Deformation-induced martensitic transformation kinetics and correlative micromechanical behavior of medium-Mn transformation-induced plasticity steel

Abstract

An in situ high-energy X-ray diffraction (HE-XRD) technique was mainly used to investigate the micromechanical behavior of medium-Mn Fe-0.12C-10.16Mn-1.87Al (in wt%) transformation-induced plasticity (TRIP) steel subjected to intercritical annealing at 625 °C, 650 °C, 675 °C and 700 °C for 1 h. As the intercritical annealing temperature increased, the volume fraction of retained austenite (RA) and ultimate tensile stress (UTS) increased, while the Lüders strain and yield stress (YS) decreased. The incremental work-hardening exponent of experimental steel increased with increasing intercritical annealing temperature. The overall trend of the transformation kinetics of the RA with respect to the true strain followed the sigmoidal shape predicted by the Olson and Cohen (OC) model. Load partitioning occurred among the ferrite, austenite and martensite immediately after entering the yielding stage. Because the stability of the RA decreased with increasing intercritical annealing temperature, the load undertaken by the martensite increased. The moderate transformation kinetics of the RA and effective load partitioning among constituent phases were found to contribute to a favorable combination of strength and ductility for this medium-Mn TRIP steel.