Bearing component and rolling bearing

Abstract

The bearing component (10) is made of steel and has a hardened layer (11) on its surface. The hardened layer contains multiple martensite grains. The martensite grains are divided into Group 1 and Group 2. The minimum grain size of the martensite grains in Group 1 is greater than the maximum grain size of the martensite grains in Group 2. The total area of ​​the martensite grains in Group 1 divided by the total area of ​​the martensite grains is greater than 0.3. The total area of ​​the martensite grains in Group 1 after removing the smallest martensite grain in Group 1 divided by the total area of ​​the martensite grains is less than 0.3. The average grain size of the martensite grains in Group 1 is less than 1.5 μm. The hardened layer (11) further contains multiple cementite grains. The number density of cementite grains with a grain size greater than 1 μm is 0.025 grains / μm. 2 above.

Description

Technical Field

[0001] This invention relates to bearing components and rolling bearings. Background Technology

[0002] In recent years, as vehicles and other vehicles have reduced fuel consumption, the operating environment for bearings has become increasingly harsh, requiring bearings with excellent wear resistance and indentation resistance.

[0003] For improving wear resistance, the refinement of martensite grains is effective (see Japanese Patent Application Publication No. 2019-108576). This is because, with the refinement of martensite grains, the plastic deformation resistance of the martensite phase increases, which further improves the interfacial energy of the martensite grains and promotes gas adsorption on the wear surface, thereby suppressing severe wear.

[0004] On the other hand, refining the martensite grains is also effective in improving indentation resistance (see Japanese Patent No. 6626918). This is because, as the resistance to plastic deformation of the martensite phase increases as described above, the resistance to indentation formation increases.

[0005] As a technique for refining martensite grains, Japanese Patent No. 6626918 discloses a technique of quenching after nitriding at a lower temperature than nitriding (low-temperature secondary quenching).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-108576

[0009] Patent Document 2: Japanese Patent No. 6626918 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] However, the inventors have discovered that even in the technique of low-temperature secondary quenching after nitriding, there is still room for improvement from the viewpoint of refining the martensite grains.

[0012] The main objective of this invention is to provide a bearing component and a rolling bearing with high wear resistance and high resistance to indentation formation.

[0013] Technical solutions adopted to solve technical problems

[0014] The bearing component of this invention is made of steel and has a hardened layer on its surface. The hardened layer contains a plurality of martensite grains. The total area ratio of the martensite grains in the hardened layer is 70% or more. The martensite grains are divided into Group 1 and Group 2. The minimum grain size of the martensite grains in Group 1 is greater than the maximum grain size of the martensite grains in Group 2. The total area of ​​the martensite grains in Group 1 divided by the total area of ​​the martensite grains is 0.3 or more. The total area of ​​the martensite grains in Group 1 after removing the smallest martensite grain in Group 1 divided by the total area of ​​the martensite grains is less than 0.3. The average grain size of the martensite grains in Group 1 is 1.5 μm or less. The hardened layer further contains a plurality of cementite grains. The number density of cementite grains with a grain size of 1 μm or more is 0.025 grains / μm. 2 above.

[0015] In the bearing component of the present invention, the average aspect ratio of the martensitic grains belonging to the first group can be 3.1 or less.

[0016] In the bearing component of the present invention, the amount of residual austenite on the surface can be more than 20% by volume.

[0017] In the bearing component of the present invention, the hardened layer may contain nitrogen. The average nitrogen concentration of the hardened layer between the surface and a location 10 μm away from the surface may be 0.15% by mass or more.

[0018] In the bearing component of the present invention, the hardness of the surface quenched and hardened layer can be above 730Hv.

[0019] In the bearing components of this invention, the steel may be high-carbon chromium bearing steel SUJ2 as specified in the JIS standard.

[0020] The method for manufacturing the bearing component of the present invention includes a step of preparing a molded body made of high-carbon chromium bearing steel, a carburizing and nitriding step of heating the molded body in a carburizing and nitriding atmosphere to a first temperature above the Al phase transformation point of the steel and then cooling the molded body to a temperature below the Ms phase transformation point of the steel, a first tempering step of holding the molded body at a second temperature of 180 degrees or more and below the Al phase transformation point after the carburizing and nitriding step, a quenching step of reheating the molded body to a third temperature above the Al phase transformation point and below the first temperature and then cooling the molded body to a temperature below the Ms phase transformation point of the steel, and a second tempering step of holding the molded body at a fourth temperature below the Al phase transformation point after the quenching step.

[0021] In the manufacturing method of the bearing component of the present invention, the second temperature is preferably between 250 degrees and 350 degrees.

[0022] Invention Effects

[0023] According to the present invention, it is possible to provide a bearing component and a rolling bearing having high wear resistance and high resistance to indentation formation. Attached Figure Description

[0024] Figure 1 The image shown is a top view of the inner ring 10 of Embodiment 1.

[0025] Figure 2 As shown Figure 1 Sectional view at point II-II.

[0026] Figure 3 As shown Figure 2 Enlarged view of section III.

[0027] Figure 4 The diagram shows the process flow of manufacturing the inner ring 10.

[0028] Figure 5 The image shown is an EBSD image of a cross-section of sample 1.

[0029] Figure 6 The image shown is an EBSD image of a cross-section of sample 2.

[0030] Figure 7 The image shown is an EBSD image of a cross-section of sample 3.

[0031] Figure 8 The image shown is an EBSD image of a cross-section of sample 4.

[0032] Figure 9 The image shown is an EBSD image of a cross-section of sample 5.

[0033] Figure 10 The graph shown is a chart showing the relationship between maximum contact surface pressure and indentation depth.

[0034] Figure 11 The graph shown is a relationship between the average grain size of martensite grains and the static load capacity.

[0035] Figure 12 The graph shown is a representation of the relationship between the average aspect ratio of martensite grains and the static load capacity.

[0036] Figure 13 The diagram shows the process flow of the bearing component manufacturing method according to Embodiment 2.

[0037] Figure 14 The diagram shows the heating mode of the bearing component manufacturing method according to Embodiment 2.

[0038] Figure 15 The image shown is an EBSD image of the orbital plane of sample 11.

[0039] Figure 16 The image shown is an EBSD image of the orbital plane of sample 12.

[0040] Figure 17 The image shown is an EBSD image of the orbital plane of sample 13.

[0041] Figure 18 The image shown is an EBSD image of the orbital plane of sample 14.

[0042] Figure 19 The graph shows the average grain size of the martensite grains belonging to Group 1 and Group 3 in samples 11-14.

[0043] Figure 20 The chart shows the average aspect ratio of the martensite grains belonging to Group 1 and Group 3 in samples 11-14.

[0044] Figure 21 The figure shows the average particle size of cementite particles belonging to group 5 and group 7 in samples 11-14.

[0045] Figure 22 The graph shows the number density of cementite particles belonging to group 5 and group 7 in samples 11-14.

[0046] Figure 23 The graph shows the relationship between the maximum contact surface pressure (in GPa) and the indentation depth (in mm) in the indentation resistance test for samples 11-14. Detailed Implementation

[0047] The embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, in the following drawings, the same or corresponding parts are labeled with the same reference numerals and will not be described repeatedly.

[0048] (The structure of the bearing component in Embodiment 1)

[0049] The configuration of the bearing component in Embodiment 1 will be described. Furthermore, as an example of the bearing component in this embodiment, the inner ring 10 (track component) of a rolling bearing will be used for description; however, the bearing component in this embodiment is not limited to this. Specifically, the bearing component in this embodiment can be the outer ring (track component) of a rolling bearing or the rolling elements of a rolling bearing.

[0050] The inner ring 10 is made of steel. The steel constituting the inner ring 10 is high-carbon chromium bearing steel as specified in JIS standard (JIS G4805:2008). Preferably, the steel constituting the inner ring 10 is SUJ2 as specified in JIS standard.

[0051] Figure 1 The image shown is a top view of the inner circle 10. Figure 2 As shown Figure 1 The sectional view at point II-II. (See image.) Figure 1 and Figure 2 As shown, the inner ring 10 is annular. The inner ring 10 has an upper surface 10a, a bottom surface 10b, an inner circumferential surface 10c, an outer circumferential surface 10d, and a central axis 10e.

[0052] The upper surface 10a and the bottom surface 10b form an end face along the direction of the central axis 10e. The bottom surface 10b is the opposite surface of the upper surface 10a. The inner circumferential surface 10c and the outer circumferential surface 10d are connected to the upper surface 10a and the bottom surface 10b. The distance between the inner circumferential surface 10c and the central axis 10e is smaller than the distance between the outer circumferential surface 10d and the central axis 10e. A track groove is provided on the outer circumferential surface 10d. The upper surface 10a, the bottom surface 10b, the inner circumferential surface 10c, and the outer circumferential surface 10d constitute the surface of the inner ring 10. The outer circumferential surface 10d constitutes the track surface of the inner ring 10.

[0053] Figure 3 As shown Figure 2 A magnified view of section III. (See image below.) Figure 3 As shown, the inner ring 10 has a hardened layer 11. The hardened layer 11 is disposed on the surface of the inner ring 10. The hardened layer 11 is disposed at least on the outer peripheral surface 10d of the track surface in the surface of the inner ring 10. The hardened layer 11 is disposed, for example, on the entire surface of the inner ring 10. The hardened layer 11 contains a plurality of martensite grains. The martensite grains are grains composed of the martensite phase.

[0054] When the crystal orientation of the first martensite grain deviates from that of the adjacent second martensite grain by more than 15°, the first martensite grain and the second martensite grain are different martensite grains. On the other hand, when the crystal orientation of the first martensite grain deviates from that of the adjacent second martensite grain by less than 15°, the first martensite grain and the second martensite grain constitute the same martensite grain.

[0055] In the quenched and hardened layer 11, martensite is the main constituent microstructure. More specifically, the total area ratio of martensite grains in the quenched and hardened layer 11 is above 70%. The total area ratio of martensite grains in the quenched and hardened layer 11 can be above 80%.

[0056] In addition to martensite grains, the quenched hardened layer 11 also contains multiple austenite grains and multiple cementite grains. The total area ratio of austenite grains in the quenched hardened layer 11 is preferably 30% or less. More preferably, the total area ratio of austenite grains in the quenched hardened layer 11 is 20% or less.

[0057] When the crystal orientation of the first cementite grain deviates from that of the adjacent second cementite grain by more than 15°, the first cementite grain and the second cementite grain are different cementite grains. On the other hand, when the crystal orientation of the first cementite grain deviates from that of the adjacent second cementite grain by less than 15°, the first cementite grain and the second cementite grain constitute the same cementite grain.

[0058] Martensite grains are divided into Group 1 and Group 2. The minimum grain size of martensite grains in Group 1 is greater than the maximum grain size of martensite grains in Group 2.

[0059] The value obtained by dividing the total area of ​​the martensite grains belonging to Group 1 by the total area of ​​the martensite grains (the sum of the total area of ​​the martensite grains belonging to Group 1 and the total area of ​​the martensite grains belonging to Group 2) is 0.3 or higher.

[0060] The value obtained by dividing the total area of ​​the martensite grains in Group 1 (excluding the smallest martensite grains in Group 1) by the total area of ​​the martensite grains is less than 0.3.

[0061] In other words, martensite grains are classified into Group 1 in descending order of grain size. The classification into Group 1 ends at a point in time where the total area of ​​the martensite grains classified into Group 1 is more than 0.3 times the total area of ​​all martensite grains. The remaining martensite grains are then classified into Group 2.

[0062] The average grain size of the martensite grains belonging to Group 1 is 1.5 μm or less. Preferably, the average grain size of the martensite grains belonging to Group 1 is 1.3 μm or less. More preferably, the average grain size of the martensite grains belonging to Group 1 is 1.26 μm or less, wherein this average grain size is particularly preferred to be 1.24 μm or less. More preferably, the average grain size of the martensite grains belonging to Group 1 is 1.2 μm or less.

[0063] The average aspect ratio of the martensite grains belonging to Group 1 is 3.3 or less. Preferably, the average aspect ratio of the martensite grains belonging to Group 1 is 3.2 or less. More preferably, the average aspect ratio of the martensite grains belonging to Group 1 is 3.1 or less, wherein this average aspect ratio is particularly preferred to be 2.9 or less.

[0064] The condition that the average aspect ratio of the plurality of grains belonging to the first group is 3.3 or less is more preferably a condition simultaneously held by a bearing component having the characteristic that the average grain size of the plurality of martensite grains belonging to the first group is 1.5 μm or less. However, in this embodiment, a bearing component that does not have the characteristic that the average grain size of the plurality of martensite grains belonging to the first group is 1.5 μm or less may only satisfy the condition that the average aspect ratio of the plurality of martensite grains is 3.3 or less.

[0065] The average grain size and aspect ratio of the martensite grains belonging to Group 1 were determined using EBSD (Electron Backscattered Diffraction).

[0066] The details are as follows. First, based on the EBSD method, a cross-sectional image of the quenched and hardened layer 11 (hereinafter referred to as the "EBSD image") is captured. The EBSD image is captured in a manner that includes a sufficient number (more than 20) of martensite grains. Based on the crystallization orientation of each grain shown in the EBSD image, the boundaries of adjacent martensite grains are determined. Second, based on the determined boundaries of the martensite grains, the area and shape of each martensite grain shown in the EBSD image are calculated.

[0067] More specifically, the equivalent diameter of each martensite grain shown in the EBSD image can be determined by calculating the square root of the area of ​​each martensite grain shown in the EBSD image by dividing the area by π / 4.

[0068] Based on the equivalent circular diameter of each martensite grain calculated above, the martensite grains belonging to group 1 in the martensite grains shown in the EBSD image can be determined. The value obtained by dividing the total area of ​​the martensite grains belonging to group 1 in the martensite grains shown in the EBSD image by the total area of ​​the martensite grains shown in the EBSD image can be regarded as the value obtained by dividing the total area of ​​the martensite grains belonging to group 1 by the total area of ​​the martensite grains.

[0069] Based on the round equivalent diameter of each martensite grain calculated above, the martensite grains shown in the EBSD images are classified into Group 1 and Group 2. The sum of the round equivalent diameters of the martensite grains shown in the EBSD images classified as Group 1, divided by the number of martensite grains shown in the EBSD images classified as Group 1, can be regarded as the average grain size of the martensite grains belonging to Group 1.

[0070] Based on the shape of each martensite grain shown in the EBSD image, an elliptical approximation of the shape of each martensite grain shown in the EBSD image is performed using the least squares method. This least squares-based elliptical approximation is performed using the method described in S. Biggin and DJ Dingley, Journal of Applied Crystallography, (1977) 10, 376-376. In this ellipse, the aspect ratio of each martensite grain shown in the EBSD image can be obtained by dividing the major axis dimension by the minor axis dimension. The sum of the aspect ratios of the martensite grains shown in the EBSD images classified as Group 1, divided by the number of martensite grains shown in the EBSD images classified as Group 1, can be regarded as the average aspect ratio of the martensite grains belonging to Group 1.

[0071] In the quenched and hardened layer 11, the number density of cementite grains with a particle size of 1 μm or larger is 0.025 grains / μm. 2 The above. Preferably, the number density of cementite grains with a particle size of 1 μm or larger is 0.040 grains / μm. 2 The above. Preferably, the number density of cementite grains with a particle size of 1 μm or larger is 0.046 grains / μm. 2 above.

[0072] The grain size and number density of cementite grains in the quenched and hardened layer 11 were determined by the following methods: First, a cross-sectional image (EBSD image) of the quenched and hardened layer 11 was captured using the EBSD method. The grain boundaries of each cementite grain were determined based on the crystal orientation of each grain as shown in the EBSD image. Second, the area of ​​each cementite grain contained in the EBSD image was calculated, and the square root of the calculated area divided by π / 4 was used as the equivalent circular diameter of each cementite grain. The equivalent circular diameter of each cementite grain obtained in this way is the grain size of each cementite grain.

[0073] Third, the number of cementite grains with a circular equivalent diameter of 1 μm or more in the cementite grains contained in the EBSD image is counted. The number of cementite grains with a circular equivalent diameter of 1 μm or more obtained by dividing the counted number of cementite grains with a circular equivalent diameter of 1 μm or more by the area of ​​the observation field of the EBSD image is the number density of cementite grains with a grain size of 1 μm or more in the quenched hardened layer 11.

[0074] The hardened layer 11 contains nitrogen. The average nitrogen concentration of the hardened layer 11 between the surface (outer peripheral surface 10d) and a location 10 μm away from the surface is preferably 0.15% by mass or more. This average nitrogen concentration is, for example, 0.20% by mass or less. Furthermore, this average nitrogen concentration is determined using an EPMA (Electron Probe Micro Analyzer).

[0075] The amount of retained austenite on the surface (outer peripheral surface 10d) is 20% by volume or more. Preferably, the amount of retained austenite on the surface (outer peripheral surface 10d) is 24% by volume or more and 26% by volume. The amount of retained austenite on the surface (outer peripheral surface 10d) is determined by X-ray diffraction of the surface. Specifically, the amount of retained austenite is calculated by comparing the integrated intensity of the X-ray diffraction peaks of the austenite phase with the integrated intensity of the X-ray diffraction peaks of the martensite phase.

[0076] The hardness of the quenched hardened layer 11 on the surface (outer peripheral surface 10d) is preferably above 730 Hv. In addition, the hardness of the quenched hardened layer 11 on the surface is measured according to JIS standard (JJSZ2244:2009).

[0077] (Manufacturing method of bearing component according to Embodiment 1)

[0078] Hereinafter, as an example of the manufacturing method of the bearing component of Embodiment 1, the manufacturing method of the inner ring 10 will be described.

[0079] Figure 4 The diagram shown illustrates the process of manufacturing a bearing component according to an embodiment. Figure 4 As shown, the manufacturing method of the bearing component in the embodiment includes: a preparation step S1, a carburizing and nitriding step S2, a first tempering step S3, a quenching step S4, a second tempering step S5, and a post-treatment step S6.

[0080] In preparation step S1, the annular component to be machined, forming the inner ring 10, is prepared through carburizing and nitriding step S2, first tempering step S3, quenching step S4, second tempering step S5, and post-treatment step S6. In preparation step S1, firstly, the component to be machined is hot-forged. In preparation step S1, secondly, the component to be machined is cold-forged. Cold forging is preferably performed with an expansion ratio (diameter of the component to be machined after cold forging ÷ diameter of the component to be machined before cold forging) of 1.1 to 1.3 or less. In preparation step S1, thirdly, machining is performed to make the shape of the component to be machined approximate the shape of the inner ring 10.

[0081] In the carburizing and nitriding process S2, firstly, the workpiece is carburized and nitrided by heating it to a first temperature or higher in a carburizing and nitriding atmosphere (an atmosphere containing carbon and nitrogen, such as an atmosphere containing an endothermic modifying gas (RX gas) and ammonia (NH3) gas). The first temperature is a temperature above the Al phase transformation point of the steel constituting the workpiece. In the second step of the carburizing and nitriding process S2, the workpiece is cooled. This cooling is performed to bring the temperature of the workpiece below the Ms phase transformation point. The average cooling rate at this time is at least 20°C / second.

[0082] In the first tempering step S3, the workpiece to be processed is tempered. The first tempering step S3 is performed by holding the workpiece at a second temperature for a first time. The second temperature is a temperature lower than the Al phase transition point. The second temperature is, for example, between 160°C and 400°C. Preferably, the second temperature is 180°C or higher. More preferably, the second temperature is 250°C or higher than 350°C. The first time is, for example, between 1 hour and 4 hours.

[0083] In quenching step S4, the workpiece to be processed is quenched. In quenching step S4, firstly, the workpiece to be processed is heated to a third temperature in an atmosphere in which ammonia is not intentionally added. The third temperature is a temperature above the Al phase transformation point of the steel constituting the workpiece. The third temperature is preferably lower than the first temperature. In quenching step S4, secondly, the workpiece to be processed is cooled. This cooling is performed in a manner that brings the temperature of the workpiece to below the Ms phase transformation point.

[0084] In the second tempering process S5, the workpiece is tempered. This process is performed by holding the workpiece at a fourth temperature for a second time. The fourth temperature is below the Al phase transformation point. For example, the fourth temperature is between 160°C and 200°C. The second time is, for example, between 1 hour and 4 hours. Furthermore, the quenching process S4 and the second tempering process S5 can be repeated multiple times.

[0085] In post-processing step S6, the workpiece to be processed is post-processed. Post-processing step S6 includes, for example, cleaning the workpiece, grinding, lapping, and other machining operations on the surface of the workpiece. Following this, the inner ring 10 is manufactured.

[0086] (Effect of the bearing component in Implementation Method 1)

[0087] The effects of the bearing component in Embodiment 1 will be explained below.

[0088] When considering material failure according to the weakest chain model, areas with relatively low strength, i.e., martensite grains with relatively large crystal sizes, have a significant impact on material failure. In the quenched and hardened layer 11 of the inner ring 10, the average grain size of the martensite grains belonging to the first group is less than 1.5 μm. Therefore, even in the inner ring 10, although the martensite grains belonging to the first group are relatively large, their grain refinement results in the surface (outer peripheral surface 10d) of the quenched and hardened layer 11 exhibiting both high wear resistance and high resistance to indentation formation.

[0089] In the quenched and hardened layer 11, the number density of cementite grains with a particle size of 1 μm or larger is 0.025 grains / μm. 2 The above-mentioned cementite grains with a particle size of 1 μm or larger have a number density of less than 0.025 grains / μm. 2Compared to the previous case, the cementite grains are highly dispersed. Therefore, due to the shear resistance of the quenched and hardened layer 11, the number density of cementite grains with a particle size of 1 μm or larger is less than 0.025 grains / μm. 2 The shear resistance of the hardened layer is higher, thus improving the wear resistance of the surface (outer peripheral surface 10d) of the hardened layer 11.

[0090] The smaller the average aspect ratio of the martensite grains, the closer the shape of the martensite grains is to spherical, and the less likely the martensite grains are to become stress concentration sources. If the average aspect ratio of the martensite grains belonging to Group 1 is below 3.3, the relatively large-sized martensite grains in the quenched hardened layer 11 become less likely to become stress concentration sources. Therefore, the wear resistance and indentation resistance of the surface (outer peripheral surface 10d) of the quenched hardened layer 11 are improved compared to the case where the average aspect ratio of the martensite grains belonging to Group 1 is higher than 3.3.

[0091] Furthermore, if the average aspect ratio of the martensite grains belonging to Group 1 is less than 3.1, the wear resistance and indentation resistance of the surface (outer peripheral surface 10d) of the quenched hardened layer 11 are improved compared to the case where the average aspect ratio of the martensite grains belonging to Group 1 is higher than 3.1.

[0092] If the average nitrogen concentration of the quenched hardened layer 11 between the surface (outer peripheral surface 10d) and a position 10 μm away from the surface is greater than 0.15% by mass, then fine precipitates will precipitate, contributing to the refinement of martensite grains at the surface (outer peripheral surface 10d) of the quenched hardened layer 11.

[0093] If the amount of retained austenite on the surface (outer peripheral surface 10d) is greater than 20% by volume, it will impart higher toughness to the surface (outer peripheral surface 10d) of the quenched hardened layer 11.

[0094] If the hardness of the quenched and hardened layer 11 on the surface (outer peripheral surface 10d) is above 730Hv, then the surface has high wear resistance and indentation resistance.

[0095] The steel constituting the inner ring 10 is high-carbon chromium bearing steel. If the steel constituting the inner ring were low-carbon steel, a long carburizing process would be required to harden it. Furthermore, low-carbon steel (e.g., chromium-molybdenum steel SCM435 as specified in JIS standards) contains higher levels of expensive alloying elements such as molybdenum (Mo) or nickel (Ni) compared to high-carbon chromium bearing steel. Therefore, the manufacturing cost of the inner ring 10 made of high-carbon chromium bearing steel is lower than that of an inner ring made of low-carbon steel. Preferably, the steel constituting the inner ring 10 is high-carbon chromium bearing steel SUJ2 as specified in JIS standards. SUJ2 is particularly inexpensive even among high-carbon chromium bearing steels.

[0096] Furthermore, in this embodiment, the average grain size and average aspect ratio of the martensite grains belonging to Group 1 are characterized by calculation based on the EBSD image of the quenched and hardened layer 11. Advantages of this method of calculating the average grain size and average aspect ratio of the martensite grains belonging to Group 1 based on EBSD images include: easy identification of grain boundaries of the relatively weak martensite grains belonging to Group 1 when considering material failure using the weakest chain model; removal of the influence of very small particles contained in the EBSD image; and mechanical and automatic measurement and calculation.

[0097] The bearing component manufacturing method of this embodiment includes a first tempering step S3 before a quenching step S4, which involves heating the formed body to a third temperature lower than the heating temperature (first temperature) of the carburizing and nitriding step S2. The inventors have discovered that if the first tempering step S3 is performed between the carburizing and nitriding step S2 and the quenching step S4, and the second temperature of the first tempering step S3 is 180°C or higher, the martensite grains in the quenched hardened layer 11 can be refined, thereby improving the wear resistance and indentation resistance of the surface of the quenched hardened layer 11. In particular, if the second temperature is between 250°C and 350°C, the martensite grains in the quenched hardened layer 11 can be further refined, and it can be confirmed that the wear resistance and indentation resistance of the surface of the quenched hardened layer 11 can be further improved.

[0098] (Rolling component of Embodiment 1)

[0099] The rolling component in Embodiment 1 is a component having a rolling surface. The rolling component of this embodiment has the same configuration as the bearing component of the above embodiment, and has a quench-hardened layer equivalent to the quench-hardened layer 11. In the rolling component of this embodiment, the quench-hardened layer is at least provided on the rolling surface. The manufacturing method of the rolling component of this embodiment has the same configuration as the manufacturing method of the bearing component of the above embodiment. The rolling component of this embodiment can be any component having a rolling surface, such as a ball screw.

[0100] (Static load capacity test)

[0101] The following describes the static load capacity test performed to confirm the effectiveness of the bearing component in Embodiment 1.

[0102] <Test Materials>

[0103] In the static load capacity test, samples 1, 2, and 3 were used as examples, and samples 4 and 5 were used as comparative examples. Samples 1, 2, 3, 4, and 5 were made of high-carbon chromium bearing steel SUJ2 as specified in the JIS standard.

[0104] Samples 1 to 3 were prepared according to the manufacturing method of the bearing component according to the embodiment. More specifically, in the preparation of sample 1, the first temperature was 850°C, the second temperature was 180°C, the third temperature was 810°C, and the fourth temperature was 180°C. In the preparation of sample 2, the first temperature was 850°C, the second temperature was 250°C, the third temperature was 810°C, and the fourth temperature was 180°C. In the preparation of sample 3, the first temperature was 850°C, the second temperature was 350°C, the third temperature was 810°C, and the fourth temperature was 180°C. The heat treatment conditions for samples 1 to 3 are shown in Table 1. The heating mode for the carburizing and nitriding treatment of samples 1 to 3 was conventional. The heating time (first time) for the first tempering process of samples 1 to 3 was 2 hours.

[0105] [Table 1]

[0106] Temperature 1 (°C) Second temperature (°C) 3rd temperature (°C) 4th temperature (°C) Sample 1 850 180 810 180 Sample 2 850 250 810 180 Sample 3 850 350 810 180

[0107] Sample 4 was prepared by quenching and tempering the above-mentioned shaped body in a carburizing and nitriding atmosphere. In the preparation of Sample 4, the quenching temperature was 850℃ and the tempering temperature was 180℃.

[0108] Sample 5 was prepared by quenching the above-mentioned molded body in an atmosphere without the intentional addition of ammonia (ordinary quenching) followed by tempering. In the preparation of Sample 5, the quenching temperature was 810℃ and the tempering temperature was 180℃.

[0109] Furthermore, in samples 1-3, the total area ratio of austenite grains at a distance of 50 μm from the surface reaches 24% to 26%. In samples 1-4, the nitrogen concentration between the surface and a location at a distance of 10 μm from the surface reaches 0.15% to 0.20% by mass. In samples 1-3, the surface hardness reaches approximately 750 Hv.

[0110] EBSD images were obtained by cross-sectional observation of the surface area of ​​samples 1–5 using field emission scanning electron microscopy (FE-SEM). Figure 5 The image shown is an EBSD image of a cross-section of sample 1. Figure 6 The image shown is an EBSD image of a cross-section of sample 2. Figure 7 The image shown is an EBSD image of a cross-section of sample 3. Figure 8 The image shown is an EBSD image of a cross-section of sample 4. Figure 9 The image shown is an EBSD image of a cross-section of sample 5. From Figures 5-9 The average grain size and average aspect ratio of the martensite grains, as well as the grain size and number density of the cementite grains, are calculated for each of the EBSD images shown for samples 1-5, belonging to group 1.

[0111] In Sample 1, the average grain size of the martensite grains belonging to Group 1 is 1.5 μm, and the average aspect ratio of the martensite grains belonging to Group 1 is 3.3. In Sample 1, the number density of cementite grains with a grain size greater than 1 μm is 0.026 grains / μm. 2 .

[0112] In Sample 2, the average grain size of the martensite grains belonging to Group 1 is 1.2 μm, and the average aspect ratio of the martensite grains belonging to Group 1 is 2.9. In Sample 2, the number density of cementite grains with a grain size greater than 1 μm is 0.048 grains / μm. 2 .

[0113] In Sample 3, the average grain size of the martensite grains belonging to Group 1 was 1.3 μm, and the average aspect ratio of the martensite grains belonging to Group 1 was 2.9. In Sample 1, the number density of cementite grains with a grain size greater than 1 μm was 0.046 particles / μm. 2 .

[0114] In Sample 4, the average grain size of the martensite grains belonging to Group 1 is 1.8 μm, and the average aspect ratio of the martensite grains belonging to Group 1 is 3.2. In Sample 4, the number density of cementite grains with a grain size greater than 1 μm is 0.024 grains / μm. 2 .

[0115] In Sample 5, the average grain size of the martensite grains belonging to Group 1 was 2.1 μm, and the average aspect ratio of the martensite grains belonging to Group 1 was 3.2. In Sample 5, the number density of cementite grains with a grain size greater than 1 μm was 0.005 particles / μm. 2 .

[0116] The results of the determination of the average grain size and average aspect ratio of the martensite grains belonging to Group 1 in Samples 1 to 5, as well as the number density of cementite grains, are shown in Table 2.

[0117] [Table 2]

[0118]

[0119] <Static Load Capacity Test Conditions>

[0120] In the static load capacity test, flat plate components were prepared using samples 1 to 5. Silicon nitride ceramic balls were pressed onto the surface of the mirror-finished flat plate components, and the relationship between the maximum contact surface pressure and the indentation depth was obtained to perform the static load capacity test. Furthermore, the static load capacity was evaluated based on the maximum contact surface pressure obtained when the value obtained by dividing the indentation depth by the ceramic ball diameter is 1 / 10000 (the value obtained by dividing the indentation depth by the ceramic ball diameter and then multiplying by 10000 is 1).

[0121] <Static load capacity test results>

[0122] The standardized ratio (static load capacity ratio) of the static load capacity measured in samples 1 to 4 relative to the static load capacity measured in sample 5 is shown in Table 3.

[0123] [Table 3]

[0124] Static load capacity ratio Sample 1 1.07 Sample 2 1.09 Sample 3 1.09 Sample 4 0.99 Sample 5 1.00

[0125] As shown in Table 3, it was confirmed that the static load capacity of samples 1 to 3 was higher than that of samples 4 and 5. It was also confirmed that the static load capacity of samples 2 and 3 was higher than that of sample 1.

[0126] Figure 10 The graph shown is a chart showing the relationship between maximum contact surface pressure and indentation depth. Figure 10 In the diagram, the horizontal axis represents the maximum contact surface pressure (unit: GPa), and the vertical axis represents the indentation depth ÷ ceramic ball diameter × 10. 4 .like Figure 10 As shown, compared to the curve corresponding to sample 1, the maximum contact surface pressure is greater in the curves corresponding to samples 2 and 3 when the vertical axis value is 1. That is, the static load capacity is greater in samples 2 and 3 than in sample 1.

[0127] Figure 11 The graph shown is a relationship between the average grain size of the martensite grains in Group 1 and the static loading capacity. Figure 12 The graph shown is a relationship between the average aspect ratio of the martensite grains in Group 1 and the static load capacity. Figure 11 In the figure, the horizontal axis represents the average grain size (in μm) of the martensite grains belonging to Group 1, and the vertical axis represents the static load capacity (in GPa). Figure 12 In the figure, the horizontal axis represents the average aspect ratio of the martensite grains belonging to Group 1, and the vertical axis represents the static load capacity (unit: GPa).

[0128] As shown in Table 2 and Table 3, Figure 11 and Figure 12 As shown, the static loading capacity improves as the average grain size of the martensite grains in Group 1 decreases. Furthermore, the static loading capacity improves as the number density of cementite grains with a grain size of 1 μm or larger increases. Furthermore, the static loading capacity improves when the average aspect ratio of the martensite grains in Group 1 is small. The number density of cementite grains with an average grain size of 1.5 μm or less and a grain size of 1 μm or larger in the martensite grains of Group 1 is 0.005 grains / μm. 2In the case of [specific conditions], a static load capacity of 5.6 GPa or higher was confirmed. Furthermore, when the average grain size of the martensite grains belonging to Group 1 is 1.4 μm or less and the average aspect ratio of the martensite grains belonging to Group 1 is 3.1 or less, a static load capacity of 5.7 GPa or higher was confirmed.

[0129] These test results also experimentally demonstrate that, according to the implementation method, the rolling component has finer grains and improved static load capacity (resistance to indentation formation).

[0130] (Abrasion test)

[0131] The following describes the wear test conducted to confirm the effectiveness of the rolling component in the embodiment.

[0132] The wear test used samples 1 to 5 as described above. In the wear test, flat plate-shaped components were prepared using samples 1 to 5. The surface roughness (arithmetic mean roughness) Ra was 0.010 μm.

[0133] <Wearing Test Conditions>

[0134] For samples 1 to 5 above, abrasion tests were conducted using a Savin abrasion testing machine. The load during the test was 50 N, and the relative speed to the target material was 0.05 m / s. The test duration was 60 minutes, and MOBILVELOCITE OIL No. 3 (registered trademark) (VG2) was used as the lubricant. The abrasion resistance was evaluated by comparing the abrasion amounts of samples 1 to 5 after the abrasion tests.

[0135] <Abrasion Test Results>

[0136] The results of the comparative evaluation of the wear amounts of samples 1 to 5 are shown in Table 4. Furthermore, samples were ranked A, B, and C in order of the lowest wear amount.

[0137] [Table 4]

[0138] Evaluation of wear Sample 1 B Sample 2 A Sample 3 A Sample 4 B Sample 5 C

[0139] As shown in Table 4, it was confirmed that the wear resistance of samples 1 to 3 was higher than that of sample 5. It was also confirmed that the wear resistance of samples 2 and 3 was higher than that of sample 1.

[0140] That is, wear resistance improves as the average grain size of the martensite grains belonging to Group 1 decreases. Furthermore, wear resistance improves as the number density of cementite grains with a grain size greater than 1 μm increases. Furthermore, wear resistance improves when the average aspect ratio of the martensite grains belonging to Group 1 is small.

[0141] The test results also experimentally showed that, according to the embodiment, the rolling component has finer grains and improved wear resistance.

[0142] (Implementation Method 2)

[0143] The bearing component of Embodiment 2 is a bearing component made of high-carbon chromium bearing steel and having a hardened layer on its surface. The hardened layer contains multiple martensitic grains. The maximum grain size of the multiple martensitic grains is 3.5 μm or less. The maximum aspect ratio of the multiple martensitic grains is 10 or less. The ratio of the maximum to the minimum crystal orientation density of the {011} facets of the multiple martensitic grains is 5.0 or less.

[0144] In the aforementioned bearing components, when multiple martensite grains are divided into Group 1 and Group 2 as shown below, the average grain size of the martensite grains in Group 1 can be less than 1.1 μm. The minimum grain size of the martensite grains in Group 1 is greater than the maximum grain size of the martensite grains in Group 2. The total area of ​​the martensite grains in Group 1 divided by the total area of ​​all martensite grains is greater than 0.5. The total area of ​​the martensite grains in Group 1 after removing the smallest martensite grain in Group 1 divided by the total area of ​​all martensite grains is less than 0.5.

[0145] Furthermore, in the aforementioned bearing component, when the multiple martensite grains are divided into Group 3 and Group 4 as shown below, the average grain size of the martensite grains belonging to Group 3 can be less than 0.8 μm. The minimum grain size of the martensite grains belonging to Group 3 is greater than the maximum grain size of the martensite grains belonging to Group 4. The value obtained by dividing the total area of ​​the martensite grains belonging to Group 3 by the total area of ​​the multiple martensite grains is greater than 0.7. The value obtained by dividing the total area of ​​the martensite grains belonging to Group 3 (excluding the smallest martensite grain in Group 3) by the total area of ​​the multiple martensite grains is less than 0.7.

[0146] In the aforementioned bearing components, the average aspect ratio of the martensite grains belonging to Group 1 can be below 3.2, and the average aspect ratio of the martensite grains belonging to Group 3 can be below 3.0.

[0147] In the aforementioned bearing component, the hardened layer further comprises multiple cementite grains. When these multiple cementite grains are divided into Group 5 and Group 6 as shown below, the average grain size of the cementite grains in Group 5 can be less than 1.4 μm. The minimum crystal size of the cementite grains in Group 5 is greater than the maximum crystal size of the cementite grains in Group 6. The total area of ​​the cementite grains in Group 5 divided by the total area of ​​the multiple cementite grains is greater than 0.5. The total area of ​​the cementite grains in Group 5 after removing the smallest crystal size cementite grain in Group 5 divided by the total area of ​​the multiple cementite grains is less than 0.5.

[0148] Furthermore, in the aforementioned bearing component, when the multiple cementite grains are divided into Group 7 and Group 8 as shown below, the average grain size of the cementite grains belonging to Group 7 can be less than 1.10 μm. The minimum crystal grain size of the cementite grains belonging to Group 7 is greater than the maximum value of the cementite grains belonging to Group 8. The value obtained by dividing the total area of ​​the cementite grains belonging to Group 7 by the total area of ​​the multiple cementite grains is greater than 0.7. The value obtained by dividing the total area of ​​the cementite grains belonging to Group 7 (excluding the cementite grain with the smallest crystal grain size) by the total area of ​​the multiple cementite grains is less than 0.7.

[0149] In the aforementioned bearing components, the number density of cementite particles belonging to group 5 can be as low as 0.05 / μm. 2 The number density of cementite particles belonging to Group 7 can be as high as 0.10 / μm. 2 above.

[0150] In the aforementioned bearing component, the hardened layer contains nitrogen. The average nitrogen concentration of the hardened layer between the aforementioned surface and a location 10 μm away from the surface can be 0.10% by mass or more.

[0151] In the aforementioned bearing components, the amount of residual austenite on the aforementioned surfaces can be 20% or more by volume.

[0152] In the aforementioned bearing components, the hardness of the quenched and hardened layer on the aforementioned surface can be above 730Hv.

[0153] In the aforementioned bearing components, the average particle size of the original austenite grains on the aforementioned surface can be below 8 μm.

[0154] In the aforementioned bearing components, the compressive residual stress on the aforementioned surfaces is above 100 MPa.

[0155] In the aforementioned bearing components, the high-carbon chromium bearing steel can be SUJ2 as specified in the JIS standard.

[0156] The method for manufacturing a bearing component according to Embodiment 2 includes the following steps: preparing a molded body made of high-carbon chromium bearing steel; performing a first quenching on the molded body by heating it to a first quenching temperature above the Al phase transformation point and then cooling it to a temperature below the Ms point; performing a first tempering on the first quenched molded body by holding it at a temperature above 200°C and below the Al phase transformation point for a first time; performing a second quenching on the first tempered molded body by heating it to a temperature above the Al phase transformation point and below the first quenching temperature and then cooling it to a temperature below the Ms point; and performing a second tempering on the second quenched molded body by holding it at a temperature below 180°C for a second time.

[0157] The manufacturing method of the bearing component described above can further include a step of nitriding the formed body before the step of quenching the formed body once.

[0158] (Specific configuration of the bearing component in Embodiment 2)

[0159] The specific configuration of the bearing component in Embodiment 2 will be described. Furthermore, the following description uses the inner ring 10 of a rolling bearing as an example of the bearing component in the embodiment, but the bearing component in the embodiment is not limited to this. The bearing component in the embodiment can be at least any one of the inner ring, outer ring, and rolling elements of a rolling bearing. For example, the rolling bearing in the embodiment may include an inner ring and outer ring as a track component in the embodiment, as well as rolling elements.

[0160] The inner ring 10 is made of high-carbon chromium bearing steel. High-carbon chromium bearing steel is, for example, SUJ2 as specified in JIS standard (JIS G4805:2008).

[0161] The inner ring 10 has the same configuration as the inner ring 10 in Embodiment 1. For example... Figure 1 and Figure 2 As shown, the inner ring 10 is annular. The inner ring 10 has an upper surface 10a, a bottom surface 10b, an inner circumferential surface 10c, an outer circumferential surface 10d, and a central axis 10e.

[0162] The upper surface 10a and the bottom surface 10b form an end face along the direction of the central axis 10e. The bottom surface 10b is the opposite surface of the upper surface 10a. The inner circumferential surface 10c and the outer circumferential surface 10d are connected to the upper surface 10a and the bottom surface 10b. The distance between the inner circumferential surface 10c and the central axis 10e is smaller than the distance between the outer circumferential surface 10d and the central axis 10e. A track groove is provided on the outer circumferential surface 10d. The outer circumferential surface 10d forms the track surface of the inner ring 10.

[0163] like Figure 3As shown, the inner ring 10 has a hardened layer 11. The hardened layer 11 is provided at least on the outer peripheral surface 10d of the track surface in the surface of the inner ring 10. The hardened layer 11 is provided, for example, on the entire surface of the inner ring 10. The hardened layer 11 contains a plurality of martensite grains and a plurality of cementite grains. The martensite grains are grains composed of the martensite phase. The cementite grains are compound grains composed of cementite (Fe3C).

[0164] Martensite grains are bulk martensite phase grains composed of crystals with aligned crystal orientations. When the crystal orientation of the first martensite grain deviates from that of the adjacent second martensite grain by more than 15°, the first and second martensite grains are different martensite grains. Conversely, when the crystal orientation of the first martensite grain deviates from that of the adjacent second martensite grain by less than 15°, the first and second martensite grains constitute the same martensite grain.

[0165] The maximum grain size of the martensite in the quenched and hardened layer 11 is less than 3.5 μm. The maximum grain size of the martensite in the quenched and hardened layer 11 is, for example, greater than 3.2 μm. The maximum grain size of the martensite is determined using EBSD (electron backscatter diffraction).

[0166] Specifically, firstly, based on the EBSD method, images of the surface of the quenched and hardened layer 11 are captured (hereinafter referred to as "EBSD images"). EBSD images are captured in a manner that includes a sufficient number (more than 20) of martensite grains. Based on the EBSD method, the boundaries of adjacent martensite grains are determined. Secondly, based on the determined boundaries of the martensite grains, the area and shape of each martensite grain shown in the EBSD images are calculated.

[0167] More specifically, the equivalent circular diameter of each martensite grain shown in the EBSD image can be determined by calculating the square root of the area of ​​each martensite grain divided by π / 4. The maximum equivalent circular diameter of each martensite grain shown in the EBSD image is the maximum grain size of the martensite grain.

[0168] The maximum aspect ratio of the martensite grains in the quenched and hardened layer 11 is 10 or less. Preferably, the maximum aspect ratio of the martensite grains is 9.5 or less. More preferably, the maximum aspect ratio of the martensite grains is 9.1 or less. The method for calculating the maximum aspect ratio of the martensite grains is described below.

[0169] The ratio of the maximum to the minimum crystal orientation density of the {011} plane of multiple martensite grains is 5.0 or less. Preferably, the ratio is 4.1 or less. More preferably, the ratio is 3.6 or less. The minimum and maximum crystal orientation densities obtained by EBSD (electron backscatter diffraction) are calculated by analyzing the crystal orientation density distribution using the method described in HJ Bunge, Mathematische Methodender Texturanalyse, Akademi-Verlag (1969) on spherical harmonic orders.

[0170] In the quenched and hardened layer 11, martensite is the main constituent microstructure. More specifically, the total area ratio of martensite grains in the quenched and hardened layer 11 is above 70%. The total area ratio of martensite grains in the quenched and hardened layer 11 can be above 80%. The total area ratio of cementite grains in the quenched and hardened layer 11 is below 30%.

[0171] Multiple martensite grains are divided into Group 1 and Group 2. According to this division, the multiple martensite grains consist of multiple martensite grains belonging to Group 1 and multiple martensite grains belonging to Group 2. The minimum grain size of the martensite grains belonging to Group 1 is greater than the maximum grain size of the martensite grains belonging to Group 2.

[0172] The value obtained by dividing the total area of ​​martensite grains belonging to Group 1 by the total area of ​​martensite grains (the sum of the total area of ​​martensite grains belonging to Group 1 and the total area of ​​martensite grains belonging to Group 2) is greater than 0.5. The value obtained by dividing the total area of ​​martensite grains belonging to Group 1 (excluding the smallest martensite grains belonging to Group 1) by the total area of ​​martensite grains is less than 0.5.

[0173] In other words, martensite grains are classified into Group 1 in descending order of grain size. The classification into Group 1 ends at a point in time where the total area of ​​the martensite grains classified into Group 1 reaches at least 0.5 times the total area of ​​all martensite grains. The remaining martensite grains are then classified into Group 2.

[0174] The average grain size of the martensite grains belonging to Group 1 is 1.10 μm or less. Preferably, the average grain size of the martensite grains belonging to Group 1 is 1.00 μm or less. More preferably, the average grain size of the martensite grains belonging to Group 1 is 0.98 μm or less.

[0175] The aspect ratio of the martensite grains belonging to Group 1 is 3.2 or less. Preferably, the aspect ratio of the martensite grains belonging to Group 1 is 3.0 or less. More preferably, the aspect ratio of the martensite grains belonging to Group 1 is 2.9 or less.

[0176] Multiple martensite grains can be classified into Group 3 and Group 4. According to this classification, multiple martensite grains consist of multiple martensite grains belonging to Group 3 and multiple martensite grains belonging to Group 4. The minimum grain size of the martensite grains belonging to Group 3 is greater than the maximum grain size of the martensite grains belonging to Group 4.

[0177] The value obtained by dividing the total area of ​​martensite grains belonging to Group 3 by the total area of ​​martensite grains (the sum of the total area of ​​martensite grains belonging to Group 3 and the total area of ​​martensite grains belonging to Group 4) is greater than 0.7.

[0178] The value obtained by dividing the total area of ​​the martensite grains in Group 3 (excluding the smallest martensite grains in Group 3) by the total area of ​​the martensite grains is less than 0.7.

[0179] In other words, the martensite grains were classified into Group 3 in descending order of grain size. The classification into Group 3 ended at a point in time where the total area of ​​the martensite grains classified into Group 3 reached more than 0.7 times the total area of ​​all martensite grains. The remaining martensite grains were then classified into Group 4.

[0180] The average grain size of the martensite grains belonging to Group 3 is 0.80 μm or less. Preferably, the average grain size of the martensite grains belonging to Group 3 is 0.78 μm or less. More preferably, the average grain size of the martensite grains belonging to Group 3 is 0.76 μm or less.

[0181] The aspect ratio of the martensite grains belonging to Group 3 is 3.0 or less. Preferably, the aspect ratio of the martensite grains belonging to Group 3 is 2.95 or less. More preferably, the aspect ratio of the martensite grains belonging to Group 3 is 2.75 or less.

[0182] The average grain size, average aspect ratio, and maximum aspect ratio of martensite grains belonging to Group 1 (Group 3) were determined using the EBSD method.

[0183] The details are as follows. Based on the round equivalent diameter of each martensite grain calculated above, the martensite grains belonging to Group 1 (Group 3) in the EBSD images can be determined. In other words, based on the round equivalent diameter of each martensite grain calculated above, the martensite grains shown in the EBSD images are classified into Group 1 and Group 2 (and similarly, Group 3 and Group 4). The sum of the round equivalent diameters of the martensite grains in the EBSD images classified as Group 1 (Group 3) divided by the number of martensite grains in the EBSD images classified as Group 1 (Group 3) can be considered as the average grain size of the martensite grains belonging to Group 1 (Group 3). Additionally, the value obtained by dividing the total area of ​​the martensite grains belonging to Group 1 (Group 3) shown in the EBSD image by the total area of ​​the martensite grains shown in the EBSD image can be regarded as the value obtained by dividing the total area of ​​the martensite grains belonging to Group 1 (Group 3) by the total area of ​​the martensite grains.

[0184] Based on the shapes of the martensite grains shown in the EBSD images, an elliptical approximation of the shapes of the martensite grains shown in the EBSD images is performed using the least squares method. This least squares-based elliptical approximation is performed using the method described in S. Biggin and DJ Dingley, Journal of Applied Crystallography, (1977) 10, 376-376. The aspect ratio of each martensite grain shown in the EBSD images can be determined by dividing the major axis by the minor axis in this ellipse. The maximum aspect ratio of each martensite grain is the maximum aspect ratio of the martensite grain.

[0185] Furthermore, the sum of the aspect ratios of the martensite grains shown in the EBSD images classified as Group 1 (Group 3) divided by the number of martensite grains shown in the EBSD images classified as Group 1 (Group 3) can be regarded as the average aspect ratio of the martensite grains belonging to Group 1 (Group 3).

[0186] Multiple cementite grains were classified into groups 5 and 6. According to this classification, the multiple cementite grains consist of multiple cementite grains belonging to group 5 and multiple cementite grains belonging to group 6. The minimum particle size of the cementite grains belonging to group 5 is greater than the maximum particle size of the cementite grains belonging to group 6.

[0187] The value obtained by dividing the total area of ​​cementite particles belonging to Group 5 by the total area of ​​multiple cementite particles (the sum of the total area of ​​cementite particles belonging to Group 5 and the total area of ​​cementite particles belonging to Group 6) is greater than 0.5. The value obtained by dividing the total area of ​​cementite particles belonging to Group 5 (excluding the smallest cementite particles belonging to Group 5) by the total area of ​​cementite particles is less than 0.5.

[0188] In other words, the cementite particles were classified into Group 5 in descending order of particle size. The classification of Group 5 ended at the point in time when the total area of ​​the cementite particles classified into Group 5 reached more than 0.5 times the total area of ​​all cementite particles. The remaining cementite particles were then classified into Group 6.

[0189] The average particle size of the cementite particles belonging to Group 5 is less than 1.40 μm. Preferably, the average particle size of the cementite particles belonging to Group 5 is less than 1.30 μm. More preferably, the average particle size of the cementite particles belonging to Group 5 is less than 1.20 μm.

[0190] The number density of cementite particles in Group 5 is 0.04 particles / μm. 2 The above. Preferably, the number density of cementite particles belonging to group 5 is 0.05 particles / μm. 2 The above. Preferably, the number density of cementite particles belonging to group 5 is 1.00 particles / μm. 2 the following.

[0191] Multiple cementite grains can be classified into groups 7 and 8. According to this classification, the multiple cementite grains consist of multiple cementite grains belonging to group 7 and multiple cementite grains belonging to group 8. The minimum particle size of the cementite grains belonging to group 7 is greater than the maximum particle size of the cementite grains belonging to group 8.

[0192] The value obtained by dividing the total area of ​​cementite particles belonging to Group 7 by the total area of ​​multiple cementite particles (the sum of the total area of ​​cementite particles belonging to Group 7 and the total area of ​​cementite particles belonging to Group 8) is greater than 0.7. The value obtained by dividing the total area of ​​cementite particles belonging to Group 7 (excluding the smallest cementite particles belonging to Group 7) by the total area of ​​cementite particles is less than 0.7.

[0193] In other words, the cementite particles were classified into Group 7 in descending order of particle size. The classification of Group 7 ended at the point in time when the total area of ​​the cementite particles classified into Group 7 reached more than 0.7 times the total area of ​​all cementite particles. The remaining cementite particles were then classified into Group 8.

[0194] The average particle size of the cementite particles belonging to Group 7 is less than 1.10 μm. Preferably, the average particle size of the cementite particles belonging to Group 7 is less than 0.90 μm. More preferably, the average particle size of the cementite particles belonging to Group 7 is less than 0.60 μm.

[0195] The number density of cementite particles in Group 7 is 0.06 particles / μm. 2 The above. Preferably, the number density of cementite particles belonging to group 7 is 0.10 particles / μm. 2The above. Preferably, the number density of cementite particles belonging to group 7 is 0.20 particles / μm. 2 The above. Preferably, the number density of cementite particles belonging to group 7 is 1.00 particles / μm. 2 the following.

[0196] Similar to the average grain size of the martensite grains belonging to Group 1 (Group 3), the average grain size of the cementite grains belonging to Group 5 (Group 7) was determined using the EBSD method described above. The number density of the cementite grains belonging to Group 5 (Group 7) was calculated by determining the number of cementite grains belonging to Group 5 (Group 7) shown in the EBSD image taken in a manner containing a sufficient number (more than 20) of martensite grains, as described above, and then dividing that number by the field of view area of ​​the EBSD image.

[0197] The hardened layer 11 contains nitrogen. The average nitrogen concentration of the hardened layer 11 between the outer peripheral surface 10d and a position 10 μm away from the outer peripheral surface 10d is preferably 0.10% by mass or more. This average nitrogen concentration is, for example, 0.20% by mass or less. Furthermore, this average nitrogen concentration is determined using an EPMA (Electron Probe Micro Analyzer).

[0198] The retained austenite content of the aforementioned outer peripheral surface 10d is preferably 20% by volume or more. The retained austenite content is determined by X-ray diffraction of the aforementioned outer peripheral surface 10d. Specifically, the retained austenite content is calculated by comparing the integrated intensity of the X-ray diffraction peaks of the austenite phase and the integrated intensity of the X-ray diffraction peaks of the martensite phase.

[0199] The hardness of the quenched and hardened layer 11 on the outer peripheral surface 10d is preferably 700 Hv or higher. More preferably, the hardness of the quenched and hardened layer 11 on the outer peripheral surface 10d is 750 Hv or higher. In addition, the hardness of the quenched and hardened layer 11 on the outer peripheral surface 10d is measured according to JIS standard (JIS Z2244:2009).

[0200] In addition to martensite and cementite grains, the hardened layer 11 also contains proto-austenite grain boundaries. Traces of austenite grain boundaries present in the steel before quenching, formed during the first or second quenching process of the bearing component manufacturing method described later, remain in the hardened layer 11. The proto-austenite grains are grains present in the steel before quenching based on these traces.

[0201] The average particle size of the original austenite grains in the outer peripheral surface 10d is preferably 8 μm or less. More preferably, the average particle size of the original austenite grains is 6 μm or less.

[0202] Furthermore, the average grain size of the proto-austenite grains on the outer 10d surface was determined by the following method: First, for a cross-section including the outer 10d surface, optical microscopy was performed to image the proto-austenite grain boundaries based on acid solution imaging (hereinafter, the image obtained by optical microscopy is referred to as an "optical microscopy image"). Additionally, optical microscopy images were taken in a manner containing a sufficient number (20 or more) of proto-austenite grains. Second, for the obtained optical microscopy images, the average grain size of each proto-austenite grain in the optical microscopy image was calculated by performing image processing based on the JIS standard (JIS G0551:2013).

[0203] The compressive residual stress of the aforementioned outer peripheral surface 10d is preferably above 100 MPa. The compressive residual stress is determined by X-ray stress measurement of the aforementioned outer peripheral surface 10d.

[0204] (Manufacturing method of bearing component according to embodiment 2)

[0205] Hereinafter, as an example of the manufacturing method of the bearing component of Embodiment 2, the manufacturing method of the inner ring 10 will be described.

[0206] Figure 13 The diagram shows the process flow of the manufacturing method of the bearing component according to the embodiment. Figure 14 The diagram shows the heating mode of the bearing component manufacturing method according to the embodiment. (As shown) Figure 13 and Figure 14 As shown, the method for manufacturing the bearing component according to the embodiment includes a preparation step S1, a carburizing and nitriding step S2, a first quenching step S3, a first tempering step S4, a second quenching step S5, a second tempering step S6, and a post-treatment step S7. The preparation step S1, the carburizing and nitriding step S2, the first quenching step S3, the first tempering step S4, the second quenching step S5, the second tempering step S6, and the post-treatment step S7 are performed in the order described above.

[0207] In preparation step S1, a ring-shaped component to be processed, becoming the inner ring 10, is prepared through carburizing and nitriding step S2, first quenching step S3, first tempering step S4, second quenching step S5, second tempering step S6, and post-treatment step S7. In preparation step S1, firstly, the component to be processed is hot-forged. In preparation step S1, secondly, the component to be processed is cold-forged. Cold forging is preferably performed with an expansion ratio (diameter of the component to be processed after cold forging ÷ diameter of the component to be processed before cold forging) of 1.1 to 1.3 or less. In preparation step S1, thirdly, machining is performed to make the shape of the component to be processed approximate the shape of the inner ring 10.

[0208] In the carburizing and nitriding process S2, firstly, the workpiece to be processed is heated to a temperature above a first temperature and held thereafter to perform carburizing and nitriding treatment. The first temperature is a temperature above the Al phase transformation point of the steel constituting the workpiece. In the carburizing and nitriding process S2, secondly, the workpiece to be processed is cooled. This cooling is performed in a manner that brings the temperature of the workpiece to below the Ms phase transformation point.

[0209] In the first quenching step S3, the workpiece to be processed, which has undergone carburizing and nitriding in the carburizing and nitriding step S2, is quenched. In the first quenching step S3, firstly, the workpiece to be processed is heated to a second temperature (first quenching temperature). The second temperature is a temperature above the Al phase transformation point of the steel constituting the workpiece. The second temperature is preferably lower than the first temperature. In the first quenching step S4, secondly, the workpiece to be processed is cooled. This cooling is performed in a manner that brings the temperature of the workpiece to below the Ms phase transformation point. Cooling is performed, for example, by oil cooling.

[0210] In the first tempering step S4, the workpiece that has been quenched in the first quenching step S3 is tempered. The first tempering step S4 is performed by holding the workpiece at a third temperature (the first tempering temperature) for a first time. The third temperature is a temperature lower than the Al phase transformation point. The third temperature is, for example, between 200°C and 450°C. Preferably, the third temperature is between 250°C and 400°C. More preferably, the third temperature is between 250°C and 350°C. The first time is, for example, between 1 hour and 4 hours.

[0211] In the secondary quenching process S5, the workpiece that has been tempered in the primary tempering process S4 is quenched. In the secondary quenching process S5, firstly, the workpiece is heated to a fourth temperature (secondary quenching temperature). The fourth temperature is a temperature above the Al phase transformation point of the steel constituting the workpiece. The fourth temperature is preferably lower than the second temperature. In the secondary quenching process S5, secondly, the workpiece is cooled. This cooling is performed to bring the temperature of the workpiece below the Ms phase transformation point. Cooling is performed, for example, by oil cooling.

[0212] In the secondary tempering process S6, the workpiece that has been quenched in the secondary quenching process S5 is tempered. The secondary tempering process S5 is performed by holding the workpiece at a fifth temperature (secondary tempering temperature) for a second time. The fifth temperature is a temperature lower than the Al phase transformation point. The fifth temperature is lower than the third temperature. The fifth temperature is, for example, above 140°C and below 200°C. Preferably, the fifth temperature is above 140°C and below 180°C.

[0213] In post-processing step S7, the workpiece that has been tempered in the secondary tempering step S6 undergoes post-processing. Post-processing step S7 includes, for example, cleaning the workpiece, grinding, lapping, or other machining operations on its surface. The grinding or lapping depth is, for example, less than 200 μm. Following this, the inner ring 10 is manufactured.

[0214] (Effects)

[0215] Next, the effects of the bearing component according to the embodiment will be explained. In the inner ring 10, the maximum grain size of the martensite grains in the hardened layer 11 is less than 3.5 μm, and the maximum aspect ratio of the martensite grains in the hardened layer 11 is less than 10. As the maximum grain size of the martensite grains becomes finer, the wear resistance and toughness of the hardened layer 11 are improved. Furthermore, as the maximum aspect ratio of the martensite grains approaches 1, the shape of the martensite grains becomes close to spherical, making it difficult for the martensite grains to become stress concentration sources. Therefore, the wear resistance and toughness of the hardened layer 11 of the inner ring 10 are improved compared to the case where the maximum grain size of the martensite grains in the hardened layer is greater than 3.5 μm and the maximum aspect ratio of the martensite grains in the hardened layer is greater than 10.

[0216] In the inner ring 10, the ratio of the maximum to the minimum crystal orientation density of the {011} facets of the martensite grains in the hardened layer 11 is less than 5.0. As the ratio of the maximum to the minimum crystal orientation density of the {011} facets of the martensite grains approaches 1, the formation state of each martensite grain becomes more uniform, and the indentation resistance, wear resistance, and toughness are improved. Therefore, the indentation resistance, wear resistance, and toughness of the hardened layer 11 of the inner ring 10 are improved compared to the case where the ratio of the maximum to the minimum crystal orientation density of the {011} facets of the martensite grains in the hardened layer is greater than 5.0. Furthermore, in this specification, indentation resistance and wear resistance are collectively referred to as surface damage resistance. The surface damage resistance and toughness of the inner ring 10 are improved.

[0217] In the quenched and hardened layer 11 of the inner ring 10, when multiple martensite grains are divided into groups 1 and 2, the average grain size of the martensite grains belonging to group 1, which has relatively larger grains, is less than 1.1 μm. Furthermore, in the quenched and hardened layer 11 of the inner ring 10, when multiple martensite grains are divided into groups 3 and 4, the average grain size of the martensite grains belonging to group 3, which has relatively larger grains, is less than 0.8 μm. That is, even for the martensite grains belonging to group 1 (group 3), which have relatively larger grains, the wear resistance of the quenched and hardened layer 11 is improved due to the refinement of the grains.

[0218] In the quenched and hardened layer 11 of the inner ring 10, when multiple martensite grains are divided into groups 1 and 2, the average aspect ratio of the martensite grains belonging to group 1 (which has relatively larger grains) is less than 3.2. Furthermore, in the quenched and hardened layer 11 of the inner ring 10, when multiple martensite grains are divided into groups 3 and 4, the average aspect ratio of the martensite grains belonging to group 3 (which has relatively larger grains) is less than 3.0. As the average aspect ratio of the martensite grains approaches 1, the shape of the martensite grains becomes nearly spherical, making it difficult for them to become stress concentration sources. Because the martensite grains belonging to group 1 (group 3) (which has relatively larger grains) are less likely to become stress concentration sources, the wear resistance and toughness of the quenched and hardened layer 11 are further improved.

[0219] In the quenched and hardened layer 11 of the inner ring 10, when multiple cementite grains are divided into groups 5 and 6, the average grain size of the cementite grains belonging to group 5, which has a relatively larger grain size, is less than 1.4 μm. Furthermore, in the quenched and hardened layer 11 of the inner ring 10, when multiple cementite grains are divided into groups 7 and 8, the average grain size of the cementite grains belonging to group 7, which has a relatively larger grain size, is less than 1.10 μm. As the average grain size of the cementite grains decreases and becomes more refined, the martensite grains also become more refined, thus improving the toughness of the quenched and hardened layer 11. That is, even in the inner ring 10, the toughness of the quenched and hardened layer 11 is improved because the cementite grains belonging to group 5 (group 7), which have relatively larger grain sizes, are refined.

[0220] In the quenched and hardened layer 11 of the inner ring 10, when multiple cementite grains are divided into group 5 and group 6, the number density of cementite grains belonging to group 5, which has a relatively larger grain size, is 0.04 grains / μm. 2 That's all. Furthermore, in the quenched and hardened layer 11 of the inner ring 10, when multiple cementite grains are divided into groups 7 and 8, the number density of cementite grains belonging to group 7, which has a relatively larger grain size, is 0.06 grains / μm. 2 That's all. If the cementite particles are dispersed at a high density as described above, the wear resistance is improved due to the increased shear resistance on the surface.

[0221] In the method for manufacturing the bearing component according to the embodiment, in the step of tempering the formed body after one quenching, the tempering temperature is 200°C or higher and lower than the Al phase transformation point. Evaluation results described later confirm that when the tempering temperature is 200°C or higher, compared to when the tempering temperature is less than 200°C, the maximum grain size of the martensite grains in the quenched hardened layer 11 is smaller, and the ratio of the maximum aspect ratio of the martensite grains to the minimum value of the {011} plane crystal orientation density of the martensite grains is lower. Furthermore, it confirms that when the tempering temperature is 200°C or higher, compared to when the tempering temperature is less than 200°C, the ratio of the maximum grain size of the martensite grains, the maximum aspect ratio of the martensite grains, and the ratio of the maximum to minimum value of the {011} plane crystal orientation density of the martensite grains in the quenched hardened layer 11 is within the aforementioned numerical range. Furthermore, it was confirmed that when the primary tempering temperature is above 200°C, the resistance to indentation formation is higher compared to when the primary tempering temperature is below 200°C.

[0222] (Example)

[0223] The following describes the tests conducted to confirm the effectiveness of the bearing component in Embodiment 2.

[0224] <Sample>

[0225] This test was conducted using samples 11 to 14, machined into the shape of the outer ring of a rolling bearing. The steel used for samples 11 to 14 was SUJ2. Samples 11 to 14 were all manufactured according to… Figure 13 The flowchart shown illustrates the preparation process, from preparation step S1 to secondary tempering step S6, with only the tempering temperature differing between the two. In sample 11, the primary tempering temperature is 180°C. In sample 12, the primary tempering temperature is 200°C. In sample 13, the primary tempering temperature is 250°C. In sample 14, the primary tempering temperature is 400°C. Furthermore, other manufacturing conditions are the same for samples 11 to 14, as follows: the first temperature of carburizing and nitriding step S2 is 850°C, the second temperature of primary quenching step S3 is 830°C, the fourth temperature of secondary quenching step S5 is 810°C, and the secondary tempering temperature of secondary tempering step S6 is 180°C. Additionally, the first time for the aforementioned primary tempering step S4 is 2 hours.

[0226] Samples 11 to 14 were evaluated as follows.

[0227] <Maximum grain size of martensite>

[0228] For samples 11 to 14, the maximum grain size of the martensite grains was determined using the method described above. Figures 15-18The images shown are EBSD images of each orbital plane of samples 11 to 14.

[0229] The maximum martensite grain size of sample 11 is 3.5 μm. In contrast, the maximum martensite grain size of sample 12 is 2.6 μm, that of sample 13 is 3.3 μm, and that of sample 14 is 3.1 μm. These results confirm that, compared to sample 11, which has a primary tempering temperature below 200 °C, samples 12–14, with primary tempering temperatures above 200 °C, exhibit a refinement of the martensite grains.

[0230] <Maximum aspect ratio of martensite grains>

[0231] For samples 11 to 14, the maximum aspect ratio of the martensite grains was calculated using the method described above. The maximum aspect ratio of the martensite grains in sample 11 was 12.5. In contrast, the maximum aspect ratio of the martensite grains in samples 12 and 13 was 9.1, and the maximum aspect ratio of the martensite grains in sample 14 was 10.0.

[0232] Based on these results, it can be confirmed that in samples 12-14 with a first tempering temperature above 200℃, the martensite grains are spheroidized compared with sample 11 with a first tempering temperature below 200℃.

[0233] <The ratio of the maximum to the minimum crystal orientation density of the {011} plane of martensite grains>

[0234] For samples 11 to 14, the ratio of the maximum to the minimum crystal orientation density of the {011} plane of the martensite grains was calculated using the method described above. The calculation results are shown in Table 5. As shown in Table 5, the ratio for sample 11 is 5.3. In contrast, the ratio for sample 12 is 3.6, for sample 13 it is 3.5, and for sample 14 it is 4.1.

[0235] [Table 5]

[0236]

[0237] Based on these results, it can be confirmed that, compared with sample 11, which has a first tempering temperature of less than 200℃, the crystal orientation of each martensite grain is homogenized in samples 12-14 with a first tempering temperature above 200℃.

[0238] <Average grain size of martensite grains belonging to Group 1>

[0239] For samples 11 to 14, the average grain size of the martensite grains belonging to group 1 and group 3 was calculated using the method described above. Figure 19 The calculation results are shown below. The average grain size of the martensite grains belonging to Group 1 of Sample 11 is 1.12 μm, and the average grain size of the martensite grains belonging to Group 3 of Sample 11 is 0.83 μm.

[0240] In contrast, the average grain size of the martensite grains belonging to Group 1 of Samples 12–14 is less than 1.10 μm, and the average grain size of the martensite grains belonging to Group 1 of Samples 12 and 13 is less than 1.00 μm. The average grain size of the martensite grains belonging to Group 1 of Sample 12 is 0.95 μm. The average grain size of the martensite grains belonging to Group 3 of Samples 12–14 is less than 0.80 μm, and the average grain size of the martensite grains belonging to Group 3 of Samples 13 and 14 is 0.77 μm. The average grain size of the martensite grains belonging to Group 3 of Sample 12 is 0.74 μm.

[0241] Based on these results, it can be confirmed that, compared with sample 11, which has a first tempering temperature of less than 200℃, the martensite grains in samples 12-14 with a first tempering temperature above 200℃ are miniaturized.

[0242] <Average aspect ratio of martensite grains>

[0243] For samples 11 to 14, the average aspect ratios of the martensite grains belonging to Group 1 and Group 3 were calculated using the method described above. Figure 20 The evaluation results are shown below. The average aspect ratio of the martensite grains belonging to Group 1 of Sample 11 is 3.23. In contrast, the average aspect ratio of the martensite grains belonging to Group 1 of Sample 12 is 2.86, the average aspect ratio of the martensite grains belonging to Group 1 of Sample 13 is 2.82, and the average aspect ratio of the martensite grains belonging to Group 1 of Sample 14 is 3.09.

[0244] Furthermore, the average aspect ratio of the martensite grains belonging to group 3 of sample 11 is 3.09. In contrast, the average aspect ratio of the martensite grains belonging to group 3 of sample 12 is 2.73, the average aspect ratio of the martensite grains belonging to group 1 of sample 13 is 2.70, and the average aspect ratio of the martensite grains belonging to group 1 of sample 14 is 2.95.

[0245] Based on these results, it can be confirmed that among samples 12 to 14 with a primary tempering temperature above 200°C, compared with sample 11 with a primary tempering temperature below 200°C, the martensite grains belonging to the first genus (third genus) with relatively larger grain size among the multiple martensite grains have become spheroidized.

[0246] <Average particle size of cementite>

[0247] For samples 11 to 14, the average particle size of the cementite particles belonging to group 5 and group 7 was determined by the above method. Figure 21 The calculation results are shown below. The average particle size of the cementite particles belonging to group 5 of sample 11 is 1.35 μm, and the average particle size of the cementite particles belonging to group 7 of sample 11 is 0.95 μm.

[0248] In contrast, the average particle size of the cementite particles belonging to Group 5 in Samples 12–14 is less than 1.32 μm, and the average particle size of the cementite particles belonging to Group 5 in Samples 12 and 13 is less than 1.20 μm. The average particle size of the cementite particles belonging to Group 5 in Sample 13 is 1.15 μm.

[0249] The average particle size of the cementite particles belonging to group 7 of samples 12–14 is below 0.93 μm, and the average particle size of the cementite particles belonging to group 7 of sample 12 is 0.93 μm. The average particle size of the cementite particles belonging to group 7 of sample 13 is 0.57 μm.

[0250] Based on these results, it can be confirmed that among samples 12-13 with a primary tempering temperature above 200℃ and below 400℃, compared with sample 11 with a primary tempering temperature below 200℃, the cementite particles belonging to the 5th group (7th group) with relatively large particle size among the multiple cementite particles have been miniaturized.

[0251] <Number density of cementite particles>

[0252] For samples 11 to 14, the number densities of cementite particles belonging to group 5 and group 7 were determined using the method described above. Figure 22 The calculation results are shown below. The number density of cementite particles belonging to group 5 of sample 11 is 0.03 particles / μm. 2 The number density of cementite particles belonging to group 7 of sample 11 is 0.07 particles / μm. 2 .

[0253] In contrast, the number density of cementite particles belonging to group 5 of samples 12–14 is 0.05 particles / μm. 2 In samples 12 and 13, the number density of cementite particles belonging to group 5 was 0.07 particles / μm. 2 above.

[0254] The number density of cementite particles belonging to group 7 of samples 12–14 is 0.08 particles / μm. 2 The number density of cementite particles belonging to group 7 of samples 12 and 13 is 0.10 particles / μm. 2 The average particle size of the cementite particles belonging to group 7 of sample 13 is 0.29 particles / μm.2 .

[0255] Based on these results, it can be confirmed that, compared with sample 11, which has a primary tempering temperature of less than 200°C, samples 12-14 with a primary tempering temperature of more than 200°C have high-density dispersion of the cementite particles belonging to the 5th group (7th group) with relatively larger particle size among the multiple cementite particles.

[0256] <Average nitrogen concentration of quenched hardened layer>

[0257] For samples 11 to 14, the average nitrogen concentration of the quenched hardened layer from the track surface to a position 10 μm away was determined using the method described above. The average nitrogen concentration of samples 11 to 14 was 0.10% by mass or more. The average nitrogen concentration of samples 11, 12, and 14 was 0.13% by mass or more.

[0258] <Residual austenite mass of the orbital plane>

[0259] For samples 11 to 14, the amount of retained austenite γ on the orbital surfaces was determined using the method described above. The amount of retained austenite γ on each orbital surface of samples 11 to 14 was greater than 20% by volume. The amount of retained austenite γ on each orbital surface of samples 13 and 14 was 24% by volume.

[0260] <Rail surface hardness>

[0261] For samples 11 to 14, the hardness of the track surface was determined using the method described above. The hardness of each track surface in samples 11 to 14 is above 700 HV. The hardness of each track surface in samples 11 to 14 is above 780 HV. The hardness of each track surface in samples 12 and 13 is harder than that of the track surface in sample 11. The hardness of each track surface in samples 12 and 13 is above 790 HV.

[0262] <Average grain size of the original austenite grains on the orbital plane>

[0263] For samples 11 to 14, the original austenite grains on the orbital surface were determined using the method described above. The average grain size of the original austenite grains in sample 11 was 3.8 μm. In contrast, the average grain size of the original austenite grains in sample 12 was 3.4 μm, in sample 13 it was 3.5 μm, and in sample 14 it was 3.4 μm.

[0264] These results confirm that, compared to sample 11, which had a first tempering temperature below 200℃, the original austenite grains on the orbital surface of samples 12-14, with a first tempering temperature above 200℃, were refined. In other words, compared to sample 11, the austenite crystals present in the steel heated to the quenching temperature during the two quenching processes and just before quenching in samples 12-14 were refined.

[0265] <Residual compressive stress on the track surface>

[0266] For samples 11 to 14, the compressive residual stress of the track surface was measured using the method described above. The compressive residual stress of each track surface in samples 11 to 14 is above 100 MPa. The compressive residual stress of each track surface in samples 13 and 14 is above 130 MPa. The compressive residual stress of the track surface in sample 13 is above 140 MPa.

[0267] Based on the above evaluation results, it can be confirmed that in samples 12-14, compared with sample 11, the fine martensite grains are formed more uniformly, and the fine cementite grains are dispersed at a high density. Therefore, it can be said that the shear resistance of each quenched and hardened layer in samples 12-14 is higher than that in the quenched and hardened layer of sample 11. It is believed that higher shear resistance leads to surface activation with the accompanying temperature increase during shearing, resulting in the adsorption of a large amount of gas on the surface. Therefore, it is assumed that when shear stress acts parallel to the track surface within each quenched and hardened layer, the wear resistance of each track surface in samples 12-14 is improved compared to sample 11 due to the activation of the track surface with the accompanying temperature increase during shearing.

[0268] <Indentation resistance of track surface>

[0269] The indentation resistance of each track surface of samples 11 to 14 was evaluated as follows. First, indentations were formed by pressing a 3 / 8-inch diameter silicon nitride ceramic ball onto each track surface of samples 11 to 14 with the maximum indentation load for 120 seconds, followed by unloading. Three different maximum indentation loads were used. That is, three indentations were formed on the track surface of each sample. Second, the depth of each indentation was measured, and the relationship between the maximum contact surface pressure and the indentation depth was determined. Furthermore, the maximum contact surface pressure was calculated by dividing the maximum indentation load by the projected area of ​​each indentation (the contact area between the track surface and the ceramic ball). Figure 23 The evaluation results are shown below.

[0270] The depth of each indentation in samples 12 and 13 is shallower than the depth of each indentation in samples 11 and 14. That is, the track surface of samples 12 and 13 has higher resistance to indentation formation than that of samples 11 and 14. The indentation depth of sample 14 is the same as that of sample 11.

[0271] Based on the above evaluation results, it can be confirmed that, compared with sample 11, the surface damage resistance and toughness of each track surface in samples 12 to 14 are improved.

[0272] The embodiments of the present invention have been described above, but various modifications can be made to these embodiments. Furthermore, the scope of the present invention is not limited to the above embodiments. The scope of the present invention is defined by the claims and is intended to include all equivalents of the claims and all modifications within that scope.

[0273] The above-described embodiments are particularly advantageously applicable to bearing components and rolling bearings using them.

[0274] 10 Inner ring, 10a Upper surface, 10b Bottom surface, 10c Inner peripheral surface, 10d Outer peripheral surface, 10e Central shaft, 11 Quenched and hardened layer, S1 Preparation process, S2 Carburizing and nitriding process, S3 First tempering process, S4 Quenching process, S5 Second tempering process, S6 Post-treatment process.

Claims

1. A bearing component, It is a bearing component made of steel with a hardened surface layer, wherein, The quenched and hardened layer contains multiple martensitic grains. The total area ratio of martensite grains in the quenched and hardened layer is above 70%. The martensite grains were divided into Group 1 and Group 2. The minimum grain size of the martensite grains belonging to Group 1 is greater than the maximum grain size of the martensite grains belonging to Group 2. The value obtained by dividing the total area of ​​the martensite grains belonging to the first group by the total area of ​​the martensite grains is 0.3 or higher. The value obtained by dividing the total area of ​​the martensite grains belonging to the first group (excluding the smallest martensite grain) by the total area of ​​the martensite grains is less than 0.

3. The average grain size of the martensite grains belonging to the first group is less than 1.4 μm. The quenched and hardened layer further comprises multiple cementite particles. The number density of the cementite particles with a particle size of 1 μm or larger is 0.040 particles / μm. 2 above, The average aspect ratio of the martensitic grains belonging to the first group is less than 3.

1.

2. The bearing component as claimed in claim 1, wherein, The quenched and hardened layer contains nitrogen. The average nitrogen concentration of the quenched hardened layer between the surface and a position 10 μm away from the surface is 0.15% by mass or more.

3. The bearing component as claimed in claim 1 or claim 2, wherein, The amount of residual austenite on the surface is above 20% by volume.

4. The bearing component as claimed in claim 1 or claim 2, wherein, The hardness of the quenched and hardened layer on the surface is above 730 Hv.

5. The bearing component as claimed in claim 1 or claim 2, wherein, The steel is SUJ2, a high-carbon chromium bearing steel as specified in the JIS standard.

6. A rolling bearing, It has an outer ring, an inner ring, and rolling elements. At least one of the outer ring, the inner ring, and the rolling element is a bearing component as described in any one of claims 1 to 5.

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