A semi-physical α-β model on bainite transformation kinetics and carbon partitioning

A semi-physical kinetic model with two adjustable parameters is proposed for prediction of the isothermal bainite transformation and carbon redistribution in steels. The model incorporates the evolution equation of the carbon concentration in bainite, employing the Fermi-Dirac statistic function, and it can phenomenologically capture the evolution of carbon contents of bainite sheaves and the carbon enrichment in the residual austenite. The parameter α reflects the probability for carbon atoms to escape from bainite sheaves into the surrounding bulky austenite, while the parameter β describes the potential for bainite to contribute to the carbon enrichment in bulky austenite. The influence of α on the kinetics of the bainite transformation is explained on the basis of carbon diffusion and carbon trapping, which show a significant temperature dependence. The present model, with its combined adjustment of α and calibrated β, is capable of reproducing the experimental kinetics of bainite transformation for a variety of different steels.