Mould slag property measurements to characterize CC mould - Shell gap phenomena

Multi-faceted experiments were conducted to measure the properties of several mould slags needed for the fundamental characterization of heat transfer and friction in the interfacial gap between the shell and mould during the continuous casting (CC) of steel. A novel apparatus was used to measure the friction coefficient between solidified mould flux and copper at elevated temperatures. The measured softening temperature is interpreted as the glass transition temperature and is used to extrapolate the slag viscosity-temperature curves far into the low temperature - high viscosity region. Continuous-cooling transformation curves were extracted from X-ray diffraction (XRD) analysis of differential scanning calorimetry (DSC) test samples and thermocouple dip tests. Time-temperature transformation curves were obtained from a similar analysis of melted mould 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, scanning electron microscopy (SEM) and energy dispersive X-ray (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 mould heat transfer, friction, slag layer fracture and steel surface quality.