WO2021002179A1

WO2021002179A1 - Raceway ring for rolling bearing

Info

Publication number: WO2021002179A1
Application number: PCT/JP2020/023395
Authority: WO
Inventors: 山田　昌弘; 大木　力
Original assignee: Ntn株式会社
Priority date: 2019-07-04
Filing date: 2020-06-15
Publication date: 2021-01-07
Also published as: JP7328032B2; JP2021011894A; JP2023156391A

Abstract

This raceway ring (10) for a rolling bearing is composed of steel and is provided with an outer circumferential surface (10d) and an inner circumferential surface (10c). One of the outer circumferential surface (10d) and the inner circumferential surface (10c) has a raceway surface (10e). The other of the outer circumferential surface (10d) and the inner circumferential surface (10c) serves as an anti-raceway surface. The volumetric fraction of residual austenite in the anti-raceway surface is smaller than the volumetric fraction of residual austenite in the raceway surface (10e). The difference between the volumetric fraction of residual austenite in the raceway surface (10e) and the volumetric fraction of residual austenite in the anti-raceway surface is at least 5 volume percent. The average particle diameter of prior austenite grains in the raceway surface (10e) is at most 8 μm.

Description

Rolling bearing bearing ring

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

Since the bearing ring of the rolling bearing is manufactured by quenching and tempering the bearing steel or the like (for example, Patent Document 1), it contains retained austenite. When rolling bearings are used in a high temperature environment, residual austenite is decomposed, causing dimensional changes in the raceway wheels. For example, if the inner ring undergoes a dimensional change due to use in a high temperature environment, the inner diameter will increase. As a result, the fit between the inner ring and the shaft is loosened, and creep occurs. Creep causes damage to rolling bearings.

JP-A-2017-187104

As a countermeasure against the above dimensional change, tempering at about 230 ° C. for several hours is performed to reduce the amount of retained austenite in advance. However, with this measure, martensite is also decomposed, so that the hardness on the raceway surface is reduced and the life of the rolling bearing is shortened.

The present invention has been made in view of the above-mentioned problems of the prior art. More specifically, the present invention provides a raceway ring of a rolling bearing capable of suppressing the occurrence of breakage due to creep while maintaining the hardness on the raceway surface.

The raceway ring of the rolling bearing of the present invention is made of steel and has an outer peripheral surface and an inner peripheral surface. One of the outer peripheral surface and the inner peripheral surface has a raceway surface. The other of the outer peripheral surface and the inner peripheral surface is an antibonding surface. The volume ratio of retained austenite on the antibonding surface is smaller than the volume ratio of retained austenite on the orbital surface. The difference between the volume ratio of retained austenite on the orbital surface and the volume ratio of retained austenite on the anti-orbital surface is 5% by volume or more. The average particle size of the former austenite crystal grains on the orbital surface is 8 μm or less.

In the above-mentioned rolling bearing raceway ring, a plurality of compound particles may be dispersed on the antibonding surface. The average particle size of the compound grains may be 2 μm or less. The area ratio of the compound grains may be 0.3% or more.

In the above-mentioned rolling bearing raceway ring, the raceway surface and the antibonding surface may be carburized and nitrided. The difference between the volume ratio of retained austenite on the orbital surface and the volume ratio of retained austenite on the anti-orbital surface may be 10% by volume or more.

In the above-mentioned rolling bearing raceway ring, the hardness on the anti-tracking surface may be 650 Hv or more. In the bearing ring of the rolling bearing, the steel may be SUJ2.

According to the raceway ring of the rolling bearing of the present invention, it is possible to suppress the occurrence of breakage due to creep while maintaining the hardness 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 a process drawing which shows the manufacturing method of the inner ring 10. It is a top view of the member 20 to be processed. It is sectional drawing in VV of FIG. It is a plane schematic diagram for demonstrating the tempering process S4. It is sectional drawing to explain the tempering process S4. 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 are designated by the same reference numerals, and duplicate explanations will not be repeated.

The raceway ring of the rolling bearing according to the embodiment is, for example, the inner ring 10 of the deep groove ball bearing. The raceway ring of the rolling bearing according to the embodiment is not limited to the inner ring 10, but the inner ring 10 will be described below as a specific example of the raceway ring of the rolling bearing according to the embodiment.

(Structure of inner ring 10)
The configuration of the inner ring 10 will be described below.

The inner ring 10 is made of steel. The steel constituting the inner ring 10 is, for example, SUJ2, which is a high carbon chrome bearing steel defined in JIS standard (JIS G 4805; 2008). However, the steel constituting the inner ring 10 is not limited to this.

The steel that makes up the inner ring 10 is hardened. From another point of view, the steel constituting the inner ring 10 contains martensite and retained austenite. Martensite is a non-equilibrium phase obtained by quenching austenite, which is a high-temperature phase of iron (Fe) having an fcc (face centered cubic) structure. Residual austenite is austenite that remains without metamorphosis to martensite when it is rapidly cooled.

A plurality of compound grains are dispersed in the steel constituting the inner ring 10. The compound granule is a compound of iron and nitrogen (N) and carbon (C). The compound granules are formed, for example, by a compound in which the carbon sites of cementite (Fe ₃ C) are partially replaced by nitrogen and the iron sites of cementite are partially replaced by chromium. That is, the compound granules are formed of, for example, (Fe, Cr) ₃ (C, N).

FIG. 1 is a plan view of the inner ring 10. As shown in FIG. 1, the inner ring 10 has an annular (ring-shaped) shape. The inner ring 10 has a central axis A. 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 upper surface 10a, a lower surface 10b, an inner peripheral surface 10c, and an outer peripheral surface 10d.

The upper surface 10a and the lower surface 10b form an end surface of the inner ring 10 in the direction along the central axis A. The bottom surface 10b is the opposite surface of the top surface 10a. The inner peripheral surface 10c extends along the circumferential direction. The inner peripheral surface 10c faces inward in the radial direction. The inner peripheral surface 10c is connected to the upper surface 10a and the bottom surface 10b. The outer peripheral surface 10d extends along the circumferential direction. The outer peripheral surface 10d faces outward in the radial direction. The outer peripheral surface 10d is connected to the upper surface 10a and the bottom surface 10b.

The outer peripheral surface 10d includes the raceway surface 10e. The raceway surface 10e is a portion of the outer peripheral surface 10d that comes into contact with a rolling element (not shown). In the inner ring 10, the inner peripheral surface 10c constitutes an antibonding surface 10f. That is, the inner peripheral surface 10c is a surface that is fitted to a shaft (not shown). The surface of the inner ring 10 (upper surface 10a, lower surface 10b, inner peripheral surface 10c and outer peripheral surface 10d) is preferably carburized and nitrided.

The volume ratio of retained austenite on the antibonding surface 10f (inner peripheral surface 10c) is smaller than the volume ratio of retained austenite on the orbital surface 10e. That is, since the decomposition of the retained austenite on the anti-tracking surface 10f is more advanced than the decomposition of the retained austenite on the bonding surface 10e, the dimensional change rate on the anti-tracking surface 10f is smaller than the dimensional change rate on the bonding surface 10e.

The difference between the volume ratio of retained austenite on the raceway surface 10e and the volume ratio of retained austenite on the anti-track surface 10f (the value obtained by subtracting the volume ratio of retained austenite on the anti-track surface 10f from the volume ratio of retained austenite on the raceway surface 10e) is 5 by volume or more. When the surface of the inner ring 10 is carburized and nitrided, the difference between the volume ratio of retained austenite on the orbital surface 10e and the volume ratio of retained austenite on the antibonding surface 10f may be 10% by volume or more. The volume ratio of retained austenite is measured using X-ray diffraction. That is, the volume ratio of retained austenite can be obtained by comparing the integrated intensity of the X-ray diffraction peak of the martensite phase with the integrated intensity of the X-ray diffraction peak of the austenite phase.

The average particle size of the former austenite crystal grains on the orbital surface 10e is 8 μm or less. The former austenite grains are the parts surrounded by the grain boundaries of austenite that existed before cooling in quenching. The average particle size of the former austenite crystal grains is determined according to the method specified in the JIS standard (JIS G 0551: 2005).

The average particle size of the compound particles on the anti-orbital surface 10f is preferably 2 μm or less. The area ratio of the compound particles on the anti-orbital surface 10f is preferably 0.3% or more.

The average particle size of the compound grains and the area ratio of the compound grains are measured by the following methods. In this measurement, first, a cross-sectional image of the inner ring 10 is taken with an electron microscope (SEM). Prior to photographing the cross section of the inner ring 10 with an electron microscope, the inner ring 10 is mirror-polished and the mirror-polished surface is corroded.

Second, the area of each compound grain is calculated by performing image processing on the cross-sectional image of the inner ring 10. By summing the areas of each compound grain, the area ratio of the compound grains can be obtained. Third, the equivalent circle diameter of each compound grain is calculated from the square root of the value obtained by dividing the area of each compound grain by π / 4. By dividing the total value of the equivalent circle diameters of each compound grain by the total number of compound grains, the average particle size of the compound grains can be obtained.

As the decomposition of retained austenite progresses, so does the decomposition of martensite. Therefore, the hardness on the orbital surface 10e is higher than the hardness on the antibonding surface 10f where the decomposition of retained austenite is relatively advanced. The hardness of the anti-tracking surface 10f is preferably 650 Hv or more. Hardness is measured according to the Vickers hardness test method specified in JIS standard (JIS Z 2244: 2009).

(Manufacturing method of inner ring 10)
The method of manufacturing the inner ring 10 will be described below.

FIG. 3 is a process diagram showing a manufacturing method of the inner ring 10. As shown in FIG. 3, the method for manufacturing the inner ring 10 includes a preparation step S1, a carburizing nitriding treatment step S2, a quenching step S3, a tempering step S4, and a post-treatment step S5. The quenching step S3 includes a first quenching step S31 and a second quenching step S32.

In the preparation step S1, the member 20 to be processed is prepared. The member 20 to be processed is made of steel. The steel constituting the member 20 to be processed is, for example, SUJ2, which is a high carbon chrome bearing steel defined in JIS standards.

FIG. 4 is a plan view of the member 20 to be processed. FIG. 5 is a cross-sectional view taken along the line VV of FIG. As shown in FIGS. 4 and 5, the processing target member 20 has an annular shape. The member 20 to be processed has an upper surface 20a, a lower surface 20b, an inner peripheral surface 20c, and an outer peripheral surface 20d. The upper surface 20a, the lower surface 20b, the inner peripheral surface 20c, and the outer peripheral surface 20d are surfaces that become the upper surface 10a, the lower surface 10b, the inner peripheral surface 10c, and the outer peripheral surface 10d, respectively, after the completion of the post-treatment step S5.

In the carburizing nitriding treatment step S2, the carburizing nitriding treatment is performed on the surface of the member 20 to be processed. In the carburizing nitriding treatment step S2, the member 20 to be processed is predetermined at a predetermined temperature in an atmospheric gas containing nitrogen and carbon (for example, an atmospheric gas containing a heat absorbing modified gas (R gas) and ammonia (NH ₃ ) gas). It is done by holding time. As a result, carbon and nitrogen are solid-solved in the steel on the surface of the member 20 to be processed.

The first quenching step S31 is performed after the carburizing nitriding treatment step S2. In the first quenching step S31, quenching is performed on the member 20 to be processed. In the first quenching step S31, the first, processing target member 20, a predetermined time is held in the processing target member 20 the construction to steel A ₁ transformation point or more temperature (first temperature). Second, the processing target member 20 is cooled to a temperature equal to or lower than the Ms transformation point of the steel constituting the processing target member 20. Cooling of the member 20 to be processed is performed by, for example, oil cooling. By heating and holding in the first quenching step S31, compound particles are precipitated in the steel constituting the member 20 to be processed.

The second quenching step S32 is performed after the first quenching step S31. In the second quenching step S32, quenching is performed on the member 20 to be processed. In the second quenching step S32, the first, processing target member 20, a predetermined time is held in the processing target member 20 the construction to steel A ₁ transformation point or more temperature (second temperature). The second temperature is lower than the first temperature. Since the second temperature is lower than the first temperature, the solid solution limit of carbon and nitrogen in the steel is narrowed, so that the compound particles are precipitated even during the heating and holding of the second quenching step S32.

Second, the machining target member 20 is cooled to a temperature equal to or lower than the Ms transformation point of the steel constituting the machining target member 20. Cooling of the member 20 to be processed is performed by, for example, oil cooling. The growth of austenite crystal grains during the heating and holding of the second quenching step S32 is suppressed by the pinning effect of the compound grains precipitated during the heating and holding of the first quenching step S31 and the second quenching step S32. There is.

By performing the quenching step S3 including the first quenching step S31 and the second quenching step S32, martensite and retained austenite are formed in the steel constituting the member 20 to be processed, and the old austenite is formed. The average particle size of the austenite crystal grains is 8 μm or less. Further, by performing the quenching step S3, fine compound particles are dispersed in the steel constituting the processing target member 20.

In the stage after the quenching step S3 is performed and before the tempering step S4 is performed, the volume ratio of the retained austenite on the inner peripheral surface 20c and the volume ratio of the retained austenite on the outer peripheral surface 20d are between. There is no significant difference (the difference between the volume ratio of retained austenite on the inner peripheral surface 20c and the volume ratio of retained austenite on the outer peripheral surface 20d is less than 5% by volume).

The tempering step S4 is performed after the quenching step S3 (first quenching step S31 and second quenching step S32). In the tempering step S4, the tempering of the member 20 to be processed is performed.

FIG. 6 is a schematic plan view for explaining the tempering step S4. FIG. 7 is a schematic cross-sectional view for explaining the tempering step S4. As shown in FIGS. 6 and 7, the heating in the tempering step S4 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 to induce and heat the inner peripheral surface 20c. When the inner peripheral surface 20c is being heated by the heating coil 30, the outer peripheral surface 20d is cooled by a cooling liquid such as water injected from the injection unit 31.

FIG. 8 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. 8, 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. 8 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. 8, in the tempering step S4, the heating temperature of the outer peripheral surface 20d is lower than the heating temperature of the inner peripheral surface 20c.

FIG. 9 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. 9, 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. 9 was performed under the same conditions as the simulation of FIG. 8 except that the heating temperature of the inner peripheral surface 20c was changed. As shown in FIG. 9, 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).

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 S4 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 S4 is performed, M ₁ = M ₀ × {A. × exp (−Q / RT) × t ⁿ } (A, Q and n are constants, R is a gas constant).

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 on the inner peripheral surface 20c. 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 S4 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 S5, the post-treatment of the member 20 to be processed is performed. 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 inner ring 10)
The effect of the inner ring 10 will be described below.

If the dimensional change over time due to the use of the rolling bearing on the anti-tracking surface 10f is large, it causes creep. The smaller the volume ratio of retained austenite, the smaller the change in dimensions over time with the use of rolling bearings. On the other hand, the larger the volume ratio of retained austenite, the higher the hardness because the decomposition of martensite accompanying the decomposition of retained austenite has not progressed.

When a general tempering process (tempering process of heating in a furnace) is performed, the volume ratio of retained austenite on the raceway surface 10e and the volume ratio of retained austenite on the anti-track surface 10f both decrease, so that rolling Although the occurrence of creep due to the change in dimensions with time due to the use of the bearing is suppressed, the hardness of the raceway surface 10e cannot be maintained.

However, in the inner ring 10, the difference between the volume ratio of retained austenite on the raceway surface 10e and the volume ratio of retained austenite on the antibonding surface 10f is 5% by volume or more. Therefore, according to the inner ring 10, it is possible to suppress damage to the rolling bearing due to the occurrence of creep while maintaining the hardness of the raceway surface 10e.

In the inner ring 10, since the average particle size of the old austenite crystal grains is refined to 8 μm or less, the amount of plastic deformation of the anti-trajectory surface when worn with the shaft can be reduced, and the generated wear powder can be reduced. It can be made smaller.

When the compound particles are dispersed on the anti-orbital surface 10f so that the average particle size is 2 μm or less and the area ratio is 0.3% or more, the amount of plastic deformation of the anti-orbital surface 10f when worn with the shaft is determined. It can be made even smaller, and the generated abrasion powder can be made even smaller.

When the hardness of the anti-tracking surface 10f is 650 Hv or more, the amount of plastic deformation of the anti-tracking surface 10f when worn with the shaft can be further reduced.

Although the embodiment of the present invention has been described as described above, it is also 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 claims and is intended to include all modifications within the meaning and scope equivalent to the claims.

The above embodiment is particularly advantageously applied to the raceway wheels of rolling bearings.

10 Inner ring, 10a upper surface, 10b bottom surface, 10c inner peripheral surface, 10d outer peripheral surface, 10e raceway surface, 10f anti-track surface, 20 machining target member, 20a upper surface, 20b bottom surface, 20c inner peripheral surface, 20d outer peripheral surface, 30 heating coil , 31 Injection part, A central axis, S1 preparation process, S2 carburizing nitriding process, S3 quenching process, S4 quenching process, S5 post-processing process, S31 first quenching process, S32 second quenching process.

Claims

Made of steel
Outer surface and
With an inner peripheral surface,
One of the outer peripheral surface and the inner peripheral surface has a raceway surface.
The other of the outer peripheral surface and the inner peripheral surface is an antibonding surface.
The volume ratio of retained austenite on the antibonding surface is smaller than the volume ratio of retained austenite on the orbital surface.
The difference between the volume ratio of retained austenite on the orbital surface and the volume ratio of retained austenite on the anti-orbital surface is 5% by volume or more.
A raceway ring of a rolling bearing in which the average particle size of the former austenite crystal grains on the raceway surface is 8 μm or less.
A plurality of compound particles are dispersed on the antibonding surface.
The average particle size of the compound grains is 2 μm or less.
The raceway ring of the rolling bearing according to claim 1, wherein the area ratio of the compound grains is 0.3% or more.
The orbital surface and the anti-orbital surface are carburized and nitrided.
The raceway ring of the rolling bearing according to claim 1 or 2, wherein the difference between the volume ratio of retained austenite on the anti-track surface and the volume ratio of retained austenite on the raceway surface is 10% by volume or more.
The raceway ring of a rolling bearing according to any one of claims 1 to 3, wherein the hardness on the anti-track surface is 650 Hv or more.
The bearing ring of the rolling bearing according to any one of claims 1 to 4, wherein the steel is SUJ2.