Simulation of lower bainitic transformation with the phase-field method considering carbide formation

Abstract

Lower bainite is a steel microstructure composed of austenite, ferrite and carbides within the ferrite. The transformation of austenite to lower bainite is one of the most complex transformations in steel. The carbon concentration of bainitic ferrite is of major importance for the carbide precipitation. A phase-field model to simulate the transformation of lower bainite including carbon diffusion and carbide formation is presented in this work. The model is based on a classical phase-field approach coupled with a viscous Cahn–Hilliard equation to simulate the separation of the carbon. During the isothermal simulation a sheaf of bainitic ferrite grows. The carbon starts to diffuse within the supersaturated ferrite which can only contain a fraction of the carbon which was stored in the austenite. At the accumulations of the carbon concentration carbides are precipitated. The simulations show successfully the described growth characteristics of the lower bainite transformation including carbide formation.