High cycle fatigue property of carburized 20Cr gear steel under axial loading

The high cycle fatigue property of carburized 20Cr gear steel was experimentally investigated under axial loading with a stress ratio of zero. The test results show that this steel exhibits gradually decreasing S-N characteristics, and the fatigue strength corresponding to 10⁹ cycles is about 455 MPa. Based on the observation of fracture surfaces, the interior inclusion fisheye-induced fracture is the predominant fracture mode in the life regime beyond 10⁵ cycles. The fine granular area (FGA) cannot be found clearly around the inclusion. Based on the evaluation of stress intensity factor ranges (DK) at the front of inclusion and fisheye, the interior crack growth rate (da/dN) equation can be characterized by da/dN = 2.39 x 10^-21(ΔK)12.32. Corresponding to the tested specimen, the predicted maximum inclusion size is about 52.02 _m. The predicted fatigue strength corresponding to 109 cycles by usingWang’s model is slightly higher than the experimental result, but that by using Murakami’s model is relatively conservative.