Strain rate effects on tensile deformation behaviors for Fe-22Mn-0.6C-(1.5Al) twinning-induced plasticity steel

In this study, the effect of strain rate on the tensile deformation behavior of Fe-22Mn-0.6C-(1.5Al) (wt%) twinning-induced plasticity (TWIP) steel was investigated. The experimental results indicated that the work hardening exponent (n), ultimate tensile strength (σu) and the uniform elongation (δu) decreased with increasing strain rates (from 10−4 to 100 s−1). This phenomenon exhibited negative strain rate sensitivity (NSRS), and the strain rate sensitivity value (m) was observed to be higher in the aluminum added FeMnC TWIP steel. In order to gain an in-depth understanding of this sensitivity and the subsequent effect of aluminum, the present research focused on the deformation twins and conducted comparative studies on their influence in terms of fractions (F), thickness (t) and spacing (s). Additionally, a twin boundary affected zone (TBAZ) model was proposed, where the relation between higher strain rates were directly applicable to the reduction of interfaces between the matrix and deformation twins. These result indicated that fewer sessile dislocations could be accommodated at high strain rates, thus weakening the work hardening ability. Finally, model calculations were performed to validate the findings, where TBAZ region fractions in FeMnC-Al were observed to be higher than that in FeMnC, corresponding to the increased strain rate sensitivity.