bearings

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

Technical Field

[0001] The present disclosure relates to bearings.

Background Art

[0002] Peeling (micro-pitting) is a typical failure mode of bearings used under thin lubrication conditions. The thin lubrication conditions mean conditions where a sufficient oil film of lubricating oil cannot be formed at the contact portion between the raceway ring and the rolling elements of the bearing. "Mechanism of the occurrence of peeling due to rolling contact and the influence of blackening treatment on peeling suppression" (Non-Patent Document 1) introduces the mechanism that the folded portion formed on the raceway surface becomes the starting point of cracks, and then the raceway surface reaches peeling due to rolling fatigue.

[0003] In addition, Japanese Patent Application Laid-Open No. 2019-095044 (Patent Document 1) proposes to apply compressive residual stress to the raceway surface by vanishing processing for the purpose of extending the peeling life starting from non-metallic inclusions protruding on the surface. Japanese Patent Application Laid-Open No. 2019-095044 discloses that compressive residual stress is applied to the surface by performing plastic processing such as vanishing processing to suppress crack propagation. In Japanese Patent Application Laid-Open No. 2019-095044, peeling of the bearing starting from non-metallic inclusions is suppressed by applying compressive residual stress, and long life is realized.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

[0006] Japanese Patent Publication No. 2019-095044 describes a method of suppressing crack propagation by filling the gap between inclusions near the raceway surface and the base material through plastic deformation of the raceway surface. However, in Japanese Patent Publication No. 2019-095044, plastic deformation is performed on a surface that has a certain degree of roughness, crushing that roughness. As a result, folded portions are formed in the uneven areas after plastic deformation, as disclosed in Non-Patent Literature 1. These folded portions of the raceway surface can be considered as initial cracks, and cracks can cause peeling. Therefore, bearings used under lean lubrication conditions may have a shorter peeling life compared to bearings that are not plastically deformed if plastic deformation such as burnishing is performed. Japanese Patent Publication No. 2019-095044 and Non-Patent Literature 1 do not provide disclosures that delve into these issues.

[0007] This disclosure has been made in view of the above-mentioned problems. The purpose of this disclosure is to provide a bearing that can suppress the reduction in lifespan caused by overlapping parts such as folding sections. [Means for solving the problem]

[0008] The bearing according to this disclosure comprises a raceway ring with a raceway surface formed thereon. The residual stress on the raceway surface is 700 MPa or more. A portion of the raceway surface is formed in which a portion of the convex portion is superimposed on a concave portion. The maximum width of the superimposed portion is 1 μm or less. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a bearing that can suppress the reduction in lifespan caused by overlapping parts such as folding sections. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing the configuration of the deep groove ball bearing in this embodiment. [Figure 2]This is a photograph taken from above of the folding section formed on the track surface. [Figure 3] This is a photograph taken from above of the first example of recesses and protrusions obtained by applying a load to a test member of a track wheel. [Figure 4] This is a photograph taken from above of a second example of recesses and protrusions obtained by applying a load to a test member of a raceway. [Figure 5] This is a photograph taken from above of a third example of recesses and protrusions obtained by applying a load to a test member of a raceway. [Figure 6] This is a schematic diagram showing the first step of the initial crack formation mechanism in the raceway surface having a folded portion according to this embodiment. [Figure 7] This is a schematic diagram showing the second step of the initial crack formation mechanism in the raceway surface having a folded portion according to this embodiment. [Figure 8] This is a schematic diagram showing the third step of the initial crack formation mechanism in the raceway surface having a folded portion according to this embodiment. [Figure 9] This is a schematic diagram showing the fourth step in the initial crack formation mechanism of peeling in the raceway surface having a folded portion of this embodiment. [Figure 10] This is a photograph taken from above of the folding section formed on the raceway surface after superfinishing. [Figure 11] This is a photograph taken from above of the folded portion of a raceway surface after burnishing, where the surface roughness Ra before burnishing was 0.223 μm. [Figure 12] This is a photograph taken from above of the folded portion of a raceway surface after burnishing, where the surface roughness Ra before burnishing was 0.417 μm. [Figure 13] This is a schematic plan view showing the state in which polishing marks have been formed on the raceway surface before burnishing. [Modes for carrying out the invention]

[0011] This embodiment will be described below with reference to the drawings. The bearings to which the present embodiment is applicable are bearings in which pitting of the raceway surface is a problem, for example, bearings with low oil film parameters. More specifically, for example, application to bearings with a low rotational speed using a low-viscosity oil is conceivable. Therefore, the type of bearing is not particularly limited. For this reason, in the following description of the overall structure of the bearing, a deep groove ball bearing is shown as an example.

[0012] FIG. 1 is a schematic cross-sectional view showing the configuration of a deep groove ball bearing according to the present embodiment. Referring to FIG. 1, the deep groove ball bearing 1 of the present embodiment includes an annular outer ring 11, an annular inner ring 12 disposed inside the outer ring 11 with respect to the center line C, a plurality of balls 13 as rolling elements disposed between the outer ring 11 and the inner ring 12, and an annular cage 14 that holds the outer ring 11, the inner ring 12, and the plurality of balls 13.

[0013] The outer ring 11 is disposed so as to contact the plurality of balls 13 on the outside of the plurality of balls 13. The outer ring 11 has an outer raceway surface 11A on an inner peripheral surface formed on the inner side with respect to the center line C. The inner ring 12 is disposed so as to contact the plurality of balls 13 on the inside of the plurality of balls 13. The inner ring 12 has an inner raceway surface 12A on an outer peripheral surface formed on the outer side with respect to the center line C. The outer ring 11 and the inner ring 12 are disposed such that the outer raceway surface 11A and the inner raceway surface 12A face each other.

[0014] The plurality of balls 13 are spherical and have a ball rolling surface 13A on their surfaces. In other words, for each of the plurality of balls 13, the entire surface thereof is the ball rolling surface 13A. The plurality of balls 13 are configured to roll between the outer raceway surface 11A and the inner raceway surface 12A. The plurality of balls 13 contact the outer raceway surface 11A and the inner raceway surface 12A at the ball rolling surface 13A, and are arranged side by side with a pitch at intervals in the circumferential direction by the cage 14. Thereby, each of the plurality of balls 13 is held rotatably on an annular track. 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.

[0015] A grease composition (not shown) is sealed in the raceway space, which is the space between the outer ring 11 and the inner ring 12, more specifically, the space between the outer ring raceway surface 11A and the inner ring raceway surface 12A. This grease composition forms an oil film between each of the outer ring 11 and the inner ring 12 and the ball 13, thereby maintaining good lubrication between each of the outer ring 11 and the inner ring 12 and the ball 13. Hereafter, the outer ring 11 and the inner ring 12 will be referred to as the raceway ring 10. Also, hereafter, the outer ring raceway surface 11A and the inner ring raceway surface 12A will be referred to as the raceway surface 10A.

[0016] Figure 2 is a photograph of the folding portion formed on the raceway surface, viewed from above. Referring to Figure 2, in the bearing such as the deep groove ball bearing 1 of this embodiment, the raceway ring 10 is formed of either SUJ2 or SUJ3, which are high-carbon chromium bearing steels as specified in the JIS standard. Alternatively, the raceway ring 10 may be formed of carburized steel.

[0017] A folding section 20 is formed on the raceway surface 10A. The maximum width W of the folding section 20 is 1 μm or less. The width W of the folding section 20 is the dimension in the direction that intersects the direction in which the folding section 20 extends (left-right direction in Figure 2) (up-down direction in Figure 2). The folding section 20 will be described in detail below.

[0018] Figure 3 is a photograph taken from above of the first example of recesses and protrusions obtained by applying a load to a test member of the raceway. Referring to Figure 3, the raceway surface 10A shown here is the state after load application by the two-cylinder test. Wrinkle-like irregularities are formed on the raceway surface 10A. That is, as shown in Figure 3, two recesses G1 and G2 are formed on the raceway surface 10A. Recesses G1 and G2 extend in the left-right direction in the figure and both have width in the vertical direction in the figure. Protrusions are formed on both sides of recesses G1 and G2 in the width direction (vertical direction in Figure 3). That is, protrusions P1 and P2 are formed adjacent to recess G1, and protrusions P3 and P4 are formed adjacent to recess G2. Hereafter, recesses will be uniformly referred to as recesses G, and protrusions will be uniformly referred to as protrusions P. Recesses G and protrusions P extend along the rolling direction of the load transfer in the two-cylinder test.

[0019] Figure 4 is a photograph taken from above of a second example of recesses and protrusions obtained by applying a load to a test member of a raceway. Figure 4 shows a different part of the raceway, which is the same test member as in Figure 3. Referring to Figure 4, the test member of the raceway here is the driven cylinder of a two-cylinder testing machine, to which a load is applied by the drive cylinder of the two-cylinder testing machine. Recesses G are formed on the raceway surface 10A, similar to recesses G1 to G2 in Figure 3. Also, protrusions P are formed on the raceway surface 10A, similar to protrusions P1 to P4 in Figure 3. In the raceway surface 10A of Figure 4, the recesses G and protrusions P extend from the upper left to the lower right along the rolling direction. A part of the protrusions P is deformed by a force applied vertically from above. This force from above is applied by the drive cylinder of the two-cylinder testing machine, which can apply a load similar to that of a burnishing tool. A part of the deformed protrusions P tilts towards the recesses G. As a result, a portion of the convex portion P is formed as a folded portion 20 that overlaps with the concave portion G. On the raceway surface 10A, a notch 21 is formed in a portion of the folded portion 20.

[0020] Figure 5 is a photograph taken from above of a third example of recesses and protrusions obtained by applying a load to a test member of a raceway. Figure 5 shows a different part of the raceway of the same test member as in Figures 3 and 4. Referring to Figure 5, recesses G and protrusions P are formed along the rolling direction, similar to Figure 4. A folded portion 20 is formed in a part of the protrusion P (the lower area in the figure) that overlaps with the recess G. A notch 21 formed by the rolling of the protrusion P is also formed in the folded portion 20 in Figure 5. However, the notch 21 in Figure 5 is hidden by the folded portion 20 and is difficult to see.

[0021] The mechanism for forming the folded portion 20 will be explained in more detail using Figures 6 to 9. Figure 6 is a schematic diagram showing the first step of the initial peeling crack formation mechanism on the raceway surface having the folded portion of this embodiment. Figure 7 is a schematic diagram showing the second step of the initial peeling crack formation mechanism on the raceway surface having the folded portion of this embodiment. Referring to Figures 6 and 7, a test member of the raceway ring 10, which is a driven cylinder, is shown here. Small projections 101 extending upward are formed on the raceway surface 10A of the raceway ring 10. The small projections 101 are formed by the surface roughness of the raceway surface 10A. On the surface of the drive cylinder 30 facing the raceway surface 10A, projections 31 extending downward are formed. The projections 31 are formed by the surface roughness of the machined surface 30A of the drive cylinder 30.

[0022] As shown in Figure 6, the drive cylinder 30 moves in the direction of movement R, which is the depth direction of the paper, while the projection 31 applies a downward force F. Here, the direction of movement R corresponds to the direction of movement (rolling direction) in Figures 3 to 5. At this time, the small projection 101 comes into contact with the projection 31, and a force is applied from above by the projection 31. As a result, as shown in Figure 7, wrinkle-like irregularities are formed on the raceway surface 10A. Specifically, because the raceway surface 10A is pushed downward by the projection 31, the pushed portion moves downward, and a concave shape 102 is formed. The concave shape 102 corresponds to the recesses G (recesses G1, G2) in Figures 3 to 5. Conversely, the region adjacent to the region that has moved downward by the concave shape 102 moves upward, becoming a convex shape 103. The convex shape corresponds to the convex parts P (convex parts P1 to P4) in Figures 3 to 5. As a portion of the track surface 10A is pushed downward in this manner, regions that periodically move upward and regions that move downward are formed in the surrounding area. This results in multiple alternating concave portions 102 and convex portions 103, creating a wrinkled surface.

[0023] Figure 8 is a schematic diagram showing the third step of the initial peeling crack formation mechanism in the raceway surface having a folded portion of this embodiment. Referring to Figure 8, as the drive cylinder 30 moves, another projection different from the first step in Figure 6, specifically, for example, the convex portion 103 of the raceway surface 10A, is pushed downward by a force F.

[0024] Figure 9 is a schematic diagram showing the fourth step of the initial peeling crack formation mechanism in the raceway surface having a folded portion of this embodiment. Referring to Figure 9, the convex portion 103 that is pressed is deformed by being pressed from above in a direction along the vertical. In other words, the convex portion 103 is deformed by being 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 a convex portion 103, is folded so that a part of it lies toward the adjacent concave portion 102. In Figure 9, the left portion of the flattened portion 104 protrudes so as to enter the concave portion 102. The left portion of the flattened portion 104 enters the concave portion 102 located to its left, and in a plan view, the flattened portion 104 overlaps with the concave portion 102. The area where the flattened portion 104 overlaps with the concave portion 102 is the folded portion 20. In addition, in the right-hand portion of the flattened portion 104 in Figure 9, there may also be a folded portion that overlaps with the concave portion 102 adjacent to its right side. Therefore, the maximum width of the folded portion 20 is the maximum dimension of the portion that protrudes in a direction perpendicular to its extension direction so as to overlap with the concave portion 102.

[0025] The formation of the folded portion 20 creates a notch 21 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 right end in Figure 9, opposite to the boundary between the flattened portion 104 and the concave portion 102), which causes an initial crack 25 to occur. Once the initial crack 25 occurs, for example, the initial crack 25 may propagate from the tip 21P of the notch 21 through the raceway ring 10, roughly from left to right in Figure 9. When this happens, peeling occurs. That is, a peeled portion 26 is formed as shown in Figure 9. Peeling is a phenomenon in which a thin region between the initial crack and the raceway surface 10A is peeled away from the raceway ring 10.

[0026] As described above, compressive residual stress is generated in the raceway surface 10A and the relatively shallow region adjacent to it, where plastic deformation such as burnishing is performed, due to macroscopic plastic deformation of the surface layer. As a result, the residual stress (compressive residual stress) in the raceway surface 10A becomes 700 MPa or higher. Specifically, a residual stress of 700 MPa or higher means that the average value measured at any three locations on the raceway surface 10A itself is 700 MPa or higher.

[0027] Next, the effects and advantages of this embodiment will be described. 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 part in which a protrusion P is superimposed on a recess G formed in the raceway surface 10A. The maximum width W of the folded portion 20 is 1 μm or less.

[0028] As a result of diligent research, the inventors of this embodiment have obtained a new finding that the occurrence of peeling on 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 deformation of the raceway surface 10A. By reducing the width W of the folded portion 20 of the raceway surface 10A formed by plastic deformation (burnishing), the propagation of the initial crack 25 originating from the folded portion 20 is suppressed. It is generally believed that the notch 21 and the initial crack 25 are formed by the folded portion 20. If the initial crack 25 propagates, peeling occurs. Therefore, if the propagation of the initial crack 25 is suppressed, the occurrence of peeling on the raceway ring 10 can also be suppressed. In this way, even under lean lubrication conditions, premature delamination of the raceway surface 10A originating from peeling generated from the folded portion 20 of the bearing can be suppressed, and the reduction in bearing life can be suppressed. Further explanation of this follows.

[0029] As shown in Figures 6 to 9, the folded portion 20 is formed by plastic deformation of the roughness components originally present on the raceway surface 10A, or the roughness components of mating parts such as the drive cylinder 30 that have been transferred to the raceway surface. In particular, if a plastic deformation process such as burnishing is performed on a polished surface (a surface that has not undergone superfinishing), it has been confirmed that the convex-shaped portions 103 of the roughness components are folded by the plastic deformation. On the other hand, when the raceway surface 10A is superfinished, a large folded portion 20 is not formed in the processing step. Figure 10 is a photograph of the folded portion formed on the raceway surface after superfinishing, viewed from above. Referring to Figure 10, even if it is observed, the maximum width of the folded portion on the superfinished raceway surface 10A is relatively small, at about 0.1 μm. Therefore, if the width of the folded portion is about 0.1 μm (a so-called submicron level size), the reduction in peeling life due to burnishing can be suppressed. From this perspective, if the width of the folded portion 20 is 1 μm or less, the reduction in peeling life can be suppressed.

[0030] As described above, the folding portion 20 is formed based on the uneven shape of the raceway surface 10A before plastic deformation. For this reason, it is preferable to reduce the unevenness of the raceway surface 10A before plastic deformation as a manufacturing method. This makes it possible to reduce the size of the folding portion 20. Figure 11 is a photograph taken from above of the folding portion after burnishing of a raceway surface with a surface roughness Ra of 0.223 μm before burnishing. Referring to Figure 11, the maximum width W of the folding portion 20 formed after burnishing of the raceway surface 10A was 1.6 μm. Figure 12 is a photograph taken from above of the folding portion after burnishing of a raceway surface with a surface roughness Ra of 0.417 μm before burnishing. Referring to Figure 12, the maximum width W of the folding portion 20 formed after burnishing of the raceway surface 10A was 6.3 μm. From Figures 11 and 12, the maximum width W of the folded section 20 after burnishing is approximately 10 times the surface roughness Ra value before burnishing. Surface roughness Ra represents the average of the absolute values ​​of roughness within a standard length range as defined in the JIS standard.

[0031] 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 deformation. More specifically, it is preferable that the Rz of the raceway surface 10A before plastic deformation be 1 μm or less, and 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 range of the reference length as defined in the JIS standard.

[0032] Burnishing smooths the surface by plastically deforming the roughness components. Therefore, the width W and other dimensions of the folded portion 20 formed on the raceway surface 10A by burnishing are affected by the roughness of the raceway surface 10A before processing. By making the roughness of the raceway surface 10A before processing sufficiently small (making it nearly flat), the folded portion 20 after burnishing can be made smaller. Since the folded portion 20 usually has an initial crack 25, the folded portion 20 can also be considered as the initial crack 25. In this case, since the peeled portion 26 is formed by the propagation of the initial crack 25, the smaller the initial crack 25, i.e., the folded portion 20, the less likely the initial crack 25 is to propagate, and the less likely peeling is to occur. As a result, by reducing the width of the folded portion 20, the peeling life can be extended compared to the case where the width of the folded portion 20 (initial crack 25) is large.

[0033] The presence or absence of crack propagation, or peeling, is basically determined by the length of the crack. The initial crack 25 is formed to extend in the width direction of the folded portion 20, as shown in Figure 9. Therefore, the width W of the folded portion 20 is more important than its length.

[0034] In the bearing described above, 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 burnishing (final product) is usually less than 0.1 μm. As described above, the width W of the folded portion 20 in the final product is about 10 times the surface roughness Ra, and due to this characteristic, the maximum width W of the folded portion 20 of the raceway surface 10A in the final product can be set to 1 μm or less. Within the above numerical range, the surface roughness Ra of the raceway surface 10A before burnishing is particularly 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, and more preferably 0.06 μm or less.

[0035] In the bearing described above, the area ratio of the folded portion within any 100 μm × 100 μm area of ​​the raceway surface may be 5% or less. This means that no matter how a 100 μm × 100 μm area is extracted from the raceway surface 10A, the area ratio of the folded portion within that area will be 5% or less. As described above, the width of the folded portion 20 greatly affects the lifespan of the bearing. On the other hand, if the area of ​​the peeling portion 26 becomes larger than a certain size, it will affect the function of the bearing. Therefore, by reducing the area of ​​the folded portion 20 as described above, the area (length) of the peeling portion 26 can be reduced. This makes it possible to suppress the deterioration of the bearing's function.

[0036] In addition, the bearing may have the following features. Figure 13 is a schematic plan view showing the raceway surface with polished marks formed before burnishing. Referring to Figure 13, multiple polished marks 40 are formed on the raceway surface 10A before burnishing. Burnishing is performed along the direction in which the polished marks 40 extend, and the folding portion 20 is usually formed along the direction in which the polished marks 40 extend. If we consider one folding portion 20 formed on one of the multiple polished marks 40 within any 100 μm × 100 μm range of the raceway surface 10A, then the number of folding portions 20 is five or less. For example, as in Figure 13, if multiple folding portions 20 are formed at intervals on a single polished mark 40, this is considered to be one folding portion 20. Therefore, in reality, there may be six or more folding portions 20 within a 100 μm × 100 μm range. By doing so, the same effects and advantages as when the area ratio of the folding portion 20 is 5% or less can be obtained.

[0037] As described above, the folded portion 20 is considered to be an initial crack 25. Therefore, by reducing the number of folded portions 20, the occurrence of widespread peeling due to the connection of initial cracks 25 can be suppressed. Widespread peeling can lead to large-scale delamination of the raceway surface 10A starting from the peeling, making continued use of the bearing impossible. Therefore, a reduction in the bearing's lifespan can be suppressed. The connection of initial cracks 25 occurs when an initial crack 25 extends in the width direction of the folded portion 20 and connects with other initial cracks 25. Therefore, the possibility of initial cracks 25 of multiple folded portions 20 on the same polished surface 40 connecting with each other is low.

[0038] The measurement methods for each of the above parameters are as follows: Compressive residual stress can be measured by cutting out a portion of the surface of the bearing component, electropolishing the surface, and using an X-ray diffractometer. The width and area of ​​the folding portion 20 are measured by cutting out a region of the raceway surface 10A to be measured, and then observing the raceway surface 10A with, for example, a Scanning Electron Microscope (SEM) for length measurement. 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, for example, by measuring it with a confocal laser microscope.

[0039] In the above description, the folded portion 20 formed by the process shown in Figures 6 to 9 is used as an example of the portion where the convex portion P is superimposed on the concave portion G. However, the "superimposed portion" in this embodiment is not limited to the so-called "folded portion" formed by the process shown in Figures 6 to 9, but includes all portions where the track surface 10A is partially overlapped two or more times, resulting from other processes.

[0040] The features described in the embodiments (and their respective examples) described above may be applied in appropriate combinations to the extent that they do not contradict the technical standards.

[0041] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of symbols]

[0042] 1 Deep groove ball bearing, 10 Raceway ring, 10A Raceway surface, 11 Outer ring, 11A Outer ring raceway surface, 12 Inner ring, 12A Inner ring 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 Machined surface, 31 Projection, 40 Polished surface, 101 Small projection, 102 Concave shape, 103 Convex shape, 104 Flattened part, G, G1, G2 Concave, P, P1, P2, P3, P4 Convex, R Direction of movement.

Claims

1. A bearing comprising a raceway ring with a raceway surface formed thereon, The residual stress on the aforementioned raceway surface is 700 MPa or more. A portion is formed in which a part of the protrusion overlaps a recess formed in the aforementioned raceway surface. A bearing in which the maximum width of the overlapping portion is 1 μm or less.

2. The bearing according to claim 1, wherein within any 100 μm × 100 μm range of the raceway surface, the area ratio of the superimposed portion is 5% or less.

3. The bearing according to claim 1 or 2, wherein the surface roughness Ra of the raceway surface is less than 0.1 μm.

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