Rolling members and rolling components

Abstract

The present invention provides rolling elements that can improve rolling life while suppressing hydrogen intrusion through a passivation coating. [Solution] The rolling element is made of steel with a surface. The rolling element has a surface layer. The steel contains 0.20 mass percent to 1.10 mass percent of carbon, 0.5 mass percent or less of nitrogen, 0.10 mass percent to 1.00 mass percent of silicon, 0.10 mass percent to 1.00 mass percent of manganese, 8.0 mass percent to 18.0 mass percent of chromium, 2.00 mass percent or less of molybdenum, 0.50 mass percent or less of copper, 0.50 mass percent or less of vanadium, and 0.50 mass percent or less of nickel, with the remainder being iron and unavoidable impurities. The corrosion resistance index of the steel is 10 to 33. The carbon content in the steel is greater than or equal to the nitrogen content in the steel.

Description

[Technical Field]

[0001] The present invention relates to a rolling member. [Background Art]

[0002] In recent years, the development of fuel cell vehicles, hydrogen gas engines, and the like has been promoted, and the use of hydrogen as a power source has been advanced. In these devices, rolling components are exposed to hydrogen gas, and the penetration of hydrogen into the rolling member may cause hydrogen embrittlement. Hydrogen embrittlement causes a reduction in the service life of the device.

[0003] In the rolling bearing described in Japanese Patent Laid-Open No. 2007-277674 (Patent Document 1), the rolling member is formed of steel containing a large amount of chromium. Therefore, in the rolling bearing described in Patent Document 1, a passive film is formed on the surface of the rolling member, and the penetration of hydrogen is suppressed. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Laid-Open No. 2007-277674 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] However, in steel containing a large amount of chromium, chromium-based carbides are prone to coarsening, and peeling starting from the carbides is likely to occur, so there is room for improvement in rolling fatigue life. The present invention provides a rolling member capable of improving rolling fatigue life while suppressing the penetration of hydrogen by a passive film. [Means for Solving the Problem]

[0006] The rolling member according to the present invention is made of steel having a surface. The rolling member has a surface layer on its surface. The steel contains 0.20 mass percent to 1.10 mass percent of carbon, 0.5 mass percent or less of nitrogen, 0.10 mass percent to 1.00 mass percent of silicon, 0.10 mass percent to 1.00 mass percent of manganese, 8.0 mass percent to 18.0 mass percent of chromium, 2.00 mass percent or less of molybdenum, 0.50 mass percent or less of copper, 0.50 mass percent or less of vanadium, and 0.50 mass percent or less of nickel, with the remainder being iron and unavoidable impurities. The corrosion resistance index of the steel is 10 to 33. The carbon content in the steel is greater than or equal to the nitrogen content in the steel. In the first region of the surface layer located between the surface and a position 50 μm from the surface, the hardness is 59.5 HRC to 65.0 HRC. In the second region of the surface located between the surface and a position 200 μm from the surface, the average aspect ratio of martensite block grains at a comparative area ratio of 30 percent is 3.0 or greater. [Effects of the Invention]

[0007] According to the rolling element of the present invention, it is possible to improve rolling life while suppressing hydrogen intrusion with a passivated coating. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view of the rolling bearing 100. [Figure 2] This is a cross-sectional view of the inner ring 10 near the surface. [Figure 3] This is a manufacturing process diagram for inner ring 10. [Figure 4] This is an electron microscope image of the processed part after the cooling process S3. [Figure 5] This is an electron microscope image of sample 7. [Figure 6] This is an electron microscope image of sample 16. [Modes for carrying out the invention]

[0009] The details of the embodiments will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions will not be repeated. In the following, the rolling bearing 100 will be described as an example of a rolling component according to the embodiment, and the inner ring 10 will be described as an example of a rolling member according to the embodiment. However, the rolling components and rolling members according to the embodiment are not limited to these. For example, the rolling components according to the embodiment include rolling bearings (including hub bearings), cam followers, etc. Also, the rolling members according to the embodiment include, for example, gears and drive shafts.

[0010] (Configuration of rolling bearing 100) Figure 1 is a cross-sectional view of a rolling bearing 100. As shown in Figure 1, the rolling bearing 100 has an inner ring 10, an outer ring 20, a plurality of rolling elements 30, and a cage 40. The central axis of the rolling bearing 100 is called the central axis A. The direction along the central axis A is called the axial direction. The direction passing through the central axis A and perpendicular to the central axis A is called the radial direction. The direction along the circumference of the circle centered on the central axis A when viewed along the axial direction is called the circumferential direction.

[0011] The inner ring 10 is a ring-shaped member. The inner ring 10 has a width surface 10a, a width surface 10b, an inner circumferential surface 10c, and an outer circumferential surface 10d as its surfaces.

[0012] The width surfaces 10a and 10b are the end faces of the inner ring 10 in the axial direction, respectively. Width surface 10b is the opposite side of width surface 10a in the axial direction. Width surfaces 10a and 10b face one side (left side in Figure 1) and the other side (right side in Figure 1), respectively, in the axial direction.

[0013] The inner circumferential surface 10c and the outer circumferential surface 10d extend along the circumferential direction. The inner circumferential surface 10c faces toward the central axis A, i.e., radially inward. The outer circumferential surface 10d faces toward the opposite side of the central axis A, i.e., radially outward. The outer circumferential surface 10d is the opposite surface of the inner circumferential surface 10c in the radial direction. One end and the other end of the inner circumferential surface 10c in the axial direction are connected to the width surface 10a and the width surface 10b, respectively. One end and the other end of the outer circumferential surface 10d in the axial direction are connected to the width surface 10a and the width surface 10b, respectively.

[0014] The inner ring 10 is attached to a rotating shaft (not shown) that rotates around a central axis A on its inner circumferential surface 10c. The outer circumferential surface 10d has a raceway surface 10da. The raceway surface 10da is located in the center of the outer circumferential surface 10d in the axial direction. The outer circumferential surface 10d is concave toward the inner circumferential surface 10c on the raceway surface 10da. In a cross-sectional view perpendicular to the circumferential direction, the raceway surface 10da forms a partial circular arc. The raceway surface 10da is in contact with the rolling element 30.

[0015] The outer ring 20 is a ring-shaped member. The outer ring 20 has a width surface 20a, a width surface 20b, an inner circumferential surface 20c, and an outer circumferential surface 20d as its surfaces.

[0016] The width surfaces 20a and 20b are the end faces of the outer ring 20 in the axial direction, respectively. Width surface 20b is the opposite side of width surface 20a in the axial direction. Width surfaces 20a and 20b face one side (left side in Figure 1) and the other side (right side in Figure 1), respectively, in the axial direction.

[0017] The inner circumferential surface 20c and the outer circumferential surface 20d extend along the circumferential direction. The inner circumferential surface 20c faces toward the central axis A, i.e., radially inward. The outer circumferential surface 20d faces toward the opposite side of the central axis A, i.e., radially outward. The outer circumferential surface 20d is the opposite surface of the inner circumferential surface 20c in the radial direction. One end and the other end of the inner circumferential surface 20c in the axial direction are connected to the width surface 20a and the width surface 20b, respectively. One end and the other end of the outer circumferential surface 20d in the axial direction are connected to the width surface 20a and the width surface 20b, respectively.

[0018] The outer ring 20 is attached to a housing (not shown) at an outer peripheral surface 20d thereof. An inner peripheral surface 20c has a raceway surface 20ca. The raceway surface 20ca is located at a central portion of the inner peripheral surface 20c in the axial direction. The inner peripheral surface 20c is recessed toward the outer peripheral surface 20d at the raceway surface 20ca. In a cross-sectional view perpendicular to the circumferential direction, the raceway surface 20ca forms a partial circular arc. The raceway surface 20ca is in contact with rolling elements 30.

[0019] The outer ring 20 is arranged radially outward of an inner ring 10 such that the raceway surface 20ca and a raceway surface 10da face each other with a gap therebetween in the radial direction.

[0020] The rolling elements 30 are spherical. The rolling elements 30 are arranged between the raceway surface 10da and the raceway surface 20ca in the radial direction. The plurality of rolling elements 30 are arranged along the circumferential direction. A retainer 40 is arranged between an outer peripheral surface 10d and the inner peripheral surface 20c. The retainer 40 retains the plurality of rolling elements 30 such that the distance between two circumferentially adjacent rolling elements 30 falls within a predetermined range.

[0021] (Detailed Configuration of Inner Ring 10) The inner ring 10 is made of steel. The steel constituting the inner ring 10 contains 0.20 mass% to 1.10 mass% of carbon, 0.5 mass% or less of nitrogen, 0.10 mass% to 1.00 mass% of silicon, 0.10 mass% to 1.00 mass% of manganese, 8.0 mass% to 18.0 mass% of chromium, 2.00 mass% or less of molybdenum, 0.50 mass% or less of copper, 0.50 mass% or less of vanadium, and 0.50 mass% or less of nickel, with the balance being iron and unavoidable impurities.

[0022] The nitrogen content is, for example, 0 mass percent or more. The silicon content is, for example, 0.1 mass percent or more. The manganese content is, for example, 0.1 mass percent or more. The chromium content is, for example, 8.0 mass percent or more. The molybdenum content is, for example, 0 mass percent or more. The copper content is, for example, 0 mass percent or more. The vanadium content is, for example, 0 mass percent or more. The nickel content is, for example, 0 mass percent or more.

[0023] If the carbon content is less than 0.20 mass percent, the hardness of the steel constituting the inner ring 10 will be insufficient. If the carbon content is greater than 1.10 mass percent, there is a concern that the steel constituting the inner ring 10 may crack during quenching. Therefore, the carbon content of the steel constituting the inner ring 10 is between 0.20 mass percent and 1.10 mass percent.

[0024] Nitrogen is added to the steel constituting the inner ring 10 to improve hardness, stabilize the austenite phase, and promote the formation of a passivation film on the surface. Considering steelmaking costs, the nitrogen content in the steel constituting the inner ring 10 is 0.5 mass percent or less.

[0025] Silicon is added to the steel constituting the inner ring 10 to stabilize the austenite phase. Considering the reduction in workability, the silicon content in the steel constituting the inner ring 10 is between 0.10 mass percent and 1.00 mass percent.

[0026] Manganese is added to the steel constituting the inner ring 10 to stabilize the austenite phase. In the steel constituting the inner ring 10, the manganese content is between 0.10 mass percent and 1.00 mass percent to suppress the precipitation of manganese-based nonmetallic inclusions.

[0027] Chromium is added to the steel constituting the inner ring 10 to stabilize the austenite phase and to promote the formation of a passive film on the surface. In the steel constituting the inner ring 10, the chromium content is between 8.0 mass percent and 18 mass percent, taking into consideration the suppression of carbide growth and steelmaking costs.

[0028] Vanadium is added to the steel constituting the inner ring 10 to stabilize the austenite phase, thereby suppressing grain coarsening by forming fine carbides and improving wear resistance. In the steel constituting the inner ring 10, the vanadium content is 0.50 mass percent or less to suppress carbide segregation.

[0029] Molybdenum is added to the steel constituting the inner ring 10 to stabilize the austenite phase and to promote the formation of a passive film on the surface. Considering steelmaking costs, the molybdenum content in the steel constituting the inner ring 10 is 2.00 mass percent or less.

[0030] Copper is added to the steel constituting the inner ring 10 to promote the formation of a passive film on the surface. In the steel constituting the inner ring 10, the copper content is 0.5 mass percent or less, taking into consideration the reduction in hot workability.

[0031] Nickel is added to the steel constituting the inner ring 10 to stabilize the austenite phase and to promote the formation of a passive film on the surface. Considering steelmaking costs, the nickel content in the steel constituting the inner ring 10 is 0.50 mass percent or less.

[0032] The steel constituting the inner ring 10 has a corrosion resistance index of 10 or higher. For example, the steel constituting the inner ring 10 has a corrosion resistance index of 33 or lower. The corrosion resistance index is calculated using the following formula: (Corrosion Resistance Index) = (Chromium Content in Steel) + 3.3 × (Molybdenum Content in Steel) + 16 × (Nickel Content in Steel). In this formula, the unit of each content is mass percent. In the steel constituting the inner ring 10, the carbon content in the steel is greater than or equal to the nitrogen content in the steel. That is, in the steel constituting the inner ring 10, the ratio of the nitrogen content in the steel to the carbon content in the steel is 1.0 or less.

[0033] Figure 2 is a cross-sectional view of the inner ring 10 near the surface. As shown in Figure 2, the inner ring 10 has a surface layer 50 on its surface. The region of the surface layer 50 located between the surface and position P1 is defined as region R1. The region of the surface layer 50 located between the surface and position P2 is defined as region R2. The distance between the surface and position P1 is 50 μm. The distance between the surface and position P2 is 200 μm. Although not shown, a passivation film is formed on the surface of the inner ring 10.

[0034] The hardness in region R1 is 59.5 HRC or higher. The hardness in region R1 is, for example, 65 HRC or lower. The hardness in region R1 is measured according to the Rockwell hardness test method specified in JIS Z 2245 (ISO 6508-1).

[0035] Region R1 contains dispersed precipitates primarily composed of chromium, vanadium, manganese, and silicon. The precipitates primarily composed of chromium (vanadium, manganese, or silicon) are carbides, carbonitrides, or nitrides.

[0036] In region R2, the average aspect ratio of martensite block grains at a comparative area ratio of 30 percent is 3.0 or greater. Furthermore, the difference in crystal orientation between two adjacent martensite block grains at the grain boundary is 15° or greater. 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.

[0037] The average aspect ratio of martensite block grains in region R2 at a comparative area ratio of 30 percent is measured by the following method. First, a cross-sectional observation is performed on the inner ring 10 containing region R2. At this time, martensite block grains included in the observation field are identified by the EBSD method. The magnification of this observation field is set to 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.

[0038] Thirdly, the area of ​​each martensite block grain included in the observation field is added up in descending order of area. This addition is continued until it reaches 30 percent of the total area of ​​the martensite block grains included in the observation field. Fourthly, the aspect ratio is calculated for each of the martensite block grains that have been added up as described above. The aspect ratio is calculated by approximating the martensite block grain as an ellipse and using the ratio of the major axis to the minor axis of the ellipse. The average of the aspect ratios of the martensite block grains that have been added up as described above is considered to be the average aspect ratio of the martensite block grains at a comparison area ratio of 30 percent.

[0039] In region R2, the average particle size of martensite block grains with a comparative area ratio of 30 percent is, for example, 5.0 μm or less. In region R2, the average particle size of martensite block grains with a comparative area ratio of 30 percent is 0.5 μm or more. The average particle size of martensite block grains with a comparative area ratio of 30 percent in region R2 is measured by the following method.

[0040] Firstly, a cross-sectional observation is performed on the inner ring 10 containing region R2. At this time, martensite block grains included in the observation field are identified by the EBSD method. The magnification of this observation field is set to 1500x. Secondly, the area of ​​each martensite block grain included in the observation field is analyzed from the crystal orientation data obtained by the EBSD method.

[0041] Thirdly, the area of ​​each martensite block grain included in the observation field is added up in descending order of area. This addition is continued until the total area of ​​the martensite block grains included in the observation field reaches 30 percent. For each of the martensite block grains that have been added up, 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 that have been added up is considered to be the average grain size of the martensite block grains at a comparative area ratio of 30 percent.

[0042] In region R2, the amount of retained austenite is less than 20 volume percent. In region R2, the amount of retained austenite is, for example, 0 volume percent or more. The amount of retained austenite in region R2 is measured by X-ray diffraction. That is, the amount of retained austenite is calculated by comparing the integrated intensity of the diffraction peak in X-ray diffraction showing austenite with the integrated intensity of the diffraction peak in X-ray diffraction showing a phase other than austenite.

[0043] In the above description, the inner ring 10 was explained as an example of a rolling member according to the embodiment, but the outer ring 20 or the rolling element 30 may also be rolling members according to the embodiment. That is, the outer ring 20 or the rolling element 30 may be made of steel with the same composition as the inner ring 10, and the same surface layer 50 as described above may be formed on the surface of the outer ring 20 or the surface of the rolling element 30.

[0044] (Method for manufacturing the inner ring 10) Figure 3 is a diagram of the manufacturing process for the inner ring 10. As shown in Figure 3, the manufacturing method for the inner ring 10 includes a preparation step S1, a quenching step S2, a cooling step S3, a tempering step S4, and a post-processing step S5. The quenching step S2 is performed after the preparation step S1. The cooling step S3 is performed after the quenching step S2. The tempering step S4 is performed after the cooling step S3. The post-processing step S5 is performed after the tempering step S4. In the preparation step S1, the workpiece to be processed is prepared.

[0045] In the quenching process S2, the workpiece to be processed is quenched. Quenching the workpiece involves heating the workpiece to a temperature above the A1 transformation point of the steel that makes up the workpiece and holding it there, and then the workpiece is subjected to M S This is carried out by cooling to a temperature below the transformation point. The quenching process S2 generates martensite and retained austenite in the steel constituting the workpiece. The heating temperature in the quenching process S2 is set to a high temperature (e.g., 1000°C or higher) to suppress the coarsening of carbides. In addition, the cooling rate in the quenching process S2 is set to a slow rate (e.g., 30°C / second or less) to increase the amount of retained austenite before the cooling process S3 is performed.

[0046] In the cooling process S3, sub-zero treatment is performed on the workpiece to be processed. By performing sub-zero treatment on the workpiece to be processed, that is, the workpiece to be processed is M fBy cooling to a temperature below the transformation point (for example, -65°C), the retained austenite generated in the quenching process S2 undergoes martensite transformation at low temperatures. This increases the amount of hard martensite with a large aspect ratio, such as butterfly martensite, plate-like martensite, and lens martensite. Figure 4 is an electron microscope image of the workpiece after the cooling process S3. As shown in Figure 4, it can be seen that high-aspect-ratio martensite is dispersed in the workpiece after going through the quenching process S2 and the cooling process S3 described above.

[0047] In the tempering process S4, the workpiece is tempered. Tempering of the workpiece is performed by heating it to a temperature below the A1 transformation point (for example, 500°C or lower). In the post-processing process S5, the surface of the workpiece is machined, such as grinding or polishing. Through these steps, the inner ring 10 is formed.

[0048] (Effect of inner ring 10) When rolling bearings are used in environments exposed to hydrogen gas, hydrogen can penetrate the rolling elements (raceways and rolling elements) used in the rolling bearing, causing hydrogen embrittlement. In the inner ring 10, elements that promote the formation of a passive film, such as chromium, are added to the steel, so a passive film is formed on the surface of the inner ring 10, suppressing the penetration of hydrogen.

[0049] Furthermore, in steels containing a large amount of chromium, such as stainless steel, chromium-based carbides tend to coarseen. In addition, carbon accumulates in the carbides, reducing the concentration of carbon dissolved in the base material surrounding the carbides, thus lowering the hardness around the carbides. Due to stress concentration or localized hardness reduction in the coarse carbides, delamination is likely to occur starting from the coarse chromium-based carbides. In the inner ring 10, the carbides are dissolved by high-temperature heating, suppressing their coarsening. When the carbides are dissolved, the concentration of dissolved carbon in the base material increases, and the crystal lattice of the martensite becomes larger. In other words, the aspect ratio of the martensite block grains increases. Furthermore, by sub-zero treatment to transform retained austenite into martensite at low temperatures, the amount of hard martensite with a high aspect ratio, such as butterfly martensite, plate-like martensite, and lenticular martensite, is increased. Therefore, the inner ring 10 achieves both suppression of carbide coarsening and high hardness of the base material, making delamination starting from carbides less likely. In this way, the inner ring 10 makes it possible to achieve both suppression of hydrogen embrittlement and extended lifespan.

[0050] (Examples) Samples 1 through 17 were prepared, and each of the steel grades A through K shown in Table 1 was used.

[0051] [Table 1]

[0052] Condition 1 is that the steel contains 0.20 mass percent to 1.10 mass percent of carbon, 0.5 mass percent or less of nitrogen, 1.00 mass percent or less of silicon, 1.00 mass percent or less of manganese, 18.0 mass percent or less of chromium, 2.00 mass percent or less of molybdenum, 0.50 mass percent or less of copper, 0.50 mass percent or less of vanadium, and 0.50 mass percent or less of nickel, with the remainder being iron and unavoidable impurities. Condition 2 is that the carbon content in the steel is greater than the nitrogen content in the steel. Condition 3 is that the corrosion resistance index of the steel is 10 or higher. All steel types except steel type K satisfied conditions 1 to 3, but steel type K did not satisfy any of conditions 1 to 3.

[0053] As shown in Table 2, the cooling process S3 (sub-zero treatment) was not performed on samples 1 through 5. On the other hand, the cooling process S3 was performed on samples 6 through 17.

[0054] [Table 2]

[0055] Regarding whether the hardness in region R1 was 59.5 HRC (Condition 4), Samples 1 to 4 and 6 did not satisfy Condition 4, but Samples 5 and 7 to 17 did. In addition, rolling life was evaluated for each sample. This evaluation was performed using a line contact type rolling life test. In the line contact type rolling life test, the shape of the test piece was cylindrical with a diameter of 12 mm and a length of 12 mm. In the line contact type rolling life test, the shape of the mating test piece was cylindrical with a diameter of 20 mm and a length of 20 mm, and was formed using SUJ2. In the line contact type rolling life test, the contact pressure was 4.2 GPa, the stress loading rate was 20,400 cycles / min, and lubrication was performed by circulating turbine oil VG6. Details of the line contact type rolling life test are described in Japanese Patent Application Publication No. 2007-277674. Rolling life was evaluated as a ratio to the rolling life of Sample 1, which was set to 1 (reference value). In samples 1 through 4 and sample 6, condition 4 was not met (low hardness in region R1), resulting in a short rolling life.

[0056] Samples 7 and 16 showed similar hardness in region R1, but the rolling life of sample 7 was shorter than that of sample 16. Figure 5 is an electron microscope image of sample 7. Figure 6 is an electron microscope image of sample 16. Regarding whether the average aspect ratio of martensite block grains in region R2 is 3.0 or higher at a comparative area ratio of 30 percent (condition 5), as shown in Figure 5, the precipitates in sample 7 were coarse and condition 5 was not met, but as shown in Figure 6, the precipitates in sample 16 were not coarse and condition 5 was met. From the above, it was experimentally clear that rolling life can be improved even if the steel contains a lot of chromium when conditions 1 to 5 are met. In sample 16, the amount of retained austenite was 20 volume percent or more, so the hardness decreased and it could not withstand the contact pressure of the line contact type rolling life test, resulting in indentation (i.e., insufficient load capacity), and the line contact type rolling life test could not be performed.

[0057] The above embodiment includes the following configuration: <Note 1> A rolling member made of steel having a surface, The surface is provided with a surface layer, The steel contains 0.20 mass percent to 1.10 mass percent of carbon, 0.5 mass percent or less of nitrogen, 0.10 mass percent to 1.00 mass percent of silicon, 0.10 mass percent to 1.00 mass percent of manganese, 8.0 mass percent to 18.0 mass percent of chromium, 2.00 mass percent or less of molybdenum, 0.50 mass percent or less of copper, 0.50 mass percent or less of vanadium, and 0.50 mass percent or less of nickel, with the remainder being iron and unavoidable impurities. The corrosion resistance index of the aforementioned steel is between 10 and 33. The carbon content in the steel is greater than or equal to the nitrogen content in the steel. In the first region of the surface located between the surface and a position 50 μm away from the surface, the hardness is 59.5 HRC or more and 65.0 HRC or less. A rolling member in which, in a second region of the surface located between the surface and a position 200 μm away from the surface, the average aspect ratio of martensitic block grains with a comparative area ratio of 30 percent is 3.0 or greater.

[0058] <Note 2> The rolling member as described in Appendix 1, wherein a precipitate mainly composed of chromium, manganese, and silicon is dispersed in the first region.

[0059] <Note 3> The rolling member according to Appendix 1 or Appendix 2, wherein in the second region, the average particle size of the martensitic block grains at a comparative area ratio of 30 percent is 0.5 μm or more and 5.0 μm or less.

[0060] <Note 4> The rolling member according to any one of the appendices 1 to 3, wherein the amount of retained austenite in the second region is less than 20 volume percent.

[0061] <Note 5> Rolling parts, A rolling component comprising the rolling member described in any one of the appendices 1 to 4.

[0062] <Note 6> The aforementioned rolling component is a rolling bearing, as described in Appendix 5.

[0063] While embodiments of the present invention have been described above, various modifications of these embodiments are possible. 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]

[0064] 10 Inner ring, 10a, 10b width, 10c inner circumference, 10d outer circumference, 10da raceway, 20 outer ring, 20a, 20b width, 20c inner circumference, 20ca raceway, 20d outer circumference, 30 rolling elements, 40 cage, 50 surface, 100 rolling bearing, A Central axis, P1, P2 position, R1, R2 area, S1 preparation process, S2 quenching process, S3 cooling process, S4 tempering process, S5 post-treatment process.

Claims

1. A rolling member made of steel having a surface, The surface is provided with a surface layer, The steel contains 0.20 mass percent to 1.10 mass percent of carbon, 0.5 mass percent or less of nitrogen, 0.10 mass percent to 1.00 mass percent of silicon, 0.10 mass percent to 1.00 mass percent of manganese, 8.0 mass percent to 18.0 mass percent of chromium, 2.00 mass percent or less of molybdenum, 0.50 mass percent or less of copper, 0.50 mass percent or less of vanadium, and 0.50 mass percent or less of nickel, with the remainder being iron and unavoidable impurities. The corrosion resistance index of the aforementioned steel is between 10 and 33. The carbon content in the steel is greater than or equal to the nitrogen content in the steel. In the first region of the surface layer located between the surface and a position 50 μm away from the surface, the hardness is 59.5 HRC or more and 65.0 HRC or less. A rolling member in which, in a second region of the surface located between the surface and a position 200 μm away from the surface, the average aspect ratio of martensitic block grains with a comparative area ratio of 30 percent is 3.0 or more.

2. The rolling member according to claim 1, wherein a precipitate mainly composed of chromium, manganese, and silicon is dispersed in the first region.

3. The rolling member according to claim 1, wherein in the second region, the average particle size of the martensitic block grains at a comparative area ratio of 30 percent is 0.5 μm or more and 5.0 μm or less.

4. The rolling member according to claim 1, wherein the amount of retained austenite in the second region is less than 20 volume percent.

5. Rolling parts, A rolling component comprising the rolling member described in any one of claims 1 to 4.

6. The rolling component according to claim 5, wherein the rolling component is a rolling bearing.

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