A new effect of retained austenite on ductility enhancement of low carbon Q-P-T steel

Abstract

A low carbon Fe-0.25C-1.48Mn-1.20Si-1.51Ni-0.05Nb (mass fraction, %) steel exhibits the combination of high tensile strength and good elongation after treated by a novel quenching-partitioning-tempering (Q-P-T) process. The variation in volume fraction of retained austenite in this steel with strain is measured by XRD, and the deformed twin-type martensite plates are also observed by TEM, from which the transformation induced plasticity (TRIP) effect in this steel is confirmed. Based on the measurement of average dislocation densities in both martensite and retained austenite combined with TEM observation, the effect of dislocation absorption by retained austenite (DARA) is found in the low carbon steel, similar to that in the medium carbon steel proposed recently, from which the generation conditions of DARA effect is proposed, and the mechanism of retained austenite on ductility enhancement of high strength steel is clarified. © Copyright.