JP2004115919A - Roller bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive roller bearing of high quality with the long life, through clarifying a relationship between a central segregation rate of carbon (C/C<SB>0</SB>) in a material composing a steel ball as a rolling body in a roller bearing and the finished product, and the rolling life. <P>SOLUTION: The material composing the steel ball is made from a wire rod of a bearing steel, which is continuously cast while being electromagnetically stirred and lightly pressed in the last period of solidification; has the central segregation rate of carbon in the above material and the above finished steel ball so as to satisfy 0.90≤C/C<SB>0</SB>≤1.10, (wherein C/C<SB>0</SB>means the central segregation rate of carbon; and C means a carbon concentration (wt.%) in a central part; and C<SB>0</SB>means an average carbon concentration (wt.%)); has an oxygen content of 10 ppm or less in the above wire rod of the bearing steel; and has a sulfur content of 0.008 wt.% or less in the above wire rod of the bearing steel, to improve the rolling life by inhibiting flaking and cracking from occurring in a local part of the above steel ball in service. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a rolling bearing, and more particularly, to an improvement in a rolling bearing used for an automobile, a construction machine, a railway vehicle, other industrial machines, and the like.

様 々 Various studies have been made to improve the life of rolling bearings. For example, in order to reduce the presence of oxide-based inclusions such as alumina, which is one of the factors that hinder the improvement of the rolling life of a bearing, the oxygen content in steel (hereinafter referred to as “oxygen content in steel”) is reduced. Is most effective. For this reason, each steelmaker is improving various steelmaking technologies.

On the other hand, vacuum degassing and ladle refining (LF) have also been adopted in the field of bearing steel, and in the late 1975's, bearing steel from any manufacturer could be manufactured by the conventional ingot casting method , "IC material"), a material manufactured by a continuous casting method (hereinafter, referred to as "CC material") has come to be used.
In this continuous casting method of bearing steel, since the concentration of carbon contained in the material is high, the temperature difference between the start of solidification of the steel and the completion of solidification is large. For this reason, there has been a problem that elements such as carbon, chromium, manganese, phosphorus, and sulfur are locally concentrated and segregated particularly in the center of the material, thereby reducing the rolling life of the bearing. Therefore, in order to improve the quality such as the center segregation, the floating of inclusions, and the stability of the solidified structure, an advanced steelmaking technique was required.

In recent years, the difference between the rolling life of the IC material and the rolling life of the CC material has almost disappeared by the use of electromagnetic stirring, the pinch roll method under light pressure, the continuous forging method, and the like. For example, as described in Non-Patent Document 1, when the rolling life was evaluated by a thrust life test using a sample cut in parallel to the rolling direction including the center of the material, the rolling made of CC material was performed. The rolling life of the bearing was much longer than the rolling life of the rolling bearing made of an IC material.

It is also reported that the relationship between the flaking occurrence position and the rolling life does not tend to shorten the life at the center of the CC material.
A report similar to the above is also described in Non-Patent Document 2 using the same test method.
Based on these grounds, many CC materials as well as IC materials are used for the inner and outer rings of current rolling bearings. The inner ring and outer ring are mainly made of rods and tubes as raw materials.Either of them is used in the process of turning, hot forging, warm forging, etc., to be processed into inner and outer rings. In addition, the center segregation portion is rarely exposed on the functional surface (particularly, the groove surface) of the bearing.

That is, when the inner ring and the outer ring are manufactured from a bar by hot forging and warm forging, the central segregation harmful portion is removed in the forging process because the central portion of the material goes through a blanking process.
In the case where the inner ring and the outer ring are manufactured from the tube material by turning, when the outer ring is formed, the center segregated portion on the inner diameter surface of the tube material is harmless because the cut amount of the groove is large. On the other hand, when the inner ring is formed, it does not affect the rolling life because it corresponds to the inner diameter surface of the bearing.

From these viewpoints, even if there is some concern about the central segregation quality of CC materials, in recent years, as a material for the inner ring and outer ring, due to the realization of low cost, the achievement of excellent cleanliness, and the superiority of ground flaw quality, , CC materials are used.
On the other hand, the rolling element is generally made of a wire, and is formed by cold working (cold header processing) as shown in FIG.

Specifically, as shown in FIG. 6A, for example, a raw material (a billet) 20 is rolled to produce a coil material 21.
Next, as shown in FIG. 6 (2), the coil material 21 is cut into a desired length by a cold header, and then the cut material is formed to obtain a spherical molded product 23. Burrs 24 remain in the molded product 23 in this state. Next, after the burrs 24 of the molded product 23 are removed by grinding, heat treatment is performed on the burrs 24. Next, polishing and lapping are sequentially performed to obtain a rolling element 25 having a desired size.

The rolling element 25 formed by this cold working has a state in which the center segregation portion of the raw material (billet) 20 is exposed to the poles 30A and 30B of the rolling element 25 shown in FIG. Become. The problem that the poles 30A and 30B are exposed on a surface perpendicular to the rolling direction is combined, and flaking and cracks are liable to occur in this portion, and the rolling life is shortened and the strength is liable to deteriorate. was there.

For this reason, it has been difficult to employ a CC material having a concern about the quality of center segregation as a material for the rolling elements. Therefore, at present, an IC material is used as a material of the rolling elements.
ASTM, SPT 987, 1988, p28 Iron and Steel, 73rd year, (1987), No. 3, p116 JP-A-3-254339 JP-A-3-254340 JP-A-3-254341 JP-A-3-254342 JP-A-49-121733

However, in general, it is difficult to continuously cast an IC material because it is necessary to cut off an inhomogeneous portion of a top portion and a bottom portion of the ingot in a rolling process. Therefore, there is a problem that the manufacturing cost is higher than that of the CC material that can be continuously cast.
In addition, the IC material has a problem that fragments of debris and deoxidized products are trapped in the initial solidified layer at the time of ingot making due to an accidental factor at the time of ingot making, and the ground flaw is easily generated. On the other hand, with respect to the improvement of the quality of center segregation of CC materials, for example, a continuous forging method disclosed in Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, and the like, and Patent Literature 5 disclose. There is a technology to improve macro-segregation by applying pressure at the end of continuous solidification solidification and deforming it while solidifying molten steel such as carbon and chromium while pushing it up.

However, in this technique for improving macro-segregation, the center segregation rate of carbon (C / C ₀ , where C is the carbon concentration (% by weight) in the center of the material, and C ₀ is the average carbon concentration (% by weight) of the material. ) Or the center segregation rate of sulfur (S / S ₀ , where S is the central sulfur concentration (% by weight), S ₀ is the average sulfur concentration (% by weight)) and the rolling life of the rolling element. The problem is that the relationship has not yet been elucidated.
An object of the present invention is to solve such a conventional problem, and the center segregation ratio of carbon (C / C ₀ ) or the center segregation ratio of sulfur (S / S) in a completed steel ball is to be solved. It is an object of the present invention to clarify the relationship between ₀ ) and the rolling life and to provide a low-cost, high-quality and long-life rolling bearing.

In order to achieve this object, the present invention relates to a rolling bearing comprising an inner ring, an outer ring and a steel ball, wherein a material constituting the steel ball is a continuous casting bearing subjected to electromagnetic stirring and light reduction at the end of solidification. Consisting of a steel wire rod, the center segregation rate of carbon of the material and the completed steel ball is:
0.90 ≦ C / C ₀ ≦ 1.10.
Where C / C ₀ is the center segregation rate of carbon C is the carbon concentration (% by weight) at the center
C ₀ is the average carbon concentration (% by weight)
And the oxygen content in the bearing steel wire is 10 ppm or less, and the sulfur content in the bearing steel wire is 0.008% by weight or less. It is characterized in that the occurrence of flaking and cracks is suppressed and the rolling life is improved.

According to the present invention, the material constituting the rolling element is a bearing steel wire rod made by continuous casting subjected to electromagnetic stirring and light reduction at the end of solidification, and the center segregation ratio of carbon (C / C) of the completed steel ball is made. ₀ )
0.90 ≦ C / C ₀ ≦ 1.10.
And the use of steel having an oxygen content of 10 ppm or less in the bearing steel wire and a sulfur content of 0.008% by weight or less in the bearing steel wire achieves cost reduction and quality improvement. In addition, the rolling life is improved.
The reason is described below.
In the present invention, since a bearing steel wire (CC material) formed by continuous casting is used as a material constituting a rolling element, productivity is improved, cost reduction is achieved, cleanliness is improved, and Superiority to scratch quality is improved.
Then, the center segregation quality, which has conventionally been a problem of the CC material, is greatly improved for the following reasons.

Most of the flaking and cracks of the rolling elements occur from the exposed portion of the central segregation portion, that is, the pole. The present inventors have found that by reducing the center segregation ratio (C / C ₀ ) of carbon to some extent, the occurrence of flaking and cracks is suppressed and the rolling life is improved.
That is, the center segregation rate of carbon (C / C ₀ ) indicates how much the carbon concentration in the center of the material is segregated with respect to the average carbon concentration (C ₀ ) of the material. However, the present inventors have confirmed that by setting the center segregation ratio (C / C ₀ ) of carbon in the raw material and the finished product to 1.1 or less, the rolling life is remarkably improved.

When the center segregation rate (C / C ₀ ) of carbon in the raw material and the finished product exceeds 1.1, carbon and sulfur as a trace impurity element segregate in a portion corresponding to the pole of the rolling element. For this reason, carbide-based inclusions and sulfide-based inclusions increase, and in use, flaking and cracks are generated starting from a portion (pole) where the center segregation portion is exposed, which causes a reduction in rolling life. .
The lower limit of the carbon center segregation rate (C / C ₀ ) is about 0.9 in a general center segregation control method such as electromagnetic stirring or a pinch roll light reduction method, which is a manufacturing limit. Accordingly, the center segregation rate (C / C ₀ ) of carbon in the material and the finished product constituting the rolling element is
0.9 ≦ C / C ₀ ≦ 1.10.
Limited to.
In the present invention, the center segregation ratio of the material of carbon (C / C ₀₎ and carbon PVC center segregation rate (C / C ₀₎ is evaluated by the following methods.

[Central segregation rate of carbon of material (C / C ₀ )]
As shown in FIG. 2, the carbon concentration (C) at the center of the material is the center C of the material (billet) 20 which is the base material of the bearing steel wire, and the cross-sectional diameter (cross-section) of the material (billet) 20 If the shape is a circle, the diameter, if the cross-sectional shape is polygonal, the portion of the length of one side) When D _X, from the center to a radius of 0.01 × D _X ~0.02 × D _X Is obtained by cutting using a drill or the like, and measuring the concentration of carbon present in this portion by a combustion method.
On the other hand, as shown in FIG. 2, the average carbon concentration (C ₀ ) of the material is set at the desired locations (C ₁ , C ₂ , C ₃ and C ₄ ) of the portion having a radius of D _X / 4 as described above It is cut off using a drill or the like, and the concentration of carbon present in each portion is measured by a combustion method, and the values are obtained by averaging these values.
Then, the center segregation rate (C / C ₀ ) of carbon of the material was evaluated using these values.

[Central segregation rate of carbon in finished product (C / C ₀ )]
As shown in FIG. 3, the carbon concentration (C) at the center of the finished product is obtained by cutting out a cross section passing through the poles of the finished product, and measuring the EPMA in the direction perpendicular to the fiber flow at the center of the finished product (rolling element). (Electron beam microanalyzer) was used to perform line analysis, and the results were obtained based on the results. The carbon concentration at the center (C) is the measurement result of the carbon concentration at a portion between the radius of 0.01 × D _{Y and} 0.02 × D _Y from the center assuming that the cross-sectional diameter of the finished product is D _Y. The average is calculated based on

On the other hand, the average carbon concentration (C ₀ ) of the finished product is, as shown in FIG. 3, based on the measurement results of the carbon concentration in the portion (two places) whose distance from the center in the radial direction is D _Y / 4. It is determined by calculating the value.
Then, the center segregation rate (C / C ₀ ) of carbon in the finished product was evaluated using these values.
Further, the present inventors have conducted research, and found that even if the center segregation ratio (C / C ₀ ) of the carbon is 1.1 or less, if the oxygen content in the steel of the material exceeds 10 ppm, Oxide-based inclusions increase, and during use, flaking and cracks are likely to occur starting from the portion (pole) where the center segregation portion is exposed. As a result, it has been found that the rolling life is shortened.

Furthermore, even if the carbon center segregation ratio (C / C ₀ ) is 1.1 or less, if the sulfur content in the steel of the material exceeds 0.008% by weight, the sulfide-based inclusions During use, flaking and cracks are likely to occur from the part (pole) where the center segregation part is exposed during use. As a result, it has been found that the rolling life is shortened.
In the present invention, the oxygen content in the steel and the sulfur content in the steel were measured by a combustion method for an arbitrary plurality of portions, and determined by an average value of the obtained values.

Further, the center segregation ratio (C / C ₀ ) of the carbon is 1.1 or less, the oxygen content in the steel is 10 ppm or less, and the sulfur content in the steel is 0.008% by weight. Comparing the rolling life of the rolling element made of the CC material (the CC material according to the present invention) with the rolling life of the rolling element made of the IC material, the rolling life of the rolling bearing made of the CC material according to the present invention is better. It was confirmed that it was excellent.
Therefore, a bearing steel wire (CC material) by continuous casting is used as a material constituting the rolling element, and the center segregation ratio (C / C ₀ ) of carbon in the material and the finished product is set to 1.1 or less, and further, The oxygen content in the bearing steel wire was limited to 10 ppm or less, and the sulfur content in the bearing steel wire was limited to 0.008% by weight.

The rolling bearing according to the present invention, the material constituting the steel ball, the material constituting the steel ball is a bearing steel wire rod by continuous casting subjected to electromagnetic stirring and light reduction at the end of solidification, the material and the completed The center segregation rate of carbon of the steel ball is
0.90 ≦ C / C ₀ ≦ 1.10.
Where C / C ₀ is the center segregation rate of carbon C is the carbon concentration (% by weight) at the center
C ₀ is the average carbon concentration (% by weight)
And the oxygen content in the bearing steel wire is 10 ppm or less, and the sulfur content in the bearing steel wire is 0.008% by weight or less. The rolling life is improved by suppressing the occurrence of flaking and cracks, so that the rolling life can be significantly improved, the cost and quality are improved, and a long life rolling bearing is provided. Can be.

Next, an embodiment according to the present invention will be described.
A raw material (a billet) that is a rod-shaped member (base material of a wire) having a circular cross section and having the chemical components (% by weight) shown in Table 1 is prepared.
In this example, the material (billet) having a cross-sectional diameter of 180 mm was selected.

Next, the oxygen content in steel of each material (Examples No. 1 to No. 4) having the chemical components shown in Table 1 is measured by the following method.
From each material (Examples No. 1 to No. 4), cutting was performed from any four places using a drill having a diameter of 5 mm, and the amount of oxygen contained in the sample obtained by the combustion method ( ppm), and these values are averaged to obtain the oxygen content in steel (ppm) of each material.
Table 2 shows the results.
Next, the center segregation ratio (C / C ₀ ) of carbon of each of the materials having the chemical components shown in Table 1 (Examples No. 1 to No. 4) is evaluated by the following method.
A 2.5 mm radius portion is cut at the center of each material using a drill having a diameter of 5 mm to obtain a sample. Next, the concentration (% by weight) of carbon contained in this sample is measured by a combustion method, and this is defined as the carbon concentration (C ₀ ) at the center of each material.

Next, cutting is performed using a drill having a diameter of 5 mm at four locations at a position 45 mm from the radial center of each material to obtain samples C ₁ , C ₂ , C ₃ and C ₄ .
Next, the concentration (% by weight) of carbon contained in each sample is measured by the combustion method, and this value is averaged, and the obtained value is defined as the average carbon concentration (C ₀ ) of each material.
Next, the center segregation rate (C / C ₀ ) of carbon of each material is determined from the carbon concentration (C) and the average carbon concentration (C ₀ ) at the center of each material obtained by the above method.

Table 2 shows the results.
Next, the rolling elements (balls) are manufactured using the above-mentioned materials (Examples No. 1 to No. 4) by the method shown in FIGS. 6 (1) and 6 (2). In this example, as a countermeasure for suppressing center segregation, a light pressure reduction method was applied at the end of solidification using electromagnetic stirring (EMS) and pinch rolls.
The finished product (rolling element) had a ball diameter of 3/8 inch and was finished to JIS grade grade 10. Next, a rolling life test is performed on each rolling element by the following method. Using the radial type life tester shown in FIGS. 4 and 5 and using the inner ring and the outer ring of a deep groove ball bearing 6206 (a ball bearing having an inner diameter of 30 mm) as the test bearing 54, each rolling element according to the present embodiment was used. A durability test is performed under the following conditions.

(conditions)
Bearing Deep groove ball bearing 6206 (inner and outer rings)
Rolling element Nine 3 / 8-inch rolling elements are incorporated simultaneously. Bearing clearance C3
Cage Nylon Cage Rotation speed 3900rpm
Lubrication Turbine oil (VG68 oil bath)
Radial load 13.8KN
Flaking detection Acceleration sensor

In the present example, the test under the above conditions was performed 20 times for one type of rolling element (for each rolling element, 9 tests were performed 20 times for each test, and the total number of balls = 180). If flaking occurs on either the inner ring or the outer ring before the rolling elements, replace the inner ring or outer ring with flaking with a new one and continue the test. When flaking occurred, the rolling time was defined as the time.
In addition, the rolling life was evaluated by an Hv Weibull plot and a 10% probability of failure life (L ₁₀ ).
Table 2 shows the results.

Next, after the end of the rolling life test, all the rolling elements (Examples No. 1 to No. 4) were pickled (1: 1 hydrochloric acid, temperature = 70 ° C., pickling time = 20 minutes). As a result, for all the rolling elements, it was confirmed that the positions where flaking occurred coincided with the poles of the rolling elements.
(Comparative example)
Next, as a comparison, the sample was provided with the chemical components (% by weight) shown in Table 3, and was prepared in Example No. 1 described above. 1 to No. A material (a billet) having the same shape as that of No. 4 is prepared.

Next, the oxygen content (ppm) in steel of each of the materials having the chemical components shown in Table 3 (Comparative Examples No. 5 to No. 25) is measured in the same manner as in the above-mentioned Example.
Table 4 shows the results.
Next, the center segregation ratio (C / CO) of carbon of each of the materials having the chemical components shown in Table 3 (Comparative Examples No. 5 to No. 25) is determined in the same manner as in the above-described embodiment.
Table 4 shows the results.
Next, among materials having the chemical components shown in Table 3, Comparative Examples No. 5-No. Using No. 17, a rolling element is manufactured by the same continuous casting method as in the above embodiment. In addition, the comparative example No. 5-No. In No. 17, only electromagnetic stirring (EMS) was performed as a countermeasure for center segregation.
Next, among the materials having the chemical components shown in Table 3, Comparative Examples No. 18-No. The rolling element is manufactured by the conventional ingot casting method by using 25.
Next, a rolling life test similar to that of the above-described embodiment is performed on these rolling elements (Comparative Examples Nos. 5 to 25).
Table 4 shows the results.

Next, after the end of the rolling life test, when all the rolling elements were pickled under the same conditions as in the above-described embodiment, the flaking occurrence positions of all the rolling elements coincided with the poles of the rolling elements. It was confirmed that.
From Tables 1 to 4, the rolling elements obtained from the materials according to the present embodiment (Examples No. 1 to No. 4) are comparative examples No. 1 to No. 4. 5-No. It is confirmed that the rolling life (L10) is significantly improved as compared with No. 25.
In Comparative Example No. 5-No. No. 17 uses a CC material, but at least one of the center segregation ratio (C / C ₀ ) of carbon of the material, the oxygen content in steel and the sulfur content deviates from the conditions described in claim 1. It can be seen that the rolling life (L ₁₀ ) was reduced.
Then, in Comparative Example No. 18 and no. 19 indicates that the center segregation rate of carbon (C / C ₀ ), the oxygen content in steel and the sulfur content of the material satisfy the conditions described in claim 1, but since the IC material is used, the CC material is used. Example No. used. 1 to No. 4, it can be seen that the rolling life (L ₁₀ ) is shorter.

This is because the quality of the IC material is inferior to that of the CC material, such as deoxidation products trapped in the initial solidification layer due to accidental factors at the time of agglomeration, causing ground flaws and large inclusions. It is. In Comparative Example No. 20-No. In Comparative Example No. 25, at least one of the carbon center segregation ratio (C / C ₀ ), oxygen content in steel, and sulfur content of the material deviated from the conditions described in claim 1. 5-No. It can be seen that the rolling life (L ₁₀ ) is shorter than that of No. 17. That is, the reason why the CC material has a longer rolling life (L ₁₀ ) than the IC material is that the cleanliness and the quality of the scratches are superior to the IC material.

Further, when the center segregation ratio (C / C ₀ ) of carbon in the material is 1.1 or less, when the oxygen content in the steel satisfies the conditions of 10 ppm or less and the sulfur content of 0.008% by weight or less, particularly, It can also be seen that the rolling life is improved.
Next, the rolling elements after the test, the measuring method of the finished product the carbon of the central segregation rate in the (rolling elements) (C / C _0), the measurement of the center segregation rate of carbon (C / C ₀₎ As a result, it was confirmed that the value was almost the same as that of the material. Therefore, the center segregation ratio (C / C ₀ ) measured by the above two methods is 1.1 or less, and the oxygen content and the sulfur content in the steel satisfy the conditions described in claim 1. It was confirmed that the rolling element (the rolling element according to the present invention) having a good rolling life was obtained as described above.

Next, in Example No. 1 to No. No. 4 and Comparative Example No. 5-No. For 25, the center segregation ratio (S / S ₀ ) of sulfur (which is an impurity element other than carbon) in the material is determined. Here, S is the sulfur concentration (% by weight) at the center of the material, and S ₀ is the average sulfur concentration (% by weight) of the material, which was determined by the same method as in the above-described example.
The result is shown in FIG.
The center segregation rate (C / C ₀ ) of carbon in the raw materials obtained from the examples and the comparative examples is shown in FIG. 1 (2).
From FIGS. 1 (1) and (2), it is confirmed that the center segregation ratio (S / S ₀ ) of the sulfur shows almost the same tendency as the center segregation ratio (C / C ₀ ) of carbon. . From this, it is understood that the rolling life can be improved by specifying the center segregation rate (S / S ₀ ) of sulfur.

Next, the amount of nonmetallic inclusions at the center of the raw materials obtained from the above Examples and Comparative Examples is measured by the following method. A cross section in the rolling direction including the center of the material was inspected using a microscope at an inspection area of 320 mm ² based on JIS G0555 described in “JIS Handbook, 1993, Iron and Steel, p302 to p303, Published by the Japan Standards Association”.
Example No. 1 to No. No. 4 and Comparative Example No. 5-No. FIG. 1 (3) shows the amount of sulfide-based inclusions in the center of the material in Example No. 25. 1 to No. No. 4 and Comparative Example No. 5-No. FIG. 1 (4) shows the amount of oxide-based inclusions at the center of the material at 25.
From FIGS. 1 (3) and (4), the amount of sulfide-based inclusions and the amount of oxide-based inclusions in the center of the material are respectively the center segregation rate of carbon (C / C ₀ ) and the center segregation rate of sulfur (S / S ₀ ).

Sulfide-based inclusions are classified as A-based inclusions according to JIS and ASTM standards, and have a slender form extending in the material rolling direction. This sulfide-based inclusion is particularly large in the segregation portion at the center of the material due to an increase in the center segregation rate, and increases the sulfide-based inclusion and the oxide-based inclusion. On the poles of rolling elements made from CC material (wires), elongated sulfide-based inclusions are perpendicular to the surface, and, like oxide-based inclusions, are concentrated under repeated rolling contact stress. It has been confirmed that it becomes a source and has an adverse effect on the improvement of the rolling life.
The lower limit of the center segregation rate (C / C ₀ ) of carbon is about 0.9 because the electromagnetic stirring and the pinch roll light reduction method are used.
In the present embodiment, a rod-shaped member having a circular cross section is used as a material, but the material may be a rod-shaped member having a polygonal cross-section.

(1) is a diagram showing the center segregation ratio of sulfur in the materials of the examples and comparative examples according to the present invention, (2) is a diagram showing the center segregation ratio of carbon in the materials of the examples and comparative examples, and (3) is a diagram showing FIG. 4 is a diagram showing the amount of sulfide-based inclusions at the center of the material in Examples and Comparative Examples. FIG. 4D is a diagram showing the amount of oxide-based inclusions at the center of the material in Examples and Comparative Examples. It is a figure which shows a part of method of evaluating the center segregation rate of carbon in the raw material which concerns on the Example of this invention. It is a figure which shows a part of method of evaluating the center segregation rate of carbon in the finished product (rolling element) which concerns on the Example of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing of the well-known radial type life test machine used for the rolling life test which concerns on the Example of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing of the well-known radial type life test machine used for the rolling life test which concerns on the Example of this invention. (1) is a view showing a part of a method of manufacturing a rolling element (ball) for a ball bearing using a wire, and (2) is a view showing a part of a method of manufacturing a rolling element (ball) for a ball bearing using a wire. is there. It is a fiber flow figure of the rolling direction of the raw material axial direction cross section of a rolling element (ball).

Explanation of reference numerals

20 materials (billet)
25 rolling elements 30 poles

Claims (1)

In a rolling bearing provided with an inner ring, an outer ring and a steel ball, a material forming the steel ball is made of a bearing steel wire rod by continuous casting subjected to electromagnetic stirring and light reduction at the end of solidification, and the material and the finished The center segregation rate of carbon in the steel ball is
0.90 ≦ C / C ₀ ≦ 1.10.
Where C / C ₀ is the center segregation rate of carbon C is the carbon concentration (% by weight) at the center
C ₀ is the average carbon concentration (% by weight)
And the oxygen content in the bearing steel wire is 10 ppm or less, and the sulfur content in the bearing steel wire is 0.008% by weight or less. A rolling bearing characterized in that the occurrence of flaking and cracks is suppressed to improve the rolling life.

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