Fracture toughness characterization of austempered ductile iron produced using both conventional and two-step austempering processes

The aim of the present study is to characterize mainly fracture toughness as well as the other mechanical properties of austempered ductile iron produced using both single-step and two-step austempering processes. The effect of alloying with Ni and Mo has been investigated. Austempering heat treatment was conducted at temperatures between 260 °C and 390 °C. Plane strain fracture toughness was evaluated for each material and heat treatment condition. It was found that two-step austempering process resulted in improving the fracture toughness of the material, while maintaining reasonable levels of strength. Alloyed samples showed higher fracture toughness than un-alloyed ones.