Effect of deformation twin on mechanical properties of a lean manganese twinning induced plasticity (twip) steel deformed at quasi-static strain rates

The high Mn (≥25 wt%) TWIP steels with low stacking fault energy are currently one of the most attractive materials in the automotive industry due to their unique combination of high strength and good ductility. However, the conventional manufacturing processes have many problems with alloying high Mn. Therefore, many efforts are being made to reduce the Mn content, but the steels could not have an appropriate stacking fault energy SFE for twinning with decreasing Mn content. In this study, TWIP steel with lean Mn less than 20 wt% (Fe-18Mn-1.5Al-0.6C) was made. Tensile properties of the lean 18 Mn TWIP steel were measured at a strain rate range of 10^-4s^{-1 ≤}ε ≤ 10¹s^-1o investigate the correlation between twinning behavior and stress at various strain rates. The lean 18 Mn TWIP steel possessed an austenite single phase before and after tensile tests at room temperature and exhibited a total elongation of about 60% and ultimate tensile strength of about 1000 MPa by strain-induced twinning. The stress decreased with an increasing strain rate, showing a negative strain rate sensitivity. That was because the volume fraction of twinned grains decreased with an increasing strain rate at the same strain. Stress was directly related to the volume fraction of twinned grains at quasi-static strain rates.