Warm ductility of 0.2% C-1.5% Si-5% Mn TRIP-aided steel

Warm tensile properties of 0.2% C-1.5% Si-5.0% Mn transformation-induced plasticity (TRIP)-aided steel sheets with annealed martensite matrix and retained austenite of 39.4 vol% were investigated for automotive applications. The product of tensile strength and total elongation (TS×TEl) of the TRIP-aided steel was enhanced to 50 GPa% by warm deformation at 150 and 200 °C which is significantly higher than that (30 GPa%) required for third generation advanced high-strength steels. The thermal stability of the retained austenite was low, because the low stacking fault energy promotes the ε-martensitic transformation. The mechanical stability of the retained austenite, however, increased with an increase in the deformation temperature of the steel, because the ε-martensitic and the strain-induced α′-martensitic transformations were suppressed with increasing deformation temperature. Therefore, the high value of the TS × TEl of the steel subjected to warm deformation is principally associated with the high volume fraction of the retained austenite and its optimum metastability which maximizes the TRIP effect.