Effect of shot-peening treatment on high cycle fatigue property of ductile cast iron

Rotating bending fatigue tests were carried out on shot-peening (SP) treated specimens of two types of ductile cast iron (ferrite–pearlitic ductile cast iron, FPDI, and pearlitic ductile cast iron, PDI). The SP treatment gives high-level work hardening and high-level compressive residual stress near the surface layer thereby improving the fatigue strength. In addition, it can reduce the number of casting defects that initiate the fatigue cracks near the surface. In this report, the fracture morphology and the fatigue properties were investigated from the viewpoints of crack behavior and residual stress change. Therefore, the initial residual stress distribution and its change during the high cycle fatigue test of the SP-treated specimen were investigated. Furthermore, from detailed observations of crack initiation sites using a scanning electron microscope (SEM), the difference in the fatigue fracture morphology between the shorter and longer fatigue life regions was investigated and the shape of the S–N diagram was discussed.