Correlation between strain rate sensitivity and characteristics of Portevin-LeChátelier bands in a twinning-induced plasticity steel

Abstract

The effects of strain rates on the deformation behaviors of a twinning-induced plasticity (TWIP) steel (Fe23Mn0.6C) have been investigated using uniaxial continuous tensile tests at different strain rates and strain-rate jump tests, coupled with digital image correlation (DIC) method. A positive instantaneous strain rate sensitivity (ISRS), a negative strain rate sensitivity of work hardening (SRSW) and a negative overall strain rate sensitivity (SRS) have been revealed in the present TWIP steel. The critical strain for appearance of Portevin-LeChátelier (PLC) bands increases while the height of serrated flow behaviors decreases with increasing strain rate, which indicates that the dynamic strain aging (DSA) effect is suppressed at higher strain rates. The strain concentration in PLC bands is found to be more severe at higher strain rates. Moreover, the appearance/disappearance of PLC band in strain-rate jump tests is found to be highly dependent on the deformation and microstructure evolution histories. Thus, the negative SRSW can be attributed to the higher strain concentration in the PLC bands and the restriction of DSA at higher strain rates, which are related to the suppression of deformation twins at higher strain rates.