Ooki, C., "Improving Rolling Contact Fatigue Life of Bearing Steels Through Grain Refinement," SAE Technical Paper 2004-01-0634, 2004, doi:10.4271/2004-01-0634.
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.