JPH10122243A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lengthen an span of service life in a rolling bearing being used under the high vibro-load of a bearing or the like available in an alternator. SOLUTION: An outer ring 2 or a fixed ring is made up of the following constituent steel material. In brief, this steel material includes C as 0.70 to 0.93wt.% Si as 0.15 to 0.50wt.%, Ms as 0.50 to 1.0wt.%, and Cr as 0.30 to 0.65wt.% within the range as alloy content, and an equation of 0.4<=Cr/C<=0.7 is satisfied. In addition, a residual austenite quantity after the heat treatment of this outer ring 2 should be less than 5 volume percentage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing, and more particularly to a grease-filled bearing for an engine auxiliary machine (for an alternator, an electromagnetic clutch, an intermediate pulley, etc.).

[0002]

2. Description of the Related Art In recent years, as automobiles have become smaller and lighter, engine accessories have been required to be smaller and lighter and have higher performance and higher output. For example, bearings for alternators include high vibration,
Since a high load (approximately 4 G to 20 G in terms of gravitational acceleration) acts via the belt, premature peeling tends to occur particularly on the raceway surface of the outer ring, which is a fixed ring, which causes a reduction in the life of the bearing.

Techniques for improving the life of bearings used under high vibration and high load include, for example, Japanese Patent Publication No. 7-7256.
No. 5 discloses that a fixed wheel made of high-carbon chromium bearing steel (SUJ2) is subjected to normal quenching, then to a sub-zero treatment, and then to a high-temperature tempering treatment, so that the retained austenite of the fixed wheel is obtained. It is disclosed that the amount (γ _R ) is set to 10% by volume or less. That is, by reducing the amount of retained austenite of the fixed wheel, the hardness of the fixed wheel is increased, and plastic deformation of the raceway surface of the fixed wheel under high vibration and high load is reduced, thereby preventing early peeling.

Japanese Patent Application Laid-Open No. Sho 62-218542 discloses that C is 0.95 to 1.10% by weight, Si or Al
Is formed by using a steel containing 1-2% by weight of Mn, 0.50% by weight or less of Mn, and 0.90% to 1.65% by weight of Cr, and the amount of retained austenite (γ _R ) Is set to 8% by volume or less.

[0005]

However, in the bearing disclosed in Japanese Patent Publication No. 7-72565, the ratio of Cr to C in the high carbon chromium bearing steel (SUJ2) is not less than 0.8, Later, a large amount of C is taken into the Cr carbide, and the strength of the matrix decreases and the structure becomes unstable. Therefore, even if the amount of retained austenite (γ _R ) is reduced, sufficient hardness is obtained as a fixed ring. Can not do.

[0006] In the bearing disclosed in Japanese Patent Application Laid-Open No. 62-218542, the steel forming the fixed ring has a large Si or Al content of 1 to 2% by weight, so that oxidization harmful to rolling fatigue is caused. Physical inclusions are likely to form. Also,
Similarly to the above, since the ratio of Cr to C is 0.8 or more, even if the amount of retained austenite (γ _R ) is reduced,
HRC (Rockwell hardness for scale C) 52-
57, it is not possible to obtain sufficient hardness as a fixed ring.

Therefore, the bearings disclosed in the above publications cannot sufficiently prevent early separation of the raceway surface under high vibration and high load, so that the conventional art has a limit in extending the life of the bearing.

The present invention has been made in view of such problems of the prior art. In a rolling bearing used under high vibration and high load, early peeling is sufficiently prevented, and the life of the bearing is reduced. It is an object to provide a rolling bearing that is significantly extended.

[0009]

In order to achieve the above object, a rolling bearing according to the present invention comprises a plurality of rolling elements disposed between a fixed wheel and a rotating wheel. 0.70 to 0.93% by weight of C, 0.15 to 0.50% by weight of Si, and 0.5% of Mn as alloy components.
0 to 1.10% by weight, Cr 0.30 to 0.65% by weight
, And is formed of a steel material satisfying 0.4 ≦ Cr / C ≦ 0.7, and the amount of retained austenite after heat treatment is 5% by volume or less.

When ordinary quenching and tempering (for example, a quenching temperature of 840 ° C. and a tempering temperature of 180 ° C.) are performed on the steel material having the above composition, the amount of retained austenite becomes 10%.
~ 15% by volume, for example, a quenching temperature of 840 ° C,
Quenching and tempering at a tempering temperature of 240 ° C. or sub-zero treatment (eg, −
90 ° C.) and then tempering (eg, 180 ° C.)
) Can reduce the amount of retained austenite to 5% by volume or less.

In the present invention, as described above, the composition of the steel material forming the fixed ring includes C, Si, Mn,
By limiting the content range of Cr and Cr and (Cr / C), the effect resulting from the small amount of retained austenite after the heat treatment is sufficiently exhibited, so that the hardness of the fixed wheel can be reduced under high vibration and high load. This is sufficient as a fixed ring for the rolling bearing used.

The critical significance of each numerical limitation in the present invention will be described below. [C: 0.70 to 0.93% by weight] C is an element imparting hardness to steel, and when the content of C is less than 0.70,
In some cases, the hardness (Rockwell hardness (HRC) of 58 or more in the case of scale C) required for the rolling bearing cannot be secured. In addition, C forms a solid solution with the matrix and combines with other alloying elements (especially Cr) to form carbides. If the content of C exceeds 0.93% by weight, large carbides are easily formed during steelmaking. As a result, fatigue life and impact resistance may be reduced. [Si: 0.15 to 0.50% by weight] Si acts as a deoxidizing agent during steel making to improve hardenability and strengthen martensite of the parent phase, so that it is effective in extending bearing life. Element. In order to substantially obtain such a life extension effect, it is necessary to contain Si in an amount of 0.15% by weight or more. Further, as the content of Si increases, workability such as machinability, forgeability, and cold workability decreases. In order to make this workability comparable to SUJ2, the upper limit of the Si content is set to 0.5% by weight. [Mn: 0.50 to 1.10% by weight] Mn is an element that strengthens ferrite in steel and has a content of 1.10% by weight.
If the amount exceeds the range, the cold workability is significantly deteriorated. Mn is an element that improves the deoxidizing action and hardenability, but when the content is less than 0.50% by weight, these actions are not substantially exerted. [Cr: 0.30 to 0.65% by weight] Cr is an element exhibiting effects such as improvement of hardenability, improvement of tempering softening resistance and improvement of abrasion resistance, but the content is 0.30% by weight. If less than these, these effects are not substantially exhibited. Also,
Cr may combine with C to form a huge carbide, but in order to avoid this, the lower limit of Cr is set to 0.30% by weight. [0.4 ≦ Cr / C ≦ 0.7] As described above, C forms a carbide by forming a solid solution with the matrix and particularly by combining with Cr. However, C is used for forming Cr carbide to form a carbide. When the amount of dissolved C decreases, the strength of the matrix decreases and the structure becomes unstable. Even if the amount of retained austenite is reduced to 5% by volume or less, the hardness does not sufficiently increase. To avoid this, (Cr / C) is set to 0.7 or less. The lower limit of (Cr / C) is C
The ratio of the lower limit (0.30) of the Cr content to the upper limit (0.93) of the content (0.30 / 0.93 = 0.32 ·
・ ・) Was set to 0.4. [Retained austenite amount is 5% by volume or less] A number of fixed rings are formed by using steel materials having the same composition satisfying the limitation of the present invention, and heat treatment is performed under different conditions to obtain fixed rings having different residual austenite amounts. A rolling bearing was assembled using this, and a rolling life test under vibration and high load was performed. The amount of retained austenite was 5% by volume.
It was found that the life was extremely shortened when it exceeded.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to specific examples and comparative examples. FIG. 1 is a sectional view showing a rolling bearing according to one embodiment of the present invention.

The rolling bearing 1 has a JIS designation number 6303.
The outer ring 2 is fixed to the housing 8 to form a fixed ring, and the inner ring 3 is externally fitted to the shaft 7 to form a rotating ring. Also, between the outer ring 2 and the inner ring 3,
A number of rolling elements 4 held by a holder 5 are provided,
Seal members 6 and 6 are mounted between the outer ring 2 and the inner ring 3 on both sides of the retainer 5.

In the space surrounded by the sealing members 6 and 6, grease E (SAE Technical Paper: S
AE950944 (scheduled date: February 27-March 2, 1995) "on page 1-14 and the same as the E-grease sealed in the alternator bearing.

The rolling bearing 1 has a shaft 7
The inner ring 3 rotates with the rotation of the
The load acts on the load zone of the outer ring 2 from the shaft 7 via the inner ring 3 and the rolling elements 4.

Here, the outer ring 2 is formed of a steel material having the composition shown in Tables 1 and 2 below, and is hardened and tempered under any of the following conditions to obtain the hardness (HRC) and the amount of retained austenite. (Γ _R ) is a value shown in Tables 3 and 4 below. [Quenching and tempering conditions] Condition A: quenching at 840 ° C, oil cooling, and tempering at 240 ° C.

Condition B: After quenching at 840 ° C. and cooling with oil,
Subzero treatment at 90 ° C. Then tempered at 180 ° C. Condition C: quenched at 840 ° C., tempered at 180 ° C. after oil cooling.

Condition D: quenching at 840 ° C.
Tempered at 10 ° C. The surface roughness of the outer ring is 0.01 to 0.03 μm in Ra.
And In both the examples and the comparative examples, the inner race 3 and the rolling elements 4 are formed of the same bearing steel (SUJ2), subjected to a normal heat treatment (condition C), and have a surface hardness of HRC59-62.
The surface roughness of the inner ring 3 is 0.01 to 0.03 μm in Ra, and the surface roughness of the rolling elements 4 is 0.003 to 0.010 μm in Ra.
And

Different outer rings (Examples Nos. 1 to 10 and Comparative Examples Nos. 1 to 18) 2 thus manufactured
A life test was performed on the rolling bearing 1 provided with the same inner ring 3 and rolling element 4 as follows.

As a tester, a bench rapid acceleration / deceleration tester that switches the number of revolutions between 9000 rpm and 18000 rpm at predetermined time intervals (for example, every 9 seconds) was used. The load condition was P (load load) / C (dynamic load rating) = 0.10. Here, the calculated service life (theoretical maximum service life) of the rolling bearing 1 under this condition is 1350 hours, so the test discontinuation time was set to 1000 hours. Furthermore, this study is to provide a test of Examples No. 1 to 10 and Comparative Examples No. 1 to 18 by 10 pieces, respectively, were measured L ₁₀ life. The results are shown in Tables 3 and 4 below.

Tables 1 and 2 show the steel materials used.
P and S contained as impurities in addition to the composition shown in FIG.
Is 0.025% by weight or less, and the Ti content is 40% by weight or less.
ppm or less, and the O content was 15 ppm or less. The underlined numerical values in Tables 3 and 4 denote values outside the numerical limit range of the present invention.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4] As can be seen from the life test results, the composition of the steel material forming the outer ring 2 is as follows: C: 0.70 to 0.93% by weight Si: 0.15 to 0.50% by weight Mn: 0.50 to 1.10 % By weight Cr: 0.30 to 0.65% by weight (Cr / C): 0.4 ≦ Cr / C ≦ 0.7, and the amount of retained austenite after heat treatment is 5% by volume or less (Example Nos. 1 to 1
Only 0), L ₁₀ life is long as 1,000 hours or more.

In other cases (Comparative Examples Nos. 1 to 1)
In 8), the amount of retained austenite in the outer ring 2 is 5% by volume or less. However, for the test pieces (Comparative Examples Nos. 1 to 12) in which the composition of the steel material used is out of the limits of the present invention, the calculated life value is It was ４ or less, and the bearing life due to rolling fatigue was short. In addition, for the test specimens (Comparative Examples Nos. 13 and 14) in which the amount of retained austenite exceeds 5% by volume and the composition of the steel material used is also out of the range of the present invention, it is about 1/10 of the calculated life value. The bearing life was particularly shortened due to rolling fatigue. Further, the composition of the steel material used satisfies the limitations of the present invention, but the specimen having a retained austenite amount exceeding 5% by volume (Comparative Example No. 1)
5-18), it was about 1/2 of the calculated life value.

That is, in a rolling bearing used under high vibration and high load, it is difficult to sufficiently improve the bearing life only by limiting the composition of the steel material forming the outer ring 2. In addition, it is essential that the amount of retained austenite be 5% by volume or less.

Incidentally, in the outer race 2 of each comparative example, all of the peelings in the test occurred in the load bearing zone of the outer race 2. When the structure of the peeled portion was examined with a microscope, a structure change called a white structure was observed.

[0030]

As described above, according to the present invention, high vibration and high load transmitted from the rolling elements to the fixed wheel are absorbed by limiting the composition of the steel material forming the fixed wheel and the amount of retained austenite. As a result, a sufficient anti-vibration effect is exerted, and the time to reach the fatigue life of the rolling bearing can be delayed. As a result, premature peeling of the fixed ring is prevented, and the life of the bearing can be significantly extended as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a rolling bearing corresponding to one embodiment of the present invention.

[Description of Signs] 1 Rolling bearing 2 Outer ring (fixed ring) 3 Inner ring (rotating wheel) 4 Rolling element

Claims (1)

[Claims] In a rolling bearing having a plurality of rolling elements disposed between a fixed wheel and a rotating wheel, at least the fixed wheel contains 0.70 to 0.93% by weight of C as an alloy component and 0% of Si as an alloy component. .15 to 0.50% by weight, Mn is 0.50 to 1.10
% By weight, made of a steel material containing Cr in the range of 0.30 to 0.65% by weight and satisfying 0.4 ≦ Cr / C ≦ 0.7, and the residual austenite amount after heat treatment is 5% by volume. A rolling bearing characterized by the following.