Modeling of steel grade transition in continuous slab casting processes

Abstract

Mathematical models have been developed and applied to investigate the composition distributions that arise during steel grade changes in the continuous slab casting processes. Three-dimensional turbulent flow and transient mixing phenomena in the mold and the strand were calculated under conditions corresponding to a sudden change in grade. The composition distribution in the final slab was then predicted. Reasonable agreement was obtained between predicted and experimental concentration profiles in the slab centerlines. Intermixing in the center extends many meters below the transition point while intermixing at the surface extends above. Higher casting speed increases the extent of intermixing. Mold width, ramping of casting speed, and nozzle design have only small effects. Slab thickness, however, significantly influences the intermixing length of the slab.The axial transport of solute due to turbulent eddy motion was found to be many orders of magnitude greater than molecular diffusion and thus dominates the resulting composition distribution. Different elements, therefore, exhibited the same mixing behavior under the same casting conditions, despite having different molecular properties. Numerical diffusion caused by the finite difference schemes was investigated and confirmed to be much less important than turbulent diffusion. In the lower portion of the strand (lower than 3 meters below the meniscus), the convection and diffusion can be reasonably approximated as one dimensional axial flow.2

Assessment of Turbulence Models for Prediction of Intermixed Amount with Free Surface Variation Using Coupled Level-Set Volume of Fluid Method

“…conductivity in the fluid; Fold and Fnew are the fractions of that element measured in the previous and new grades respectively. 31) Figure 2(b) illustrates the process involved in variation of flow rate throughout the ladle change-over process. In solution methodology, coupling of LS and VOF variables are carried out in the interface reconstruction step.…”

A Practical Model for Predicting Intermixed Zone During Grade Transition

“…Another method [5][6][7][8][9] is the 3-D transient numerical simulation considering tundish filling and casting speed changes. Although these methods give us precise data on mixing during the grade transition, they require much effort and time.…”

Transient Fluid Flow Phenomena during Continuous Casting: Part II—Cast Speed Change, Temperature Fluctuation, and Steel Grade Mixing

“…The numerical simulation is an alternative for this purpose and has been used for the prediction of steel behavior during transient stages, such as steel concentration distribution in the strand during steel grade change, [9][10][11] transient phenomena in ladle 12) and tundish, 13,14) and unsteady fluid flow in casting mold. 8,15) Among these studies, the steel quality is more sensitive to the transient behavior inside the casting mold cavity.…”