Roles of (Fe, Mn)₃Al Precipitates and MBIP on the Hot Ductility Behavior of Fe–30Mn–9Al–0.9C Lightweight Steels

In the automotive industry, lightweight steel has received much attention because steel comprises a significant portion of a vehicle’s total weight. Fe–Mn–Al–C steel is a representative lightweight steel due to its high performance and low density. However, there is insufficient research into the welding characteristics of Fe–Mn–Al–C lightweight steels. In this study, hot ductility tests were conducted on austenitic Fe–30Mn–9Al–0.9C steel in order to understand the welding characteristics (cracking resistance) of the heat affected zone. During the on-heating thermal cycle, ductility was altered by a decrease in microband induced plasticity (MBIP) (softening) and an increase in dynamic recrystallization (DRX) (softening) as the temperature increased. Specifically, in the range of 773–1073 K, ductility was fairly degraded because neither MBIP nor DRX took place. During the on-cooling thermal cycle, ductility behavior was changed by both softening and hardening factors, including formation of brittle (Fe, Mn)₃Al intermetallic compounds with grain growth and re-solidified grain boundaries. However, the hardening effect of precipitated κ-carbide was insignificant and might not play a significant role in the hot ductility behavior of the lightweight alloy used in this study.