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

Rotating bending fatigue tests were carried out on shot-peening (SP) treate d specimens of two types of ductile cast iron (ferrite-pearlitic ductile ca st iron, FPDI, and pearlitic ductile cast iron, PDI). The SP treatment give s 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 n ear the surface. In this report, the fracture morphology and the fatigue pr operties were investigated from the viewpoints of crack behavior and residu al stress change. Therefore, the initial residual stress distribution and i ts change during the high cycle fatigue test of the SP-treated specimen wer e investigated. Furthermore, from detailed observations of crack initiation sites using a scanning electron microscope (SEM), the difference in the fa tigue fracture morphology between the shorter and longer fatigue life regio ns was investigated and the shape of the S-N diagram was discussed. (C) 200 1 Elsevier Science Ltd. All rights reserved.