Abstract
Macrosegregation, serving as a major defect in billets, can severely degrade material homogeneity. Better understanding of the physical characteristics of macrosegregation through numerical simulation could significantly contribute to the segregation control. The main purpose of this study was to predict macrosegregation in continuously cast billets with a newly developed three-dimensional macrosegregation model. The fluid flow, solidification, and solute transport in the entire billet region were solved and analyzed. Flow patterns, revealing a typical melt recirculation at the upper region of mold and thermosolutal convection at the secondary cooling zone, significantly affect the solidification and solute distribution. The solute redistribution occurring with thermosolutal convection at the solidification front contributes significantly to continued macrosegregation as solidification proceeds. The results of this study show that the equilibrium partition coefficient is mostly responsible for the magnitude of macrosegregation, while comparison between solute P and S indicated that diffusion coefficients also have some amount of influence. Typical macrosegregation patterns containing a positively segregated peak at the centerline and negatively segregated minima at either side were obtained via the proposed three-dimensional macrosegregation model, which validated by the measured surface temperatures and segregation degree.
Highlights
Macrosegregation is one of the major defects in continuously cast billets, especially for high-carbon steel
Flemings et al [3] first discovered the importance of convection within the mushy zone during alloy solidification and proposed the Local Solute Redistribution Equation (LSRE) to numerically study the macrosegregation caused by interdendritic flow
A 3D macrosegregation model containing both the low Reynolds number k − ε turbulence model and Voller–Beckermann microsegregation model was developed in this study based on the model and Voller–Beckermann microsegregation model was developed in this study based on the continuum model proposed by Bennon and Incropera
Summary
Macrosegregation is one of the major defects in continuously cast billets, especially for high-carbon steel. It can severely degrade material homogeneity and affect the final properties and performance of billet-based products. Macrosegregation is known as the main cause of cup fracture during wire cord drawing due to the formation of martensite and carbide networks [1]. Flemings et al [3] first discovered the importance of convection within the mushy zone during alloy solidification and proposed the Local Solute Redistribution Equation (LSRE) to numerically study the macrosegregation caused by interdendritic flow. The flow of interdendritic liquid was modeled with a fixed dendritic solid network ignoring the effect of mushy zone. Mehrabian et al [4]
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