JPWO2015098981A1 - Base material for hydrogen equipment and method for producing the same - Google Patents

Abstract

As a base material used in hydrogen equipment, the surface of an aluminum-based steel material is subjected to hot-dip plating using an Al-Si-based aluminum alloy with an added Si amount of 1 to 5% for a steel material that is affected by hydrogen alone. An intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated to form a hydrogen-resistant permeation film having a three-layer structure in which the thickness of the aluminum-based intermetallic compound layer is 1 to 22 μm and the average thickness of the film is less than 35 μm. It is what you did. The base steel material is a steel material affected by hydrogen, such as carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel. As a base material used in hydrogen equipment used in high-pressure hydrogen environments, hydrogen embrittlement is prevented and durability is increased, and production costs are kept low.

Description

  The present invention relates to a base material for a hydrogen device and a method for producing the same, and more specifically, for a hydrogen device in which a hydrogen-resistant permeation film excellent in both hydrogen gas barrier properties and strength properties is applied to a steel material affected by hydrogen. The present invention relates to a substrate and a manufacturing method thereof.

  In recent years, there is a strong demand in the industrial world to suppress the generation of global warming gases such as carbon dioxide from the viewpoint of environmental protection. As part of this, development of automobiles and transportation equipment using fuel cells as power sources is underway. Since fuel cells generate electric power using hydrogen as fuel, they do not generate carbon dioxide and have high energy conversion efficiency, so they are expected to be a powerful power source.

  In a fuel cell using hydrogen as a fuel and a device including a hydrogen station for supplying hydrogen to the fuel cell, components are exposed to a hydrogen gas environment. In a metal material exposed to a hydrogen gas environment, a phenomenon is known in which tensile strength, elongation, drawing, or the like decreases due to hydrogen that has entered the material. This phenomenon is called hydrogen embrittlement. Due to such problems of hydrogen embrittlement, Japan Automobile Research Institute Technical Standard JARIS001 (2004) stipulates the use of only austenitic stainless steel SUS316L and aluminum alloy 6061-T6 for high-pressure hydrogen containers for automobiles with a pressure of 35 MPa. doing. In addition, in the general high-pressure gas safety regulation related illustration standard, only the material (referred to as Ni equivalent material) in which the Ni equivalent of austenitic stainless steel (SUS316 and SUS316L) is limited to the hydrogen infrastructure equipment of pressure 70 MPa and pressure 82 MPa. It regulates use.

  However, 6061-T6 and Ni equivalent material have low strength and high cost. In fuel cell vehicles and hydrogen infrastructure equipment, high-pressure hydrogen gas at a maximum pressure of 100 MPa (1000 atm) is used. The hydrogen equipment is required to have high durability without causing hydrogen embrittlement under such use conditions, and it is required to suppress the equipment manufacturing cost as much as possible. For this reason, development of a low-cost material excellent in both hydrogen embrittlement resistance and strength characteristics is expected to replace 6061-T6 and Ni equivalent materials.

  Since hydrogen embrittlement is caused by hydrogen that has penetrated into the material, hydrogen embrittlement may be suppressed if a technology can be developed that prevents hydrogen from entering the material in a high-pressure hydrogen gas environment. A surface film capable of suppressing hydrogen intrusion is expected to be one of the leading technologies for suppressing hydrogen embrittlement of materials. Here, the high-pressure hydrogen gas is a hydrogen gas pressure of atmospheric pressure (0.1 MPa) or more.

  If carbon steel or low alloy steel that is affected by hydrogen but has low tensile strength and high tensile strength can be given a surface coating that can suppress hydrogen intrusion, the hydrogen embrittlement of the material can be suppressed. The cost of hydrogen equipment such as containers and piping can be greatly reduced.

  Carbon steel and low alloy steel with a surface coating are expected to be used for high pressure hydrogen gas pressure vessels and high pressure hydrogen gas piping. If hydrogen embrittlement can be suppressed by providing a surface film capable of suppressing hydrogen intrusion, instead of 6061-T6 and Ni equivalent material, carbon steel or low alloy steel that is affected by hydrogen alone is used. It can be used for pressure vessels and piping.

  Martensitic stainless steel having a tensile strength of 1000 MPa or more has a large elastic region, and is therefore used for flow meters and pressure gauges. In martensitic stainless steel, the influence of hydrogen is extremely large, so if a surface coating capable of suppressing hydrogen intrusion is applied to suppress hydrogen embrittlement, a flow meter or pressure gauge can be used even in high-pressure hydrogen gas. It is possible to use martensitic stainless steel.

  Patent Document 1 discloses a pressure vessel for high-pressure hydrogen gas and a pipe for high-pressure hydrogen gas in which a base material that is extremely less affected by hydrogen is covered with aluminum or an aluminum alloy. In Patent Document 1, the target hydrogen equipment is limited to only a pressure vessel for high-pressure hydrogen gas and a pipe for high-pressure hydrogen gas. Furthermore, it is intended to apply a film to a base material that is extremely less affected by hydrogen, and is not intended for base materials that are affected by hydrogen (carbon steel, low alloy steel, martensitic stainless steel). It is considered that the formation state of the surface film and the hydrogen penetration characteristics strongly depend on the type of the base material. However, the examples are only austenitic stainless steel and duplex stainless steel including austenitic phase, and the film formation state and hydrogen on steel materials (carbon steel, low alloy steel, martensitic stainless steel) affected by hydrogen The intrusion characteristics are not clear. Furthermore, Patent Document 1 defines only the thickness of the aluminum layer, and the formation state and film thickness of the aluminum-based intermetallic compound layer (Fe—Al alloy layer), which are extremely important from the viewpoint of the film strength, are unknown. .

  Patent Document 2 discloses an alumina film formed on ferritic stainless steel as a component of a solid oxide fuel cell. Patent Document 3 discloses a catalyst supporting layer of an alumina film formed in a tunnel-like flow path on a bonding surface of a set of substrates as a hydrogen production apparatus for a fuel cell. In Patent Document 2, an alumina coating is used to prevent cracking due to thermal stress in a high temperature environment, and does not prevent hydrogen from entering the base material in a high temperature and high pressure hydrogen environment. The alumina coating of Patent Document 3 absorbs thermal strain due to the difference in thermal expansion coefficient between the metal substrate and the catalyst by increasing the surface area of the catalyst support layer, and can be used as a base material in a high temperature / high pressure hydrogen environment. It is not a technology to prevent hydrogen intrusion.

  Patent Document 4 discloses a catalyst carrier having a layer of niobium, titanium, tantalum or the like between a stainless steel plate of a base material and a porous alumina layer formed by anodization in a dehydrogenation catalyst body of a hydrogen supply device. Has been. This catalyst carrier is intended to improve the high-temperature heat resistance of the hydrogen supply device by uniformly forming an anodic oxide film, and does not prevent hydrogen from entering the base material.

JP 2004-324800 A JP 2006-236600 A JP 2007-8731 A JP 2010-82513 A

  Under the usage conditions of hydrogen equipment in which high-pressure hydrogen gas is used, it is required to obtain a hydrogen-resistant permeation film for hydrogen equipment having excellent strength characteristics at low cost without causing hydrogen embrittlement. Yes. However, until now, no hydrogen-resistant permeation film has been provided that sufficiently satisfies the safety and economics of hydrogen equipment composed of steel materials affected by hydrogen.

  According to Patent Documents 2 to 4, it is impossible to effectively prevent hydrogen intrusion into the base material in a high-temperature and high-pressure hydrogen environment. According to Patent Document 1, it is important between aluminum and metal to increase the strength of the film. Since no consideration is given to the thickness of the compound layer, it is not possible to effectively prevent hydrogen from entering the base metal in a high-temperature and high-pressure hydrogen environment, and the base metal is susceptible to hydrogen other than austenitic stainless steel. The applicability to this case was not given.

  For this reason, hydrogen equipment that uses high-pressure hydrogen gas is constructed using a hydrogen-resistant permeation film that is excellent in both hydrogen permeation resistance and strength characteristics, even in the case of a base material that is susceptible to hydrogen. It has been desired to effectively prevent hydrogen intrusion and to provide a base material for a hydrogen device having a durable coating structure and to suppress the manufacturing cost as much as possible. An object of the present invention is to positively impart a durable surface film to a steel material affected by hydrogen, to suppress hydrogen embrittlement of the steel material, and to reduce manufacturing costs.

  The present invention is intended to solve the above-mentioned problems with respect to imparting a hydrogen permeation film to steel materials (carbon steel, low alloy steel, martensitic stainless steel, etc.) that are affected by hydrogen alone. The base material for hydrogen equipment according to claim 1 of the present invention has one selected from carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel as a base material on the surface of the base material. A hydrogen device base material in which a hydrogen permeation film is formed, wherein the hydrogen permeation film is a three-layer structure film in which an aluminum-based intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated on the surface of a base material. The average thickness of the hydrogen-resistant permeation film is 3 μm or more and less than 35 μm.

  The base material for hydrogen equipment according to claim 2 is a base material selected from carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel, and a hydrogen permeation film is formed on the surface of the base material. A base material for hydrogen equipment formed, wherein the hydrogen-resistant permeation film is a three-layer structure film in which an aluminum intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated on a surface of a base material, and the aluminum metal The thickness of the intermetallic compound layer is 1 to 22 μm, and the average thickness of the hydrogen-resistant permeation film is less than 35 μm.

  The base material for hydrogen equipment according to claim 3 is an Al-Si-based aluminum alloy in which the hydrogen-resistant permeation film has an added Si amount of 1 to 5%, and is hot-dip plated at a temperature range above the melting temperature and below the transformation point. Is formed on the base material.

  The base material for hydrogen equipment according to claim 4 is such that the material of the base material is low alloy steel or martensitic stainless steel.

  According to a fifth aspect of the present invention, there is provided a method for producing a base material for hydrogen equipment, wherein one selected from carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel is used as a base material, and the surface of the base material is resistant to hydrogen. A method for producing a base material for a hydrogen device having a permeable film, wherein an Al-Si-based aluminum alloy having an added Si amount of 1 to 5% at the time of forming the hydrogen-resistant permeable film is used above a melting temperature. In the temperature range below the transformation point, an aluminum intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated on the surface of the base material to form a three-layer structure film, and the average of the hydrogen permeation resistance film The thickness is 3 μm or more and less than 35 μm.

  According to a sixth aspect of the present invention, there is provided a method for manufacturing a base material for hydrogen equipment, wherein one selected from carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel is used as a base material, and the surface of the base material is resistant to hydrogen. A method for producing a base material for a hydrogen device having a permeable film, wherein an Al-Si-based aluminum alloy having an added Si amount of 1 to 5% at the time of forming the hydrogen-resistant permeable film is used above a melting temperature. The aluminum-based intermetallic compound layer is formed by forming a three-layer structure film in which an aluminum-based intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated on the surface of the base material by performing hot-dip plating in a temperature range below the transformation point. And the average thickness of the hydrogen permeation-resistant film is less than 35 μm.

  According to a seventh aspect of the present invention, there is provided a method for producing a base material for a hydrogen device, wherein the base material is low alloy steel or martensitic stainless steel.

  The base material for hydrogen equipment according to the present invention is made of a molten aluminum alloy for a steel material (carbon steel, low alloy steel, martensitic stainless steel, etc.) that is affected by hydrogen alone, and an aluminum base material. A three-layer structure film (referred to as a hydrogen permeation film) having an average thickness of less than 35 μm is formed by sequentially laminating an intermetallic compound layer, an aluminum layer, and an alumina layer. A film obtained by further laminating a layer on the surface of the alumina layer is used as a base material for the hydrogen equipment of the present invention regardless of the material / structure. By providing a hydrogen-resistant permeation film, it is possible to suppress hydrogen intrusion into a base material of a hydrogen device used in a high-pressure hydrogen environment, and substantially prevent hydrogen embrittlement. As a result, the hydrogen equipment can be used safely, and the production cost of the hydrogen equipment can be kept low.

FIG. 2 is an optical micrograph of a hydrogen resistant permeation film and a normal film when austenitic stainless steel SUS304 is used as a base material, (a) is a hydrogen permeation film, (b) is a normal film, and (c) is a test piece. It is a figure which shows the observation method. It is the reflection electron image which observed the cross section of the aluminum layer-intermetallic compound layer part especially of a hydrogen-resistant permeation | transmission film | membrane. It is an optical microscope photograph of the Vickers indentation of the aluminum system intermetallic compound layer of a hydrogen-resistant permeation | transmission film | membrane and a normal film | membrane, (a) is a hydrogen-permeation permeation film, (b) is a normal film | membrane. It is an optical microscope photograph of a hydrogen-resistant permeation | transmission film | membrane, (a) is a thing in case a base material is the low alloy steel SCM435, (b) is a thing in case a base material is martensitic stainless steel SUS630. It is an optical microscope photograph of the film | membrane formed on the surface of low alloy steel SCM435 using the molten Al alloy which changed Si amount, (a) is Si amount 0%, (b) is Si amount 3%, (c ) Is the state of film formation when the Si content is 6%. (A) Secondary electron image and (b) Si mapping by energy dispersive X-ray analysis of a film formed on the surface of low alloy steel SCM435 using a molten Al alloy with 6% Si content added. The figure which shows the relationship between the hydrogen-resistant permeation | transmission film | membrane formed in SUS304, SUS630, and SCM435, the thickness of the Fe-Al layer of the normal film | membrane formed in SUS304, and the Vickers hardness by holding | maintenance for 30 second with the load of 100 mN of a Fe-Al layer. It is. It is a graph which shows the relationship between the hydrogen penetration | invasion amount and the exposure pressure of the base material of austenitic stainless steel SUS304, martensitic stainless steel SUS630, and low alloy steel SCM435. It is a graph which shows the relationship between the hydrogen penetration | invasion amount and the exposure pressure of the test piece which gave the surface film of the surface film | membrane without a surface film | membrane which uses austenitic stainless steel SUS304 as a base material, a hydrogen-resistant permeation | transmission film | membrane, and an aluminum type | system | group bilayer film. A test piece with a surface coating of a surface coating made of an austenitic stainless steel SUS304 exposed to hydrogen gas at a pressure of 100 MPa and a temperature of 270 ° C. for 200 hours, a hydrogen permeation coating, and an aluminum two-layer coating. It is a TDA spectrum. It is a graph which shows the relationship between the hydrogen penetration | invasion amount and the exposure pressure of the test piece which gave the surface film of the surface filmless test piece which made the martensitic stainless steel SUS630 a base material, a hydrogen-resistant permeation | transmission film | membrane, and an aluminum type | system | group bilayer film. Test piece without surface film and hydrogen permeation film, aluminum type two-layer film with martensite stainless steel SUS630 exposed to hydrogen gas at a pressure of 100 MPa and temperature of 270 ° C. for 200 hours as a base material This is a TDA spectrum. It is a graph which shows the relationship between the hydrogen penetration | invasion amount and the exposure pressure of the test piece which did not have the surface membrane | film | coat which uses low alloy steel SCM435 as a base material, and the test piece which gave the hydrogen-permeable permeable film. (A) is a figure which shows the shape and dimension of the round bar test piece which uses SUS304 for evaluating the hydrogen penetration | invasion amount as a base material, (b) is an unexposed material and hydrogen of the round bar test piece of (a). It is a nominal stress-stroke curve by the result implemented at room temperature and air | atmosphere with respect to the exposed material. It is the external appearance and fractured surface after the tensile test of the unexposed test piece which has not provided the film | membrane observed by the scanning electron microscope (SEM). It is the external appearance after a tensile test of the unexposed test piece which provided the film | membrane observed by SEM, and a fracture surface. It is the external appearance after a tensile test of a hydrogen exposure test piece which has not given the film observed by SEM, and a fracture surface. It is the external appearance and fracture surface of the hydrogen exposure test piece which provided the film | membrane observed by SEM after the tension test. It is the relationship between the amount of hydrogen of a cylindrical test piece provided with a surface coating using SUS304 exposed to hydrogen gas at a pressure of 100 MPa and a temperature of 270 ° C. for 200 hours as measured by TDA and the diameter of the test piece. It is a hydrogen intensity distribution inside the film of a cylindrical test piece provided with a surface film based on SUS304 analyzed using a secondary ion mass spectrometer (SIMS), (a) and (b) are hydrogen exposed materials, (C) is the distribution of the unexposed material. (A) is a figure which shows the shape and dimension of the round bar test piece of the base material of SUS304 for evaluating membrane | film | coat strength, (b) is air | atmosphere with respect to the unexposed material of the round bar test piece of (a). It is a nominal stress-nominal strain curve by the result implemented by. After a single load of (a) σ = 332 MPa, (b) σ = 376 MPa, (c) σ = 442 MPa, and (d) σ = 588 MPa on a round specimen of a SUS304 base material with a coating applied to the entire surface, respectively. It is a figure which shows the optical microscope photograph of the film cross section of this, and the hydrogen penetration | invasion amount in each case with a bar graph. It is the external appearance photograph of the test piece after the single load of the round bar test piece of the base material of SUS304 which respectively gave the hydrogen-resistant permeation film and the normal film on the entire surface, (a) is a hydrogen-resistant permeation film, and (b) is usually This is the case with a film. Fig. 2 shows the state of cracking of the coating after a single load of a round bar test piece made of SUS304 with a hydrogen resistant permeation coating and a normal coating applied to the entire surface, (a) is a hydrogen permeation coating, (b) Is the case of a normal film. It is a schematic diagram of the crack generation-peeling process of the test piece which provided the hydrogen-resistant permeation | transmission film | membrane and the normal film | membrane under single load. It is a figure which shows the FEM model used for a stress analysis, and pays attention to the stress of the direction perpendicular | vertical to the tension | tensile_strength direction generate | occur | produced in the layer and between layers after crack generation. It is a figure which shows the boundary conditions and material property value of a FEM model. It is a figure which shows the stress distribution in the layer calculated | required by FEM, and between layers, and shows the stress of the direction perpendicular | vertical to the tension | tensile_strength generate | occur | produced in the layer and between layers after crack generation. It is a figure which shows the relationship between the degree of the stress concentration in the Fe-Al layer and base material interface computed by FEM, and the thickness of a Fe-Al layer, and the direction perpendicular | vertical to the tensile direction which generate | occur | produces in a layer and between layers after crack generation This shows the stress. It is a perspective view which shows the piping test piece shape of SCM435 used for the pressure cycle test in high-pressure hydrogen gas, and SUS630. It is an optical micrograph of a hydrogen-resistant permeation film after a pressure cycle test about the case of (a) base material of SCM435 and (b) base material of SUS630.

  For materials exposed to high-pressure hydrogen gas environments, a film is formed on the surface of the material to prevent hydrogen from entering the material. It is thought that the conversion can be suppressed. In that case, it is important that the surface film is excellent in both hydrogen gas barrier properties and strength characteristics under the use conditions.

The hydrogen permeation film in the base material for hydrogen equipment of the present invention has a three-layer structure of an aluminum-based intermetallic compound layer, an aluminum layer, and an alumina layer (Al ₂ O ₃ ), and has an average film thickness. The surface film is less than 35 μm. The average film thickness is about 1/5 to 1/10 of a normal film having an order of 100 μm. Here, the normal film is a film thickness that satisfies the standard of JISH8642 molten aluminum plating (HAD1: film thickness 60 μm or more, HAD2: film thickness 70 μm or more, HAD3: aluminum-based intermetallic compound layer thickness 50 μm or more) It is what has. In the hydrogen-resistant permeation film of the present invention, the material as a base material is not limited, and is particularly applicable to steel materials (carbon steel, low alloy steel, martensitic stainless steel, etc.) that are affected by hydrogen.

[Materials used]
In order to clarify the influence of the base material on the formation state of the surface film, austenitic stainless steel SUS304, martensitic stainless steel SUS630 and low alloy steel SCM435 were used as the base material. The chemical components of SUS304, SUS630 and SCM435 are as shown in Table 1. The unit is mass%. The low alloy steel is an alloy steel having an alloy element amount other than iron and carbon of 5% or less.

  SUS304 is subjected to solution treatment, SUS630 is subjected to aging treatment after solution treatment, and SCM435 is subjected to quenching / tempering treatment.

[Specimen shape]
In SUS304 and SUS630, a cylindrical test piece having a diameter of 10 mm and a length of 50 mm was used. In SCM435, a cylindrical test piece having a diameter of 20 mm and a length of 25 mm was used.

[Surface film formation]
A method for forming a hydrogen permeation-resistant film according to the present invention will be described. The material to be the base material is not particularly limited. The base material is degreased, washed with water and pickled, then washed with water and dried. The base material is immersed in a bath in which the aluminum alloy is melted. After soaking for a predetermined time, post-treatment and finishing are performed. Through the above steps, when the base material is austenitic stainless steel SUS304, the three-layer structure film shown in FIG. 1A is formed.

  In the present invention, the average thickness of the hydrogen-resistant permeation film, in particular, the thickness of the aluminum-based intermetallic compound layer that greatly affects the strength and durability of the film is 1 to 22 μm, and the average thickness of the hydrogen-resistant film is less than 35 μm. For this purpose, the molten aluminum alloy in which the base material is immersed is added with 1 to 5% of Si, and the temperature of the molten aluminum alloy in the bath is equal to or higher than the melting temperature. Hot dipping is performed in a temperature range below the transformation point. The thickness of the aluminum-based intermetallic compound layer does not depend on the immersion time, but greatly depends on the immersion temperature and the amount of Si added.

  In order to clarify the influence of the surface film on the hydrogen penetration characteristics, a test piece with a film formed on the entire surface and a non-coated film were prepared. As the surface film, a hydrogen-resistant permeation film and an aluminum-based two-layer film composed of a two-layer structure of an aluminum-based intermetallic compound layer and an alumina layer were prepared for comparison. The aluminum-based two-layer coating is obtained by heat-treating the hydrogen-resistant permeation coating.

The hydrogen permeation film according to the present invention was compared with a normal film. FIG. 1B shows an optical micrograph of the normal film. The base material is austenitic stainless steel SUS304. Both the hydrogen permeation resistant film and the normal film have a three-layer structure of an aluminum-based intermetallic compound layer, an aluminum layer, and an alumina layer (Al ₂ O ₃ ). The average thickness of the film and the hardness of the aluminum-based intermetallic compound layer are Different. Usually, the average film thickness of the film is 100 μm or more. On the other hand, the average film thickness of the hydrogen-resistant permeation film (aluminum-based three-layer film) is less than about 15 μm regardless of the type of the base material. It is about twice as thick. FIG. 1 also shows the Vickers hardness HV of the aluminum-based intermetallic compound layer measured with a load of 100 mN and holding for 30 seconds. It is about ½ compared to. FIG. 1C shows a method for observing a test piece. Since the first alumina layer is thin and difficult to observe with an optical microscope, the test piece is embedded in a resin and observed.

  FIG. 2 is a backscattered electron image obtained by observing a cross section of the hydrogen-resistant permeation film, and points B1 (aluminum layer), B2 (intermetallic compound layer), and B3 (intermetallic compound layer) in the cross-sectional direction in the hydrogen-resistant permeation film part. Table 2 shows the results of measurement of local chemical components in the sample by energy dispersive X-ray analysis (EDX).

  In the hydrogen-resistant permeation film shown in Table 2, particularly in terms of the component ratio of the aluminum layer, the component ratio of Si at B1 in the aluminum layer is significantly reduced from the component ratio in the case of the molten aluminum alloy, On the other hand, it is increased at the locations B2 and B3 of the intermetallic compound layer on the aluminum layer side. This indicates that Si in the molten aluminum alloy is shifted to the intermetallic compound layer side during the formation of the hydrogen permeation-resistant film, and the Si component in the aluminum layer is reduced accordingly. As shown in FIG. 2, since Si segregates in the intermetallic compound layer and makes the intermetallic compound layer itself brittle, it is necessary to avoid the addition of a large amount of Si.

  In FIG. 3, the optical microscope photograph of the Vickers impression of the aluminum type intermetallic compound layer of a hydrogen-resistant permeation | transmission film | membrane and a normal film | membrane is shown. In contrast to the hydrogen permeation resistant film, a crack is generated around the indentation in the aluminum-based intermetallic compound layer of the normal film. As described above, in the normal film satisfying the film thickness of JISH8642 hot-dip aluminum plating with respect to the hydrogen permeation-resistant film, an aluminum-based intermetallic compound layer having high hardness and brittleness is formed.

  As shown in the result shown in FIG. 22 described later, the hydrogen-resistant permeation film is broken from the aluminum-based intermetallic compound layer. For this reason, it is considered that the hydrogen-resistant permeation film has better durability as the hardness of the aluminum-based intermetallic compound layer is lower and the intermetallic compound is more flexible. From the results shown in FIGS. 1A and 1B, the thinner the aluminum-based intermetallic compound layer, the lower the hardness of the intermetallic compound layer. Therefore, in order to keep the hardness of the aluminum-based intermetallic compound layer low, it is important to control the average thickness of the film by adjusting the components and processing conditions of the molten aluminum alloy.

  FIG. 4 shows an optical micrograph when a hydrogen-resistant permeation film is applied to the base materials of low alloy steel SCM435 and martensitic stainless steel SUS630. Regardless of the type of base material, a three-layer structure film having an average film thickness of less than 35 μm is formed on the surface of the base material. The figure also shows the Vickers hardness HV of the aluminum-based intermetallic compound layer measured with a load of 100 mN and holding for 30 seconds, and between the aluminum-based metal of the hydrogen-resistant permeation film formed on the surface of SUS304, SUS630, and SCM435. The Vickers hardness of the compound layer shows almost the same value, and is usually about ½ of the Vickers hardness of the aluminum-based intermetallic compound of the film.

From a series of experimental results, if the average thickness of the film can be controlled to be less than 35 μm regardless of the type of the base material, the hardness of the aluminum-based intermetallic compound layer constituting the film is about ½ that of the normal film. Can be suppressed. The Fe—Al alloy includes an Fe ₃ Al phase, an FeAl phase, an Fe ₂ Al ₅ phase, and the like depending on the component ratio of Fe and Al. Among these phases, the Fe ₂ Al ₅ phase has a high hardness and a brittle structure. In an actual aluminum-based intermetallic compound layer, these phases are considered to be mixed. From the experimental results that the thinner the aluminum-based intermetallic compound layer, the lower the hardness of the intermetallic compound layer, it is surmised that the formation of a brittle alloy phase with high hardness was suppressed by suppressing interdiffusion of Fe and Al. The

  In order to reduce the thickness of the aluminum-based intermetallic compound layer, it is necessary to adjust the components and processing conditions of the molten aluminum alloy to suppress interdiffusion of Fe and Al. Specifically, pure aluminum is used in the dipping process for forming a film, whereas an Al—Si-based aluminum alloy is used in the hydrogen permeation film. 5 (a) to 5 (c) show optical micrographs of a film formed on the surface of the low alloy steel SCM435 using a molten Al alloy in which the amount of Si is changed. (A) shows 0% Si, (b ) Is for 3% Si and (c) 6% Si. In contrast to the case where pure Al is used, the Fe—Al layer becomes thinner by adding Si. However, when 6% of Si is added, as shown in FIG. 6, a eutectic Si phase is formed in the Al layer, and the film (Al layer + Fe—Al layer) becomes thick. FIG. 6 shows a film formed on the surface of low alloy steel SCM435 using a molten Al alloy to which 6% of Si is added, (a) is a secondary electron image, and (b) is an energy dispersive X-ray analysis. Si mapping.

  Since addition of Si lowers the melting point of Al, a thin film can be easily formed by using an Al—Si alloy with respect to pure Al. Further, from the hydrogen strength analysis inside the film using SIMS, which will be described later in [0072], a hydrogen trap is performed at the interface between the Al layer and the Fe—Al layer and in the region where the Si concentration in the Fe—Al layer changes. Intrusion of hydrogen into the material is prevented. From this, it is thought that Si addition is effective in suppressing hydrogen intrusion. However, when Si is added in a large amount, embrittlement of the Fe—Al layer is promoted by Si segregation, and a eutectic Si phase is formed in the Al layer, so the Si amount is reduced to 1 to 5%. It is preferable to do. Moreover, the immersion treatment for forming the hydrogen permeation-resistant film is performed at a temperature not lower than the melting temperature and not higher than the transformation point.

  FIG. 7 shows the hydrogen permeation film formed on SUS304, SUS630 and SCM435 and the thickness of the Fe—Al layer of the normal film formed on SUS304 and the Vickers hardness of the Fe—Al layer (held at a load of 100 mN for 30 seconds). The relationship is shown. The Vickers hardness of the Fe—Al layer increases in proportion to the thickness of the Fe—Al layer. In the figure, the average value of the Vickers hardness of the Fe—Al layer in the hydrogen permeation film formed on SUS304, SUS630 and SCM435 is HV = 645, and the standard deviation Σ is HV = 22. Considering a variation of ± 3Σ, which is a probability of 99.7% of the Vickers hardness, the range of the Vickers hardness of the Fe—Al layer of the hydrogen-resistant permeation film is HV = 579 to 711. The thickness of the Fe—Al layer of the hydrogen-resistant permeation film corresponding to this range is 1 to 22 μm.

  The thickness of the Al layer of the hydrogen resistant permeation film formed on SUS304, SUS630 and SCM435 is 6 μm. Considering a variation of ± 3Σ, which is a probability of 99.7% of the thickness of the Al layer, the range of the thickness of the Al layer of the hydrogen-resistant permeation film is 2 to 10 μm.

  From stress analysis by FEM shown in FIG. 29 described later, when the film becomes thicker, a crack perpendicular to the tensile direction occurs in the Fe-Al layer, and then a high stress is generated at the interface between the Fe-Al layer and the base material. Peeling is encouraged. By reducing the thickness of a normal coating having an average coating thickness of the order of 100 μm, it is possible to reduce the stress in the direction perpendicular to the tensile direction after the occurrence of cracks. That is, the difference in the peeling behavior between the hydrogen-resistant permeation film and the normal film in FIG. 23 described later is due to the difference in the structure of the Fe—Al layer and the generated stress. Thus, it is desirable that the film is thinner from the viewpoint of the film strength. However, from the viewpoint of suppressing hydrogen intrusion, a certain film thickness is required. Actually, when a hydrogen-resistant permeation film is applied to various base materials, although the film thickness and the Vickers hardness of the Fe-Al layer are not the same, it has an excellent hydrogen barrier function and is superior to the normal film. Film strength is secured. Therefore, the range of the film thickness of the hydrogen-resistant permeation film is determined from the variation in the Vickers hardness of the Fe—Al layer constituting the hydrogen-resistant permeation film applied to various base materials.

  From the examination of the film thickness considering the variation, the thickness of the Fe—Al layer of the hydrogen permeation film formed on SUS304, SUS630 and SCM435 is 1 to 22 μm, and the total thickness of the film is 3 to 35 μm. As shown in FIGS. 1 and 3 and FIG. 23 to be described later, in the case of the film thickness within the range implemented in the present invention, the hydrogen-resistant permeation film has an excellent hydrogen barrier function, and the scope of the present invention is Excellent film strength compared to normal film with film thickness exceeding. In order to form both excellent hydrogen permeation resistance and strength characteristics, it is necessary to use an Al—Si based aluminum alloy having an appropriate Si amount. The addition of a large amount of Si not only promotes embrittlement of the Fe—Al layer by Si segregation, but also causes the formation of a eutectic Si phase in the Al layer, so the Si layer is controlled to 1 to 5%, It is necessary to control the thickness of the Fe—Al layer to 1 to 22 μm and the total thickness of the coating to 3 to 35 μm.

  The formation state of the film is slightly different depending on the type of the base material. In low alloy steel and carbon steel, which have a smaller amount of alloy component in the base material than stainless steel, the film thickness increases when the film is processed under the same conditions. In order for the average thickness of the film to be less than 35 μm, it is necessary to adjust the components and processing conditions of the molten aluminum alloy for each base material within the range of the Si amount and the processing temperature described in [0043]. .

[Hydrogen exposure test]
A hydrogen exposure test was performed on a test piece provided with a hydrogen permeation film on the base material. The hydrogen exposure test is a test in which a test piece is exposed to high-pressure hydrogen gas, and the amount of hydrogen that has entered the test piece is measured using a gas chromatograph mass spectrometer (TDA).

  In the hydrogen exposure test, the test piece was exposed to a hydrogen gas environment at an exposure pressure of 10 to 100 MPa and an exposure temperature of 270 ° C. for 200 hours. Under this exposure condition, regardless of the material, the amount of hydrogen in the test piece not provided with the surface film is saturated, and the hydrogen concentration distribution in the base material becomes uniform.

(Measurement of hydrogen content)
In the hydrogen amount measurement by TDA, the test piece was heated from room temperature to a temperature of 600 ° C. under a temperature increase rate of 100 ° C./h, and the amount of hydrogen released from the test piece was measured. In the relationship between the obtained hydrogen release rate and temperature (hydrogen thermal desorption spectrum), the amount of hydrogen at the first peak was defined as the amount of hydrogen that penetrated into the test piece (hydrogen penetration amount).

[Hydrogen penetration characteristics]
After exposing the cylindrical test piece in a hydrogen gas environment, in SUS304 and SUS630, the test piece was cut into thicknesses of 0.5 mm and 5 mm, respectively, and the amount of hydrogen was measured. In SCM435, the amount of hydrogen was measured without cutting the test piece. In FIG. 8, the relationship between the hydrogen penetration | invasion amount and exposure pressure of the cylindrical test piece which has not provided the surface film is shown.

The saturated hydrogen amount C _S of hydrogen entering the steel material is generally calculated by the following equation using the exposure pressure P and the exposure temperature T. The saturated hydrogen amount is the amount of hydrogen in an equilibrium state where the hydrogen concentration inside the test piece of the material determined by the external pressure and temperature is uniform.
Here, S: hydrogen solubility, f: fugacity, R: gas constant (= 8.314 J / (mol · K), b: constant (= 15.84 cm ³ / mol) (for b, CSMarchi et al., International Journal of Hydrogen Energy, Vol. 32 (2007), pp. 100-116) S ₀ and ΔH _S are coefficients determined depending on the material.

In FIG. 8, the saturated hydrogen amount of the base material of each material is approximated by least squares using equation (1). The hydrogen solid solubility S of the base material at a temperature of 270 ° C. is 8.53 mass ppm · MPa ^−1/2 for SUS304, 1.33 mass ppm · MPa ^{−1/2 for} SUS630, and 0.098 mass ppm · for SCM435. MPa ^-1/2 . The hydrogen solubility of SUS630 is about 1/6 that of SUS304. On the other hand, the hydrogen solid solubility of SCM435 is about 1/100 that of SUS304, and the amount of saturated hydrogen is extremely small.

  FIG. 9 shows the relationship between the amount of hydrogen intrusion and the exposure pressure of a test piece without a coating using austenitic stainless steel SUS304 as a base material and a test coating provided with a surface coating (hydrogen permeation resistant coating, aluminum-based two-layer coating). The amount of hydrogen in the unexposed specimen without coating is 1 mass ppm. FIG. 10 shows a hydrogen thermal desorption spectrum of a test piece using SUS304 exposed in hydrogen gas at a pressure of 100 MPa and a temperature of 270 ° C. as a base material.

  In the result of FIG. 9, the hydrogen penetration amount of the test piece provided with the hydrogen permeation resistant film is extremely small compared to the test piece without the film, and the hydrogen permeation resistant film has a high hydrogen penetration suppression function. On the other hand, the aluminum-based two-layer coating has a function of suppressing hydrogen intrusion, similar to the hydrogen-resistant permeation coating, but its function is inferior to that of the hydrogen-resistant permeation coating.

  In the hydrogen temperature-programmed desorption spectrum shown in FIG. 10, the peak of the hydrogen release rate of the test piece without the film and the test piece provided with the aluminum-based two-layer film is almost the same (around 330 ° C.). On the other hand, the peak of the hydrogen release rate of the test piece provided with the hydrogen permeation resistant film is around 300 ° C. From this result, the hydrogen content of the test piece provided with the hydrogen permeation film is mainly measured because the amount of hydrogen that has entered the base material is small.

  FIG. 11 shows the relationship between the hydrogen intrusion amount and the exposure pressure of a test piece without a film using a martensitic stainless steel SUS630 as a base material and a test film provided with a surface film (hydrogen-resistant permeation film, aluminum-based two-layer film). The amount of hydrogen in the unexposed specimen without a film is 0.05 mass ppm. FIG. 12 shows a hydrogen thermal desorption spectrum of a test piece using SUS630 exposed in hydrogen gas at a pressure of 100 MPa and a temperature of 270 ° C. as a base material.

  In the results shown in FIG. 12, as in the case of using SUS304 as a base material, the hydrogen penetration amount of the test piece provided with the hydrogen-resistant permeation film is extremely small compared to the test piece without the surface film, and the hydrogen-resistant permeation film has a high hydrogen content. Has an intrusion suppression function. On the other hand, the amount of hydrogen penetration of the test piece provided with the aluminum-based two-layer coating is larger than that of the test piece provided with the hydrogen-resistant permeation coating, and the hydrogen penetration suppression function of the aluminum-based two-layer coating is inferior to that of the hydrogen-resistant permeation coating. Yes.

  In the hydrogen temperature-programmed desorption spectrum shown in FIG. 12, the peak of the hydrogen release rate of the test piece without the coating and the test piece provided with the aluminum-based bilayer coating is almost the same (near 270 ° C.) regardless of the exposure pressure. Yes. On the other hand, the peak of the hydrogen release rate of the test piece provided with the hydrogen permeation resistant film is around 300 ° C. The peak temperature of the test piece provided with the hydrogen-resistant permeation film is different from the other test pieces as in the case where SUS630 is used as the base material. This is because the amount of hydrogen entering the surface film is mainly measured.

  From the hydrogen thermal desorption spectrum of the test piece with the hydrogen permeation film, the hydrogen penetration amount of the test piece with the hydrogen permeation film is small because the amount of hydrogen intrusion into the base material is small. Measured mainly. When exposed to hydrogen at a pressure of 100MP and a temperature of 270 ° C, the influence of hydrogen that has penetrated the surface film is large. Therefore, with SCM435 where the amount of saturated hydrogen in the base material is very small compared to SUS304 and SUS630, only hydrogen exposure at a pressure of 10MPa and a temperature of 270 ° C The hydrogen permeation resistance characteristics of the surface film were evaluated.

  FIG. 13 shows the relationship between the hydrogen intrusion amount and the exposure pressure of a test piece without a coating made of the low alloy steel SCM435 and a test piece provided with a hydrogen permeation resistant coating. The amount of hydrogen in the unexposed film-free test piece is 0 mass ppm. Moreover, the hydrogen amount in the unexposed of the test piece which provided the hydrogen-permeable permeation film is 0.01 mass ppm.

  From the results shown in FIG. 13, the hydrogen penetration amount of the test piece using SCM435 provided with a hydrogen permeation film as a base material is very small compared to the test piece without the surface film. Thus, regardless of the base material, the hydrogen-resistant permeation film has an excellent hydrogen intrusion suppression function.

  In the hydrogen permeation-resistant film and the aluminum-based two-layer film, the amount of hydrogen intrusion of the test piece provided with the hydrogen-resistant permeation film is the same as that of the aluminum-based two-layer film even though an alumina layer having the same thickness is formed on the outermost surface. Less than the hydrogen penetration amount of the test piece provided with the layer coating. This result means that the hydrogen penetration inhibiting function of the surface film is not only due to the outermost alumina layer. An alumina layer in a low-pressure hydrogen gas having a pressure of the order of kPa is expected to suppress hydrogen invasion by suppressing the dissociation reaction of hydrogen molecules. However, such an effect cannot be expected in an alumina layer with high-pressure hydrogen gas at a pressure of the order of MPa. The difference between the hydrogen-resistant permeation film and the aluminum-based two-layer film is the presence or absence of an aluminum layer. From this, the aluminum layer which comprises a membrane | film | coat has played a big role in the hydrogen penetration suppression function which was excellent in the hydrogen-resistant permeable membrane | film | coat in high pressure hydrogen gas.

  In order to confirm that hydrogen penetration into the base metal is suppressed by applying the film, a round bar test piece provided with a hydrogen permeation film on the entire surface shown in FIG. Exposure to gas for 200 hours. After the exposure, a tensile test of the test piece was performed at room temperature and in the atmosphere. The tensile speed is 1 mm / min.

  FIG. 14B shows a nominal stress-stroke diagram of the unexposed material and the hydrogen-exposed material. The results for the unexposed and hydrogen-exposed materials for the specimens without the coating and the unexposed and hydrogen-exposed materials for the specimen with the coating are shown. When the film is not applied, the elongation at break is significantly reduced by exposure to high-pressure hydrogen gas. On the other hand, when the film is applied, the elongation at break is almost the same as that of the unexposed material regardless of exposure to high-pressure hydrogen gas. The restriction is 77.1% for the unexposed specimen without the coating, 76.5% for the unexposed specimen with the coating, 37.8% for the hydrogen exposed specimen without the coating, and the coating. It is 74.4% in the hydrogen exposure test piece to which was given. The relative aperture of the test piece with no coating applied is 0.49, whereas the relative aperture of the test piece with the coating applied is 0.97. I can't. In FIG. 14B, the graphs of hydrogen exposure and non-exposure when the film is present are almost overlapped.

  15 to 18 show the appearance and fracture surface of a test piece after a tensile test observed using a scanning electron microscope (SEM). 15 is an unexposed test piece without coating, FIG. 16 is an unexposed test piece with coating, FIG. 17 is a hydrogen exposed test piece without coating, and FIG. 18 is a hydrogen exposure test with coating. The appearance and fracture surface of the piece. 15 to 18, (a) is observed from 0 ° direction, (b) is observed from 45 ° direction, (c) is observation of visual field 1, (d) is observation of visual field 1-1, (e) Indicates a fracture surface. In the hydrogen-exposed test piece to which no film is applied, the fracture proceeds from the surface, and a large number of cracks are observed on the surface of the test piece as shown in FIG. A pseudo-cleavage surface was observed on the fracture surface in the vicinity of the starting point, and it is surmised that the generation and propagation of surface cracks were promoted by hydrogen that had penetrated into the specimen. On the other hand, the hydrogen-exposed test piece (FIG. 18) provided with the film is similar to the unexposed test piece (FIG. 15) not provided with the film and the unexposed test piece (FIG. 16) provided with the film, It exhibits cup and cone destruction, and dimples are observed on the fracture surface. It can be said that the difference in the fracture behavior between the test piece not provided with the hydrogen-exposed film (Fig. 17) and the test piece provided with the film (Fig. 18) is due to the difference in the amount of hydrogen penetrating into the base material. It was confirmed from the strength test that hydrogen penetration into the base material was suppressed by the above.

  In order to elucidate the mechanism of hydrogen penetration inhibition, a film was applied to cylindrical test pieces having different diameters, and the test pieces were exposed to hydrogen gas at a pressure of 100 MPa and a temperature of 270 ° C. for 200 hours. The base material is SUS304. After the exposure, the amount of hydrogen penetrating the test piece was measured using TDA.

  FIG. 19 shows the relationship between the hydrogen penetration amount and the specimen diameter. The amount of hydrogen penetration of the cylindrical test piece provided with the coating depends on the size of the test piece. The smaller the diameter, the larger the amount of hydrogen penetration. In the figure, using the solution of the diffusion equation for hydrogen penetration of a cylindrical specimen, calculation was performed assuming that the substantial diffusion coefficient of SUS304 to which the film was applied was 1/10 to 1/10000 of the base material. The relationship between the hydrogen penetration amount and the specimen diameter is shown by a curve. The experimental data agrees well with the solution of the diffusion equation where the substantial diffusion coefficient is 1/1000 that of the base material, suggesting that hydrogen intrusion occurs at a diffusion-controlled rate.

The key point for reducing the substantial diffusion coefficient is the presence of the Al layer as described in [0064]. However, since the diffusion coefficient of Al itself is not much different from SUS304, the hydrogen barrier function of the film cannot be explained by a simple multilayer hydrogen diffusion model. For example, in the measurement of the hydrogen diffusion coefficient of SUS304 and pure Al (purity 99.9%) at a temperature of 188 ° C. using a hydrogen gas permeation method, 4.53 × 10 ⁻¹³ m ² / s (SUS304), 2.14 A result of × 10 ⁻¹³ m ² / s (SUS304) is obtained.

  In order to clarify the exact mechanism of suppression of hydrogen intrusion, the hydrogen intensity inside the film of the unexposed material to which the film was applied and the hydrogen exposed material were analyzed using a secondary ion mass spectrometer (SIMS). FIG. 20 shows the hydrogen intensity distribution by SIMS.

  FIG. 20 shows the hydrogen strength distribution inside the coating of a cylindrical test piece provided with a surface coating using SUS304 as a base material analyzed using a secondary ion mass spectrometer (SIMS). (A) and (b) are hydrogen exposed materials, and (c) is the distribution of unexposed materials. From the hydrogen intensity analysis by SIMS, a peak of hydrogen intensity is observed in the region where the Si concentration in the interface between the Al layer and the Fe—Al layer and the Fe—Al layer changes rapidly. As a result of the hydrogen trapping being blocked by the hydrogen trap in these regions, it is considered that the surface area through which hydrogen enters decreases and the substantial diffusion coefficient decreases. Due to such a mechanism, it is assumed that the presence of the Al layer was a key point for suppressing hydrogen intrusion. Similar to the interface between the Al layer and the Fe—Al layer, the region where the Si concentration in the Fe—Al layer changes abruptly also prevents hydrogen penetration, so an appropriate amount of Si addition is effective in suppressing hydrogen penetration. It is thought that.

[Evaluation of film strength]
In order to evaluate the film strength, a single load and a repeated load were applied to the round bar test piece provided with the film on the entire surface shown in FIG. FIG. 21B shows a nominal stress-nominal strain curve of the base material of SUS304. FIG. 21 (b) shows the results for the unexposed material carried out in the atmosphere. After applying the four-level load shown in FIG. 21 (b) to the round bar test piece provided with a film on the entire surface, the test piece was exposed to hydrogen gas at a pressure of 100 MPa and a temperature of 270 ° C. for 200 hours. After exposure, the amount of hydrogen penetrating the test piece was measured by TDA, and the crack occurrence state of the film was observed with an optical microscope.

FIG. 22 shows the hydrogen penetration characteristics of a round bar specimen subjected to a single load and the occurrence of cracks in the film. The base material is SUS304 (yield stress σ _y ≈350 MPa). If the single load is less than or equal to the yield stress of the base metal (σ _y = 332 MPa), the hydrogen penetration amount does not increase with respect to the unloaded test piece. However, when the single load exceeds the yield stress of the base metal, the hydrogen penetration amount increases with respect to the unloaded specimen. The higher the single load stress level, the greater the increase in hydrogen penetration for unloaded specimens. From the observation of the occurrence of cracks using an optical microscope, if a single load exceeds the yield stress of the base metal, cracks occur in the aluminum-based intermetallic compound layer. From this, it can be said that the increase in the hydrogen penetration amount of the test piece due to a single load is due to a crack generated in the Fe—Al layer.

  In FIG. 23, the external appearance photograph of the test piece after a single load is shown. (A) is a hydrogen permeation-resistant film, and (b) is a normal film. When the single load stress is 500 MPa, no cracking or peeling of the film is observed on the appearance. On the other hand, in the normal film, a plurality of cracks and peeling of the film are observed. As is apparent from the results of the test piece subjected to a single load, the hydrogen-resistant permeation film has a film strength superior to that of a normal film.

  FIG. 24 shows the crack occurrence state of the film after applying a single stress of 200 MPa, 300 MPa and 500 MPa to the hydrogen permeation resistant film and the normal film. In both the hydrogen permeation resistant film and the normal film, when the single load stress is 300 MPa or less, no crack is observed in the film. However, when the single load stress is 500 MPa, both the hydrogen-resistant permeation film and the normal film are damaged. The damage to the normal film is more severe than the hydrogen-resistant permeation film, and the normal film peels off from the interface between the Fe—Al layer and the base material. On the other hand, in the hydrogen-resistant permeation film, a crack parallel to the tensile direction involved in the peeling is generated from the region where the Si concentration in the Fe—Al layer changes rapidly.

  From the results shown in FIG. 24, in the hydrogen-resistant permeation film and the normal film, cracks in the direction perpendicular to the tensile stress are generated with the same level of stress. In other words, the critical stress for crack initiation is not significantly different between the hydrogen permeation film and the normal film. On the other hand, regarding the peel strength, the hydrogen-resistant permeation film is higher than the normal film, so that it is inferred that the difference in fracture process as shown in FIG. 24 occurred. FIG. 25 shows a schematic diagram of the hydrogen permeation-resistant film and the normal film destruction process.

  As shown in FIG. 26, FEM was used to calculate the stress generated in the Fe—Al layer and between the layers after crack generation, and the relationship between the peel strength and the film thickness was examined. FIG. 27 shows the FEM model used for the analysis. FEM analysis was performed in the plane strain state.

  FIG. 28 shows the result of FEM analysis of the stress generated in and between the Fe—Al layers. This is an analysis result when the Al layer thickness is 10 μm and the Fe—Al layer thickness is 10 μm. The stress in the direction perpendicular to the tensile direction that affects the peeling is shown. High stress is generated at the interface between the Al layer and the Fe—Al layer and the interface between the Fe—Al layer and the base material, and particularly, the stress at the interface between the Fe—Al layer and the base material is high. On the other hand, the stress in the Fe-Al layer is low compared to the interlayer, and the generation of cracks parallel to the tensile direction observed in the Fe-Al layer of the hydrogen permeation film is not a problem of the generated stress. It can be said that this is a problem of the structure of the Fe—Al layer related to Si segregation.

  FIG. 29 shows the result of FEM analysis of the stress generated at the interface between the Fe—Al layer and the base material. It is an analysis result when the vertical stress is perpendicular to the tensile direction affecting peeling and the Al layer thickness is 10 μm and the Fe—Al layer thickness is 10, 30, 50, 100 μm. The thicker the Fe—Al layer, the higher the stress at the interface. Accordingly, the difference in peel strength between the hydrogen permeation film and the normal film shown in FIG. 23 is related to the difference in the generated stress at the interface in addition to the structure of the Fe—Al layer.

[Evaluation of film durability]
In addition to the evaluation of the film strength by a single load, the measurement of cracks and the measurement of the amount of hydrogen penetration when 200 cycles of a repeated load of 0 MPa to 332 MPa below the yield stress of the base material (SUS304) are applied, It has been confirmed that the hydrogen penetration amount does not increase with respect to the unloaded specimen. In addition, the yield stress of the base material is higher than that of SUS304 SCM435 (σ _y ≈700 MPa)
Then, no crack is generated in the Fe—Al layer until the single load is about 600 MPa.

In order to evaluate the durability of the coating under a high-pressure hydrogen gas pressure cycle, a hydrogen permeation coating was applied to the inner surface of the pipe test piece having the shape shown in FIG. A pipe test piece provided with a hydrogen permeation film was subjected to a high pressure hydrogen gas pressure cycle of 0.6 MPa to 95 MPa at room temperature 16,500 times. The base materials are SCM435 and SUS630, and the circumferential maximum stress σ _max generated on the inner surface of the pipe without coating is 1/4 of the tensile strength σ _B of SCM435 (σ _max = σ _B / 4 ≈238 MPa The piping test piece was designed so that FIG. 31 shows optical microscope photographs of the hydrogen permeation film after the pressure cycle test, where (a) is for SCM435 and (b) is for SUS630.

  From the results when SCM435 and SUS630 shown in FIG. 31 are used as base materials, no cracks are observed in the surface film, and the hydrogen-resistant permeation film has excellent strength characteristics under the pressure cycle of high-pressure hydrogen gas. . Thus, regardless of the type of the base material, the hydrogen permeation-resistant film is excellent in both hydrogen permeation resistance and strength characteristics.

  Even with a material that is inferior in hydrogen embrittlement resistance, it is possible to produce a wide range of high-pressure hydrogen pipes, high-pressure hydrogen containers, etc. that ensure safety and strength characteristics by applying the hydrogen-resistant permeation film of the present invention. As a result, low-cost, high-strength materials such as carbon steel and low alloy steel can be used for main bodies such as pipes and containers.

Claims (7)

  A base material for hydrogen equipment in which one selected from carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel is used as a base material and a hydrogen-resistant permeation film is formed on the surface of the base material, The hydrogen-resistant permeation film is a three-layer structure film in which an aluminum-based intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated on the surface of a base material, and the average thickness of the hydrogen-resistant permeation film is 3 μm or more and less than 35 μm. A base material for hydrogen equipment, characterized in that it exists.   A base material for hydrogen equipment in which one selected from carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel is used as a base material and a hydrogen-resistant permeation film is formed on the surface of the base material, The hydrogen-resistant permeation film is a three-layer structure film in which an aluminum-based intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated on the surface of a base material, and the thickness of the aluminum-based intermetallic compound layer is 1 to 22 μm And the average thickness of the said hydrogen-resistant permeation | transmission film | membrane was less than 35 micrometers, The base material for hydrogen equipment characterized by the above-mentioned.   The hydrogen-resistant permeation film is formed by using an Al—Si-based aluminum alloy with an added Si content of 1 to 5% and performing hot-dip plating on the base material in a temperature range from the melting temperature to the transformation point. The base material for hydrogen equipment according to claim 1 or 2, wherein the base material is for hydrogen equipment.   The base material for hydrogen equipment according to any one of claims 1 to 3, wherein the base material is low alloy steel or martensitic stainless steel.   Method for producing a base material for a hydrogen device in which one selected from carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel is used as a base material and a hydrogen permeation film is formed on the surface of the base material In the formation of the hydrogen-resistant permeation film, an Al-Si-based aluminum alloy having an added Si amount of 1 to 5% is used and hot-dip plating is performed in a temperature range from the melting temperature to the transformation point, and the mother A three-layer structure film in which an aluminum-based intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated is formed on the surface of the material, and the average thickness of the hydrogen permeation-resistant film is 3 μm or more and less than 35 μm. A method for producing a base material for a hydrogen device.   Method for producing a base material for a hydrogen device in which one selected from carbon steel, low alloy steel, ferritic stainless steel and martensitic stainless steel is used as a base material and a hydrogen permeation film is formed on the surface of the base material In the formation of the hydrogen-resistant permeation film, an Al-Si-based aluminum alloy having an added Si amount of 1 to 5% is used and hot-dip plating is performed in a temperature range from the melting temperature to the transformation point, and the mother Forming a three-layer structure film in which an aluminum-based intermetallic compound layer, an aluminum layer, and an alumina layer are sequentially laminated on the surface of the material, the thickness of the aluminum-based intermetallic compound layer being 1 to 22 μm, and the hydrogen resistance A method for producing a substrate for a hydrogen device, wherein the average thickness of the permeable film is less than 35 μm.   The method for producing a base material for a hydrogen device according to any one of claims 5 and 6, wherein the base material is low alloy steel or martensitic stainless steel.