDS, XRD, or EELS.

[0031] Phase diagrams can be created from the compositions of the Nb-containing intermetallic compounds using Thermo-Calc (integrated thermodynamic calculation system) or similar to determine the temperatures at which the Nb-containing intermetallic compounds dissolve.

[0032] Whether the Nb-containing intermetallic compounds are dissolved in the base material or not can be confirmed by examining the stainless steel substrates before and after treatment using EPMA or TEM.

[0033] The heating temperature in the heat treatment step is the temperature at which the precipitates of Nb-containing intermetallic compounds present in the stainless steel substrate are dissolved prior to the heat treatment step. In some embodiments, the heating temperature in the heat treatment step is 950 °C or more, 1000 °C or more, 1050 °C or more, 1100 °C or more, or 1125 °C or more. By setting the heating temperature to 950 °C or more, the precipitates of Nb-containing intermetallic compounds in the base material can be effectively dissolved. In some embodiments, the heating temperature in the heat treatment step is 1200 °C or less. By setting the heating temperature to 1200 °C or less, a furnace with high heat resistance is unnecessary. The heating time orHolding time can be appropriately selected according to the state of solid solution of the precipitates of the Nb-containing intermetallic compounds, and is, for example, 0.1 to 60 minutes.

[0034] Following the heat treatment step, a quenching step is performed to rapidly reduce the temperature of the stainless steel substrate. This rapid temperature reduction suppresses the precipitation of nitrogen-containing intermetallic compounds, resulting in a stainless steel substrate that is essentially free of nitrogen-containing intermetallic precipitates.

[0035] Examples of quenching agents include gas cooling, water cooling, or oil cooling. Examples of gases used for gas cooling include argon, helium, NH3 decomposition gas, and nitrogen.

[0036] In some embodiments, the average cooling rate to 500 °C is 300 °C / s, or 500 °C / s or more. By setting the average cooling rate to 500 °C at 300 °C / s or more, the precipitation of Nb-containing intermetallic compounds can be suppressed more effectively. The average cooling rate is obtained by dividing a value obtained by subtracting 500 °C from the temperature of the heat treatment step by the time it takes to reach 500 °C from the start of cooling.

[0037] Fig. Figure 3 is a schematic diagram showing a heating device 41 for performing a heat treatment, and a cooling device 42 to perform a quenching treatment. The heating device 41 heats the stainless steel substrate 40 , which contains precipitates of Nb-containing intermetallic compounds, through the radiators 43, while the stainless steel substrate 40 is transported in the direction of the arrow. For example, the stainless steel substrate 40 , which had undergone pickling treatment, directly into the heating device 41 to be transported. Inside the heating device 41 An inert atmosphere is created. 44 This is provided by an inert gas or similar, thus allowing the heat treatment to be carried out while suppressing surface oxidation. Next, a coolant, such as a cooling gas, is applied to the heat-treated stainless steel substrate. 40 from the quench gas nozzles 45 the cooling device 42 The water is blown on for quenching. This quenching treatment can also be carried out by transport.

[0038] The heat treatment and quenching steps can also be carried out, for example, using a heating and cooling device that includes a heating chamber for heat-treating the stainless steel substrate and a cooling chamber for quenching the heated stainless steel substrate. First, the stainless steel substrate, which contains precipitates of nitrogen-containing intermetallic compounds, is placed in the heating chamber. Before an inert gas is introduced, the heating chamber is evacuated. Then, an inert gas (for example, argon or helium), whose condensation point is adjusted by a condensation point control device, is supplied to the heating chamber from an inert gas supply source. Next, the interior of the heating device is heated using a heating element to dissolve the precipitates of nitrogen-containing intermetallic compounds present in the stainless steel substrate.After the heat treatment is complete, the inert gas is discharged from the heating chamber. Next, the heat-insulated door between the heating and cooling chambers is opened, and the stainless steel substrate is transferred from the heating chamber to the cooling chamber by means of conveying or transport equipment. Once the stainless steel substrate has been transferred to the cooling chamber, the heat-insulating door is closed, and a cooled inert gas (for example, argon or helium) is supplied from the gas supply source into the cooling chamber. The cooled gas is then blown onto the stainless steel substrate for quenching. The inert gas is supplied to the cooling chamber while its temperature is adjusted to, for example, 30 °C or less. (Fuel cell structure)

[0039] A fuel cell according to the embodiments is described below with reference to the drawing. A case in which a fuel cell separator according to the embodiments is applied to a fuel cell for installation in a fuel cell vehicle or similar is described below as an example. However, the present disclosure is not limited to such an example.

[0040] Fig. Figure 4 is a diagram of a main part of a fuel cell stack (fuel cell). 10 viewed from a cross-sectional perspective. As in Fig. As shown in section 4, there is a plurality of cells (individual cells). 1 , which are the basic units in the fuel cell stack 10 laminated. Each cell 1A polymer electrolyte fuel cell generates an electromotive force through an electrochemical reaction between an oxidant gas (e.g., air) and a fuel gas (e.g., hydrogen). 1 contains a MEGA 2 and a separator 3 , which comes into contact with the MEGA 2 is to define MEGA2. In the embodiments, MEGA is 2 from a pair of separators 3 and 3 surrounded like a sandwich.

[0041] In the MEGA 2 are a membrane electrode assembly (MEA) 4 and gas diffusion layers 7 and 7 , which are located on both surfaces of the membrane electrode assembly 4 are arranged, built-in, or integrated. The membrane electrode unit 4 includes an electrolyte membrane 5 and a pair of electrodes 6 and 6, which are connected in such a way as to form the electrolyte membrane 5 to surround it in a sandwich-like manner. The electrolyte membrane 5 It comprises a proton-conducting ion exchange membrane made of a solid polymer material. The electrode 6 It is formed, for example, from a porous carbon material that carries a catalyst such as platinum. The electrode 6 , which are located on one side of the electrolyte membrane 5 It is arranged as an anode, and the electrode 6 On the other side is a cathode. The gas diffusion layer. 7 It is formed from an electrically conductive element with gas permeability. Examples of electrically conductive elements with gas permeability include porous carbon materials such as carbon paper or carbon cloth, or porous metal materials such as metal meshes or foamed metals.

[0042] The MEGA 2is the power generation section of the fuel cell 10 , and the separator 3 is in contact with the gas diffusion layer 7 the MEGA 2 If the gas diffusion layer 7 The membrane electrode unit is not present. 4 the power generation section, and in this case the separator 3 in contact with the membrane electrode unit 4 Therefore, the power generation section of the fuel cell contains 10 the membrane electrode unit 4 and is in contact with the separator 3 .

[0043] The separator 3 is a plate-shaped element that uses a metal with excellent electrical conductivity, gas impermeability, and similar properties as a substrate. A surface of the separator 3 borders the gas diffusion layer 7 the MEGA 2, and the other surface borders another, adjacent separator. 3 .

[0044] Each separator 3 It is formed in a wavy shape or form. For the shape of the separator 3 The shape of a wave is an isosceles trapezoid, and the tip of the wave is flat, and both ends of this tip form equal angles and are angular or angular. In other words, every separator 3 It has essentially the same shape, regardless of whether it is viewed from the front or the back. The tip of the separator 3 is in surface contact with a gas diffusion layer 7 the MEGA 2 , and the tip of the separator 3 is in surface contact with the other gas diffusion layer 7 the MEGA 2 .

[0045] The area between the gas diffusion layer 7 and the separator 3on the side of one electrode (that is, the anode) 6 defined gas flow paths 21 These are flow paths through which a fuel gas flows, and which lie between the gas diffusion layer 7 and the separator 3 on the side of the other electrode (that is, the anode) 6 defined gas flow paths 22 These are flow paths through which an oxidizing gas or oxidizing agent gas flows. When the fuel gas enters these gas flow paths... 21 on the opposite side across the cell 1 is supplied, and the oxidant gas to the gas flow paths. 22 When the substance is supplied, an electrochemical reaction occurs in the cell. 1 to generate an electromotive force.

[0046] Furthermore, a cell 1 and one to the cell 1 neighboring, other cell 1 to the electrode 6 , which is an anode, and to the electrode 6The cathode and the two surfaces are arranged opposite each other. Furthermore, the back surface of the separator... 3 , which along the electrode 6 , which is an anode in a cell 1 is, is arranged, and the back surface of the separator 3 , which along the electrode 6 , which is a cathode in another cell 1 is arranged in surface contact with each other. Water is used as a coolant to cool the cells. 1 flows through the rooms 23 , which are between the separators 3 and 3 , which are in surface contact with each other, are defined as being between two adjacent cells 1 .

[0047] The fuel cell separator according to the embodiments contains the stainless steel substrate according to the embodiments described above. Protective films such as tin oxide films can be applied to both surfaces of the stainless steel substrate (i.e., the surface on the side that is in contact with the gas diffusion layer). 7 should be, and the surface on the side which is adjacent to the separator 3 (should be in contact) be raised.

[0048] The fuel cell separator in the embodiments is excellent in terms of corrosion resistance, even in a highly corrosive environment.

[0049] In a fuel cell, fluoride ions are likely generated by a fluorine-based electrolyte resin, such as a perfluorosulfonic acid-based polymer, as described above. Therefore, if a fuel cell uses a solid electrolyte membrane containing a fluorine-based electrolyte resin, the fuel cell separator according to the embodiments is particularly useful. Examples of fluorine-based electrolyte resins include perfluorosulfonic acid-based polymers. Specific examples include Nafion (trade name, manufactured by DuPont), Flemion (trade name, manufactured by Asahi Glass Co., Ltd.), and Aciplex (trade name, manufactured by Asahi Kasei Corporation). Among these, Nafion (trade name, manufactured by DuPont) can be used appropriately because it has excellent proton conductivity. Examples

[0050] The embodiments are described below, based on the examples. [Example 1]

[0051] A SUS447J1L sheet material (Nb content: 0.20 wt%, Cr content: 30 wt%, Mo content: 2.0 wt%, C content: 0.015 wt%, N content: 0.015 wt%) was produced as an Nb-containing stainless steel substrate. The stainless steel substrate was placed in a heating furnace and heat-treated at 950 °C for 10 minutes. This heat treatment was performed in an inert argon gas atmosphere, and the temperature in the heating furnace was increased from room temperature to 950 °C at a rate of 50 °C / s and maintained at 950 °C for 10 minutes. Subsequently, the stainless steel substrate was removed from the heating furnace and immediately immersed in water (room temperature) and quenched to produce a stainless steel substrate. E1 to obtain. For the temperature of the stainless steel substrate in this quenching treatment from 950 °C to 500 °C, the average cooling rate was 500 °C / s. [Example 2]

[0052] A stainless steel substrate E2The result was obtained as in Example 1, except that the heating temperature was set to 1050 °C instead of 950 °C. For the temperature of the stainless steel substrate in the quenching treatment from 1050 °C to 500 °C, the average cooling rate was 500 °C / s. [Example 3]

[0053] A stainless steel substrate E3 The result was obtained as in Example 1, except that the heating temperature was set to 1100 °C instead of 950 °C. For the temperature of the stainless steel substrate in the quenching treatment from 1100 °C to 500 °C, the average cooling rate was 500 °C / s. [Example 4]

[0054] A stainless steel substrate E4 The result was obtained as in Example 1, except that the heating temperature was set to 1150 °C instead of 950 °C. For the temperature of the stainless steel substrate in the quenching treatment from 1150 °C to 500 °C, the average cooling rate was 500 °C / s. [Comparison example 1]

[0055] The stainless steel substrate was heat-treated as in Example 1. Subsequently, the stainless steel substrate was left to stand in the air (room temperature) and allowed to cool to room temperature to produce a stainless steel substrate. C1 to obtain. For the temperature of the stainless steel substrate in this cooling treatment from 950 °C to 500 °C, the average cooling rate was 100 °C / s. [Comparative example 2]

[0056] The stainless steel substrate was heat-treated as in Example 4. Subsequently, the stainless steel substrate was left to stand in the air (room temperature) and allowed to cool to room temperature to form a stainless steel substrate. C2 to obtain. For the temperature of the stainless steel substrate in this cooling treatment from 1150 °C to 500 °C, the average cooling rate was 100 °C / s. [Comparative example 3]

[0057] A SUS447J1L sheet material was used as a stainless steel substrate. C3 used. <Lochfraß- Korrosionsbeständigkeitstest>

[0058] The aforementioned stainless steel substrates E1 until E4 and C1 until C3 were used as test pieces, and the corrosion resistance of each test piece under strongly acidic conditions including fluoride ions and chloride ions was investigated using the procedure below.

[0059] First, NaF and NaCl were added to sulfuric acid (pH: 3.0) to prepare an aqueous sulfuric acid solution. Next, in an airtight apparatus, each test piece was exposed to a voiding element. 60 attached, as in Fig. 6 shown, and immersed or soaked in the aforementioned aqueous sulfuric acid solution, temperature-controlled at 90 °C. Fig. 6 was a test piece 61 from a cylindrical gap-forming material 62 , a seal 63 and washers or flat washers64 and 64' sandwich-like encasement, and furthermore a bolt was 65 into the bolt hole of the test piece 61 inserted, and then using a nut 66 screwed together. A plurality of grooves. A are located in a surface of the gap-forming material 62 formed, so that gaps between the gap-forming material 62 and are trained in the test piece. The gap-filling material 62 and the seal 63 are made of ceramic. The discs 64 and 64' , the bolt 65 , and the mother 66The electrodes are made of industrially pure titanium, but are insulated from the test piece. A counter electrode, comprising a platinum plate, and the test piece (sample electrode) were electrically connected in this state to generate a voltage difference, or potential difference, of 1.0 V between the counter electrode and the sample electrode. The voltage of the test piece was kept constant using a reference electrode, and the test duration was 2 hours. If a sudden or unexpected increase in current (current spike) was observed in this pitting corrosion resistance test (NaCl concentration: 30 ppm), the corrosion resistance was rated as C.

[0060] If no spike in the flow was observed in the pitting corrosion resistance test described above (NaCl concentration: 30 ppm), a pitting corrosion resistance test (NaCl concentration: 50 ppm) was performed as in the pitting corrosion resistance test (NaCl concentration: 30 ppm), except that the NaCl concentration was 50 ppm. If a spike in the flow was observed in this pitting corrosion resistance test (NaCl concentration: 50 ppm), the corrosion resistance was rated as B.

[0061] If no spike in the flow was observed in the pitting corrosion resistance test described above (NaCl concentration: 50 ppm), a pitting corrosion resistance test (NaCl concentration: 70 ppm) was performed as in the pitting corrosion resistance test (NaCl concentration: 50 ppm), except that the NaCl concentration was 70 ppm. If a spike in the flow was observed in this pitting corrosion resistance test (NaCl concentration: 70 ppm), the corrosion resistance was rated as A.

[0062] The results described above are summarized in Table 1. [Table 1] Heat treatment temperature Cooling treatment Cooling speed Corrosion resistance [°C] [°C / second] Example 1 950 Deter 500 B Example 2 1050 Deter 500 B Example 3 1100 Deter 500 B Example 4 1150 Deter 500 A Comparative example 1 950 Leave to stand in the air 100 C Comparative example 2 1150 Leave to stand in the air 100 C Comparative example 3 - - - C <epma-analyse>

[0063] For the stainless steel substrate obtained E1 , the stainless steel substrate E4 , the stainless steel substrate C2 and the stainless steel substrate C3 The precipitation of Nb-containing intermetallic compounds was observed using EPMA (magnification: 1000). An EPMA photograph of the stainless steel substrate. E1 is in Fig. Figure 7 shows an EPMA photograph of the stainless steel substrate. E4 is in Fig. Figure 8 shows an EPMA photograph of the stainless steel substrate. C2 is in Fig. Figure 9 shows an EPMA photograph of the stainless steel substrate. C3 is in Fig. Figure 10 shows the image size of each EPMA photo, measuring 50 µm long × 50 µm wide. It is embedded in a stainless steel substrate. C2 ( Fig. 9) and in the stainless steel substrate C3 ( Fig. 10), which correspond to the comparative examples, show many precipitates of Nb-containing intermetallic compounds, which have a particle diameter of 2 µm or more (particles with an Nb concentration of 0.5 wt% or more). On the other hand, in the stainless steel substrate E1 ( Fig. 7), which corresponds to an example, the number of precipitations of Nb-containing intermetallic compounds with a particle diameter of 2 µm or more, and in the stainless steel substrate E4 The number of precipitations of Nb-containing intermetallic compounds with a particle diameter of 2 µm or more was zero, and there were essentially no precipitations of Nb-containing intermetallic compounds.

[0064] The embodiments of the present disclosure have been described in detail above, but the specific arrangement or configuration is not limited to these embodiments. Even if design changes are made without deviating from the concept of the present disclosure, they are contained within the present disclosure. Reference symbol list 1 cell 2 MEGA 3 Separator 4 membrane electrode assembly (MEA) 5 Electrolyte membrane 6 electrode 7 Gas diffusion layer 10 fuel cell stacks 21 Gas flow path 22 Gas flow path 23 Coolant flow path 40 stainless steel substrate 41 Heating device 42 Cooling device 43 Heating 44 Inert atmosphere 45 Quenching or quench gas nozzle 60 Gap-forming element 61 test piece 62 gap-filling materials 63 Seal 64, 64' discs 65 bolts 66 Mother QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2010205443 A

[0003] WO 2016 / 052622

[0004]

Claims

[1] Stainless steel substrate used for a fuel cell separator, containing Nb in a solid solution state and essentially containing no precipitation of an Nb-containing intermetallic compound. [2] Stainless steel substrate according to claim 1, which contains Nb in a range of 0.05 to 0.50 wt%. [3] Fuel cell separator containing a stainless steel substrate, wherein the stainless steel substrate contains Nb in a state of solid solution and contains essentially no precipitation of an Nb-containing intermetallic compound. [4] Fuel cell separator according to claim 3, wherein the stainless steel substrate contains Nb in a range of 0.05 to 0.50 wt%. [5] Fuel cell, comprising: the fuel cell separator according to claim 3 or 4; and a solid electrolyte membrane. [6] Fuel cell according to claim 5, wherein the solid electrolyte membrane contains a fluorine-based electrolyte resin. [7] Method for producing a stainless steel substrate for use as a fuel cell separator, comprising: Heating a stainless steel substrate containing a precipitate of an Nb-containing intermetallic compound in an inert atmosphere to dissolve the Nb-containing intermetallic compound; and Quenching the stainless steel substrate after heat treatment. [8] Method for producing a stainless steel substrate according to claim 7, comprising producing the stainless steel substrate containing the precipitation of the Nb-containing intermetallic compound by the steps comprising Melting a raw material made of stainless steel, which contains at least Nb, Casting a stainless steel substrate from the molten raw material, Hot rolling of the cast stainless steel substrate, Cold rolling of the hot-rolled stainless steel substrate, and Pickling of the cold-rolled stainless steel substrate.

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