Interaction of MnS inclusion behaviors and macrosegregation during solidification by multi-phase modelling

Manganese sulfide (MnS) is an important kind of non-metallic inclusion in steel which precipitates at the final stage of solidification and greatly affects the properties of steels. Plenty models have been developed to simulate the dynamics of MnS during solidification, while few considered its effects on macrosegregation formation in return. Here a four-phase model has been developed to couple the formation and growth mechanisms of MnS with the evolution of macrosegregation during the solidification. Classical nucleation theory and a diffusion-governed growth model are applied to illustrate the behaviors of MnS. The nucleation and growth of inclusions are fully coupled with a columnar-equiaxed ternary alloy (Fe-C-Mn) solidification model. The model simulates the nucleation and growth of equiaxed crystal, the sedimentation of equiaxed crystal, the growth of columnar dendritic trunks, thermo-solutal convection of the melt and solute transport in a benchmark case. The prediction of MnS is verified reasonably by comparison with many experimental results in perspectives i.e., volume fraction, diameter, criteria of precipitation and so forth. The effects of inclusion on macrosegregation and preferential formation location of MnS are further discussed in detail. The critical condition of such inclusion precipitate is proposed based on various S concentration.