Cross-scale simulation for MnS precipitation of Fe-C alloy with cooling rate variation

The cooling rate is a key factor controlling casting solidification, which determines the microstructure and performance of a metal and inevitably affects the formation of inclusion in steel. MnS is a common inclusion in Fe-C alloy, and it is indispensable to determine the variations in MnS precipitation with respect to the solidification conditions. This work develops a cross-scale cellular automaton-finite difference (CA-FD) model to simulate MnS precipitation in two Fe-C-Mn-S systems, Fe-0.6%C-0.8%Mn-0.005%S (High-Mn) and Fe-0.6%C-0.2%Mn-0.02%S (High-S) with the constant factor of concentration product of elements Mn and S. The model divides the simulated area into three different grid sizes to calculate the macroscopic heat transfer, mesoscopic matrix growth and microscopic MnS precipitation. The results show that most of the MnS precipitates occur within regular belt-shaped regions in the solidified matrix. The cooling rate has a significant effect on MnS precipitation in the belt-shaped regions by affecting the matrix solidification and solute concentration in the liquid phase. High cooling rates delay MnS precipitation and reduce the number of precipitates, which narrows the belt-shaped regions and increases the number of precipitate per unit of belt area (N-ave). Reprecipitation was observed in the High-Mn system, and the reprecipitation decreases with the increase of cooling rate.