Improving Rolling Contact Fatigue Life of Bearing Steels Through Grain Refinement

Within JIS-SUJ2 (SAE52100 equivalent) bearing steel, we have succeeded in producing a prior-austenite grain size of approximately 5 μm in diameter (half that of the conventional grain size). It is believed that the packet or block size of the martensite decreases proportionally with that of the prior-austenite grain size. As a result, during RCF (RCF means Rolling Contact Fatigue, that is the most typical fatigue type of bearings) testing, the grain refined SUJ2 material demonstrated a fatigue life that was twice as long as carbonitrided steel sample under both clean and debris-contaminated lubrication conditions. In addition, the grain refined SUJ2 material was superior in fracture strength and aged dimensional stability. Therefore, it can be surmised that the grain refining of conventional bearing steels is a very useful process in greatly extending fatigue life.