Crack Initiation Behavior from Internal Defect in High Carbon-chromium Bearing Steel under Rolling Contact Fatigue

It is important to clarify the effects of nonmetallic inclusions on rolling contact fatigue life to extend or to predict the life of the rolling bearings. The observation of initial cracks from internal defects is desirable from this point of view. In this study, high carbon-chromium bearing steel, SUJ2, with a number of artificial pores as internal defects was prepared. Initial cracks around pores under rolling contact were observed and the stress was CAE analyzed with the following results: - The exposure of the initial crack surface by forced breaking and the subsequent fracture observation in this study were effective to identify the mode of the initial crack generation. - The tensile stress around the pores initiated mode-I crack, and the pore with cracks is subjected to crack propagation process by internal stress under rolling contact fatigue. - Rolling contact fatigue life is not simply dominated by the size of initial defects in steels. As observed in this study, the sum of initial defect size and rim crack size may control the fatigue life. This suggests that the inclusion types and the interfacial adhesiveness between inclusions and matrix may influence rolling contact fatigue.