Fatigue tests on a high carbon chromium steel were performed with rotating bending and ultrasonic fatigue tests. The fractography was examined to reveal that fatigue cracks initiated at specimen interior for very-high-cycle fatigue (VHCF) with fish-eye pattern embracing fine-granular-area (FGA) morphology originated from inclusions. The measurements show the dimensions of FGA and fish-eye as a function of the applied stress and fatigue failure cycles. The results also show the values of stress intensity factor range at FGA (ΔKFGA) and fish-eye (ΔKfisheye) almost keep constant with failure cycles, and the values of ΔKFGA are close to the relevant fatigue threshold (ΔKth).

The fatigue life from FGA to fish-eye and from fish-eye to the critical crack size is respectively calculated, thus to estimate the fatigue life contributed by FGA. Moreover, the crack growth rate within FGA was estimated. The present result is combined with our previous ones and with those available in literature to discuss the process of crack initiation and early growth for VHCF, which is responsible for a majority part of total fatigue life. In addition, the large scattering of fatigue life was investigated, which was ascribed to the distribution of inclusion size.