Strengthening contributions of dislocations and twins in warm-rolled TWIP steels

A twinning-induced plasticity (TWIP) steel was processed by warm rolling with different reduction ratios to elevate yield strength while maintaining considerable ductility. To investigate the effect of prior warm rolling on the deformation mechanisms during subsequent tensile straining, the contributions of individual strengthening mechanisms to the tensile flow stress of the as-received (AR) and warm-rolled (WR) steels were decoupled, based on the measured dislocation density evolutions determined by synchrotron X-ray diffraction (XRD) experiments. Whereas dislocation multiplication invariably governs the maximum flow stress of the AR and WR steels, deformation twinning becomes increasingly important for the strain hardening of steels with larger warm rolling reductions. In addition, twinning kinetics is enhanced by the pre-existing high dislocation densities caused by warm rolling, leading to an enhancement of twinning-induced hardening. The present work provides further insight into the influence of warm rolling on the deformation mechanisms of TWIP steels.