Austenite stability and deformation behavior in a cold-rolled transformation-induced plasticity steel with medium manganese content

We elucidate here the impact of grain size and manganese concentration on the austenite stability and the deformation behavior of a cold-rolled transformation-induced plasticity (TRIP) steel with a nominal chemical composition of Fe-11Mn-4Al-0.2C (wt.%). Intercritical hardening at 770 C led to a ferrite austenite mixed microstructure, which was characterized by an excellent combination of ultimate tensile strength of 1007 MPa and total elongation of 65% and a three-stage work-hardening behavior. The grain size was a critical factor in governing the stability of austenite and the optimal grain size for maximum stability was observed to be similar to 0.6 mu m. The superior mechanical properties are attributed to the discontinuous TRIP effect and the cooperative deformation of ferrite, where the discontinuous effect is a consequence of the non-uniform distribution of manganese, which is responsible for introducing varying degrees of stability in the austenite phase. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.