Influence of carbon addition on mechanical properties of Fe–Mn–C twinning-induced plasticity steels

Mechanical properties and microstructural evolution of Fe–22Mn–0.6C and Fe–22Mn–1.0C (wt.%) twinning-induced plasticity (TWIP) steels were investigated by monotonic, stress-relaxation and unloading–reloading tensile tests. The dynamic strain aging (DSA) effect, resulting from pinning of dislocations, effectively improved the dislocation activation volume of the two TWIP steels. In the meanwhile, DSA-facilitated twinning nucleation mechanism kept similar twinning capabilities of the two TWIP steels. With strain increasing, the formation of high-density deformation twins restricted the dislocation motion and reduced the activation volume with increasing strain. Furthermore, C addition simultaneously improved the ultimate tensile strength and uniform elongation, and significantly enhanced the friction stress, rather than back stress. The stronger short-range order effect, brought by friction stress, promotes the planar dislocation slipping, thus improving the work-hardening capability. As a result, the additional work-hardening capacity can be achieved in Fe–Mn–C with higher C addition.