Interactions of negative strain rate sensitivity, martensite transformation, and dynamic strain aging in 3rd generation advanced high-strength steels

Abstract

Medium Mn transformation-induced plasticity (TRIP) steels, a subgroup of third generation advanced high-strength steels (AHSS), often present a combination of both dynamic strain aging (DSA) and TRIP. It has been previously shown that TRIP coincides with the passage of strain bands due to DSA, but their interdependence has not been well-established. This study seeks to explore the interactions between the two phenomena as well as the commonly-observed negative strain rate sensitivity. Digital image correlation (DIC) and in-situ magnetic measurements of the retained austenite fraction were employed to demonstrate the variations in mechanical behavior with increasing strain rate. Strain rate jump tests provided measurements of the strain rate sensitivity and were combined with either DIC to characterize PLC bands or with magnetic measurements to measure variations in the martensite fraction during the jumps. Finally, the micromechanics defining the peculiar bursts of martensite transformation in response to strain rate jumps are discussed in terms of a competition between dislocation mobility and austenite stability.