Effect of the CaO-Al2O3-Based Top Slag on the Cleanliness of Stainless Steel During Secondary Metallurgy

The ladle treatment of a 18 pct Cr-9 pct Ni stainless steel, with desulfurization as its main purpose, was simulated on a laboratory scale. The influence of the top slag chemistry on the steel cleanliness was evaluated. A higher steel cleanliness was obtained with an optimized lime-alumina-based slag than with a lime-fluorspar-based slag. The inclusions were found to be mainly in the form of oxysulfide; the alumina content in the inclusions first increased and subsequently showed a slow drop, while the sulfide content decreased during the treatment. The equilibrium between steel and inclusions was found to be more easily reached than that between slag and steel. A slag–steel kinetic model was used to predict the steel chemistry evolution during the treatment. Furthermore, a slag–steel–inclusions interaction kinetic model was developed to calculate the change of alumina content in the inclusions during the ladle treatment. The sulfide content of inclusions was also calculated and compared with the measured values.