CN117450169A

CN117450169A - Ball bearing

Info

Publication number: CN117450169A
Application number: CN202310897177.5A
Authority: CN
Inventors: 川井崇; 大木力
Original assignee: NTN Corp
Current assignee: NTN Corp
Priority date: 2022-07-26
Filing date: 2023-07-20
Publication date: 2024-01-26
Also published as: JP2024016667A; WO2024024605A1; JP7490024B2

Abstract

The ball bearing of the present invention includes an inner ring, an outer ring, and balls. At least 1 bearing component of the inner race, the outer race and the balls has a contact surface. The bearing component is made of steel that has been nitrided, quenched and tempered. The steel contains 0.90 mass% to 1.20 mass% of carbon, 0.35 mass% to 0.80 mass% of silicon, 0.80 mass% to 1.20 mass% of manganese, less than 0.30 mass% of nickel, 0.80 mass% to 1.30 mass% of chromium, less than 0.10 mass% of molybdenum, and iron and unavoidable impurities constituting the remainder. The silicon concentration in the steel divided by the manganese concentration in the steel has a value of less than 0.51.

Description

Ball bearing

Technical Field

The present invention relates to ball bearings.

Background

For example, japanese patent application laid-open No. 2001-3139 describes a rolling bearing (tapered roller bearing). The rolling bearing described in japanese patent laying-open No. 2001-3139 has an inner ring, an outer ring, and a plurality of rolling elements (tapered rollers). The inner ring has an inner ring raceway surface in contact with the rolling elements as a contact surface. The outer ring has an outer ring raceway surface in contact with the rolling elements as a contact surface. The rolling elements have an outer peripheral surface in contact with the inner ring raceway surface and the outer ring raceway surface as contact surfaces. In the rolling bearing described in japanese patent laying-open No. 2001-3139, nitriding is performed on contact surfaces of an inner ring, an outer ring, and rolling elements. In the rolling bearing described in japanese patent application laid-open No. 2001-3139, the amount of retained austenite in steel in the surface layer portion in the vicinity of the contact surface between the inner ring, the outer ring, and the rolling element is 20% by volume or more and 40% by volume or less.

Disclosure of Invention

The bearing member (inner ring, outer ring, and rolling element) of the rolling bearing described in japanese patent application laid-open No. 2001-3139 is formed by mechanically processing a member to be processed made of steel subjected to nitriding treatment, quenching, and tempering, such as grinding and polishing. However, in the rolling bearing described in japanese patent application laid-open No. 2001-3139, there is no attention to the nitrogen concentration and the nitrogen concentration gradient in the steel in the surface layer portion in the vicinity of the contact surfaces of the inner ring, the outer ring, and the rolling elements. As a result, the rolling bearing described in japanese patent laying-open No. 2001-3139 has room for improvement in terms of workability of the bearing member.

The present invention has been made in view of the above-described problems of the prior art. More specifically, the present invention provides a ball bearing capable of improving workability of a bearing member.

The ball bearing of the present invention includes an inner ring, an outer ring, and balls. At least 1 bearing component of the inner race, the outer race and the balls has a contact surface. The bearing component is made of steel that has been nitrided, quenched and tempered. The steel contains 0.90 mass% to 1.20 mass% of carbon, 0.35 mass% to 0.80 mass% of silicon, 0.80 mass% to 1.20 mass% of manganese, less than 0.30 mass% of nickel, 0.80 mass% to 1.30 mass% of chromium, less than 0.10 mass% of molybdenum, and iron and unavoidable impurities constituting the remainder. The silicon concentration in the steel divided by the manganese concentration in the steel has a value of less than 0.51. Nitrogen is introduced into the steel in such a way that the nitrogen concentration becomes smaller as it gets farther from the contact surface. The average nitrogen concentration in the steel between the contact surface and the first position at a distance of 10 μm from the contact surface in the depth direction is 0.16 mass% or less. The second position farther from the raceway surface than the first position in the depth direction is a position where the nitrogen concentration in the steel is 0.01 mass% or less and 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%/mm or more and 1.1 mass%/mm or less.

In the ball bearing, the wall thickness of the bearing member may be 30mm or less. In the ball bearing, the amount of retained austenite in the steel may be 23% by volume or more and 40% by volume or less.

The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention which is to be read in connection with the accompanying drawings.

Drawings

Fig. 1 is a cross-sectional view of a ball bearing 100.

Fig. 2 is a process diagram showing a method of manufacturing the ball bearing 100.

Detailed Description

The embodiments will be described in detail with reference to the accompanying drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated. The ball bearing of the embodiment is referred to as a ball bearing 100.

(constitution of ball bearing 100)

The following describes the structure of the ball bearing 100.

Fig. 1 is a cross-sectional view of a ball bearing 100. As shown in fig. 1, the ball bearing 100 is a deep groove ball bearing. However, the ball bearing 100 is not limited to the deep groove ball bearing, and may be another ball bearing. The ball bearing 100 is used for, for example, an automobile drive unit (differential, transmission, EV (electric vehicle) speed reducer, HEV (hybrid electric vehicle) speed reducer, etc.), and an industrial machine device (robot speed reducer, construction machine, tractor, etc.).

The ball bearing 100 has an inner race 10, an outer race 20, a plurality of balls 30, and a cage 40. The center axis of the inner race 10 is set as the center axis a. The direction of the central axis A is taken as the axial direction. The radial direction is a direction passing through the central axis A and orthogonal to the central axis A. The circumferential direction is a direction along a circumference centered on the central axis a when viewed in the axial direction.

The inner ring 10 is an annular 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 (left side in fig. 1), and the second width surface 10b faces the other side in the axial direction (right side in fig. 1). That is, the second width surface 10b is an opposite surface of the first width surface 10a in the axial direction.

The inner diameter surface 10c extends in the circumferential direction. The inner diameter surface 10c faces the center axis a. That is, the inner diameter surface 10c is directed radially inward. One end of the inner diameter surface 10c in the axial direction and the other end thereof in the axial direction are connected to the first width surface 10a and the second width surface 10b, respectively. Although not shown, the inner race 10 is fitted to the shaft at an inner diameter surface 10 c.

The outer diameter surface 10d extends in the circumferential direction. The outer diameter surface 10d faces the opposite side of the central axis a. That is, the outer diameter surface 10d is directed radially outward and is the opposite surface of the inner diameter surface 10c in the radial direction. One end of the outer diameter surface 10d in the axial direction and the other end thereof in the axial direction 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 a portion of the outer diameter surface 10d that contacts the ball 30. That is, the raceway surface 10da is a contact surface of the inner ring 10. The outer diameter surface 10d is recessed toward the inner diameter surface 10c side at the raceway surface 10da. The track surface 10da is, for example, partially circular-arc-shaped in a cross-sectional view perpendicular to the circumferential direction. The raceway surface 10da is located at a central portion of the outer diameter surface 10d in the axial direction.

The outer ring 20 is an annular member. The outer race 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. That is, the second width surface 20b is an opposite surface of the first width surface 20a in the axial direction.

The inner diameter surface 20c extends in the circumferential direction. The inner diameter surface 20c faces the center axis a side. That is, the inner diameter surface 20c is directed radially inward. One end of the inner diameter surface 20c in the axial direction and the other end thereof in the axial direction are connected to the first width surface 20a and the second width surface 20b, respectively. The outer ring 20 is disposed such that the inner diameter surface 20c and the outer diameter surface 10d face each other 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 of the central axis a. That is, the outer diameter surface 20d is directed radially outward and is the opposite surface of the inner diameter surface 20c in the radial direction. One end of the outer diameter surface 20d in the axial direction and the other end thereof in the axial direction are connected to the first width surface 20a and the second width surface 20b, respectively. Although not shown, the outer ring 20 is fitted to the housing at an outer diameter surface 20d.

The inner diameter surface 20c has a raceway surface 20ca. The raceway surface 20ca is a portion of the inner diameter surface 20c that contacts the ball 30. That is, the raceway surface 20ca is a 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. The track surface 20ca is, for example, partially circular-arc-shaped in a cross-sectional view perpendicular to the circumferential direction. The raceway surface 20ca is located at a central portion of the inner peripheral 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 20 c. More specifically, the balls 30 are disposed between the raceway surface 10da and the raceway surface 20ca. The plurality of balls 30 are arranged in the circumferential direction. The ball 30 has a surface 30a. The surface 30a is in contact with the raceway surface 10da and the raceway surface 20ca. That is, the surface 30a is the contact surface of the ball 30.

The retainer 40 is disposed between the outer diameter surface 10d and the inner diameter surface 20 c. The retainer 40 retains the plurality of balls 30 such that the circumferential spacing between the adjacent two balls 30 is within a certain range.

The wall thickness of the inner race 10, the wall thickness of the outer race 20, and the wall thickness of the balls 30 may be 15mm or more. The wall thickness of the inner race 10, the wall thickness of the outer race 20, and the wall thickness of the balls 30 may be 20mm or more. The wall thickness of the inner ring 10, the wall thickness of the outer ring 20, and the wall thickness of the balls 30 are, for example, 30mm or less. The wall thickness of the inner ring 10 is a value obtained by dividing the difference between the outer diameter and the inner diameter of the inner ring 10 by 2. The wall thickness of the outer ring 20 is a value obtained by dividing the difference between the outer diameter and the inner diameter of the outer ring 20 by 2. The wall thickness of the ball 30 is the diameter of the ball 30. The pitch diameter of the ball bearing 100 is, for example, 15mm or more. The pitch diameter is 2 times the distance between the central axis a in the radial direction and the center of the ball 30.

The inner ring 10, the outer ring 20 and the balls 30 are made of steel which is nitrided, quenched and tempered. The steel had a composition shown in table 1. More specifically, the steel contains 0.90 mass% or more and 1.20 mass% or less of carbon, 0.35 mass% or more and 0.80 mass% or less of silicon, 0.80 mass% or more and 1.20 mass% or less of manganese, less than 0.30 mass% of nickel, 0.80 mass% or more and 1.30 mass% or less of chromium, and less than 0.10 mass% of molybdenum. The remainder of the steel is iron and unavoidable impurities. In addition, the steel may be free of nickel and molybdenum.

TABLE 1

In the steel, the value obtained by dividing the silicon concentration by the manganese concentration is less than 0.51. If the silicon concentration in the steel is low, the formation of iron oxides can be suppressed, improving hydrogen embrittlement resistance. If the manganese concentration in the steel is high, hardenability can be improved. In addition, if the manganese concentration in the steel is high, manganese combines with sulfur to form manganese sulfide, thereby fixing sulfur, and therefore grain boundary segregation of sulfur can be suppressed, and a decrease in strength of the steel can be suppressed. In addition, if the manganese concentration in the steel is high, the ductility-brittle fiber temperature of the steel is lowered and the toughness of the steel is improved. From this point of view, the value obtained by dividing the silicon concentration by the manganese concentration is set to be less than 0.51.

Since the inner ring 10, the outer ring 20, and the balls 30 are nitrided, nitrogen is introduced into the steel constituting the inner ring 10, the outer ring 20, and the balls 30 in such a manner that the nitrogen concentration becomes lower as it goes away from the contact surface.

The positions of the inner ring 10, the outer ring 20, and the balls 30 at a distance of 10 μm from the contact surface in the depth direction were set as first positions. The average nitrogen concentration in the steel from the contact surface to the first position is 0.16 mass% or less. The depth direction refers to a direction orthogonal to the contact surface. The second position is a position where the nitrogen concentration in the steel is 0.01 mass% or less and the distance from the first position in the depth direction is the smallest. The second position is further away from the contact surface in the depth direction than the first position.

The nitrogen concentration gradient between the first position and the second position is 0.12 mass%/mm or more and 1.1 mass%/mm or less. The nitrogen concentration gradient between the first position and the second position is calculated by dividing a value obtained by subtracting the nitrogen concentration in the steel at the second position from the nitrogen concentration in the steel at the first position by the distance between the first position and the second position in the depth direction. The nitrogen concentration in the steel was measured by EPMA (Electron Probe Micro Analyzer: electron probe microanalyzer).

The amount of retained austenite in the steel constituting the inner ring 10, the outer ring 20, and the balls 30 is preferably 23% by volume or more and 40% by volume or less. The amount of retained austenite in the steel was measured by an X-ray diffraction method. That is, the residual austenite amount in the steel is obtained by dividing the peak intensity of austenite in the X-ray curve by the sum of the peak intensities of austenite other than austenite in the steel.

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

< modification >

In the above, the case where the inner ring 10, the outer ring 20, and the balls 30 are made of steel having the composition shown in table 1 is described, but as long as at least one bearing member of the inner ring 10, the outer ring 20, and the balls 30 is formed of steel having the composition shown in table 1 and a value obtained by dividing the silicon concentration by the manganese concentration is less than 0.51, the other bearing members of the inner ring 10, the outer ring 20, and the balls 30 may be formed of steel other than the composition shown in table 1.

In the bearing member formed of steel other than the composition shown in table 1, the average nitrogen concentration between the contact surface and the first position may not be 0.16 mass% or less, and the nitrogen concentration gradient between the first position and the second position may not be 0.12 mass% or more/mm or 1.1 mass% or less. In the bearing member formed of steel other than the composition shown in table 1, the amount of retained austenite in the steel may not be 23% by volume or more and 40% by volume or less.

(method for manufacturing bearing 100)

A method of manufacturing the ball bearing 100 will be described below.

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

In the preparation step S1, the member to be processed is prepared. The processing target members for the inner race 10 and the outer race 20 are annular members. The processing target member for the ball 30 is a spherical member. The member to be processed was formed of steel having a composition shown in table 1 and having a value obtained by dividing the silicon concentration by the manganese concentration of less than 0.51.

The nitriding step S2 is performed after the preparation step S1. The surface of the processing object member is nitrided in the nitriding process S2. In the nitriding step S2, the member to be processed is held at a by holding it in an atmosphere containing a nitrogen source (for example, ammonia gas) ₁ The temperature above the phase transition point. Thereby, nitrogen is introduced from the surface of the processing object member, and the introduced nitrogen diffuses into the inside of the processing object member. In order to control the nitrogen concentration gradient, it is preferable to control the proportion of ammonia in the atmosphere gas and to uniformly fill the furnace with ammonia throughout by providing a device for circulating the atmosphere gas in the furnace.

The quenching step S3 is performed after the nitriding step S2. The quenching step S3 includes a heating and holding step and a cooling step.The heating and holding step holds the processing object member at A ₁ The temperature above the phase transition point. The cooling step is performed after the heating and holding step. The cooling step cools the object to be processed to M _S The temperature below the transformation point. The tempering step S4 is performed after the quenching step S3. Tempering step S4 is performed by setting the object member to be processed to be smaller than A ₁ The temperature of the phase transition point is kept and then cooled.

The post-treatment step S5 is performed after the tempering step S4. In the post-treatment step S5, the member to be processed is ground and polished. Thereby, the object member becomes the inner ring 10, the outer ring 20, and the balls 30. The assembly step S6 is performed after the post-treatment step S5. In the assembling step S6, the inner ring 10, the outer ring 20, and the balls 30 are assembled with the cage 40. Through the above-described steps, the ball bearing 100 having the structure shown in fig. 1 is formed.

(effects of ball bearing 100)

Effects of the ball bearing 100 are described below.

When it is intended to suppress peeling at the start of indentation due to foreign matter being trapped by increasing the nitrogen concentration in the vicinity of the contact surface and increasing the amount of retained austenite in the steel, the resistance at the time of grinding increases due to an increase in the amount of retained austenite having a relatively high viscosity and an increase in the amount of precipitates. As a result, the processing cost in the post-processing step S5 increases.

Since the average nitrogen concentration between the contact surface and the first position of the inner ring 10, the outer ring 20, and the balls 30 of the ball bearing 100 is 0.16 mass% or less, the nitrogen concentration at the surface of the processing target member is also low, and the amount of retained austenite and the amount of precipitates at the surface of the processing target member are also small. Therefore, by adopting the ball bearing 100, the workability in forming the inner race 10, the outer race 20, and the balls 30 can be improved.

Further, since the gradient of the nitrogen concentration from the first position to the second position is small in the inner race 10, the outer race 20, and the balls 30 of the ball bearing 100, the depth of the region where nitrogen is introduced can be ensured. Therefore, although the average nitrogen concentration from the contact surface to the first position of the ball bearing 100 is low, the durability (for example, the durability against the peeling from the indentation start point caused by the foreign matter being interposed) at the contact surface can be ensured in a lubrication environment where the foreign matter amount in the lubricating oil is, for example, 0.35g/L or less.

In addition, since the average nitrogen concentration between the contact surface and the first position of the inner ring 10, the outer ring 20, and the balls 30 of the ball bearing 100 is 0.16 mass% or less, the time required for the nitriding step S2 can be shortened, and therefore, the cost required for the heat treatment can be reduced.

For example, in a decelerator for an EV, since a parallel triaxial structure is generally formed, it is required to limit the size of the ball bearing 100 in the axial direction, and on the other hand, it is required to increase the size of the ball bearing 100 in the radial direction (the wall thicknesses of the inner ring 10, the outer ring 20, and the balls 30) to increase the load capacity of the ball bearing 100. Since the ball bearing 100 is formed of steel having a composition shown in table 1 and having a silicon concentration divided by a manganese concentration, in which the inner ring 10, the outer ring 20 and the balls 30 are less than 0.51, the steel is high in hardenability and can be free from incomplete quenching even if the wall thicknesses of the inner ring 10, the outer ring 20 and the balls 30 are large.

The balls 30 may be made of steel other than the composition shown in table 1, for example, high carbon chromium bearing steel SUJ2 specified in JIS standard. As for the ball 30, it is possible to perform not quenching and tempering as described above but ordinary quenching and tempering in an atmosphere containing no nitrogen source. The wall thickness of the balls 30 may be a normal size, or may be increased only by the inner ring 10 and the outer ring 20. The balls 30 may be made of a ceramic material.

The embodiments of the present invention have been described, but the embodiments of the present disclosure should be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the claims, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims

1. A ball bearing comprising an inner ring, an outer ring and balls,

at least 1 bearing component of the inner race, the outer race and the balls has a contact surface,

the bearing component is made of steel which has been nitrided, quenched and tempered,

the steel contains 0.90 to 1.20 mass% of carbon, 0.35 to 0.80 mass% of silicon, 0.80 to 1.20 mass% of manganese, less than 0.30 mass% of nickel, 0.80 to 1.30 mass% of chromium, less than 0.10 mass% of molybdenum, iron and unavoidable impurities constituting the remainder,

the value of the silicon concentration in the steel divided by the manganese concentration in the steel is less than 0.51,

nitrogen is introduced into the steel in such a way that the nitrogen concentration becomes smaller as it goes away from the contact surface,

the average nitrogen concentration in the steel between the contact surface and a first position at a distance of 10 μm from the contact surface in the depth direction is 0.16 mass% or less,

a second position 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% or less and a distance from the first position in the depth direction is smallest,

the nitrogen concentration gradient between the first location and the second location is above 0.12 mass%/mm and below 1.1 mass%/mm.

2. The ball bearing of claim 1, wherein the bearing component has a wall thickness of 30mm or less.

3. The ball bearing according to claim 1 or 2, wherein in the bearing member, the amount of retained austenite in the steel is 23% by volume or more and 40% by volume or less.