Tensile deformation behavior related with strain-induced martensitic transformation in a duplex Fe-Mn-Al-C low-density steel

The tensile deformation behavior of a duplex Fe-Mn-Al-C low-density steel with a structure of banded ferrite and austenite has been studied in the present work. The steel exhibits a good strength-ductility match and a typical three-stage deformation behavior, under the joint contributions of transformation-induced plasticity (TRIP) effect, twinning-induced plasticity (TWIP) effect and dislocation slipping. Even though the steel has a stacking fault energy of 53 mJ∙m−2 that is suitable for the TWIP effect, it just worked at the final deformation stage. The TRIP effect played an important role during the majority of deformation process except at an initial stage, and the austenite was dramatically consumed at the later stage. This is mainly determined by an unnormal stability of austenite. For estimating the austenite stability, the relationship between the critical size of austenite grain (Dcrit) and critical temperature for strain-induced transformation (Msσ) was established. The calculated Dcrit of 12 μm reflects that the strain-induced martensitic transformation dominates the TRIP effect in the duplex steel.