A macrosegregation model, coupling fluid flow, heat and solute transport model, was developed based on continuum model to predict the evolution of macrosegregation in continuous round billet casting, as well as the influence of microsegregation model choice on prediction of macrosegregation. Evolution and characteristics of macrosegregation corresponding to predicted solidification were revealed. As solidification proceeds, solutes are ejected from solid phase to liquid at solidification front. The resulting mushy zone is enriched by solutes, due to the low velocity and limited diffusion, which produces segregation at the billet center as the liquid available for dilution diminishes near the end of solidification. Predicted and experimental results for surface temperature and centerline segregation compare agreeably, which indicates the validity of the coupled macrosegregation model in this work. A detailed analysis was performed to investigate the influence of microsegregation model on prediction of macrosegregation, demonstrating that choice of model affects predicted segregation degree of solutes, which effect varies with type of solute, due to the solute back-diffusion coefficient.
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