Influence of cooling conditions and amount of retained austenite on the fracture of austempered ductile iron

SEM Analysis of fracture surfaces from tensile test specimens of thick-walled, austempered ductile irons (diameter 160 mm) shows different fra- cture behavior depending on the austenite retained in the matrix. The results show ductile fractures only in areas containing retained austenite sections. In section areas without or with a very low content of retained austenite, only brit- tle fracture without any plastic deformation occurs. The content of retained au- stenite determines the amount of ductile fracture in the microstructure.