Reliability evaluation on very high cycle fatigue property of GCr15 bearing steel

Very high cycle Fatigue property of a high carbon chromium bearing steel (GCr15) was experimentally examined in rotating bending. As a result, GCr15 steel represents the duplex S–N curves characteristic corresponding to surface-induced fracture and interior inclusion-induced fracture. However, the separation of two S–N curves and the surface fatigue limit are not so distinct that the single P–S–N curve is proposed to evaluate its probabilistic S–N property. The interior crack propagation process of this steel in very high cycle regime is divided into three stages: (1) small crack propagation within the Fine Granular Area (FGA), (2) crack stable propagation in the fish-eye region outside of FGA and (3) crack unstable propagation outside of fish-eye. The interior threshold stress intensity factor range, ΔKint-th, evaluated by the size of inclusion, and the stress intensity factor ranges at the front of FGA and fish-eye, ΔKFGA and ΔKfish-eye, are regarded as the threshold value controlling interior crack propagation in these three stages, not the constant and tending to increase with the increase of respective size. More than 90% of the total fatigue life is consumed in the first stage, and the corresponding crack growth rate is lower than 10−11 m/cycle. Furthermore, based on the predicted maximum sizes of inclusion and FGA, the values of fatigue limit for the control volume of specimen are 690.32 MPa and 654.07 MPa, respectively. It should be noted that fatigue design based on former involves a certain amount of risk in very high cycle regime.