Rolling bearings

Abstract

The present invention provides a rolling bearing that can sufficiently suppress wear caused by creep between the raceway ring and the housing or shaft that fixes it over a long period of time. [Solution] The rolling bearing comprises a pair of raceways and a plurality of rolling elements held rotatably between the pair of raceways. Of the pair of raceways, at least one raceway has a steel base material portion 11, an iron oxide layer 13 formed on the surface of at least the region facing the shaft or housing, and an intermediate layer 12 formed between the base material portion 11 and the iron oxide layer 13. The intermediate layer 12 has a plurality of fibrous bodies 14 that extend irregularly from the iron oxide layer 13 toward the base material portion 11.

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing. [Background Art]

[0002] A bearing is a device that rotatably supports an axle of a vehicle and a rotating shaft of other machinery, and there are various types of bearings. Among these various types of bearings, in a rolling bearing that supports a rotating shaft in a housing, "creep", a phenomenon in which the outer ring that is originally fixed rotates relative to the housing, may occur. And there is a problem that the creep causes wear on the inner peripheral surface of the housing. Therefore, for example, Patent Document 1 discloses a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, wherein a black oxide film having mesh-like cracks on the surface of a predetermined surface is formed. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2019-113126 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, the rolling bearing described in Patent Document 1 has cracks in the black oxide film, so there is a problem that the black oxide film is prone to peeling. In addition, although Patent Document 1 describes that increasing the film thickness of the black oxide film to be larger than 1 micrometer improves durability, depending on the magnitude of the load applied between the outer ring and the housing, the larger the film thickness, the more likely peeling of the black oxide film occurs. When the black oxide film peels off, the outer ring and the housing come into direct contact, making it difficult to sufficiently suppress wear of the housing over a long period of time.

[0005] The present invention has been made in view of the above problems, and aims to provide a rolling bearing that can sufficiently suppress wear due to creep that occurs between the raceway ring and the housing or shaft that fixes it over a long period of time. [Means for solving the problem]

[0006] The rolling bearing according to the present invention has the configuration shown in [1] below.

[0007] [1] A rolling bearing comprising a pair of raceway rings and a plurality of rolling elements held to roll freely between the pair of raceway rings, Of the pair of raceway rings, at least one of the raceway rings is Steel base material part, An iron oxide layer formed on the surface of at least the shaft or the area facing the housing, It has an intermediate layer formed between the base material portion and the iron oxide layer, A rolling bearing characterized in that the intermediate layer has a plurality of fibrous bodies that extend irregularly from the iron oxide layer toward the base material.

[0008] A preferred embodiment of the rolling bearing according to the present invention is configured as shown in [2] to [9] below.

[0009] [2] The rolling bearing according to [1], characterized in that the average thickness of the intermediate layer is 0.100 μm or more and 2.000 μm or less.

[0010] [3] The rolling bearing according to [1] or [2], characterized in that the intermediate layer has the fibrous material having a width of 0.005 μm or more and a length of 0.1 μm or more.

[0011] [4] The rolling bearing according to any one of [1] to [3], characterized in that the intermediate layer is a region in which the composition of the base material and the composition of the iron oxide layer are mixed.

[0012] [5] The iron oxide layer contains O in an amount of 5 mass% or more and 40 mass% or less, wherein the base material portion contains O in an amount of less than 5 mass%, the rolling bearing according to any one of [1] to [4].

[0013] [6] The rolling bearing according to any one of [1] to [5], wherein an average thickness of the intermediate layer is 10% or more relative to a total average thickness of the intermediate layer and the iron oxide layer.

[0014] [7] The rolling bearing according to any one of [1] to [6], wherein at least a part of the fibrous bodies branch in a plurality of directions toward the base material portion and have a network structure.

[0015] [8] The rolling bearing according to any one of [1] to [7], wherein the at least one race ring is an outer ring, and the iron oxide layer is formed at least on an outer diameter side of the outer ring.

[0016] [9] The rolling bearing according to any one of [1] to [7], wherein the at least one race ring is an inner ring, and the iron oxide layer is formed at least on an inner diameter side of the inner ring. Effects of the Invention

[0017] According to the present invention, it is possible to provide a rolling bearing that can sufficiently suppress wear caused by creep occurring between a race ring and a housing or a shaft that fixes the race ring over a long period of time. Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a rolling bearing according to an embodiment of the present invention. [Figure 2] FIG. 2 is a drawing-substituting photograph showing an image obtained by photographing a cross section of an outer ring with a scanning electron microscope. [Figure 3]FIG. 3 is a drawing-substitute photograph showing an image obtained by photographing a cross-section of a plurality of other regions of the outer ring with a scanning electron microscope. [Figure 4] FIG. 4 is a drawing-substitute photograph showing an image obtained by photographing a cross-section of an outer ring having a conventional iron oxide layer with a scanning electron microscope. [Figure 5] FIG. 5 is a drawing-substitute photograph showing positions where elemental analysis was performed on a cross-section of a bearing ring including a base material portion, an intermediate layer, and an iron oxide layer in the rolling bearing according to the present embodiment. [Figure 6] FIG. 6 is a drawing-substitute photograph showing a comparison between an SEM image of a cross-section of each outer ring before a creep wear test and an SEM image of a cross-section of each outer ring after the creep wear test. [Figure 7] FIG. 7 is an SEM image of another field of view of the cross-section of outer rings No. W2 and W3 before the creep wear test shown in FIG. 6, and is a drawing-substitute photograph showing the positions where EDX elemental analysis was performed. MODE FOR CARRYING OUT THE INVENTION

[0019] The inventors have diligently researched the mechanism by which a black oxide coating, conventionally formed to improve aesthetics and corrosion resistance, can suppress creep-induced wear (hereinafter referred to as creep wear) in rolling bearings. Adhesive wear is one type of wear that occurs between the outer ring and housing of a rolling bearing. Adhesive wear is a type of wear that occurs when friction occurs while pressure is applied between two surfaces, causing the two surfaces to repeatedly transfer to each other. The inventors have found that if a black oxide coating remains on the surface of the outer ring, adhesive wear of the housing can be suppressed. Therefore, creep wear tests were conducted on outer rings with a black oxide coating to clarify the coating properties that make it easier for the black oxide coating to remain. In other words, if an intermediate layer of a predetermined shape is formed between the steel base material and the iron oxide layer on the surface of the outer ring of a rolling bearing, the intermediate layer can be retained even if the surface coating peels off. This intermediate layer is chemically stable and, even when in contact with the housing, is less likely to form chemical bonds with the components constituting the housing. This prevents repeated transfer between the housing and the intermediate layer, thereby effectively suppressing the occurrence of adhesive wear. The present invention is based on the above findings.

[0020] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below. Furthermore, since both "blackening coating" and "black oxide coating" refer to a surface layer mainly composed of iron oxide, in the embodiments of the present invention, these are collectively referred to as the "iron oxide layer."

[0021] [Rolling bearings] Figure 1 is a cross-sectional view showing an example of a rolling bearing according to an embodiment of the present invention. As shown in Figure 1, the rolling bearing 10 has a steel outer ring 1 having an outer ring raceway surface 1a on its inner circumferential surface, and a steel inner ring 3 having an inner ring raceway surface 3a on its outer circumferential surface. When the outer ring 1 and the inner ring 3 are combined, a raceway ring having a pair of opposing raceway surfaces is formed. In addition, a plurality of rolling elements 5 are arranged between the pair of raceway rings (between the outer ring raceway surface 1a and the inner ring raceway surface 3a). Each of these rolling elements 5 is held to roll freely by a cage 7 while being arranged at equal intervals in the circumferential direction. Furthermore, sealing members 9 are attached to both axial sides of the outer ring 1 and the inner ring 3, and these sealing members 9 hold the lubricant sealed between the outer ring 1 and the inner ring 3.

[0022] In this embodiment, the rolling bearing 10 is of the inner ring rotation type, where the inner ring 3 is fixed to the shaft 6 and rotates along with the rotation of the shaft 6. On the other hand, the outer ring 1 is fixed to the housing 8 and supports the rotation of the inner ring 3 and rolling elements 5 while maintaining a state as stationary as possible relative to the housing 8.

[0023] Figure 2 is a photograph used as a substitute for a drawing, showing an image of the outer ring's cross-section taken with a scanning electron microscope (SEM). Figure 3 is also a photograph used as a substitute for a drawing, showing images of cross-sections of several other regions of the outer ring taken with a scanning electron microscope. Regions R1 to R4 in Figures 2 and 3 represent arbitrary regions of the outer ring facing the housing. The upper and lower rows in Figure 2, and the left and right columns in Figure 3, each show photographs of the same field of view. The lower row in Figure 2 and the right column in Figure 3 are attached to clearly show the various layers described later.

[0024] As shown in Figures 1 to 3, the outer ring 1 of the rolling bearing 10 according to this embodiment has a steel base material portion 11, an iron oxide layer 13 formed on the surface of the region facing the housing 8, and an intermediate layer 12 formed between the base material portion 11 and the iron oxide layer 13. The intermediate layer 12 is a layer having a plurality of fibrous bodies 14 that extend irregularly from the iron oxide layer 13 toward the base material portion 11. Upon closer observation, not only do the fibrous bodies 14 extend linearly toward the base material portion 11, but some extend away from the iron oxide layer 13 and then bend. In addition, at least some of the fibrous bodies 14 branch in multiple directions toward the base material portion 11, forming a mesh structure within the intermediate layer 12. Thus, the fibrous bodies 14 in this embodiment include all those that appear fibrous, including those that bend midway, or those that branch to form a dendritic or mesh-like structure. As an example, in the upper row of Figure 2 and the left column of Figure 3, one of the fibrous bodies 14 is shown enclosed in an ellipse.

[0025] Specifically, in SEM observation, the iron oxide layer 13 represents the region exhibiting a generally uniform color from the surface of the outer ring 1, and the line connecting the points where fibrous material begins to appear is defined as the boundary line L1 between the iron oxide layer 13 and the intermediate layer 12. Furthermore, the line connecting the tips of the fibrous material 14 extending to the furthest point from the surface of the outer ring 1 is defined as the boundary line L2 between the base material 11 and the intermediate layer 12. Depending on the formation conditions of the iron oxide layer 13, the fibrous material 14 may also expand in the region at the tip of the fibrous material 14 extending toward the base material 11, forming a region exhibiting a uniform color similar to that of the iron oxide layer 13. In such cases, if fibrous material is present near the iron oxide layer 13, the region at the tip of the fibrous material 14 exhibiting a uniform color is also considered part of the intermediate layer 12.

[0026] Furthermore, dark black circular objects are observed in the SEM image. These are thought to be carbides originally present in the steel that makes up the outer ring, and they appear in the SEM image due to the treatment that forms the iron oxide layer 13. Therefore, when determining the boundary line L1 between the iron oxide layer 13 and the intermediate layer 12, and the boundary line L2 between the base material 11 and the intermediate layer 12, these circular objects should be ignored.

[0027] In the rolling bearing 10 configured in this embodiment, when friction occurs while pressure is applied between the outer ring 1 and the housing 8, at least a portion of the iron oxide layer 13 peels off, but the intermediate layer 12 tends to remain. Therefore, the occurrence of creep wear between the outer ring 1 and the housing 8 can be suppressed. The mechanism by which the intermediate layer 12 remains even when friction occurs is not clear, but the structure of the intermediate layer 12 is considered to be important. As shown in Figures 2 and 3, the intermediate layer 12 is a region in which the fibrous material 14 has penetrated and spread into the region that was the base material portion 11. That is, unlike the iron oxide layer 13 which has a generally uniform composition, the intermediate layer 12 has a mixture of regions having the composition of the base material portion 11 and regions having the composition of the iron oxide layer 13, so it is considered that peeling due to friction is less likely to occur. In addition, since both the iron oxide layer 13 and the intermediate layer 12 have the effect of suppressing adhesive wear, the region that has the effect of suppressing wear on the shaft or housing becomes thicker compared to an outer ring that has only an iron oxide layer and no intermediate layer. Therefore, it is considered that the occurrence of creep wear can be suppressed for a long period of time.

[0028] The outer ring in this embodiment and a conventional outer ring having an iron oxide layer will be described with reference to the drawings for comparison. Figure 4 is a photograph used as a substitute for a drawing, showing a cross-section of a conventional outer ring having an iron oxide layer, taken with a scanning electron microscope. In the outer ring shown in Figure 4, similar to Figures 2 and 3, an iron oxide layer 13 is formed on the surface of the base material portion 11, and needle-like irregularities are observed at the interface, but no clear fibrous material can be confirmed. Therefore, when friction occurs between the outer ring and the housing shown in Figure 4, the base material portion 11 is exposed along with the peeling of the iron oxide layer 13, making creep wear more likely to occur.

[0029] In many applications, rolling bearings involve inner ring rotation, meaning the inner ring and shaft are firmly fixed. However, a small gap exists between the outer ring and the housing, and this gap causes creep. In the embodiments shown in Figures 1 to 3 above, an iron oxide layer is formed in the region of the outer ring facing the housing, i.e., at least on the outer diameter side of the outer ring, to suppress creep wear occurring between the outer ring and the housing. However, the present invention is not limited to rolling bearings with inner ring rotation, but can also be applied to rolling bearings with outer ring rotation. When applying the present invention to a rolling bearing with outer ring rotation, it is sufficient that an iron oxide layer is formed in the region of the inner ring facing the shaft, i.e., at least on the inner diameter side of the inner ring.

[0030] Next, the intermediate layer and fibrous material, as well as the composition of the base material and iron oxide layer, will be explained in more detail. Hereinafter, the outer ring and inner ring will be referred to as raceways, including cases where the iron oxide layer is formed on the outer diameter side of the outer ring and on the inner diameter side of the inner ring.

[0031] [Middle class] <Average thickness: 0.100 μm or more and 2.000 μm or less> If the average thickness of the intermediate layer is 0.100 μm or more, the likelihood of the intermediate layer remaining even after the iron oxide layer has peeled off increases, and the effect of suppressing wear can be sufficiently obtained. Therefore, the average thickness of the intermediate layer is preferably 0.100 μm or more, more preferably 0.200 μm or more, and even more preferably 0.300 μm or more. Furthermore, there is no particular upper limit to the thickness of the intermediate layer, but the intermediate layer can be formed in a range of substantially 2.000 μm or less. Therefore, the average thickness of the intermediate layer is preferably 2.000 μm or less, and more preferably 1.500 μm or less.

[0032] The average thickness of the intermediate layer can be obtained by scanning a cross-section of the raceway ring with a SEM, identifying the region where fibrous material is clearly visible in the resulting image as the intermediate layer, calculating the area of ​​the intermediate layer within the field of view by integration, and dividing by the length in the planar direction. Alternatively, the average thickness of the intermediate layer can be obtained simply by dividing the SEM image into approximately four sections, creating three dividing lines along the thickness direction of the intermediate layer and iron oxide layer, measuring the thickness of the intermediate layer along these three dividing lines with a ruler or similar tool, and calculating the average. Figure 3 shows the results of measuring the thickness of the intermediate layer along the three dividing lines using this simple measurement method. When using this simple measurement method, it is preferable to create five dividing lines and calculate the average thickness of the intermediate layer along the dividing lines, and it is even more preferable to create ten dividing lines and calculate the average thickness of the intermediate layer along the dividing lines.

[0033] <Average thickness of the intermediate layer: 10% or more of the average thickness of the combined intermediate layer and iron oxide layer> The ratio of the average thickness of the intermediate layer to the average combined thickness of the intermediate layer and the iron oxide layer also affects the period during which the creep wear suppression effect can be maintained. A thicker average intermediate layer provides a greater wear suppression effect, but if the iron oxide layer is made thicker and the intermediate layer is made thicker in line with the increase in the thickness of the iron oxide layer, the iron oxide layer becomes more prone to peeling as it gets thicker, leading to earlier exposure of the intermediate layer. As a result, the overall period during which wear can be suppressed becomes shorter. If the average thickness of the intermediate layer is 10% or more of the average combined thickness of the intermediate layer and the iron oxide layer, the wear suppression effect can be sufficiently maintained even after the iron oxide layer has peeled off. Therefore, the average thickness of the intermediate layer is preferably 10% or more of the average combined thickness of the intermediate layer and the iron oxide layer, more preferably 30% or more, and even more preferably 50% or more.

[0034] <Width of fibrous material: 0.005 μm or more and 0.10 μm or less, length: 0.1 μm or more> As described above, the intermediate layer has multiple fibrous bodies that extend irregularly from the iron oxide layer toward the base material. If the width of the fibrous bodies is 0.005 μm or more, a sufficient effect of suppressing creep wear can be obtained when the iron oxide layer peels off and the intermediate layer is exposed. Furthermore, if the width of the fibrous bodies is 0.10 μm or less, peeling of the intermediate layer itself can be suppressed. Moreover, if the length of the fibrous bodies is 0.1 μm or more, the effect of suppressing creep wear can be maintained for a long period of time even after the iron oxide layer peels off and the intermediate layer is exposed. Therefore, it is preferable that the intermediate layer has fibrous bodies with a width of 0.005 μm or more and a length of 0.1 μm or more. It is more preferable that the intermediate layer has fibrous bodies with a width of 0.01 μm or more and 0.05 μm or less, and it is even more preferable that it has fibrous bodies with a width of 0.02 μm or more and 0.04 μm or less. Furthermore, the intermediate layer is more preferably made of fibrous material with a length of 0.2 μm or more, and even more preferably made of fibrous material with a length of 0.3 μm or more.

[0035] In the cross-section of the raceway, fibrous material with a width of, for example, 0.10 μm or more may be observed. However, even if there is fibrous material with a large width, if the width and length of the fibrous material are within the above range, that range can be considered an intermediate layer. However, it is preferable that the length of the fibrous material is at least twice the width of the fibrous material.

[0036] While there is no particular upper limit to the length of the fibrous material in the intermediate layer, it is generally easier to form fibrous material with a length of 1.5 μm or less. Therefore, it is preferable that the intermediate layer has fibrous material with a length of 1.5 μm or less.

[0037] The length of the fibrous material can be determined by taking a cross-section of the raceway ring using a SEM, selecting the fibrous material that extends toward the base material in the resulting image, and measuring its length with a ruler or similar tool. If the fibrous material branches in multiple directions, branches extending in the thickness direction of the intermediate layer and iron oxide layer should be selected as much as possible. The width of the fibrous material can also be determined by measuring the width of randomly selected fibrous material in the SEM image with a ruler or similar tool. In this embodiment, since it is preferable that the intermediate layer has fibrous material of the above-mentioned preferred width and length, it is not necessary for the width and length of all fibrous material to be within the above range, but it is preferable that there is at least one fibrous material with a width of 0.005 μm or more and 0.10 μm or less and a length of 0.1 μm or more.

[0038] The width and length of the fibrous material 14, shown as an example in the lower section of Figure 2 and the right column of Figure 3, as well as the thickness of the intermediate layer, were measured and the results are shown in Table 1 below.

[0039] [Table 1]

[0040] [Composition of base material, intermediate layer, and iron oxide layer] Figure 5 shows the locations where elemental analysis was performed on the cross-section of a raceway ring having a base material portion 11, an intermediate layer 12, and an iron oxide layer 13 in a rolling bearing according to this embodiment. The analysis locations were selected evenly from areas with a different color tone from the surrounding area or areas that appeared fibrous in the backscattered electron image (BSE image), as shown by position P1 in the iron oxide layer 13, positions P2 to P8 in the intermediate layer 12, and position P9 in the base material portion 11. The analysis results of elemental analysis performed on the above positions P1 to P9 are shown in Table 2 below. In Table 2 below, "ND" indicates that the result was below the detection limit.

[0041] [Table 2]

[0042] <Oxygen content in the iron oxide layer: 5% by mass or more and 40% by mass or less> In this embodiment, the iron oxide layer 13 is a layer obtained by, for example, performing a blackening treatment on a steel material formed into the shape of a raceway ring, and contains iron oxide. Therefore, the iron oxide layer has a higher oxygen content than other regions. As a result, it is preferable that the oxygen content in the iron oxide layer 13 is 5% by mass or more and 40% by mass or less, regardless of the measurement location.

[0043] <Oil content in the base material: less than 5% by mass> The base material portion 11 is, for example, a region having the same composition as the steel material formed into the shape of a raceway ring before blackening treatment, and is a region whose composition is not affected by the formation of the iron oxide layer. Since the steel material contains virtually no oxygen, the oxygen content in the base material portion 11 is extremely low and may be below the detection limit. Specifically, it is preferable that the oxygen content in the base material portion 11 be less than 5% by mass, regardless of the measurement location.

[0044] <Oil content in the middle layer> As described above, the intermediate layer 12 is a region where fibrous material is formed. Therefore, the oxygen content in the intermediate layer 12 varies depending on the analysis location. However, the content of the components in the intermediate layer 12 is generally between the content of each component in the base material 11 and the content of each component in the iron oxide layer 13. As shown in Figure 5 and Table 2 above, at position P3 where fibrous material is formed in the intermediate layer 12, the oxygen content approaches that of the iron oxide layer 13, resulting in an oxygen content of 28.1% by mass. Furthermore, at positions P5 to P7 where the color indicating fibrous material is lighter, the oxygen content also approaches that of the base material 11, ranging from 5.4% by mass to 6.2% by mass. Thus, in the intermediate layer 12, the oxygen content differs depending on the measurement location, but it falls within the range from the oxygen content of the base material 11 to the oxygen content of the iron oxide layer 13. The specific range of oxygen content in the intermediate layer 12 can range from 0% by mass, which is the lower limit of the oxygen content in the base material 11, to 40% by mass, which is the upper limit of the oxygen content in the iron oxide layer 13.

[0045] Furthermore, the C and Fe content of the intermediate layer is influenced by the composition of the steel constituting the raceway ring, so the range of these content cannot be uniformly defined. On the other hand, when at least three points are randomly selected from the area considered to be the intermediate layer and the C and Fe content is measured, it is preferable that the average value of all measured values ​​falls within the range between the C and Fe content of the base material and the C and Fe content of the iron oxide layer. In particular, when comparing the O, C, and Fe content in each region, if the average value of the content of each element at the three points in the intermediate layer falls between the base material and the iron oxide layer, it can be determined that "the intermediate layer is a region where the composition of the base material and the composition of the iron oxide layer are mixed." It is even more preferable that the content of each element at all selected points in the intermediate layer falls within the range between the C and Fe content of the base material and the C and Fe content of the iron oxide layer.

[0046] However, due to measurement errors in the EDX analysis described later, and local compositional variations in the measurement area, the above magnitude relationship does not always need to be strictly maintained. Specifically, even if the Fe content at a single point in the intermediate layer slightly exceeds the Fe content in the base material, or the O content in the intermediate layer slightly falls below the O content in the base material, causing the apparent magnitude relationship to be reversed, this is still within the scope of the present invention. The reason for the apparent magnitude relationship to be reversed is thought to be that the content of elements other than Fe and O, i.e., C, increases in the base material due to measurement errors and variations in the cleanliness of the measurement area. Therefore, by focusing on the ratio of O content to Fe content calculated by the following formula, the relationship Ro>Rm>Rb can be theoretically satisfied. Ratio Rb = [O]b / [Fe]b Ratio Rm = [O]m / [Fe]m Ratio Ro = [O]o / [Fe]o However, R represents the ratio of O content to Fe content, [O] is the O content expressed in mass%, and [Fe] is the Fe content expressed in mass%. In addition, the subscripts b indicates the ratio or content in the base material, m indicates the ratio or content in the intermediate layer, and o indicates the ratio or content in the iron oxide layer. Note that if the O content is below the detection limit, [O] is set to 0.

[0047] The content of each element in the intermediate layer is preferably measured at at least three randomly selected points, more preferably at five randomly selected points, even more preferably at seven randomly selected points, and even more preferably at ten randomly selected points. For the base material and iron oxide layer, since the variation in the content of each element is considered to be small, it is preferable to measure the content of each element at only one randomly selected point, more preferably at three randomly selected points to measure the content of each element and calculate the average value, even more preferably at five randomly selected points to calculate the average value, and even more preferably at ten randomly selected points to calculate the average value.

[0048] The O, Fe, and C content at each measurement location can be obtained by performing point analysis using energy dispersive X-ray spectroscopy (EDX).

[0049] <Types of steel used in the raceway rings> In this embodiment, the steel grade used for the raceway rings can be any general steel grade used for raceway rings. Various steel grades can be used for the raceway rings of rolling bearings, such as SUJ2, SUJ3, and SUJ4 as specified in JIS G 4805:2019, and SUS440C as specified in JIS G 4303:2021, etc. For example, SUJ2 is a steel grade that is commonly used as bearing steel and has low cost and excellent fatigue life. SUJ3 is suitable for large-diameter raceway rings. SUJ4 is suitable for heavy-load raceway rings and has excellent toughness and high-temperature properties. SUS440C is suitable for use in corrosive environments and has high hardness and excellent corrosion resistance. Therefore, the material of the raceway rings can be appropriately selected according to the required properties.

[0050] The rolling bearing shown in Figure 1 above is just one example of a rolling bearing according to the present invention, and its configuration is not particularly limited. For example, the present invention can be applied to various rolling bearings, such as rolling bearings without a sealing member 9, or rolling bearings with a cage shape different from that shown in Figure 1.

[0051] <Housing> The shape and material of the housing that fixes the outer ring of the rolling bearing according to this embodiment are not particularly limited. Examples of housing materials include steel and aluminum alloy, and the effects of this embodiment can be obtained regardless of the material of the housing. Aluminum alloy is lightweight and easy to form into complex shapes by casting, but it also has the property of low wear resistance. Therefore, by using the rolling bearing according to this embodiment in combination with an aluminum alloy housing, the effect of this embodiment, which can suppress wear of the housing, can be exhibited more significantly.

[0052] <Manufacturing method for rolling bearings> Next, as an example of a method for manufacturing a rolling bearing according to this embodiment, a method for manufacturing the raceway ring, which is characteristic of this embodiment, will be briefly described below.

[0053] (Degreasing and washing process) First, the processed material, which has been shaped into the predetermined raceway ring shape, is degreased using an alkaline degreasing agent, and then the degreasing agent is removed by rinsing with water. As an alkaline degreasing agent, for example, a degreasing agent containing sodium silicate can be used.

[0054] (Blackening process) Next, the degreased raceway material is immersed in a blackening solution. As the blackening solution, a commercially available solution mainly composed of NaOH with NaNO3 and NaNO2 added as oxidizing agents can be used. In the blackening process, conditions such as a processing temperature of 125±1℃, a processing time of 101 minutes, and one processing cycle can be used. Note that it is not necessary to form an iron oxide layer over the entire surface of the raceway material in the blackening process; in the case of inner rings, it is sufficient to apply the blackening treatment to at least the area facing the shaft, and in the case of outer rings, to at least the area facing the housing.

[0055] The inventors focused on the processing temperature in the blackening process as an example of the conditions for forming an intermediate layer having a specific fibrous material as described above, and found that lowering the processing temperature compared to a general temperature tends to increase the thickness of the intermediate layer having the fibrous material. Specifically, when adjusting the processing temperature for the blackening process, it is preferable to set the processing temperature below 135°C, more preferably below 130°C, and even more preferably below 128°C. Since the processing time is affected by the processing temperature, it is advisable to determine the processing time required to form the desired intermediate layer at the selected temperature. However, the conditions for forming the desired intermediate layer are not limited to temperature conditions alone. Regardless of the manufacturing conditions, the effects of the present invention can be obtained if the desired intermediate layer described above is formed.

[0056] (Water washing process) The blackening treatment solution adhering to the surface is then removed by washing with water and drying. In this way, a raceway ring having a base material, an intermediate layer, and an iron oxide layer can be manufactured. [Examples]

[0057] The rolling bearing according to this embodiment will be described in detail below with reference to examples. However, the manufacturing conditions for the outer ring shown below are just examples, and the present invention is not limited to these manufacturing conditions.

[0058] Outer rings of rolling bearings were manufactured using SUJ2 steel under various manufacturing conditions. Cross-sections of the areas where blackening treatment was performed were observed using SEM, and elemental analysis was conducted at multiple locations using EDX.

[0059] Subsequently, using outer rings manufactured under the same conditions as those subjected to SEM observation and EDX analysis, a deep groove ball bearing of designation 6206 as specified in JIS B 1513 was assembled. The inner ring was fitted onto the shaft, and the outer ring was fitted into an aluminum alloy housing, thereby assembling the deep groove ball bearing onto the shaft and housing. A creep wear test was then conducted to measure the specific wear. The creep wear test conditions involved applying a load of 40% of the basic dynamic load rating C of the bearing used, rotating the bearing at 3900 rpm for 96 hours. Lubricating oil was forcibly supplied to the inside of the bearing, and the lubricating oil used was automatic transmission fluid (ATF) equivalent to Toyota standard JWS3324. After that, the weight of the housing measured beforehand was compared with the weight of the housing measured after the creep wear test, and the amount of wear was calculated. Furthermore, the specific wear amount was calculated by determining the sliding distance between the housing and the bearing outer ring from the rotational speed of the outer ring after rotating for 96 hours under a radial load of 7762N. In addition, the cross-section of the region of each outer ring facing the housing was observed using a scanning electron microscope (SEM).

[0060] Figure 6 shows a comparison of SEM images of the cross-section of each outer ring before and after the creep wear test. Note that the SEM images before and after the creep wear test in Figure 6 are of different bearings manufactured under the same conditions, and not of the same location. Furthermore, the processing conditions in the blackening process for forming the iron oxide layer, etc., and the specific wear amount calculated from the creep wear test are shown in Table 3 below, and the EDX elemental analysis results before the creep wear test are shown in Table 4 below. The measurement results for outer ring No. W1 are already described in Table 2, but are also shown in Table 4 below for comparison. In Table 4 below, the subscript of the formula ([O] / [Fe]) is omitted. Also, "-" indicates that measurement was not performed.

[0061] [Table 3]

[0062] [Table 4]

[0063] As shown in Figure 6, the outer ring No. W1, an example of the invention, has an intermediate layer formed between the base material and the surface iron oxide layer, having multiple fibrous bodies that extend irregularly toward the base material. Therefore, even after the creep wear test, an intermediate layer of sufficient thickness remained. Consequently, even after the creep wear test, the combined thickness of the iron oxide layer and the intermediate layer was sufficient. In outer ring No. W1, the C, O, and Fe content in the intermediate layer was all between the content of each element in the iron oxide layer and the content of each element in the base material. The average thickness of the intermediate layer before the creep wear test was 0.800 μm, and when the width and length were measured by selecting multiple fibrous bodies, the width was 0.01 μm to 0.04 μm and the length was 0.1 μm to 1.0 μm. Furthermore, the average thickness of the intermediate layer was 55% of the combined average thickness of the intermediate layer and the iron oxide layer. Furthermore, the average combined thickness of the intermediate layer and the iron oxide layer after the creep abrasion test was 0.83 μm.

[0064] In contrast, in the comparative example, outer ring No. W2, although spiky irregularities were observed extending from the iron oxide layer toward the base material, no intermediate layer with fibrous material was formed. The average thickness of the iron oxide layer after the creep wear test was 0.40 μm. Similarly, in the comparative example, outer ring No. W3, irregularities were observed between the iron oxide layer and the base material, but no intermediate layer was formed.

[0065] Furthermore, as shown in Table 3, the specific wear amount for bearing No. B1 manufactured using the outer ring No. W1, which is an example of the invention, is 0.032 × 10⁻⁶. -6 (mm 2 The specific wear of bearings No. B2 and B3, manufactured using the comparative examples of outer rings No. W2 and W3, was 0.042 × 10⁻⁶. -6 (mm 2 / N), 0.067 × 10 -6 (mm 2 The specific wear amount of the housing measured for the bearing using the outer ring of the invention example was significantly lower compared to the comparative example. These results demonstrate that according to the present invention, adhesive wear between the outer ring and the housing can be sufficiently suppressed, and this effect can be maintained for a long period of time. [Explanation of symbols]

[0066] 1 Outer ring 1a Outer ring raceway surface 3. Inner Ring 3a Inner ring raceway surface 5 Rolling element 6 axes 7 Cage 8 Housing 9. Sealing member 10 Rolling bearings 11 Base material part 12 Middle Class 13 Iron oxide layer 14 Fibrous body

Claims

1. A rolling bearing comprising a pair of raceway rings and a plurality of rolling elements held to roll freely between the pair of raceway rings, Of the pair of raceway rings, at least one of the raceway rings is Steel base material part, An iron oxide layer formed on the surface of at least the shaft or the area facing the housing, It has an intermediate layer formed between the base material portion and the iron oxide layer, A rolling bearing characterized in that the intermediate layer has a plurality of fibrous bodies that extend irregularly from the iron oxide layer toward the base material.

2. The rolling bearing according to claim 1, characterized in that the average thickness of the intermediate layer is 0.100 μm or more and 2.000 μm or less.

3. The rolling bearing according to claim 1, characterized in that the intermediate layer has a fibrous body having a width of 0.005 μm or more and a length of 0.1 μm or more.

4. The rolling bearing according to claim 1, characterized in that the intermediate layer is a region in which the composition of the base material and the composition of the iron oxide layer are mixed.

5. The iron oxide layer contains O: 5% by mass or more and 40% by mass or less. The rolling bearing according to claim 1, characterized in that the base material portion has an O: less than 5% by mass.

6. The rolling bearing according to claim 1, characterized in that the average thickness of the intermediate layer is 10% or more of the average thickness of the combined intermediate layer and the iron oxide layer.

7. The rolling bearing according to claim 1, characterized in that at least a portion of the fibrous material branches in multiple directions toward the base material and has a mesh structure.

8. A rolling bearing according to any one of claims 1 to 7, characterized in that at least one of the raceways is an outer ring, and the iron oxide layer is formed at least on the outer diameter side of the outer ring.

9. A rolling bearing according to any one of claims 1 to 7, characterized in that at least one of the raceways is an inner ring, and the iron oxide layer is formed at least on the inner diameter side of the inner ring.

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