Influence of surface integrity on fatigue life of bearing rings finished by precision hard turning and grinding

Machined surface integrity of bearing rings is often the main concern for the bearing manufacturers as it affects their fatigue life. The present study investigates the surface integrity of AISI 52100 bearing rings finished by precision hard turning and grinding and its influence on fatigue life. A twin-disk machine is used to evaluate the RCF life. As main results, precision hard turning can achieve low surface roughness 0.1 μm Ra with respect to the required 0.2 μm Ra obtained by grinding. Both processes introduce microstructural changes. At subsurface, precision hard turning induces subsurface compressive and maximum residual stresses at 10–50 μm depth, corresponding to the transition zone formed after a thin white layer (<1 μm); however, grinding induces tensile residual stresses from 15 μm depth, corresponding to the bulk material. The residual stresses measured during RCF test (after running-in process and after spalling) of ground ring specimens exhibit peak compressive value in subsurface from 140 μm depth. The ring specimens machined by precision hard turning have fatigue life four times higher than those machined by grinding. This enhancement of RCF life is due to the low roughness reached and also to the subsurface compressive residual stresses at shallow depth before RCF test.