Conventional life theory defines the rolling contact fatigue (RCF) life as being determined by the maximum contact pressure (P) and the total number of stress cycles (N). However, when the life test results of bearings were analyzed, it was found that there were cases where there was little correlation between the RCF life, maximum contact pressure and the number of stress cycles. An extensive investigation has revealed that the slip velocity is an additional factor that influences the RCF life of bearings. Under special test conditions it was discovered that when the PV value, which is a product of contact pressure and slip velocity, was higher than the threshold value, a unique type of flaking occurred. The flaking originated from white microstructure that was generated at the point of the maximum PV value. Although regarded as a conventional means of increasing the maximum contact pressure, increasing the raceway curvature is an effective counter measure against the formation of white microstructure. It was also found that adding chromium to bearing material was an additional counter measure.

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