Very high cycle fatigue of surface carburized CrNi steel at variable stress ratio: Failure analysis and life prediction

High cycle fatigue and very high cycle fatigue properties of a surface-carburized CrNi steel were examined under axial loading with stress ratios of −1 and 0. The positive stress ratio overcomes the effect of carburized layer and promotes crack initiation from the carburized layer. The morphology of fine granular area (FGA) is more distinct under the negative stress ratio with more obvious crack closure effect. Two models concerning the inclusion-fisheye failure and the inclusion-FGA-fisheye failure are proposed. The predicted fatigue lives based on the concept of crack initiation are in good agreement with experimental results.