Tensile deformation behavior analysis of low density Fe-18Mn-10Al-xC steels

Three low density Fe-18Mn-10Al-xC steels containing 0.5, 0.8 and 1.2 C (wt%) were utilized to investigate the differences in microstructures and their influence on mechanical behaviors during plastic deformation. The 0.5C steel had a duplex ferritic-austenitic structure and the fraction of austenite was ~59.2%, while the fraction of austenite was ~84.8% for the 0.8C steel and some ordered phases existed in both ferrite and austenite. In contrast, a fully austenitic microstructure with some κ carbides was achieved in the 1.2C steel. Due to the existence of the ordered phases by the addition of C from 0.5% to 0.8%, the 0.8C steel exhibited a highest tensile strength of ~979 MPa, and a moderate strain hardening capacity. The 1.2C steel revealed a superior combination of strength and ductility (ultimate tensile strength of 946.7 MPa and elongation to failure of 56%), with a much more pronounced strain hardening than the other two steels. The differential Crussard-Jaoul (C-J) analysis demonstrated a two-stage strain hardening behavior in both 0.5C and 0.8C steels, while a three-stage one in the 1.2C steel. This difference in strain hardening behavior was further understood in terms of microstructural analysis at the different stages of plastic deformation.