A study on microstructure and toughness of copper alloyed and austempered ductile irons

In this study, ductile irons with and without 1 wt% copper alloy were austempered to become austempered ductile irons (ADIs). Microstructure, impact toughness, and fracture toughness were evaluated to determine how both the copper alloying and austempering treatments influenced the toughness properties of ductile irons. The results show that, because copper increases the retained austenite content in ADI, the Cu-alloyed ADI has better impact toughness and fracture toughness (KIC value) than does the unalloyed one. In particular, the impact toughness and the fracture toughness of ADI could be efficiently improved by treating the Cu-alloyed ductile iron at a higher austempering temperature (360 °C) to obtain more retained austenite in its microstructure.

► Austempered ductile iron (ADI) with 1 wt% copper addition could increase the retained austenite content in its microstructure.
► The fracture toughness (KIC value) and impact toughness properties of ADI depend on the content of retained austenite.
► For ADI, the correlation between the KIC value and the impact toughness seems to reveal a line proportion.