The influence of lattice strain on pearlite formation in Fe–C

The effect of stress and strain on the transformation kinetics of pearlite is investigated by phase-field simulation. Strain is considered in terms of expansion/contraction during transformation and due to concentration gradients in austenite. It is demonstrated that due to the concentration dependence of the eigenstrain, an inhomogeneous stress distribution ahead of the transformation front enhances diffusion in the austenitic phase and reduces chemical supersaturation in both austenite and ferrite. The main result of the investigation is that transformation strain inhibits the cooperative growth mode of cementite and ferrite, as considered by the Zener–Hillert model, and provokes the salient growth of cementite needles ahead of the ferrite front, which we call “staggered growth”. The predicted growth velocities give the right order of magnitude compared to the experiment and close the gap between theoretical models based on diffusion only, and experimental observations.