A cellular automaton model for austenite to ferrite transformation in carbon steel under non-equilibrium interface conditions

Abstract

The isothermal decomposition of austenite into ferrite is investigated using a two-dimensional cellular automaton (CA) algorithm. This CA model provides a simple solution for the difficult moving boundary problem that governs the ferrite grain growth. In this model, the growth of ferrite grains is controlled by both the austenite–ferrite (γ–α) interface mobility and the carbon diffusion in the retained austenite. The competition between the γ–α interface dynamics and the carbon diffusion in the austenite results in a non-equilibrium γ–α interface condition. In order to predict the growth kinetics of ferrite grains, the carbon diffusion coupled with the γ–α interface dynamics is resolved numerically. The driving force for the γ–α interface mobility is calculated using a regular solute sub-lattice model. The kinetics of ferrite transformation predicted by this CA method is compared with that of a JMA model and experiments in the literature. The simulation provides an insight into the carbon diffusion in austenite and the microstructure evolution during transformation. Meanwhile, the results also show that the γ–α interface under the present non-equilibrium condition is numerically stable in two dimensions and the simulated morphology of the ferrite grains is an almost equiaxed polygon.