Bearing parts

Abstract

To provide a highly durable bearing component, a method of manufacturing the bearing component, and a rolling bearing equipped with the bearing component.SOLUTION: A bearing component of the present invention is made of steel containing carbon of 0.6 mass% or more and 0.95 mass% or less, and hardness A in an area from a raceway groove surface to depth of 0.2 mm is within a range of 750-880 Hv, and hardness B in an area from the raceway groove surface to depth over 0.2 mm is within a range of 633-832 Hv. A residual austenite amount C in the raceway groove surface is 20 volume% or less, and a total average residual austenite amount D is 8 volume% or less.SELECTED DRAWING: None

Description

【Technical Field】 【0001】 The present invention relates to bearing parts, a method for manufacturing the same, and a rolling bearing. 【Background Art】 【0002】 Conventionally, a rolling bearing has been used as a member for rotatably supporting a rotating shaft. A rolling bearing is required to have high dimensional stability, wear resistance, and fatigue strength under high loads. In order to meet these requirements, the bearing parts used in rolling bearings are heat-treated, and various studies have been made on the methods and conditions of the heat treatment. In particular, the carbonitriding treatment in which carbon and nitrogen are diffused and infiltrated into steel and then quenched is known to be effective in improving the durability of bearing parts (see, for example, Patent Documents 1 and 2). 【0003】 In recent years, with the further increase in load and temperature in the use environment of rolling bearings, characteristics that can be used under larger load conditions and at higher temperatures (long life under high loads, high dimensional stability under high temperatures, etc.) are required. Therefore, bearing parts having even higher durability are desired. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2007-277648 【Patent Document 2】 Japanese Patent Application Laid-Open No. 2008-267402 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 An example of the problem of the present invention is to provide bearing parts having high durability, a method for manufacturing the same, and a rolling bearing including the bearing parts. 【Means for Solving the Problems】 【0006】 The above problems can be solved, for example, by the following embodiment of the present invention. That is, one embodiment of the present invention is a bearing component made of steel containing 0.6% by mass or more and 0.95% by mass or less of carbon, wherein the hardness A in the region from the surface of the raceway groove to a depth of 0.2 mm is in the range of 750 to 880 Hv, the hardness B in the region beyond a depth of 0.2 mm from the surface of the raceway groove is in the range of 633 to 832 Hv, the amount of retained austenite C on the surface of the raceway groove is 20 volume% or less, and the overall average amount of retained austenite D is 8 volume% or less. [Brief explanation of the drawing] 【0007】 [Figure 1] This is a cross-sectional view of a rolling bearing according to an embodiment of the present invention, showing a plane cross-section including the shaft. [Figure 2] This is a schematic plan view showing a ring-shaped bearing component that is the subject of hardness and retained austenite content measurement. [Figure 3] This is a schematic cross-sectional view of a ring-shaped bearing component, which is the subject of hardness and retained austenite content measurement, when cut in the axial direction, and corresponds to the AA cross-sectional view in Figure 2. [Figure 4] This is a schematic enlarged view of region B in Figure 3. [Figure 5] This is an explanatory diagram showing the process of measuring the amount of retained austenite on the surface of the raceway groove. [Figure 6] This is an explanatory diagram showing the measurement of the overall average amount of residual austenite in bearing components. [Figure 7] This is an explanatory diagram showing a cross-section for measuring the overall average amount of residual austenite in a bearing component. [Figure 8] This is a schematic cross-sectional view of a ring-shaped bearing component, which is the object of nitrogen concentration measurement, when it is cut in the axial direction, and corresponds to cross-sectional view AA in Figure 2. [Figure 9] This graph shows the results of the durability evaluation test for the bearing component in Example 6. [Modes for carrying out the invention] 【0008】 The following describes bearing components, their manufacturing methods, and rolling bearings according to embodiments of the present invention. For the sake of explanation, the rolling bearings, bearing components, and the manufacturing methods of bearing components will be described in that order. 【0009】 [Rolling bearings] Figure 1 is a cross-sectional view of a rolling bearing (ball bearing) 10 according to an embodiment of the present invention, including the axis. The rolling bearing 10 has a basic structure similar to that of a conventional rolling bearing, and comprises an annular inner ring 11, an annular outer ring 12, a plurality of rolling elements (balls) 13, a cage (retainer) 14, and annular sealing members 15a, 15b. 【0010】 The inner ring 11 is a cylindrical structure installed coaxially with the central axis (rotation axis) x of the shaft. The outer ring 12 is a cylindrical structure arranged coaxially with the inner ring 11 on the outer circumference side of the inner ring 11. Each of the multiple rolling elements 13 is a sphere (ball) placed in a raceway within the bearing space (annular space) 16 formed between the inner ring 11 and the outer ring 12. In other words, the rolling bearing 10 in this embodiment is a ball bearing. 【0011】 A lubricant G, such as a grease composition, is sealed within the bearing space 16. The lubricant G acts to reduce friction between the rolling elements 13 and the cage 14, and between the rolling elements 13 and the inner ring 11 or outer ring 12. The annular sealing members 15a and 15b are formed, for example, from steel plates and protrude from the inner circumferential surface of the outer ring 12 toward the inner ring 11, isolating the bearing space 16, which forms the raceway, from the outside. 【0012】 On the inner circumferential surface of the outer ring 12, a recess 12a with an arc-shaped cross-section is formed in the circumferential direction of the outer ring 12. Similarly, on the outer circumferential surface of the inner ring 11, a recess 11a with an arc-shaped cross-section is formed in the circumferential direction of the inner ring 11. The multiple rolling elements 13 are guided in the circumferential direction by the groove-shaped recesses 11a and 12a. 【0013】 The concave portion 12a constitutes the raceway groove of the outer ring 12, which is a bearing component of the rolling bearing 10. Hereinafter, this concave portion 12a is referred to as the outer ring raceway groove 12a. Further, the concave portion 11a constitutes the raceway groove of the inner ring 11, which is a bearing component of the rolling bearing 10. Hereinafter, this concave portion 11a is referred to as the inner ring raceway groove 11a. Note that the "raceway groove" is a member or part having many names such as "bearing groove" and "rolling groove". 【0014】 The cage 14 is disposed in the raceway and holds a plurality of rolling elements 13. The cage 14 is an annular body installed coaxially with the central axis x of the shaft, and has a plurality of concave portions for holding the rolling elements 13 on one side in the direction of the central axis, and has a structure in which the rolling elements 13 are accommodated in each concave portion. Note that the shape (such as crown shape or corrugated shape) and material (such as made of steel plate or resin) of the cage 14 are arbitrary and are not limited to specific shapes and materials. 【0015】 In the rolling bearing 10 having the above configuration, either one or both of the outer ring 12 and the inner ring 11, which are bearing components, correspond to the bearing components according to the present embodiment described below. It is preferable that both the outer ring 12 and the inner ring 11 correspond to the bearing components according to the present embodiment. 【0016】 Also, for bearing components other than the outer ring 12 and the inner ring 11 (rolling elements 13, cage 14, annular seal members 15a, 15b, etc.), those satisfying the same conditions as the following present embodiment may be used. Note that for the rolling elements 13, high durability may be achieved by using ceramics such as ZrO2, SiC, and Si3N4. 【0017】 [Bearing Component] The bearing component according to the present embodiment satisfies the following conditions, which are the findings obtained as a result of the intensive research by the inventors. (a) Carbon Content It is made of steel containing 0.6% by mass or more and 0.95% by mass or less of carbon. 【0018】 (b) Hardness The hardness of the area from the surface of the raceway groove (inner raceway groove 11a or outer raceway groove 12a) to a depth of 0.2 mm is in the range of 750 to 880 Hv, and the hardness of the area beyond a depth of 0.2 mm from the surface of the raceway groove is in the range of 633 to 832 Hv. 【0019】 (c) Amount of retained austenite (amount of retained gamma) The amount of retained austenite on the surface of the raceway groove (inner raceway groove 11a or outer raceway groove 12a) is 20 volume% or less, and the overall average amount of retained austenite is 8 volume% or less. 【0020】 Furthermore, for the bearing components according to this embodiment, it is desirable that the nitrogen concentration also satisfies the following conditions. (d) Nitrogen concentration The nitrogen concentration at a depth of 0.08 mm from the surface is in the range of approximately 0.2 to 0.8 mass%. Each of the above conditions (a) to (d) will be explained in detail. 【0021】 <(a) Carbon content> The carbon content of the steel used significantly affects the hardness and carbide content of the bearing components after quenching. Higher carbon content makes it easier to obtain high-hardness bearing components. However, from the viewpoint of manufacturing costs, it is desirable to keep the carbon content within a range that can be formed by cold forging. Therefore, in this embodiment, the carbon content range that can be cold forged is set to 0.6% by mass or more and 0.95% by mass or less. 【0022】 If the carbon content of the steel used is less than 0.6% by mass, it becomes difficult to secure sufficient carbide content in the bearing components after quenching and hardening, making it difficult to achieve sufficient hardness. On the other hand, if the carbon content of the steel used exceeds 0.95% by mass, it becomes difficult to form the components by cold forging, forcing a large portion to be formed by machining, which raises concerns about increased costs. 【0023】 The chemical composition of the steel used, other than iron (Fe) and carbon (C), is as follows, for example: ·Si…0.5% by mass or less ·Mn…1% by mass or less ·Cr…1~2% by mass ·P…0.1% by mass or less ·S…0.1% by mass or less 【0024】 The chemical composition is not limited to those listed above. Other elements, such as Mo, Ni, V, B, Al, N, etc., may be added to the constituent elements depending on the purpose. Furthermore, the presence of various common impurities is also acceptable. 【0025】 <(b) Hardness> The surface of the raceway groove (inner ring raceway groove 11a or outer ring raceway groove 12a) is a part that comes into contact with the rolling element 13 and is subjected to mechanical load, so high hardness is desirable. In particular, high hardness is desired in the region from the surface to a depth of 0.2 mm in order to ensure mechanical strength against contact with the rolling element 13. 【0026】 However, if the surface hardness is made too high, a large amount of nitride will precipitate on the raceway groove surface, resulting in poor durability as a bearing component. Therefore, in this embodiment, the hardness of the region from the raceway groove surface to a depth of 0.2 mm (hereinafter referred to as "surface hardness A") is set to be in the range of 750 to 880 Hv. Preferably, surface hardness A is in the range of 800 to 880 Hv. 【0027】 On the other hand, if we try to achieve high hardness not only on the surface but also in a wider area at deeper depths, the cost will increase. Therefore, in this embodiment, the hardness in the area beyond 0.2 mm in depth from the surface of the raceway groove (hereinafter referred to as "deep hardness B") is set to be in the range of 633 to 832 Hv. 【0028】 In addition, "hardness" in surface hardness A and depth hardness B refers to Vickers hardness as defined in Japanese Industrial Standard JIS Z2244, and the test force (load) F was set to 4.903 N. The method for measuring the hardness (surface hardness A and deep hardness B) in a region at a predetermined depth from the surface of the raceway groove will be described later. 【0029】 <(c) Amount of retained austenite (amount of retained gamma)> Since retained austenite after heat treatment can cause age deformation, it is preferable to have less of it from the standpoint of dimensional stability. Therefore, in this embodiment, the average amount of retained austenite in the entire bearing component (hereinafter referred to as "average retained γ amount D") is set to 8 volume% or less. 【0030】 On the other hand, from the standpoint of fatigue life, it is known that a larger amount of retained austenite improves the fatigue life of the rolling groove when the raceway grooves 11a and 12a are subjected to repeated fatigue. In this respect, it is desirable that some amount of retained austenite remains on the groove surface. Therefore, in this embodiment, the amount of retained austenite on the raceway groove surface (hereinafter referred to as "surface retained γ amount C") is set to 20 volume% or less. 【0031】 As mentioned above, from the standpoint of dimensional stability, it is desirable to minimize the amount of retained austenite. However, from the standpoint of fatigue life, leaving a small amount of retained austenite can improve the fatigue life of the rolling groove. 【0032】 Therefore, in this embodiment, the surface residual γ amount C is preferably 10 volume% or more, and more preferably 10 volume% to 20 volume%. Furthermore, in this embodiment, the average residual γ amount D is preferably 2 volume% or more, and more preferably 2 volume% to 8 volume%. 【0033】 <(d) Nitrogen concentration> The nitrogen concentration at a depth of 0.08 mm from the surface is preferably in the range of approximately 0.2 to 0.8 mass%, and more preferably in the range of approximately 0.3 to 0.7 mass%. If the nitrogen concentration near the surface is too low, it becomes difficult to secure the surface hardness that contributes to improved durability. On the other hand, if the nitrogen concentration near the surface is too high, a large amount of nitride will precipitate near the surface, raising concerns that the bearing component will have poor durability. Note that (d) the nitrogen concentration only needs to be within the above preferred concentration range as long as the average value of the measured nitrogen concentration at a depth of 0.08 mm from the surface is within the above preferred concentration range, and it is acceptable for there to be measured values ​​outside the above preferred concentration range within the measurement range from the surface to 0.08 mm. 【0034】 <(b) Method for measuring hardness, (c) amount of retained austenite, and (d) nitrogen concentration> Examples of methods for measuring (b) hardness, (c) retained austenite content, and (d) nitrogen concentration in this embodiment will be described with reference to the drawings. (b) Measurement of hardness Figures 2 to 4 are explanatory diagrams illustrating an example of (b) a hardness measurement method in this embodiment. 【0035】 More specifically, Figure 2 is a schematic plan view illustrating the ring-shaped bearing component that is the subject of measurement for (b) hardness and (c) retained austenite content, and Figure 3 is a schematic cross-sectional view of the ring-shaped bearing component cut in the axial direction. Figure 3 corresponds to the AA cross-sectional view in Figure 2. Since Figures 2 and 3 show both the inner ring 11 and the outer ring 12, the contours are not accurate and are merely schematic diagrams. Furthermore, Figure 4 is a partially enlarged view of Figure 3, schematically enlarging area B in Figure 3. However, the dimensional balance of each component is not consistent in Figure 4, and Figure 4 is also merely a schematic diagram. 【0036】 As shown in Figure 2, the inner ring 11 or outer ring 12 (hereinafter referred to as "bearing parts 11, 12") is first cut along a plane containing the central axis x (dashed line C in the figure) to obtain a cross-section c. Figure 3 shows the cross-section c of the obtained bearing parts 11, 12, including the inner ring raceway groove 11a or outer ring raceway groove 12a (hereinafter referred to as "raceway grooves 11a, 12a"). 【0037】 In measuring hardness, as shown in Figure 3, the center b in the width direction of the raceway grooves 11a and 12a is considered the "surface" of the object to be measured, and the measurement target in the depth direction is along the center line O passing through the center b of the raceway grooves 11a and 12a. In practice, as shown in Figure 4, the first measurement point is set at a position 50 μm from the center b in the depth direction (direction of arrow d), and the second measurement point is set at a position 50 μm further in the depth direction (direction of arrow d) and shifted 100 μm from the center line O. Further in the depth direction (direction of arrow d), at 50 μm intervals, odd-numbered measurement points are set on the center line O, and even-numbered measurement points are set at positions shifted 100 μm from the center line O. 【0038】 The hardness was measured at a total of 18 points down to a depth of 0.9 mm. The four points from the center b of the raceway grooves 11a and 12a to the fourth point at a depth of 0.2 mm were defined as the "region from the raceway groove surface to a depth of 0.2 mm" and were used as measurement points for surface hardness A. In addition, the 14 points from the fifth point beyond 0.2 mm from the center b of the raceway grooves 11a and 12a to the last point (the 18th point) were defined as the "region from the raceway groove surface to a depth of 0.2 mm" and were used as measurement points for deep hardness B. 【0039】 Vickers hardness was measured using the number of measurement points for surface hardness A and depth hardness B, respectively, as the n-number for each hardness measurement (n=4 and n=14). A commercially available Vickers hardness tester or micro-Vickers hardness tester was used for hardness measurement, with a test force (load) F of 4.903 N, and other specifications conforming to the Japanese Industrial Standard JIS Z2244. 【0040】 (c) Measurement of the amount of retained austenite Figures 5 to 7 are explanatory diagrams illustrating an example of the method for measuring (c) the amount of retained austenite in this embodiment. 【0041】 First, Figure 5 is an explanatory diagram showing the measurement of the amount of retained austenite (surface retained γ amount C) on the surface of the raceway groove, and shows the DD cross-section of the bearing components 11 and 12 in Figure 2. As shown in Figure 5, the collimator 21 of the measuring device is set on the center line O, and the amount of retained austenite is measured toward the center b in the width direction of the raceway grooves 11a and 12a. As shown in Figure 5, the measurement area is a narrow area (area E in Figure 5) centered on the center b in the width direction of the raceway grooves 11a and 12a, within the range of the diameter (1 mm) of the collimator 21. 【0042】 The amount of retained austenite can be measured by using an X-ray diffraction retained austenite analyzer to measure the surface of the raceway grooves 11a and 12a, thereby determining the amount of retained gamma (γ) C. 【0043】 Figure 6 is an explanatory diagram showing the measurement of the average residual austenite content (average residual γ content D) of the bearing components. As shown in Figure 6, in order to measure the average residual γ content D, a test piece TP was prepared by embedding fragments 11' and 12' of bearing components 11 and 12 in resin 22 so that the cross-section c of the plane containing the central axis x (see Figures 2 and 3) was exposed on the surface. 【0044】 The average amount of retained austenite (average retained γ amount D) of the entire bearing component was measured using the same measuring device as used for measuring the surface of the raceway groove, on the cross-section c that appeared on the surface of this test piece TP. 【0045】 Figure 7 is an explanatory diagram showing the cross-section c used to measure the average residual γ amount D. For bearing components 11 and 12, the DD cross-section is shown in Figure 2, similar to Figure 5. As shown in Figure 7, the measurement area is measured along the center line O passing through the center b in the width direction of the raceway grooves 11a and 12a, such that the range of the collimator 21 diameter (3 mm) covers the entire area of ​​bearing components 11 and 12 (area F in Figure 7). 【0046】 (d) Measurement of nitrogen concentration Figure 8 is an explanatory diagram illustrating an example of the method for measuring nitrogen concentration (d) in this embodiment. More specifically, it is a schematic cross-sectional view of a ring-shaped bearing component, which is the object of measurement for nitrogen concentration (d), when it is cut in the axial direction. Figure 8 corresponds to the AA cross-sectional view in Figure 2, and, like Figure 3, the contour is not precise and is merely a schematic diagram. 【0047】 (d) In measuring the nitrogen concentration, similar to (b) measuring the hardness, the bearing components 11 and 12 (inner ring 11 or outer ring 12) are cut along a plane containing the central axis x (dashed line C in the figure) to obtain a cross-section c, as shown in Figure 2. Figure 8 shows the obtained cross-section c of the bearing components 11 and 12, including the raceway grooves 11a and 12a. 【0048】 As shown in Figure 8, the widthwise center b of the raceway grooves 11a and 12a was defined as the "surface" of the measurement target, and the line segment L on the center line O passing through the center b of the raceway grooves 11a and 12a was defined as the measurement target in the depth direction. To measure the nitrogen concentration at a depth of 0.08 mm from the surface, an EPMA (electron beam microanalyzer) was used to perform a line analysis in the depth direction along the line segment L shown in Figure 8 on the cross-sections of the raceway grooves 11a and 12a of the inner ring 11 and outer ring 12. 【0049】 In this embodiment, as an example of the conditions for measuring (d) nitrogen concentration, the nitrogen concentration was measured with an acceleration voltage of 15kV, an irradiation current of 100nA, a beam diameter of 10μm, and a step interval of 10μm. Of the measurement data, the ninth analysis point from the surface of the track grooves 11a and 12a (the boundary position between the embedded resin and the metal) corresponds to a position of 0.08mm in the depth direction (direction of arrow d) from the center b, so the values ​​of these nine points were taken as the measurement results for (d) nitrogen concentration. 【0050】 [Manufacturing method for bearing components] The manufacturing method for bearing components according to this embodiment includes two types, manufacturing method A and manufacturing method B, and both include one of the following steps, which are the result of diligent research conducted by the inventors. By going through the operations of either manufacturing method A or manufacturing method B according to this embodiment, as shown below, the bearing components according to this embodiment described above can be manufactured. 【0051】 (Manufacturing method A) (1) Carburizing and nitriding process: This is performed at a temperature range of above the A1 transformation point to 900°C. (2) Quenching hardening process: Cool to a temperature below the A1 transformation point. (3) Low-temperature tempering process: This is performed in a temperature range of 90 to 170°C. (4) Sub-zero treatment process: This is performed in a temperature range of 0°C or lower. (5) Tempering process: This is performed at a temperature range of 160 to 240°C. 【0052】 (Manufacturing method B) (1) Carburizing and nitriding process: This is performed at a temperature range of above the A1 transformation point to 900°C. (2) Quenching hardening process: Cool to a temperature below the A1 transformation point. (4) Sub-zero treatment process: This process is performed within 24 hours after the completion of the quenching and hardening process in (2), at a temperature of 0°C or lower. (5) Tempering process: This is performed at a temperature range of 160 to 240°C. 【0053】 Manufacturing method B includes the same steps as manufacturing method A, except that (3) the low-temperature tempering step is omitted and (4) certain conditions are added in the sub-zero treatment step. Therefore, manufacturing methods A and B will be explained together below, noting the differences between them. In the following explanation, each step will be explained in order. 【0054】 <(1) Carburizing and nitriding process> In this embodiment, (1) the carburizing and nitriding process is a process in which carburizing and nitriding are performed in a temperature range of A1 transformation point to 900°C. The A1 transformation point is the temperature at which the transformation from austenite to ferrite + cementite (Fe3C) begins, and regardless of the carbon content of the steel, the A1 transformation point is 727°C in equilibrium. 【0055】 While the order of carburizing and nitriding can be used, our diligent research has revealed that it is preferable to perform nitriding first, followed by carburizing. Although carburizing is generally performed first, performing nitriding first allows for greater nitrogen penetration into the steel surface and to a deeper depth. 【0056】 Generally, nitrogen cannot penetrate very deeply in nitriding, but carbon can penetrate relatively deeply in carburizing. Therefore, it is presumed that performing carburizing after nitriding pushes the nitrogen that has already penetrated the surface into place with the help of carbon. 【0057】 Furthermore, since nitriding can generally be performed at lower temperatures than carburizing, the nitriding treatment is first carried out by raising the temperature to a suitable temperature for allowing a large amount of nitrogen to penetrate (for example, 800°C), and then the carburizing treatment is carried out by raising the temperature to a suitable temperature (for example, 850°C). 【0058】 Carburizing and nitriding treatments may be repeated multiple times, either individually or in combination. In particular, our diligent research has revealed that it is preferable to perform nitriding first, followed by carburizing, and then repeat the nitriding treatment. When nitriding is performed at a relatively low temperature, a large amount of nitrogen can penetrate, but penetration in the depth direction tends to be shallow. On the other hand, when nitriding is performed at a high temperature, nitrogen can penetrate deeper, but the amount of nitrogen that penetrates tends to be small. Therefore, it is presumed that by first performing a nitriding treatment at a relatively low temperature (e.g., 750-800°C) to allow a large amount of nitrogen to penetrate the surface, then raising the temperature (e.g., 830-880°C) and performing carburizing, and then performing a second nitriding treatment at the same temperature, it is possible to penetrate nitrogen in the depth direction. 【0059】 In this process, for example, it is preferable to perform at least a portion of the operation under reduced pressure. Here, "perform under reduced pressure" means reducing the pressure inside the furnace and performing the carburizing and nitriding process under reduced pressure conditions. Furthermore, "at least a portion of the operation" includes the concept of performing only one of the carburizing or nitriding processes under reduced pressure, or performing only a portion of the carburizing or nitriding processes under reduced pressure if they are performed multiple times. 【0060】 Performing carburizing and nitriding treatments under reduced pressure suppresses non-uniformity caused by oxygen penetration into the steel or denitrification, resulting in a uniform treated surface with minimal unevenness. In particular, it is desirable to perform carburizing under reduced pressure. The degree of reduced pressure should be such that it is considered a vacuum in heat treatment technology, specifically, for example, 3000 Pa or less, and preferably around 50 Pa to 2000 Pa. 【0061】 If carburizing and nitriding operations are performed consecutively, the pressure may be reduced at the beginning of each operation and then the operations may be performed continuously without reducing the pressure between operations, or the pressure may be reduced occasionally or each time before performing each operation. However, if nitriding is performed first, the operation of that first nitriding operation may be performed without reducing the pressure. 【0062】 Nitriding is performed by placing the object to be treated (bearing parts) in an atmosphere of a nitrogen-supplied gas at a predetermined temperature for a set period of time. In practice, the object to be treated (bearing parts) is placed in the furnace for the predetermined time while maintaining the temperature inside the furnace by supplying gas at a predetermined flow rate. Ammonia is generally used as the nitrogen-supplied gas. In addition to the nitrogen-supplied gas, other gases such as nitrogen gas may also be included. 【0063】 As previously mentioned, the temperature for the nitriding treatment is within the range of the A1 transformation point and 900°C or less, but the range of 700 to 900°C is particularly preferred. For example, 800°C may be selected for the first nitriding treatment, and 850°C for subsequent nitriding treatments. 【0064】 The duration of the nitriding treatment should be selected from a range of approximately 30 to 270 minutes, regardless of the number of treatments, and preferably within the range of 90 to 240 minutes. Furthermore, when the nitriding treatment is performed in multiple stages, the duration of each stage should be selected from a range of approximately 10 to 90 minutes, and preferably within the range of 30 to 80 minutes. 【0065】 Carburizing is performed by placing the object to be treated (bearing component) in a reduced-pressure atmosphere of a carbon-supplying gas at a predetermined temperature for a certain period of time. Acetylene is particularly preferred as the carbon-supplying gas. 【0066】 As previously mentioned, the carburizing temperature is within the range of A1 transformation point to 900°C, but the range of 750 to 900°C is particularly preferred, and for example, 850°C may be selected. 【0067】 The total processing time for the carburizing treatment, regardless of the number of treatments, should be selected from a range of approximately 20 to 100 minutes, and preferably within the range of 30 to 70 minutes. Furthermore, when the carburizing treatment is performed in multiple stages, the processing time for each stage should be selected from a range of approximately 10 to 50 minutes, and preferably within the range of 15 to 35 minutes. 【0068】 Time may be provided for soaking and diffusion before and after the start of the processing operation in this process, before and after the start and end of the heating operation and the depressurization operation, and between the carburizing and nitriding operations. 【0069】 <(2) Hardening treatment process> In this embodiment, (2) the quenching and hardening process is a process in which the temperature is cooled to below the A1 transformation point after the final operation of (1) the carburizing and nitriding process is completed. In practice, the temperature is cooled to below the A1 transformation point, to the processing temperature for the next process, or to a temperature near it. 【0070】 Cooling methods in the quenching and hardening process include oil cooling, water cooling, and air cooling, and these cooling methods are used individually or in combination. In this embodiment, oil cooling is preferred. Oil cooling is performed by immersing the object to be treated (bearing component) in oil for oil cooling. 【0071】 The oil temperature for oil cooling is selected from a range of approximately 0 to 170°C. Lower oil temperatures result in higher cooling efficiency and greater hardening of the steel surface, but there is a concern that quenching distortion may increase. In practice, the oil temperature should be appropriately selected considering the temperature and size of the object being treated (bearing component) before oil cooling begins, the target cooling temperature and rate, and the capacity of the oil bath. Conventional known oils can be used without any problems for this oil cooling. 【0072】 <(3) Low-temperature tempering process> In manufacturing method A, the operation of step (3) low-temperature tempering is performed. On the other hand, in manufacturing method B, the operation of step (3) low-temperature tempering is omitted. In this embodiment, step (3) low-temperature tempering is a process in which the workpiece (bearing part) is held in a temperature range of 90 to 170°C, which is lower than the processing temperature in general tempering, in order to perform tempering. 【0073】 The operation of (3) low-temperature tempering has the effect of maintaining the state immediately after quenching by (2) hardening. In other words, after the operation of (3) low-temperature tempering, the workpiece (bearing part) stabilizes in the state immediately after quenching by (2) hardening, and the operation can be temporarily interrupted. 【0074】 (3) The period from the completion of the low-temperature tempering process to (4) the start of the sub-zero treatment process (hereinafter referred to as the "standing time") can exceed 24 hours without issue, and good bearing parts can be manufactured even if it exceeds 72 hours. However, if the processed object (bearing part) is left for too long in an incomplete process, it becomes difficult for the desired performance to be achieved, so the standing time is preferably within 120 hours, and more preferably within 72 hours. 【0075】 For example, the operation of the next step, (4) sub-zero treatment step, is preferably carried out in a facility equipped with a dedicated processing device. Even in facilities that do not have such a device, by performing the operations up to (3) low-temperature tempering treatment step, the processing of the unfinished product (bearing part) can be transferred to another facility for processing from (4) sub-zero treatment step onward. 【0076】 Furthermore, even if a facility is equipped with a dedicated processing device for the next step, (4) sub-zero treatment, it is possible to improve work efficiency by performing the operations up to (3) low-temperature tempering treatment together, temporarily storing the unfinished processing targets (bearing parts), and then performing the subsequent processes from (4) sub-zero treatment onwards together at a later date. 【0077】 (3) The processing temperature in the low-temperature tempering process is within the range of 90 to 170°C, as described above, and preferably within the range of 120 to 160°C. 【0078】 Furthermore, (3) the processing time (the time to maintain the processing temperature) in the low-temperature tempering process is selected from a range of approximately 30 to 180 minutes, and is preferably within the range of approximately 60 to 120 minutes. 【0079】 <(4) Subzero treatment process> In this embodiment, (4) the sub-zero treatment step is a step of rapidly cooling the object to be treated (bearing part) to 0°C or below and holding the object to be treated (bearing part) in a temperature range of 0°C or below. By performing the operation of (4) the sub-zero treatment step, the amount of residual austenite in the object to be treated (bearing part) can be suppressed. 【0080】 (1) In the carburizing and nitriding process, the workpiece (bearing part) is heated to austenite, and (2) in the quenching and hardening process, it is cooled to a temperature below the A1 transformation point. When this happens, the austenite in the workpiece (bearing part) is converted to martensite, but some remains as retained austenite. This retained austenite causes age deformation, which transforms into martensite over time, and leads to a decrease in dimensional stability. This retained austenite that has not transformed into martensite will transform into martensite by lowering the temperature. Sub-zero treatment (deep quenching) is a treatment performed to promote this martensite transformation. 【0081】 (4) In manufacturing method A, the sub-zero treatment process is performed immediately following the (3) low-temperature tempering process, and in manufacturing method B, it is performed immediately following the (2) quenching and hardening process. As previously stated, in manufacturing method A, it is acceptable for the period between the completion of the (3) low-temperature tempering process and the start of the (4) sub-zero treatment process to exceed 24 hours. 【0082】 On the other hand, in manufacturing method B, it is desirable to start the (4) sub-zero treatment process within 24 hours after the completion of the (2) quenching and hardening process. The state of the workpiece (bearing part) immediately after the completion of the (2) quenching and hardening process is unstable, and if a long time passes, there is a risk that cracks will occur in the workpiece due to residual stress generated during quenching. 【0083】 (2) The time between the completion of the quenching and hardening process and the start of the sub-zero treatment process is preferably within 24 hours, and more preferably within 2 hours. 【0084】 (4) As previously described, the processing temperature in the sub-zero treatment process is in the temperature range of 0°C or lower, but it is preferably in the temperature range of -120 to -40°C, and more preferably in the temperature range of -80 to -65°C. 【0085】 Furthermore, (4) the processing time (the time to maintain the processing temperature) in the sub-zero processing step is selected from a range of approximately 5 to 120 minutes, and is preferably within a range of approximately 20 to 90 minutes. 【0086】 To rapidly cool the object to be processed (bearing parts) to the target processing temperature, a refrigerant mixture of ethanol and dry ice (for example, adjusted to -72°C) or liquid nitrogen (boiling point at 1013.25 hPa = 1 atmosphere: -196°C) can be used as appropriate. 【0087】 (5) Tempering process In this embodiment, (5) tempering process is a process in which the object to be processed (bearing part), which has been cooled by the operation of (4) sub-zero process, is heated again and held in the temperature range of 160 to 240°C to perform tempering. In this embodiment, the holding temperature in (5) tempering process is generally higher than the holding temperature in (3) low-temperature tempering process, but it is within the range generally considered to be low-temperature tempering (a range of about 150 to 250°C). 【0088】 (4) Since the quenched martensite after the sub-zero treatment process is brittle, tempering is performed. (5) The temperature during the tempering process is in the range of 160 to 240°C as described above, but it is preferably in the range of 190 to 230°C, and more preferably in the range of 190 to 210°C. 【0089】 Furthermore, (5) the processing time (the time to maintain the processing temperature) in the tempering process is selected from a range of approximately 60 to 300 minutes, and is preferably within the range of approximately 120 to 180 minutes. 【0090】 Although preferred embodiments of the bearing component, its manufacturing method, and rolling bearing of the present invention have been described above, the bearing component, its manufacturing method, and rolling bearing of the present invention are not limited to the configurations of the above embodiments. For example, in the above embodiments, a rolling bearing comprising a cage 14 and annular sealing members 15a and 15b was described as an example, but the present invention can be applied to various configurations, such as configurations in which either of these is omitted, configurations in which either or both of these are replaced by other members, or configurations in which other components are added. 【0091】 Furthermore, those skilled in the art may modify the bearing components and their manufacturing methods, as well as the rolling bearings of the present invention, in accordance with prior knowledge. Such modifications, insofar as they still possess the configuration of the present invention, are of course included within the scope of the present invention. [Examples] 【0092】 The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to the following examples. 【0093】 <Preparing bearing components> For the test, the inner ring 11 and outer ring 12 shown in Figure 1 were prepared as test materials (bearing components). These test materials are cold-forged products. The chemical composition of the test materials is the same for both the inner ring 11 and the outer ring 12, as shown in Table 1 below. 【0094】 [Table 1] 【0095】 <Heat treatment> [Example 1] The following procedure was used to perform heat treatment on each test specimen. 【0096】 (1) Carburizing and nitriding process The furnace containing the test material was supplied with nitrogen gas (N2) at a rate of 16.4 liters / min to create a nitrogen atmosphere, and the temperature was raised to 800°C. After soaking for 10 minutes, the temperature was maintained at 800°C for 60 minutes while supplying ammonia gas (NH3) at a rate of 83.4 liters / min to perform the first nitriding treatment (I). 【0097】 After the completion of nitriding treatment (I), the supply of ammonia (NH3) gas was stopped, and the temperature inside the furnace was raised to 850°C. After soaking for 10 minutes, the supply of nitrogen (N2) gas was stopped, and the furnace pressure was reduced to below 50 Pa by vacuum evacuation over 20 minutes. Subsequently, the temperature was maintained at 850°C for 20 minutes while supplying acetylene (C2H2) gas at a rate of 53 liters / pulse, and the first carburizing treatment (I) was performed. 【0098】 After the completion of carburizing treatment (I), the supply gas was switched from acetylene (C2H2) to nitrogen (N2) and ammonia (NH3), and the former was supplied at a rate of 16.4 liters / min and the latter at 50 liters / min while the temperature was maintained at 850°C for 60 minutes to perform the second nitriding treatment (II). 【0099】 After the completion of nitriding treatment (II), the supply of nitrogen (N2) and ammonia (NH3) gases was stopped, and the furnace was evacuated over 40 minutes to reduce the pressure inside the furnace to below 50 Pa. Then, the second carburizing treatment (II) was performed by supplying acetylene (C2H2) gas at a rate of 53 liters / pulse while maintaining the temperature at 850°C for 30 minutes. 【0100】 After the completion of carburizing treatment (II), the supply of acetylene C2H2 gas was stopped and allowed to diffuse for 2 minutes. Then, nitrogen N2 gas and ammonia NH3 gas were supplied at a rate of 16.4 liters / min and 50 liters / min respectively, while the temperature was maintained at 850°C for 45 minutes to perform the third nitriding treatment (III). As described above, the (1) carburizing and nitriding treatment process was carried out. 【0101】 (2) Hardening treatment process (1) After the completion of the carburizing and nitriding treatment process, the test material was immersed in oil for oil cooling, which was heated to 120°C, to perform the (2) quenching and hardening treatment process. 【0102】 (3) Low-temperature tempering process (2) After the completion of the quenching and hardening process, the test material was placed back into the furnace, heated to 150°C, and held at 150°C for 90 minutes to perform the (3) low-temperature tempering process. 【0103】 (4) Subzero treatment process (3) After the low-temperature tempering process was completed, the specimen was removed from the furnace and moved to a facility equipped with a sub-zero treatment device, where it was left at room temperature for 3 days (72 hours, including transport time). After this period, the specimen was cooled to approximately -80°C and held at that temperature for 60 minutes, thereby performing the (4) sub-zero treatment process. 【0104】 (5) Tempering process (4) After the sub-zero treatment process was completed, the test material was placed back into the furnace and heated to 190°C, and held at 190°C for 150 minutes to perform the (5) tempering process. 【0105】 Subsequently, the part was removed from the furnace and allowed to cool completely to room temperature, completing the heat treatment operation according to the manufacturing method of Example 1, and obtaining the bearing part of Example 1. The main operating conditions and details of the processing steps according to the manufacturing method of Example 1 are summarized in Table 2 below. 【0106】 [Example 2] In Example 1, the same operations as in Example 1 were performed up to (2) the quenching and hardening process, but the (3) low-temperature tempering process was omitted. Within two hours of the completion of the (2) quenching and hardening process, the part was immersed in a bath of refrigerant adjusted to approximately -72°C using ethanol and dry ice. After being left for approximately 30 minutes, the same operations as in Example 1 were performed from (4) the sub-zero treatment process onward, thereby completing the heat treatment operation according to the manufacturing method of Example 2 and obtaining the bearing part of Example 2. The main operating conditions and contents of the processing steps according to the manufacturing method of Example 2 are summarized in Table 2 below. 【0107】 [Table 2] 【0108】 [Examples 3-9] Except for changing the operating conditions of each processing step as shown in Table 2 above, the heat treatment operation was performed using the manufacturing methods of Examples 3 to 9 in the same manner as in Example 1, to obtain the bearing parts of Examples 3 to 9. 【0109】 [Comparative Examples 1-6] In Example 1, the same procedure as in Example 1 was followed up to (2) the hardening treatment step, (3) the low-temperature tempering treatment step was omitted and the material was left for 72 hours, and (4) the sub-zero treatment step was performed. At this time, the operating conditions for each treatment step were changed as shown in Table 2 above. Except for the above changes, the heat treatment procedure was carried out using the manufacturing method of Comparative Examples 1 to 6 in the same procedure as in Example 1, and bearing parts of Comparative Examples 1 to 6 were obtained. 【0110】 <Measurement Test> (a) Vickers hardness The surface hardness A and depth hardness B of the bearing components obtained in Examples 1-9 and Comparative Examples 1-6 were measured using the method described above. A micro-Vickers hardness tester was used for the measurements. The evaluation results are summarized in Table 3 below. 【0111】 The evaluation results were determined based on the following criteria. ·Surface hardness A ◎(Excellent): 800Hv or more and 880Hv or less ○ (Good): 750 Hv or higher but less than 800 Hv × (Not good): Less than 750 Hv or more than 880 Hv 【0112】 ·Deep hardness B ◎(Good): 633Hv or more and 832Hv or less × (Not good): Less than 633Hv or more than 832Hv 【0113】 (b) amount of retained austenite For the bearing components obtained in Examples 1-9 and Comparative Examples 1-6, the surface residual γ amount C and the average residual γ amount D were measured using the method described above. An X-ray diffraction retained austenite amount analyzer was used for the measurements. 【0114】 The measurement conditions for the measuring device were as follows: (Measurement conditions for surface residual γ amount C) • Collimator diameter: 1mm Voltage: 25kV ·Current: 1.5mA ·Measurement time: 200sec 【0115】 By measuring using the above method and conditions, the amount of residual γ C on the surface can be measured in the region up to a depth of approximately 0.05 mm from the bearing groove surface. 【0116】 (Measurement conditions for average residual gamma-γ amount D) • Collimator diameter: 3mm Voltage: 25kV ·Current: 1.0mA • Measurement time: 100 seconds The evaluation results are summarized in Table 3 below. 【0117】 The evaluation results were determined based on the following criteria. ·Surface residual γ amount C ◎(Excellent): 10% to 20% by volume ○ (Good): Less than 10% by volume × (Not good): Exceeds 20% by volume 【0118】 ·Average residual γ amount D ◎(Excellent): 2% to 8% by volume ○ (Good): Less than 2% by volume × (Not good): Exceeds 8% by volume 【0119】 [Table 3] 【0120】 <Durability Evaluation Test> The bearing component of Example 6 obtained was subjected to a durability evaluation test as shown below. 【0121】 Specifically, using the inner ring 11 and outer ring 12 obtained as bearing components in Example 6, with nominal number 608 as defined in JIS B1513 "Nominal Numbers for Rolling Bearings", a rolling bearing 10 shown in Figure 1 was manufactured and designated as the rolling bearing of Example 6. The obtained rolling bearing was subjected to a radial load of 1275N and inner ring rotation of 5400 min⁻¹. -1 A durability test was conducted under conditions of 50°C. The results are shown in Figure 9 as a graph. Figure 9 is a graph showing the results of the durability evaluation test of the bearing components of Example 6, with the duration of the durability test (h) on the horizontal axis and the cumulative probability F(t) of fatigue delamination of the outer ring, inner ring, or balls on the vertical axis, both plotted on a logarithmic scale. 【0122】 The results of the durability test showed that the rolling bearing of Example 6, which satisfies the conditions of the present invention, exhibited excellent durability. This is because its surface hardness and retained austenite content met the standards. 【0123】 <Measuring Nitrogen Concentration> The nitrogen concentration of the bearing components obtained from Example 6, Comparative Example 5, and Comparative Example 6 was measured using the method described above. 【0124】 The nitrogen concentration from the surface of the raceway groove to a depth of 0.08 mm was a minimum of 0.26 to a maximum of 0.72 mass% (average 0.45 mass%) for the bearing component of Example 6, a minimum of 0.078 mass% to a maximum of 0.098 mass% (average 0.09 mass%) for the bearing component of Comparative Example 5, and a minimum of 0.37 mass% to a maximum of 0.52 mass% (average 0.42 mass%) for the bearing component of Comparative Example 6. [Explanation of Symbols] 【0125】 10...Rolling bearing (ball bearing), 11...Inner ring, 11′,12′...Fragment, 11a...Recess, inner ring raceway groove (raceway groove), 12...Outer ring, 12a...Recess, outer ring raceway groove (raceway groove), 13...Rolling element, 14...Cage, 15a,15b...Annular sealing member, 16...Bearing space, 21...Collimator, 22...Resin, TP...Test piece

Claims

[Claim 1] It consists of steel containing 0.6% to 0.95% by mass of carbon, 0.5% by mass or less of silicon, 1.0% by mass or less of manganese, and 1.0% to 2.0% by mass of chromium. The hardness A in the region from the surface of the raceway groove to a depth of 0.2 mm is in the range of 750 to 880 Hv, and the hardness B in the region beyond a depth of 0.2 mm from the surface of the raceway groove is in the range of 633 to 832 Hv. The amount of retained austenite C on the surface of the raceway groove is 20 volume% or less, and the overall average amount of retained austenite D is 8 volume% or less. A bearing component in which the amount of retained austenite C on the surface of the raceway groove is 10 volume percent or more, and the overall average amount of retained austenite D is 2 volume percent or more. [Claim 2] The bearing component according to claim 1, wherein the amount of retained austenite C on the surface of the raceway groove is 13.4 volume percent or less.

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