Modeling of Continuous Casting Mold Powder Behavior: Heat Transfer, Combustion, Sintering, and Melting

A model of temperature distribution, carbon and gas concentrations, and powder and melt pool thickness evolution has been developed for the top-surface powder layers in the continuous-casting process. Mold powder is added to the continuous caster to provide thermal and chemical insulation (prevent re-oxidation of steel), to supply liquid flux into the gap to provide lubrication, and to control horizontal heat transfer across the air gap between the copper mold and re-solidified flux, and to absorb and remove inclusions from molten steel. Therefore, maintaining sufficient powder and liquid flux layer thicknesses is important to achieve these functions. Understanding the powder melting behavior is key to maintaining a stable and adequate liquid pool thickness. Free carbon in the mold powder controls the melting rate and its concentration evolution is influenced by heat, mass transfer, and gas transport through the porous powder bed. The powder/slag region is modeled with a 1-D, fixed-grid, transient, advection-diffusion finite-volume model, and includes phase change and melting, powder densification, carbon burning, gas evolution, gas transport, and exhaust phenomena. The steady-state model has been verified with an analytical solution, and with a model with a commercial package. The transient heat transfer model has been validated with plant measurements in operating commercial slab casters, and applied to study the effect of powder properties/casting conditions, and automated vs. manual feeding. The multiphysics model including the effects of heat and mass transfer, sintering, combustion, and gas transport has been validated with lab sintering measurements. Finally, the multiphysics model has been applied to the continuous caster. The carbon in the mold powder is advected due to powder shrinkage, and liquid flux consumption, which results in carbon enrichment in the sinter layer near the bottom of the powder, which is more than in the lab experiment. This novel multiphysics model of top-surface powder behavior is a valuable tool in understanding the phenomena governing temperature, powder/slag thickness, and powder melting rate in the continuous casting process.