Rolling member and rolling part

Abstract

To provide a rolling member in which generation of hydrogen brittleness is suppressed.SOLUTION: A rolling member includes a rolling member body. The rolling member body is made of steel that has been quenched and tempered. The steel contains carbon in an amount of 0.80 mass% or more and 1.10 mass% or less, silicon in an amount of 0.15 mass% or more and 0.50 mass% or less, manganese in an amount of 0.30 mass% or more and 0.70 mass% or less, chromium in an amount of 1.30 mass% or more and 1.60 mass% or less, molybdenum in an amount of 0.50 mass% or less, and vanadium in an amount of 0.50 mass% or less, with the remainder consisting of iron and unavoidable impurities. The rolling member body has a raceway surface, on which a nitrogen diffusion region is formed. A carbon concentration in a first surface layer of the rolling member body, which is a region having a depth of 5 μm or less from the raceway surface, is lower than an average value of a carbon concentration in a core portion of the rolling member body, which is a region farther from the raceway surface than the nitrogen diffusion region.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a rolling member and a rolling component. [Background technology]

[0002] In recent years, the operating conditions for rolling parts such as rolling bearings have become increasingly severe. More specifically, a reduction in the amount of lubricating oil or a decrease in the viscosity of the lubricating oil can prevent the formation of a sufficient oil film on the raceway surface, which can lead to hydrogen embrittlement caused by the lubricating oil. Furthermore, with the recent trend toward energy conservation, the development of fuel cell vehicles and hydrogen gas engines has been promoted, and the use of hydrogen as a power source is being promoted. Even in these devices, exposure of rolling parts to hydrogen gas can cause hydrogen embrittlement.

[0003] Examples of conventional rolling parts include those described in Patent Document 1 (JP 2009-7614 A), Patent Document 2 (JP Patent No. 6735589 A), and Patent Document 3 (JP Patent No. 6356881 A). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-7614 [Patent Document 2] Patent No. 6735589 [Patent Document 3] Patent No. 6356881 Summary of the Invention [Problem to be solved by the invention]

[0005] The rolling components described in Patent Documents 1 to 3 have room for improvement in terms of suppressing hydrogen embrittlement. The present invention provides a rolling member in which the occurrence of hydrogen embrittlement is suppressed. [Means for solving the problem]

[0006] The rolling contact member of the present invention includes a rolling contact member body. The rolling contact member body is made of quenched and tempered steel. The steel contains 0.80 to 1.10 mass percent carbon, 0.15 to 0.50 mass percent silicon, 0.30 to 0.70 mass percent manganese, 1.30 to 1.60 mass percent chromium, 0.50 mass percent or less molybdenum, and 0.50 mass percent or less vanadium, with the balance consisting of iron and inevitable impurities. The rolling contact member body has a raceway surface. A nitrogen-diffused region is formed on the raceway surface. The carbon concentration in a first surface layer of the rolling contact member body, which is a region 5 μm or less deep from the raceway surface, is lower than the average carbon concentration in the core of the rolling contact member body, which is a region farther from the raceway surface than the nitrogen-diffused region. Precipitates containing manganese, silicon, chromium, or vanadium as a main component are precipitated in the first surface layer. The area ratio of precipitates in the first surface layer is 2.0% or more. [Effects of the Invention]

[0007] The rolling contact member of the present invention can suppress the occurrence of hydrogen embrittlement. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view of the inner ring 100. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the inner ring body 10. [Figure 3] 1 shows an example of the results of an EPMA analysis performed on the inner ring body 10. [Figure 4] 3 is a manufacturing process diagram of the inner ring 100. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated.

[0010] A rolling member according to an embodiment will be described. Here, a rolling part is a part that transmits power while rotating. Specific examples of rolling parts include rolling bearings, ball screws, drive shafts, cam followers, and gears. A rolling member is a component used in rolling parts. Note that rolling bearings also include hub bearings. The rolling part according to an embodiment is preferably a rolling part used in hydrogen-utilizing equipment. In the following, a raceway ring (inner ring 100) of a rolling bearing will be described as a specific example of a rolling member according to an embodiment.

[0011] (Configuration of inner ring 100) The configuration of the inner ring 100 will be described below.

[0012] FIG. 1 is a cross-sectional view of the inner ring 100. As shown in FIG. 1, the central axis of the inner ring 100 is defined as the central axis A. The direction of the central axis A is defined as the axial direction. The direction of the circumference centered on the central axis A is defined as the circumferential direction. The direction passing through the central axis A and perpendicular to the central axis A is defined as the radial direction. The inner ring 100 is ring-shaped and extends along the circumferential direction.

[0013] The inner ring 100 has an inner ring body 10 (rolling member body). The inner ring body 10 has a width surface 10a and a width surface 10b. The width surface 10a and the width surface 10b each form an end surface of the inner ring body 10 in the axial direction. The width surface 10b is the opposite surface in the axial direction to the width surface 10a. The width surface 10a faces one side in the axial direction (the left side in Figure 1), and the width surface 10b faces the other side in the axial direction (the right side in Figure 1).

[0014] The inner ring body 10 further has an inner peripheral surface 10c and an outer peripheral surface 10d. The inner peripheral surface 10c and the outer peripheral surface 10d each extend circumferentially. The outer peripheral surface 10d is the opposite surface to the inner peripheral surface 10c in the radial direction. One axial end of the inner peripheral surface 10c and one axial end of the outer peripheral surface 10d are continuous with the width surface 10a. The other axial end of the inner peripheral surface 10c and the other axial end of the outer peripheral surface 10d are continuous with the width surface 10b. The width surface 10a, the width surface 10b, the inner peripheral surface 10c, and the outer peripheral surface 10d are sometimes collectively referred to as the surface of the inner ring body 10.

[0015] The inner ring body 10 is attached to a shaft (not shown) at its inner peripheral surface 10c. The outer peripheral surface 10d has a raceway surface 10da. The raceway surface 10da is located at the center of the outer peripheral surface 10d in the axial direction. The outer peripheral surface 10d is recessed toward the inner peripheral surface 10c at the raceway surface 10da. In a cross-sectional view perpendicular to the circumferential direction, the raceway surface 10da has, for example, a partial arc shape. The inner ring body 10 contacts a rolling element (not shown) at the raceway surface 10da.

[0016] The inner ring body 10 is made of hardened and tempered steel. The steel used for the inner ring body 10 contains 0.80 to 1.10 percent by mass of carbon, 0.15 to 0.50 percent by mass of silicon, 0.30 to 0.70 percent by mass of manganese, 1.30 to 1.60 percent by mass of chromium, 0.50 percent by mass or less of molybdenum, and 0.50 percent by mass or less of vanadium, with the balance being iron and unavoidable impurities. Examples of unavoidable impurities include 0.005 to 0.05 percent by mass of aluminum, 0.02 percent by mass or less of phosphorus, 0.01 percent by mass or less of sulfur, 0.015 percent by mass or less of nitrogen, and 0.0015 percent by mass or less of oxygen. The composition of the steel used for the inner ring body 10 is shown in Table 1.

[0017] [Table 1]

[0018] The carbon content of the steel used in the inner ring body 10 may be 0.90 mass percent or more and 1.10 mass percent or less, and the silicon content of the steel used in the inner ring body 10 may be 0.20 mass percent or more and 0.30 mass percent or less. The manganese content of the steel used in the inner ring body 10 may be 0.40 mass percent or more and 0.50 mass percent or less, and the chromium content of the steel used in the inner ring body 10 may be 1.40 mass percent or more and 1.60 mass percent or less.

[0019] Furthermore, the molybdenum content of the steel used for the inner ring body 10 may be 0.20 mass percent or more and 0.30 mass percent or less. The vanadium content of the steel used for the inner ring body 10 may be 0.20 mass percent or more and 0.30 mass percent or less.

[0020] If the carbon content of the steel used for the inner ring body 10 is less than 0.80 percent, the hardness of the steel may be insufficient. On the other hand, if the carbon content of the steel used for the inner ring body 10 is more than 1.10 percent, quench cracking may occur in the steel. From this perspective, the carbon content of the steel used for the inner ring body 10 is set to 0.80 to 1.10 percent by mass.

[0021] If the silicon content in the steel used for the inner ring body 10 is less than 0.15 mass percent, temper softening resistance and workability may be insufficient. On the other hand, if the silicon content in the steel used for the inner ring body 10 is more than 0.50 mass percent, workability may actually decrease. From this perspective, the silicon content in the steel used for the inner ring body 10 is set to 0.15 mass percent or more and 0.50 mass percent or less.

[0022] If the manganese content in the steel used for the inner ring body 10 is less than 0.30 percent by mass, the hardenability of the steel may be insufficient. On the other hand, if the manganese content in the steel used for the inner ring body 10 is more than 0.70 percent by mass, the amount of manganese-based non-metallic inclusions, which are impurities, increases. From this perspective, the manganese content in the steel used for the inner ring body 10 is set to 0.30 percent by mass or more and 0.70 percent by mass or less.

[0023] If the chromium content of the steel used for the inner ring body 10 is less than 1.30 mass percent, the hardenability may be insufficient, and nitrides and carbonitrides may not easily form. On the other hand, if the chromium content of the steel used for the inner ring body 10 exceeds 1.60 mass percent, coarse precipitates may form, potentially shortening the life. From this perspective, the chromium content of the steel used for the inner ring body 10 is set to 1.30 mass percent or more and 1.60 mass percent or less.

[0024] The inclusion of molybdenum in the steel used for the inner ring body 10 causes fine precipitation of nitrides and carbonitrides. However, if the molybdenum content in the steel used for the inner ring body 10 exceeds 0.50 mass percent, the cost of the steel increases. From this perspective, the molybdenum content in the steel used for the inner ring body 10 is set to 0.50 mass percent or less. Note that the steel used for the inner ring body 10 does not have to contain molybdenum.

[0025] The inclusion of vanadium in the steel used for the inner ring body 10 causes fine precipitation of nitrides and carbonitrides. However, if the vanadium content in the steel used for the inner ring body 10 exceeds 0.50 mass percent, the cost of the steel increases. From this perspective, the vanadium content in the steel used for the inner ring body 10 is set to 0.50 mass percent or less. Note that the steel used for the inner ring body 10 does not have to contain vanadium.

[0026] The inner ring 100 further has a coating 20. The coating 20 is formed on the surface of the inner ring body 10. In the example shown in FIG. 1, the coating 20 is formed on the entire surface of the inner ring body 10, but it is sufficient that the coating 20 is formed on at least the raceway surface 10da. The coating 20 may also be formed on portions of the surface of the inner ring body 10 other than the raceway surface 10da.

[0027] FIG. 2 is an enlarged cross-sectional view of the inner ring body 10. As shown in FIG. 2, the region of the inner ring body 10 that is 5 μm or less deep from its surface (raceway surface 10da) is referred to as the surface layer 11. The nitrogen-diffused region formed on the surface of the inner ring body 10 is referred to as the surface layer 12. The region of the inner ring body 10 that is 100 μm or more deep from its surface is referred to as the core portion 13. The nitrogen concentration in the surface layer 12 (nitrogen-diffused region) is higher than that in the core portion 13 (0.0 mass percent). That is, the surface layer 12 is determined by cutting the inner ring body 10 axially at one location in the circumferential direction, mirror-polishing the cut surface, and then performing line analysis using an EPMA from the raceway surface 10da to the interior of the inner ring body 10. The region where the nitrogen concentration obtained by the line analysis using the EPMA is greater than 0.0 mass percent is the surface layer 12. The boundary between the surface layer 12 (nitrogen-diffused region) and the core portion 13 is, for example, farther from the surface of the inner ring body 10 (raceway surface 10da) than the surface layer 11. The depth of the surface layer 12 (nitrogen diffusion region), that is, the distance from the raceway surface 10da to the boundary between the surface layer 12 (nitrogen diffusion region) and the core portion 13, is, for example, 500 μm or less.

[0028] The average grain size of cementite in the steel in the surface layer 11 is, for example, 2.0 μm or less or 1.0 μm or less. The average grain size of cementite in the steel is measured by image analysis of an SEM image. More specifically, first, an SEM image is obtained so that 20 or more cementite particles are included in the observation field. Second, the average length in the vertical and horizontal directions is calculated for the 20 or more cementite particles included in the SEM image. This average length is defined as the average grain size of the cementite. In the surface layer 11, the steel used for the inner ring body 10 may be substantially free of cementite. FIG. 3 shows an example of the results of an EPMA analysis performed on the inner ring body 10. When elemental analysis is performed using an EPMA (Electron Probe Micro Analyzer), the carbon concentration profile shows sharp peaks at positions where cementite is present. As shown in FIG. 3, the carbon concentration profile in the surface layer 11 does not show sharp peaks. Thus, in a region where there is no sharp peak in the carbon concentration profile obtained by EPMA analysis, cementite is considered to be substantially absent.

[0029] The carbon concentration in the steel in the surface layer 11 is lower than the average value of the carbon concentration in the steel in the core portion 13. The carbon concentration in the steel in the surface layer 11 is, for example, 0.90 mass percent or less. The carbon concentration in the steel is measured using an EPMA. The surface layer 11 may be subjected to a nitriding treatment. That is, the nitrogen concentration in the steel in the surface layer 11 may be, for example, 0.20 mass percent or more. The nitrogen concentration in the steel is measured using an EPMA.

[0030] In the surface layer 11, a plurality of precipitates are precipitated in the steel. The main component of the precipitates is chromium, vanadium, manganese, or silicon. The main component of the precipitate refers to the component with the highest content, evaluated in terms of mass percent, among the components of the precipitate. The maximum grain size of the precipitates in the steel in the surface layer 11 is 2.0 μm or less. The maximum grain size of the precipitates in the steel is measured by image analysis of the SEM observation image. More specifically, first, an SEM observation image is obtained so that 20 or more precipitates are included in the observation field. Second, the average length and width of the 20 or more precipitates included in the SEM observation image are calculated. This average length is taken as the average grain size of the precipitates. The area ratio of the precipitates in the steel in the surface layer 11 is, for example, 2.0% or more. The area ratio of the precipitates in the steel is measured by image analysis of the SEM observation image. More specifically, the area ratio of precipitates is calculated by dividing the number of pixels occupied by precipitates in the SEM observation image by the number of pixels in the observation field and multiplying the result by 100.

[0031] The maximum grain size of the martensite block grains in the steel in the surface layer 11 is, for example, 5 μm or less. The maximum grain size of the martensite block grains in the steel is measured by the electron backscattered diffraction (EBSD) method. More specifically, the martensite block grains included in the observation field are identified by the EBSD method. The observation field is set to include at least 20 martensite blocks. The difference in crystal orientation between adjacent martensite block grains at the grain boundary is 15° or more. From another perspective, even if there is a location where the crystal orientation is misaligned, if the difference in crystal orientation is less than 15°, the location is not considered to be the grain boundary of the martensite block grains. Second, the circle-equivalent diameter of each of the multiple martensite block grains included in the observation field is calculated. This circle-equivalent diameter is the square root of the area of ​​the martensite block grain divided by π / 4. The maximum value of these circle-equivalent diameters is considered to be the maximum grain size of the martensite block grains.

[0032] The amount of retained austenite in the steel in the surface layer 12 is, for example, less than 20 volume percent. The amount of retained austenite in the steel is measured by X-ray diffraction. More specifically, first, the integrated intensity of the diffraction peak of austenite in X-ray diffraction and the integrated intensity of the diffraction peak of phases other than austenite in X-ray diffraction are measured. Second, the volume ratio of retained austenite in the steel is calculated by comparing the integrated intensity of the diffraction peak of austenite in X-ray diffraction with the integrated intensity of the diffraction peak of phases other than austenite in X-ray diffraction.

[0033] Oxide-based inclusions and sulfide-based inclusions may be present in the steel in the surface layer 12 and the core portion 13. Examples of oxide-based inclusions include simple substances and complexes of Al2O3, CaO, SiO2, MnO, MgO, and FeO. Examples of sulfide-based inclusions include MnS. The maximum particle size of the oxide-based inclusions in the steel in the surface layer 12 is, for example, 40 μm or less, 30 μm or less, or 20 μm or less. The maximum particle size of the sulfide-based inclusions in the steel in the surface layer 12 and the core portion 13 is, for example, 60 μm or less, 50 μm or less, or 40 μm or less.

[0034] The maximum grain size of oxide inclusions and sulfide inclusions in steel is calculated by the extreme value statistics method. 2 If so, the measurement area is 3000mm 2 That is all.

[0035] Residual compressive stress may be applied to the surface (raceway surface 10da) of the inner ring body 10. The residual compressive stress applied to the surface of the inner ring body 10 is, for example, 80 MPa or more. The residual compressive stress applied to the surface of the inner ring body 10 is measured by X-ray diffraction.

[0036] The hardness of the coating 20 is 3000 Hv or less. The hardness of the coating 20 is measured in accordance with the Vickers hardness test method specified in the JIS standard (JIS Z 2244). The hydrogen diffusion coefficient of the coating 20 is smaller than the hydrogen diffusion coefficient of the surface layer 11.

[0037] The hydrogen diffusion coefficient is measured as follows. First, a test piece having a thickness of 1 mm is prepared. When the hydrogen diffusion coefficient of the coating 20 is to be measured, the coating 20 is formed on the surface of the test piece. Second, the hydrogen diffusion coefficient of the test piece prepared as described above is measured by electrochemical permeation method. The hydrogen diffusion coefficient is measured at room temperature. The thickness of the coating 20 is defined as thickness T. Thickness T may be 1 μm or more, or may be 5 μm or more. Thickness T is, for example, 50 μm or less.

[0038] The coating 20 is, for example, a film containing nickel (nickel film). The nickel film may contain phosphorus and boron. In this case, the sum of the phosphorus content and the boron content in the nickel film is, for example, less than 10 mass percent. The nickel content in the nickel film is, for example, 90 mass percent or more. Preferably, the nickel content, phosphorus content, and boron content in the nickel film are, respectively, 97 mass percent or more, 1 mass percent or more to 3 mass percent or less, and 1 mass percent or less.

[0039] The nickel film is, for example, a film formed by electroless plating (electroless plated film). The nickel film may be a film formed by PVD (Physical Vapor Deposition) or electrolytic plating. The nickel film may be baked. Specific examples of PVD include ion plating and sputtering.

[0040] The coating 20 may also be a film containing tungsten carbide (WC film). The WC film is a film formed by, for example, unbalanced magnetron sputtering (UBMS). The coating 20 may also be a film containing diamond-like carbon (DLC film). The DLC film is formed by, for example, ion plating, sputtering, or UBMS. The hardness of the DLC film can be adjusted by changing the bias voltage during formation to change the composition ratio of graphite structure and diamond structure. The coating 20 may also be a film containing both diamond-like carbon and tungsten carbide (WC / DLC film). The WC / DLC film is a film formed by, for example, UBMS.

[0041] The coating 20 may have a first layer 20a and a second layer 20b. The first layer 20a is formed on the surface (raceway surface 10da) of the inner ring body 10. The second layer 20b is formed on the first layer 20a. The first layer 20a is, for example, a nickel film. The second layer 20b is, for example, a DLC film. In this case, an intermediate layer 20c may be formed between the first layer 20a and the second layer 20b to improve adhesion between the first layer 20a and the second layer 20b. The intermediate layer 20c is, for example, a WC / DLC film.

[0042] (Manufacturing method of inner ring 100) Fig. 4 is a manufacturing process diagram of the inner ring 100. As shown in Fig. 4, the manufacturing method of the inner ring 100 includes a preparation step S1, a nitriding treatment step S2, a decarburization treatment step S3, a first quenching step S4, a subzero treatment step S5, a second quenching step S6, a first tempering step S7, a second tempering step S8, a grinding step S9, and a coating formation step S10.

[0043] In the preparation step S1, a ring-shaped workpiece is prepared. The workpiece is made of steel having the composition shown in Table 1. After the preparation step S1, a nitriding treatment step S2 is carried out.

[0044] In the nitriding treatment step S2, the workpiece is heated in an atmospheric gas containing a nitrogen source, thereby performing nitriding treatment. As a result, nitrogen is introduced from the surface of the workpiece and diffuses throughout the workpiece. After the nitriding treatment step S2, a decarburization treatment step S3 is performed. In the decarburization treatment step S3, the workpiece is placed in a decarburization atmosphere, thereby performing decarburization. This reduces the carbon concentration in the steel at the surface of the workpiece. The nitriding treatment step S2 and the decarburization treatment step S3 are usually performed simultaneously. Note that the decarburization treatment step S3 promotes the precipitation of fine precipitates. Furthermore, the decarburization treatment step S3 reduces the grain size of cementite in the steel in the surface layer 11, or causes cementite to disappear from the surface layer 11. After the nitriding treatment step S2 and the decarburization treatment step S3, a first quenching step S4 is performed.

[0045] In the first quenching step S4, the workpiece is heated to a temperature equal to or higher than the A1 transformation point, and then subjected to M S The workpiece is cooled to a temperature below the transformation point. As a result, martensite and retained austenite are formed in the steel used for the workpiece. After the first quenching step S4, a sub-zero treatment step S5 is performed. After the first quenching step S4, a sub-zero treatment step S5 is performed. In the sub-zero treatment step S5, the workpiece is cooled to a temperature below the transformation point. As a result, martensite and retained austenite are formed in the steel used for the workpiece. After the first quenching step S4, a sub-zero treatment step S5 is performed. f The material is cooled to a temperature below the transformation point. After the sub-zero treatment step S5, a second quenching step S6 is performed.

[0046] In the second quenching process S6, heating to a temperature above the A1 transformation point and then M S The workpiece is quenched again by cooling to a temperature below the transformation point, and the crystal grains in the steel are refined. After the second quenching step S6, a first tempering step S7 is performed.

[0047] In the first tempering step S7, the workpiece is heated to a temperature below the A1 transformation point, thereby tempering the steel used in the workpiece. After the first tempering step S7, a second tempering step S8 is performed. In the second tempering step S8, the workpiece is heated to a temperature below the A1 transformation point, thereby further tempering the steel used in the workpiece. By performing tempering multiple times in this manner, the amount of retained austenite in the steel is reduced. Note that the heating temperature in the second tempering step S8 is preferably higher than the heating temperature in the first tempering step S7. After the second tempering step S8, a grinding step S9 is performed. In the grinding step S9, the workpiece is ground, thereby forming the shape of the inner ring body 10. After the grinding step S9, a coating formation step S10 is performed.

[0048] In the coating formation step S10, the coating 20 is formed on the surface of the inner ring body 10. The formation method for each type of coating 20 is as described above. If the coating 20 contains a nickel film, the nickel film may be baked to increase its hardness.

[0049] In the above, an example has been described in which the manufacturing method of the inner ring 100 includes a preparation step S1, a nitriding treatment step S2, a decarburization treatment step S3, a first quenching step S4, a subzero treatment step S5, a second quenching step S6, a first tempering step S7, a second tempering step S8, a grinding step S9, and a coating formation step S10, but in the manufacturing method of the inner ring 100, at least any of the nitriding treatment step S2, the decarburization treatment step S3, the subzero treatment step S5, the second quenching step S6, the second tempering step S8, and the coating formation step S10 may not be performed.

[0050] (100% inner circle effect) The effects of the inner ring 100 will be described below.

[0051] When a new metal surface forms on the raceway surface 10da due to wear, hydrogen is generated at the new metal surface through a reaction with the lubricant, causing hydrogen embrittlement. In the inner ring 100, the carbon concentration in the surface layer 11 is reduced, which promotes the precipitation of precipitates in the surface layer 11, resulting in fine, plentiful precipitates in the surface layer 11. This improves the wear resistance of the surface of the inner ring body 10, making it less likely for a new metal surface to form. Hydrogen is trapped in these precipitates, making it harmless. Therefore, the inner ring 100 can suppress the occurrence of hydrogen embrittlement.

[0052] Furthermore, in the inner ring 100, tempering at high temperature (second tempering step S8) reduces the dislocation density and the amount of retained austenite in the steel. This reduces the amount of hydrogen (diffusible hydrogen) that is trapped in dislocations and retained austenite and causes hydrogen embrittlement. Furthermore, in the inner ring 100, the nitrogen introduced in the nitriding treatment step S2 dissolves in the martensite in the steel, suppressing dislocation movement through solid solution strengthening. From this perspective as well, the occurrence of hydrogen embrittlement is suppressed in the inner ring 100.

[0053] In the inner ring 100, a coating 20 is formed on the surface of the inner ring body 10. The hydrogen diffusion coefficient of the coating 20 is smaller than the diffusion coefficient in the inner ring body 10 (surface layer 11). Therefore, the inner ring 100 can suppress hydrogen penetration into the inner ring body 10 and prevent hydrogen embrittlement from occurring.

[0054] (Example) Samples 1 to 5 were produced using steels with the compositions shown in Table 2. The first and second compositions were within the composition ranges shown in Table 1. Samples 1 to 5 were subjected to the heat treatments shown in Table 3. The material of the surface of each sample after grinding step S9 was performed is shown in Table 4.

[0055] [Table 2]

[0056] [Table 3]

[0057] [Table 4]

[0058] A wear test was performed on Samples 1 to 3 under the conditions shown in Table 5. As shown in Table 6, the wear resistance of Sample 1 was superior to that of Sample 2, and the wear resistance of Sample 2 was superior to that of Sample 3. While Sample 1 used steel of the first composition and was subjected to the nitriding treatment step S2, Samples 2 and 3 did not satisfy at least one of these conditions. As a result, the area ratio of precipitates in the surface layer 11 of Sample 1 was 2.0 percent or more, while the area ratio of precipitates in the surface layer 11 of Samples 2 and 3 was less than 2.0 percent. Furthermore, cementite was absent from the surface layer 11 of Samples 1 and 2, but cementite was present in the surface layer 11 of Sample 3. This demonstrates that eliminating cementite from the surface layer 11 results in the precipitation of fine, abundant precipitates in the surface layer 11, improving the wear resistance of the raceway surface and suppressing the occurrence of hydrogen embrittlement.

[0059] [Table 5]

[0060] [Table 6]

[0061] As shown in Table 4, the amount of retained austenite in the surface layer 12 of Sample 4 was 20 volume percent or more, while the amount of retained austenite in the surface layer 12 of Sample 5 was less than 20 volume percent. Table 7 shows the cumulative amount of hydrogen released in the temperature range from room temperature to 400°C measured by thermal desorption spectroscopy, and this value corresponds to the amount of hydrogen trapped in the retained austenite in the manufacturing process up to grinding step S9. The amount of hydrogen trapped in the retained austenite of Sample 5 was reduced compared to Sample 4. This comparison revealed that the amount of trapped hydrogen was reduced by reducing the amount of retained austenite.

[0062] [Table 7]

[0063] (Addendum) The above embodiment includes the following configurations.

[0064] <Appendix 1> A rolling member, A rolling member body is provided, the rolling member body is made of quenched and tempered steel; The steel comprises 0.80 to 1.10 percent by weight of carbon, 0.15 to 0.50 percent by weight of silicon, 0.30 to 0.70 percent by weight of manganese, 1.30 to 1.60 percent by weight of chromium, 0.50 percent by weight or less of molybdenum, and 0.50 percent by weight or less of vanadium, with the balance being iron and unavoidable impurities; the rolling member body has a raceway surface, a nitrogen diffusion region is formed on the raceway surface, the carbon concentration in the first surface layer of the rolling member body, which is a region at a depth of 5 μm or less from the raceway surface, is lower than the average carbon concentration in the core portion of the rolling member body, which is a region farther from the raceway surface than the nitrogen diffusion region; a precipitate containing any one of manganese, silicon, chromium, and vanadium as a main component is deposited on the first surface layer; A rolling member, wherein the area ratio of the precipitates in the first surface layer is 2.0 percent or more.

[0065] <Appendix 2> 2. The rolling member according to claim 1, wherein the carbon concentration in the first surface layer is 0.90 mass percent or less.

[0066] <Appendix 3> 3. The rolling contact member according to claim 1, wherein the maximum particle size of oxide-based inclusions in the second surface layer of the rolling contact member body, which is the region from the raceway surface to the boundary between the nitrogen diffusion region and the core, is 40 μm or less.

[0067] <Appendix 4> 3. The rolling contact member according to claim 1, wherein the maximum particle size of sulfide-based inclusions in the second surface layer of the rolling contact member body, which is a region from the raceway surface to a boundary between the nitrogen-diffused region and the core portion, is 60 μm or less.

[0068] <Appendix 5> 5. The rolling contact member according to claim 4, wherein the sulfide-based inclusions in the second surface layer have a maximum particle size of 50 μm or less.

[0069] <Appendix 6> 6. The rolling member according to claim 1, wherein the amount of retained austenite in the second surface layer of the rolling member body, which is a region at a depth of 500 μm or less from the raceway surface, is less than 20 volume percent.

[0070] <Appendix 7> 7. The rolling contact member according to any one of claims 1 to 6, wherein the average grain size of cementite in the first surface layer is 2.0 μm or less.

[0071] <Appendix 8> 8. The rolling contact member according to claim 1, wherein the maximum grain size of the precipitates in the first surface layer is 2.0 μm or less.

[0072] <Appendix 9> Further comprising a coating, the coating is formed on at least the raceway surface, 9. The rolling member according to any one of claims 1 to 8, wherein the coating has a hardness of 3000 Hv or less.

[0073] <Appendix 10> 10. The rolling member according to claim 9, wherein the coating has a thickness of 1 μm or more.

[0074] <Appendix 11> The rolling contact member according to any one of appendixes 1 to 10, wherein the maximum grain size of the martensite block grains in the first surface layer is 5 μm or less.

[0075] <Appendix 12> A rolling component comprising the rolling member according to any one of Supplementary Note 1 to Supplementary Note 11.

[0076] Although the embodiments of the present invention have been described above, the above-described embodiments can be modified in various ways. Furthermore, the scope of the present invention is not limited to the above-described embodiments. The scope of the present invention is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0077] 10 inner ring body, 10a width surface, 10b width surface, 10c inner peripheral surface, 10d outer peripheral surface, 10da raceway surface, 11,12 surface layer, 13 core, 20 coating, 20a 1st layer, 20b 2nd layer, 20c intermediate layer, 100 inner ring, A center shaft, S1 preparation process, S2 nitriding process, S3 Decarburization treatment process, S4 first quenching process, S5 sub-zero treatment process, S6 second quenching process, S7 first tempering process, S8 second tempering process, S9 grinding process, S10 film formation process, T thickness.

Claims

1. A rolling member, A rolling member body is provided, the rolling member body is made of quenched and tempered steel, The steel comprises 0.80 to 1.10 percent by weight of carbon, 0.15 to 0.50 percent by weight of silicon, 0.30 to 0.70 percent by weight of manganese, 1.30 to 1.60 percent by weight of chromium, 0.50 percent or less by weight of molybdenum, and 0.50 percent or less by weight of vanadium, with the balance being iron and inevitable impurities; the rolling member body has a raceway surface, a nitrogen diffusion region is formed on the raceway surface; the carbon concentration in the first surface layer of the rolling member body, which is a region at a depth of 5 μm or less from the raceway surface, is lower than the average carbon concentration in the core portion of the rolling member body, which is a region farther from the raceway surface than the nitrogen diffusion region; a precipitate containing any one of manganese, silicon, chromium, and vanadium as a main component is deposited on the first surface layer; A rolling member, wherein the area ratio of the precipitates in the first surface layer is 2.0% or more.

2. 2. The rolling member according to claim 1, wherein the carbon concentration in the first surface layer is 0.90 mass percent or less.

3. 2. The rolling contact member according to claim 1, wherein the maximum grain size of oxide-based inclusions in the second surface layer of the rolling contact member body, which is the region from the raceway surface to the boundary between the nitrogen diffusion region and the core, is 40 μm or less.

4. 2. The rolling contact member according to claim 1, wherein the maximum particle size of sulfide-based inclusions in the second surface layer of the rolling contact member body, which is a region from the raceway surface to a boundary between the nitrogen-diffused region and the core portion, is 60 μm or less.

5. 5. The rolling contact member according to claim 4, wherein the sulfide-based inclusions in the second surface layer have a maximum particle size of 50 μm or less.

6. 2. The rolling contact member according to claim 1, wherein the amount of retained austenite in the second surface layer of the rolling contact member body, which is a region at a depth of 500 [mu]m or less from the raceway surface, is less than 20 volume percent.

7. 2. The rolling contact member according to claim 1, wherein the average grain size of the cementite in the first surface layer is 2.0 μm or less.

8. 2. The rolling member according to claim 1, wherein the maximum grain size of the precipitates in the first surface layer is 2.0 μm or less.

9. Further comprising a coating, the coating is formed on at least the raceway surface, 2. The rolling member according to claim 1, wherein the hardness of the coating is 3000 Hv or less.

10. 10. The rolling member according to claim 9, wherein the coating has a thickness of 1 [mu]m or more.

11. 2. The rolling contact member according to claim 1, wherein the maximum grain size of the martensite block grains in the first surface layer is 5 [mu]m or less.

12. A rolling component comprising the rolling member according to any one of claims 1 to 11.

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