Fatigue strength optimization of compacted graphite cast iron processed by austempering process

The fatigue property optimization of compacted graphite cast iron (CGI) by the austempering process was investigated. The austenitizing at 850 °C firstly then austempering at 280 °C and 370 °C respectively were selected. The tensile and fatigue properties and corresponding damage mechanism of the CGI and austempered CGI (ACGI) samples were carried out. The highest fatigue strength of 221 MPa for CGI materials was obtained by austempering at 370 °C. The fatigue strength decreases first and then increases in CGI and ACGI samples with the increase of austempering temperature. The general relation between the tensile and fatigue strength of CGI was further investigated. The corresponding physical significance in the relations was proposed based on the different defect morphologies in cast iron alloys, which provides implications for understanding the relation between metal fatigue and tensile strength and optimizing fatigue properties.