Deformation twinning and martensitic transformation and dynamic mechanical properties in Fe–0.07C–23Mn–3.1Si–2.8Al TRIP/TWIP steel

In the study described here, we have explored the evolution of microstructure and mechanical properties in Fe–0.07C–23Mn–3.1Si–2.8Al steel with a stacking fault energy (SFE) in the intermediate range of 15–20 mJ m−2 during dynamic deformation and in the strain rate range of 101–103 s−1. The results showed that the transformation induced plasticity (TRIP) effect and twinning induced plasticity (TWIP) effect coexist during dynamic deformation. The mode of austenite-to-martensite transformation is γ→ε, ε→α′. With increase in the strain rate, the volume fraction intermediate ε-martensite was increased and α′-martensite remained nearly constant, and the frequency of the intersecting deformation twins was also increased. This behavior of steel was responsible for a good combination of ultimate tensile strength of 913 MPa and total elongation of 75.4% at a strain rate of 103 s−1. The strength and elongation increased significantly with an increase in strain rate in the range of 101–103 s−1. The dominant plasticity enhancing mechanisms with increase in strain rate were strain-induced intermediate ε-martensite and intersecting deformation twins.