Evolution of mixed cementite morphologies during non-cooperative eutectoid transformation in Fe-C steels

We numerically investigate the characteristics of concurrent carbon redistribution pathways, as the ferrite- austenite front evolves during an isothermal eutectoid transformation starting from a random distribution of preexisting cementite particle. By analyzing the influence of initial interparticle spacing, arrangement and undercooling (below A(1) temperature) on the curvature-driven coarsening, we generalize the present criteria of non-cooperative eutectoid transformation. We also propose plausible mechanisms that result in mixed cementite morphologies (spherical and non-spherical) in the transformed microstructure. For the chosen set of parameters, the present phase-field simulations suggest a strong competition between the cooperative, non-cooperative and coarsening regimes, as the transformation proceeds. The predominance of one or more of the three regimes during the intermittent stages, which depend on the local conditions, determine the cementite size distribution in the transformed microstructure. (C) 2015 Elsevier B.V. All rights reserved.