Thermo-kinetic design of retained austenite in advanced high strength steels

Design of metastable retained austenite has been one of the most key issues in the development of advanced high strength steels (AHSSs) as mechanical properties of AHSSs are directly linked to the amount of retained austenite and its stability. In the past decades, several approaches, e.g. isothermal bainitic transformation, quenching & partitioning, austenite reversion transformation et al. have been successfully proposed to obtain retained austenite in the AHSSs. However, up to now, optimization of alloy composition and processing parameters in the above approaches is primarily by trial and error experiments or thermodynamic calculations. In this study, an integrated thermo-kinetic computational model, in which thermodynamics-kinetics of phase transformations and alloying elements partitioning are carefully considered, is used to design multi-phase microstructure of AHSSs with an emphasis on retained austenite. The current model is benchmarked by a comparison with the available experimental data for the conventional transformation-induced plasticity and quenching & partitioning steels, and the effects of alloy composition and processing parameters on the amount of retained austenite and its composition will also be discussed. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.