Rolling bearing and manufacturing method thereof

Abstract

Provided is a rolling bearing that can have an oxide film having excellent durability and that can minimize occurrence of brittle fracture due to hydrogen, thereby being able to improve durability of raceway surfaces and rolling elements. The rolling bearing is provided with a first bearing ring (11) having a first raceway surface (13), a second bearing ring (12) having a second raceway surface (14), and a plurality of rolling elements (15) held in a rollable manner between the first raceway surface (13) and the second raceway surface (14). At least either one of the first raceway surface (13) and the second raceway surface (14) or the rolling element (15) has, on the surface thereof, an oxide film (17) containing Fe3O4. The thickness of the oxide film is 0.6-2.0 μm, and the crystallite size of Fe3O4 calculated from a peak belonging to a plane (311) thereof is 2.5-3.2 nm.

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing and a method for manufacturing the same. [Background technology]

[0002] When rolling bearings are used under conditions where water is present, where sliding occurs, or where electricity is applied, hydrogen is generated by the decomposition of water or lubricant. This generated hydrogen penetrates into the steel material that makes up the rolling bearing and causes hydrogen embrittlement. Therefore, in order to prevent hydrogen embrittlement caused by hydrogen penetration, rolling bearings with oxide films on their surfaces have been proposed. For example, Patent Document 1 discloses a rolling bearing that has an oxide film on the surface of the rolling components that make up the rolling bearing, which suppresses the hydrogen generation reaction from occurring.

[0003] Furthermore, in the case of a rolling bearing that supports a rotating shaft inside a housing, creep can occur between the outer ring and the housing, causing wear on the inner peripheral surface of the housing.In light of this, for example, Patent Document 2 discloses a rolling bearing that includes an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and in which a black oxide coating with a network of cracks is formed on the surface of a predetermined face. The above-mentioned Patent Document 2 describes that it is possible to suppress creep, which tends to occur when the rolling bearing is under no or light radial load, and to suppress wear on the inner surface of the housing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-39523 [Patent Document 2] Japanese Patent Application Publication No. 2019-113126 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, Patent Document 1 states that by making the thickness of the oxide film on the surface of the rolling component 0.5 μm or more, even if the oxide film is worn, new surfaces on the rolling component are less likely to be created, and the hydrogen generation reaction can be suppressed. Also, Patent Document 2 states that by making the thickness of the black oxide film greater than 1 μm, durability is improved.

[0006] However, even if the thickness of the oxide film (black oxide film) is controlled within the above range, the durability of the oxide film is not sufficient, and if the oxide film is damaged, hydrogen penetrates into the steel material, generating white structure, which then becomes the starting point for peeling off the raceway surfaces and rolling element surfaces of the rolling bearing.

[0007] The present invention has been made in light of the above-mentioned problems, and aims to provide a rolling bearing and a manufacturing method thereof that can obtain an oxide film with excellent durability and suppress the occurrence of hydrogen embrittlement fracture, thereby improving the durability of the raceway surfaces and rolling elements. [Means for solving the problem]

[0008] As a result of extensive research to solve the above problems, the inventors have discovered that the main damage modes of oxide films formed on the raceway surfaces or rolling elements of rolling bearings are "film wear" and "film breakdown," and that the durability of the oxide film varies greatly depending on the processing conditions and film thickness used when forming the oxide film. "Film wear" refers to the phenomenon in which the oxide film is damaged almost uniformly, while "film breakdown" refers to the phenomenon in which the oxide film is damaged non-uniformly, such as intra-film peeling or interfacial peeling.

[0009] The inventors also discovered that the damage mode of "coating wear" varies depending on the crystallite size of the Fe3O4 that makes up the oxide film, and that "coating breakdown" varies depending on the residual stress, which is caused by the thickness of the oxide film. In other words, the smaller the crystallite size of Fe3O4, the denser the film becomes, which can reduce film wear, and the thinner the oxide film, the less film damage can be prevented. The present invention was made based on these findings.

[0010] The rolling bearing according to the present invention has the following configuration [1].

[0011] [1] A rolling bearing comprising a first raceway ring having a first raceway surface, a second raceway ring having a second raceway surface, and a plurality of rolling elements held so as to be rollable between the first raceway surface and the second raceway surface, an oxide film containing Fe3O4 is formed on at least one of the first raceway surface, the second raceway surface, and the surface of the rolling element; The oxide film has a thickness of 0.6 μm or more and 2.0 μm or less, A rolling bearing characterized in that the crystallite size calculated from the peak attributed to the (311) plane of the Fe3O4 is 2.5 nm or more and less than 3.2 nm.

[0012] A preferred embodiment of the rolling bearing according to the present invention is as follows: [2]

[0013] [2] The rolling bearing according to [1], wherein the oxide film is formed on the surfaces of the first raceway surface and the second raceway surface, and on the surfaces of the rolling elements.

[0014] The method for manufacturing a rolling bearing according to the present invention is as configured in [3] below. [3] In the method for manufacturing the rolling bearing according to [1] or [2], forming an oxide film containing Fe3O4 on at least one of the first raceway surface, the second raceway surface, and the surface of the rolling element; A method for manufacturing a rolling bearing, characterized in that the oxide film is formed at a rate of 0.003 μm / min or more and 0.034 μm / min or less. [Effects of the Invention]

[0015] According to the present invention, the thickness of the oxide film and the crystallite size of the Fe3O4 constituting the oxide film are appropriately controlled, thereby obtaining an oxide film with excellent durability and suppressing the occurrence of hydrogen embrittlement fracture. As a result, it is possible to provide a rolling bearing and a method for manufacturing the same that can improve the durability of the raceway surfaces and rolling elements. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view showing a rolling bearing according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic diagram of a damage testing device. [Figure 3] FIG. 3 is a graph showing the effect of crystallite size on damage resistance, with the vertical axis representing the initial film thickness (μm) and damaged film thickness (μm) of the black-dyed film, and the horizontal axis representing the crystallite size (nm). [Figure 4] FIG. 4 is a graph showing the effect of crystallite size on damage resistance as an approximate straight line, with the vertical axis representing the damaged film thickness (μm) of the black-dyed film and the horizontal axis representing the crystallite size (nm). [Figure 5] FIG. 5 is a graph showing the relationship between the film formation rate and the Fe3O4 crystallite size as an approximate straight line, with the vertical axis representing the film formation rate (μm / min) of the black dyed film and the horizontal axis representing the crystallite size (nm). [Figure 6] FIG. 6 is a graph showing the effect of film thickness on damage resistance, with the vertical axis representing the initial film thickness (μm) and damaged film thickness (μm) of the black dyed film, and the horizontal axis representing the initial film thickness (μm) of the black dyed film. [Figure 7] FIG. 7 is a graph showing the influence of initial film thickness on damage resistance, with the vertical axis representing the average damage rate (%) and the horizontal axis representing the initial film thickness (μm). [Figure 8A] FIG. 8A is a photograph substituting for a drawing showing the state of peeling when the initial film thickness of the black dyed film is 0.42 μm. [Figure 8B] FIG. 8B is a photograph substituting for a drawing showing the state of peeling when the initial film thickness of the black dyed film is 0.84 μm. [Figure 8C]FIG. 8C is a photograph substituting for a drawing showing the state of peeling when the initial film thickness of the black dyed film is 1.83 μm. [Figure 8D] FIG. 8D is a photograph substituting for a drawing showing the state of peeling when the initial film thickness of the black dyed film is 1.97 μm. [Figure 9] FIG. 9 is a graph showing the effect of initial film thickness on film breakdown as an approximate straight line, with the vertical axis representing the average peel distance (μm) and the horizontal axis representing the initial film thickness (μm) of the black-dyed film. [Figure 10] FIG. 10 is a graph showing the relationship between the initial film thickness and the crystallite size for each sample, with the vertical axis representing the initial film thickness (μm) and the horizontal axis representing the crystallite size (nm). [Figure 11] FIG. 11 is a graph showing the average damage rate (%) for each sample, with the vertical axis representing the average damage rate (%) and the horizontal axis representing the sample number. [Figure 12] FIG. 12 is a graph showing the relationship between the initial film thickness and the film formation rate for each sample, with the vertical axis representing the initial film thickness (μm) and the horizontal axis representing the film formation rate (μm / min). DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to the embodiments described below.

[0018] [Rolling bearings] 1 is a cross-sectional view showing a rolling bearing according to an embodiment of the present invention, in which a thrust bearing, for example, is used as the rolling bearing. 1, thrust bearing 10 includes first raceway ring 11 having first raceway surface 13, second raceway ring 12 having second raceway surface 14, and a plurality of rolling elements 15 held so as to be rollable between first raceway surface 13 and second raceway surface 14. A cage 16 is disposed between first raceway surface 13 and second raceway surface 14 to hold the plurality of rolling elements 15 at predetermined intervals.

[0019] In the present embodiment shown in FIG. 1, oxide films 17 containing Fe3O4 are formed on the first and second raceway surfaces 13 and 14, respectively. Furthermore, the thickness of the oxide film 17 and the crystallite size of the Fe3O4 constituting the oxide film 17 are appropriately controlled. Because the oxide film 17 is formed by a process generally known as "black dyeing," hereinafter, the process for forming the oxide film 17 may be referred to as "black dyeing process" and the oxide film 17 may be referred to as "black dyeing film." Furthermore, hereinafter, "crystallite size of Fe3O4" refers to the crystallite size calculated from the peak attributable to the (311) plane of Fe3O4.

[0020] In the rolling bearing according to this embodiment, an oxide film 17 containing Fe3O4 must be formed on the surface of a predetermined region of the thrust bearing 10 (specifically, at least one of the first raceway surfaces 13 and second raceway surfaces 14 and the rolling elements 15). This makes it possible to suppress hydrogen generation from the first raceway surfaces 13, second raceway surfaces 14 and rolling elements 15 that constitute the thrust bearing 10, thereby suppressing the occurrence of hydrogen embrittlement. Furthermore, because the film thickness of the oxide film 17 and the crystallite size of the Fe3O4 that constitutes the oxide film 17 are appropriately controlled, the durability of the oxide film 17 can be improved, and the durability of the first raceway surfaces 13, second raceway surfaces 14 and rolling elements 15 can be improved.

[0021] Next, conditions for improving the durability of the black dyed film will be explained below. To improve the durability of the oxide film, it is important to suppress both the "film wear" and "film breakdown" mentioned above. Furthermore, the crystallite size of Fe3O4 affects "film wear." Furthermore, the crystallite size is affected by the film formation rate, and depends on the processing temperature of the black oxide treatment, the treatment solution, and the type of steel material being blackened. Meanwhile, the residual stress affects "film breakdown," which is affected by the film thickness of the black oxide film. Furthermore, the film thickness is affected by the processing time of the black oxide treatment and the film formation rate. In determining durability, since it is difficult to completely distinguish between "wear resistance" and "breakage resistance" and measure them separately, both are collectively referred to as "damage resistance."

[0022] <Relationship between the crystallite size of Fe3O4 and the damage resistance> The results and discussions of Experiment 1 and Experiment 2 conducted to investigate the relationship between the crystallite size of Fe3O4 and the damage resistance are described below.

[0023] (Experiment 1: Influence of crystallite size on damage resistance) By keeping the film thickness of the oxide film formed by black dyeing treatment almost constant and varying the film formation rate in various ways, the crystallite size was changed, and the influence on the damage resistance of the black dyeing film was investigated. The crystallite size was measured by X-ray diffraction (XRD) using cobalt (Co) as the radiation source for the oxide film formed by black dyeing treatment, and was calculated using the Scherrer equation based on the peak attributed to the (311) plane of Fe3O4. First, a black dyeing film was formed on the surfaces of the first raceway surface 13 and the second raceway surface 14 of the thrust bearing 10 made of SUJ2 steel material specified in JIS G 4805:2019. Specifically, the first raceway ring 11 and the second raceway ring that are the objects of black dyeing film formation were immersed in a treatment liquid mainly composed of sodium hydroxide (NaOH) to form a black dyeing film containing Fe3O4. In Experiment 1, the same treatment liquid was used, and various crystallite sizes were set by performing immersion treatment under various treatment conditions. Thereafter, a damage test of the black dyeing film was performed using a damage test apparatus, and the damage film thickness was calculated from the difference by measuring the film thickness before the test (initial film thickness) and the film thickness after the test.

[0024] Figure 2 is a cross-sectional view schematically showing the damage test apparatus. The damage test apparatus 20 has a container-shaped support base 21 with an open upper end, a rotating shaft 22 for rotating the thrust bearing 10, and a rotating disk 24 fixed to the rotating shaft 22. Also, lubricating oil 23 is injected inside the support base 21. During the damage test, thrust bearing 10 is placed between the inner bottom surface of support base 21 and rotating disk 24, with second bearing ring 12 of thrust bearing 10 fixed to the inner bottom surface of support base 21 and first bearing ring 11 fixed to rotating disk 24. Thereafter, thrust bearing 10 is rotated at a predetermined rotational speed while pressure is applied to it by rotating shaft 22 via rotating disk 24, and the thickness of the black dye film after the test is measured.

[0025] FIG. 3 is a graph showing the effect of crystallite size on damage resistance, with the vertical axis representing the initial film thickness (μm) and damaged film thickness (μm) of the black-dyed film, and the horizontal axis representing the crystallite size (nm). FIG. 4 is a graph showing the effect of crystallite size on damage resistance as an approximate straight line, with the vertical axis representing the damaged film thickness (μm) of the black-dyed film and the horizontal axis representing the crystallite size (nm). The initial film thickness was 0.83 μm to 0.96 μm, and the crystallite sizes were four points: 2.73 nm, 2.85 nm, 3.08 nm, and 3.47 nm.

[0026] As shown in FIG. 3, when the film thickness was kept almost constant at 0.9±0.1 μm, the larger the crystallite size, the greater the damage film thickness. Furthermore, as shown in Figure 4, there was a proportional relationship between the crystallite size and the damage film thickness. These results show that when comparing films with the same film thickness, films with smaller crystallite size have better damage resistance.

[0027] (Experiment 2: Effect of deposition rate on damage resistance) Next, the effect of the film formation rate was investigated for thrust bearings with crystallite sizes of 2.73 nm, 2.85 nm, 3.08 nm, and 3.47 nm, out of the thrust bearings fabricated in Experiment 1. The film formation rate is the thickness of the oxide film formed per unit time (μm / min).

[0028] Figure 5 is a graph showing the relationship between the deposition rate (μm / min) of the black-dyed film and the crystallite size (nm) of Fe3O4 as an approximate linear curve. As in Experiment 1, the crystallite size was calculated using the Scherrer equation based on the peak attributable to the (311) plane of Fe3O4 measured by X-ray diffraction using a cobalt (Co) radiation source. As shown in Figure 5, it was confirmed that there is a proportional relationship between the Fe3O4 crystallite size during black oxide treatment and the deposition rate. Furthermore, as mentioned above, there is a proportional relationship between the crystallite size and the deposition rate, and there is also a proportional relationship between the crystallite size and the damage film thickness. This indicates that the lower the deposition rate, the smaller the crystallite size and the better the damage resistance.

[0029] The above experiments 1 and 2 were conducted to investigate factors that mainly affect "coating wear." In contrast, the following experiment 3 was conducted to investigate factors that mainly affect "coating breakdown."

[0030] <Relationship between black dye film thickness and damage resistance> Next, we will describe the results and discussion of Experiments 3 and 4, which were conducted to investigate the relationship between the thickness of the black dyed film and its damage resistance.

[0031] (Experiment 3: Effect of thickness of black dyed film on damage resistance) During the black oxide treatment, the same treatment solution and treatment conditions were used, and the crystallite size was kept constant by keeping the film formation rate constant.The film thickness was changed by varying the treatment time, and the effect on damage resistance was investigated. First, a black dye film was formed on the surfaces of the first raceway surface 13 and the second raceway surface 14 of the thrust bearing 10 using the same method as in Experiment 1. The crystallite size was set to 3±0.04 nm, and a damage test similar to that in Experiment 1 was carried out on the resulting thrust bearings 10 having various film thicknesses.

[0032] FIG. 6 is a graph showing the effect of film thickness on damage resistance, with the vertical axis representing the initial film thickness (μm) and damaged film thickness (μm) of the black dyed film, and the horizontal axis representing the initial film thickness (μm) of the black dyed film. FIG. 7 is a graph showing the influence of the initial film thickness on the damage resistance, with the vertical axis representing the average damage rate (%) and the horizontal axis representing the initial film thickness (μm). In Experiment 3, the same processing solution was used for the black oxide process, and the film formation rate was constant, so the film quality, i.e., the Fe3O4 crystallite size, was almost the same. The average damage rate was calculated by dividing the average damaged film thickness at multiple locations by the initial film thickness. As shown in Figs. 6 and 7, when the crystallite size of Fe3O4 is approximately the same, it is clear that a thinner initial film thickness of the black dyed film results in better damage resistance.

[0033] (Experiment 4: Effect of thickness of black dyed film on film fracture resistance) The thickness of the black dye film was varied to investigate its effect on damage resistance, particularly on film fracture. Specifically, thrust bearings 10 with black dye films of various thicknesses were fabricated using the same method as in Experiment 3 above. Next, five indentations were made on the surface of the black dye film using a load and indenter specified by the Rockwell hardness test scale C (HRC). The black dye film around the indentations was then observed, and the distance from the outermost edge of each indentation to the peeled area of ​​the black dye film (peeling distance) was measured. The peeling distance was measured at four locations for each of the five indentations, and the average was calculated.

[0034] Figures 8A to 8D are photographs showing the state of peeling for each initial thickness of the black-dyed film. The initial thickness in Figure 8A is 0.42 μm, in Figure 8B it is 0.84 μm, in Figure 8C it is 1.83 μm, and in Figure 8D it is 1.97 μm. An example of the peeling distance is indicated by an arrow in the figure. FIG. 9 is a graph showing the effect of the initial film thickness on film breakdown as an approximate straight line, with the vertical axis representing the average peel distance (μm) and the horizontal axis representing the initial film thickness (μm) of the black dyed film.

[0035] As shown in Figures 8A to 8D and 9, it can be seen that the initial film thickness of the black dye film and the average peel distance are proportional to each other. The black dye film is formed by the oxidation of Fe to form Fe3O4, and volume expansion occurs when Fe3O4 is formed. Therefore, the black dye film has residual stress, and the thicker the black dye film, the greater the volume expansion and the greater the residual stress. The peel distances shown in Figures 8A to 8D and 9 are thought to be due to the residual stress of the black dye film, and it was shown that the thinner the initial film thickness, the better the coating fracture resistance.

[0036] Based on the considerations obtained from the above Experiments 1 to 4, the film thickness and the Fe3O4 crystallite size ranges that can improve the damage resistance of the black dyed film were obtained. The reasons for these limitations will be explained below.

[0037] [Black dye film thickness: 0.6 μm to 2.0 μm] The thickness of the black dye film particularly affects the film's resistance to damage. If the film thickness is less than 0.6 μm, the black dye film becomes too thin, shortening its lifespan against damage and reducing its effect in suppressing the hydrogen generation reaction. Therefore, it is preferable that the film thickness be 0.6 μm or more. On the other hand, if the film thickness exceeds 2.0 μm, the black dye film is more likely to break down and its durability is reduced. Therefore, the film thickness of the black dye film is set to 2.0 μm or less, preferably 1.5 μm or less, more preferably 1.2 μm or less, and even more preferably 0.8 μm or less.

[0038] [Fe3O4 crystallite size: 2.5nm to 3.2nm] The Fe3O4 crystallite size particularly affects the abrasion resistance of the coating. Since the Fe3O4 crystallite size is greatly affected by the film formation speed, if the Fe3O4 crystallite size is set to less than 2.5 nm, film formation takes too long, resulting in reduced productivity. Therefore, the Fe3O4 crystallite size is set to 2.5 nm or more, and preferably 2.7 nm or more. On the other hand, if the crystallite size of Fe3O4 exceeds 3.2 nm, the desired damage resistance of the black dyed film cannot be obtained. Therefore, the crystallite size of Fe3O4 is set to 3.2 nm or less, preferably 3.0 nm or less, and more preferably 2.9 nm or less.

[0039] In the above embodiment, an example was shown in which the thrust bearing 10 was used as the rolling bearing on which the black dye film (oxide film 17) was formed, but the present invention is not limited to the thrust bearing 10 and can also be applied to, for example, a radial bearing. Furthermore, the region where the oxide film 17 is formed is not limited to the raceway surface (first raceway surface 13, second raceway surface 14) side as explained in the above embodiment, but may be formed on the surface side of the rolling elements 15, or on both. However, in order to more effectively suppress the occurrence of hydrogen embrittlement fracture, it is preferable that the oxide film 17 is formed on both the first raceway surface 13 and second raceway surface 14 and the surface of the rolling elements 15. Furthermore, the rolling elements 15 may be balls or rollers. Furthermore, the black oxide treatment may be performed only once or multiple times. Although the above embodiment shows an example in which SUJ2 steel is used, the present invention is not limited to SUJ2 steel, and can also be applied to steel that can be blackened.

[0040] [Method for manufacturing rolling bearings] The method for manufacturing a rolling bearing according to this embodiment is a method for manufacturing the above-mentioned rolling bearing, and includes a step of forming a black oxide film (oxide film 17) containing Fe3O4 on at least one of the first raceway surface 13, the second raceway surface 14, and the surface of the rolling elements 15. The conditions for the method for manufacturing a rolling bearing according to this embodiment are described below.

[0041] [Black dye film deposition rate: 0.003 μm / min to 0.034 μm / min] As mentioned above, the deposition rate of the black dyed film has a significant effect on the crystallite size of Fe3O4. Smaller Fe3O4 crystallite sizes provide better damage resistance, but a deposition rate of less than 0.003 μm / min reduces productivity. Therefore, the deposition rate of the black dyed film is set to 0.003 μm / min or higher. On the other hand, if the deposition rate of the black dyed film exceeds 0.034 μm / min, the crystallite size of Fe3O4 will exceed 3.2 nm, and the desired damage resistance cannot be obtained. Therefore, the deposition rate of the oxide film is set to 0.034 μm / min or less, and preferably 0.026 μm / min or less. [Example]

[0042] A thrust bearing 10 shown in FIG. 1 was manufactured using SUJ2 steel material specified in JIS G 4805:2019, and the thrust races constituting the first raceway surface 13 and the second raceway surface 14 were subjected to a black oxide treatment under various treatment conditions to form oxide films 17 containing Fe3O4 and having various crystallite sizes. The crystallite size of Fe3O4 was adjusted appropriately by controlling the film formation rate of the oxide film 17. The thrust bearing 10 had an inner diameter of 25 mm, an outer diameter of 52 mm, and a width of 18 mm, and used six rolling elements 15 with a diameter of 3 / 8 inch.

[0043] The processing conditions for the blackening process, the film formation rate, and the Fe3O4 crystallite size are shown in Table 1 below. Note that the processing solutions A, B, and C in Table 1 below are processing solutions with different compositions, each containing NaOH as the main component, and are commonly used as processing solutions for blackening processes. Sample No. (2) was subjected to two consecutive 30-minute blackening processes at different processing speeds in accordance with DIN 50938:2018-01. The other samples were subjected to a single blackening process. The crystallite size was measured in the same manner as in Experiment 1.

[0044] Next, the initial thickness of the black dye film was measured for the obtained thrust bearings 10 of Samples No. (1) to (11), and then a damage test for the black dye film was carried out three times (n=3) for each condition using a damage test device 20 shown in Figure 2. The damage test device 20 was rotated for five days at the rotational speeds shown below while applying pressure to the thrust bearings 10. Specific conditions for the damage test are shown below. Note that the "number of stress cycles" shown below refers to the number of times the rolling element passed through a predetermined position on the raceway.

[0045] Surface pressure: 2.2 (GPa) Lubricant viscosity (ISO viscosity grade number): VG 68 Rotation speed: 1000 (rpm) Number of stress cycles: 2.16 x 10 7 (times)

[0046] After the damage test, the thrust race of each sample was cut, and the remaining black film (remaining film thickness) was measured at four points using a scanning electron microscope (SEM). The film thickness of the black film in areas not contacted by the rolling elements was defined as the initial film thickness (μm), and the remaining film thickness at each point was averaged to determine the average damaged film thickness (μm). The average damaged film thickness was then divided by the initial film thickness and multiplied by 100 to determine the average damage rate (%). The initial film thickness and the results of the damage test are also shown in Table 1 below.

[0047] [Table 1]

[0048] Figure 10 is a graph showing the relationship between initial film thickness and crystallite size for each sample, with the vertical axis representing initial film thickness (μm) and the horizontal axis representing crystallite size (nm). Figure 11 is a graph showing the average damage rate (%) for each sample, with the vertical axis representing average damage rate (%) and the horizontal axis representing sample number. Figure 12 is a graph showing the relationship between initial film thickness and film formation rate for each sample, with the vertical axis representing initial film thickness (μm) and the horizontal axis representing film formation rate (μm / min).

[0049] As shown in Table 1 and Figures 10 to 12, sample No. (8) had a black film thickness (initial film thickness) exceeding the upper limit of the range of the present invention, resulting in an average damage rate of 100%, indicating the formation of a black film with poor durability. Samples Nos. (9) to (11) also had crystallite sizes exceeding the upper limit of the range of the present invention, resulting in an average damage rate of 100%, indicating the formation of a black film with poor durability.

[0050] On the other hand, for all of Samples (1) to (7), the film formation rate was appropriately controlled and a black film with the desired initial thickness of 0.6 μm to 2.0 μm was formed, resulting in an Fe3O4 crystallite size of 2.5 nm to 3.2 nm. Therefore, for Samples (1) to (7), regardless of the treatment solution and number of treatments, the black film remained even after severe damage tests, and a black film with good durability was obtained. In addition, the film formation did not take too long, resulting in good productivity.

[0051] In particular, as shown in Figure 10, samples (1) to (3), (5), and (7) had initial film thicknesses of 1.2 μm or less, which is the preferred upper limit of the present invention, and crystallite sizes of 2.5 nm to 3.2 nm, so all of them had average damage rates of 65% or less, and black-dyed films with excellent durability were obtained. Furthermore, sample (7) had the smallest crystallite size, so although the time required for film formation was longer than that of samples (1) to (6), it had the lowest average damage rate and excellent durability.

[0052] 12, for samples (1) to (3), (5), and (7), the deposition rate was controlled to 0.003 μm / min to 0.034 μm / min, and the blackened film was formed so that the initial film thickness was 1.2 μm or less, which is a more preferred range of the present invention. As a result, the average damage rate was 65% or less, and blackened films with excellent durability were obtained. In particular, the deposition rate was controlled to 0.026 μm / min or less, which is a preferred range, and the blackened film was formed so that the initial film thickness was 0.8 μm or less, which is a particularly preferred range. As a result, the average damage rate was 40% or less, and further improvement in durability was confirmed.

[0053] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0054] This application is based on a Japanese patent application (Patent Application No. 2022-111257) filed on July 11, 2022, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0055] 10 Thrust bearing 11 1st bearing ring 12 2nd bearing ring 13 1st orbital plane 14 2nd orbital plane 15 Rolling elements 16 Cage 17 Oxide film containing Fe3O4 20 Damage Testing Equipment 21 Support stand 22 Rotation axis 23 Lubricating oil 24 Turntable

Claims

1. A rolling bearing comprising a first raceway ring having a first raceway surface, a second raceway ring having a second raceway surface, and a plurality of rolling elements held so as to be rollable between the first raceway surface and the second raceway surface, At least one of the first raceway surface, the second raceway surface, and the surface of the rolling element is provided with Fe. ３ O ４ an oxide film containing The oxide film has a thickness of 0.6 μm or more and 2.0 μm or less, The Fe ３ O ４ The rolling bearing is characterized in that the crystallite size calculated from the peak attributed to the (311) plane is 2.5 nm or more and 3.2 nm or less.

2. 2. The rolling bearing according to claim 1, wherein the oxide film is formed on the surfaces of the first raceway surface and the second raceway surface and on the surfaces of the rolling elements.

3. 3. The method for manufacturing a rolling bearing according to claim 1 or 2, At least one of the first raceway surface, the second raceway surface, and the surface of the rolling element is provided with Fe. ３ O ４ forming an oxide film containing A method for manufacturing a rolling bearing, characterized in that the rate of formation of the oxide film is 0.003 μm / min or more and 0.034 μm / min or less.

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