Rolling parts and rolling bearings

Abstract

To provide a rolling component for a hydrogen utilization device which can suppress dimensional change accompanying decomposition of residual austenite and occurrence of hydrogen embrittlement accompanying hydrogen intrusion from the surface.SOLUTION: A rolling component has a surface, and is made of steel. The rolling component has a surface layer part in a region of a depth of 20 μm from the surface. The rolling component is used for a hydrogen utilization device. The steel contains 0.70 mass% or more and 1.10 mass% or less of carbon, 0.15 mass% or more and 0.35 mass% or less of silicon, 0.30 mass% or more and 0.60 mass% or less of manganese, 1.30 mass% or more and 1.60 mass% or less of chromium, 0.01 mass% or more and 0.50 mass% or less of molybdenum, and 0.01 mass% or more and 0.50 mass% or less of vanadium, and the balance consists of iron and inevitable impurities. Nitrogen concentration in the steel in the surface layer part is 0.2 mass% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to rolling parts and rolling bearings. More specifically, the present invention relates to rolling parts and rolling bearings for hydrogen utilization equipment.

Background Art

[0002] Patent Document 1 (Japanese Patent No. 3990212) describes rolling parts. The rolling parts described in Patent Document 1 are made of SUJ2, which is a high-carbon chromium bearing steel defined by JIS standards. The bearing parts described in Patent Document 1 are formed by nitriding treatment, quenching and tempering.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the rolling parts described in Patent Document 1 are used in hydrogen utilization equipment, that is, in an environment exposed to hydrogen, there is a risk of premature peeling occurring on the contact surface due to hydrogen embrittlement. In addition, the rolling parts described in Patent Document 1 may have insufficient indentation resistance.

[0005] The present invention has been made in view of the problems of the prior art as described above. More specifically, the present invention provides a rolling part for hydrogen utilization equipment that can suppress the occurrence of hydrogen embrittlement associated with hydrogen intrusion from the surface and has improved indentation resistance.

Means for Solving the Problems

[0006] The rolling component according to the present invention has a surface and is made of steel. It comprises a surface layer extending up to a depth of 20 μm from the surface. The rolling component is for use in hydrogen utilization equipment. The steel contains 0.70 mass percent to 1.10 mass percent of carbon, 0.15 mass percent to 0.35 mass percent of silicon, 0.30 mass percent to 0.60 mass percent of manganese, and 1.30 mass percent to 1.60 mass percent of chromium. Precipitates mainly composed of chromium or vanadium are deposited in the steel in the surface layer. The compressive residual stress at a distance of 50 μm from the surface is 80 MPa or more.

[0007] In the rolling components described above, the steel may further contain 0.01% by mass or more and 0.50% by mass or less of vanadium, and 0.01% by mass or more and 0.5% by mass or more of molybdenum.

[0008] In the rolling components described above, the steel may contain 0.90 mass percent to 1.10 mass percent of carbon, 0.20 mass percent to 0.30 mass percent of silicon, 0.40 mass percent to 0.50 mass percent of manganese, 1.40 mass percent to 1.60 mass percent of chromium, 0.10 mass percent to 0.30 mass percent of molybdenum, and 0.20 mass percent to 0.30 mass percent of vanadium, with the remainder being iron and unavoidable impurities.

[0009] In the rolling components described above, the maximum particle size of the precipitates may be 2.0 μm or less. In the rolling components described above, the average area ratio of the precipitates may be 1.0 percent or more. In the rolling components described above, the hardness of the steel at a distance of 50 μm from the surface may be 64 HRC or more. In the rolling components described above, the amount of retained austenite in the steel at a distance of 50 μm from the surface may be less than 25 volume percent.

[0010] In the rolling components described above, the nitrogen concentration in the steel at the surface may be 0.2 mass percent or more. In the rolling components described above, the average particle size of the martensitic block grains in the top 50 percent area of ​​the steel at the surface is 1.5 μm or less.

[0011] The rolling bearing according to the present invention comprises an inner ring, an outer ring, and rolling elements. At least one of the inner ring, outer ring, and rolling elements is the rolling component described above. The rolling bearing is for use in hydrogen utilization equipment. [Effects of the Invention]

[0012] The rolling components and rolling bearings of the present invention can suppress the occurrence of hydrogen embrittlement due to hydrogen intrusion from the surface, and can also improve the ability to withstand indentations. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view of the rolling bearing 100. [Figure 2] This is an enlarged cross-sectional view of ball valve 200. [Figure 3] This is a cross-sectional view of the hydrogen circulation pump 300. [Figure 4] This is a process diagram showing the manufacturing method of the rolling bearing 100. [Figure 5] This is a process diagram showing a modified example of the manufacturing method of the rolling bearing 100. [Figure 6] This is an EBSD phase map of the cross-section near the orbital plane of Sample 1. [Figure 7] This is an EBSD phase map of the cross-section near the orbital plane of Sample 2. [Figure 8] This is an EBSD phase map of the cross-section near the orbital plane of sample 3. [Figure 9] This is an EBSD phase map of the cross-section near the orbital plane of sample 4. [Figure 10] This graph shows the average grain size of martensitic block grains in steel in the region up to a depth of 20 μm from the orbital plane for samples 1 through 4.

Embodiments for Carrying Out the Invention

[0014] Details of embodiments of the present invention will be described while referring to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and duplicate descriptions will not be repeated.

[0015] The configuration of a rolling bearing (hereinafter referred to as "rolling bearing 100") according to an embodiment will be described below. The rolling bearing 100 is, for example, a deep groove ball bearing. However, the rolling bearing 100 is not limited thereto. The rolling bearing 100 may be, for example, an angular ball bearing, a cylindrical roller bearing, a tapered roller bearing, or a self-aligning roller bearing.

[0016] The rolling bearing 100 is for hydrogen utilization equipment. The hydrogen utilization equipment is, for example, a ball valve or a compressor for a hydrogen station. The type of the compressor is not particularly limited. For example, the compressor may be any of a reciprocating (reciprocating), rotary (screw), centrifugal, or axial flow type. The hydrogen utilization equipment may also be a high-pressure hydrogen pressure reducing valve or a hydrogen circulation pump for a fuel cell vehicle. The rolling bearing 100 may be used for any application exposed to hydrogen.

[0017] FIG. 1 is a cross-sectional view of the rolling bearing 100. As shown in FIG. 1, the rolling bearing 100 has a central axis A. FIG. 1 shows a cross-section parallel to the central axis A and passing through the central axis A. The rolling bearing 100 has an inner ring 10, an outer ring 20, a plurality of rolling elements 30, and a cage 40. The inner ring 10 and the outer ring 20 are ring-shaped. The rolling elements 30 are balls (spherical).

[0018] The direction along the central axis A is defined as the axial direction. The direction passing through the central axis A and perpendicular to the central axis A is defined as the radial direction. The direction along the circumference centered on the central axis A is defined as the circumferential direction.

[0019] The inner ring 10 has a first end face 10a, a second end face 10b, an inner circumferential surface 10c, and an outer circumferential surface 10d. The first end face 10a, the second end face 10b, the inner circumferential surface 10c, and the outer circumferential surface 10d constitute the surface of the inner ring 10. The first end face 10a and the second end face 10b are the end faces of the inner ring 10 in the axial direction. The second end face 10b is the opposite side of the first end face 10a.

[0020] The inner circumferential surface 10c extends along the circumferential direction. The inner circumferential surface 10c faces the central axis A. Although not shown, the inner ring 10 is fitted onto the shaft at the inner circumferential surface 10c. The inner circumferential surface 10c is connected to the first end surface 10a at one end in the axial direction and to the second end surface 10b at the other end in the axial direction.

[0021] The outer circumferential surface 10d extends along the circumferential direction. The outer circumferential surface 10d faces away from the central axis A. In other words, the outer circumferential surface 10d is the opposite surface to the inner circumferential surface 10c in the radial direction. The outer circumferential surface 10d is connected to the first end surface 10a at one end in the axial direction and to the second end surface 10b at the other end in the axial direction.

[0022] The outer circumferential surface 10d has a raceway surface 10da. The raceway surface 10da is the portion of the outer circumferential surface 10d that contacts the rolling element 30. The raceway surface 10da extends along the circumferential direction. The raceway surface 10da is located in the central part of the outer circumferential surface 10d in the axial direction. In cross-sectional view, the raceway surface 10da has a partial arc shape that is concave toward the inner circumferential surface 10c.

[0023] The outer ring 20 has a first end face 20a, a second end face 20b, an inner circumferential surface 20c, and an outer circumferential surface 20d. The first end face 20a, the second end face 20b, the inner circumferential surface 20c, and the outer circumferential surface 20d constitute the surface of the outer ring 20. The outer ring 20 is positioned radially outward of the inner ring 10 with the inner circumferential surface 20c facing the outer circumferential surface 10d at a distance from it.

[0024] The first end face 20a and the second end face 20b are the end faces of the outer ring 20 in the axial direction. The second end face 20b is the opposite side of the first end face 20a.

[0025] The inner circumferential surface 20c extends along the circumferential direction. The inner circumferential surface 20c faces the central axis A. The inner circumferential surface 20c is connected to the first end surface 20a at one end in the axial direction and to the second end surface 20b at the other end in the axial direction.

[0026] The inner circumferential surface 20c has a raceway surface 20ca. The raceway surface 20ca is the portion of the inner circumferential surface 20c that contacts the rolling element 30. The raceway surface 20ca extends along the circumferential direction. The raceway surface 20ca is located in the central part of the inner circumferential surface 20c in the axial direction. In cross-sectional view, the raceway surface 20ca has a partial arc shape that is concave toward the outer circumferential surface 20d.

[0027] The outer circumferential surface 20d extends along the circumferential direction. The outer circumferential surface 20d faces away from the central axis A. In other words, the outer circumferential surface 20d is the opposite surface to the inner circumferential surface 20c in the radial direction. Although not shown, the outer ring 20 is fitted into the housing at the outer circumferential surface 20d. The outer circumferential surface 20d is connected to the first end surface 20a at one end in the axial direction and to the second end surface 20b at the other end in the axial direction.

[0028] The rolling elements 30 are positioned between the outer circumferential surface 10d and the inner circumferential surface 20c, more specifically, between the raceway surface 10da and the raceway surface 20ca. Multiple rolling elements 30 are arranged along the circumferential direction. Each rolling element 30 has a surface 30a. The cage 40 holds multiple rolling elements 30. The cage 40 holds multiple rolling elements 30 such that the circumferential distance between two adjacent rolling elements 30 is within a certain range.

[0029] The inner ring 10, outer ring 20, and rolling elements 30 are made of steel. More specifically, the inner ring 10, outer ring 20, and rolling elements 30 are formed of steel with the composition shown in Table 1 (referred to as "composition 1").

[0030] [Table 1]

[0031] Carbon affects the hardness of the steel surface of rolling components (inner ring 10, outer ring 20, and rolling elements 30) after quenching. If the carbon content in the steel is less than 0.70 mass percent, it is difficult to ensure sufficient hardness on the surface of the rolling components. If the carbon content in the steel is less than 0.70 mass percent, it is necessary to supplement the carbon content on the surface of the rolling components by carburizing or other treatments, which leads to a decrease in production efficiency and an increase in manufacturing costs. On the other hand, if the carbon content in the steel exceeds 1.10 mass percent, there is a risk of cracking (quench cracking) during quenching. For this reason, the carbon content of the first composition steel is set to be between 0.70 mass percent and 1.10 mass percent.

[0032] Silicon is added to steel during deoxidation and to ensure machinability before nitrification treatment. If the silicon content in the steel is less than 0.15 mass percent, the resistance to tempering softening will be insufficient. As a result, the hardness of the surface of the rolling components may decrease due to tempering after quenching or the temperature rise during use of the rolling bearing 100. In this case, the machinability of the rolling components during processing will also be insufficient.

[0033] If the silicon content in steel exceeds 0.35 mass percent, the steel becomes too hard, which actually reduces its machinability when processing rolling components. Furthermore, this increases the material cost of the steel. Therefore, the silicon content of the first composition of steel is set to be between 0.15 mass percent and 0.35 mass percent.

[0034] Manganese is added to ensure the hardenability and hardness of steel. If the manganese content in the steel is less than 0.30 mass percent, it is difficult to ensure the hardenability of the steel. If the manganese content in the steel exceeds 0.60 mass percent, the amount of manganese-based nonmetallic inclusions, which are impurities, increases. Therefore, in the first composition of steel, the manganese content is set to be between 0.30 mass percent and 0.60 mass percent.

[0035] Chromium is added to ensure the hardenability of steel and to form fine precipitates (nitrides, carbonitrides) during nitriding. If the chromium content in the steel is less than 1.30 mass percent, it is difficult to ensure the hardenability of the steel and to sufficiently form fine precipitates. If the chromium content in the steel exceeds 1.60 mass percent, the material cost of the steel increases. Therefore, in the first composition of steel, the chromium content is set to be between 1.30 mass percent and 1.60 mass percent.

[0036] Molybdenum is added to ensure the hardenability of steel and to form fine precipitates during nitriding. Because molybdenum has a strong affinity for carbon, it precipitates in the steel as undissolved carbides during nitriding. These undissolved molybdenum carbides act as precipitation nuclei during quenching, thus increasing the amount of precipitates after quenching.

[0037] If the molybdenum content in steel is less than 0.01 mass percent, it is difficult to ensure the hardenability of the steel and to sufficiently form fine precipitates. If the molybdenum content in steel exceeds 0.50 mass percent, the material cost of the steel increases. Therefore, in the first composition of steel, the molybdenum content is set to be between 0.01 mass percent and 0.50 mass percent.

[0038] Vanadium is added to ensure the hardenability of steel and to form fine precipitates during nitriding. If the vanadium content in the steel is less than 0.01 mass percent, it is difficult to ensure the hardenability of the steel and to sufficiently form fine precipitates. If the vanadium content in the steel exceeds 0.50 mass percent, the material cost of the steel increases. Therefore, in the first composition of steel, the vanadium content is set to be between 0.01 mass percent and 0.50 mass percent.

[0039] The inner ring 10, outer ring 20, and rolling elements 30 may be formed from steel of the composition shown in Table 2 (referred to as "second composition"). The inner ring 10, outer ring 20, and rolling elements 30 may also be formed from steel of the composition shown in Table 3 (referred to as "third composition"). When the inner ring 10, outer ring 20, and rolling elements 30 are formed from steel of the first or second composition, precipitates are more finely dispersed in the steel of the surface layer 50, which will be described later. It is not necessary for all of the inner ring 10, outer ring 20, and rolling elements 30 to be formed from steel of the first, second, or third composition; it is sufficient if at least one of the inner ring 10, outer ring 20, and rolling elements 30 is formed from steel of the first, second, or third composition.

[0040] [Table 2]

[0041] [Table 3]

[0042] As shown in Figure 1, the inner ring 10, outer ring 20, and rolling elements 30 each have a surface layer 50. In the inner ring 10, the surface layer 50 extends to a depth of 20 μm from the surface of the inner ring 10. In the outer ring 20, the surface layer 50 extends to a depth of 20 μm from the surface of the outer ring 20. In the rolling elements 30, the surface layer 50 extends to a depth of 20 μm from the surface 30a. The surface layer 50 is formed by nitriding. Note that in the inner ring 10, it is sufficient for the surface layer 50 to be formed on at least the raceway surface 10da, and in the outer ring 20, it is sufficient for the surface layer 50 to be formed on the raceway surface 20ca.

[0043] Precipitates are deposited in the steel in the surface layer 50. The precipitates are mainly composed of chromium or vanadium. The precipitates are nitrides mainly composed of chromium or vanadium. The precipitates may also be carbonitrides mainly composed of chromium or vanadium. The precipitates may be a mixture of the above nitrides and carbonitrides.

[0044] Furthermore, the surface layer 50 does not need to be formed on all of the surfaces of the inner ring 10, the outer ring 20, and the rolling element 30; it is sufficient if it is formed on at least one of the surfaces of the inner ring 10, the outer ring 20, and the rolling element 30.

[0045] Nitrides primarily composed of chromium (vanadium) are chromium (vanadium) nitrides or in which some of the chromium (vanadium) sites in said nitrides are replaced by alloying elements other than chromium (vanadium). Carbonitrides primarily composed of chromium (vanadium) are in which some of the carbon sites in chromium (vanadium) carbides are replaced by nitrogen. The chromium (vanadium) sites in carbonitrides primarily composed of chromium (vanadium) may be replaced by alloying elements other than chromium (vanadium).

[0046] The compressive residual stress at the position where the inner ring 10 is 50 μm from the surface, the outer ring 20 is 50 μm from the surface, and the rolling element 30 is 50 μm from the surface (surface 30a) is 80 MPa or greater. The compressive residual stress at the position where the inner ring 10 is 50 μm from the surface and the outer ring 20 is 50 μm from the surface is measured, for example, in the circumferential direction. The above compressive residual stress is measured by X-ray diffraction.

[0047] The maximum particle size of the precipitates is preferably 2.0 μm or less. The average area ratio of the precipitates is preferably 1.0 percent or more. When the maximum particle size of the precipitates is 2.0 μm or less and the average area ratio of the precipitates is 1.0 percent or more, the wear resistance on the surface of the inner ring 10, the surface of the outer ring 20, and the surface of the rolling elements 30 is improved by the fine dispersion of the precipitates. The maximum particle size of the precipitates is more preferably 1.0 μm or less. The average area ratio of the precipitates is more preferably 2.0 percent or more.

[0048] The average area ratio of precipitates is calculated by acquiring a cross-sectional image of the surface layer 50 at a magnification of 5000x using a field emission scanning electron microscope (FE-SEM), binarizing the cross-sectional image, and then performing image processing on the binarized cross-sectional image. Cross-sectional images of the surface layer 50 are acquired from three or more fields of view, and the average area ratio is the average value of the area ratios of precipitates obtained from these multiple cross-sectional images.

[0049] The particle size of each precipitate is obtained by acquiring the area of ​​each precipitate using the same method as described above, and then multiplying the square root of the value obtained by dividing the area by π by 2. The largest particle size among the obtained precipitates is then considered to be the maximum particle size of the precipitate.

[0050] The nitrogen concentration in the steel at the surface layer 50 is preferably 0.2 mass percent or higher. The nitrogen concentration in the steel at the surface layer 50 is measured using an electron probe microanalyzer (EPMA). For example, the nitrogen concentration in the steel at the surface layer 50 is 0.5 mass percent or lower.

[0051] The hardness of the steel at the position where the depth from the surface of the inner ring 10 is 50 μm, the position where the depth from the surface of the outer ring 20 is 50 μm, and the position where the depth from the surface (surface 30a) of the rolling element 30 is 50 μm is preferably 64 HRC or higher.

[0052] The hardness of the steel at the position where the depth from the surface of the inner ring 10 is 50 μm, the position where the depth from the surface of the outer ring 20 is 50 μm, and the position where the depth from the surface (surface 30a) of the rolling element 30 is 50 μm is measured by the Rockwell hardness test method specified in the JIS standard (JIS Z 2245:2016).

[0053] The steel in the surface layer 50 contains martensite block grains. At the grain boundary between two adjacent martensite block grains, the difference in crystal orientation is 15° or more. From another perspective, even if there are areas with a difference in crystal orientation, if the difference in crystal orientation is less than 15°, those areas are not considered to be grain boundaries of martensite block grains. The grain boundaries of martensite block grains are determined by the EBSD (Electron Back Scattered Diffraction) method.

[0054] In the steel of the surface layer 50, it is preferable that the average particle size of the martensitic block grains in the upper 50 percent area ratio is 1.5 μm or less. When the martensitic block grains in the steel of the surface layer 50 are refined so that the average particle size in the upper 50 percent area ratio is 1.5 μm or less, the shear resistance near the surface of the inner ring 10, outer ring 20, and rolling elements 30 is improved due to the increased toughness of the surface layer 50.

[0055] The average grain size of martensite block grains with a top area ratio of 50 percent is measured by the following method. First, a cross-sectional observation is performed on a section including the surface layer 50. At this time, martensite block grains included in the observation field are identified by the EBSD method. This observation field is the region observed at a magnification of 1500x. Second, the area of ​​each martensite block grain included in the observation field is analyzed from the crystal orientation data obtained by the EBSD method.

[0056] Thirdly, the areas of each martensite block grain included in the observation field are added together in descending order of area. This addition is continued until the total area of ​​the martensite block grains included in the observation field reaches 50 percent. For each of the martensite block grains included in the above addition, the equivalent circle diameter is calculated. This equivalent circle diameter is the square root of the value obtained by dividing the area of ​​the martensite block grain by π / 4. The average of the equivalent circle diameters of the martensite block grains included in the above addition is considered to be the average grain size of the martensite block grains when the top area ratio is 50 percent.

[0057] Preferably, the amount of retained austenite in the steel at a depth of 50 μm from the surface of the inner ring 10, at a depth of 50 μm from the surface of the outer ring 20, and at a depth of 50 μm from the surface (surface 30a) of the rolling element 30 is less than 25 volume percent. In this case, changes in the dimensions of the inner ring 10, outer ring 20, and rolling element 30 over time due to the decomposition of retained austenite are suppressed. More preferably, the amount of retained austenite in the steel at a depth of 50 μm from the surface of the inner ring 10, at a depth of 50 μm from the surface of the outer ring 20, and at a depth of 50 μm from the surface (surface 30a) of the rolling element 30 is less than 20 volume percent.

[0058] The amount of retained austenite in the steel at a depth of 50 μm from the surface of the inner ring 10, at a depth of 50 μm from the surface of the outer ring 20, and at a depth of 50 μm from the surface (surface 30a) of the rolling element 30 is measured by X-ray diffraction. More specifically, the amount of retained austenite in the steel at a depth of 50 μm from the surface of the inner ring 10, at a depth of 50 μm from the surface of the outer ring 20, and at a depth of 50 μm from the surface (surface 30a) of the rolling element 30 is measured using an MSF-3M manufactured by Rigaku Corporation.

[0059] In the above description, the case in which the rolling member according to the embodiment is a component of a rolling bearing 100 has been explained, but the rolling member according to the embodiment may also be a sliding bearing.

[0060] <Example of application of the rolling member according to the embodiment> The rolling member according to this embodiment is used in a ball valve 200. Figure 2 is an enlarged cross-sectional view of the ball valve 200. As shown in Figure 2, the ball valve 200 includes a body 210, a seat retainer 220, balls 230, stems 231 and 232, and a sliding bearing 240.

[0061] The seat retainer 220 is located inside the body 210. The seat retainer 220 has an internal space 220a and two flow paths 220b and 220c. Flow paths 220b and 220c are connected to the internal space 220a. The ball 230 is located in the internal space 220a. The wall surface of the internal space 220a is in contact with the surface of the ball 230 in the sealing portion 220aa.

[0062] Stems 231 and 232 are connected to the upper and lower ends of the ball 230, respectively. As stems 231 and 232 rotate around a central axis, flow paths 220b and 220c are connected through through holes (not shown) formed in the ball 230. Stems 231 and 232 are passed through through holes formed in the body 210 and the seat retainer 220. Hydrogen flows through flow paths 220b and 220c and the through holes formed in the ball 230.

[0063] The sliding bearing 240 is cylindrical and attached to the body 210 on its outer circumferential surface. The sliding bearing 240 rotatably supports the stem 231 (stem 232). The sliding bearing 240 is a rolling member according to the embodiment. That is, the sliding bearing 240 is made of steel of the first composition, second composition, or third composition, and has a surface layer 50 formed on its contact surface.

[0064] <Examples of applications of rolling bearings according to the embodiment> Figure 3 is a cross-sectional view of the hydrogen circulation pump 300. The hydrogen circulation pump 300 includes a motor housing 310, a pump housing 320, a rotating shaft 331 and a rotating shaft 332, a motor stator 341 and a motor rotor 342, gears 351 and 352, rotors 361 and 362, and rolling bearings 371, 372, 373, 374, 375, and 376.

[0065] The motor housing 310 is attached to the pump housing 320. One end of the rotating shaft 331 is located inside the motor housing 310, and the other end of the rotating shaft 331 is located inside the pump housing 320. The one end and the other end of the rotating shaft 331 are rotatably supported by a rolling bearing 371 located inside the motor housing 310 and a rolling bearing 372 located inside the pump housing 320, respectively. Between the one end and the other end, the rotating shaft 331 is rotatably supported by a rolling bearing 373 and a rolling bearing 374 located inside the pump housing 320.

[0066] The rotating shaft 332 is located within the pump housing 320. One end of the rotating shaft 332 is rotatably supported by a rolling bearing 375 located within the pump housing 320. The rotating shaft 332 is also rotatably supported at a position away from the other end by a rolling bearing 376 located within the pump housing 320.

[0067] The motor stator 341 is located inside the motor housing 310. The motor rotor 342 is mounted on the rotating shaft 331 so as to face the motor stator 341. The motor stator 341 and motor rotor 342 rotate the rotating shaft 331. Gears 351 and 352 are mounted on the rotating shaft 331 and rotating shaft 332, respectively. The rotation of the rotating shaft 331 is transmitted to the rotating shaft 332 by gears 351 and 352. Gear 351 is located between rolling bearings 373 and 374, and gear 352 is located between rolling bearings 375 and 376.

[0068] A pump chamber 320a is formed inside the pump housing 320. Rotors 361 and 362 are arranged inside the pump chamber 320a. Rotors 361 and 362 are attached to the rotating shafts 331 and 332, respectively. As rotor 361 rotates with the rotation of the rotating shaft 331, and rotor 362 rotates with the rotation of the rotating shaft 332, hydrogen is drawn into the pump chamber 320a and discharged from the pump chamber 320a.

[0069] Rolling bearings 371, 372, 373, and 375 are deep groove ball bearings. Rolling bearings 374 and 375 are double-row angular contact ball bearings. Rolling bearings 371, 372, 373, 374, 375, and 376 are rolling bearings according to the embodiment. That is, in rolling bearings 371, 372, 373, 374, 375, and 376, the raceway members and rolling elements are made of steel of the first, second, or third composition, and a surface layer 50 is formed on the contact surface.

[0070] Figure 4 is a process diagram showing the manufacturing method of the rolling bearing 100. As shown in Figure 4, the manufacturing method of the rolling bearing 100 includes a preparation step S1, a nitrogen treatment step S2, a first quenching step S3, a first tempering step S4, a second quenching step S5, a second tempering step S6, a post-processing step S7, and an assembly step S8. Note that the manufacturing method of the rolling bearing 100 does not necessarily include the first tempering step S4 and the second quenching step S5.

[0071] In preparation step S1, the workpiece to be processed is prepared. If an inner ring 10 and an outer ring 20 are to be formed, a ring-shaped member is prepared as the workpiece; if a rolling element 30 is to be formed, a spherical member is prepared. This workpiece is formed from steel of a first composition or a second composition.

[0072] In the nitriding treatment step S2, the surface of the workpiece is subjected to nitriding. This nitriding treatment is carried out by holding the workpiece at a temperature above the A1 transformation point for a predetermined time in an atmospheric gas containing a nitrogen source gas (e.g., ammonia gas). In the first quenching step S3, the workpiece is quenched. This quenching is carried out by holding the workpiece at a temperature above the A1 transformation point for a predetermined time, and then cooling the workpiece to a temperature below the Ms transformation point.

[0073] In the first tempering step S4, the workpiece to be processed is tempered. This tempering is performed by holding the workpiece at a temperature below the A1 transformation point for a predetermined time.

[0074] In the second quenching step S5, the workpiece is quenched. This quenching is performed by holding the workpiece at a temperature above the A1 transformation point for a predetermined time, and then cooling the workpiece to a temperature below the Ms transformation point.

[0075] In the second tempering step S6, the workpiece is tempered. This tempering is performed by heating and holding the workpiece at a temperature below the A1 transformation point for a predetermined time.

[0076] In the post-processing step S7, the workpiece is subjected to finishing (grinding and polishing) and cleaning. This forms the inner ring 10, outer ring 20, and rolling elements 30. In the assembly step S8, the inner ring 10, outer ring 20, and rolling elements 30 are assembled together with the cage 40. Through these steps, a rolling bearing 100 with the structure shown in Figure 1 is manufactured.

[0077] The holding temperature in the second quenching step S5 is lower than the holding temperatures in the nitriding step S2 and the first quenching step S3. The holding temperatures in the nitriding step S2 and the first quenching step S3 are, for example, 850°C. The holding temperature in the second quenching step S5 is, for example, 810°C. The holding temperature and holding time in the first tempering step S4 and the second tempering step S6 are, for example, 180°C and 2 hours, respectively.

[0078] Figure 5 is a process diagram showing a modified example of the manufacturing method of the rolling bearing 100. As shown in Figure 5, the manufacturing method of the rolling bearing 100 does not necessarily have to include the first tempering step S4, and the second quenching step S5 may be replaced with a sub-zero treatment step S9. In the sub-zero treatment step S9, the workpiece is cooled to a temperature of, for example, -100°C or higher and room temperature or lower.

[0079] (Effects of the rolling bearing according to this embodiment) The effects of the rolling bearing 100 are explained below.

[0080] In the rolling bearing 100, the inner ring 10, outer ring 20, and rolling elements 30 are formed from steel of the first, second, or third composition. As a result, fine precipitates form in the steel within the surface layer 50 formed by the nitriding treatment. The vicinity of these fine precipitates in the surface layer 50 becomes a hydrogen trapping site, reducing the amount of hydrogen entering the surface layer 50. Therefore, premature delamination damage caused by hydrogen embrittlement is less likely to occur in the rolling bearing 100.

[0081] In the rolling bearing 100, the compressive residual stress at the position where the inner ring 10 is 50 μm from the surface, the outer ring 20 is 50 μm from the surface, and the rolling element 30 is 50 μm from the surface (surface 30a) is 80 MPa or more. This compressive residual stress suppresses the formation of indentations on the surfaces of the inner ring 10, the outer ring 20, and the rolling element 30 (surface 30a), and also suppresses the propagation of cracks originating from indentations. Thus, the rolling bearing 100 can suppress the occurrence of hydrogen embrittlement due to hydrogen intrusion from the surface and improve the resistance to indentation formation.

[0082] (Examples) Samples 1 through 4 were prepared as examples of raceway rings. Samples 1 and 2 were made from steel with the compositions shown in Table 4, and Samples 3 and 4 were made from steel with the compositions shown in Table 5. The steel compositions shown in Table 4 correspond to the first composition (second composition), and the compositions shown in Table 5 correspond to the SUJ2 composition (third composition) specified in the JIS standard.

[0083] [Table 4]

[0084] [Table 5]

[0085] Sample 1 underwent a nitrogen treatment process S2, a first quenching process S3, a sub-zero treatment process S9, and a second tempering process S6. Sample 2 underwent a nitrogen treatment process S2, a first quenching process S3, a first tempering process S4, a second quenching process S5, and a second tempering process S6. Sample 3 underwent a nitrogen treatment process S2, a first quenching process S3, and a second tempering process S6. Sample 4 underwent a first quenching process S3 and a first tempering process S4.

[0086] As shown in Table 6, in samples 1 to 3, the circumferential compressive residual stress near the raceway surface (at a depth of 50 μm from the raceway surface) was 80 MPa or higher. On the other hand, in sample 4, the circumferential compressive residual stress near the raceway surface (at a depth of 50 μm from the raceway surface) was 30 MPa or lower. Samples 1 to 3 showed superior raceway indentation resistance compared to sample 4. From this comparison, it became clear that the indentation resistance of the raceway surface is improved by setting the compressive residual stress near the raceway surface to 80 MPa or higher.

[0087] As shown in Table 6, in Sample 1 and Sample 2, the nitrogen concentration in the steel in the region up to a depth of 20 μm from the raceway surface was between 0.2 mass percent and 0.5 mass percent. In Sample 3, the nitrogen concentration in the steel in the region up to a depth of 20 μm from the raceway surface was between 0.3 mass percent and 0.5 mass percent. In Sample 4, no nitrogen was present in the steel in the region up to a depth of 20 μm from the raceway surface.

[0088] As shown in Table 6, in samples 1 to 3, precipitates mainly composed of chromium or vanadium were finely precipitated (maximum particle size of 2.0 μm or less) and densely precipitated (average area ratio of 1.0 percent or more) in the region up to a depth of 20 μm from the orbital plane. In sample 4, no precipitates mainly composed of chromium or vanadium were precipitated in the region up to a depth of 20 μm from the orbital plane.

[0089] As shown in Table 6, in Sample 1 and Sample 2, precipitates mainly composed of chromium or vanadium were dispersed particularly finely and densely (maximum particle size of 1.0 μm or less and average area ratio of 2.0 percent or more) in the region up to a depth of 20 μm from the raceway surface. Consequently, in Sample 1 and Sample 2, the hardness of the steel at a depth of 50 μm from the raceway surface was 64 HRC or higher, indicating particularly good indentation resistance of the raceway surface.

[0090] As shown in Table 6, in Sample 1, the amount of retained austenite in the steel at a depth of 50 μm from the raceway surface was less than 20 volume percent, and in Sample 2, the amount of retained austenite in the steel at a depth of 50 μm from the raceway surface was less than 25 volume percent. In Sample 3, the amount of retained austenite in the steel at a depth of 50 μm from the raceway surface exceeded 25 volume percent, and in Sample 4, the amount of retained austenite in the steel at a depth of 50 μm from the raceway surface was less than 20 volume percent. From this, it became clear that in Samples 1 and 2, the dimensional changes over time due to the decomposition of retained austenite were suppressed because the amount of retained austenite in the steel near the raceway surface was less than 20 volume percent or less than 25 volume percent.

[0091] [Table 6]

[0092] Figure 6 shows the EBSD phase map of the cross-section near the orbital plane of sample 1. Figure 7 shows the EBSD phase map of the cross-section near the orbital plane of sample 2. Figure 8 shows the EBSD phase map of the cross-section near the orbital plane of sample 3. Figure 9 shows the EBSD phase map of the cross-section near the orbital plane of sample 4. In Figures 6 to 9, martensite block grains are indicated by white regions.

[0093] Figure 10 is a graph showing the average particle size of martensitic block grains in steel in the region up to a depth of 20 μm from the raceway surface for samples 1 to 4. The vertical axis of Figure 10 represents the average particle size (in μm) of martensitic block grains in steel in the region up to a depth of 20 μm from the raceway surface. As shown in Figure 10 and Table 7, for samples 1 and 2, the average particle size of martensitic block grains in the top 50 percent area of ​​the steel in the region up to a depth of 20 μm from the raceway surface was 1.5 μm or less.

[0094] On the other hand, in Sample 3, the average particle size of martensite block grains in the top 50 percent area within the steel in the region up to a depth of 20 μm from the raceway surface exceeded 1.5 μm. From this, it became clear that in Samples 1 and 2, in the region up to a depth of 20 μm from the raceway surface, precipitates mainly composed of chromium or vanadium precipitate finely and at high density in the steel, resulting in refinement of the martensite block grains, improvement of shear resistance near the raceway surface, and consequently, improvement of the raceway surface durability.

[0095] [Table 7]

[0096] <Hydrogen intrusion characteristics> The hydrogen penetration characteristics into the surface layers of Sample 1 to Sample 4 were evaluated using the following methods. Firstly, the amount of hydrogen released from Sample 1 to Sample 4 before use was measured by heating Sample 1 to Sample 4 from room temperature to 400°C. Secondly, the amount of hydrogen released from the orbital members of Sample 1 to Sample 4 after 50 hours of use in a hydrogen environment was measured by heating Sample 1 to Sample 4 from room temperature to 400°C.

[0097] As shown in Table 8, in Sample 4, the ratio of hydrogen release before and after use (i.e., the amount of hydrogen released after use divided by the amount of hydrogen released before use) was 3.0 or higher. On the other hand, in Samples 1 and 2, the ratio of hydrogen release before and after use was within the range of 0.9 to 1.2. In Sample 3, the ratio of hydrogen release before and after use was within the range of 1.3 to 2.0.

[0098] [Table 8]

[0099] As described above, in samples 1 to 3, precipitates mainly composed of chromium or vanadium were deposited in the region up to a depth of 20 μm from the orbital plane, whereas in sample 4, no precipitates mainly composed of chromium or vanadium were deposited in the region up to a depth of 20 μm from the orbital plane. From this comparison, it was revealed that the deposition of precipitates mainly composed of chromium or vanadium in the surface layer 50 creates a hydrogen trapping site around it, that is, hydrogen penetration into the surface layer 50 is suppressed, thereby suppressing premature delamination caused by hydrogen embrittlement.

[0100] Although embodiments of the present invention have been described above, it is possible to modify these embodiments in various ways. Furthermore, the scope of the present invention is not limited to the embodiments described above. The scope of the present invention is indicated by the claims and is intended to include all modifications within the meaning and scope equivalent to the claims. [Explanation of Symbols]

[0101] 100 Rolling bearing, 10 Inner ring, 10a First end face, 10b Second end face, 10c Inner circumferential surface, 10d Outer circumferential surface, 10da Raceway surface, 20 Outer ring, 20a First end face, 20b Second end face, 20c Inner circumferential surface, 20ca Raceway surface, 20d Outer circumferential surface, 30 Rolling element, 30a Surface, 40 Cage, 50 Surface layer, A Central axis, S1 Preparation process, S2 Nitrogen treatment process, S3 First quenching process, S4 First tempering process, S5 Second quenching process, S6 Second tempering process, S7 Post-processing process, S8 Assembly process, S9 Sub-zero treatment process.

Claims

1. A steel rolling component having a surface, The surface portion comprises a region up to 20 μm in depth from the surface, The aforementioned rolling component is for hydrogen utilization equipment, The steel contains 0.70 mass percent to 1.10 mass percent of carbon, 0.15 mass percent to 0.35 mass percent of silicon, 0.30 mass percent to 0.60 mass percent of manganese, 1.30 mass percent to 1.60 mass percent of chromium, 0.01 mass percent to 0.50 mass percent of vanadium, and 0.01 mass percent to 0.50 mass percent of molybdenum, with the remainder being iron and unavoidable impurities. In the steel in the surface layer, precipitates mainly composed of chromium or vanadium are deposited. The compressive residual stress at a distance of 50 μm from the surface is 80 MPa or more. The hardness of the steel at a distance of 50 μm from the surface is 64 HRC or higher. A rolling component in which the nitrogen concentration in the steel at the surface layer is 0.2 mass percent or more.

2. The rolling component according to claim 1, wherein the steel contains 0.90 mass percent to 1.10 mass percent of carbon, 0.20 mass percent to 0.30 mass percent of silicon, 0.40 mass percent to 0.50 mass percent of manganese, 1.40 mass percent to 1.60 mass percent of chromium, 0.10 mass percent to 0.30 mass percent of molybdenum, and 0.20 mass percent to 0.30 mass percent of vanadium, with the remainder being iron and unavoidable impurities.

3. The rolling component according to claim 1 or claim 2, wherein the maximum particle size of the precipitate is 2.0 μm or less.

4. The rolling component according to any one of claims 1 to 3, wherein the average area ratio of the precipitate is 1.0 percent or more.

5. The rolling component according to any one of claims 1 to 4, wherein the amount of retained austenite in the steel at a distance of 50 μm from the surface is less than 25 volume percent.

6. The rolling component according to any one of claims 1 to 5, wherein the average particle size of martensitic block grains in the upper 50 percent area ratio of the steel in the surface layer is 1.5 μm or less.

7. It is a rolling bearing, Insider, Outer ring and, Equipped with rolling elements, The aforementioned rolling bearing is for hydrogen utilization equipment, A rolling bearing in which at least one of the inner ring, the outer ring, and the rolling elements is the rolling component described in any one of claims 1 to 6.

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