Fatigue strength optimization of gray cast iron processed by different austempering temperatures

Abstract

It is generally accepted that the mechanical properties of gray cast iron (GCI) can be enhanced by microstructure refinement, while this perhaps needs to be reconsidered to improve the fatigue properties treated by austempering technology. Although the maximum tensile strength can be up to 480 MPa for austempered gray iron (AGI) with finer bainite fabricated by austempering transformations, the value of fatigue strength is less than the coarse counterpart with lower tensile strength. This suggests that tensile strength can be effectively improved by microstructure refinement, while fatigue cannot. It is mainly attributed to the initial defects induced by graphite and the structural toughness increased by austenite in AGI. Therefore, the general relationship between tensile strength and fatigue strength of GCI and AGI was investigated and the roles of fitting parameters were analyzed. The inverted relation provides some new insights into the fatigue strength optimization of GCI.