Manufacturing method of rolling parts and bearings

Abstract

To provide a rolling component, a bearing, and manufacturing methods of these capable of suppressing peeling caused by a fiber flow, and both of inclusion origin type pealing and surface origin type peeling.SOLUTION: A rolling component has a surface. A fiber flow FF is included in the rolling component. An angle α formed by the surface and the fiber flow FF is equal to or larger than 15°. In a region within a depth of 100 μm from the surface, a maximum compression residual stress is equal to or higher than 700 MPa. A residual austenite amount on the surface is 11% or more and 28% or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to rolling parts, bearings, and methods for manufacturing them, and particularly to rolling parts, bearings, and methods for manufacturing them in which the constituent members include fiber flow.

Background Art

[0002] In order to extend the life of a bearing, for example, in Japanese Unexamined Patent Application Publication No. 2019-095044 (Patent Document 1), rolling parts constituting a bearing are proposed in which the angle formed by the fiber flow and the raceway surface is 15° or more and the surface compressive residual stress is 700 MPa or more. In Japanese Unexamined Patent Application Publication No. 2019-095044, sufficient compressive residual stress is imparted to the surface by performing plastic working such as burnishing on the surface of the rolling part. As a result, the gap between the non-metallic inclusions in the rolling part and the base material of the rolling part is reduced, and crack propagation is suppressed. For this reason, peeling of the bearing surface starting from the non-metallic inclusions is suppressed, and the life of the bearing is extended.

[0003] On the other hand, peeling of the bearing surface includes, in addition to inclusion-initiated peeling starting from non-metallic inclusions as described above, surface-initiated peeling starting from indentations generated on the surface due to the biting-in of foreign matter mixed in the lubricating oil. Surface-initiated peeling may occur in a shorter time than inclusion-initiated peeling. In order to prevent the occurrence of surface-initiated peeling, for example, it is conceivable to adopt a design in which foreign matter is not allowed to enter the bearing by adding a seal or the like. In addition, in order to prevent the occurrence of surface-initiated peeling, for example, Japanese Unexamined Patent Application Publication No. 2016-108596 (Patent Document 2) proposes a technique of increasing the amount of retained austenite on the surface by a special heat treatment. This is because if the amount of retained austenite is increased, the shape of the indentation on the surface caused by foreign matter is deformed, and stress concentration around the indentation is alleviated.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] The hub bearing used in an automobile has a structure of a double-row angular ball bearing. For this reason, in the hub bearing, the fiber flow is likely to form a large angle with respect to the raceway surface. In some cases, it is necessary to apply residual stress to the hub bearing in order to prevent shortening of the service life due to fiber flow. However, if residual stress is applied by burnishing as in Japanese Unexamined Patent Application Publication No. 2019-095044, the amount of retained austenite decreases. If the amount of retained austenite decreases, stress concentration around the indentation on the surface due to foreign matter is induced, and surface-initiated peeling is likely to occur. Neither Japanese Unexamined Patent Application Publication No. 2019-095044 nor Japanese Unexamined Patent Application Publication No. 2016-108596 has considered a configuration in which the angle of the fiber flow with respect to the raceway surface is large, compressive residual stress is applied to the surface, and surface-initiated peeling due to the intrusion of foreign matter is suppressed.

[0006] The present disclosure has been made in view of the above problems. An object thereof is to provide a rolling component, a bearing, and a method for manufacturing them that can suppress any of peeling caused by fiber flow, inclusion-initiated peeling, and surface-initiated peeling. [Means for Solving the Problems]

[0007] The rolling component according to the present disclosure has a surface. The rolling component includes a fiber flow. The angle formed by the surface and the fiber flow is 15° or more. In a region within 100 μm from the surface, the maximum compressive residual stress is 700 MPa or more. The amount of retained austenite on the surface is 11% or more and 28% or less.

[0008] The bearing according to the present disclosure includes an outer ring, rolling elements, and an inner ring. The rolling elements are arranged on the inner circumferential surface of the outer ring. The inner ring is arranged on the inner circumferential side of the rolling elements. At least one of the outer ring, the rolling elements, and the inner ring is the above-described rolling component. The surface of the rolling component is any one of the raceway surface of the outer ring, the raceway surface of the inner ring, and the rolling surface of the rolling elements.

[0009] A method for manufacturing a rolling component having a surface according to the present disclosure includes preparing a member having a surface to be machined and including fiber flow. The surface to be machined is subjected to polishing. After the polishing, the surface to be machined is subjected to plastic working. The angle formed by the surface and the fiber flow is 15° or more. The maximum compressive residual stress is formed to be 700 MPa or more in a region within 100 μm from the surface. The amount of retained austenite on the surface is 11% or more and 28% or less. Burnishing is performed in the step of performing the above-described plastic working.

[0010] The bearing in the method for manufacturing a bearing according to the present disclosure includes an outer ring, rolling elements, and an inner ring. The rolling elements are arranged on the inner circumferential surface of the outer ring. The inner ring is arranged on the inner circumferential side of the rolling elements. At least one of the outer ring, the rolling elements, and the inner ring is the above-described rolling component. The surface of the rolling component is any one of the raceway surface of the outer ring, the raceway surface of the inner ring, and the rolling surface of the rolling elements.

Advantages of the Invention

[0011] According to the present disclosure, rolling components, bearings, and methods for manufacturing them that can suppress any of peeling caused by fiber flow, inclusion-initiated peeling, and surface-initiated peeling can be obtained.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

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Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present embodiment will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a partial structure of a hub bearing according to the present embodiment. Referring to FIG. 1, the bearing according to the present embodiment is an automotive hub bearing 10. The hub bearing 10 is for a driven wheel. The hub bearing 10 mainly includes rolling elements 1 included in a plurality in each of two rows, an inner ring 2, an outer ring 3, a hub ring 4, and a cage 5. The rolling element 1 has a rolling surface 1a. The inner ring 2 has a raceway surface 2a. The outer ring 3 has a double row (two rows in FIG. 1) of raceway surfaces 3a. The outer ring 3 is connected to a knuckle (not shown) by bolts (not shown). The hub ring 4 has a raceway surface 4a. The plurality of rolling elements 1 in two rows are sandwiched between the raceway surface 2a, the raceway surface 3a, and the raceway surface 4a and held by the cage 5. A high load is applied to the raceway surfaces 2a, 3a, 4a from the rolling elements 1. For this reason, a surface hardened layer is formed on the raceway surfaces 2a, 3a, 4a by induction hardening or the like. The hub ring 4 has a non-cut portion. A seal 6 is disposed to close the gap between the outer ring 3 and the inner ring 2 and the hub ring 4.

[0014] The hub ring 4 functions as a part of the inner ring of the hub bearing 10. In other words, both the inner ring 2 and the hub ring 4 are inner rings disposed on the inner peripheral side of the rolling element 1 in the hub bearing 10. Although only a part of the hub ring 4 in FIG. 1 is disposed on the inner peripheral side of the rolling element 1 and the other part is disposed outside the rolling element 1, the hub ring 4 in this case is regarded as being disposed on the inner peripheral side of the rolling element 1 here. The hub bearing 4 is caulked so as to clamp the inner ring 2 provided separately in the hub bearing 10. Specifically, a caulking portion 4b is formed on the hub ring 4, and the inner ring 2 is caulked by the caulking portion 4b. The above caulking process uses a rocking caulking method. The hub ring 4 has a stepped wall 4s. The inner ring 2 is coupled to the hub ring 4 in a state of being pressed against the stepped wall 4s.

[0015] Hub bolts 11 are arranged on the hub ring 4. The hub ring 4 is connected to a tire (not shown) and is rotatably supported. In FIG. 1, the holes through which the hub bolts 11 pass are provided in the wheel mounting flange 4c. For weight reduction, a structure may be adopted in which the wheel mounting flange 4c is an arm for each hub bolt. The hub ring 4 has surfaces 4d on the inboard side of the wheel mounting flange 4c and on the outside of the central portion, and by making these non-machined surfaces, the manufacturing cost is reduced.

[0016] The vehicle body load of the automobile reaches the wheel via the outer ring 3 → rolling elements 1 → inner ring 2 and hub ring 4 and balances with the reaction force from the ground.

[0017] As described above, the hub bearing 10 includes rolling elements 1 as rolling parts, an inner ring 2 as an inner ring, a hub ring 4, and an outer ring 3. In other words, at least one of the rolling elements 1, inner ring 2, outer ring 3, and hub ring 4 is the above-mentioned rolling part. FIG. 2 is a schematic cross-sectional view of the area II surrounded by the dotted line in FIG. 1. (A) of FIG. 2 shows a state in which a fiber flow FF is formed in the inner ring 2. Referring to FIG. 2(A), for example, the rolling surface 1a of the rolling element 1 and the raceway surface 2a of the inner ring 2 are in contact with each other. Each rolling part such as the rolling surface 1a and the raceway surface 2a has a surface that contacts another rolling part. Although not shown in FIG. 2, the rolling surface 1a of the rolling element 1 and the raceway surface 3a of the outer ring 3 are also in contact with each other. That is, the outer ring 3, which is a rolling part, also has a raceway surface 3a that is a surface that contacts the rolling element 1, which is another rolling part. The rolling surface 1a of the rolling element 1 and the raceway surface 4a of the hub ring 4 are also in contact with each other. That is, the hub ring 4, which is a rolling part, also has a raceway surface 4a that is a surface that contacts the rolling element 1, which is another rolling part.

[0018] As shown in FIG. 2(A), for example, the inner ring 2, which is a rolling part, includes a fiber flow FF in its structure. The angle α formed by the raceway surface 2a, which is the surface of the inner ring 2, and the fiber flow FF included in the inner ring 2 is 15° or more. (A) of FIG. 2 shows that the inner ring 2 may be replaced with the hub ring 4 and the raceway surface 2a may be replaced with the raceway ring 4a.

[0019] (B) of FIG. 2 shows a state where the fiber flow FF is formed on the rolling element 1. Referring to FIG. 2(B), the fiber flow FF may be included on the side of the rolling element 1. Even in this case, the angle α formed between the rolling surface 1a, which is the surface of the rolling element 1, and the fiber flow FF included in the rolling element 1 is 15° or more.

[0020] In the rolling surface 1a of the rolling element 1, the raceway surface 2a of the inner ring 2, the raceway surface 3a of the outer ring 3, the raceway surface 4a of the hub ring 4, and the region within 100 μm in the vertical direction from the surface, the maximum compressive residual stress, which is the maximum of the compressive residual stresses, is 700 MPa or more. Also, the rolling surface 1a and the raceway surfaces 2a, 3a, 4a have a retained austenite amount of 11% or more and 28% or less. Here, the retained austenite amount in the surface layer including the rolling surface 1a and the raceway surfaces 2a, 3a, 4a is shown. The surface layer means not only the exposed rolling surface 1a and the raceway surfaces 2a, 3a, 4a, but also a very shallow region within the rolling parts adjacent to the exposed rolling surface 1a and the raceway surfaces 2a, 3a, 4a.

[0021] FIG. 3 is a schematic cross-sectional view showing the gap between the base material of the rolling part and the non-metallic inclusions present in the base material. In particular, FIG. 3(A) shows the state of the non-metallic inclusions arranged so as to be exposed on the surface of the base material, and FIG. 3(B) shows the state of the non-metallic inclusions inside away from the surface of the base material. Referring to FIGS. 3(A) and 3(B), in rolling parts such as the inner ring 2, the gap 42 between the non-metallic inclusion 41 existing on the surface side (the upper side in FIG. 3(A)) of the raceway surface 2a and the base material constituting the inner ring 2 is smaller than the gap 42 between the non-metallic inclusion 41 existing on the inner side away from the raceway surface 2a of the inner ring 2 and the base material constituting the inner ring 2. This is the same for the rolling element 1, the outer ring 3, and the hub ring 4. As shown in FIG. 3(A), there may be no gap between the non-metallic inclusion 41 on the surface side of the raceway surface 2a and the base material.

[0022] The materials constituting the rolling element 1, inner ring 2, outer ring 3, and hub ring 4 may be steel. Needless to say, the steel has iron (Fe) as the main component and may contain inevitable impurities in addition to the above elements. Examples of the inevitable impurities include phosphorus (P), sulfur (S), nitrogen (N), oxygen (O), aluminum (Al), and the like. The amounts of these inevitable impurity elements are each 0.1 mass% or less. The rolling element 1, inner ring 2, outer ring 3, and hub ring 4 may be formed of a steel material having an oxygen content of, for example, 5 ppm or more.

[0023] The steel is, for example, JIS standard S53C, which is an example of a material for a shaft. S53C contains 0.5 mass% or more and 0.56 mass% or less of carbon, 0.15 mass% or more and 0.35 mass% or less of silicon, and 0.6 mass% or more and 0.9 mass% or less of manganese. Further, S53C contains 0.03 mass% or less of phosphorus, 0.035 mass% or less of sulfur, 0.2 mass% or less of chromium, and 0.02 mass% or less of nickel.

[0024] Next, a method for manufacturing a rolling component having the above configuration and a hub bearing 10 including the same will be described with reference to FIGS. 4 to 9. Note that FIGS. 4 to 9 below show an example of the manufacturing process of the inner ring 2. However, the manufacturing processes of the rolling element 1, the outer ring 3 disposed on the outer peripheral surface of the rolling element 1, and the hub ring 4 including a portion disposed on the inner peripheral surface of the rolling element 1 are the same as those of the inner ring 2.

[0025] FIG. 4 is a schematic view showing a first step of a method for manufacturing a rolling component. Referring to FIG. 4, first, a steel material 101 for forming any one of the rolling element 1, inner ring 2, outer ring 3, and hub ring 4, which are rolling components, is prepared. The material of the steel material 101 is as described above. The steel material 101 includes, for example, a fiber flow FF extending in the left-right direction of the figure. A rolling component forming region 103 is cut out from the steel material 101 by a cutting tool 102.

[0026] FIG. 5 is a schematic view showing a second step of a method for manufacturing a rolling component. Referring to FIG. 5, a member having a cavity 104 in the central portion is formed to form the inner ring 2.

[0027] Figure 6 is a schematic view showing the third step of the method for manufacturing a rolling part. Referring to Figure 6, machining such as grinding, which is generally known, and heat treatment such as quenching are performed on the outer peripheral surface of the inner ring 2. As a result, a member is formed that includes a fiber flow FF and has an outer peripheral surface, i.e., a surface to be machined 2B, that is inclined with respect to the direction in which the fiber flow FF extends. The surface to be machined 2B is formed such that the angle formed with the fiber flow FF is 15° or more.

[0028] Figure 7 is a schematic view showing the fourth step of the method for manufacturing a rolling part. Referring to Figure 7, polishing is performed on the surface to be machined 2B of the inner ring 2. Here, for example, it is preferable to perform polishing using an internal grinding machine.

[0029] After the step of performing the polishing of Figure 7, plastic working is performed on the surface to be machined 2B. As a result, the surface to be machined 2B becomes the raceway surface 2a of the inner ring.

[0030] Figure 8 is a schematic view showing the fifth step of the method for manufacturing a rolling part. In particular, Figure 8 shows an example of the above plastic working. Referring to Figure 8, in the step of performing plastic working, for example, it is preferable to perform burnishing. In burnishing, for example, a pressing portion CC such as a ceramic hard ball or a diamond protrusion is used as a tool. In Figure 8, a spherical pressing portion CC is shown as an example. The pressing portion CC is rotated in the direction of arrow R1 in the figure, and while the inner ring 2 is rotated in the circumferential direction of arrow R2 about an imaginary axis L passing through the cavity 104, the pressing portion CC presses on the surface to be machined 2B with the force shown by arrow F. This pressing is performed such that the burnishing tool 25 to which the pressing portion CC is attached applies a force in the direction of arrow F to the pressing portion CC. Also, the burnishing tool 25 is caused to move on the surface to be machined 2B so that the pressing portion CC moves in the direction of arrow M. As a result, minute uneven shapes and the like existing on the surface to be machined 2B are flattened.

[0031] Before the step of performing plastic working, the member may be subjected to carbonitriding treatment. The carbonitriding treatment is carried out, for example, in a gas furnace in an atmosphere of 850°C or higher and 960°C or lower, in which a carbon having a volume ratio of 1.0% and ammonia having a volume ratio of 7% are mixed in endothermic modified gas (Rx gas). The rolling parts obtained as described above have the same properties as the rolling parts shown in FIGS. 2(A) and (B) above.

[0032] Next, the operation and effect of the present embodiment will be described. The rolling parts (rolling element 1, inner ring 2, outer ring 3, hub ring 4) according to the present disclosure have a surface. The rolling parts contain fiber flow FF. The angle formed by the surface and the fiber flow FF is 15° or more. In a region within 100 μm from the surface, the maximum compressive residual stress is 700 MPa or more. The amount of retained austenite on the surface is 11% or more and 28% or less. Here, the region within 100 μm from the surface includes the surface.

[0033] In the rolling parts, in the raceway surface 2a of the inner ring 2 which is the surface, and the region within 100 μm from there, the maximum compressive residual stress is 700 MPa or more. As a result, the gap between the non-metallic inclusions exposed on the surface of the raceway surface and the surrounding base material becomes narrow or is filled and blocked so as to disappear.

[0034] That is, in particular, as shown in FIG. 3, by plastic working, the gap 42 between the non-metallic inclusions 41 on the surface side such as the raceway surface 2a and the base material becomes smaller than the gap 42 between the non-metallic inclusions 41 on the inner side of the rolling parts and the base material. Therefore, the cause of early breakage of the rolling parts due to cracks is reduced (or eliminated). As a result, the propagation of cracks (inclusion-originated peeling) starting from the gap 42 between the non-metallic inclusions 41 and the base material on the rolling surfaces 1a and the raceway surfaces 2a, 3a, 4a can be suppressed, and the long life of the bearing can be achieved.

[0035] Also, from the viewpoint of suppressing peeling caused by opening cracks, it is preferably that the angle formed by the fiber flow FF and the rolling surfaces 1a and the raceway surfaces 2a, 3a, 4a is 15° or less as described above. Also, from the viewpoint of using clean steel materials, it is considered preferable that the oxygen content of the rolling parts is 5 ppm or less. However, in the present embodiment, even if the above angle is 15° or more, the generation of peeling caused by opening cracks can be suppressed by the above plastic working, and the long life of the bearing can be achieved. Also, in the present embodiment, the oxygen content of the rolling element 1, the inner ring 2, the outer ring 3, and the hub ring 4 may be 5 ppm or more. Even if the oxygen content is 5 ppm or more, the generation of peeling caused by opening cracks can be suppressed by the above plastic working, and the long life of the bearing can be achieved.

[0036] Also, by setting the retained austenite amount on the surface of the rolling parts to 11% or more, when an indentation is formed on the surface and the rolling element 1 rolls in contact thereover, the deformation of the indentation shape and stress concentration can be alleviated. This is because retained austenite is softer than martensite, which is the main structure constituting the material of the rolling parts after quenching, and is more likely to deform than martensite. Therefore, surface-initiated peeling starting from indentations generated on the surface due to foreign matters or the like can be suppressed. However, in order to obtain this effect, it is necessary that the retained austenite amount is 11% or more. However, if the retained austenite amount on the surface of the rolling parts exceeds 28%, the dimensional stability of the rolling parts will decrease. Therefore, by setting the retained austenite amount to 28% or less, it is possible to suppress a decrease in dimensional stability while suppressing a reduction in the service life due to surface-initiated peeling caused by foreign matter intrusion or the like. The retained austenite amount can be measured by cutting out a part of the surface of the bearing parts, electro-polishing the surface, and using an X-ray diffractometer. Also, the maximum compressive residual stress can be measured in the same manner as the retained austenite amount, by cutting out a part of the surface of the bearing parts, electro-polishing the surface, and using an X-ray diffractometer.

[0037] The bearing according to the present disclosure includes an outer ring 3, rolling elements 1, and an inner ring 2 (the inner ring 2 includes both cases with and without a hub ring 4 described below). The rolling elements 1 are arranged on a raceway surface 3a which is the inner peripheral surface of the outer ring 3. The inner ring 2 is arranged on the inner peripheral side of the rolling elements 1. At least one of the rolling elements 1, the inner ring 2, and the outer ring 3 is the above-described rolling component. The surface of the above-described rolling component is any one of the raceway surface 3a of the outer ring 3, the raceway surface 2a of the inner ring 2 (which may include the raceway ring 4a), and the rolling surface 1a of the rolling elements 1. Thereby, the bearing can obtain the effect of improving the lifespan by suppressing the occurrence of peeling as described above.

[0038] The above-described bearing is used as an automotive hub bearing, and the automotive hub bearing may further include a hub ring 4 as at least a part of the inner ring 2. In this case, the above-described inner ring 2 includes, for example, both the inner ring 2 and the hub ring 4 in FIG. 1. When plastic working such as burnishing is performed on the rolling components constituting the automotive bearing, the retained austenite in the surface layer undergoes processing-induced transformation, and the amount of retained austenite in the surface layer decreases. When the amount of retained austenite in the surface layer is small, the surface layer becomes sensitive to foreign substances, and surface-initiated peeling is likely to occur.

[0039] In addition, since the automotive hub bearing has a structure of a double-row angular ball bearing, there is a possibility that mud and water may enter during the running of the vehicle. Therefore, the automotive hub bearing is required to have high durability against foreign substances.

[0040] In general, fiber flow in a hub bearing tends to form a large angle with the raceway surface. However, in the automotive hub bearing 10 according to the present disclosure, in the region within 100 μm from the surface, the maximum compressive residual stress is 700 MPa or more as described above. Therefore, even if the angle between the surface and the fiber flow FF becomes as large as 15° or more, the life can be extended against peeling starting from the non-metallic inclusions 41. Further, the automotive hub bearing 10 includes rolling elements having a retained austenite amount of 11% or more and 28% or less. For this reason, even if the angle between the surface and the fiber flow FF is as large as 15° or more and peeling due to an open crack is likely to occur, surface-originated peeling can be suppressed, and even if foreign matter enters during the running of the vehicle, the bearing life can be extended.

[0041] The manufacturing method according to the present disclosure is a method for manufacturing a rolling element having a surface. The manufacturing method includes a workpiece surface 2B, and a member including a fiber flow FF is prepared. The workpiece surface 2B is subjected to polishing. After the polishing, the workpiece surface 2B is subjected to plastic working. The angle formed between the surface (rolling surfaces 1a and raceway surfaces 2a, 3a, 4a) and the fiber flow FF is 15° or more. In the region within 100 μm from the surface, the maximum compressive residual stress is formed to be 700 MPa or more. The retained austenite amount on the surface is 11% or more and 28% or less. In the step of performing plastic working, burnishing is performed.

[0042] Due to having the above configuration, according to the manufacturing method of the present embodiment, even under conditions where peeling is likely to occur, inclusion-originated peeling and surface-originated peeling can be suppressed, and the bearing life can be extended.

[0043] In the manufacturing method of the above rolling element, before the step of performing plastic working, a step of subjecting the member to carbonitriding treatment may be further provided. By the carbonitriding treatment, the retained austenite amount on the surface (surface layer) of the rolling element can be increased. Specifically, for example, the retained austenite amount on the surface can be made 11% or more and 28% or less. Thereby, stress concentration around the indentation due to the biting-in of foreign matter can be alleviated, and by suppressing surface-originated peeling, the bearing life can be extended.

[0044] The bearing according to the manufacturing method of the present disclosure includes an outer ring 3, rolling elements 1, and an inner ring 2 (the inner ring 2 includes both the case of having a hub ring 4 described below and the case of not having it). The rolling elements 1 are arranged on a raceway surface 3a which is the inner peripheral surface of the outer ring 3. The inner ring 2 is arranged on the inner peripheral side of the rolling elements 1. At least one of the rolling elements 1, the inner ring 2, and the outer ring 3 is the above-mentioned rolling component. The surface of the above-mentioned rolling component is any one of the raceway surface 3a of the outer ring 3, the raceway surface 2a of the inner ring 2 (which may include the raceway ring 4a), and the rolling surface 1a of the rolling elements 1. The bearing obtained by the manufacturing method can obtain the effect of improving the life by suppressing the occurrence of peeling as described above. The bearing according to the manufacturing method is used as an automotive hub bearing, and the automotive hub bearing may further include a hub ring 4 as at least a part of the inner ring 2.

Example

[0045] The results of investigating how the amount of retained austenite in the surface layer of the rolling component changes by plastic working (burnishing) are shown below. FIG. 9 is a graph showing the amount of retained austenite in the surface layer of a rolling component made of SUJ2 before and after burnishing. FIG. 10 is a graph showing the amount of retained austenite in the surface layer of a rolling component made of SCM445H before and after burnishing. In each of the graphs of FIG. 9 and FIG. 10, the horizontal axis represents the depth from the surface of the rolling component (the unit is μm), and the vertical axis represents the amount of retained austenite at that depth (the unit is %). Here, the amount of retained austenite indicates the volume ratio occupied by the retained austenite with respect to the entire depth region.

[0046] Referring to Fig. 9, in the case of a rolling part made of SUJ2, if the amount of retained austenite in the surface layer before the vanishing process ( "without vanishing" in the graph) is about 12% or more and 14% or less, after the vanishing process ( "with vanishing" in the graph), the amount of retained austenite in the surface layer of the same sample is generally 6% or more and 8% or less. On the other hand, referring to Fig. 10, in the case of a rolling part made of SCM445, if the amount of retained austenite in the surface layer before the vanishing process is about 5% or more and 7% or less, the amount of retained austenite in the surface layer of the same sample after the vanishing process is generally 3% or more and 5% or less. From this, it can be seen that if the amount of retained austenite in the surface layer is less than 10% before the vanishing process, almost no retained austenite remains in the surface layer after the vanishing process.

Example

[0047] The results of investigating the relationship between the depth from the surface and the amount of retained austenite in a rolling part with a larger amount of retained austenite compared to a normal product quenched with SUJ2 are shown below. Fig. 11 is a graph showing the amount of retained austenite in the surface layer of a rolling part made of SUJ3 that has been carbonitrided before and after the vanishing process. In the graph of Fig. 11, the horizontal axis indicates the depth from the surface of the rolling part (unit: μm), and the vertical axis indicates the amount of retained austenite at that depth (unit: %).

[0048] Referring to Fig. 11, by performing carbonitriding treatment on SUJ3, it was confirmed that for a rolling part of a bearing made of SUJ3 with a larger amount of retained austenite compared to a normally quenched product made of SUJ2, the amount of retained austenite on the surface after the vanishing process is 11% or more and 28% or less.

[0049] Here, SUJ3 specifically refers to a type of high-carbon chromium bearing steel with a higher manganese ratio than, for example, SUJ2. The above carburizing nitrocarburizing treatment was carried out in a gas furnace with an atmosphere of 850°C or higher and 960°C or lower, in which endothermic reformed gas (Rx gas) was mixed with carbon having a volume ratio of 1.0% and ammonia having a volume ratio of 7%. Particularly in FIG. 11, the amount of retained austenite on the surface after burnishing is 15% or more and 23% or less. After the SUJ3 that has undergone the carburizing nitrocarburizing treatment in FIG. 11, in the initial state before burnishing, the amount of retained austenite in the region within about 50 μm from the surface was about 30% (22% or more and 33% or less).

Example

[0050] FIG. 12 is a graph showing the relationship between the depth from the surface of a rolling component and the residual stress before and after burnishing of SUJ3 that has undergone carburizing nitrocarburizing treatment. In the graph of FIG. 12, the horizontal axis represents the depth from the surface of the rolling component (unit: μm), and the vertical axis represents the residual stress at that depth (unit: MPa). Here, the residual stress indicates the average value of the residual stress for the entire depth region.

[0051] Referring to FIG. 12, by performing carburizing nitrocarburizing treatment on SUJ3 in the same manner as in Example 2, it was confirmed that after burnishing, the maximum compressive residual stress becomes 700 MPa or more in the region within 100 μm from the surface.

[0052] The features described in the above-described embodiments (including each example) may be applied by appropriately combining them within a technically consistent range.

[0053] The embodiments and examples disclosed this time should be considered illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Signs

[0054] 1 Rolling element, 1a Rolling surface, 2 Inner ring, 2a, 3a, 4a Raceway surface, 2B Work surface, 3 Outer ring, 4 Hub ring, 4b Clamping portion, 4c Wheel mounting flange, 4d Surface, 4s Step wall, 5 Retainer, 6 Seal, 11 Hub bolt, 25 Vanishing tool, 41 Non-metallic inclusion, 42 Gap, 101 Steel material, 102 Cutting tool, 103 Rolling component forming region, 104 Cavity, CC Pressing portion, FF Fiber flow.

Claims

1. A method for manufacturing a rolling component having a surface, comprising the steps of: Providing a member having a work surface and including fiber flows; a step of polishing the surface to be processed; and a step of performing plastic working on the processed surface after the step of performing the polishing process, The angle between the surface and the fiber flow is 15° or more; The maximum compressive residual stress is 700 MPa or more in a region within a depth of 100 μm from the surface, The amount of retained austenite on the surface is 11% or more and 28% or less, In the step of performing the plastic working, a burnishing process is performed, The method for manufacturing a rolling component further comprises the step of subjecting the member to a carbonitriding treatment before the step of subjecting the member to the plastic working.

2. The outer ring and A rolling element disposed on an inner circumferential surface of the outer ring; and an inner ring disposed on an inner circumferential side of the rolling elements, At least one of the outer ring, the rolling elements, and the inner ring is a rolling component according to claim 1, The method for manufacturing a bearing, wherein the surface of the rolling component is any one of a raceway surface of the outer ring, a raceway surface of the inner ring, and a rolling surface of the rolling element.

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