An analytic approach to the effect of anisotropic growth on diffusion-controlled transformation kinetics

The effects of the anisotropic growth and soft-impingement (SI) on the kinetics of diffusion-controlled (DC) transformation are investigated. An analytic approach to describe the kinetics of DC transformation subjected to anisotropic effect is presented, assuming pre-existing nuclei, one-dimensional growth, and linear approximation of concentration gradient. The anisotropic effect and SI effect are evaluated from the varying Avrami exponent. SI effect only occurs at the last stage of transformation, although anisotropic effect broadens its range. This approach is applied to predict the isothermal thickening of ferrite layer in Fe–0.17 wt% C alloy at 973 K and isothermal transformation of austenite to allotriomorphic ferrite in 0.37C–1.45Mn–0.11V microalloyed steel at 913 K; good agreements are achieved.