JP2021110032A - Production method of bearing ring of rolling bearing - Google Patents

Abstract

To provide a production method of a bearing ring of a rolling bearing, capable of improving creep resistance on an anti-raceway surface while improving rolling motion fatigue characteristics on a raceway surface.SOLUTION: A production method of a bearing ring of a rolling bearing includes: a step for preparing a metal member to be processed with an annular shape, having a first circumferential surface and a second circumferential surface which is an opposite surface in the radial direction of the first circumferential surface; a quenching step for quenching the member to be processed; and a tempering step for tempering the member to be processed. The quenching step includes: a heating step for heating the member to be processed at a temperature equal to or higher than the A1 transformation point of steel; and a cooling step for cooling the member to be processed at a temperature equal to or lower than the Mf point of steel. The tempering step is performed by heating the second circumferential surface while cooling the first circumferential surface.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method for manufacturing a raceway ring of a rolling bearing.

For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 2017-187104) describes an inner ring of a rolling bearing. The inner ring of Patent Document 1 is made of hardened steel. The inner ring described in Patent Document 1 has an inner layer portion inside the inner ring and a surface layer portion surrounding the entire periphery of the inner layer. The surface layer portion exists not only on the outer peripheral surface side including the raceway surface but also on the inner peripheral surface side (anti-tracking surface side). The amount of retained austenite in the steel in the surface layer portion is larger than the amount of retained austenite in the steel in the inner layer portion.

JP-A-2017-187104

As described above, in the inner ring described in Patent Document 1, since the surface layer portion exists not only on the outer peripheral surface side but also on the inner peripheral surface side, the inner diameter expands due to aging and the fit with the shaft becomes loose. , Creep may occur. Further, in the inner ring described in Patent Document 1, the minimum value of the compressive residual stress on the raceway surface is low, and there is room for improvement in the rolling fatigue characteristics on the raceway surface.

The present invention has been made in view of the above-mentioned problems of the prior art. More specifically, the present invention provides a method for manufacturing a raceway ring of a rolling bearing capable of improving the rolling fatigue characteristics on the raceway surface and improving the creep resistance on the anti-track surface.

In the method for manufacturing a raceway ring of a rolling bearing of the present invention, a member to be machined made of steel, which is annular and has a first peripheral surface and a second peripheral surface which is the opposite surface in the radial direction of the first peripheral surface, is prepared. It is provided with a step of performing quenching, a quenching step of quenching the member to be processed, and a tempering step of tempering the member to be processed. Quenching process is a processing target member comprises a heating step of heating the A ₁ transformation point or more temperature of the steel, and a cooling step of cooling the processing target member to Mf point below the temperature of the steel. The tempering step is performed by heating the second peripheral surface while cooling the first peripheral surface.

In the above method for manufacturing a raceway ring of a rolling bearing, the tempering step may be performed while rotating the member to be machined around the central axis of the member to be machined.

In the above method for manufacturing a raceway ring of a rolling bearing, in the tempering step, the first peripheral surface may be cooled by injecting a cooling liquid.

In the above method for manufacturing a raceway ring of a rolling bearing, the second peripheral surface may be heated by induction heating in the tempering step.

In the above method for manufacturing a raceway ring of a rolling bearing, the second peripheral surface may be heated so that the average temperature becomes 300 ° C. or higher in the tempering step.

According to the method for manufacturing a raceway ring of a rolling bearing of the present invention, it is possible to improve the creep fatigue resistance on the anti-track surface while improving the rolling fatigue characteristics on the raceway surface.

It is a top view of the inner ring 10. It is sectional drawing in II-II of FIG. It is sectional drawing of the inner ring 10 which concerns on a modification. It is a process drawing which shows the manufacturing method of the inner ring 10. It is a plane schematic diagram for demonstrating the tempering process S3. It is sectional drawing to explain the tempering process S3. It is a graph which shows the simulation result about the relationship between the heating time by a heating coil 30 and the temperature on the inner peripheral surface 20c and the outer peripheral surface 20d. It is a graph which shows the simulation result of the heating temperature of the outer peripheral surface 20d when the heating temperature of the inner peripheral surface 20c is changed.

The details of the embodiment will be described with reference to the drawings. In the following drawings, the same or corresponding parts shall be designated by the same reference numerals, and duplicate explanations shall not be repeated.

(Structure of raceway ring of rolling bearing according to embodiment)
The configuration of the raceway ring of the rolling bearing according to the embodiment will be described below.

The raceway ring of the rolling bearing according to the embodiment is, for example, an inner ring of a deep groove ball bearing (hereinafter, referred to as “inner ring 10”). However, the raceway ring of the rolling bearing according to the embodiment is not limited to this. The raceway ring of the rolling bearing according to the embodiment may be an outer ring of a deep groove ball bearing, or may be a raceway ring of a rolling bearing other than the deep groove ball bearing.

The inner ring 10 is made of hardened steel. That is, this steel contains martensite crystal grains and retained austenite crystal grains. This steel may contain other than martensite crystal grains and retained austenite crystal grains (for example, ferrite crystal grains and carbide grains). This steel is, for example, SUJ2, which is a high carbon chromium bearing steel defined in the JIS standard (JIS G 4805: 2008).

FIG. 1 is a plan view of the inner ring 10. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. As shown in FIGS. 1 and 2, the inner ring 10 has an annular shape. The inner ring 10 has a central axis A.

The inner ring 10 has a first end surface 10a and a second end surface 10b, an inner peripheral surface 10c, and an outer peripheral surface 10d. The first end surface 10a, the second end surface 10b, the inner peripheral surface 10c, and the outer peripheral surface 10d may be collectively referred to as the surface of the inner ring 10.

The first end face 10a and the second end face 10b form end faces in a direction along the central axis A (hereinafter, referred to as "axial direction"). The second end surface 10b is the opposite surface of the first end surface 10a in the axial direction.

The inner peripheral surface 10c extends in a direction along the circumference centered on the central axis A (hereinafter, referred to as “circumferential direction”). The inner peripheral surface 10c faces the central axis A side. The inner peripheral surface 10c is connected to the first end surface 10a and the second end surface 10b. The inner ring 10 is fitted to a shaft (not shown) on the inner peripheral surface 10c.

The outer peripheral surface 10d extends in the circumferential direction. The outer peripheral surface 10d faces the side opposite to the central axis A. That is, the outer peripheral surface 10d is the opposite surface of the inner peripheral surface 10c in the direction orthogonal to the central axis A and passing through the central axis A (hereinafter, referred to as “diameter direction”).

The outer peripheral surface 10d has a raceway surface 10da. The outer peripheral surface 10d is recessed on the inner peripheral surface 10c side in the raceway surface 10da. The raceway surface 10da has an arc shape in a cross-sectional view passing through the central axis A. The raceway surface 10da is a surface that comes into contact with a rolling element (not shown). The anti-orbital plane is a plane on the opposite side of the orbital plane 10da in the radial direction. In the inner ring 10, the inner peripheral surface 10c is an anti-orbital plane.

The amount of retained austenite on the inner peripheral surface 10c, which is the anti-orbital plane, is smaller than the amount of retained austenite on the raceway surface 10da. The average value of the amount of retained austenite in the steel constituting the inner ring 10 is preferably 10% by volume or less. The "average value of the amount of retained austenite in the steel constituting the inner ring 10" is a plurality of points arranged at equal intervals between the raceway surface 10da and the inner peripheral surface 10c along the radial direction of the inner ring 10. It is a value obtained by integrating the distribution curve of the retained austenite amount obtained by the measurement along the circumferential direction and dividing it by the cross-sectional area of the raceway ring (inner ring 10) parallel to the circumferential direction.

The difference between the amount of retained austenite on the inner peripheral surface 10c and the amount of retained austenite on the raceway surface 10da is preferably 3% by volume or more. The amount of retained austenite on the inner peripheral surface 10c is preferably 5% by volume or less.

The amount of retained austenite in the steel constituting the inner ring 10 is measured by an X-ray diffraction method. More specifically, the amount of retained austenite is obtained by comparing the intensities of the diffraction peaks of each phase obtained by irradiating with X-rays.

The minimum value of compressive residual stress on the raceway surface 10 da is 100 MPa or more. In the region where the distance from the raceway surface 10 da is 0.2 mm or less, the compressive residual stress is preferably 100 MPa or less. The residual stress on the orbital plane 10 da is measured by the X-ray diffraction method. More specifically, the residual stress on the orbital plane 10da is measured based on the change in the diffraction peak angle when the orbital plane 10da is irradiated with X-rays.

The hardness on the raceway surface 10da is higher than the hardness on the inner peripheral surface 10c. The hardness of the raceway surface 10da and the hardness of the inner peripheral surface 10c are preferably 700 Hv or more. The hardness of the raceway surface 10da and the hardness of the inner peripheral surface 10c are measured according to the Vickers hardness test method defined in the JIS standard (JIS Z 2244: 2009).

<Modification example>
FIG. 3 is a cross-sectional view of the inner ring 10 according to the modified example. As shown in FIG. 3, a nitrification layer 10e may be formed on the surface of the inner ring 10. The nitrogen concentration in the steel located in the immersion layer 10e is higher than the nitrogen concentration in the steel located in the steel other than the immersion layer 10e. The nitrogen concentration in steel is measured by EPMA (Electron Probe Micro Analyzer).

When the nitriding layer 10e is formed on the surface of the inner ring 10, the average value of the amount of retained austenite in the steel constituting the inner ring 10 is preferably 20% by volume or less.

(Method of manufacturing a raceway ring of a rolling bearing according to an embodiment)
The method of manufacturing the inner ring 10 will be described below.

FIG. 4 is a process diagram showing a method for manufacturing the inner ring 10. As shown in FIG. 4, the method for manufacturing the inner ring 10 includes a preparation step S1, a quenching step S2, a tempering step S3, and a post-treatment step S4. In the preparation step S1, the annular work target member 20 to be the inner ring 10 is prepared by going through the quenching step S2, the tempering step S3, and the post-treatment step S4.

When the nitriding layer 10e is formed on the surface of the inner ring 10, the surface of the member 20 to be processed is subjected to a nitriding treatment prior to the quenching step S2. The immersion treatment is performed by holding the member 20 to be processed at a predetermined temperature for a predetermined time in, for example, an atmospheric gas containing nitrogen (for example, ammonia (NH _{3) gas).}

In the quenching step S2, the member 20 to be processed is quenched. The quenching step S2 includes a heating step S21 and a cooling step S22. In the heating step S21, the member 20 to be processed _{is heated to a temperature of A 1} point or higher and held for a predetermined time. A ₁ point is the temperature at which ferrite in steel begins to transform into austenite. By performing the heating step S21, austenite crystal grains are generated in the steel constituting the member 20 to be processed.

The cooling step S22 is performed after the heating step S21. In the cooling step S22, the member 20 to be processed is cooled to a temperature equal to or lower than the Ms point. The Ms point is the temperature at which the transformation from austenite to martensite begins. Therefore, in the cooling step S22, some of the austenite crystal grains in the steel constituting the processing target member 20 become martensite crystal grains.

In the cooling step S22, the temperature falls below the Ms point and is cooled to a temperature below or near the Mf point. The Mf point is the temperature at which the transformation from austenite to martensite ends. That is, in the cooling step S22, a so-called sub-zero treatment (deep cooling treatment) is performed. As a result, the amount of retained austenite in the steel that affirms the member 20 to be processed is considerably reduced.

The tempering step S3 is performed after the quenching step S2. In the tempering step S3, the member 20 to be processed is tempered.

FIG. 5 is a schematic plan view for explaining the tempering step S3. FIG. 6 is a schematic cross-sectional view for explaining the tempering step S3. As shown in FIGS. 5 and 6, the heating in the tempering step S3 is performed by, for example, induction heating.

More specifically, the heating coil 30 is rotated in the circumferential direction along the inner peripheral surface 20c of the member 20 to be processed to induce and heat the inner peripheral surface 20c. When the inner peripheral surface 20c is heated by the heating coil 30, the outer peripheral surface 20d of the member 20 to be processed is cooled by a cooling liquid such as water injected from the injection unit 31.

FIG. 7 is a graph showing the simulation results regarding the relationship between the heating time by the heating coil 30 and the temperatures on the inner peripheral surface 20c and the outer peripheral surface 20d. In FIG. 7, the horizontal axis is the heating time (unit: seconds) by the heating coil 30, and the vertical axis is the temperature (unit: ° C.) on the inner peripheral surface 20c and the outer peripheral surface 20d. The simulation of FIG. 7 was performed under the conditions that the heating temperature of the inner peripheral surface 20c was 420 ° C., the outer peripheral surface 20d was water-cooled, and the distance between the inner peripheral surface 20c and the outer peripheral surface 20d was 3 mm. As shown in FIG. 7, in the tempering step S3, the heating temperature of the outer peripheral surface 20d is lower than the heating temperature of the inner peripheral surface 20c.

FIG. 8 is a graph showing a simulation result of the heating temperature of the outer peripheral surface 20d when the heating temperature of the inner peripheral surface 20c is changed. In FIG. 8, the horizontal axis represents the heating temperature (unit: ° C.) of the inner peripheral surface 20c, and the vertical axis represents the heating temperature (unit: ° C.) of the outer peripheral surface 20d. The simulation of FIG. 8 was performed under the same conditions as the simulation of FIG. 7 except that the heating temperature of the inner peripheral surface 20c was changed. As shown in FIG. 8, the heating temperature of the outer peripheral surface 20d is a linear expression of the heating temperature of the inner peripheral surface 20c. Assuming that the heating temperature of the inner peripheral surface 20c is x and the heating temperature of the outer peripheral surface 20d is y, y = a × x + b (a is a positive number less than 1 and b is a positive number). Is called "Equation 1").

For example, as described in Japanese Patent Application Laid-Open No. 10-102137, the volume ratio (M ₁ ) of retained austenite in the steel constituting the work target member 20 after the tempering step S3 is performed is tempered. _{Using the volume ratio (M 0} ), heating temperature (T), and heating time (t) of the retained austenite in the steel constituting the member 20 to be processed before the step S3 is performed _{, M 1} = M ₀ × {A. × exp (−Q / RT) × t ⁿ } (A, Q and n are constants, R is a gas constant) (hereinafter, this equation is referred to as “Equation 2”).

Therefore, by appropriately adjusting the heating temperature and heating time of the inner peripheral surface 20c by the heating coil 30, the heating temperature of the outer peripheral surface 20d can be appropriately adjusted, and accordingly, the volume ratio of the retained austenite in the inner peripheral surface 20c. And the volume ratio of retained austenite on the outer peripheral surface 20d can be adjusted as appropriate.

For example, as described in References (Takeshi Inoue, "New Tempering Parameters and Application to Tempering Integration Method Along Its Continuous Temperature Curve", Iron and Steel, 66, 10 (1980), 1533). The hardness (Hv) of the steel constituting the work target member 20 after the tempering step S3 is determined by using the heating time (t) and the heating temperature (T) as Hv = c × log + d / T + e ( c, d and e are constants). Therefore, the hardness of the inner peripheral surface 20c can be appropriately adjusted by appropriately adjusting the heating temperature and the heating time of the inner peripheral surface 20c by the heating coil 30.

In the post-treatment step S4, post-treatment is performed on the member 20 to be processed. This post-treatment includes grinding of the processing target member 20, cleaning of the processing target member 20, and the like. With the above, the manufacturing process of the inner ring 10 is completed.

(Effect of rolling bearing according to the embodiment)
The effect of the inner ring 10 will be described below.

In the inner ring 10, the amount of retained austenite on the anti-orbital plane (inner peripheral surface 10c) is smaller than the amount of retained austenite on the raceway surface 10da. The dimensional change of is small. Therefore, in the inner ring 10, the fitting with the shaft is hard to loosen, and the creep resistance on the anti-track surface can be improved.

In the inner ring 10, the amount of retained austenite on the inner peripheral surface 10c is smaller than the amount of retained austenite on the raceway surface 10da (from another viewpoint, the amount of decrease in retained austenite on the inner peripheral surface 10c is the amount of retained austenite on the raceway surface 10da. The shrinkage on the inner peripheral surface 10c side after the end of the tempering step S3 is larger than that on the raceway surface 10da side.

Due to this difference in the amount of shrinkage, compressive residual stress acts on the raceway surface 10da. In the inner ring 10, the difference between the amount of retained austenite on the inner peripheral surface 10c and the amount of retained austenite on the raceway surface 10da is 3% by volume or more, so that the raceway surface 10da has a large compressive residual stress (specifically, , The minimum value is 100 MPa or more). Therefore, according to the inner ring 10, the rolling fatigue characteristic on the raceway surface 10da can be improved.

When the average value of the amount of retained austenite in the steel constituting the inner ring 10 is 10% by volume or less (when the nitriding layer 10e is formed, it is 20% by volume or less). , The transformation of retained austenite to martensite with the passage of time is less likely to occur, and the creep resistance can be further improved.

By performing the sub-zero treatment in the cooling step S22, the average value of the amount of retained austenite in the steel constituting the inner ring 10 is 10% by volume or less (20% by volume when the nitriding layer 10e is formed). The following) can be used. If the average value of the amount of retained austenite in the steel is reduced before the tempering step S3, the time required for the tempering step S3 can be shortened, and the inner peripheral surface 10c is heated in the tempering step S3. The temperature can be lowered. As a result, the hardness can be maintained not only on the raceway surface 10da but also on the inner peripheral surface 10c.

<Experimental example>
Samples 1 to 4 were prepared as samples to be used in the experiment. Samples 1 to 4 are annular members formed by SUJ2 defined in JIS standards. The surfaces of Sample 1 and Sample 2 have not been subjected to nitrification treatment. The surfaces of Samples 3 and 4 are subjected to a nitrogen immersion treatment. The samples 1 and 3 are not subjected to the sub-zero treatment in the cooling step S22, and the samples 2 and the sample 4 are subjected to the sub-zero treatment in the cooling step S22. The tempering step S3 is performed on the samples 1 to 4.

As shown in Table 1, the amount of retained austenite on the orbital plane of Sample 1 was 11% by volume. On the other hand, the amount of retained austenite on the orbital plane of Sample 2 was 7% by volume. The amount of retained austenite on the orbital plane of Sample 3 was 31% by volume, while the amount of retained austenite on the orbital plane of Sample 4 was 16% by volume.

Since the amount of retained austenite in the steel constituting the member 20 to be processed decreases from the raceway surface to the anti-track plane in the tempering step S3, the inner ring 10 is formed by performing the subzero treatment in the cooling step S22. The average value of the amount of retained austenite in the steel can be 10% by volume or less (20% by volume or less when the immersion layer 10e is formed).

The tempering step S3 was performed on the sample 2. At this time, the heating temperature on the inner peripheral surface side of the sample 2 was set to 300 ° C., and the outer peripheral surface side of the sample 2 was water-cooled. The heating time was set so that the difference between the amount of retained austenite on the outer peripheral surface and the retained austenite on the inner peripheral surface was 3% by volume based on the formulas 1 and 2.

As shown in Table 2, in the sample 2 before the tempering step S3 was performed, the residual tensile stress was acting on the outer peripheral surface, but in the sample 2 after the tempering step S3 was performed, the residual tensile stress was acting. A compressive residual stress of 100 MPa or more was generated at a position where the distance from the outer peripheral surface was up to 0.2 mm. From this, it is possible that a compressive residual stress of 100 MPa or more is generated on the raceway surface 10da because the difference between the amount of retained austenite on the inner peripheral surface 10c and the amount of retained austenite on the raceway surface 10da is 3% by volume or more. It was also clarified experimentally.

Although the embodiment of the present invention has been described above, it is possible to modify the above-described embodiment in various ways. Moreover, the scope of the present invention is not limited to the above-described embodiment. The scope of the present invention is indicated by the scope of claims and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

The above embodiments are particularly advantageously applied to the raceway rings of rolling bearings.

10 Inner ring, 10a 1st end surface, 10b 2nd end surface, 10c Inner peripheral surface, 10d Outer surface, 10da Orbital surface, 10e Quenching layer, 20 Processing target member, 20c Inner peripheral surface, 20d Outer surface, 30 Heating coil, 31 Injection part, A central axis, S1 preparation process, S2 quenching process, S3 tempering process, S4 post-treatment process, S21 heating process, S22 cooling process.

Claims (5)

A step of preparing a member to be processed made of steel, which is annular and has a first peripheral surface and a second peripheral surface which is an opposite surface in the radial direction of the first peripheral surface.
A quenching process for quenching the member to be processed and
It is provided with a tempering process for tempering the member to be processed.
The quenching step includes a heating step of heating the processing target member to the A ₁ transformation point or more temperature of the steel, and a cooling step of cooling the processing target member to a temperature below Mf point of the steel ,
The tempering step is a method for manufacturing a raceway ring of a rolling bearing, which is performed by heating the second peripheral surface while cooling the first peripheral surface. The method for manufacturing a raceway ring of a rolling bearing according to claim 1, wherein the tempering step is performed while rotating the machining target member around the central axis of the machining target member. The method for manufacturing a raceway ring of a rolling bearing according to claim 1 or 2, wherein in the tempering step, the first peripheral surface is cooled by injecting a cooling liquid. The method for manufacturing a raceway ring of a rolling bearing according to any one of claims 1 to 3, wherein in the tempering step, the second peripheral surface is heated by induction heating. The method for manufacturing a raceway ring of a rolling bearing according to any one of claims 1 to 4, wherein in the tempering step, the second peripheral surface is heated so that the average temperature becomes 300 ° C. or higher. ..

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