Correlation for measured mold heat flux and CON1D simulations for feasible operating conditions in thin-slab continuous casting

In steel continuous casting, controlling heat flux from top of the mold to caster exit is very essential for the production of high quality slabs in a safe environment. Cooling in steel continuous casting comprises primary cooling in mold followed by secondary cooling in spray cooling zone. In this work, various parameters affecting heat flux are studied, first in mold from plant measurements and second in spray cooling zone based on simulations from the numerical model CON1D. Heat flux in the continuous casting mold is critical to strand surface quality and solidification of the shell. Two years of plant measurements for the thin-slab caster at Nucor Decatur Steel mill and one year of measurements for the thin-slab caster at Nucor Tuscaloosa Steel mill are analyzed to relate average mold heat flux with casting conditions, including casting speed (most important), steel grade, mold powder properties, slab width, superheat, mold level deviation and mold plate thickness. Performing multiple regression analysis, different equations to predict mold heat flux are presented and discussed. The best model based on the combined measurements of both the casters fits better for both the plants than previous equations in the literature. Secondary cooling of the strand after the mold is used to regulate strand surface temperature profile and metallurgical length. Control of heat removal is critical for the production of high quality slabs without defects and to achieve full solidification in desired region of the machine. To accomplish these, two constraints are considered in this work: First, controlling metallurgical length between straightener and end of containment to avoid stress related cracks and whales respectively; Secondly, to regulate surface temperature profile to avoid unbending in the temperature range of the ductility trough. In this work, using the heat-transfer model CON1D, feasible windows of operation like range of casting speeds and combination of critical speed and superheat satisfying the given constraints are determined for a thin-slab caster at Nucor Decatur steel mill in Alabama. The procedure is repeated for different compositions of steel with different superheats. The prior knowledge of determined feasible windows of operation is very helpful for production of high quality slabs without defects in a safe environment