A phase-field investigation of the effect of grain-boundary diffusion on austenite to ferrite transformation

We study the transformation of austenite to ferrite under the influence of Grain-Boundary (GB) diffusion. In order to simulate identical level of penetration of solute through GB as predicted by theory, diffusivity gradient at the boundary of a bulk austenitic domain is calibrated by numerical simulations. Applying a phase-field model for mixed-mode of transformation, it has been found that GB allotriomorph has a constant lengthening rate and the sharp tip of the allotriomorph displaces carbon due to its curvature. The accumulated solute has a significant effect on the thickening behaviour in terms of growth coefficient and exponent. We also discuss the morphological evolution of `perturbed' allotriomorphic ferrite.