JP2024022880A - bearing - Google Patents

Abstract

To provide a bearing that can suppress a decrease in service life caused by an overlapping portion such as a folded portion.SOLUTION: A bearing has a raceway ring on which a raceway surface 10A is formed, and the residual stress of the raceway surface 10A is 700 MPa or more. A folded portion 20 is formed, in which a part of a convex portion P overlaps with a concave portion G formed in the raceway surface 10A. The maximum value of the width of the folded portion 20 is 1 μm or less.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to bearings.

Peeling (micro pitting) is a typical form of failure of bearings used under lean lubrication conditions. Note that the lean lubrication condition means a condition in which a lubricating oil film cannot be sufficiently formed at the contact portion between the bearing raceway and the rolling elements. "Mechanism of occurrence of peeling due to rolling contact and influence of black dyeing on suppression of peeling" (Non-patent Document 1) states that the folding portion formed on the raceway surface becomes the starting point of the crack, and the subsequent rolling contact The mechanism by which raceway surfaces peel due to fatigue is introduced.

In addition, JP 2019-095044 A (Patent Document 1) discloses that compressive residual stress is reduced by burnishing the raceway surface, with the aim of extending the life of peeling starting from non-metallic inclusions protruding from the surface. Grant is proposed. JP 2019-095044 A discloses that compressive residual stress is applied to the surface by applying plastic working such as burnishing to suppress crack propagation. In JP-A No. 2019-095044, by applying compressive residual stress, peeling of the bearing starting from non-metallic inclusions is suppressed, thereby achieving a longer service life.

JP2019-095044A

“Peeling generation mechanism due to rolling contact and the influence of black dyeing on peeling suppression”, Tribologist Vol. 63, No. 8, June 2018, p. 551-562

In JP-A-2019-095044, plastic working is performed on the raceway surface to fill the gap between inclusions near the raceway surface and the base material, thereby suppressing crack propagation. However, in Japanese Unexamined Patent Publication No. 2019-095044, a surface having a certain degree of roughness is subjected to plastic working to crush the roughness. Therefore, a folded portion as disclosed in Non-Patent Document 1 is formed in the uneven portion after plastic working. The folded portion of the raceway surface can be considered as an initial crack, and cracks can cause peeling. For this reason, when a bearing used under lean lubrication conditions is subjected to plastic working such as burnishing, the peeling life may be shorter than when no plastic working is performed. Japanese Unexamined Patent Publication No. 2019-095044 and Non-Patent Document 1 do not disclose in-depth information on such issues.

The present disclosure has been made in view of the above problems. An object of the present disclosure is to provide a bearing that can suppress reduction in life caused by overlapping parts such as folded parts.

A bearing according to the present disclosure includes a raceway ring in which a raceway surface is formed. The residual stress on the raceway surface is 700 MPa or more. A portion is formed in which a portion of the convex portion overlaps with a concave portion formed on the raceway surface. The maximum width of the overlapped portion is 1 μm or less.

According to the present disclosure, it is possible to provide a bearing that can suppress a decrease in life caused by overlapping portions such as folded portions.

FIG. 1 is a schematic cross-sectional view showing the configuration of a deep groove ball bearing in this embodiment. This is a photograph of the folded portion formed on the raceway surface viewed from above. It is a photograph seen from above of a first example of concave portions and convex portions obtained by applying a load to a test member of a bearing ring. It is a photograph seen from above of a second example of concave portions and convex portions obtained by applying a load to a test member of a bearing ring. It is a photograph seen from above of a third example of concave portions and convex portions obtained by applying a load to a test member of a bearing ring. FIG. 2 is a schematic diagram showing the first step of the mechanism for forming initial peeling cracks on a raceway surface having folded portions according to the present embodiment. FIG. 6 is a schematic diagram showing the second step of the mechanism for forming initial peeling cracks on the raceway surface having folded portions according to the present embodiment. FIG. 6 is a schematic diagram showing the third step of the mechanism for forming initial peeling cracks on the raceway surface having folded portions according to the present embodiment. FIG. 7 is a schematic diagram showing a fourth step of the mechanism for forming initial peeling cracks on a raceway surface having folded portions according to the present embodiment. This is a photograph of the folded portion formed on the raceway surface after superfinishing, viewed from above. This is a photograph of a folded portion of a raceway surface with a surface roughness Ra of 0.223 μm before burnishing, viewed from above. This is a photograph of a folded portion of a raceway surface with a surface roughness Ra of 0.417 μm before burnishing, viewed from above. FIG. 3 is a schematic plan view showing a state in which polishing marks are formed on the raceway surface before burnishing.

The present embodiment will be described below with reference to the drawings.
The bearing to which this embodiment is applied is a bearing in which peeling of the raceway surface is a problem, for example, a bearing with a low oil film parameter. More specifically, it can be applied to, for example, bearings with low viscosity oil and low rotational speeds. Therefore, the type of bearing does not particularly matter. Therefore, in the following description of the overall structure of the bearing, a deep groove ball bearing will be shown as an example.

FIG. 1 is a schematic cross-sectional view showing the configuration of a deep groove ball bearing in this embodiment. Referring to FIG. 1, a deep groove ball bearing 1 according to the present embodiment includes an annular outer ring 11, an annular inner ring 12 disposed inside the outer ring 11 with respect to a center line C, and a space between the outer ring 11 and the inner ring 12. It has a plurality of balls 13 as rolling elements disposed in the outer ring 11, an inner ring 12, and an annular retainer 14 that holds the plurality of balls 13.

The outer ring 11 is arranged so as to be in contact with the plurality of balls 13 on the outside of the plurality of balls 13. The outer ring 11 has an outer ring raceway surface 11A on an inner peripheral surface formed on the inside with respect to the center line C. The inner ring 12 is arranged inside the balls 13 so as to be in contact with the balls 13. The inner ring 12 has an inner ring raceway surface 12A on an outer peripheral surface formed on the outside with respect to the center line C. The outer ring 11 and the inner ring 12 are arranged such that the outer ring raceway surface 11A and the inner ring raceway surface 12A face each other.

The plurality of balls 13 have a spherical shape and have a ball rolling surface 13A on the surface thereof. In other words, the entire surface of each of the plurality of balls 13 is the ball rolling surface 13A. The plurality of balls 13 are configured to roll between an outer ring raceway surface 11A and an inner ring raceway surface 12A. The plurality of balls 13 are in contact with the outer ring raceway surface 11A and the inner ring raceway surface 12A on the ball rolling surface 13A, and are arranged in a plurality of lines in the circumferential direction by the retainer 14 so as to have a certain pitch. As a result, each of the plurality of balls 13 is held on an annular track so as to be able to freely roll. With the above configuration, the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1 can rotate relative to each other.

A grease composition (not shown) is sealed in the space sandwiched between the outer ring 11 and the inner ring 12, more specifically, the raceway space that is the space sandwiched between the outer ring raceway surface 11A and the inner ring raceway surface 12A. This grease composition forms an oil film between the balls 13 and each of the outer ring 11 and inner ring 12, and maintains a good lubrication state between the balls 13 and each of the outer ring 11 and inner ring 12. In the following, the outer ring 11 and the inner ring 12 will be collectively referred to as a bearing ring 10. Further, in the following description, the outer ring raceway surface 11A and the inner ring raceway surface 12A are collectively referred to as a raceway surface 10A.

FIG. 2 is a photograph of the folded portion formed on the raceway surface viewed from above. Referring to FIG. 2, in a bearing such as deep groove ball bearing 1 of the present embodiment, raceway ring 10 is formed of either SUJ2 or SUJ3 specified in the JIS standard, which is a high carbon chromium bearing steel. Alternatively, the bearing ring 10 may be formed of carburized steel.

A folding portion 20 is formed on the raceway surface 10A. The maximum value of the width W of the folded portion 20 is 1 μm or less. The width W of the folding portion 20 is a dimension in a direction (vertical direction in FIG. 2) intersecting the direction in which the folding portion 20 extends (horizontal direction in FIG. 2). The folding section 20 will be explained in detail below.

FIG. 3 is a photograph of a first example of concave portions and convex portions obtained by applying a load to a test member of a bearing ring, viewed from above. Referring to FIG. 3, the raceway surface 10A shown here is the state after loading by the two-cylinder test. Wrinkle-like unevenness is formed on the raceway surface 10A. That is, as shown in FIG. 3, two recesses G1 and G2 are formed in the raceway surface 10A. The recess G1 and the recess G2 extend in the left-right direction in the figure, and both have widths in the vertical direction in the figure. Convex portions are formed on both sides of each of the recessed portion G1 and the recessed portion G2 in the width direction (vertical direction in FIG. 3). That is, the convex portion P1 and the convex portion P2 are formed adjacent to the concave portion G1, and the convex portion P3 and the convex portion P4 are formed adjacent to the concave portion G2. Hereinafter, the concave portions will be uniformly referred to as concave portions G, and the convex portions will be uniformly referred to as convex portions P. The concave portion G and the convex portion P extend along the rolling direction of the two-cylinder test.

FIG. 4 is a photograph of a second example of concave portions and convex portions obtained by applying a load to the test member of the bearing ring, viewed from above. FIG. 4 shows parts of the bearing ring of the same test member as in FIG. 3 that are different from those in FIG. 3. Referring to FIG. 4, the bearing ring test member here is the driven cylinder of the two-cylinder tester, to which a load is applied by the drive cylinder of the two-cylinder tester. A recess G is formed in the raceway surface 10A, similar to the recesses G1 and G2 in FIG. Furthermore, a convex portion P is formed on the raceway surface 10A, similar to the convex portions P1 to P4 in FIG. In the raceway surface 10A in FIG. 4, the concave portion G and the convex portion P extend from the upper left to the lower right along the rolling direction. A portion of the convex portion P is deformed by a force applied from above in a vertical direction. This force from above is applied by the drive cylinder of the two-cylinder tester, which can be loaded similarly to the burnishing tool. A part of the deformed convex portion P falls toward the concave portion G side. As a result, a portion of the convex portion P is formed as a folded portion 20 that overlaps with the concave portion G. A notch 21 is formed in a part of the folded portion 20 on the raceway surface 10A.

FIG. 5 is a photograph of a third example of concave portions and convex portions obtained by applying a load to the test member of the bearing ring, viewed from above. FIG. 5 shows parts of the bearing ring of the same test member as in FIGS. 3 and 4 that are different from those in FIGS. 3 and 4. Referring to FIG. 5, similarly to FIG. 4, recesses G and protrusions P are formed along the rolling direction. A folded portion 20 that overlaps with the recessed portion G is formed in a portion of the convex portion P (lower region in the figure). A notch 21 is also formed in the folded portion 20 in FIG. 5 by rolling the convex portion P. However, the notch 21 in FIG. 5 is hidden behind the folded portion 20 and is difficult to visually recognize.

The formation mechanism of the folded portion 20 will be explained in more detail with reference to FIGS. 6 to 9. FIG. 6 is a schematic diagram showing the first step of the formation mechanism of initial peeling cracks on the raceway surface having the folded portion according to the present embodiment. FIG. 7 is a schematic diagram showing the second step of the formation mechanism of initial peeling cracks on the raceway surface having the folded portion according to the present embodiment. Referring to FIGS. 6 and 7, a test member of the bearing ring 10, which is a driven cylinder, is shown. A small protrusion 101 extending upward is formed on the raceway surface 10A of the raceway ring 10. The small protrusion 101 is formed by the surface roughness of the raceway surface 10A. A projection 31 extending downward is formed on the surface of the drive cylinder 30 that faces the raceway surface 10A. The protrusion 31 is formed by the surface roughness of the machined surface 30A of the drive cylinder 30.

As shown in FIG. 6, the protrusion 31 applies a force F downward while the drive cylinder 30 moves in the moving direction R, which is the depth direction of the plane of the drawing. The moving direction R here corresponds to the rolling direction in FIGS. 3 to 5. At this time, the small protrusion 101 comes into contact with the protrusion 31, and a force is applied from above by the protrusion 31. As a result, as shown in FIG. 7, wrinkle-like unevenness is formed on the raceway surface 10A. Specifically, since the raceway surface 10A is pushed downward by the protrusion 31, the pushed portion moves downward and the concave portion 102 is formed. The recessed portion 102 corresponds to the recessed portion G (recessed portions G1, G2) in FIGS. 3 to 5. Further, an area adjacent to the area moved downward by the concave portion 102 moves upward in the opposite direction, and becomes a convex portion 103 . The convex portion corresponds to the convex portion P (convex portions P1 to P4) in FIGS. 3 to 5. By pushing a part of the orbital surface 10A downward in this way, a region that periodically moves upward and a region that moves downward are formed in the surrounding region. As a result, a plurality of concave portions 102 and convex portions 103 are alternately obtained, and wrinkle-like unevenness is formed.

FIG. 8 is a schematic diagram showing the third step of the mechanism for forming initial peeling cracks on the raceway surface having the folded portion according to the present embodiment. Referring to FIG. 8, as the drive cylinder 30 moves, another protrusion different from that in the first step in FIG.

FIG. 9 is a schematic diagram showing the fourth step of the formation mechanism of initial peeling cracks on the raceway surface having the folded portion according to the present embodiment. Referring to FIG. 9, the pressed convex portion 103 is deformed by being pressed in a vertical direction from above. In other words, the convex portion 103 is deformed so as to be crushed and rolled so that its vertical dimension becomes smaller. As a result, the convex portion 103 becomes a flattened portion 104. The flattened portion 104, which was originally the convex portion 103, is partially folded so as to fall toward the adjacent concave portion 102. In FIG. 9, the left side portion of the flattened portion 104 protrudes into the concave portion 102. As shown in FIG. The left side portion of the flattened portion 104 enters into the concave portion 102 existing to the left, and the flattened portion 104 overlaps the concave portion 102 in plan view. The region where the flattened portion 104 overlaps the concave portion 102 is the folded portion 20 . In addition, the concave-shaped part 102 is adjacent to the right side of the flattened part 104 in FIG. 9, and a folded part that overlaps therewith may be formed in some cases. Therefore, the maximum value of the width of the folded portion 20 is the maximum value of the dimension of the portion that protrudes so as to overlap the concave portion 102 in the direction perpendicular to the direction in which the folded portion 20 extends.

By forming the folded portion 20, a notch 21 is formed starting from the boundary between the flattened portion 104 and the concave portion 102. Stress concentration occurs at the tip 21P of the notch 21 (the end on the right side in FIG. 9, opposite to the boundary between the flattened portion 104 and the concave portion 102), thereby generating an initial crack 25. . If the initial crack 25 occurs, the initial crack 25 may propagate within the raceway ring 10 from the tip 21P of the notch 21, for example, generally from the left side to the right side in FIG. If this happens, peeling will occur. That is, as shown in FIG. 9, a peeling portion 26 in which the crack has grown is formed. Peeling is a phenomenon in which a thin region between the initial crack and the raceway surface 10A is peeled off from the raceway ring 10.

As described above, in the raceway surface 10A and the relatively shallow region adjacent thereto where plastic working such as burnishing is performed, compressive residual stress is generated due to macroscopic plastic deformation of the surface layer. Therefore, the residual stress (compressive residual stress) on the raceway surface 10A is 700 MPa or more. Specifically, the residual stress of 700 MPa or more means that the average value measured at three arbitrary locations on the raceway surface 10A itself is 700 MPa or more.

Next, the effects of this embodiment will be explained.
The bearing according to this embodiment includes a raceway ring 10 on which a raceway surface 10A is formed. The residual stress of the raceway surface 10A is 700 MPa or more. A folded portion 20 is formed as a portion where a portion of a convex portion P overlaps a concave portion G formed in the raceway surface 10A. The maximum value of the width W of the folded portion 20 is 1 μm or less.

As a result of intensive research, the inventor of this embodiment has found that the occurrence of peeling of the raceway surface 10A can be suppressed by reducing the width W of the folded portion 20 formed on the raceway surface 10A by plastic working of the raceway surface 10A. I gained new knowledge. By reducing the width W of the folded portion 20 of the raceway surface 10A formed by plastic working (burnishing), the growth of the initial crack 25 starting from the folded portion 20 is suppressed. It is considered that the above-mentioned notch 21 and initial crack 25 are normally formed by the folded portion 20. If the initial crack 25 develops, peeling will occur. Therefore, if the growth of the initial crack 25 is suppressed, the occurrence of peeling of the bearing ring 10 can also be suppressed. In this way, even under lean lubrication conditions, early peeling of the raceway surface 10A caused by peeling occurring from the folded portion 20 of the bearing can be suppressed, and a decrease in the life of the bearing can be suppressed. A supplementary explanation will be given below.

As described with reference to FIGS. 6 to 9, the folding portion 20 has unevenness due to the roughness component originally existing on the raceway surface 10A, or unevenness generated by transferring the roughness component of a mating component such as the drive cylinder 30. It is deformed due to plastic deformation. In particular, when plastic processing such as burnishing is performed on a polished surface (a surface that has not been superfinished), it has been confirmed that the convex portions 103 in particular of the roughness components are folded due to the plastic processing. . On the other hand, when superfinishing the raceway surface 10A, the large folded portion 20 is not formed in the processing step. FIG. 10 is a photograph of the folded portion formed on the raceway surface after superfinishing, viewed from above. Referring to FIG. 10, in the raceway surface 10A that has been superfinished, the maximum width of the folded portion is relatively small at about 0.1 μm, even if it is confirmed. Therefore, if the width of the folded portion is about 0.1 μm (so-called submicron level), it is possible to suppress the reduction in peeling life due to burnishing. From this point of view, if the width of the folded portion 20 is 1 μm or less, deterioration in peeling life can be suppressed.

As described above, the folded portion 20 is formed based on the uneven shape of the raceway surface 10A before plastic working. Therefore, as a manufacturing method, it is preferable to reduce the unevenness of the raceway surface 10A before plastic working. Thereby, the folding portion 20 can be made smaller. FIG. 11 is a photograph of the folded portion of the track surface after burnishing, which has a surface roughness Ra of 0.223 μm before burnishing, viewed from above. Referring to FIG. 11, the maximum width W of the folded portion 20 formed after burnishing the raceway surface 10A was 1.6 μm. FIG. 12 is a photograph of the folded portion of the track surface after burnishing, which has a surface roughness Ra of 0.417 μm before burnishing, viewed from above. Referring to FIG. 12, the maximum width W of the folded portion 20 formed after burnishing the track surface 10A was 6.3 μm. From FIGS. 11 and 12, the maximum value of the width W of the folded portion 20 after the burnishing process is about 10 times the numerical value of the surface roughness Ra before the burnishing process. The surface roughness Ra represents the average absolute value of roughness within a reference length defined by the JIS standard.

Therefore, from the viewpoint of making the folded portion 20 1 μm or less, it is preferable to reduce the maximum height Rz of the raceway surface 10A before plastic working. More specifically, the Rz of the raceway surface 10A before plastic working is preferably 1 μm or less, and even more preferably 0.5 μm or less. The maximum height Rz represents the sum of the height of the highest peak and the depth of the deepest valley in the contour curve within the reference length range defined by the JIS standard.

Burnishing smoothes the roughness components of the surface by plastically deforming them. Therefore, the width W and other dimensions of the folded portion 20 formed on the raceway surface 10A by the burnishing process are influenced by the roughness of the raceway surface 10A before the burnishing process. By sufficiently reducing the roughness of the raceway surface 10A before processing (making it nearly flat), the folded portion 20 after burnishing can be made small. Since the folded portion 20 usually has an initial crack 25, the folded portion 20 can also be considered to be the initial crack 25. In this way, the peeling portion 26 is formed by the growth of the initial crack 25, so that the smaller the initial crack 25, that is, the folded portion 20, the harder the initial crack 25 will grow, and the more difficult peeling will occur. As described above, by reducing the width of the folded portion 20, the peeling life can be extended compared to when the width of the folded portion 20 (initial crack 25) is large.

The presence or absence of peeling, which is crack propagation, is basically determined by the length of the crack. The initial crack 25 is formed so as to extend in the width direction of the folded portion 20, as shown in FIG. Therefore, the width W of the folded portion 20 is more important than the length thereof.

In the above bearing, the surface roughness Ra of the raceway surface 10A before burnishing may be 0.2 μm or less. If the surface roughness Ra of the raceway surface 10A before burnishing is 0.2 μm or less, the surface roughness Ra of the raceway surface 10A after the burnishing process (final product) is usually less than 0.1 μm. As mentioned above, the width W of the folded portion 20 in the final product is about 10 times the surface roughness Ra, so this feature allows the maximum width W of the folded portion 20 of the raceway surface 10A in the final product to be 1 μm or less. . Note that, within the above numerical range, the surface roughness Ra of the raceway surface 10A before burnishing is preferably 0.15 μm or less, and more preferably 0.12 μm or less. As a result, in the final product after burnishing, the surface roughness is preferably 0.08 μm or less, more preferably 0.06 μm or less.

In the above bearing, the area ratio of the folded portion may be 5% or less within an arbitrary range of 100 μm×100 μm on the raceway surface. This means that no matter how a range of 100 μm×100 μm is extracted from the raceway surface 10A, the area ratio of the folded portion within it will be 5% or less. As described above, the width of the folded portion 20 greatly affects the life of the bearing. On the other hand, if the area of the peeling portion 26 becomes larger than a certain level, the function of the bearing will be affected. Therefore, by reducing the area of the folding part 20 as described above, the area (length) of the peeling part 26 can be reduced. Thereby, deterioration in the function of the bearing can be suppressed.

In addition, the above bearing may have the following features. FIG. 13 is a schematic plan view showing a state in which polishing marks are formed on the raceway surface before burnishing. Referring to FIG. 13, a plurality of polishing marks 40 are formed on the raceway surface 10A before burnishing. The burnishing process is performed along the direction in which the polishing marks 40 extend, and the folded portion 20 is usually formed along the direction in which the polishing marks 40 extend. If the folded part 20 formed in one of the plurality of polishing marks 40 is considered to be one folded part 20 within an arbitrary 100 μm x 100 μm range of the raceway surface 10A, the number of folded parts 20 is 5 or less. . For example, as shown in FIG. 13, when a plurality of folded parts 20 are formed at intervals on a single polishing line 40, this is considered to be one folded part 20. Therefore, in reality, there may be six or more folded portions 20 within a range of 100 μm×100 μm. By doing so, the same effects as in the case where the area ratio of the folded portion 20 is 5% or less can be obtained.

As described above, the folded portion 20 is considered to be the initial crack 25. Therefore, by reducing the number of folded portions 20, it is possible to suppress the occurrence of widespread peeling due to the connection of initial cracks 25. Extensive peeling leads to large-scale peeling of the raceway surface 10A starting from the peeling, making it impossible to continue using the bearing. Therefore, it is possible to suppress a decrease in the life of the bearing. The initial cracks 25 are connected to each other by the initial cracks 25 extending in the width direction of the folded portion 20 and connecting with other initial cracks 25 . Therefore, there is little possibility that the initial cracks 25 of the plurality of folded portions 20 on the same polishing pattern 40 will connect with each other.

The method for measuring each of the above parameters is as follows. Compressive residual stress can be measured by cutting out a part of the surface of a bearing component, electrolytically polishing the surface, and using an X-ray diffraction device. The width and area of the folded portion 20 are measured by cutting out a region of the track surface 10A to be measured, and then observing the track surface 10A with, for example, a length measuring SEM (Scanning Electron Microscope). The surface roughness Ra and maximum height Rz of the raceway surface 10A are calculated based on the surface shape of the raceway surface 10A measured by, for example, a confocal laser microscope.

In the above description, the folded portion 20 formed by the steps shown in FIGS. 6 to 9 is used as a portion where the convex portion P overlaps the concave portion G. However, the "overlapping part" in this embodiment is not limited to the so-called "folding part" formed by the steps shown in FIGS. Includes all parts that overlap.

The features described in the embodiments (examples included therein) described above may be applied in appropriate combinations within a technically consistent range.

The embodiments and examples disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and it is intended that all changes within the meaning and range equivalent to the claims are included.

1 Deep groove ball bearing, 10 Raceway ring, 10A Raceway surface, 11 Outer ring, 11A Outer raceway surface, 12 Inner ring, 12A Inner raceway surface, 13 Ball, 13A Ball raceway surface, 14 Cage, 20 Folding part, 21 Notch, 21P Tip, 25 Initial crack, 26 Peeling part, 30 Drive cylinder, 30A Processed surface, 31 Protrusion, 40 Grinding, 101 Small protrusion, 102 Concave part, 103 Convex part, 104 Flattened part, G, G1, G2 Concave portion, P, P1, P2, P3, P4 Convex portion, R Movement direction.

Claims (3)

A bearing comprising a raceway ring with a raceway surface formed thereon,
The residual stress of the raceway surface is 700 MPa or more,
A part is formed in which a part of the convex part overlaps with the concave part formed in the raceway surface,
The bearing, wherein the maximum width of the overlapped portion is 1 μm or less. The bearing according to claim 1, wherein within an arbitrary 100 μm x 100 μm range of the raceway surface, the area ratio of the overlapping portion is 5% or less. The bearing according to claim 1 or 2, wherein the raceway surface has a surface roughness Ra of less than 0.1 μm.

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