JP7490024B2 - Ball bearings - Google Patents

Description

The present invention relates to a ball bearing.

For example, JP 2001-3139 A (Patent Document 1) describes a rolling bearing (tapered roller bearing). The rolling bearing described in Patent Document 1 has an inner ring, an outer ring, and multiple rolling elements (tapered rollers). The inner ring has an inner ring raceway surface that contacts the rolling elements as a contact surface. The outer ring has an outer ring raceway surface that contacts the rolling elements as a contact surface. The rolling elements have an outer peripheral surface that contacts the inner ring raceway surface and the outer ring raceway surface as a contact surface. In the rolling bearing described in Patent Document 1, nitriding is performed on the contact surfaces of the inner ring, outer ring, and rolling elements. In the rolling bearing described in Patent Document 1, the amount of retained austenite in the steel in the surface layer near the contact surfaces of the inner ring, outer ring, and rolling elements is 20 volume percent or more and 40 volume percent or less.

JP 2001-3139 A

The bearing components (inner ring, outer ring, and rolling elements) of the rolling bearing described in Patent Document 1 are formed by performing machining such as grinding and polishing on a steel workpiece that has been subjected to nitriding, quenching, and tempering. However, the rolling bearing described in Patent Document 1 does not focus on the nitrogen concentration and the gradient of the nitrogen concentration in the steel in the surface layer near the contact surfaces of the inner ring, outer ring, and rolling elements. As a result, the rolling bearing described in Patent Document 1 leaves room for improvement in terms of the workability of the bearing components.

The present invention was made in consideration of the problems of the conventional technology as described above. More specifically, the present invention provides a ball bearing that can improve the workability of bearing parts.

The ball bearing according to the present invention comprises an inner ring, an outer ring, and balls. At least one of the bearing components, the inner ring, the outer ring, and the balls, has a contact surface. The bearing component is made of steel that has been nitriding, quenching, and tempering. The steel contains 0.90 to 1.20 mass percent carbon, 0.35 to 0.80 mass percent silicon, 0.80 to 1.20 mass percent manganese, less than 0.30 mass percent nickel, 0.80 to 1.30 mass percent chromium, less than 0.10 mass percent molybdenum, and the balance being iron and inevitable impurities. The value obtained by dividing the silicon concentration in the steel by the manganese concentration in the steel is less than 0.51. Nitrogen is introduced into the steel so that the nitrogen concentration decreases with increasing distance from the contact surface. The average nitrogen concentration in the steel between the contact surface and a first position that is 10 μm away from the contact surface in the depth direction is 0.16 mass percent or less. The second position, which is farther from the raceway surface in the depth direction than the first position, is a position where the nitrogen concentration in the steel is 0.01 mass percent or less and where the distance from the first position in the depth direction is the smallest. The nitrogen concentration gradient between the first position and the second position is 0.12 mass percent/mm or more and 1.1 mass percent/mm or less.

In the above ball bearing, the thickness of the bearing component may be 30 mm or less. In the above ball bearing, the amount of retained austenite in the steel may be 23 volume percent or more and 40 volume percent or less.

The ball bearing of the present invention can improve the workability of bearing components.

FIG. 2 is a cross-sectional view of a ball bearing 100. 3A to 3C are process diagrams showing a manufacturing method of the ball bearing 100.

Details of the embodiment will be described with reference to the drawings. In the following drawings, the same or corresponding parts will be given the same reference symbols, and duplicate explanations will not be repeated. The ball bearing according to the embodiment will be referred to as ball bearing 100.

(Configuration of ball bearing 100)
The configuration of the ball bearing 100 will be described below.

Figure 1 is a cross-sectional view of a ball bearing 100. As shown in Figure 1, the ball bearing 100 is a deep groove ball bearing. However, the ball bearing 100 is not limited to a deep groove ball bearing, and may be another type of ball bearing. The ball bearing 100 is a ball bearing used, for example, in automobile drive units (differentials, transmissions, reducers for EVs (Electric Vehicles), reducers for HEVs (Hybrid Electric Vehicles), etc.) and industrial machinery devices (reducers for robots, construction machinery, tractors, etc.).

The ball bearing 100 has an inner ring 10, an outer ring 20, a number of balls 30, and a cage 40. The central axis of the inner ring 10 is defined as the central axis A. The direction of the central axis A is defined as the axial direction. The direction passing through the central axis A and perpendicular to the central axis A is defined as the radial direction. The direction along the circumference centered on the central axis A when viewed along the axial direction is defined as the circumferential direction.

The inner ring 10 is a ring-shaped member. The inner ring 10 has a first width surface 10a, a second width surface 10b, an inner diameter surface 10c, and an outer diameter surface 10d. The first width surface 10a and the second width surface 10b are end surfaces of the inner ring 10 in the axial direction. The first width surface 10a faces one side in the axial direction (the left side in FIG. 1), and the second width surface 10b faces the other side in the axial direction (the right side in FIG. 1). In other words, the second width surface 10b is the opposite surface in the axial direction to the first width surface 10a.

The inner diameter surface 10c extends in the circumferential direction. The inner diameter surface 10c faces the central axis A. That is, the inner diameter surface 10c faces inward in the radial direction. One end of the inner diameter surface 10c in the axial direction and the other end of the inner diameter surface 10c in the axial direction are connected to the first width surface 10a and the second width surface 10b, respectively. Although not shown, the inner ring 10 is fitted to the shaft at the inner diameter surface 10c.

The outer diameter surface 10d extends in the circumferential direction. The outer diameter surface 10d faces the opposite side to the central axis A. In other words, the outer diameter surface 10d faces outward in the radial direction and is the opposite side to the inner diameter surface 10c in the radial direction. One end and the other end in the axial direction of the outer diameter surface 10d are connected to the first width surface 10a and the second width surface 10b, respectively.

The outer diameter surface 10d has a raceway surface 10da. The raceway surface 10da is the portion of the outer diameter surface 10d that contacts the balls 30. In other words, the raceway surface 10da is the contact surface of the inner ring 10. The outer diameter surface 10d is recessed toward the inner diameter surface 10c at the raceway surface 10da. The raceway surface 10da is, for example, partially arc-shaped in a cross section perpendicular to the circumferential direction. The raceway surface 10da is located in the center of the outer diameter surface 10d in the axial direction.

The outer ring 20 is a ring-shaped member. The outer ring 20 has a first width surface 20a, a second width surface 20b, an inner diameter surface 20c, and an outer diameter surface 20d. The first width surface 20a and the second width surface 20b are end surfaces of the outer ring 20 in the axial direction. The first width surface 20a faces one side in the axial direction. The second width surface 20b faces the other side in the axial direction. In other words, the second width surface 20b is the opposite surface in the axial direction to the first width surface 20a.

The inner diameter surface 20c extends in the circumferential direction. The inner diameter surface 20c faces the central axis A. That is, the inner diameter surface 20c faces inward in the radial direction. One end and the other end in the axial direction of the inner diameter surface 20c are connected to the first width surface 20a and the second width surface 20b, respectively. The outer ring 20 is arranged such that the inner diameter surface 20c faces the outer diameter surface 10d with a gap therebetween in the radial direction.

The outer diameter surface 20d extends in the circumferential direction. The outer diameter surface 20d faces the opposite side to the central axis A. That is, the outer diameter surface 20d faces outward in the radial direction and is the opposite side to the inner diameter surface 20c in the radial direction. One end and the other end in the axial direction of the outer diameter surface 20d are connected to the first width surface 20a and the second width surface 20b, respectively. Although not shown, the outer ring 20 is fitted into the housing at the outer diameter surface 20d.

The inner diameter surface 20c has a raceway surface 20ca. The raceway surface 20ca is the portion of the inner diameter surface 20c that contacts the balls 30. In other words, the raceway surface 20ca is the contact surface of the outer ring 20. The inner diameter surface 20c is recessed toward the outer diameter surface 20d at the raceway surface 20ca. In a cross-sectional view perpendicular to the circumferential direction, the raceway surface 20ca is, for example, partially arc-shaped. The raceway surface 20ca is located at the center of the inner diameter surface 20c in the axial direction. The raceway surface 20ca faces the raceway surface 10da with a gap therebetween in the radial direction.

The balls 30 are spherical. The balls 30 are disposed between the outer diameter surface 10d and the inner diameter surface 20c. More specifically, the balls 30 are disposed between the raceway surface 10da and the raceway surface 20ca. The multiple balls 30 are arranged in the circumferential direction. The balls 30 have a surface 30a. The surface 30a is in contact with the raceway surface 10da and the raceway surface 20ca. In other words, the surface 30a is the contact surface of the balls 30.

The retainer 40 is disposed between the outer diameter surface 10d and the inner diameter surface 20c. The retainer 40 holds a number of balls 30 so that the circumferential distance between two adjacent balls 30 is within a certain range.

The thickness of the inner ring 10, the thickness of the outer ring 20, and the thickness of the balls 30 may be 15 mm or more. The thickness of the inner ring 10, the thickness of the outer ring 20, and the thickness of the balls 30 may be 20 mm or more. The thickness of the inner ring 10, the thickness of the outer ring 20, and the thickness of the balls 30 are, for example, 30 mm or less. The thickness of the inner ring 10 is the difference between the outer diameter and the inner diameter of the inner ring 10 divided by 2. The thickness of the outer ring 20 is the difference between the outer diameter and the inner diameter of the outer ring 20 divided by 2. The thickness of the balls 30 is the diameter of the balls 30. In the ball bearing 100, the pitch circle diameter is, for example, 15 mm or more. The pitch circle diameter is twice the distance between the central axis A and the center of the balls 30 in the radial direction.

The inner ring 10, the outer ring 20, and the balls 30 are made of steel that has been nitriding, quenching, and tempering. The steel has the composition shown in Table 1. More specifically, the steel contains 0.90 to 1.20 mass percent carbon, 0.35 to 0.80 mass percent silicon, 0.80 to 1.20 mass percent manganese, less than 0.30 mass percent nickel, 0.80 to 1.30 mass percent chromium, and less than 0.10 mass percent molybdenum. The balance of the steel is iron and unavoidable impurities. The steel does not have to contain nickel and molybdenum.

In steel, the value obtained by dividing the silicon concentration by the manganese concentration is less than 0.51. When the silicon concentration in steel is low, the formation of iron oxides is suppressed, and hydrogen embrittlement resistance is improved. When the manganese concentration in steel is high, hardenability is improved. Furthermore, when the manganese concentration in steel is high, manganese bonds with sulfur to form manganese sulfide, thereby fixing the sulfur, thereby suppressing grain boundary segregation of sulfur and suppressing a decrease in the strength of the steel. Furthermore, when the manganese concentration in steel is high, the ductile-brittle fiber temperature of the steel is lowered, improving the toughness of the steel. From this perspective, the value obtained by dividing the silicon concentration by the manganese concentration is set to less than 0.51.

The inner ring 10, outer ring 20 and ball 30 have been nitriding-treated, so that nitrogen is introduced into the steel that makes up the inner ring 10, outer ring 20 and ball 30 so that the nitrogen concentration decreases with increasing distance from the contact surface.

The first position is the position at a depth direction distance of 10 μm from the contact surface of the inner ring 10, the outer ring 20, and the balls 30. The average nitrogen concentration in the steel from the contact surface to the first position is 0.16 mass percent or less. The depth direction is the direction perpendicular to the contact surface. The second position is the position at which the nitrogen concentration in the steel is 0.01 mass percent or less and at the smallest distance from the first position in the depth direction. The second position is farther from the contact surface in the depth direction than the first position.

The nitrogen concentration gradient between the first and second positions is 0.12 mass percent/mm or more and 1.1 mass percent/mm or less. The nitrogen concentration gradient between the first and second positions is calculated by subtracting the nitrogen concentration in the steel at the second position from the nitrogen concentration in the steel at the first position, and dividing the result by the distance between the first and second positions in the depth direction. The nitrogen concentration in the steel is measured using an EPMA (Electron Probe Micro Analyzer).

The amount of retained austenite in the steel constituting the inner ring 10, the outer ring 20, and the ball 30 is preferably 23 volume percent or more and 40 volume percent or less. The amount of retained austenite in the steel is measured by X-ray diffraction. That is, the amount of retained austenite in the steel is determined by dividing the peak intensity of austenite in the X-ray profile by the sum of the peak intensities other than austenite in the steel.

Lubricating oil may be supplied to the bearing space (the space between the outer diameter surface 10d and the inner diameter surface 20c). It is preferable that the amount of foreign matter in the lubricating oil is 0.35 g/L or less.

<Modification>
In the above, we have described the case where the inner ring 10, outer ring 20, and balls 30 are made of steel having the composition shown in Table 1, but it is sufficient that at least one of the bearing parts among the inner ring 10, outer ring 20, and balls 30 is formed of steel having a composition shown in Table 1 and in which the value obtained by dividing the silicon concentration by the manganese concentration is less than 0.51, and the other bearing parts among the inner ring 10, outer ring 20, and balls 30 may be formed of steel with a composition other than that shown in Table 1.

In bearing components made of steels with compositions other than those shown in Table 1, the average nitrogen concentration between the contact surface and the first position does not have to be 0.16 mass percent or less, and the nitrogen concentration gradient between the first position and the second position does not have to be 0.12 mass percent/mm or more and 1.1 mass percent/mm or less. In bearing components made of steels with compositions other than those shown in Table 1, the amount of retained austenite in the steel does not have to be 23 volume percent or more and 40 volume percent or less.

(Method of manufacturing ball bearing 100)
A method for manufacturing the ball bearing 100 will now be described.

Figure 2 is a process diagram showing the manufacturing method of ball bearing 100. As shown in Figure 2, the manufacturing method of ball bearing 100 includes a preparation process S1, a nitriding process S2, a quenching process S3, a tempering process S4, a post-treatment process S5, and an assembly process S6.

In the preparation step S1, the workpiece to be processed is prepared. The workpiece for the inner ring 10 and the outer ring 20 is a ring-shaped member. The workpiece for the ball 30 is a spherical member. The workpiece is made of steel having the composition shown in Table 1, and in which the silicon concentration divided by the manganese concentration is less than 0.51.

The nitriding step S2 is performed after the preparation step S1. In the nitriding step S2, the surface of the workpiece is nitrided. In the nitriding step S2, the workpiece is maintained at a temperature equal to or higher than the _A1 transformation point in an atmosphere containing a nitrogen source (e.g., ammonia gas). This allows nitrogen to be introduced from the surface of the workpiece, and the introduced nitrogen diffuses into the workpiece. In order to control the nitrogen concentration gradient, it is preferable to install a device for circulating the atmospheric gas in the furnace, thereby controlling the ratio of ammonia gas in the atmospheric gas and uniformly filling the furnace with ammonia gas.

The quenching step S3 is performed after the nitriding step S2. The quenching step S3 has a heating and holding step and a cooling step. The heating and holding step is performed by holding the workpiece at a temperature equal to or higher than the _A1 transformation point. The cooling step is performed after the heating and holding step. The cooling step is performed by cooling the workpiece to a temperature equal to or lower than the M _S transformation point. The tempering step S4 is performed after the quenching step S3. The tempering step S4 is performed by holding the workpiece at a temperature lower than the _A1 transformation point and then allowing it to cool.

The post-processing step S5 is carried out after the tempering step S4. In the post-processing step S5, the workpiece is ground and polished. As a result, the workpiece becomes the inner ring 10, the outer ring 20, and the balls 30. The assembly step S6 is carried out after the post-processing step S5. In the assembly step S6, the inner ring 10, the outer ring 20, and the balls 30 are assembled together with the cage 40. As a result, the ball bearing 100 having the structure shown in FIG. 1 is formed.

(Effects of Ball Bearing 100)
The effects of the ball bearing 100 will be described below.

When trying to suppress indentation-induced peeling caused by foreign matter getting caught by increasing the amount of retained austenite in the steel by increasing the nitrogen concentration near the contact surface, the resistance during grinding increases due to the increase in the amount of highly tenacious retained austenite and the increase in precipitates. As a result, the processing costs in the post-processing step S5 increase.

The average nitrogen concentration between the contact surface and the first position in the inner ring 10, outer ring 20, and balls 30 of the ball bearing 100 is 0.16 mass percent or less, so the nitrogen concentration on the surface of the workpiece is also low, and the amount of retained austenite and precipitates on the surface of the workpiece is also low. Therefore, the ball bearing 100 can improve the workability when forming the inner ring 10, outer ring 20, and balls 30.

In addition, the inner ring 10, outer ring 20, and balls 30 of the ball bearing 100 have a small nitrogen concentration gradient between the first position and the second position, so the depth of the area into which nitrogen is introduced is ensured. Therefore, although the average nitrogen concentration between the contact surface and the first position is low in the ball bearing 100, durability at the contact surface (e.g., durability against indentation-type peeling caused by foreign matter getting caught) can be ensured in a lubricating environment where, for example, the amount of foreign matter in the lubricating oil is 0.35 g/L or less.

In addition, the average nitrogen concentration between the contact surface and the first position of the inner ring 10, outer ring 20, and balls 30 of the ball bearing 100 is 0.16 mass percent or less, which shortens the time required for the nitriding process S2 and therefore reduces the cost required for heat treatment.

For example, EV reducers often have a structure with three parallel axes, so while there is a limit to the dimensions of the ball bearing 100 in the axial direction, it is necessary to increase the dimensions of the ball bearing 100 in the radial direction (the thickness of the inner ring 10, outer ring 20, and balls 30) to increase the load capacity of the ball bearing 100. In the ball bearing 100, the inner ring 10, outer ring 20, and balls 30 are shown in Table 1, and are formed from steel with a composition in which the silicon concentration divided by the manganese concentration is less than 0.51, so the hardenability of the steel is high, and incomplete hardening can be prevented even if the thicknesses of the inner ring 10, outer ring 20, and balls 30 are large.

The balls 30 may be made of a steel other than that shown in Table 1, for example SUJ2, a high carbon chromium bearing steel specified in the JIS standard. The balls 30 may be subjected to normal quenching and tempering in an atmosphere not containing a nitrogen source, rather than the quenching and tempering described above. The thickness of the balls 30 may be of normal size, or only the thicknesses of the inner ring 10 and the outer ring 20 may be increased. The balls 30 may be made of a ceramic material.

Although the embodiment of the present invention has been described above, the above embodiment can be modified in various ways. Furthermore, the scope of the present invention is not limited to the above embodiment. The scope of the present invention is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

A central shaft, 100 ball bearing, 10 inner ring, 10a first width surface, 10b second width surface, 10c inner diameter surface, 10d outer diameter surface, 10da raceway surface, 20 outer ring, 20a first width surface, 20b second width surface, 20c inner diameter surface, 20ca raceway surface, 20d outer diameter surface, 30 ball, 30a surface, 40 retainer, S1 preparation process, S2 nitriding process, S3 quenching process, S4 tempering process, S5 post-treatment process, S6 assembly process.

Claims (3)

With the inner circle,
The outer ring and
Equipped with a ball,
At least one of the bearing components of the inner ring, the outer ring, and the balls has a contact surface;
the contact surface being a raceway surface of the inner ring when the bearing component is the inner ring, a raceway surface of the outer ring when the bearing component is the outer ring, or a surface of the ball when the bearing component is the ball;
the bearing component is made of steel that has been nitrided, hardened and tempered;
The steel comprises, by weight, 0.90 to 1.20 percent carbon, 0.35 to 0.80 percent silicon, 0.80 to 1.20 percent manganese, less than 0.30 percent nickel, 0.80 to 1.30 percent chromium, less than 0.10 percent molybdenum, and the balance being iron and unavoidable impurities;
The value obtained by dividing the silicon concentration in the steel by the manganese concentration in the steel is less than 0.51,
Nitrogen is introduced into the steel such that the nitrogen concentration decreases with increasing distance from the contact surface;
an average nitrogen concentration in the steel between the contact surface and a first position that is 10 μm away from the contact surface in a depth direction is 0.16 mass percent or less;
a second position that is farther from the raceway surface than the first position in the depth direction is a position where a nitrogen concentration in the steel is 0.01 mass percent or less and where a distance from the first position in the depth direction is a minimum,
A ball bearing, wherein a nitrogen concentration gradient between the first position and the second position is equal to or greater than 0.12 mass percent/mm and equal to or less than 1.1 mass percent/mm. The thickness of the bearing component is 30 mm or less,
2. The ball bearing of claim 1, wherein the thickness of the bearing part is the difference between the outer diameter and the inner diameter of the inner ring divided by 2 when the bearing part is the inner ring, the difference between the outer diameter and the inner diameter of the outer ring divided by 2 when the bearing part is an outer ring, and the diameter of the ball when the bearing part is the ball. The ball bearing according to claim 1 or 2, wherein the amount of retained austenite in the steel in the bearing component is 23 volume percent or more and 40 volume percent or less.

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