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 773-1073K, 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)(3)Al intermetallic compounds with grain growth and re-solidified grain boundaries. However, the hardening effect of precipitated kappa-carbide was insignificant and might not play a significant role in the hot ductility behavior of the lightweight alloy used in this study.