JP5070907B2 - Rolling bearing device for supporting wheel and method for manufacturing raceway ring thereof - Google Patents

Description

  The present invention relates to a wheel-supporting rolling bearing device that rotatably supports a wheel of an automobile with respect to a suspension device, and a method for manufacturing the bearing ring thereof.

  A wheel-supporting rolling bearing device that rotatably supports a wheel of an automobile with respect to a suspension device is generally formed on a hub wheel (rotating side raceway) that rotates integrally with the wheel and an outer peripheral surface of the hub wheel. The outer ring (outer ring raceway) having an outer ring raceway groove facing the inner ring raceway groove on the inner peripheral surface, and a large number of rolling elements provided between the raceway grooves of the raceway ring are provided. ing.

Conventionally, the bearing ring of such a wheel-supporting rolling bearing device is manufactured by hot forging a high carbon steel material such as S50-S55C equivalent material (medium carbon steel material) or SAE1070, and then turning and induction hardening. However, in recent years, in order to reduce the manufacturing cost, a technique is known in which a steel plate is used as a race ring material, and this is plastic processed to produce a race ring for a wheel bearing rolling bearing device (Patent Literature). 1-5).
JP 2003-25803 A Japanese Patent No. 3352226 JP-A-9-151950 JP 7-317777 A JP 2006-64036 A

  However, Patent Documents 1-4 only disclose a method of plastic working a steel plate as a race ring material into a predetermined shape. Regarding the hardness and metal structure of the race ring material before plastic working, Not mentioned. For this reason, if the state of the steel plate used as the bearing ring material is hard, there is a possibility that a crack will occur at the time of plastic working for a portion where the amount of plastic working becomes large.

Further, Patent Document 5 discloses that softening annealing is performed before plastic processing of a steel plate as a raceway material. After plastic processing of a steel plate subjected to soft annealing into a predetermined shape, high frequency is applied. When quenching is performed, the quenching time is as short as several seconds, so that an incompletely quenched structure may be generated on the surface layer of the raceway surface of the raceway, which may reduce the rolling life of the wheel bearing rolling bearing device. That is, when the raceway ring material is subjected to short-term quenching such as induction quenching for a few seconds, the metal structure before quenching is easily affected. When softening annealing is performed on the raceway ring material, it is considered that if the spheroidized carbide is large, it takes time to dissolve, and if the carbide interval is long, it is difficult for carbon to be uniformly dissolved in the matrix. Therefore, incompletely hardened structure occurs, there is a risk of reducing the rolling life and fatigue characteristics,
The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide a wheel support rolling bearing device that can increase the rolling life of the raceway. Another object of the present invention is to provide an incompletely quenched structure that causes flaking when the bearing ring material is cold worked to produce a bearing ring for a wheel support rolling bearing device. An object of the present invention is to provide a method for manufacturing a bearing ring for a wheel-supporting rolling bearing device capable of suppressing occurrence of a surface surface layer portion.

In order to achieve the above object, a rolling bearing device for supporting a wheel according to the first aspect of the present invention includes a rotating side race ring that rotates integrally with a wheel, and an inner ring formed on an outer peripheral surface of the rotary side race ring. A stationary side bearing ring having an outer ring raceway groove facing the raceway groove on an inner peripheral surface, and a number of rolling elements provided between the raceway grooves of the bearing ring, the rotating side bearing ring and the stationary side bearing ring A rolling bearing device for supporting a wheel, in which at least one of the race rings plastically processes a steel material into a predetermined shape and is subjected to induction hardening after plastic processing, the steel material having a carbon content of 0.1. It is a material equivalent to “JIS S45C to S75C” of 45 mass% or more and 0.75 mass% or less , and the aspect ratio of the major axis diameter to the minor axis diameter of all carbides existing in the metal structure of the steel material before plastic working is A sphere with a minor axis diameter of 0.7 μm or more with 2 or less The area ratio of the activated carbide is 70% or more, the average interval of the spheroidized carbide is 15 μm or less, the grain size number of the prior austenite crystal grains of the raceway grooves after induction hardening is 6 or more, and the surface hardness is HV650 or more. It is characterized by being.

  The invention according to claim 2 is a method for producing a bearing ring of the wheel-supporting rolling bearing device according to claim 1, wherein a steel material having a carbon content of 0.45 mass% to 0.75 mass% is raced. Used as a ring material, before plastic processing the race ring material into a predetermined shape, after heating for 0.1 hour or more at a temperature of 740 to 860 ° C., a temperature of 720 to 680 ° C. at a rate of 20 to 70 ° C./hr And then held at a temperature of 720-680 ° C. for about 1-5 hours, then cooled to a temperature of 620-680 ° C. at a rate of 10-100 ° C./hr, and further at a rate of 10-15 ° C./hr. The bearing ring material is subjected to softening annealing for cooling to a temperature of 500 to 560 ° C.

Here, the reason why the carbon content of the bearing ring material is 0.45 mass% or more and 0.75 mass% or less is that when the carbon content of the bearing ring material is less than 0.45 mass%, the surface hardness is HV650 or more. This is because the cold workability of the raceway material deteriorates when the carbon content of the raceway material exceeds 0.75 mass%.
The area ratio of spheroidized carbides having an aspect ratio of the major axis diameter to the minor axis diameter of 2 or less and a minor axis diameter of 0.7 μm or more among all the carbides existing in the metal structure of the softened and annealed raceway ring material. 70% or more and the average interval between the spheroidized carbides is 15 μm or less is as follows. In general, if the carbide spheroidization is insufficient and the carbide aspect ratio exceeds 2, stress concentration occurs around the carbide and the cold workability of the bearing ring material is reduced. The aspect ratio of the carbide was 2 or less. Moreover, when the area ratio of the spheroidized carbide having an aspect ratio of 2 or less and a minor axis diameter of 0.7 μm or less is less than 70%, the hardness and deformation resistance of the softened and annealed steel material increase, and the coldness of the raceway ring material becomes cold. Since the workability deteriorates, in the present invention, the area ratio of the spheroidized carbide having an aspect ratio of 2 or less and a minor axis diameter of 0.7 μm or more is set to 70% or more. Furthermore, if the average interval between the spheroidized carbides exceeds 15 μm, it is difficult to obtain a proper induction-quenched structure, and if the carbide interval is long, it is disadvantageous for carbon to diffuse uniformly into the matrix. The average interval between the activated carbides was set to 15 μm or less. If the area ratio of the spheroidized carbide having a minor axis diameter of 0.7 μm or more is not 70% or more, as shown in FIG. Therefore, the above numerical values were specified. The area ratio of spheroidized carbide having a minor axis diameter of 0.7 μm or more is desirably 80 to 90%.

The reason why the surface hardness of the raceway groove after induction hardening is set to HV650 or more is that if the surface hardness of the raceway groove is lower than HV650, it is difficult to ensure a sufficient rolling life.
Moreover, the reason why the grain size number of the prior austenite crystal grains of the softened and annealed raceway ring material is 6 or more is that when the grain size is less than 6, the rolling life is remarkably reduced.

According to the rolling bearing device for supporting a wheel according to the first aspect of the invention, it is possible to suppress the occurrence of incompletely hardened structure due to induction hardening in the surface layer portion of the raceway surface, thereby increasing the rolling life of the raceway ring. Can do.
According to the bearing ring manufacturing method of the wheel bearing rolling bearing device according to the second aspect of the present invention, when the softened and annealed bearing ring material is subjected to short time quenching such as induction hardening for a few seconds, Carbide solid solution does not become insufficient, and generation of an incompletely hardened structure that causes flaking on the raceway surface layer portion of the raceway ring can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a wheel support rolling bearing device according to an embodiment of the present invention. The wheel support rolling bearing device shown in FIG. 1, a stationary-side bearing ring 2 having an outer ring raceway groove 2 a opposed to an inner ring raceway groove 1 a formed on the outer peripheral surface of the rotation-side raceway ring 1, and raceway grooves 1 a of these raceway rings 1, 2. , 2a and a large number of spherical rolling elements 3 provided so as to be freely rollable.

  The rotating side race ring 1 and the stationary side race ring 2 are formed on the groove surfaces of the raceway grooves 1a and 2a after plastic processing a steel sheet having a carbon content of 0.45 mass% or more and 0.75 mass% or less into a predetermined shape. Although formed by induction hardening, in this embodiment, after plastically processing a steel plate as a raceway material into a predetermined shape, after heating at a temperature of 740 to 860 ° C. for 0.1 hour or more, 20 After cooling to a temperature of 720-680 ° C. at a rate of ˜70 ° C./hr, and then holding for about 1-5 hours at a temperature of 720-680 ° C., a temperature of 620-680 ° C. at a rate of 10-100 ° C./hr Then, it is further cooled to a temperature of 500 to 560 ° C. at a rate of 10 to 15 ° C./hr, and softened annealing is applied to the raceway ring material.

  The inventor has earnestly studied the problems in the case of forming the ring material of the rolling bearing device for supporting a wheel by cold working such as plastic working. A steel material having a carbon content of 0.45 mass% or more and 0.75 mass% or less is used as a bearing ring material, and softening annealing is performed under a predetermined heat treatment condition before plastic processing of the bearing ring material into a predetermined shape. The knowledge that the rolling life of the bearing ring can be increased by applying to the above was obtained from the test results of the rolling life test and the upsetting test described in detail below.

  Table 1 shows the test results of the rolling life test and the upsetting test performed by the present inventors.

  In Table 1, Examples 1-12 use JIS S45C-S75C (carbon content: 0.45 mass% or more and 0.75 mass% or less) as a bearing ring material of a rolling bearing device for wheel support, and a bearing ring material is used. For example, after cold forming into a predetermined shape through a forward extrusion process, a stepping process, and a side extrusion process (see FIG. 2), after heating at a temperature of 740 to 860 ° C. for 0.1 hour or more, 20 to 70 After cooling to a temperature of 720-680 ° C. at a rate of ℃ / hr, then holding at a temperature of 720-680 ° C. for about 1-5 hours, then cooling to a temperature of 620-680 ° C. at a rate of 10-100 ° C./hr Further, a test example is shown in which the bearing ring material is softened and annealed by cooling to a temperature of 500 to 560 ° C. at a rate of 10 to 15 ° C./hr.

  On the other hand, Comparative Examples 1, 3, 5, 7, 9, and 11 use JIS S45C to S75C as the race ring material of the wheel bearing rolling bearing device, and test examples in which the race rings are produced by hot forging. Is shown. In Comparative Examples 2, 4, 6, 8, 10, and 12, JIS S45C to S75C are used as the raceway material of the wheel bearing rolling bearing device, and for example, the forward extrusion process, the stepping process, and the lateral extrusion process ( 2), before the cold forming into a predetermined shape, the average interval of spherical carbides having a major axis diameter / minor axis diameter ratio of 2 or less and a minor axis diameter of 0.7 μm or more exceeds 15 μm. The test example at the time of performing softening annealing on the raceway ring material under heat treatment conditions is shown.

In addition, the spherical carbide area ratio, spherical carbide average interval, surface hardness, crystal grain size, rolling life ratio, and limit upsetting ratio in Table 1 are values obtained by the following methods.
(1) Spherical carbide area ratio After mirror-polishing the raceway surface of the raceway ring, it is corroded by pyracool, and a metal structure as shown in FIG. Image analysis of spherical carbides with an aspect ratio of the major axis diameter to the minor axis diameter of 2 or less and a minor axis diameter of 0.7 μm or more among all the carbides present in the metal structure of the raceway ring material Thus, the area ratio of the spherical carbide was obtained.

(2) Spherical carbide average interval After mirror-polishing the raceway surface of the raceway ring, it was corroded with a nita roll, and a metal structure as shown in FIG. 3 was photographed in a region up to 0.25 mm directly below the raceway surface. Image analysis of spherical carbides with an aspect ratio of the major axis diameter to the minor axis diameter of 2 or less and a minor axis diameter of 0.7 μm or more among all the carbides present in the metal structure of the raceway material. The average interval was determined.

(3) Surface hardness The surface hardness in Table 1 is a measurement value obtained by measuring the raceway surface hardness of a raceway ring that has been subjected to induction hardening after cold forming with a Vickers hardness tester.
(4) Crystal grain size Based on the JIS G0051 steel austenite grain size test method, the crystal grain size was determined.

(5) Rolling life ratio The rolling life ratio shown in Table 1 is evaluated based on the total number of rotations of the raceway until flaking occurs on the inner ring raceway surface of the wheel bearing rolling bearing device. It is a relative value with a rolling life of 5 as 1. Specifically, a rotational test of the rolling bearing device for wheel support is performed under the test conditions of radial load: 7000 N, axial load: 5000 N, and rotational speed: 300 min ⁻¹ , and the raceway ring until flaking occurs on the inner ring raceway surface. The total number of revolutions was measured. At that time, the suspension device mounting flange 4 (see FIG. 1) provided on the outer peripheral portion of the stationary side race ring is fixed, and the wheel mounting flange 5 (see FIG. 1) provided on the outer peripheral surface of the rotation side race ring. The occurrence of flaking was detected by measuring the vibration of the rotating side raceway and the stationary side raceway with a load applied to it, and the life was evaluated by the total number of revolutions until flaking occurred on the inner ring raceway surface.

(6) Limit Upsetting Ratio The limit upsetting ratio in Table 1 is a relative value where the critical upsetting ratio of the test piece is calculated from the following formula and the critical upsetting ratio of Comparative Example 12 is 1.
Critical upsetting rate = {(HO−HF) / HO] × 100
However, HO: initial height of the test piece, Hf: upsetting test (a lubricant is applied to the end face of the test piece, and a load is applied to the test piece at a processing speed of 2 mm / min to generate cracks in the test piece. The height of the specimen for which cracks were confirmed in (Test).

FIG. 4 is a diagram showing the relationship between the grain size of the prior austenite grains obtained by the above-described method and the rolling life ratio, and when the grain size of the prior austenite grains of the softened and annealed bearing ring material exceeds 6, It can be seen from FIG. 4 that the rolling life ratio of the race ring rapidly increases.
Table 2 and FIG. 5 show the results of upsetting tests for the purpose of investigating the relationship between the area ratio of spherical carbides having a minor axis diameter of 0.7 μm or more and the limit upsetting ratio, separately from this test. .

  FIG. 5 is a diagram showing the relationship between the area ratio of the spherical carbide obtained by the above-described method and the limit upsetting ratio, and the major axis of all the carbides present in the metal structure of the softened and annealed race ring material. When the area ratio of the spherical carbide having an aspect ratio between the diameter and the minor axis diameter of 2 or less and the minor axis diameter of 0.7 μm or more increases, the limit upsetting ratio increases and cracks are less likely to occur. I understand.

  Therefore, as in Examples 1 to 12, among all the carbides present in the metal structure of the raceway material before induction hardening, the aspect ratio between the major axis diameter and the minor axis diameter is 2 or less and the minor axis diameter is 0. The area ratio of spheroidized carbides of 7 μm or more is 70% or more, the average interval of spheroidized carbides having an aspect ratio between the major axis diameter and minor axis diameter of 2 or less and the minor axis diameter of 0.7 μm or more is 15 μm or less, soft annealing The rolling life of the bearing ring can be increased by setting the grain size number of the prior austenite crystal grains of the produced bearing ring material to 6 or more and the raceway surface hardness of the bearing ring after induction hardening to HV650 or more. .

In Comparative Examples 2, 4, 6, 8, 10, and 12, since the average carbide spacing was greater than 15 μm, or the area ratio in the total carbide was less than 70%, the surface hardness of the raceway groove was reduced, or rolling. The life ratio decreased, the limit upsetting ratio decreased, and a fine incomplete structure occurred.
As described above, a steel material having a carbon content of 0.45 mass% or more and 0.75 mass% or less is used as a race ring material, and the temperature of 740 to 860 ° C. is obtained before plastic working the race ring material into a predetermined shape. And then cooled to a temperature of 720-680 ° C. at a rate of 20-70 ° C./hr, and then kept at a temperature of 720-680 ° C. for about 1-5 hours, then 10-100 ° C. It was softened and annealed by cooling to a temperature of 620 to 680 ° C. at a rate of / hr and further cooling to a temperature of 500 to 560 ° C. at a rate of 10 to 15 ° C./hr and applying softening annealing to the bearing ring material. Of all the carbides present in the metal structure of the raceway ring material, the ratio of the spheroidized carbides with an aspect ratio of the major axis diameter to the minor axis diameter of 2 or less and a minor axis diameter of 0.7 μm or more is 70% or more in area ratio. And the ascending length of the major axis and minor axis Transfected ratio minor axis diameter average distance more spheroidized carbides 0.7μm is 15μm or less 2 or less.

Therefore, when short-time quenching such as induction quenching for a few seconds is applied to the raceway ring material after soft annealing, the solid solution of carbide in the matrix does not become insufficient, and the number that causes flaking It is possible to suppress generation of an incompletely hardened structure of a 10 μm level on the raceway surface layer portion of the raceway ring.
In the present invention, among the bearing ring materials having a carbon content of 0.45 mass% or more and 0.75 mass% or less, it is possible to reduce the cost and heat treatment quality by using the carbon steel for machine structure defined in JIS and SAE. Preferred for satisfaction.

It is sectional drawing which shows schematic structure of the rolling bearing apparatus for wheel support which concerns on one Embodiment of this invention. It is a figure which shows an example in the case of shape | molding the bearing ring of a rolling bearing apparatus for wheel support by cold work. It is a figure which shows the metal structure of a bearing ring material. It is a figure which shows the relationship between the crystal grain size of the former austenite crystal grain of a bearing ring material, and the rolling life ratio of a bearing ring. It is a figure which shows the relationship between the area ratio of the spherical carbide of a bearing ring material, and a limit upsetting ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotating side raceway 1a Inner ring raceway groove 2 Fixed side raceway 2a Outer ring raceway groove 3 Rolling element

Claims (2)

A rotation-side bearing ring that rotates integrally with the wheel; a stationary-side bearing ring that has an outer ring raceway groove that is opposed to an inner ring raceway groove formed on the outer peripheral surface of the rotation-side raceway ring; A plurality of rolling elements provided between the grooves, and at least one of the rotating side raceway and the stationary side raceway plastically processes the steel material into a predetermined shape, and induction hardening is performed after the plastic processing. A rolling bearing device for supporting a wheel formed by applying,
The steel material is a material equivalent to “JIS S45C to S75C” having a carbon content of 0.45 mass% or more and 0.75 mass% or less , and is a major axis among all carbides present in the metal structure of the steel material before plastic working After subjecting induction hardening to an area ratio of spheroidized carbide having an aspect ratio between the diameter and the minor axis diameter of 2 or less and a minor axis diameter of 0.7 μm or more, an average interval of the spheroidized carbides of 15 μm or less. A rolling bearing device for supporting a wheel, wherein the grain size number of the prior austenite crystal grains of the raceway groove is 6 or more and the surface hardness is HV650 or more.   A method of manufacturing a bearing ring for a wheel-supporting rolling bearing device according to claim 1, wherein a steel material having a carbon content of 0.45 mass% or more and 0.75 mass% or less is used as the bearing ring material. Before being plastically processed into a predetermined shape, it is heated at a temperature of 740 to 860 ° C. for 0.1 hour or more, then cooled to a temperature of 720 to 680 ° C. at a rate of 20 to 70 ° C./hr, and then 720 to 680 ° C. After maintaining at a temperature of 1 ° C. for about 1 to 5 hours, it is cooled to a temperature of 620 to 680 ° C. at a rate of 10 to 100 ° C./hr, and further cooled to a temperature of 500 to 560 ° C. at a rate of 10 to 15 ° C./hr. A method for manufacturing a bearing ring for a rolling bearing device for supporting a wheel, characterized by subjecting the bearing ring material to soft annealing.

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