Non-equilibrium transformation kinetics and primary grain size distribution in the rapid solidification of Fe–B hypereutectic alloy

Considering nucleation, growth and impingement, a numerical model was proposed to describe the transformation kinetics of rapid solidification in bulk undercooled Fe–B hypereutectic alloy. Applying heat balance and solute conservation, the changes of temperature and composition of residual liquid are proved to be not only dependent of time, but also associated with the solidified fraction during the transformation. Accordingly, the driving force for non-equilibrium solidification, as well as the determined nucleation and growth rates, decreases with the process of transformation. On this basis, the primary grain size distribution formed in this process can be predicted with the combination of classical Kolmogorov–Johnson–Mehl–Avrami (KJMA) equation and a probability statistic analysis. Good agreement between the model prediction and experimental results has shown the validity of the proposed model.

Research highlights▶ Quantitative calculations of nucleation and growth rates were performed. ▶ Primary transformation kinetics of bulk undercooled liquid is time-dependent. ▶ Transformation rate increases firstly and then decreases after reaching peak point. ▶ Primary grain size distribution formed in this process can also be predicted.