Fatigue Crack Property and Fracture Surface Observation of SP Treated Ductile Cast Iron

Abstract

Rotating bending fatigue tests were carried out on specimens of ferrite-pearlitic cast irons and pearlitic ductile cast irons with a shot-peening (SP) treatment. It has been reported that sites of the fatigue crack initiation are transferred from the surface to subsurface in the range of longer life region over (10)^7 cycles. So the initiation and the propagation behaviors of the surface fatigue cracks with the compressive residual induced by the SP treatment and also the subsurface fatigue crack were investigated by the detailed observations of the specimen surface and the fracture surface. As a result, the non-propagating surface cracks under the influence of the SP treatments were observed. And the flat area of subsurface fatigue cracks similar to the fish-eye region increased with decreasing of the stress amplitude.