A PHYSICAL CONSTITUTIVE MODEL FOR Fe-22Mn-0.6C TWIP STEEL BASED ON DISLOCATION DENSITY

Based on the evolution of dislocation density and volume fraction of twins, a physically based constitutive model of Fe-22Mn-0.6C twinning induced plasticity (TWIP) steel has been developed. By taking the influence of slip inside twins on the plastic deformation and the difference of the average Taylor factors between the twinned regions and matrix regions into account, the plastic strain at the representative element was presented as the weighted sum of matrix slip, twinning and slip in twinned regions in this model. A linear function between yield stress and strain rate with natural logarithm was established by considering the effect of strain rate on thermally activated stress. And then, The Euler method was adopted and the parameters of this model were obtained in order to describe as accurately as the experimental results. The results from the model are in good agreement with the experimental results and the average relative error is only 0.84%. Compared with the model free of slip and the model free of the difference of Taylor factor at twinned regions, the average relative error is reduced 1.1% and 2.9%, respectively. The interaction between two twins and the sliding mechanism and its impact on the macro-deformation were investigated. The results show that there is a negative correlation between gliding rate and twinning rate and slip rate decreases with the increase of twinning rate. When the twins become saturated, the twin rate decreases rapidly, being opposite to the slip rate. The yield stress increases and the rate of strain hardening remains approximately unchanged with the increase of strain rate.