Twinning and dynamic strain aging behavior during tensile deformation of Fe-Mn-C TWIP steel

Abstract

The twinning and dynamic strain aging(DSA) induced work hardening in Fe-Mn-C TWIP steel has been experimentally investigated in view of grain morphology, stress strain response, local strain rate(LSR) and strain hardening rate. A strain of 0.3 should be the critical value for the saturation of twined grains in Fe-Mn-C TWIP steel with 0.4–0.6wt% carbon and 18–22wt% manganese. DSA can occur in the very beginning of plastic deformation in Fe-Mn-C TWIP steel with the unpronounced fluctuation in stress strain response but obvious discontinuity in work hardening and LSR. The mechanism on strain hardening of Fe-Mn-C TWIP steel during tensile deformation can be distinguished by the variation of LSR. Twinning induced hardening rate is around 3.0GPa with a steady LSR, while DSA induced hardening rate is about 2.0GPa with a periodic and unstable fluctuation of LSR. There are mainly three stages in the work hardening of Fe-Mn-C TWIP steel divided by the inducing mechanism: twinning dominant, twinning+DSA dominant and DSA dominant. A strong correlation between the fluctuating characteristic of LSR and work hardening rate has been observed. In twinning dominant stage, they are largely steady; while in the other two stages, more significant fluctuation is observed where DSA is more pronounced for both curves. The serration in stress corresponds to the plateau in strain and low LSR, as well as the peak of strain hardening rate, due to the occurrence of DSA; and the smooth stress evolution between two serrations correlates the apparent increase of strain, and high LSR, together with the trough of strain hardening rate, relating to the preparation time for next DSA.