Mold slag property measurements to characterize CC mold - Shell gap phenomena

Multi-faceted experiments were conducted to measure the properties of several mold slags, needed for fundamental characterization of heat transfer and friction in the interfacial gap between the shell and mold during the continuous casting of steel. A novel apparatus was used to measure the friction coefficient between solidified mold flux and copper at elevated temperatures. The measured softening temperature is interpreted to extrapolate the slag viscosity-temperature curves far into the low temperature - high viscosity region. Continuous-cooling transformation curves were extracted from XRD analysis of DSC test samples and thermocouple dip tests. Time-temperature transformation curves were obtained from similar analysis of melted mold powder samples that were atomized into droplets, quenched to form glass, and then partially devitrified by reheating to different temperatures for different times and quenched. Polarized light microscopy, SEM, and EDX analysis revealed distinct crystalline and glassy layers, but no severe macro-segregation in a tail-out slag film taken from an operating caster. The results from these new measurements have important implications for the prediction of interfacial gap phenomena, including mold heat transfer, friction, slag layer fracture, and steel surface quality.