EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The use of bainitic steels in the steel industry has significantly increased over time due to their potential to combine high strength and high ductility. Therefore, modelling the complex microstructural transformation of bainite has been a topic of intensive research over the last years. Bainite occurs as upper and lower bainite, distinguished by the size and place of carbides precipitation. While there exist a considerable number of phase-field models to describe austenite-to-ferrite, austenite-to-pearlite and austenite-to-martensite transformations, the treatment of bainitic transformation has received less attention. This study presents a framework to describe the transformation from austenite to upper and lower bainite taking into account the displacive phase transition, different diffusion mechanisms, carbides precipitation and anisotropic growth of the phase fractions. The phase-field approaches, namely Ginzburg-Landau-type and Cahn-Hilliard-type are used to simulate the microstructure evolution on the mesoscale. A point of departure from existing works is the introduction of transformation strain tensor based on crystallography. Furthermore, plasticity induced by the displacive transformation from austenite-to-bainitic ferrite is also taken into account. Selected numerical examples which serve the purpose of evaluating the model qualitatively are presented at the end.