The Significance of Microstructure Evolution on Governing Impact Toughness of Fe–0.2C–8.5Mn–3Al Medium‐Mn TRIP Steel Studied by a Novel Heat Treatment

Abstract

Herein, the continuing challenge and scientific gap in obtaining high‐impact toughness in medium‐Mn steels are discussed. While addressing the challenge, the objective of the study described herein is to obtain a fundamental understanding via critical experimental analysis of the reasons underlying high‐impact toughness that is successfully obtained in Fe–0.2C–8.5Mn–3Al medium‐Mn transformation induced plasticity (TRIP) steel. This is enabled by a novel and effective heat treatment involving the combination of intercritical hardening and tempering to obtain high‐impact toughness. Electron microscopy and X‐ray diffraction studies clearly underscore the absence of TRIP effect in Fe–0.2C–8.5Mn–3Al medium‐Mn steel during impact and the volume fraction of austenite plays a determining role in governing impact toughness. The highest impact toughness of 255.96 J cm−2 is obtained when the steel is subjected to intercritical hardening temperature of 750 °C and low tempering temperature of 200 °C. The presence of martensite in the microstructure reduces the impact toughness on quenching from 800 °C. The fracture mode is ductile after intercritical hardening in the temperature range of 600–750 °C.