Macrosegregation is a critical factor that limits the mechanical properties of materials. The impact of equiaxed crystal sedimentation on macrosegregation has been extensively studied, as it plays a significant role in determining the distribution of alloying elements and impurities within a material. To improve macrosegregation in steel connecting shafts, a multiphase solidification model that couples melt flow, heat transfer, microstructure evolution, and solute transport was established based on the volume-averaged Eulerian-Eulerian approach. In this model, the effects of liquid phase, equiaxed crystals, columnar dendrites, and columnar-to-equiaxed transition (CET) during solidification and evolution of microstructure can be considered simultaneously. The sedimentation of equiaxed crystals contributes to negative macrosegregation, where regions between columnar dendrites and equiaxed crystals undergo significant A-type positive macrosegregation due to the CET. Additionally, noticeable positive macrosegregation occurs in the area of final solidification in the ingot. The improvement in macrosegregation is beneficial for enhancing the mechanical properties of connecting shafts. To mitigate the thermal convection of molten steel resulting from excessive superheating, reducing the superheating during casting without employing external fields or altering the design of the ingot mold is indeed an effective approach to control macrosegregation.