Stress-induced martensitic transformation and impact toughness of cast irons and high-carbon Fe-Ni-C steel

The relationship between the impact toughness and stress-induced martensiti c transformation, which occurs during the impact process, has been studied in white cast irons and an Fe-Ni-C alloy at different temperatures. The exp erimental results have shown that in the brittle white cast irons, the stre ss-induced martensitic transformation makes a positive contribution to the impact toughness, and lowering the stability of austenite increases the tou ghness. In contrast, the transformation makes a negative contribution to th e toughness of high-carbon austenitic steels, and lowering the stability of austenite decreases the toughness. The present work supports the early the ory([1]) that the magnitude of the toughness change depends on the fracture properties of the new phase and the energy being dissipated during the tra nsformation process. Using the crystallographic model for the stress-induce d martensitic transformation, which was originally developed in ceramics an d was then refined and extended to irons and steels, the effect of the stre ss-induced martensitic transformation on the impact toughness can be predic ted.