The effect of matrix structure on the fatigue behavior of austempered ductile iron

The primary objective of this study has been to investigate the fatigue behavior of the austempered unalloyed ductile iron. Ductile iron specimens were austenized at 900 °C for 110 min and then one group specimens were austempered at 230, 330, 430 °C for 60 min, and another one group specimens were austempered at 330 °C for 30, 60, 120 min to obtain different microstructures. Rotating bending tests (10 million cycles) were conducted on the ductile iron and the austempered specimens selecting completely reversed cycle of stress (R = minimum stress/maximum stress = −1). The highest fatigue strength was found in the bainitic structure (ausferritic). The presence of martensite or carbide phases in the structure of austempered ductile iron reduces the fatigue strength.