Effects of Partial Replacement of Si by Al on Impact Toughness of 0.2%C-Si-Mn-Cr-B TRIP-Aided Martensitic Steel

Abstract

The effects of partial replacement of Si by Al on the microstructure, tensile properties, and Charpy impact toughness were investigated using 0.2%C-Si/Al-Mn-Cr-B TRIP-aided martensitic steels to promote the application of galvanized third-generation ultrahigh- and high-strength steels. The impact toughness was related to the microstructural and mechanical properties. The partial replacement decreased the volume fraction of retained austenite and increased the mechanical stability, accompanied by softening and an increase in the volume fraction of the primary martensite. Resultantly, the partial replacement decreased strength and ductility. The impact absorbed energy (value) at 25 °C was slightly increased by the partial replacement. The increased impact absorbed energy was mainly caused by high crack/void propagation energy due to the softened primary martensite and a small contribution of the stabilized retained austenite. The 50% shear fracture ductile-to-brittle transition temperature was marginally raised by the partial replacement. The raised transition temperature was mainly associated with an increase in a unit crack path of quasi-cleavage/cleavage fracture.