As part of an ongoing development of third-generation advanced high-strength steels with acceptable cost, austenite reversion treatment of medium Mn steels becomes attractive because it can give rise to a microstructure of fine mixture of ferrite and austenite, leading to both high strength and large elongation. The growth of austenite during intercritical annealing is crucial for the final properties, primarily because it determines the fraction, composition, and phase stability of austenite. In the present work, the growth of austenite from as-quenched lath martensite in medium Mn steels has been simulated using the DICTRA software package. Cementite is added into the simulations based on experimental observations. Two types of systems (cells) are used, representing, respectively, (1) austenite and cementite forming apart from each other, and (2) austenite forming on the cementite/martensite interface. An interfacial dissipation energy has also been added to take into account a finite interface mobility. The simulations using the first type of setup with an addition of interfacial dissipation energy are able to reproduce the observed austenite growth in medium Mn steels reasonably well.

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This work studies the microstructure and tensile properties of a cold-rolled Fe–0.20C–4.86Mn (mass %) steel after short intercritical annealing (IA) times using scanning and transmission electron microscopy, and uniaxial tensile tests. The short IA time is applied to represent the process characteristics of the industrial continuous annealing line. The experimental results show that IA temperature has a strong influence on the final microstructure and tensile properties while IA time has less. The fractions of retained austenite are much higher after IA at 650 and 675°C than the other IA temperatures, and thus improving elongation. Simulations using the DICTRA software and constitutive modelling are further performed to assist the understanding of the microstructure evolution and stress–strain curves.