Fatigue strength of spheroidal graphite cast iron at elevated temperatures under axial load

Abstract

Axial-load fatigue tests ( R=0.1) and static tensile tests were performed on as-cast and heat-treated materials of spheroidal graphite cast iron from room temperature to 500°C. The macroscopic and microscopic observations of fatigue-fracture surfaces of the specimens were carried out using scanning electron microscopy (SEM) to interpret the fatigue strength data. The tensile strength at elevated temperatures decreased with the elevation of the testing temperature. However, remarkably, the effects of normalizing and austempering heat treatments were noticed. The fatigue strength decreased as the testing temperature was elevated, which is the same behaviour as for the tensile strength, but the effect of heat treatment was noticed very slightly. The fatigue limit at 500°C for bainitized material was σ u = 92 MPa and for annealed material σ u = 77 MPa. Fatigue cracks appeared from internal defects such as small-shrinkage cavities. Therefore, it is considered that heat treatment does not affect the fatigue strength significantly.