Numerical simulation on inclusion transport in continuous casting mold

Abstract

Turbulent flow, the transport of inclusions and bubbles, and inclusion removal by fluid flow transport and by bubble flotation in the strand of the continuous slab caster are investigated using computational models, and validated through comparison with plant measurements of inclusions. Steady 3-D flow of steel in the liquid pool in the mold and upper strand is simulated with a finite-difference computational model using the standard k-ɛ turbulence model. Trajectories of inclusions and bubbles are calculated by integrating each local velocity, considering its drag and buoyancy forces. A “random walk” model is used to incorporate the effect of turbulent fluctuations on the particle motion. The attachment probability of inclusions on a bubble surface is investigated based on fundamental fluid flow simulations, incorporating the turbulent inclusion trajectory and sliding time of each individual inclusion along the bubble surface as a function of particle and bubble size. The change in inclusion distribution due to removal by bubble transport in the mold is calculated based on the computed attachment probability of inclusions on each bubble and the computed path length of the bubbles. The results indicate that 6%–10% inclusions are removed by fluid flow transport, 10% by bubble flotation, and 4% by entrapment to the submerged entry nozzle (SEN) walls. Smaller bubbles and larger inclusions have larger attachment probabilities. Smaller bubbles are more efficient for inclusion removal by bubble flotation, so long as they are not entrapped in the solidifying shell. A larger gas flow rate favors inclusion removal by bubble flotation. The optimum bubble size should be 2–4 mm.