Modeling of kinetics of austenite-to-allotriomorphic ferrite transformation in 0.37C-1.45Mn-0.11V microalloyed steel

The present article is concerned with the theoretical and experimental stud y of the growth kinetics of allotriomorphic ferrite in medium carbon vanadi um-titanium microalloyed steel. A theoretical model is presented in this wo rk to calculate the evolution of austenite-to-allotriomorphic ferrite trans formation with time at a very wide temperature range. At temperatures above eutectoid temperature, where allotriomorphic ferrite is the only austenite transformation product, the soft-impingement effect should be taken into a ccount in the modeling. In that case, the Gilmour et al. analysis reliably predicts the progress of austenite-to-allotriomorphic ferrite transformatio n in this steel. By contrast, since pearlite acts as a carbon sink, the car bon enrichment of austenite due to the previous ferrite formation is avoide d, and carbon concentration in austenite far from the alpha/gamma interface remains the same as the overall carbon content of the steel. Hence, the so ft-impingement effect should be neglected, and allotriomorphic ferrite is c onsidered to grow under a parabolic law. Therefore, assumption of a semi-in finite extent austenite with constant boundary conditions is suitable for t he kinetics of the isothermal decomposition of austenite. An excellent agre ement (higher than 93 pet in R-2) has been obtained between the experimenta l and predicted values of the volume fraction of ferrite in all of the rang es of temperature studied.