Investigation of factors influencing rotating bending fatigue properties of carburized steel using large data source

Abstract

Large data source for rotating bending fatigue tests of carburized steels obtained from a common research project were analyzed, and the factors influencing their fatigue properties were investigated from the viewpoint of microstructural characteristics and reliability engineering. The fatigue test results indicated that carburizing increased the fatigue strength of AISI 4120 steel, although the residual stress induced by carburizing did not affect the scatter of the fatigue strength of the steels. The carburizing pretreatment procedure affected the fatigue properties of the steels, indicating that the effect of the surface morphology of the carburized steels on their fatigue properties is significant. Large amounts of data from the fatigue tests indicated that the carburized steel exhibited a duplex S-N curve because of the occurrence of both surface and internal fracture modes. When post-treatments such as peening were performed on carburized steels, subsurface fatigue crack initiation occurred. The (100) plane of the body centered cubic structure, parallel to the fracture surface, acted as the fatigue crack origin and formed a facet-like pattern with a fish-eye. Fractographic analysis assisted by electron backscattered diffraction can be applied to identify microstructures related the subsurface fatigue fractures.