Study on high-cycle fatigue fracture mechanism and strength prediction of RuT450

Fatigue failure is the most common failure mode of structural materials. In this study, the high-cycle fatigue properties at different temperatures, fracture surface morphologies and corresponding damage mechanisms of a widely used vermicular graphite cast iron RuT450 were investigated. It is found that the fatigue strength values are 150 MPa, 143 MPa and 108 MPa for room temperature, 400 °C and 500 °C, respectively. The decrease rate of fatigue strength is affected by the change of morphology. At high temperature, the proportion of pearlite decreases and graphite becomes blunt. In general, the cracks initiate from the graphite phase boundary and propagate through the pearlite lamellae. In addition, according to the change of matrix micro-structure and crack growth processes under different temperature conditions, and by the quantitative analysis of micro-structure, the effect of temperature can be transformed into related parameters of matrix. Based on the changes, a fatigue strength prediction model for vermicular graphite cast iron at different temperatures was proposed, which predicts the trend well.