Rigid-film-coated object, machine component, and bearing

Abstract

Provided is a rigid-film-coated object, a machine component using the same, and a bearing, in which hydrogen embrittlement resistance and wear resistance are improved and sufficient strength is ensured. This rigid-film-coated object 1 has, on the surface of a base material 2, a rigid film 3 that suppresses the penetration / diffusion of hydrogen atoms. The base material 2 is made of martensitic stainless steel or martensitic precipitation hardening stainless steel and has a surface Vickers hardness of 500 Hv to 1,000 Hv. The Vickers hardness of the rigid film 3 is at least 0.9 times that of the base material 2 and is 3,000 Hv or less, and the rigid film 3 is a Ni film.

Description

Hard film forming body, machine part, and bearing

[0001] The present invention relates to a hard-film-formed body having a hard film on the surface of an iron-based alloy substrate, and to a machine part and a bearing using the same.

[0002] In recent years, there has been a demand for lighter and stronger mechanical parts used in automobiles, industrial machinery, and other applications. These mechanical parts are often used in environments prone to hydrogen intrusion. For example, when rolling parts such as rolling bearings and gears are used under conditions where water is mixed into the lubricant or where sliding occurs, the water and lubricant decompose to generate hydrogen. The penetration of this hydrogen into steel can lead to premature damage due to hydrogen embrittlement.

[0003] Conventionally, the following techniques have been proposed as countermeasures against hydrogen embrittlement. For example, Patent Document 1 describes a steel material having a crystalline FeS layer with a thickness of 1 μm or more on the surface. According to Patent Document 1, the crystalline FeS layer has the function of preventing hydrogen from penetrating from the outside and of discharging hydrogen that has once penetrated into the steel.

[0004] Patent Documents 2 and 3 describe stainless steels having resistance to hydrogen embrittlement, in which the surface of the stainless steel is subjected to electrolytic polishing treatment and coated with a passivated film.

[0005] Patent Document 4 describes a hydrogen engine in which components of the engine, such as cylinders and pistons, that come into contact with hydrogen gas are provided with a coating layer made of stainless steel.

[0006] Japanese Patent Publication No. 2023-109165 Japanese Patent No. 6853536 Japanese Patent No. 6869495 Japanese Utility Model Publication No. 51-137004

[0007] In recent years, hydrogen has been attracting attention as an alternative energy source to fossil fuels. When hydrogen is used as an energy source, it only produces water and no carbon dioxide (CO ２), it is expected to be a clean energy source. It is expected that the use of hydrogen will expand throughout society in the future, and as a result, hydrogen-utilizing equipment (for example, ball valves and compressors for hydrogen stations) will become more widespread. Mechanical parts such as bearings used in such hydrogen-utilizing equipment may be used in environments exposed to hydrogen. In such cases, the presence of hydrogen supplied from outside may promote early spalling due to the aforementioned hydrogen embrittlement, making it increasingly important to take measures against hydrogen embrittlement.

[0008] In the above Patent Document 1, an FeS layer is proposed, but this FeS layer reacts with hydrogen gas to produce H ２ If S is generated and mixed in, it may become a catalyst poison and cause problems in the use of hydrogen.

[0009] Furthermore, passive films are generally very thin (several nanometers thick) and may be physically destroyed depending on the application. Furthermore, the passive films of stainless steels such as those described in Patent Documents 2 and 3 are generally destroyed in the presence of halogen ions, which may cause pitting corrosion or crevice corrosion.

[0010] Austenitic stainless steel, which has excellent corrosion resistance, is sometimes used to counter hydrogen embrittlement, but it may not be strong enough for applications requiring high yield strength.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a hard film-coated body that has improved hydrogen embrittlement resistance and wear resistance while ensuring sufficient strength, and a mechanical part and a bearing that use the hard film-coated body.

[0012] The hard film-formed body of the present invention is a hard film-formed body having a hard film on the surface of a substrate that suppresses the penetration and diffusion of hydrogen atoms, characterized in that the substrate is made of martensitic stainless steel or martensitic precipitation hardening stainless steel, the Vickers hardness of the surface is 500 Hv to 1000 Hv, and the Vickers hardness of the hard film is 0.9 times or more the Vickers hardness of the substrate and 3000 Hv or less.

[0013] The substrate is a martensitic stainless steel containing N (nitrogen) and 0.05% to less than 0.60% by mass of C (carbon). The substrate further contains 0.20% to 0.50% by mass of carbon, 0.10% to 0.50% by mass of manganese, 0.30% or less by mass of nickel, 14.00% to 17.00% by mass of chromium, 1.00% to 2.50% by mass of molybdenum, and 0.10% to 0.40% by mass of nitrogen. In this specification, the symbol "to" denotes a range that includes the numerical values ​​before and after it.

[0014] The hard film that suppresses the penetration and diffusion of hydrogen atoms is a Ni coating, and the Ni coating includes a Ni-P-B coating containing 90 mass % or more of Ni.

[0015] The present invention is characterized in that a diamond-like carbon (DLC) layer is formed on the surface of the hard film, and an intermediate layer is formed on the substrate side of the DLC layer.

[0016] In an electrochemical hydrogen permeation method using a test piece (thickness of the substrate: 1 mm) made of the hard film-formed body, the area of ​​the test piece in contact with the electrolyte solution in each of the cathode and anode chambers was set to 3.14 cm ２ The current density on the anode tank side was set to 1 mA / cm ２ When electrolysis is performed as described above, the extended time of the breakdown time of the test piece is 0.4 times or more the breakdown time of a control piece made of the above substrate having a thickness of 1 mm.

[0017] The mechanical part of the present invention is characterized by using the hard film-formed body of the present invention. The mechanical part is characterized by being a bearing member.

[0018] The bearing of the present invention is characterized by using the above-described bearing member.

[0019] The hard film-coated body of the present invention has a hard film on the surface of a substrate that suppresses the penetration and diffusion of hydrogen atoms, and the substrate is made of martensitic stainless steel or martensitic precipitation-hardening stainless steel. By using these stainless steels for the substrate, the substrate can be made strong and corrosion-resistant at the same time, and can also be combined with the low hydrogen diffusion coefficient of these stainless steels. Furthermore, the Vickers hardness of the hard film that suppresses the penetration and diffusion of hydrogen atoms is 0.9 times or more the Vickers hardness of the substrate and 3000 Hv or less, thereby improving the peeling resistance of the hard film, improving hydrogen embrittlement resistance and wear resistance, and providing a hard film-coated body that ensures sufficient strength.

[0020] The base material is a martensitic stainless steel that contains nitrogen and 0.10 mass % or more but less than 0.60 mass % of carbon. Therefore, compared with, for example, nitrogen-free martensitic stainless steel, the amount of carbon can be reduced to obtain the same hardness. As a result, the generation of coarse carbides can be suppressed, and a decrease in strength of mechanical parts, etc. due to stress concentration can be reduced.

[0021] The hard film is a Ni coating, and in particular, the Ni coating includes a Ni--P--B coating containing 90 mass % or more of Ni, so that the hard film has better wear resistance.

[0022] The intermediate layer and DLC layer formed on the surface of the hard film provide superior wear resistance, and these layers also improve hydrogen embrittlement resistance. Furthermore, the presence of the intermediate layer improves adhesion between the hard film and the DLC layer, resulting in a hard film-formed body with excellent peel resistance as a whole.

[0023] Fig. 1 is a schematic cross-sectional view showing a first embodiment of a hard film-formed body of the present invention. Fig. 2 is a schematic cross-sectional view showing a second embodiment of a hard film-formed body of the present invention. Fig. 3 is a cross-sectional view showing an example of a bearing of the present invention. Fig. 4 is a cross-sectional view showing a hydrogen circulation pump using a bearing of the present invention. Fig. 5 is a photograph of the cross-sectional structure of a hard film-formed body of Example 2. Fig. 6 is a schematic view of an electrochemical hydrogen permeation test. Fig. 7 is a view showing an outline of an electrochemical hydrogen permeation test. Fig. 8 is a graph showing the behavior of ionization current in Examples and Comparative Examples.

[0024] In order to solve the above problems, the inventors of the present invention have investigated the steel material of the substrate and the hard film, and have found that by using martensitic stainless steel or martensitic precipitation hardening stainless steel as the substrate, it is possible to improve the strength compared to austenitic stainless steel, and by combining the corrosion resistance of the substrate itself with the hard film, it is possible to achieve sufficient measures against hydrogen embrittlement. The present invention is based on this finding.

[0025] The hard film-coated body of the present invention will be described below with reference to the drawings. The hard film-coated body of the present invention is used, for example, in machine parts that require high strength, and is particularly used in bearings that are used in a hydrogen penetration environment. A hydrogen penetration environment refers to an environment in which various forms of hydrogen, such as hydrogen gas and moisture in the usage environment and hydrogen atoms in lubricating oil, can penetrate and diffuse into the substrate.

[0026] (First embodiment) Figure 1 is a schematic cross-sectional view of a first embodiment of a hard film-formed body of the present invention. As shown in Figure 1, the hard film-formed body 1 has a substrate 2 and a hard film 3 formed on the surface of the substrate 2. The hard film 3 is stable in a hydrogen environment and has the property of suppressing the penetration or diffusion of hydrogen, for example, delaying the penetration and diffusion of hydrogen into the substrate 2. As a result, it is possible to delay the occurrence of hydrogen embrittlement in the substrate 2. The hard film 3 is formed of a material different from that of the substrate 2.

[0027] In the present invention, martensitic stainless steel or martensitic precipitation-hardening stainless steel is used for the substrate 2. For example, for mechanical components used in hydrogen-containing or even moisture-containing environments, such as fuel cell peripheral components, it is preferable to ensure corrosion resistance of the base material in case the hard film cannot be fully coated depending on the component shape or if a problem occurs with the hard film. Therefore, stainless steel is used in the present invention. Furthermore, from the perspective of using the component in a portion requiring strength, a predetermined hard film is formed on the martensitic stainless steel or martensitic precipitation-hardening stainless steel. As a countermeasure against hydrogen embrittlement, it is also possible to use martensitic stainless steel (e.g., SUS440C) or martensitic precipitation-hardening stainless steel as the substrate without a coating.

[0028] Martensitic stainless steel is stainless steel made of a metal structure called martensite, and is distinguished from austenitic stainless steel, ferritic stainless steel, and austenitic-ferritic (duplex) stainless steel. Martensitic stainless steel is inferior in corrosion resistance to, for example, austenitic stainless steel, but is extremely hard and strong, resulting in excellent wear resistance. Furthermore, the hardness can be adjusted by heat treatment, making it easy to adjust the hardness difference with the hard film, thereby improving the peeling resistance of the hard film.

[0029] Examples of martensitic stainless steels include SUS403, SUS420, and SUS440C. For example, the chemical components (mass%) of SUS403 are 0.15 or less, 0.50 or less, 1.00 or less, 0.040 or less, 0.030 or less, 11.50 to 13.00, and 0.60 or less. The chemical components (mass%) of SUS440C are 0.95 to 1.20, 1.00 or less, 1.00 or less, 1.00 or less, 0.040 or less, 0.030 or less, 16.00 to 18.00, and 0.60 or less.

[0030] The martensitic stainless steel is preferably a nitrogen-containing martensitic stainless steel containing N (nitrogen). By containing nitrogen, the carbon content can be reduced while maintaining hardness, making it easier to suppress the formation of coarse carbides. As a result, it is easier to suppress the reduction in strength of machine parts and the like due to stress concentration. Furthermore, it is preferable that C (carbon), Mn (manganese), and Mo (molybdenum) be added to the martensitic stainless steel in order to increase the solubility of nitrogen in molten steel under atmospheric pressure.

[0031] Martensitic precipitation hardening stainless steel is stainless steel that has a martensite transformation start temperature above room temperature and develops a martensite structure after solution treatment. Examples of this stainless steel include SUS630.

[0032] The chemical components of the martensitic stainless steel used in the present invention will be explained below.

[0033] From the viewpoint of ensuring hardness, the C (carbon) content is, for example, 0.05 mass% or more, preferably 0.10 mass% or more, more preferably 0.20 mass% or more, and may be 0.30 mass% or more. Since a large carbon content makes it easier for coarse carbides to be formed in the structure, the carbon content is preferably less than 0.60 mass%, more preferably 0.50 mass% or less, and may be 0.45 mass% or less. Generally, to obtain the maximum hardness during quenching in steel, the carbon content is set to 0.6 mass% or more, but from the viewpoint of carbides, a lower carbon content is preferable.

[0034] If the amount of Si (silicon) is too large, toughness may be impaired and embrittlement may occur, so the content is, for example, 0.50 mass% or less. The silicon content is preferably 0.10 mass% to 0.50 mass%, and may be 0.20 mass% to 0.40 mass%.

[0035] While Mn (manganese) improves hardenability, if the amount is too high, austenite is stabilized, resulting in a large amount of retained austenite after heat treatment, making it difficult to obtain hardness. The manganese content is, for example, 1.00 mass% or less, preferably 0.10 mass% to 0.50 mass%, and may be 0.20 mass% to 0.40 mass%.

[0036] Ni (nickel) improves hardenability, toughness, and corrosion resistance, but is expensive. The nickel content is, for example, 0.60 mass% or less, preferably 0.30 mass% or less, and may be 0.10 mass% to 0.20 mass%.

[0037] The Cr (chromium) content is, for example, 14.00% by mass to 17.00% by mass. Within this range, sufficient corrosion resistance is exhibited while reducing the toughness caused by coarse carbides. The chromium content is preferably 15.00% by mass to 16.50% by mass, and may be 15.00% by mass to 16.00% by mass.

[0038] The content of Mo (molybdenum) is, for example, 1.00 mass % to 2.50 mass %, preferably 1.00 mass % to 2.00 mass %, or may be 1.50 mass % to 2.00 mass %, or may be 1.50 mass % to 1.80 mass %. By including a predetermined amount of Mo, corrosion resistance can be improved.

[0039] The N (nitrogen) content is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and may be 0.15% by mass or more. Furthermore, since an excessively high nitrogen content may cause blowholes, the nitrogen content is preferably 0.50% by mass or less, more preferably 0.40% by mass or less, and may be 0.30% by mass or less.

[0040] The martensitic stainless steel used in the present invention may further contain P (phosphorus), Cu (copper), Co (cobalt), and V (vanadium). The phosphorus content may be, for example, 0.04 mass% or less, or 0.01 to 0.03 mass%. The copper content may be, for example, 0.04 mass% or less, or 0.01 to 0.03 mass%. The cobalt content may be, for example, 0.04 mass% or less, or 0.01 to 0.03 mass%. The vanadium content may be, for example, 1.00 mass% or less, or 0.10 to 0.50 mass%.

[0041] The Vickers hardness of the substrate 2 (the Vickers hardness of the surface on which the hard film 3 is formed) is preferably 500 Hv to 1000 Hv, more preferably 600 Hv to 900 Hv, and even more preferably 650 Hv to 750 Hv. By setting the Vickers hardness within these ranges, it is possible to ensure the wear resistance of the hard film-formed body while easily achieving a hardness ratio within a predetermined range relative to the hard film.

[0042] Before forming the hard film 3, the substrate 2 may be hardened by heat treatment including quenching. Alternatively, a nitride layer may be formed by nitriding. As the nitriding treatment, for example, plasma nitriding treatment may be performed, which is less likely to produce an oxide layer that hinders adhesion on the substrate surface. Alternatively, the substrate 2 may be pretreated to improve the adhesion of the hard film 3 to the substrate 2. Examples of pretreatment include degreasing treatment using a solvent or alkaline solution, and acid immersion treatment.

[0043] The surface roughness Ra of the substrate 2 is, for example, 0.1 μm or less, and preferably 0.05 μm or less. In order to adjust the surface roughness Ra of the substrate 2, various processing treatments (surface finishing processing, etc.) may be performed.

[0044] The higher the strength of the steel material, the greater the effect of hydrogen embrittlement, and in particular, the form known as delayed fracture is prominent in high-strength steels having a yield stress of 1 GPa or more. However, in the hard film-coated body of the present invention, the hard film or DLC layer described below is formed on the surface of the steel material, thereby making it possible to suitably suppress delayed fracture due to hydrogen embrittlement.

[0045] The hard film 3 may be any coating that suppresses the penetration and diffusion of hydrogen atoms, and the Vickers hardness of the hard film 3 is at least 0.90 times the Vickers hardness of the substrate 2 and is not more than 3000 Hv. As a result, the hard film 3 has excellent adhesion to the substrate 2, and the hard film 3 can stably exhibit hydrogen embrittlement resistance and wear resistance. From the viewpoint of adhesion, the above-mentioned ratio is preferably 0.90 to 1.50, may be 0.95 to 1.30, or may be 1.05 to 1.20.

[0046] Examples of the hard film 3 include a Ni coating containing Ni as the main component, a Cu coating containing Cu as the main component, a Zn coating containing Zn as the main component, a WC coating, a DLC coating, and combinations thereof. Among these coatings, the hard film 3 is preferably a Ni coating or a WC coating, since these coatings can further delay the penetration and diffusion of hydrogen, such as hydrogen gas and moisture in the usage environment and hydrogen atoms in lubricating oil, into the substrate 2.

[0047] For example, Ni coatings can be Ni-P coatings, Ni-B coatings, Ni-P-B coatings, Ni-P-B-SiC dispersion coatings, or combinations thereof. These Ni coatings can be formed by physical vapor deposition (PVD) methods such as ion plating and sputtering, or plating methods such as electrolytic plating and electroless plating. For example, in the case of electroless plating, an electroless plating coating can be formed using a plating bath containing nickel salts and various reducing agents. In particular, the hard film 3 is preferably a Ni plating coating, and the Ni plating coating preferably includes a Ni-P-B coating.

[0048] The Ni-P-B coating is a composite coating of Ni, P, and B, and is formed by electroless plating. The Ni content in the Ni-P-B coating is, for example, 90% by mass or more, preferably 95% by mass or more, and more preferably 97% by mass or more. The Ni-P-B coating preferably has a composition of 97% by mass or more of Ni, 1% to 3% by mass of P, and 1% by mass or less of B. This composition can be adjusted appropriately depending on the properties desired for the coating. The Ni-P-B coating is harder than, for example, a Ni-P coating, and also has excellent abrasion resistance. A commercially available Ni-P-B coating is, for example, Kaniboron (trade name) manufactured by Nippon Kanigen Co., Ltd.

[0049] In terms of the relationship between the heat treatment temperature after plating and hardness, the harder the Ni-P-B coating, the higher the heat treatment (baking) temperature is up to 400°C. This is because the heat treatment promotes Ni crystallization. The Ni-P-B coating has a microcrystalline (polycrystalline) structure, and Ni-derived peaks can be observed in the X-ray diffraction pattern. Furthermore, the Ni-P-B coating is harder than the Ni-P coating, exhibiting a Vickers hardness of 700 Hv or more upon deposition and a Vickers hardness of 800 Hv or more at 200°C during heat treatment.

[0050] For example, in the case of a Ni coating, the Vickers hardness is preferably 500 Hv to 1000 Hv, more preferably 600 Hv to 900 Hv, and even more preferably 700 Hv to 800 Hv.

[0051] For example, when the hard film 3 includes a Ni-P-B coating, the higher the heat treatment temperature, the greater the hardness of the coating. However, the hardness of the substrate 2 obtained by quenching or other processes decreases, potentially resulting in a decrease in the overall strength of the hard film-coated body. Therefore, by using a steel material hardened by heat treatment and then aging the Ni-P-B coating on the surface at an appropriate temperature, it is possible to achieve both a strong steel material and a hard film, resulting in a hard film-coated body with overall strength. Furthermore, even in situations where distortion occurs in the steel material, it is possible to prevent the hard film from yielding, plastically deforming, and peeling. Depending on the hardness of the steel material, aging may not be necessary.

[0052] For example, by setting the baking temperature for the Ni-P-B coating to 200° C. or less, preferably 180° C. or less, it is possible to reduce the influence of tempering the substrate 2. In this way, in manufacturing the hard film 3, it is preferable to appropriately select the tempering temperature and required strength of the substrate 2 and the hardness required for the hard film 3 on its surface so as to prevent problems from occurring due to the difference in hardness between the substrate 2 and the hard film 3.

[0053] For example, in the case of a Ni coating, the lower limit of the thickness is preferably 1 μm, taking into consideration ease of manufacturing control and the possibility of thickness reduction due to wear. On the other hand, the upper limit is preferably 50 μm in order to suppress manufacturing costs, processing time, and uneven stress distribution within the film. The thickness of the hard film 3 is more preferably 3 μm to 30 μm, and even more preferably 3 μm to 10 μm. This thickness can be set depending on the required hydrogen embrittlement resistance, etc. Furthermore, in the case of a plated coating, the thickness can be adjusted by adjusting the immersion time in the plating bath, for example.

[0054] As the hard film 3, for example, a WC film is formed by using an unbalanced magnetron sputtering (UBMS) method using a WC target. The thickness of the WC film is preferably 0.2 μm or more and less than 1 μm, and may be 0.2 μm or more and 0.6 μm or less. The Vickers hardness of the WC film is, for example, 1000 Hv to 2000 Hv, and a hardness exceeding 2000 Hv is also possible.

[0055] The hard film 3 may be, for example, a DLC coating formed by using an UBMS method using a graphite target and a hydrocarbon gas as a carbon source. The Vickers hardness of the DLC coating may be, for example, 3000 Hv or less, and preferably 1000 Hv or more and 2500 Hv or less.

[0056] The hydrogen diffusion coefficient in the hard film 3 is 5.00×10 －１２ m ２ / s or less, and preferably 1.00 × 10 －１２ m ２ / s or less, and may be 8.00 × 10 －１３ m ２ / s or less. A specific range is, for example, 1.00 × 10 －１３ m ２ / s ~ 8.00 x 10 －１３ m ２ The hydrogen diffusion coefficient is determined by an electrochemical hydrogen permeation method. Details are given in the examples.

[0057] As an example of a method for forming the hard film 3, the formation of a Ni-P-B coating will be described. The plating bath used contains nickel salt and a phosphorus compound and a boron compound as reducing agents. More specifically, nickel chloride, nickel sulfate, etc. are used as the nickel salt, sodium hypophosphite, potassium hypophosphite, etc. are used as the phosphorus compound, and dimethylaminoboron, sodium borohydride, etc. are used as the boron compound. The ratio of the nickel salt, phosphorus compound, and boron compound in the plating bath can be adjusted appropriately depending on the composition of the resulting plated coating. The plating bath can also contain an organic acid such as acetic acid or a chelating agent such as ethylenediaminetetraacetic acid (EDTA).

[0058] From the viewpoints of stability, deposition rate, etc., the pH of the plating bath is preferably in the range of 6 to 7. The temperature of the plating bath is, for example, 60°C to 90°C, and preferably 70°C to 90°C.

[0059] The film hardness of the obtained plating film can be increased by heat treatment (baking). The heat treatment temperature is, for example, 100°C to 200°C, preferably 100°C to 180°C, and more preferably 120°C to 160°C. The heat treatment time is, for example, 30 minutes to 120 minutes. This heat treatment is carried out in an atmosphere of air, an inert gas, a reducing gas, or the like.

[0060] Regarding the physical properties of the hard film-formed body 1, in an electrochemical hydrogen permeation method using a test piece (substrate 2 thickness: 1 mm) made of the hard film-formed body, the area of ​​the test piece in contact with the electrolyte solution in each of the cathode and anode chambers was 3.14 cm ２ The current density on the anode tank side was 1 mA / cm ２ When electrolysis is performed as described above, the extension time of the breakthrough time of the test piece is preferably 0.4 times or more, more preferably 1.0 times or more, even more preferably 2.0 times or more, and may be 5.0 times or more, or may be 10.0 times or more, relative to the breakthrough time of a control piece made of a substrate 2 having a thickness of 1 mm. Details of the electrochemical hydrogen permeation method will be described in the examples.

[0061] Second Embodiment Fig. 2 is a schematic cross-sectional view of a second embodiment of the hard film-formed body of the present invention. As shown in Fig. 2, the hard film-formed body 4 has a substrate 5, a hard film 6 formed on the surface of the substrate 5, an intermediate layer 7 formed on the hard film 6, and a DLC layer 8 formed on the intermediate layer 7. In this case, the coating formed on the substrate 5 has a roughly three-layer structure. Note that the configurations of the substrate 5 and the hard film 6 are similar to those of the substrate 2 and the hard film 3 described in the first embodiment, and therefore will not be described here.

[0062] The intermediate layer 7 is a layer interposed between the hard film 6 and the DLC layer 8. A tungsten carbide (WC) layer, a mixed layer mainly composed of WC and DLC, or the like can be used as the intermediate layer 7. WC has intermediate hardness and elastic modulus between those of the hard film 6 and the DLC layer 8, and is less likely to cause concentration of residual stress after film formation.

[0063] The intermediate layer 7 is preferably a mixed layer mainly composed of WC and DLC. More preferably, the WC content of the intermediate layer decreases and the DLC content increases continuously or stepwise from the hard film 6 side to the DLC layer 8 side. This provides excellent adhesion between the hard film 6 and the DLC layer 8 on both sides. Furthermore, the WC and DLC are physically bonded within the intermediate layer, preventing damage within the intermediate layer. Furthermore, the DLC content is higher on the DLC layer 8 side, providing excellent adhesion between the DLC layer 8 and the intermediate layer 7. In this case, the intermediate layer 7 functions as a layer in which the highly non-adhesive DLC is bonded to the hard film 6 side by the WC through an anchor effect.

[0064] The DLC layer 8 is a film mainly made of DLC. DLC has a graphite structure (sp ２ ) and diamond structure (sp ３ The DLC layer 8 can be formed by a physical vapor deposition method such as sputtering or ion plating, a chemical vapor deposition method, or an UBMS method.

[0065] The DLC layer 8 preferably has a relaxation layer portion (not shown) adjacent to the intermediate layer 7. This portion is obtained by continuously or stepwise changing at least one of the UBMS deposition condition parameters (amount of hydrocarbon-based gas introduced, degree of vacuum, bias voltage) to avoid abrupt changes in these parameters when the intermediate layer 7 and the DLC layer 8 differ. More specifically, the deposition condition parameters for forming the outermost layer of the intermediate layer 7 are used as the starting point, and the final deposition condition parameters for the DLC layer 8 are used as the end point, and each parameter is changed continuously or stepwise within this range. This eliminates abrupt differences in physical properties (hardness, elastic modulus, etc.) between the intermediate layer 7 and the DLC layer 8, thereby further improving adhesion between the intermediate layer 7 and the DLC layer 8. For example, by continuously or stepwise increasing the bias voltage, the graphite structure (sp) in the DLC structure can be improved. ２ ) and diamond structure (sp ３ ) and the composition ratio becomes biased towards the latter, resulting in a slope (increase) in hardness.

[0066] In the hard film-formed body 4 of the second embodiment, the Vickers hardness of the DLC layer 8 serving as the surface layer is, for example, 1000 Hv or more and 3000 Hv or less.

[0067] The total thickness of the intermediate layer 7 and the DLC layer 8 is preferably 1.0 μm to 5.0 μm, and more preferably 1.0 μm to 3.0 μm. By setting the thickness within these ranges, it is possible to improve the wear resistance and mechanical strength while suppressing peeling of the intermediate layer 7 and the DLC layer 8. Furthermore, it is preferable that the total thickness of the intermediate layer 7 and the DLC layer 8 is smaller than the thickness of the hard film 6. In the hard film-formed body 4, the total thickness of the coating formed on the substrate 5 is preferably 3.0 μm to 30 μm, and more preferably 3.0 μm to 10 μm.

[0068] As an example of a method for forming the intermediate layer 7 and the DLC layer 8, an example using a UBMS apparatus using Ar gas as the sputtering gas will be described.

[0069] For example, when the intermediate layer 7 is a mixed layer mainly composed of WC and DLC, the film can be formed by continuously or stepwise increasing the sputtering power applied to the graphite target serving as the carbon supply source and decreasing the power applied to the WC target, thereby forming a layer with a gradient composition in which the WC content decreases and the DLC content increases toward the DLC layer 8. The degree of vacuum within the UBMS apparatus (inside the film formation chamber) during film formation of the intermediate layer 7 is, for example, 0.2 to 1.2 Pa. The bias voltage applied to the substrate is, for example, 20 to 100 V.

[0070] The DLC layer 8 can be formed by using a graphite target and a hydrocarbon gas (methane gas, acetylene gas, benzene, etc.) as a carbon source in combination, setting the ratio of the amount of the hydrocarbon gas introduced into the apparatus to the amount of Ar gas introduced into the apparatus at 100, for example, between 1 and 15, and depositing carbon atoms generated from the carbon source on the intermediate layer 7. The degree of vacuum inside the apparatus is, for example, 0.2 to 0.9 Pa.

[0071] In the embodiment shown in Fig. 2, an intermediate layer 7 is interposed between the hard film 6 and the DLC layer 8, but the intermediate layer 7 may be omitted. The hard film-formed body of the present invention is not limited to the embodiments shown in Figs. 1 and 2. For example, an intermediate layer 7 and a DLC layer 8 may be repeatedly laminated on the hard film 6. Furthermore, for example, the hard film-formed body may have a structure including a substrate, a WC film formed on the surface of the substrate, and a DLC layer formed on the WC film.

[0072] In addition, various combinations of the substrate and the multilayer structure including the hard film can be selected depending on the use conditions and hydrogen exposure environment. For example, the outermost layer can have the lowest hydrogen diffusion coefficient, and the second layer inside it can have a higher hydrogen diffusion coefficient than the outermost layer. In this case, hydrogen penetration is prevented as much as possible in the outermost layer, and even a small amount of hydrogen that has penetrated is prevented from diffusing in the second layer (specifically, the intermediate layer or the hard film). However, a higher hydrogen diffusion coefficient can prevent hydrogen from accumulating between the outermost layer and the second layer, causing blisters. In addition, to prevent hydrogen that has reached the substrate from concentrating in the substrate, the substrate may have the highest hydrogen diffusion coefficient in the multilayer structure including the substrate and the hard film so that it diffuses quickly.

[0073] (Uses of Hard Film-Coated Body) The use of the hard film-coated body of the present invention is not particularly limited, but due to its excellent mechanical properties, it is preferably used in mechanical parts. Examples of mechanical parts include mechanical parts used in rolling or sliding parts of equipment, and specific examples include sliding members, bearing members, rolling roll materials, compressor vanes, engine parts such as gas turbine blades, cutting tools (chips), gears, etc. Examples of bearing members include raceways such as inner and outer rings, rolling elements for bearings, and cages. The bearing of the present invention is a bearing in which the hard film-coated body of the present invention is used as a bearing member. Examples of bearings include rolling bearings, sliding bearings (spherical bushings, etc.), linear guide bearings, ball screws, linear bearings, etc.

[0074] An example of a bearing of the present invention will be described with reference to Figure 3. Figure 3 shows a cross-sectional view of a deep groove ball bearing that uses the hard film-coated body of the first embodiment as a rolling element. The deep groove ball bearing 11 includes an inner ring 12 having an inner ring raceway surface 12a on its outer periphery, an outer ring 13 having an outer ring raceway surface 13a on its inner periphery, and a plurality of balls (rolling elements) 14 that roll between the inner ring raceway surface 12a and the outer ring raceway surface 13a. The balls 14 are held at regular intervals by a cage 15. Seal members 16 seal the openings at both axial ends of the inner and outer rings, and grease 17 is sealed in the bearing space.

[0075] In the rolling bearing of Fig. 3, hard film 18 is formed over the entire spherical surface of ball 14. In Fig. 3, hard film 18 is formed only on ball 14, but depending on the bearing type and its application, it may also be formed on the surfaces (including parts) of other bearing components such as inner ring 12 and outer ring 13. In a configuration in which two or more components come into contact or slide, it is preferable that a hard film-formed body be used on one or more of the components.

[0076] The bearing of the present invention, in which at least a portion of the bearing member is made of the hard film-formed body of the present invention, can suitably suppress premature flaking caused by hydrogen embrittlement when used in an environment where hydrogen penetrates, and is therefore suitable for use in an environment where premature flaking due to hydrogen embrittlement is likely to occur.

[0077] For example, they are used as bearings for transaxles of vehicles (fuel cell vehicles (FCVs), electric vehicles (EVs), etc.), vehicle transmissions (continuously variable transmissions, etc.), and vehicle motors (drive units, transmissions). Bearings for these applications are required to be able to withstand sudden changes in rotation speed associated with gear changes, as well as high rotation speeds and heavy loads. Furthermore, these devices use low-viscosity lubricants to reduce power loss. In such harsh operating environments, sliding easily accelerates wear of raceways and rolling elements. When this wear forms a new steel surface, water and lubricant components decompose, generating hydrogen, which then penetrates into the steel, potentially causing early spalling due to hydrogen embrittlement. Furthermore, in fuel cell vehicles and other applications, hydrogen leakage from hydrogen facilities may potentially promote hydrogen embrittlement in rolling bearings.

[0078] Furthermore, the bearing of the present invention is used as a bearing for hydrogen-using equipment. It is particularly useful as a bearing used in an environment exposed to hydrogen supplied from outside. As hydrogen use progresses in the future, it is expected that there will be an increasing number of cases in which bearings are used in hydrogen atmospheres (including mixed atmospheres containing hydrogen). In such cases, it is thought that in addition to hydrogen generated with grease decomposition (hydrogen due to internal factors), hydrogen supplied from outside (hydrogen due to external factors) also affects early flaking due to hydrogen embrittlement. Compared to conventional bearings, the bearing of the present invention can effectively suppress early flaking due to hydrogen embrittlement by using a hard film-formed body, even in cases where early flaking due to hydrogen embrittlement is a greater concern.

[0079] Examples of hydrogen-utilizing equipment include ball valves and compressors for hydrogen stations. The type of compressor is not particularly limited and may be any of reciprocating, rotary (screw), centrifugal, and axial flow types. Hydrogen-utilizing equipment also includes the high-pressure hydrogen pressure reducing valves and hydrogen circulation pumps for the above-mentioned fuel cell vehicles.

[0080] 4 shows a cross-sectional view of a hydrogen circulation pump in which the bearing of the present invention is applied. The hydrogen circulation pump 21 includes a motor housing 22, a pump housing 23, rotating shafts 24 and 25, a motor stator 26, a motor rotor 27, gears 28 and 29, rotors 30 and 31, and rolling bearings 32, 33, 34, 35, 36, and 37.

[0081] The motor housing 22 is attached to the pump housing 23. One end of the rotating shaft 24 is disposed within the motor housing 22, and the other end of the rotating shaft 24 is disposed within the pump housing 23. One end and the other end of the rotating shaft 24 are rotatably supported by a rolling bearing 32 disposed within the motor housing 22 and a rolling bearing 33 disposed within the pump housing 23, respectively. Furthermore, the rotating shaft 24 is rotatably supported between its one and other ends by a rolling bearing 34 and a rolling bearing 35 disposed within the pump housing 23.

[0082] The rotating shaft 25 is disposed within the pump housing 23. One end of the rotating shaft 25 is rotatably supported by a rolling bearing 36 disposed within the pump housing 23. The rotating shaft 25 is rotatably supported at a position away from the one end by a rolling bearing 37 disposed within the pump housing 23.

[0083] Motor stator 26 is disposed within motor housing 22. Motor rotor 27 is attached to rotating shaft 24 so as to face motor stator 26. Rotating shaft 24 is rotated by motor stator 26 and motor rotor 27. Gears 28 and 29 are attached to rotating shafts 24 and 25, respectively. The rotation of rotating shaft 24 is transmitted to rotating shaft 25 by gears 28 and 29. Gear 28 is located between rolling bearing 34 and rolling bearing 35, and gear 29 is located between rolling bearing 36 and rolling bearing 37.

[0084] A pump chamber 23a is formed within the pump housing 23. A rotor 30 and a rotor 31 are disposed within the pump chamber 23a. The rotors 30 and 31 are attached to the rotary shafts 24 and 25, respectively. The rotors 30 and 31 rotate in conjunction with the rotation of the rotary shaft 24 and the rotor 31 rotates in conjunction with the rotation of the rotary shaft 25, causing hydrogen to be drawn into the pump chamber 23a and discharged from the pump chamber 23a.

[0085] In Fig. 4, rolling bearings 32, 33, 34, and 36 are deep groove ball bearings. Rolling bearing 33 is used in an environment exposed to hydrogen supplied from outside (e.g., in a hydrogen atmosphere). Rolling bearings 35 and 37 are double-row angular contact ball bearings. In the configuration of Fig. 4, at least one of rolling bearings 32, 33, 34, 35, 36, and 37 is used as the bearing of the present invention.

[0086] The mechanical component of the present invention may, for example, have the hard film-formed body of the present invention at least in part. For example, even if it is difficult to apply a hard film to the entire surface of a substrate due to the convenience of the hard film formation process, the effect can be achieved by applying a hard film to areas exposed to large amounts of hydrogen, such as in a hydrogen gas environment, and arranging areas without a hard film. In this case, even in areas without a hard film, the stainless steel, which has excellent corrosion resistance, can suppress the generation and penetration of trace amounts of hydrogen due to corrosion reactions. Furthermore, by applying one or more types of hard film two or more times, shifting the areas where a hard film cannot be applied, the entire surface can be covered with at least one layer of hard film.

[0087] The present invention will be specifically explained by way of examples and comparative examples, but is not limited to these examples in any way.

[0088] [Example 1] A nitrogen-containing martensitic stainless steel plate (thickness 1 mm) with a surface Vickers hardness of 693 Hv was used as the substrate. The chemical composition of this stainless steel is shown below. Chemical composition: C: 0.41 mass%, Si: 0.27 mass%, Mn: 0.41 mass%, P: 0.02 mass%, Cu: 0.02 mass%, Ni: 0.14 mass%, Cr: 15.57 mass%, Mo: 1.65 mass%, Co: 0.02 mass%, N: 0.19 mass%, and the balance being Fe and unavoidable impurity elements.

[0089] The surface of the steel sheet was subjected to a carbon-boron plating process, which is a type of electroless plating process. The composition of the resulting coating was 97% by mass to 98% by mass of Ni, 1.5% by mass to 2.5% by mass of P, and 0.05% by mass to 0.5% by mass of B. After the carbon-boron plating process, the steel sheet was baked at 150°C for 1 hour to perform age hardening, thereby forming an electroless Ni-P-B plating coating as a hard film. The thickness of the Ni plating coating was 5 μm (Example 1).

[0090] [Example 2] In the same manner as in Example 1, the surface of the nitrogen-containing martensitic stainless steel sheet was subjected to a nickel-boron plating treatment to form a 5 μm-thick Ni-plated coating (hard coating), on which a WC / DLC coating was formed as an intermediate layer, and a DLC coating was formed on the outermost surface.

[0091] The WC / DLC coating was formed by the UBMS method. Specifically, while supplying methane gas, a hydrocarbon gas, the sputtering power applied to the WC target and the graphite target was adjusted to gradient the composition ratio of WC and DLC, forming a WC / DLC gradient layer with more WC on the Ni-plated coating side and more DLC on the surface side. The DLC coating was also formed by the UBMS method. In this case, the graphite target and methane gas, a hydrocarbon gas, were used in combination as carbon sources.

[0092] 5 shows a photograph of the cross-sectional structure of the hard film-formed body of Example 2. Strictly speaking, this Ni plating coating is formed by forming an electroless Ni-P plating coating on a substrate, forming an electroless Ni-P-B plating coating on that, and further forming a WC / DLC coating and a DLC coating on that.

[0093] [Reference Examples 1 and 2] Steel sheets with a thickness of approximately 1 mm were prepared by quenching SUJ2 and then tempering at 190°C to a hardness of 61.5 HRC (730 Hv). The surfaces of these steel sheets were subjected to a carbon-boron plating treatment in the same manner as in Example 1 above, to form Ni plating films with a thickness of 5 μm (Reference Example 1) and 30 μm (Reference Example 2).

[0094] Comparative Example 1 In Comparative Example 1, a quenched and tempered SUJ2 steel plate was used, which was not subjected to the plating treatment of Reference Examples 1 and 2.

[0095] <Hardness Test> The Vickers hardness of the hard film of Example 1 was measured according to JIS Z 2244. As a result, the hardness of the hard film in Example 1 was 783 Hv (same as in Example 2), which was roughly equivalent to the hardness of the substrate (1.13 times).

[0096] <Electrochemical Hydrogen Permeation Test> An electrochemical hydrogen permeation test was conducted to evaluate the hydrogen that penetrated and diffused into each test piece of Examples 1 and 2, Reference Examples 1 and 2, and Comparative Example 1. FIG. 6 is a schematic diagram of this test apparatus. As shown in FIG. 6, test apparatus 41 has a cathode chamber 42, an anode chamber 45, a cathode electrode 44 (e.g., a Pt electrode), an anode electrode 47 (e.g., a Pt electrode), a galvanostat, and a potentiostat. The cathode chamber 42 and the anode chamber 45 are separated by a test piece 51. In Examples 1 and 2 and Reference Examples 1 and 2, the test piece 51 was positioned so that the hard film formed on the test piece 51 faced the cathode chamber 42.

[0097] The cathode chamber 42 contains an electrolyte solution 43, in which a cathode electrode 44 is immersed. The anode chamber 45 contains an electrolyte solution 46, in which an anode electrode 47 is immersed. In this test, an aqueous solution of 0.1 N sulfuric acid mixed with thiouric acid was used as the electrolyte solution 43, and a 1 N aqueous solution of sodium hydroxide was used as the electrolyte solution 46. A galvanostat is connected to the cathode electrode 44 and a test piece 51. A potentiostat is connected to the anode electrode 47, the test piece 51, and a reference electrode 49 (e.g., an Ag / AgCl electrode). The reference electrode 49 is immersed in a saturated KCl aqueous solution 48 and is connected to the anode chamber 45 by a salt bridge 50.

[0098] In the test device 41, a predetermined potential is applied between the test piece 51 and the cathode electrode 44 by a galvanostat to perform electrolysis, generating hydrogen on the surface of the test piece 51 facing the cathode chamber 42. The generated hydrogen penetrates into the test piece 51 from the surface facing the cathode chamber 42. Meanwhile, a potentiostat is used to maintain the surface potential of the test piece 51 at a potential at which hydrogen atoms are oxidized to hydrogen ions. As a result, hydrogen atoms that penetrate from the cathode chamber 42, diffuse through the test piece 51, and reach the surface facing the anode chamber 45 are quickly oxidized to hydrogen ions, generating an ionization current. In this test, a breakthrough time method was employed to calculate a diffusion coefficient based on the time until the ionization current begins to increase. Specifically, the time from the start of the test until the ionization current begins to increase (breakthrough time) is defined as tb, and the thickness of the test piece 51 is defined as L (the total thickness of the substrate and the hard film), and the diffusion coefficient D Ｈ was calculated from the following formula (1) (Reference: Takahiro Kushida, "Research on Hydrogen Embrittlement Using Electrochemical Hydrogen Permeation Method," Materials and Environment, 2000, Vol. 49, pp. 195-200). The diffusion coefficient was measured in the temperature range of 20 to 25°C.

[0099]

[0100] Specifically, the area of ​​the test piece 51 in contact with the electrolyte solutions 43 and 46 in the cathode chamber 42 and the anode chamber 45, respectively, was set to 3.14 cm ２ and the current density on the anode tank 45 side was 1 mA / cm ２ The electrolysis was carried out under the condition that the ionization current on the cathode side was measured in units of 0.1 μA, and the increase in the ionization current was judged. Ｈ The average values ​​are shown in Table 1.

[0101] Here, in the electrochemical hydrogen permeation test, it is necessary to pass a current through the surface of the test piece and measure the current. However, the test piece of Example 2 has a DLC coating on the surface on the cathode chamber side where hydrogen is generated and penetrated, and the electrical resistance is extremely high, making it difficult to perform the electrochemical hydrogen permeation test in the same manner as above. Therefore, a gold vapor deposition film of about several nm was formed on the DLC coating to reduce the electrical resistance of the outermost surface, and then the electrochemical hydrogen permeation test was performed. Furthermore, a separate test showed that the gold vapor deposition film had little ability to prevent hydrogen permeation.

[0102]

[0103] As shown in Table 1, first comparing Comparative Example 1 and Reference Examples 1 and 2, Reference Examples 1 and 2, in which a Ni-plated coating was formed, showed thickness increases of about 0.5% and about 3%, respectively, compared to Comparative Example 1 (SUJ2 with a plate thickness of 1 mm), but the breakthrough time was extended by 41% and 269%, respectively. In addition, the diffusion coefficient D calculated by the breakthrough time method Ｈ was 75% in Reference Example 1 and 31% in Reference Example 2 compared to Comparative Example 1. These results show that the Ni plating film inhibits hydrogen from penetrating and diffusing.

[0104] Next, comparing Reference Example 1 and Example 1, it is found that the use of nitrogen-containing martensitic stainless steel significantly extends the breakthrough time and reduces the diffusion coefficient D Ｈ The results showed that nitrogen-containing martensitic stainless steel is superior to bearing steel in terms of preventing hydrogen embrittlement. Although martensitic stainless steel is weaker in strength than alloy steels such as bearing steel, it has excellent corrosion resistance, and this corrosion resistance is also effective against hydrogen caused by corrosion reactions. It is also believed that the alloying elements in martensitic stainless steel and the distribution of precipitates (carbides) in the metal structure contributed to the reduction in the diffusion coefficient.

[0105] Furthermore, in Example 2, in which a WC / DLC coating and a DLC coating were formed on the Ni plating coating of Example 1, the breakthrough time was significantly extended and the diffusion coefficient D ＨThe hydrogen diffusion coefficients of the WC / DLC coating and the DLC coating were smaller than that of the Ni-plated coating, and were 1.00 × 10 －１５ m ２ / s ~ 1.00 x 10 －１４ m ２ / s (specifically, about 1.18 × 10 －１５ m ２ The results of Example 2 show that the WC / DLC coating and DLC coating also inhibit the penetration and diffusion of hydrogen, and that by forming these on the Ni-plated coating, the effect of the Ni-plated coating can be dramatically improved.

[0106] In this example, the breakthrough time is a measure of the time it takes for hydrogen atoms to diffuse to a depth of 1 mm from the surface of the hard film-formed body.

[0107] The hydrogen diffusion coefficient of Comparative Example 1, determined by the electrochemical hydrogen permeation method, was 3.16×10 －１１ m ２ The hydrogen diffusion coefficient of the Ni-plated film was estimated by the finite element method using the breakdown voltage / s and the breakthrough time of Reference Example 1, and the breakthrough time of Reference Example 1. As a result, the hydrogen diffusion coefficient of the Ni-plated film of Reference Example 1 was 4.95 × 10 －１３ m ２ / s. The method for estimating the hydrogen diffusion coefficient using the finite element method is as follows: (1) The concentration on one side of the 1 mm plate is set to 1, and the hydrogen diffusion coefficient of Comparative Example 1 is used to analyze the concentration diffused to the opposite side after the breakdown time has elapsed (this is assumed to be the lower limit of detection). (2) A concentration of 1 is given to one side of the plate, and the hydrogen diffusion coefficient of Comparative Example 1 is given to the SUJ2 portion. The hydrogen diffusion coefficient of the coating portion is treated as an unknown and is changed appropriately, and the analysis is repeated until the concentration diffused to the opposite side after the breakdown time of Comparative Example 1 becomes the concentration determined in (1) above.

[0108] In the electrochemical hydrogen permeation test, thiourea was added to the electrolyte solution on the cathode side. As a result, as shown in FIG. 7(a), the hydrogen atoms (H ａｄ) recombine to form H ２ By mechanisms such as inhibiting the formation of H ａｄ →H ａｂ In the invasion reaction of H ａｄ It is thought that excess H ａｄ When there is, H ２ａｄ On the other hand, when hydrogen gas is used to infiltrate a test piece or when strength tests such as fatigue tests are performed, the dissociation and adsorption reaction of hydrogen molecules (H ２ ⇔H ２ａｄ Ya, H ２ａｄ ⇔2 hours ａｄ ) can also slow down hydrogen penetration and diffusion and prevent strength reduction due to hydrogen embrittlement (see Figure 7(b)). However, in this case, if the hydrogen source is not hydrogen molecules but hydrogen atoms or hydrogen ions in some molecule, it may not be effective as a countermeasure against hydrogen embrittlement. Therefore, in this example, to be able to deal with various hydrogen sources such as not only hydrogen gas but also moisture in the usage environment and hydrogen atoms in lubricating oil, an electrochemical hydrogen permeation test was performed, focusing on hydrogen penetration and diffusion.

[0109] Fig. 8 is a graph summarizing the results of Examples 1 and 2, Reference Examples 1 and 2, and Comparative Example 1. As shown in Fig. 8, by combining the type of substrate with the Ni plating coating as a hard film, it is possible to effectively exhibit the effect of delaying hydrogen embrittlement.

[0110] Furthermore, because the rate and duration of hydrogen penetration vary depending on the application and environment of use, it is believed that by combining measures that focus on the rate of penetration as well as the rate of diffusion of hydrogen atoms, it will be possible to adapt to a wider variety of usage conditions.

[0111] The hard film-coated article of the present invention has hydrogen embrittlement resistance and wear resistance, and also has sufficient strength, so it can be suitably used for mechanical parts such as bearings used in hydrogen penetration environments. According to the present invention, a hard film that is stable in a hydrogen environment and reduces hydrogen penetration or diffusion is provided on the surface of a specified iron-based alloy substrate, thereby suppressing hydrogen embrittlement in mechanical parts that require high strength.

[0112] REFERENCE SIGNS LIST 1 Hard film-formed body 2 Substrate 3 Hard film 4 Hard film-formed body 5 Substrate 6 Hard film 7 Intermediate layer 8 DLC layer 11 Deep groove ball bearing (bearing) 12 Inner ring 13 Outer ring 14 Ball (rolling element) 15 Cage 16 Seal member 17 Grease 18 Hard film 21 Hydrogen circulation pump 22 Motor housing 23 Pump housing 24, 25 Rotating shaft 26 Motor stator 27 Motor rotor 28, 29 Gear 30, 31 Rotor 32, 33, 34, 35, 36, 37 Rolling bearing 41 Test device 42 Cathode tank 43 Electrolyte solution 44 Cathode electrode 45 Anode tank 46 Electrolyte solution 47 Anode electrode 48 KCl saturated aqueous solution 49 Reference electrode 50 Salt bridge 51 test piece

Claims

1. A hard film-formed body having a hard film on the surface of a substrate that suppresses the penetration and diffusion of hydrogen atoms, wherein the substrate is made of martensitic stainless steel or martensitic precipitation hardening stainless steel and has a surface Vickers hardness of 500 Hv to 1000 Hv, and the hard film has a Vickers hardness that is 0.9 times or more the Vickers hardness of the substrate and 3000 Hv or less.

2. The hard film-formed body according to claim 1, characterized in that the substrate is a martensitic stainless steel containing nitrogen and 0.05 mass % or more but less than 0.60 mass % carbon.

3. The hard film-forming body according to claim 2, characterized in that the substrate contains 0.20 mass % to 0.50 mass % carbon, 0.10 mass % to 0.50 mass % manganese, 0.30 mass % or less nickel, 14.00 mass % to 17.00 mass % chromium, 1.00 mass % to 2.50 mass % molybdenum, and 0.10 mass % to 0.40 mass % nitrogen.

4. The hard film-formed body according to claim 1, wherein the hard film that suppresses the penetration and diffusion of hydrogen atoms is a Ni coating.

5. The hard film-formed body according to claim 4, wherein the Ni film includes a Ni-P-B film containing 90 mass % or more of Ni.

6. The hard film-formed body according to claim 1, wherein a diamond-like carbon layer is formed on the surface of said hard film, and an intermediate layer is formed on the substrate side of said diamond-like carbon layer.

7. In an electrochemical hydrogen permeation method using a test piece (thickness of the substrate: 1 mm) made of the hard film-formed body, the area of ​​the test piece in contact with the electrolyte solution in each of the cathode and anode chambers was 3.14 cm ２ The current density on the anode tank side was 1 mA / cm ２ 2. The hard film-formed body according to claim 1, wherein, when electrolysis is performed at 1000 K, the extension time of the breakthrough time of the test piece is 0.4 times or more compared to the breakthrough time of a control piece made of the base material having a thickness of 1 mm.

8. A mechanical part using the hard film-formed body according to claim 1.

9. The machine part according to claim 8, which is a bearing member.

10. A bearing using the bearing member according to claim 9.

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