Stainless steel material for alkaline water electrolysis device, member for alkaline water electrolysis device and method for producing same, and alkaline water electrolysis device

Abstract

This stainless steel material for an alkaline water electrolysis device comprises, by mass, 0.100% or less C, 1.00% or less Si, 0.30-3.00% Mn, 10.00-35.00% Ni, 0.0300% or less P, 0.0030% or less S, 16.0-28.0% Cr, 0.01-0.25% N, 0.01-1.00% Cu, 0.10-8.00% Mo, and 0.005-0.100% Al, the balance being Fe and impurities.

Description

Stainless steel material for alkaline water electrolysis device, alkaline water electrolysis device component and manufacturing method thereof, and alkaline water electrolysis device

[0001] The present invention relates to a stainless steel material for an alkaline water electrolysis apparatus, a component for an alkaline water electrolysis apparatus and a method for manufacturing the same, and an alkaline water electrolysis apparatus.

[0002] Countermeasures against global warming have become a global issue, and one of the solutions is the promotion of renewable energy, which does not emit CO2. However, because renewable energy uses natural energy, it is difficult to match the amount of power generated to the demands of people's lifestyles. For example, solar power generation cannot generate electricity during bad weather or at night when electricity is needed for daily life. Furthermore, in climates with mild daytime temperatures, surplus solar power generation may occur due to the balance with other power generation methods. Depending on the power transmission system, this surplus power may have a negative impact. As a result, contradictions may arise in which the surplus power cannot be utilized even in good weather. While surplus power can be stored in storage batteries, current methods require large storage batteries and are expensive, posing challenges for their application in large-scale power generation.

[0003] One way to effectively utilize this surplus electricity is to produce hydrogen by electrolysis of water. If hydrogen can be produced and stored, it is expected that a stable supply of carbon-free renewable energy will be achieved by generating electricity using fuel cells that use hydrogen at night or during bad weather. Furthermore, it is possible to produce methane from the hydrogen produced in this way, which is easier to store and is a more environmentally friendly fuel than hydrogen.

[0004] Water electrolysis methods are generally broadly divided into alkaline water electrolysis, solid polymer water electrolysis, and high-temperature water electrolysis. Of these, alkaline water electrolysis is considered promising for industrial applications where strict cost-effectiveness is required, as it has the potential to use low-cost materials such as iron-based materials.

[0005] Some water electrolysis devices have already begun to be put into practical use. For example, an example of a water electrolysis device is described in Figures 1 and 2 of Patent Document 1. In the water electrolysis device described in Patent Document 1, a diaphragm is placed between electrodes placed in water to electrolyze water, generating oxygen on the anode side and hydrogen on the cathode side, and extracting the hydrogen.

[0006] Patent Document 1 describes the use of nickel electrodes because stainless steel is not durable in an alkaline water electrolysis environment. However, nickel is a rare metal, and is not only expensive, but also produced in limited countries, posing geopolitical risks. Speculative fluctuations in raw material prices are also problematic.

[0007] Stainless steel is widely known as a corrosion-resistant material that is cheaper than nickel. As an example of the application of stainless steel to alkaline water electrolysis, Patent Document 2 describes a stainless steel anode that is electrolyzed by immersing the stainless steel anode in a corrosive solution primarily consisting of an aqueous potassium hydroxide solution before use in an alkaline water electrolytic cell. Patent Document 2 describes that electrolytic treatment in a corrosive solution improves the corrosion resistance of stainless steel compared to untreated stainless steel. However, the evaluation time was short, about 160 hours, and there is no track record of long-term evaluation, so it is unclear whether the long-term durability is sufficient.

[0008] Patent Document 3 describes a stainless steel material for an alkaline water electrolysis device, which comprises a substrate made of stainless steel and a coating formed on the surface of the substrate, the coating containing fluorine. This stainless steel material is produced by either a preliminary immersion treatment in which the stainless steel material is immersed in an aqueous solution containing hydrofluoric acid or an inorganic compound containing fluorine, or an electrolysis treatment in which the stainless steel material is electrolyzed in the aqueous solution, followed by anodic electrolysis in an alkaline aqueous solution.

[0009] Furthermore, Patent Document 4 describes a stainless steel material for electrolytic processing equipment, which includes a substrate made of stainless steel and a coating formed on the surface of the substrate, in which at least Ni is present in the coating, and in which the Ni concentration, Fe concentration, and Cr concentration in the coating satisfy a predetermined relationship. This stainless steel material is produced by performing anodic electrolysis in an alkaline aqueous solution, but it also describes that prior to the treatment, preliminary treatment may be performed, either or both of a dipping treatment in which the stainless steel material is dipped in an aqueous solution containing hydrofluoric acid or an inorganic compound containing fluorine, or an electrolysis treatment in which the stainless steel material is electrolyzed in the aqueous solution.

[0010] JP 2017-122255 A JP 2008-45205 A JP 2020-164915 A JP 2021-161482 A

[0011] Alkaline water electrolysis devices perform electrolysis in an alkaline environment at a high potential, exposing various components such as electrodes to a severely corrosive environment. Because elution of metals such as Fe and Cr from components can lead to concerns about deterioration of the electrolytic membrane, materials used for components are required to have high resistance to metal elution in a severely corrosive environment. Ni-containing stainless steel materials are advantageous for improving durability (resistance to metal elution) during alkaline water electrolysis because they can form a Ni-containing coating on the surface of the stainless steel material. However, simply increasing the Ni content in the stainless steel material may not always result in the formation of a coating with excellent corrosion resistance during alkaline water electrolysis. Furthermore, when the Ni content in the stainless steel material is low, durability during alkaline water electrolysis is often not ensured unless pretreatment is performed in an alkaline aqueous solution prior to anodic electrolysis. This poses the problem of high costs and labor involved in the pretreatment.

[0012] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a stainless steel material for an alkaline water electrolysis system that provides a component for an alkaline water electrolysis system that can ensure durability during alkaline water electrolysis without pretreatment. Another object of the present invention is to provide a component for an alkaline water electrolysis system that can ensure durability during alkaline water electrolysis without pretreatment, and a method for manufacturing the same. A further object of the present invention is to provide an alkaline water electrolysis system that includes the stainless steel material for an alkaline water electrolysis system or the component for an alkaline water electrolysis system that has the above-mentioned characteristics.

[0013] In order to solve the above-described problems, the present inventors conducted extensive research on stainless steel materials for alkaline water electrolysis equipment and found that, by increasing the Ni content and adding a predetermined amount of Al, a coating having excellent durability during alkaline water electrolysis can be formed without pretreatment, leading to the completion of the present invention.

[0014] That is, the present invention provides a stainless steel material for an alkaline water electrolysis apparatus containing, by mass, 0.100% or less C, 1.00% or less Si, 0.30 to 3.00% Mn, 10.00 to 35.00% Ni, 0.0300% or less P, 0.0030% or less S, 16.0 to 28.0% Cr, 0.01 to 0.25% N, 0.01 to 1.00%, Mo: 0.10 to 8.00%, 0.005 to 0.100% Al, and the balance being Fe and impurities.

[0015] The present invention also relates to a member for an alkaline water electrolysis system, comprising: a substrate made of the stainless steel material for an alkaline water electrolysis system; and a Ni-enriched coating formed on the surface of the substrate.

[0016] The present invention also relates to a method for producing a member for an alkaline water electrolysis system, comprising placing a substrate made of the stainless steel material for an alkaline water electrolysis system in an alkaline water electrolysis system and performing electrolysis.

[0017] The present invention further relates to an alkaline water electrolysis apparatus comprising the stainless steel material for an alkaline water electrolysis apparatus or the component for an alkaline water electrolysis apparatus.

[0018] The present invention can provide a stainless steel material for an alkaline water electrolysis apparatus that provides a component for an alkaline water electrolysis apparatus that can ensure durability during alkaline water electrolysis without pretreatment. The present invention can also provide a component for an alkaline water electrolysis apparatus that can ensure durability during alkaline water electrolysis without pretreatment, and a method for producing the same. Furthermore, the present invention can provide an alkaline water electrolysis apparatus that includes the stainless steel material for an alkaline water electrolysis apparatus or the component for an alkaline water electrolysis apparatus having the above-mentioned characteristics.

[0019] Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements to the following embodiments, as appropriate, based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the present invention, also fall within the scope of the present invention. In this specification, the "%" designation for components means "% by mass" unless otherwise specified.

[0020] <Stainless Steel Material for Alkaline Water Electrolysis Apparatus> A stainless steel material for an alkaline water electrolysis apparatus according to an embodiment of the present invention (hereinafter may be abbreviated as "stainless steel material") contains C: 0.100% or less, Si: 1.00% or less, Mn: 0.30 to 3.00%, Ni: 10.00 to 35.00%, P: 0.0300% or less, S: 0.0030% or less, Cr: 16.0 to 28.0%, N: 0.01 to 0.25%, Cu: 0.01 to 1.00%, Mo: 0.10 to 8.00%, Al: 0.005 to 0.100%, and the balance consisting of Fe and impurities.

[0021] In this specification, the term "alkaline water electrolysis apparatus" refers to an apparatus that produces hydrogen and oxygen in an alkaline solution. The alkaline solution used in the alkaline water electrolysis apparatus is not particularly limited, and a solution with a pH greater than 7, such as a strong alkaline solution (pH 14 or greater) or a weak alkaline solution (pH 11 to 13), can be used. Specific examples of the alkaline solution include a KOH solution, a NaOH solution, and a K2CO3 solution. The alkaline water electrolysis apparatus is preferably an alkaline water electrolysis apparatus that uses an anion exchange membrane (AEM).

[0022] In this specification, the term "stainless steel material" refers to a material made from stainless steel, and its shape is not particularly limited. Examples of the shape include plate (including strip), rod, and tube. The cross-sectional shape may also be various shaped steels, such as T-shaped and I-shaped. In this specification, the term "impurities" refers to components that are mixed in during the industrial production of stainless steel materials due to raw materials such as ore and scrap, or various factors in the manufacturing process, and are acceptable within a range that does not adversely affect the present invention. For example, impurities also include unavoidable impurities. Regarding the content of each element, "including xx% or less" means that the content is xx% or less, but includes an amount greater than 0% (particularly, above the impurity level). In this specification, a numerical range expressed using "to" refers to a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0023] The stainless steel material according to the embodiment of the present invention may further contain, as necessary, one or more selected from Nb: 1.00% or less, Ti: 1.00% or less, Mg: 0.1000% or less, Ca: 0.1000% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.10% or less, Sn: 0.10% or less, and B: 0.0100% or less. Each component will be described in detail below.

[0024] <C: 0.100% or Less> C is an element effective in stabilizing the austenite phase. However, because C promotes the precipitation of Cr carbides, an excessively high C content causes intergranular corrosion and reduces durability during alkaline water electrolysis. Therefore, the C content is set to 0.100% or less, preferably 0.095% or less, more preferably 0.090% or less, even more preferably 0.085% or less, and particularly preferably 0.080% or less. On the other hand, the lower limit of the C content is not particularly limited, but is 0.001% from the viewpoint of obtaining the above-mentioned effects of C. Note that the numerical value (lower limit) or numerical range of the C content may be any combination of the numerical values ​​or numerical ranges. Therefore, for example, the C content may be 0.001 to 0.100%, 0.001 to 0.095%, 0.001 to 0.090%, 0.001 to 0.085%, or 0.001 to 0.080%. The same applies to the numerical values ​​(upper or lower limit values) or numerical ranges of the contents of other elements described below.

[0025] <Si: 1.00% or less> Si is an element effective for deoxidation and improving oxidation resistance. However, if the Si content is too high, the stainless steel material becomes hard, and workability and toughness (particularly, the toughness of a welded portion when welded) decrease. Therefore, the Si content is set to 1.00% or less, preferably 0.95% or less, more preferably 0.90% or less, even more preferably 0.85% or less, and particularly preferably 0.80% or less. On the other hand, the lower limit of the Si content is not particularly limited, but is set to 0.01% from the viewpoint of obtaining the above-mentioned effects of Si.

[0026] <Mn: 0.30 to 3.00%> Mn is an element necessary for forming a Ni-enriched film on the surface of the stainless steel material during alkaline water electrolysis. To ensure this effect, the Mn content is set to 0.30% or more, preferably 0.35% or more, and more preferably 0.40% or more. However, if the Mn content is too high, corrosion resistance decreases. Therefore, the Mn content is set to 3.00% or less, preferably 2.80% or less, more preferably 2.50% or less, even more preferably 2.00% or less, and particularly preferably 1.50% or less.

[0027] <Ni: 10.00 to 35.00%> Ni is an element effective in improving durability (resistance to metal elution) during alkaline water electrolysis. To ensure this effect, the Ni content is set to 10.00% or more, preferably 10.50% or more, more preferably 11.00% or more, and even more preferably 11.50% or more. However, if the Ni content is too high, costs increase. For this reason, the Ni content is set to 35.00% or less, preferably 34.50% or less.

[0028] <P: 0.0300% or less> P is an element contained in various raw materials. If the P content is too high, weldability and workability will decrease. Therefore, the P content is set to 0.0300% or less, preferably 0.0290% or less, and more preferably 0.0250% or less. On the other hand, the lower limit of the P content is not particularly limited, but removing P requires very high refining costs. Therefore, in consideration of economic efficiency, the P content can be set to 0.0001% or more.

[0029] <S: 0.0030% or less> S is an element contained in various raw materials. If the S content is too high, toughness (particularly the toughness of a welded portion when welded) decreases and inclusions that serve as corrosion initiation sites are more likely to be generated. Therefore, the S content is set to 0.0030% or less, preferably 0.0029% or less, and more preferably 0.0025% or less. On the other hand, the lower limit of the S content is not particularly limited, but removing S requires very high refining costs. Therefore, in consideration of economic efficiency, the S content can be set to 0.0001% or more.

[0030] <Cr: 16.0 to 28.0%> Cr is an element effective in ensuring corrosion resistance. To ensure this effect, the Cr content is set to 16.0% or more, preferably 16.5% or more, and more preferably 17.0% or more. However, if the Cr content is too high, costs increase. For this reason, the Cr content is set to 28.0% or less, preferably 27.5% or less, and more preferably 27.0% or less.

[0031] <N: 0.01 to 0.25%> N is an element effective in reducing costs. N also dissolves in the austenite phase to increase strength and corrosion resistance, contributing to reduced alloying. To ensure these effects, the N content is set to 0.01% or more, preferably 0.02% or more, more preferably 0.03% or more, and even more preferably 0.05% or more. However, if the N content is too high, bubbles are more likely to form in the stainless steel material. Therefore, the N content is set to 0.25% or less, preferably 0.23% or less, and more preferably 0.20% or less.

[0032] <Cu: 0.01 to 1.00%> Cu is an element effective for desulfurization and deoxidation. Cu also contributes to improving corrosion resistance. To ensure this effect, the Cu content is set to 0.01% or more, preferably 0.03% or more, more preferably 0.05% or more, and even more preferably 0.10% or more. However, if the Cu content is too high, costs increase. For this reason, the Cu content is set to 1.00% or less, preferably 0.95% or less, and more preferably 0.90% or less.

[0033] <Mo: 0.10 to 8.00%> Mo is an element effective in improving corrosion resistance. To ensure this effect, the Mo content is set to 0.10% or more, preferably 0.13% or more, more preferably 0.15% or more, and even more preferably 0.20% or more. However, if the Mo content is too high, costs increase. For this reason, the Mo content is set to 8.00% or less, preferably 7.80% or less, and more preferably 7.50% or less.

[0034] <Al: 0.005 to 0.100%> Although Al dissolves in the operating environment of an alkaline water electrolysis device (an alkaline environment and a high-potential environment), it hydrates on the surface of the stainless steel material, resulting in a slower dissolution rate than other metals such as Fe and Cr, and also has the effect of reducing the dissolution rates of other metals. Furthermore, Al is also an element effective in improving oxidation resistance, deoxidation, and workability. To ensure these effects, the Al content is set to 0.005% or more, preferably 0.010% or more, more preferably 0.020% or more, even more preferably 0.028% or more, and particularly preferably 0.030% or more. However, if the Al content is too high, oxidation resistance and deoxidation may be adversely affected, and inclusions may be more likely to form. For this reason, the Al content is set to 0.100% or less, preferably 0.098% or less, and more preferably 0.095% or less.

[0035] <Nb: 1.00% or less, Ti: 1.00% or less> Nb and Ti are elements effective in suppressing sensitization and improving intergranular corrosion resistance. However, if the Nb and Ti contents are too high, workability decreases and costs increase. Therefore, the Nb and Ti contents are each set to 1.00% or less, preferably 0.90% or less, and more preferably 0.80% or less. On the other hand, the lower limits of the Nb and Ti contents are not particularly limited, but can be set to 0.01% or more, 0.03% or more, or 0.05% or more, respectively, to ensure the above effects.

[0036] <Mg: 0.1000% or less, Ca: 0.1000% or less> Mg and Ca are elements effective in suppressing the formation of inclusions and improving corrosion resistance. However, if the Mg and Ca contents are too high, hot workability deteriorates. Therefore, the Mg and Ca contents are each set to 0.1000% or less, preferably 0.0900% or less, and more preferably 0.0800% or less. On the other hand, the lower limits of the Mg and Ca contents are not particularly limited, but can be set to 0.0001% or more, 0.0003% or more, or 0.0005% or more, respectively, to ensure the above effects.

[0037] <Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less> Zr, Co, V, and W are elements effective in improving oxidation resistance. However, if the contents of Zr, Co, V, and W are too high, workability and toughness decrease and costs increase. Therefore, the contents of Zr, Co, V, and W are each set to 1.00% or less, preferably 0.90% or less, and more preferably 0.80% or less. On the other hand, the lower limits of the contents of Zr, Co, V, and W are not particularly limited, but can be set to 0.01% or more, 0.02% or more, or 0.03% or more, respectively, to ensure the above-mentioned effects.

[0038] <REM: 0.10% or Less> REM (rare earth element) is an element effective in improving oxidation resistance. However, if the REM content is too high, manufacturability is impaired and costs increase. Therefore, the REM content is set to 0.10% or less, preferably 0.09% or less, and more preferably 0.08% or less. On the other hand, the lower limit of the REM content is not particularly limited, but can be set to 0.01% or more, 0.02% or more, or 0.03% or more to ensure the above-mentioned effects. Note that REM is a collective term for 17 elements, including Sc, Y, and 15 elements (lanthanoids) from La to Lu, and the REM content refers to the total content of these elements. These elements can be used alone or in combination of two or more. Furthermore, lanthanoids are industrially added in the form of misch metal.

[0039] <Sn: 0.10% or less> Sn is an element effective in improving oxidation resistance. However, if the Sn content is too high, hot workability deteriorates. Therefore, the Sn content is set to 0.10% or less, preferably 0.09% or less, and more preferably 0.08% or less. On the other hand, the lower limit of the Sn content is not particularly limited, but can be set to 0.01% or more or 0.02% or more to ensure the above-mentioned effect.

[0040] <B: 0.0100% or less> B is an element effective in improving hot workability. However, if the B content is too high, corrosion resistance decreases. Therefore, the B content is set to 0.0100% or less, preferably 0.0095% or less, and more preferably 0.0090% or less. On the other hand, the lower limit of the B content is not particularly limited, but in order to ensure the above-mentioned effects, it can be set to 0.0001% or more, preferably 0.0003% or more, and more preferably 0.0005% or more.

[0041] The stainless steel material according to the embodiment of the present invention has an austenitic metallographic structure. In this specification, "austenitic" refers to a metallographic structure that is primarily austenitic at room temperature. Therefore, "austenitic" also includes structures that contain small amounts of phases other than austenitic (e.g., ferrite or martensite). However, "austenitic" does not include a multi-phase structure of ferrite and austenite, a multi-phase structure of ferrite and martensite, or a multi-phase structure of ferrite, austenite, and martensite.

[0042] In the stainless steel material according to the embodiment of the present invention, the arithmetic mean height Sa of the surface is preferably 0.70 μm or less, more preferably 0.65 μm or less, and even more preferably 0.60 μm or less. By controlling the arithmetic mean height Sa of the surface within this range, a Ni-enriched film is uniformly formed on the surface during alkaline water electrolysis, thereby improving durability (resistance to metal elution) during alkaline water electrolysis. The lower limit of the arithmetic mean height Sa of the surface is not particularly limited, as the effect is more easily obtained as the lower limit is, but is, for example, 0.01 μm, 0.03 μm, or 0.05 μm. Here, the "arithmetic mean height Sa of the surface" in this specification can be obtained by measuring and analyzing the surface shape in accordance with ISO 25178-2:2012.

[0043] In the stainless steel material according to the embodiment of the present invention, it is preferable that the Ni-enriched film formed when the stainless steel material is immersed in a 0.1 M KOH aqueous solution at 60°C and electrolyzed at a potential of 1.2 V (vs. SHE) for 100 hours satisfies the following formula (1): CNi ×C Al ≧100.0...(1) In the formula, C Ni is the average concentration (atomic %) of Ni relative to the total of Ni, Fe, and Al in the region from the surface to a depth of 4 nm of the Ni-enriched coating, and C Al is the average concentration (atomic %) of Al relative to the total of Ni, Fe, and Al in the region from the surface to a depth of 4 nm of the Ni-enriched coating.

[0044] Here, C represented by formula (1) Ni ×C Al The value of C is an index representing the concentration balance of Ni and Al in the Ni-enriched film formed on the surface of the stainless steel material. Ni ×C Al If the value of C is 100.0 or more, the Ni and Al concentrations in the Ni-enriched coating are well balanced, and therefore durability (resistance to metal elution) during alkaline water electrolysis can be ensured. Ni ×C Al The value of C is preferably 105.0 or more, more preferably 108.0 or more. Ni ×C Al The upper limit of the value is not particularly limited, but is, for example, 300.0 or less, 250.0 or less, or 200.0 or less. The amounts of Ni, Fe, and Al in the region from the surface of the Ni-enriched coating to a depth of 4 nm can be calculated by measuring the depth profile of elements from the surface using FE-AES (field emission Auger electron spectroscopy). The elements measured in this elemental analysis are C, O, Fe, Cr, Ni, and Mn, and the concentrations of each element can be calculated from the measured amounts of these elements. The average concentration of Ni relative to the total of Ni, Fe, and Al is the percentage of the amount of Ni when the total of Ni, Fe, and Al is 100. Furthermore, it is the percentage of the amount of Al when the total amount of Ni, Fe, and Al is 100.

[0045] The stainless steel material according to the embodiment of the present invention may be a hot-rolled material or a cold-rolled material, and the hot-rolled or cold-rolled material may be annealed or pickled. The thickness of the stainless steel material according to the embodiment of the present invention is not particularly limited and may be adjusted appropriately depending on the type of part to be manufactured, but is preferably 0.2 to 5.0 mm, more preferably 0.2 to 4.0 mm, even more preferably 0.2 to 3.0 mm, and particularly preferably 0.2 to 2.0 mm. When the stainless steel material is a rod, the thickness refers to the equivalent circle diameter of the cross section. When the stainless steel material is a shaped steel, the thickness refers to the thickness at any point on the cross section.

[0046] The method for producing a stainless steel material according to an embodiment of the present invention is not particularly limited as long as it is a method capable of producing a stainless steel material having the above-described characteristics. An example of a method for producing a stainless steel material according to an embodiment of the present invention is described below. First, a steel adjusted to the above-described chemical composition is melted and cast by a conventional method to obtain a slab to be subjected to hot rolling. Next, hot rolling is performed by a conventional method. The conditions for hot rolling are not particularly limited, but the heating temperature of the slab is usually preferably 1050 to 1250°C, and more preferably 1180 to 1250°C. The finishing temperature for hot rolling is preferably 950 to 1000°C. After hot rolling, annealing and pickling may be performed as necessary. The conditions for annealing are not particularly limited, but for example, the slab may be held at 1000 to 1150°C (preferably 1050 to 1150°C) for 3 to 6 minutes. The pickling is not particularly limited and may be performed according to a known method.

[0047] Subsequently, cold rolling and annealing are performed. After annealing, pickling may be performed as necessary. The conditions for cold rolling are not particularly limited, and the cold rolling may be performed in accordance with a known method. The conditions for annealing after cold rolling are not particularly limited, but holding at 1000 to 1150°C for 30 to 60 seconds may be sufficient. Cold rolling, annealing, and pickling may be repeated multiple times in order to obtain a stainless steel material of the final required thickness.

[0048] After annealing, the surface of the stainless steel material may be mechanically polished or electrolytically polished in order to control the surface roughness (particularly the arithmetic mean height Sa of the surface to 0.70 μm or less). Mechanical polishing is preferably performed within a range of 10 μm from the surface in the thickness direction of the stainless steel material. Mechanical polishing may be performed using abrasive paper or abrasive stone, or a solid abrasive may also be used. Furthermore, electrolytic polishing may be performed using a commercially available electrolytic polishing solution. The electrolytic polishing treatment is preferably performed at 40 to 60°C. Other conditions for electrolytic polishing include a current density of 1 to 20 dm 2 The time is preferably in the range of 1 to 10 minutes.

[0049] <Member for alkaline water electrolysis system and manufacturing method thereof> The member for alkaline water electrolysis system according to an embodiment of the present invention comprises a substrate made of the above-described stainless steel material and a Ni-enriched coating formed on the surface of the substrate. With this configuration, the member for alkaline water electrolysis system according to an embodiment of the present invention can ensure durability (resistance to metal elution) during alkaline water electrolysis due to the Ni-enriched coating formed on the surface of the substrate.

[0050] In this specification, the term "alkaline water electrolysis device member" refers to a member (component) used in alkaline water electrolysis. Specifically, the term "alkaline water electrolysis device member" refers to a member (component) that may be exposed to an alkaline environment and a high-potential environment. Therefore, examples of the alkaline water electrolysis device member include an anode electrode, an electrolytic cell, a separator, piping, and other related members used in the alkaline water electrolysis device. Of these, the alkaline water electrolysis device member is preferably an anode electrode.

[0051] The Ni-enriched coating has an average Ni concentration relative to the total of Fe, Ni, and Cr at a position 1 nm deep from the surface of the coating, of preferably 35.0 atomic % or more, more preferably 38.0 atomic % or more, and even more preferably 40.0 atomic % or more. Controlling the average Ni concentration within this range can stably enhance durability during alkaline water electrolysis. The upper limit of the average Ni concentration is not particularly limited, but may be 80.0 atomic %, 70.0 atomic %, or 65.0 atomic % or less. The average Ni concentration relative to the total of Fe, Ni, and Cr at a position 1 nm deep from the surface can be measured in the same manner as the method using FE-AES (field emission Auger electron spectroscopy) described above, except that the measurement position for the average Ni concentration is set to a position 1 nm deep from the surface.

[0052] The thickness of the Ni-enriched coating is not particularly limited, but is preferably 1 to 300 nm. If the thickness of the Ni-enriched coating is too small, the durability of the alkaline water electrolysis device component may be reduced when used as the anode electrode of the alkaline water electrolysis device.

[0053] The alkaline water electrolysis system member according to the embodiment of the present invention can be produced by placing a substrate made of the above-described stainless steel in an alkaline water electrolysis system and performing electrolysis. Specifically, the electrolysis can be performed by immersing the substrate made of the above-described stainless steel in an alkaline aqueous solution. Since the alkaline water electrolysis system member according to the embodiment of the present invention can form a Ni-enriched film simply by placing it in an alkaline water electrolysis system and performing electrolysis, durability during alkaline water electrolysis can be ensured without performing pretreatment.

[0054] The electrolytic potential of the electrolytic treatment is not particularly limited and may be adjusted depending on the type of stainless steel material. For example, the electrolytic potential of the electrolytic treatment can be the electrolytic potential when the alkaline water electrolysis apparatus is actually operating, and is generally 1.0 to 1.8 V (vs. SHE). Note that this electrolytic potential is a potential based on the standard hydrogen electrode (SHE). The electrolysis time of the electrolytic treatment is not particularly limited, but is typically 10 hours or more, for example, 24 to 100 hours. An inorganic compound may be added to the alkaline aqueous solution as a pH adjusting reagent to control the pH of the alkaline aqueous solution. Examples of inorganic compounds include KOH, NaOH, Ca(OH), KCO, NaCO, and CaCO. These may be used alone or in combination. The temperature of the alkaline aqueous solution is also not particularly limited, but is preferably 20 to 90°C, more preferably 30 to 80°C, from the viewpoint of the rate of formation of the Ni-enriched film.

[0055] <Alkaline water electrolysis device> An alkaline water electrolysis device according to an embodiment of the present invention includes the above-described stainless steel material or the above-described alkaline water electrolysis device component. With this configuration, the alkaline water electrolysis device according to an embodiment of the present invention can ensure durability (resistance to metal elution) during alkaline water electrolysis because a Ni-enriched film is formed on the surface of the stainless steel material during alkaline water electrolysis or a Ni-enriched film is formed in advance on the surface of the stainless steel material (substrate).

[0056] As long as the alkaline water electrolysis device according to the embodiment of the present invention has the above-described configuration, other configurations are not particularly limited. For example, the alkaline water electrolysis device according to the embodiment of the present invention includes an electrolytic cell, an anode electrode, and a cathode electrode. Of these, the electrolytic cell and the anode electrode are preferably made of the above-described stainless steel material or the above-described alkaline water electrolysis device member, and the anode electrode is more preferably made of the above-described stainless steel material or the above-described alkaline water electrolysis device member.

[0057] The present invention will be described in detail below with reference to examples, but the present invention should not be construed as being limited to these examples.

[0058] (Examples 1 to 10 and Comparative Examples 1 and 2) Stainless steel sheets were produced according to the following procedure. Slabs having the compositions shown in Table 1 were melted, and the 50 mm thick slabs were heated for 1 hour at the temperatures shown in Table 2. The slabs were then hot-rolled at the finishing temperatures shown in Table 2 to obtain hot-rolled sheets having the thicknesses shown in Table 2. The hot-rolled sheets were then annealed by holding them at the temperatures and times shown in Table 2, and then pickled to obtain hot-rolled annealed sheets. The hot-rolled annealed sheets were then cold-rolled to obtain cold-rolled sheets having the thicknesses shown in Table 2. The cold-rolled sheets were then annealed by holding them at the temperatures and times shown in Table 2 to obtain cold-rolled annealed sheets. The cold-rolled annealed sheets were then polished as shown in Table 2. In Table 2, "#600 wet" means that wet polishing was performed for 15 minutes or more using #600 SiC abrasive paper. "#120 wet" means that wet polishing was performed for 15 minutes or more using #120 SiC abrasive paper. "Mirror polishing" means that the sample was wet polished with SiC polishing paper for 15 minutes or more, and then buffed with diamond paste for 15 minutes or more.

[0059]

[0060]

[0061] The stainless steel sheets obtained as described above were evaluated as follows.

[0062] <Arithmetic mean height Sa of surface> The arithmetic mean height Sa of the surface of the stainless steel plate was measured in accordance with ISO 25178-2:2012. A laser microscope (VK-X3000 manufactured by Keyence Corporation) was used as the surface roughness measuring device. In the measurement, the surface of the stainless steel plate was observed in one field of view using a 50x objective lens. Five regions of 50 μm × 50 μm were selected from the observed field of view, and the arithmetic mean height Sa of each region was calculated. The average value of the calculated arithmetic mean heights Sa of the five regions was used as the evaluation result.

[0063] <Alkaline Water Electrolysis Test> Test pieces measuring 50 mm (rolling direction) x 10 mm (width direction) x 2 mm (thickness direction) were taken from the stainless steel plate. Next, alkali-resistant tape was wrapped around the taken test piece, and an electrolysis sample was prepared so that only the bottom 2 cm of the test piece was electrolyzed. The prepared electrolysis sample was immersed in a 0.1 M KOH aqueous solution at 60 °C, and a constant-potential electrolysis test was performed for 100 hours at an electrolysis potential of 1.2 V (vs. SHE). Next, after the constant-potential electrolysis test, the KOH aqueous solution was sampled, and the amount of metal elution was measured by ICP-OES (inductively coupled plasma optical emission spectroscopy). For ICP-OES, an ICPS-8100 manufactured by Shimadzu Corporation was used. The metals to be measured were Fe, Cr, Ni, and Mn. The total amount of elution of these metals [μg] was divided by the volume [L] of the KOH aqueous solution and the electrolysis time [h] to obtain the amount of metal elution [μg / (L h)]. In this evaluation, if the amount of metal elution is 0.60 [μg / L·h] or less, it can be determined that the amount of metal elution is very small; if the amount of metal elution is more than 0.60 [μg / L·h] but less than 1.50 [μg / L·h], it can be determined that the amount of metal elution is small; and if the amount of metal elution is more than 1.50 [μg / L·h], it can be determined that the amount of metal elution is large.

[0064] <C Ni ×C Al The depth profile of elements from the surface of the test piece (surface of the Ni-enriched film) after the alkaline water electrolysis test was measured using an FE-AES (JUMP-9510F manufactured by JEOL Ltd.). The average concentration of Ni relative to the total of Ni, Fe, and Al in the region from the surface to a depth of 4 nm (C Ni ), and the average concentration of Al relative to the total of Ni, Fe, and Al in the region from the surface to a depth of 4 nm (C Al ) and C Ni ×C Al In this evaluation, C Ni ×C Al If the value is 100.0 or more, it can be determined that the durability during alkaline water electrolysis is good.

[0065] <Average Ni concentration on the surface of the Ni-enriched coating> The depth profile of elements from the surface of the test piece (surface of the Ni-enriched coating) after the alkaline water electrolysis test was measured in the same manner as described above. Then, the average Ni concentration relative to the total of Fe, Ni, and Cr at a position 1 nm deep from the surface was calculated. In this evaluation, if the average Ni concentration on the surface of the Ni-enriched coating was 35.0 atomic % or more, it could be determined that the durability during alkaline water electrolysis was good.

[0066] The results of the above evaluation are shown in Table 3.

[0067]

[0068] As shown in Table 3, Examples 1 to 10 had predetermined compositions, resulting in small amounts of metal elution and ensuring durability during alkaline water electrolysis. In contrast, Comparative Example 2 had too little Ni content, which prevented the formation of an appropriate Ni-enriched film, resulting in a large amount of metal elution. Comparative Example 1 did not contain Al, resulting in the formation of an appropriate Ni-enriched film, resulting in a large amount of metal elution.

[0069] As can be seen from the above results, the present invention can provide a stainless steel material for an alkaline water electrolysis system that provides a component for an alkaline water electrolysis system that can ensure durability during alkaline water electrolysis without pretreatment. The present invention can also provide a component for an alkaline water electrolysis system that can ensure durability during alkaline water electrolysis without pretreatment, and a method for producing the same. Furthermore, the present invention can provide an alkaline water electrolysis system that includes the stainless steel material for an alkaline water electrolysis system or the component for an alkaline water electrolysis system having the above-mentioned characteristics.

[0070] Therefore, by adopting the following features [1] to [4], the present invention can provide a stainless steel material for an alkaline water electrolysis apparatus that provides a component for an alkaline water electrolysis apparatus that can ensure durability during alkaline water electrolysis without pretreatment. Furthermore, by adopting the following features [5] to [7], the present invention can provide a component for an alkaline water electrolysis apparatus that can ensure durability during alkaline water electrolysis without pretreatment, and a method for manufacturing the same. Furthermore, by adopting the following feature [8], an alkaline water electrolysis apparatus can be provided that includes the stainless steel material for an alkaline water electrolysis apparatus or the component for an alkaline water electrolysis apparatus having the above-mentioned characteristics.

[0071] [1] A stainless steel material for alkaline water electrolysis equipment comprising, on a mass basis, C: 0.100% or less, Si: 1.00% or less, Mn: 0.30 to 3.00%, Ni: 10.00 to 35.00%, P: 0.0300% or less, S: 0.0030% or less, Cr: 16.0 to 28.0%, N: 0.01 to 0.25%, Cu: 0.01 to 1.00%, Mo: 0.10 to 8.00%, Al: 0.005 to 0.100%, and the balance being Fe and impurities. [2] The stainless steel material for an alkaline water electrolysis apparatus according to [1], further comprising, by mass, one or more selected from Nb: 1.00% or less, Ti: 1.00% or less, Mg: 0.1000% or less, Ca: 0.1000% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.10% or less, Sn: 0.10% or less, and B: 0.0100% or less. [3] The stainless steel material for an alkaline water electrolysis apparatus according to [1] or [2], wherein when the stainless steel material for an alkaline water electrolysis apparatus is immersed in a 0.1 M KOH aqueous solution at 60°C and electrolyzed at a potential of 1.2 V (vs. SHE) for 100 hours, a Ni-enriched film formed thereon satisfies the following formula (1): Ni ×C Al ≧100.0...(1) In the formula, C Ni is the average concentration (atomic %) of Ni relative to the total of Ni, Fe, and Al in the region from the surface of the Ni-enriched coating to a depth of 4 nm, and C Alis the average concentration (atomic %) of Al relative to the total of Ni, Fe, and Al in the region from the surface of the Ni-enriched coating to a depth of 4 nm.

[0072] [4] The stainless steel material for an alkaline water electrolysis apparatus according to any one of [1] to [3], wherein the arithmetic mean height Sa of the surface is 0.70 μm or less. [5] A component for an alkaline water electrolysis apparatus, comprising a substrate made of the stainless steel material for an alkaline water electrolysis apparatus according to any one of [1] to [4], and a Ni-enriched coating formed on the surface of the substrate. [6] The component for an alkaline water electrolysis apparatus according to [5], wherein the Ni-enriched coating has an average Ni concentration of 35.0 atomic % or more relative to the total of Fe, Ni, and Cr at a depth of 1 nm from the surface. [7] A method for manufacturing a component for an alkaline water electrolysis apparatus, comprising placing a substrate made of the stainless steel material for an alkaline water electrolysis apparatus according to any one of [1] to [4] in an alkaline water electrolysis apparatus and performing electrolysis treatment. [8] An alkaline water electrolysis apparatus comprising the stainless steel material for an alkaline water electrolysis apparatus according to any one of [1] to [4], or the component for an alkaline water electrolysis apparatus according to [5] or [6].

Claims

1. A stainless steel material for an alkaline water electrolysis device, containing, by mass, C: 0.100% or less, Si: 1.00% or less, Mn: 0.30 to 3.00%, Ni: 10.00 to 35.00%, P: 0.0300% or less, S: 0.0030% or less, Cr: 16.0 to 28.0%, N: 0.01 to 0.25%, Cu: 0.01 to 1.00%, Mo: 0.10 to 8.00%, Al: 0.005 to 0.100%, with the balance being Fe and impurities.

2. The stainless steel material for an alkaline water electrolysis device according to claim 1, further containing one or more selected from the following, by mass: Nb: 1.00% or less, Ti: 1.00% or less, Mg: 0.1000% or less, Ca: 0.1000% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.10% or less, Sn: 0.10% or less, B: 0.0100% or less.

3. The stainless steel material for an alkaline water electrolysis device, when immersed in a 0.1 M KOH aqueous solution at 60° C. and electrolyzed at a potential of 1.2 V (vs. SHE) for 100 hours, forms a Ni-enriched film that satisfies the following formula (1). The stainless steel material for an alkaline water electrolysis device according to claim 1 or 2. C Ni × C Al ≧ 100.0... (1) In the formula, C Ni is the average concentration (atomic %) of Ni with respect to the total of Ni, Fe, and Al in the region from the surface of the Ni-enriched film to a depth of 4 nm, and C Al is the average concentration (atomic %) of Al with respect to the total of Ni, Fe, and Al in the region from the surface of the Ni-enriched film to a depth of 4 nm.

4. The stainless steel material for an alkaline water electrolysis device according to claim 1 or 2, wherein the arithmetic mean height Sa of the surface is 0.70 μm or less.

5. A member for an alkaline water electrolysis device, comprising a base material made of the stainless steel material for an alkaline water electrolysis device according to claim 1 or 2, and a Ni-enriched film formed on the surface of the base material.

6. The member for an alkaline water electrolysis device according to claim 5, wherein the average concentration of Ni with respect to the total of Fe, Ni, and Cr at a position 1 nm deep from the surface of the Ni-enriched film is 35.0 atomic% or more.

7. A method for manufacturing a member for an alkaline water electrolysis device, comprising arranging a base material made of the stainless steel material for an alkaline water electrolysis device according to claim 1 or 2 in an alkaline water electrolysis device and performing electrolysis treatment.

8. An alkaline water electrolysis device comprising the stainless steel material for an alkaline water electrolysis device according to claim 1 or 2, or the member for an alkaline water electrolysis device according to claim 5.