Use of CaO-Al2O3 Synthetic Slag on EAF Tapping for Steel Desulfurization.

Steel desulfurization is usually performed by CaO-Al₂O₃-based top slags. However, in the steelmaking process at a steel mill in the city of Cariacica, ES, Brazil, deoxidation is carried out on tapping with the addition of ferrosilicon-manganese and silicon carbide, and desulfurization is carried out in the ladle furnace with the addition of lime and calcium carbide. The present work aims to change this process by adding a CaO-Al₂O₃ system slag during the electric arc furnace (EAF) steel tapping, so that the desulfurization occurs already in this step, thus enabling CaC₂ economy in the ladle furnace. Three lime/alumina briquette ratios were determined, where the CaO activity, liquid slag ratio and viscosity were analyzed. Then, the desulfurization yields of these heats were compared to the conventional route. The influence of additions and of the slag carryover on desulfurization efficiency was analyzed by correlation charts and a mathematical model developed. It was found that the slag carryover from the EAF impairs the desulfurization, causing sulfur reversion from tapping until the ladle furnace arrival, and decreasing the desulfurization rate on the ladle furnace treatment by promoting high-equilibrium sulfur content, close to the real reached value. The most efficient slags were the ones with the greatest calcium oxide activities, which is in line with the steel desulfurization factor. [ABSTRACT FROM AUTHOR]