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.

In-mould electromagnetic stirring (M-EMS) is a widely used technique during continuously casting (CC). To investigate the M-EMS effect on the inclusion motion and entrapment in a billet CC mould, a coupling mathematical model was developed. The result indicates that the M-EMS changes molten steel flow pattern and transient inclusion distributions in the mould. Inclusions have a tendency to move close to the mould centre under M-EMS. When the M-EMS is off, the distributions of inclusions in the solidified shell is relatively uniform. When the M-EMS is applied, many inclusions are entrapped near the stirrer mid-plane. Furthermore, distances of captured inclusions below the billet surface become larger. Additionally, the M-EMS has a significant effect on the overall removal fraction of inclusions. At last, detection of inclusions in samples obtained from a plant has been performed. A similar tendency can be found between the predicted and experimental results.

To investigate the gas agitation characteristics of side blowing, the fluid flow and mixing phenomenon in a 1:3 scale model ladle of a 150 t industrial gas-stirred ladle with bottom and side plugs were studied by using physical and numerical modelings together. Side blowing enhanced the horizontal flow of water in the model ladle. Compared with bottom blowing, side blowing that is close to the ladle bottom with more than two plugs increases the average velocity of water, which represents the agitation power, improves the uniformity of water velocity distribution, reduces the stagnant region rate, and shortens the mixing time. The mixing time of dual bottom plugs is almost 1.5 times of that of four side plugs at 116 mm under the same flow rate. The mixing time is not only influenced by the agitation power but also by the uniformity of water velocity distribution. Although the agitation power of four side plugs at 450 mm under the flow rate of 1.8 m³/h is about 1.5 times of that at 116 mm with 0.6 m³/h. The mixing time of the 1.8 m³/h flow rate is about 1.2 times of that of the 0.6 m³/h because of the different water velocity distributions.

In-mould electromagnetic stirring (M-EMS) is a widely used technique during slab continuous casting. To investigate the effect of M-EMS on the flow and initial solidification in a slab mould, a three-dimensional model coupling electromagnetic field, flow and solidification was developed. To track the steel/slag interface, the volume of fraction (VOF) model was coupled in the model. The electromagnetic force presents a centrally symmetrical distribution on the cross-section. The influences of stirring current and stirrer position on flow, initial solidification and level fluctuation have been discussed. M-EMS enhances the transversal flow and shrinks the lower recirculation in mould. The results indicate that both a higher stirring current and a lower stirrer position produce a reduction of the temperature in the mould centre. Furthermore, a higher stirrer position and a lower stirring current are favourable to the solidified shell growth. However, M-EMS aggravates the level fluctuation, which may lead to slag entrainment.