Multi-phase field simulation of multi-grain peritectic transition in multiple phase transformation

Taking Fe-C binary alloy as an example, based on the multi-phase field model, the nucleation and growth of δ phase, peritectic reaction, peritectic transformation, and the growth of subsequent austenite are simulated. Effects of the nucleation site of austenite on the peritectic reaction rate and the starting time of the peritectic transformation were studied. The simulation results show that the γ phase, as a shell, surrounds the δ phase and grows rapidly when the peritectic reaction occurs between the dendritic δ grains, and a layer of γ phase shell is formed around δ phase after the peritectic reaction. After the δ phase is surrounded by γ phase completely, the membrane shell separates the L phase from the δ phase, so that the phase transfers from peritectic reaction to peritectic transformation. During the peritectic transformation, since the solute diffusion coefficient of the liquid phase is much greater than that of the solid phase, the average growth rate of austenite in the liquid phase is visibly higher than that of the δ phase. The peritectic reaction rate is related to the curvature of the nucleation site of the γ phase on the δ phase grains. The peritectic reaction rate at the large curvatures is faster than that at small curvatures.