JP2022107970A - Bearing component and rolling bearing - Google Patents

Abstract

To provide a bearing component improved in durability.SOLUTION: A bearing component has a surface and is made of steel. The bearing component comprises a surface layer portion which is a region at a distance up to 20 μm from the surface. The steel contains carbon in an amount from 0.70 mass% to 1.10 mass% inclusive, silicon in an amount from 0.15 mass% to 0.35 mass% inclusive, manganese in an amount from 0.30 mass% to 0.60 mass% inclusive, chromium in an amount from 1.30 mass% to 1.60 mass% inclusive, vanadium in an amount of 0.50 mass% or less, and molybdenum in an amount of 0.50 mass% or less, with the remaining portion being iron and unavoidable impurities. The steel in the surface layer portion has martensite block grains and a precipitate. The precipitate is a nitride whose main constituent is chromium or vanadium, or a carbonitride whose main constituent is chromium or vanadium.SELECTED DRAWING: Figure 2

Description

The present invention relates to bearing components and rolling bearings.

Patent Document 1 (Japanese Patent No. 5489111) describes a bearing component. The bearing component described in Patent Document 1 is formed by performing nitriding, quenching, and tempering on a steel member to be processed. The bearing component described in Patent Document 1 has high wear resistance because cementite is dispersed in the steel of the surface layer.

Patent Document 2 (Japanese Patent No. 6023422) describes a bearing component. The bearing component described in Patent Document 2 is formed by performing nitriding, quenching, and tempering on a steel member to be processed. In the bearing component described in Patent Document 2, since the amount of retained austenite in the steel of the surface layer is large, the durability against indentation-induced flaking under lubrication mixed with foreign matter is high.

Japanese Patent No. 5489111 Japanese Patent No. 6023422

As a result of extensive studies by the present inventors, the bearing components described in Patent Document 1 and Patent Document 2 have room for further improvement in durability. The present invention provides bearing components and rolling bearings with improved durability.

The bearing component of the invention has a surface and is made of steel. The bearing component comprises a surface layer which is an area up to 20 μm away from the surface. The steel contains 0.70 to 1.10 mass percent carbon, 0.15 to 0.35 mass percent silicon, and 0.30 to 0.60 mass percent manganese. , 1.30 mass percent or more and 1.60 mass percent or less of chromium, 0.50 mass percent or less of vanadium, and 0.50 mass percent or less of molybdenum, and the balance being iron and unavoidable impurities. The surface layer steel has martensite block grains and precipitates. The precipitates are nitrides based on chromium or vanadium or carbonitrides based on chromium or vanadium. In the steel of the surface layer portion, the average grain size of martensite block grains with a comparative area ratio of 30% is 2.0 μm or less.

In the above bearing component, the steel comprises 0.90 mass percent to 1.10 mass percent carbon, 0.20 mass percent to 0.30 mass percent silicon, and 0.40 mass percent to 0.50 mass percent. 1.40 to 1.60 mass percent of manganese, 0.20 to 0.30 mass percent of vanadium, and 0.10 to 0.30 mass percent and molybdenum below, and the balance may be iron and unavoidable impurities.

In the above bearing component, the area ratio of precipitates in the steel of the surface layer portion may be 2.0% or more.

In the above bearing component, the maximum grain size of precipitates in the steel of the surface layer portion may be 0.5 μm or less.

In the above bearing component, the steel of the surface layer portion may further contain cementite. The maximum grain size of cementite in the steel of the surface layer portion may be 1.5 μm or less.

In the above bearing component, the nitrogen concentration in the steel of the surface layer portion may be 0.15% by mass or more.

In the above bearing component, the volume ratio of retained austenite in the steel may be 15% or more at a position 50 μm from the surface.

In the bearing component described above, the steel may have a hardness of 58 HRC or more at a distance of 50 μm from the surface.

In the above bearing component, the volume ratio of retained austenite in the steel may be 25% or more and 35% or less at the position where the distance from the surface is 50 μm. The hardness of the steel may be 58 HRC or more and 64 HRC or less at the position where the distance from the surface is 50 μm.

A rolling bearing of the present invention includes an inner ring, an outer ring, and rolling elements. At least one of the inner ring, outer ring and rolling elements is the above bearing component.

Durability is improved with the bearing component of the invention and the rolling bearing of the invention.

3 is a cross-sectional view of an inner ring 10; FIG. It is an enlarged view in II in FIG. 4A to 4C are process diagrams showing a method of manufacturing the inner ring 10. FIG. 1 is a cross-sectional view of a rolling bearing 100; FIG. 4 is a graph showing measurement results of nitrogen concentration and carbon concentration in the vicinity of the raceway surface of the bearing washer of Sample 1. FIG. 7 is a graph showing measurement results of nitrogen concentration and carbon concentration in the vicinity of the raceway surface of the raceway washer of sample 2; 4 is an SEM image of the surface layer portion of the bearing washer of Sample 1. FIG. 4 is an SEM image of the surface layer portion of the bearing washer of Sample 2. FIG. 4 is a phase map of EBSD in the surface layer portion of the bearing washer of Sample 1. FIG. 4 is a phase map of EBSD in the surface layer portion of the bearing washer of Sample 2. FIG. 3 is a phase map of EBSD in the surface layer portion of the bearing washer of sample 3. FIG. 3 is a bar graph showing the average grain size of martensite block grains in surface layer portions of bearing washers of Samples 1 to 3. FIG. It is a graph which shows the result of a rolling contact fatigue life test.

Details of embodiments of the present invention will be described with reference to the drawings. Here, the same reference numerals are given to the same or corresponding parts, and redundant description will not be repeated.

A bearing component according to the embodiment is, for example, an inner ring 10 of a rolling bearing. In the following, the inner ring 10 will be described as an example of the bearing component according to the embodiment. However, the bearing component according to the embodiment is not limited to this. A bearing component according to an embodiment may be an outer ring of a rolling bearing or a rolling element of a rolling bearing.

(Configuration of inner ring 10)
FIG. 1 is a cross-sectional view of the inner ring 10. FIG. As shown in FIG. 1, the inner ring 10 is ring-shaped. Let the central axis of the inner ring 10 be central axis A. As shown in FIG. The inner ring 10 has a width surface 10a, a width surface 10b, an inner peripheral surface 10c, and an outer peripheral surface 10d. The width surface 10a, the width surface 10b, the inner peripheral surface 10c, and the outer peripheral surface 10d form the surface of the inner ring 10. As shown in FIG.

Hereinafter, the direction of the central axis A is defined as the axial direction. Also, hereinafter, the direction along the circumference centered on the central axis A when viewed in the axial direction is defined as the circumferential direction. Furthermore, in the following description, the direction orthogonal to the axial direction is defined as the radial direction.

The width surface 10a and the width surface 10b are end surfaces of the inner ring 10 in the axial direction. The width surface 10b is the opposite surface of the width surface 10a in the axial direction.

The inner peripheral surface 10c extends in the circumferential direction. The inner peripheral surface 10c faces the central axis A side. One end in the axial direction of the inner peripheral surface 10c is continuous with the width surface 10a, and the other end in the axial direction is continuous with the width surface 10b. The inner ring 10 is fitted to a shaft (not shown) at the inner peripheral surface 10c.

The outer peripheral surface 10d extends in the circumferential direction. 10 d of outer peripheral surfaces face the side opposite to the central axis A. As shown in FIG. That is, the outer peripheral surface 10d is the opposite surface of the inner peripheral surface 10c in the radial direction. One end in the axial direction of the outer peripheral surface 10d is continuous with the width surface 10a, and the other end in the axial direction is continuous with the width surface 10b.

The outer peripheral surface 10d has a raceway surface 10da. The raceway surface 10da extends in the circumferential direction. The outer peripheral surface 10d is recessed toward the inner peripheral surface 10c on the raceway surface 10da. In a cross-sectional view, the raceway surface 10da has a partially circular shape. The raceway surface 10da is located in the center of the outer peripheral surface 10d in the axial direction. The raceway surface 10da is a portion of the outer peripheral surface 10d that contacts the rolling elements (not shown in FIG. 1).

The inner ring 10 is made of steel. More specifically, the inner ring 10 is made of steel that has been hardened and tempered. The steel forming the inner ring 10 contains 0.70 mass percent or more and 1.10 mass percent or less of carbon, 0.15 mass percent or more and 0.35 mass percent or less of silicon, and 0.30 mass percent or more and 0.60 mass percent. 1.30 to 1.60 weight percent chromium, 0.50 weight percent or less vanadium, and 0.50 weight percent or less molybdenum. In this steel, the content of molybdenum is 0.01% by mass or more, and the content of vanadium is 0.01% by mass or more.

The reason why the carbon content in the steel forming the inner ring 10 is 0.70% by mass or more is to improve the hardness. The reason why the carbon content in the steel forming the inner ring 10 is 1.10% by mass or less is to suppress quench cracking.

The reason why the silicon content in the steel forming the inner ring 10 is 0.15% by mass or more is to increase temper softening resistance and to improve workability. The reason why the silicon content in the steel forming the inner ring 10 is 0.35% by mass or less is that an excessive amount of silicon lowers workability.

The content of manganese in the steel forming the inner ring 10 is 0.30% by mass or more to ensure hardenability. The reason why the content of manganese in the steel forming the inner ring 10 is 0.60% by mass or less is that an excessive amount of manganese increases manganese-based non-metallic inclusions in the steel.

The reason why the content of chromium in the steel forming the inner ring 10 is 1.30% by mass or more is to ensure hardenability and to form nitrides and carbonitrides. The reason why the content of chromium in the steel forming the inner ring 10 is 1.60% by mass or less is to suppress the formation of coarse precipitates.

The reason why the steel forming the inner ring 10 contains vanadium is to refine nitrides and carbonitrides. The reason why the vanadium content in the steel forming the inner ring 10 is 0.50% by mass or less is to suppress an increase in cost due to the addition of vanadium.

Molybdenum is contained in the steel forming the inner ring 10 in order to refine nitrides and carbonitrides and to improve hardenability. The reason why the molybdenum content in the steel forming the inner ring 10 is 0.50% by mass or less is to suppress an increase in cost due to the addition of molybdenum.

The steel forming the inner ring 10 contains 0.90 mass percent or more and 1.10 mass percent or less of carbon, 0.20 mass percent or more and 0.30 mass percent or less of silicon, and 0.40 mass percent or more and 0.50 mass percent. 1.40 to 1.60 mass percent chromium, 0.20 to 0.30 mass percent vanadium, and 0.10 to 0.30 mass percent molybdenum may contain. The rest of the steel forming the inner ring 10 is iron and unavoidable impurities.

FIG. 2 is an enlarged view at II in FIG. As shown in FIG. 2 , in the inner ring 10 , a region up to 20 μm from the surface is the surface layer portion 11 . For example, the surface of the inner ring 10 is subjected to nitriding treatment. As a result, the nitrogen concentration in the steel of the surface layer portion 11 is, for example, 0.15% by mass or more. The nitrogen concentration in the steel of the surface layer portion 11 is preferably 0.20% by mass or more and 0.30% by mass or less. The nitrogen concentration in the steel of the surface layer portion 11 is measured using an EPMA (Electron Probe Micro Analyzer).

Precipitates are dispersed in the steel of the surface layer portion 11 . The precipitates are nitrides based on chromium or vanadium or carbonitrides based on chromium or vanadium.

Chromium (vanadium) nitrides are nitrides of chromium (vanadium) or those in which some of the chromium (vanadium) sites in the nitrides are replaced by alloying elements other than chromium (vanadium). is.

A carbonitride containing chromium (vanadium) as a main component is obtained by substituting part of the carbon sites in the chromium (vanadium) carbide with nitrogen. The chromium (vanadium) sites of the carbonitride containing chromium (vanadium) as a main component may be substituted with an alloying element other than chromium (vanadium).

The area ratio of precipitates in the steel of the surface layer portion 11 is preferably 2.0% or less. The maximum grain size of precipitates in the steel of the surface layer portion 11 is preferably 0.5 μm or less.

The area ratio and maximum grain size of precipitates in the steel of the surface layer portion 11 are measured by the following methods. First, a cross-sectional image (hereinafter referred to as “SEM image”) is acquired using a SEM (Scanning Electron Microscope) in a cross section of the inner ring 10 including the surface layer portion 11 . The magnification for acquiring this SEM image is 15000 times.

Second, image processing is performed on the acquired SEM image. More specifically, since the precipitate appears white in the SEM image, the area of each of the white portions in the SEM image and the total area are calculated by image processing.

The total area of the white portion in the SEM image is regarded as the area ratio of the precipitates in the steel of the surface layer portion 11 . The square root of the value obtained by dividing the maximum area of each white portion in the SEM image by π/4 is regarded as the maximum grain size of precipitates in the steel of the surface layer portion 11 .

Cementite (Fe ₃ C) may be further dispersed in the steel of the surface layer portion 11 . Some of the iron sites in the cementite may be replaced by alloying elements, and some of the carbon sites in the cementite may be replaced by nitrogen. The maximum grain size of cementite in the steel of the surface layer portion 11 is preferably 1.5 μm or less.

The maximum grain size of cementite in the steel of the surface layer portion 11 is measured by the following method. First, a SEM image is acquired in a cross section of the inner ring 10 including the surface layer portion 11 . The magnification for acquiring this SEM image is 15000 times. Second, image processing is performed on the acquired SEM image. More specifically, since cementite appears oval gray in the SEM image, the area of each oval gray portion in the SEM image is calculated by image processing. Then, the square root of the value obtained by dividing the maximum value of the area of each elliptical gray portion in the SEM image by π/4 is regarded as the maximum grain size of cementite in the steel of the surface layer portion 11. be.

At a position where the distance from the surface of the inner ring 10 is 50 μm, the volume ratio of retained austenite in the steel is preferably 15% or more. More preferably, the volume ratio of retained austenite in the steel is 25% or more and 35% or less at the position where the distance from the surface of the inner ring 10 is 50 μm.

The volume ratio of retained austenite in steel is measured by an X-ray diffraction method. That is, the volume ratio of retained austenite in the steel is calculated by comparing the integrated intensity of the diffraction peak in X-ray diffraction of austenite and the integrated intensity of the diffraction peak in X-ray diffraction of phases other than austenite.

The hardness of the steel is preferably 58 HRC or more at the position where the distance from the surface of the inner ring 10 is 50 μm. More preferably, the hardness of the steel at the position where the distance from the surface of the inner ring 10 is 50 μm is 58 HRC or more and 64 HRC or less. The hardness of steel is measured according to the Rockwell hardness test method defined in JIS (JIS Z 2245:2016).

The steel of the surface layer portion 11 has martensite block grains. Two adjacent martensite block grains have a crystal orientation difference of 15° or more at the grain boundary. From another point of view, even if there is a location with a deviation in crystal orientation, if the difference in crystal orientation is less than 15°, the location is different from the grain boundary of the martensite block grain. not considered. Grain boundaries of martensite block grains are determined by an EBSD (Electron Back Scattered Diffraction) method.

In the steel of the surface layer portion 11, the average grain size of martensite block grains with a comparative area ratio of 30% is 2.0 μm or less. In the steel of the surface layer portion 11, the average grain size of martensite block grains with a comparative area ratio of 50% is preferably 1.5 μm or less.

The average grain size of martensite block grains with a comparative area ratio of 30 percent (50 percent) is measured by the following method. First, cross-sectional observation is performed on a cross section of the inner ring 10 including the surface layer portion 11 . At this time, martensite block grains included in the observation field are specified by the EBSD method. This observation field of view is an area of 50 μm×45 μm. Second, the area of each martensite block grain included in the observation field is analyzed from the crystal orientation data obtained by the EBSD method.

Thirdly, the area of each martensite block grain included in the observation field is added in descending order of area. This addition is performed until thirty percent (50 percent) of the total area of martensite block grains contained in the field of view is reached. The equivalent circle diameter is calculated for each of the martensite block grains subjected to the above addition. This equivalent circle diameter is the square root of the value obtained by dividing the area of martensite block grains by π/4. The average value of the circle-equivalent diameters of the martensite block grains subjected to the above addition is regarded as the average grain size of the martensite block grains with a comparative area ratio of 30% (50%).

(Manufacturing method of inner ring 10)
FIG. 3 is a process diagram showing a method of manufacturing the inner ring 10. As shown in FIG. As shown in FIG. 3, the method for manufacturing the inner ring 10 includes a preparation step S1, a nitriding step S2, a quenching step S3, a tempering step S4, and a post-treatment step S5. The nitriding step S2 is performed after the preparatory step S1. The hardening step S3 is performed after the nitriding step S2. The tempering step S4 is performed after the hardening step S3. The post-treatment step S5 is performed after the tempering step S4.

In the preparation step S1, a member to be processed is prepared. The member to be processed is a ring-shaped member made of the same steel as the inner ring 10 .

In the nitriding step S2, a nitriding treatment is performed on the surface of the member to be processed. The nitriding treatment is performed by holding the member to be processed in an atmosphere containing a nitrogen source (for example, ammonia) at a temperature equal to or higher than the A1 transformation _point of the steel forming the member to be processed.

In the quenching step S3, the member to be processed is quenched. In quenching, the member to be processed is held at a temperature equal to or higher than the _A1 transformation _point of the steel constituting the member to be processed, and then rapidly cooled to a temperature equal to or lower than the MS transformation point of the steel constituting the member to be processed. It is done by It is preferable that the heating and holding temperature in the quenching step S3 is equal to or lower than the heating and holding temperature in the nitriding step S2. The hardening step S3 may be performed twice. The heating and holding temperature in the second hardening step S3 is preferably lower than the heating and holding temperature in the first hardening step S3. As a result, precipitates are finely and abundantly dispersed in the surface layer of the member to be processed.

In the tempering step S4, the member to be processed is tempered. Tempering is carried out by holding the workpiece at _a temperature below the A1 transformation point of the steel from which the workpiece is constructed. In the post-processing step S5, machining (grinding, polishing), cleaning, and the like are performed on the surface of the member to be processed. As described above, the inner ring 10 having the structure shown in FIGS. 1 and 2 is formed.

In addition, since the precipitates are finely and abundantly dispersed in the steel of the surface layer portion 11, the martensite block grains are less likely to become large. The average grain size of block grains is 2.0 μm or less.

(Effect of inner ring 10)
In the inner ring 10 , the martensite block grains in the steel of the surface layer portion 11 are refined so that the average grain size at a comparative area ratio of 30% is 2.0 μm or less. As a result, in the inner ring 10, the surface layer portion 11 is toughened, and the shear resistance of the surface of the inner ring 10 (specifically, the raceway surface 10da) in contact with the rolling elements is improved. Thus, the inner ring 10 has improved durability.

When the area ratio of the precipitates in the steel of the surface layer portion 11 is 2.0% or more, that is, when the precipitates are dispersed in the steel of the surface layer portion 11 at a high density, contact with the rolling elements Durability is further improved by improving the shear resistance of the surface of the inner ring 10 (specifically, the raceway surface 10da).

When the maximum grain size of the precipitates in the steel of the surface layer portion 11 is 0.5 μm, the precipitates are dispersed finely and at high density in the steel of the surface layer portion 11, so wear resistance and toughness are improved. As a result, the durability of the inner ring 10 is further improved. When the maximum grain size of cementite in the steel of the surface layer portion 11 is 1.5 μm or less, fine dispersion of cementite further improves the wear resistance and toughness of the inner ring 10 .

When the volume ratio of retained austenite in the steel at the position where the distance from the surface of the inner ring 10 is 50 μm is 15% or more (25% or more and 35% or less), durability against dent-initiated flaking in an environment containing foreign matter is improved. When the hardness of the steel at the position where the distance from the surface of the inner ring 10 is 50 μm is 58 HRC or more (58 HRC or more and 64 HRC or less), the wear resistance of the inner ring 10 is further improved.

(Rolling bearing according to the embodiment)
A rolling bearing (referred to as "rolling bearing 100") according to the embodiment will be described below.

FIG. 4 is a cross-sectional view of the rolling bearing 100. FIG. As shown in FIG. 4, rolling bearing 100 is a deep groove ball bearing. However, the rolling bearing 100 is not limited to this. Rolling bearing 100 may be, for example, a thrust ball bearing. The rolling bearing 100 has an inner ring 10 , an outer ring 20 , rolling elements 30 and a retainer 40 .

The outer ring 20 has a width surface 20a, a width surface 20b, an inner peripheral surface 20c, and an outer peripheral surface 20d. The surface of the outer ring 20 is composed of a width surface 20a, a width surface 20b, an inner peripheral surface 20c and an outer peripheral surface 20d.

The width surface 20a and the width surface 20b are end surfaces of the outer ring 20 in the axial direction. The width surface 20b is the opposite surface of the width surface 20a in the axial direction.

The inner peripheral surface 20c extends in the circumferential direction. The inner peripheral surface 20c faces the central axis A side. One end in the axial direction of the inner peripheral surface 20c is continuous with the width surface 20a, and the other end in the axial direction is continuous with the width surface 20b. The outer ring 20 is arranged such that the inner peripheral surface 20c faces the outer peripheral surface 10d.

The inner peripheral surface 20c has a raceway surface 20ca. The raceway surface 20ca extends in the circumferential direction. The inner peripheral surface 20c is recessed toward the outer peripheral surface 20d on the raceway surface 20ca. In a cross-sectional view, the raceway surface 20ca has a partially circular shape. The raceway surface 20ca is located in the center of the inner peripheral surface 20c in the axial direction. The raceway surface 20ca is a portion of the inner peripheral surface 20c that contacts the rolling elements 30 .

The outer peripheral surface 20d extends in the circumferential direction. 20 d of outer peripheral surfaces face the side opposite to the central axis A. As shown in FIG. That is, the outer peripheral surface 20d is the opposite surface of the inner peripheral surface 20c in the radial direction. The outer peripheral surface 20d is continuous with the width surface 20a at one end in the axial direction, and is continuous with the width surface 20b at the other end in the axial direction. The outer ring 20 is fitted to a housing (not shown) on the outer peripheral surface 20d.

The rolling elements 30 are spherical. The rolling elements 30 are arranged between the outer peripheral surface 10d (raceway surface 10da) and the inner peripheral surface 20c (raceway surface 20ca). The retainer 40 is ring-shaped and arranged between the outer peripheral surface 10d and the inner peripheral surface 20c. The retainer 40 holds the rolling elements 30 such that the distance between the two rolling elements 30 adjacent in the circumferential direction is within a certain range.

Outer ring 20 and rolling elements 30 may be made of the same steel as inner ring 10 . In addition, the surface layer portion of the outer ring 20 (the region up to 20 μm from the surface of the outer ring 20) and the surface layer portion of the rolling element 30 (the region up to 20 μm from the surface of the rolling element 30) are the same as the surface layer portion 11. may be configured.

(Rolling contact fatigue life test)
A rolling contact fatigue life test was conducted to confirm the effect of the bearing component according to the embodiment. Samples 1, 2 and 3 were used for the rolling contact fatigue life test. Samples 1 to 3 are thrust ball bearings of type 51106 specified in JIS.

In sample 1, bearing washer (inner ring and outer ring) was formed of the first steel material. In samples 2 and 3, bearing washer was formed of the second steel material. The compositions of the first steel material and the second steel material are shown in Table 1. As shown in Table 1, the ingredients of the first steel material and the second steel material are almost the same except for the contents of molybdenum and vanadium. The second steel material corresponds to SUJ2, which is a high-carbon chromium bearing steel specified in JIS standards.

FIG. 5 is a graph showing the measurement results of the nitrogen concentration and carbon concentration in the vicinity of the raceway surface of the raceway washer of Sample 1. FIG. FIG. 6 is a graph showing the measurement results of the nitrogen concentration and carbon concentration in the vicinity of the raceway surface of the raceway washer of sample 2. In FIG. The horizontal axis in FIGS. 5 and 6 is the distance from the orbital plane (unit: mm), and the vertical axis in FIGS. 5 and 6 is the concentration of carbon or nitrogen (unit: mass percent). As shown in FIGS. 5 and 6, in samples 1 and 2, the surface of the washer was subjected to nitriding treatment. The heating and holding temperature during this nitriding treatment was set to 850°C. On the other hand, in sample 3, the bearing washer surface was not subjected to nitriding treatment.

Table 2 shows the nitrogen concentrations in the surface layers of the bearing washer of Samples 1 to 3 (area up to 20 μm from the raceway surface). As shown in Table 2, the nitrogen concentration in the surface layer steel of the bearing washers of samples 1 and 2 was 0.3% or more and 0.5% or less. The nitrogen concentration in the surface layer steel of the washer of Sample 3 was 0.0%.

Quenching and tempering were performed on bearing washers of samples 1 to 3. The heating and holding temperature during quenching was set to 850°C. The heating and holding temperature during tempering was set to 180°C. The heating and holding time during tempering was set to 2 hours.

FIG. 7 is an SEM image of the surface layer of the bearing washer of Sample 1. FIG. FIG. 8 is an SEM image of the surface layer of the bearing washer of Sample 2. FIG. In the SEM images of FIGS. 7 and 8, white portions are precipitates, and oval gray portions are cementite.

As shown in Table 3, the area ratio of precipitates in the surface layer steel of the bearing washer of sample 1 was 2.7 percent. As shown in Table 3, the area ratio of precipitates in the surface layer steel of sample 2 was 1.6 percent. That is, in the surface layer portion of the bearing washer of Sample 1, the precipitates were dispersed at a higher density than in the surface layer portion of the bearing washer of Sample 2. From this comparison, it became clear that the addition of vanadium and molybdenum in an amount of 0.5% by mass or less resulted in a dense dispersion of precipitates in the surface layer steel of the bearing washer.

In the surface layer portion of the bearing washer of Sample 1, the maximum grain size of precipitates was 0.5 μm. In the surface layer portion of the bearing washer of sample 2, the maximum grain size of precipitates was 1.1 μm. That is, in the surface layer portion of the bearing washer of sample 1, compared with the surface layer portion of the bearing washer of sample 2, the precipitates were finely dispersed. From this comparison, it became clear that the addition of vanadium and molybdenum in an amount of 0.5% by mass or less resulted in a high density and fine dispersion of precipitates in the surface layer steel of the bearing washer.

As shown in Table 4, in the surface layers of bearing washer of sample 1 and sample 2, the maximum grain size of cementite was 1.5 μm or less. In the surface layer portion of the bearing washer of sample 3, the maximum grain size of cementite exceeded 1.5 μm.

As shown in Table 5, in samples 1 and 2, the volume ratio of retained austenite in the steel was 15% or more at the position where the distance from the raceway surface was 50 μm. In sample 3, the volume ratio of retained austenite in the steel was less than 15% at the position where the distance from the raceway surface was 50 μm. In samples 1 to 3, the hardness of the steel was 58 HRC or more at the position where the distance from the raceway surface was 50 μm.

FIG. 9 is a phase map of EBSD in the surface layer portion of the bearing washer of Sample 1. FIG. FIG. 10 is a phase map of EBSD in the surface layer of the bearing washer of Sample 2. FIG. FIG. 11 is a phase map of EBSD in the surface layer of the bearing washer of sample 3. FIG. In FIGS. 9-11, the martensite block grains are white. FIG. 12 is a bar graph showing the average grain size of martensite block grains in the surface layer portion of bearing washer of Samples 1 to 3. FIG. The vertical axis of the graph in FIG. 12 is the average grain size (unit: μm) of martensite block grains.

As shown in FIGS. 9 to 12, in the surface layer portion of the bearing washer of Sample 1, the average grain size of martensite block grains at a comparative area ratio of 30% was 2.0 μm or less. On the other hand, in the surface layers of the bearing washer of Sample 2 and Sample 2, the average grain size of martensite block grains at a comparative area ratio of 30% exceeded 2.0 μm.

In the surface layer portion of the bearing washer of Sample 1, the average grain size of martensite block grains at a comparative area ratio of 50% was 1.5 μm or less. On the other hand, in the surface layers of the bearing washer of Sample 2 and Sample 2, the average grain size of martensite block grains at a comparative area ratio of 50% exceeded 1.5 μm.

FIG. 13 is a graph showing the results of a rolling contact fatigue life test. The horizontal axis of the graph in FIG. 13 indicates life (unit: hours), and the vertical axis of the graph in FIG. 13 indicates cumulative damage probability (unit: percent). The rolling contact fatigue life test was conducted under the conditions shown in Table 6. That is, the maximum contact surface pressure between the rolling elements and the washer is 2.3 GPa, the washer is rapidly accelerated and decelerated between 0 rpm and 2500 rpm, and the lubricating fluid is polyglycol oil. was added with pure water.

As shown in FIG. 13 and Table 7, Sample 1 exhibited better rolling contact fatigue life than Sample 2. More specifically, the L10 life of sample 1 (the life at which the cumulative failure probability reaches ₁₀ percent) is 2.7 times the L10 life of sample ₃ , and the L10 life of sample 2 is the _L10 life of sample 3. It was 2.1 times the ₁₀ life.

As described above, in the surface layer portion of the bearing washer of Sample 1, the average grain size of martensite grains at a comparative area ratio of 30% was 2.0 μm or less. On the other hand, in the surface layer portion of the bearing washer of Samples 2 and 3, the average grain size of martensite grains at a comparative area ratio of 30% exceeded 2.0 μm. From this comparison, it became clear that the bearing component according to the embodiment has improved durability.

Further, as described above, in the surface layer portion of the bearing washer of Sample 1, the precipitates were dispersed more finely and densely than in the surface layer portion of the bearing washer of Sample 2. From this comparison, it is clear that the durability of the bearing component according to the embodiment is further improved by setting the area ratio and maximum grain size of precipitates in the surface layer to 2.0% or more and 0.5 μm or less, respectively. Became.

Also, the L _{10 life of sample 2 was longer than the L 10 life} of sample 3. As described above, the maximum grain size of cementite in the surface layer of the washer of sample 2 was 1.5 µm or less, while the maximum grain size of cementite in the surface layer of the washer of sample 3 exceeded 1.5 µm. rice field. In addition, in the bearing washer of sample 2, the volume ratio of retained austenite at the position where the distance from the raceway surface is 50 μm is 15% or more, while in the bearing washer of sample 3, the distance from the raceway surface is 50 μm. The volume fraction of retained austenite at the location was less than 15 percent.

From this comparison, by setting the maximum grain size of cementite to 1.5 μm or less in the surface layer of the bearing component and setting the volume ratio of retained austenite to 15% or more at a position where the distance from the surface of the bearing component is 50 μm, , the durability of the bearing components is improved.

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

This embodiment applies particularly advantageously to bearing components and rolling bearings having the same.

10 inner ring, 10a, 10b width surface, 10c inner peripheral surface, 10d outer peripheral surface, 10da raceway surface, 11 surface layer portion, 20 outer ring, 20a, 20b width surface, 20c inner peripheral surface, 20ca raceway surface, 20d outer peripheral surface, 30 rolling element, 40 cage, 100 rolling bearing, A center shaft, S1 preparation process, S2 nitriding process, S3 quenching process, S4 tempering process, S5 post-treatment process.

Claims (10)

A steel bearing component having a surface,
A surface layer portion having a distance of up to 20 μm from the surface,
The steel contains 0.70 mass percent to 1.10 mass percent carbon, 0.15 mass percent to 0.35 mass percent silicon, and 0.30 mass percent to 0.60 mass percent manganese. and 1.30% by mass or more and 1.60% by mass or less of chromium, 0.50% by mass or less of vanadium, and 0.50% by mass or less of molybdenum, and the balance being iron and inevitable impurities,
The steel of the surface layer portion has martensite block grains and precipitates,
The precipitate is a nitride containing chromium or vanadium as a main component or a carbonitride containing chromium or vanadium as a main component,
A bearing component, wherein in the steel of the surface layer portion, the average grain size of the martensite block grains at a comparative area ratio of 30% is 2.0 μm or less. The steel contains 0.90 to 1.10 mass percent carbon, 0.20 to 0.30 mass percent silicon, and 0.40 to 0.50 mass percent manganese. and 1.40% by mass or more and 1.60% by mass or less of chromium, 0.20% by mass or more and 0.30% by mass or less of vanadium, and 0.10% by mass or more and 0.30% by mass or less of molybdenum 2. A bearing component according to claim 1, comprising iron and the balance being iron and incidental impurities. 3. The bearing component according to claim 1, wherein an area ratio of said precipitates in said steel in said surface layer portion is 2.0% or more. The bearing component according to any one of claims 1 to 3, wherein the maximum grain size of said precipitates in said steel of said surface layer portion is 0.5 µm or less. The steel of the surface layer further has cementite,
The bearing component according to any one of claims 1 to 4, wherein the cementite has a maximum grain size of 1.5 µm or less in the steel of the surface layer portion. The bearing component according to any one of claims 1 to 5, wherein the steel in the surface layer portion has a nitrogen concentration of 0.15% by mass or more. The bearing component according to any one of claims 1 to 6, wherein the volume ratio of retained austenite in the steel is 15% or more at a position 50 µm from the surface. The bearing component according to any one of claims 1 to 7, wherein the steel has a hardness of 58 HRC or more at a distance of 50 µm from the surface. At a position where the distance from the surface is 50 μm, the volume ratio of retained austenite in the steel is 25% or more and 35% or less,
The bearing component according to any one of claims 1 to 8, wherein the steel has a hardness of 58 HRC or more and 64 HRC or less at a position where the distance from the surface is 50 µm. inner ring;
an outer ring;
a rolling element;
A rolling bearing, wherein at least one of the inner ring, the outer ring and the rolling element is the bearing component according to any one of claims 1 to 9.

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