Numerical Simulation of A-Segregation Evolution in a 55-Ton Ingot Using Four-Phase Solidification Model

A four-phase solidification model is introduced to comprehensively investigate the formation of macrosegregation, especially the A-segregation during the solidification of a 55-ton ingot (Fe-3.3 wt pct C). The model considers the simulations of melt convection, shrinkage, dendritic equiaxed grains nucleation and sedimentation, and competitive growth of solid phases, etc. The final patterns of macrosegregation, especially the A-segregation, fit well with experimental results including the characteristics and location. The results show that the A-segregation always exists close to the columnar-to-equiaxed transition zone, which results from the melt flow collision occurring in the triangle area of the mushy zone that composed dendritic equiaxed grains zone, liquid zone, and columnar and equiaxed crystals mixed zone. In addition, the A-segregation evolves with the changing of the columnar-to-equiaxed transition zone, which indicates that the A-segregation occurrence has a correlation with the columnar-to-equiaxed transition zone in large-scale ingots.