Steel ball used for the deep groove ball bearing (hereafter steel ball) is an important mechanical component which supports the industries and our daily lives. The usage environment of steel ball has increasingly become multifaceted and severe with downsizing and souped-up on especially automotive and industrial machine applications. Since steel ball is under heavily-loaded environment, the improvement of steel ball reliability is one of the most important action assignments. Authors have been focusing on steel ball and researching for the improvement of steel ball reliability^1,2,3). In general, steel ball is given the residual stress to constrict the indentation on treating, but residual stress influences rolling fatigue life of steel ball. In this report, the rolling fatigue lives of steel balls with various residual stress distributions were evaluated under dynamic load condition which could make the flaking preferentially on steel ball in bearing. It was examined how residual stress affected on rolling fatigue of steel ball by investigating residual stress variations particularly under rolling fatigue with X-ray diffraction. In the result, initial residual stress of steel ball was changed drastically by rolling contact, and increasing of radial residual stress mainly caused the flaking of steel ball.

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