Enhancement of strength-ductility combination in recovery-annealed Fe-Mn-C twinning-induced plasticity steels by Si alloying

Deformation and recovery annealing is a simple metallurgical way to obtain higher yield strength and higher strain hardening in Fe-Mn-C based twinning-induced plasticity (TWIP) steels by introducing nanoscale mechanical twins. The decreased ductility of below 20% limits the application of recovery-annealed TWIP steels. We proposed that carbide precipitations were responsible for the decreased ductility. To address the carbide-induced lower ductility in the recovery-annealed TWIP steels, an Fe-16.5Mn-1.1C-2.2Si steel (in wt%) was designed based on the fact that the addition of Si can suppress carbide precipitation by reducing carbon diffusivity. Our results showed that the Fe-16.5Mn-1.1C-2.2Si steel had a better combination of ductility (39%) and yield strength (962 MPa) after 30% tensile deformation and subsequent recovery annealing at 673 K for 1 h. Microstructural observation revealed that Si addition not only prevented the carbides precipitation during the recovery annealing but also promoted the occurrence of mechanical twins. The recovery annealing combined with Si alloying, which realizes the function of suppressing the carbides precipitation will be a direction for obtaining a better strength-ductility combination in the Fe-Mn-C based TWIP steels by exploiting the mechanical induced nanoscale twins.