Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Patent
1997-10-20
1999-09-28
Speer, Timothy M.
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
428639, 428688, 428698, 252572, 508103, 508108, B22F 300
Patent
active
059602503
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to bearing materials used for rolling bearings, such as roller bearings and ball bearings. In particular, the present invention relates to a bearing material having an extended rolling contact fatigue life.
2. Background Art
Bearings require excellent durability against fatigue, and thus bearing materials also require an extended rolling contact fatigue life.
One of generally known methods for extending the rolling contact fatigue lives of bearing materials is reduction of nonmetal oxide inclusions contained in the materials. Such reduction of the nonmetal oxide inclusions have been achieved by decreasing the oxygen content in the materials. At present, the oxygen content in the materials can be decreased to 10 ppm or less by weight due to the progress in refining technologies. The reduction of the oxygen content, however, has reached its limit, and further extension of the rolling contact fatigue life is not expected by such a method.
Under such circumstances, several methods other than reduction of the oxygen content have been proposed for extending the rolling contact fatigue life. For example, Laid-Open Patent No. 3-126839 discloses a bearing material having an extended life which is achieved by the reduction of the number of nonmetal oxide inclusions per unit area or volume. Japanese Laid-Open Patent No. 5-25587 discloses a bearing material having an extended life which is achieved by the reduction of a maximum diameter of nonmetal oxide inclusions, which is estimated from statistics of extreme-value. Further, Japanese Laid-Open Patent No. 4-280941 discloses a bearing steel having an extended rolling contact fatigue life, in which the length and number of nonmetal sulfide inclusions in the steel are controlled so that the inclusions having a maximum length of not greater than 100 .mu.m and the number of the inclusions each having a length of greater than 40 .mu.m are 50 or less in an observation area of 160 mm.sup.2.
SUMMARY OF THE INVENTION
The present inventors also have studied the further extension of the rolling contact fatigue life of bearing materials. First, the present inventors have studied the effects of statistics on the rolling contact fatigue life using high-carbon chromium-based bearing steel (JIS G4805 SUJ2). Herein, rolling fatigue tests were performed with a Mori thrust-type rolling fatigue tester under operating conditions of a Hertzian maximum contact stress of 5,260 MPa and a number of stress cycles of 30 Hz, using #68 turbine oil as a lubricant oil. The test results were plotted onto a probability paper for Weibull distribution, and were evaluated as B.sub.10 life (a total number of loads which are repeatedly applied until flaking occurs at a failure probability of 10%).
FIG. 1 is a graph illustrating the effect on B.sub.10 life of the number of nonmetal oxide inclusions each having a particle size of 3 .mu.m or more in an observation area of 320 mm.sup.2. FIG. 2 is a graph illustrating the effect on B.sub.10 life of the maximum diameter of nonmetal oxide inclusions in an observation area of 320 mm.sup.2. The comparison of FIG. 1 with FIG. 2 demonstrates that the maximum diameter of the nonmetal oxide inclusions has an adequate correlation with B.sub.10 life. Further, B.sub.10 life noticeably fluctuates at a maximum diameter region of 10 .mu.m or less.
FIG. 3 is a graph illustrating the effect on B.sub.10 life of the number of nonmetal sulfide inclusions each having a length of more than 40 .mu.m, wherein the open circle represents that the maximum length of the nonmetal sulfide inclusions is less than 100 .mu.m, and the black dot represents that the maximum length of the nonmetal sulfide inclusions is more than 100 .mu.m. When the maximum length of the nonmetal sulfide inclusions is less than 100 .mu.m, the more the number of nonmetal sulfide inclusions decreases, the more B.sub.10 life is extended. On the other hand, when the maximum length of the nonmetal sulfide inclusions is more than 100 .mu.m,
Amano Keniti
Hamanoue Michiro
Hosino Tosiyuki
Ohta Atsuhiko
Yasumoto Satosi
Kawasaki Steel Corporation
Koyo Seiko Co. Ltd.
Speer Timothy M.
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