Numerical modelling of macrosegregation and shrinkage in large diameter steel roll castings: a mould study

Minimising macrosegregation and shrinkage defects during uphill teeming of medium carbon roll ingots has always presented a major technical challenge. Process improvements have been achieved by balancing the total heat input of a cast roll and the rate of heat extraction from the roll surface. Injecting dilute alloy through a submerged entry nozzle (SEN) into the net shaped roll ingot further mitigated the undesirable consequences of solute enrichment especially at the ingot centreline. Both the centreline segregation problems and midradius channel segregates can be significantly minimised, by combining these techniques. The objectives of this study are to determine the effect of mould thickness and material type (steel versus cast iron) on the centreline and especially on the midradius segregation, the solidification behavior in the transition region between the outer shell and the diluted interior region, as well as the mould durability. To accomplish these objectives, a multiphase multicomponent computational fluid dynamics (CFD) code was developed for studying the macrosegregation and shrinkage under various casting conditions for a 65 tonne, 1.6 m diameter steel roll processed via SEN. The developed CFD framework consists of solving for the volume fraction of phases (air and steel mixture), temperature, flow and solute balance in multicomponent alloy systems.