The prediction of the macrosegregation in large ingot is a challenging issue due to the size of the ingots and the variety of the phenomena to be accounted for, such as thermal- solutal convection of the liquid, equiaxed grain motion, evolution of grain morphology by suitably considering a coupled grain growth model in the
macroscopic solidification model, the columnar- to- equiaxed transition (CET), and shrinkage, etc.. Each of these phenomena is very important to the solidification pattern, while it is impossible for one model to consider all the
phenomena together until now due to the computation power limited. Thus, the model capability and computational cost should be counterpoised for the simulation of large ingot. In this work, a mixed three-phase (simplified dendritic-
equiaxed, columnar and liquid) solidification model is described based on Eulerian-Eulerian approach and volume
average method. The model considers the thermosolutal buoyancy flow, the movement of equiaxed crystal,
and the capture of the equiaxed crystals by growing columnar tree trunks. The mechanical interaction and impingement
between columnar and equiaxed crystals are considered which give the capability to predict CET. In order to
enhance the model capability without increasing the computational cost significantly, a simplified method is proposed to consider the dendritic of equiaxed crystal. This model is employed to simulate the formation process of macrosegregation for two different steel ingots (3.25 and 25 t). The general macrosegregation pattern predicted by this model includes the cone of negative segregation in the bottom of ingot, quasi-A-segregation in the columnar
zone, and positive segregation in the top region, which are quite similar to the classic knowledge. The CET zones are also predicted. Although there is still some quantitative discrepancy, the macrosegregation distribution predicted
by this model is quite similar to the experimental measurements. The non-globular equiaxed three-phase mixed model results are compared with the globular- equiaxed mixed three- phase model ones, which indicated that for
large ingots the equiaxed dendritic structure plays an important role in liquid flow and it affects final characteristic of macrosegregation. It is predicted successfully that a negative segregation zone would be formed in the upper region
due to the formation of a local mini-ingot and the subsequent sedimentation and piling up of equiaxed grains within the mini-ingot.