Analysis of the influence of the solid and liquid phases on steel desulfurization with slags from the CaO–Al2O3 systems using computational thermodynamics

Abstract

Normally, CaO is used in steel desulfurization in slags from the systems: CaO–CaF2, CaO–Al2O3, and CaO–SiO2. Among these, the CaO–CaF2 slags are more efficient. This paper uses computational thermodynamics to study the influence of solid and liquid phases in the efficiency of desulfurizing slags in the CaO–Al2O3 system. Desulfurizing slags were prepared to produce steels with sulfur levels below 20 ppm. Simulations using computational thermodynamics were made to determine the properties of the slags at 1600 °C. The experimental tests were carried out in an induction furnace at 1600 °C. The experimental results showed that slags from CaO–Al2O3 system can be as efficient as slags from CaO–CaF2 system, reaching final sulfur contents lower than 10 ppm. The conclusion was that slags containing higher quantities of liquid phase are more efficient. However, the presence of some amount of solid CaO is necessary to keep the liquid phase of slag always saturated in CaO and its activity equal to unity. A Steel Desulfurization Factor was proposed as an easy way to estimate the desulfurization efficiency. Keywords: Desulfurization, Secondary steelmaking, Ultra-low-sulfur steel, Liquid and solid phases, Top slag, Computational thermodynamics