Effect of CaO/Al2O3 Ratio in Fluorine-Free Refining Slag with Low Basicity on the Cleanliness of SWRS82B Steel

Abstract

A fluorine-free quaternary CaO–Al₂O₃–SiO₂–MgO refining slag for SWRS82B coil steel is studied by considering the requirements of the steel wire. Laboratory experiments are conducted to study the equilibrium and kinetics of steel–slag reactions. The physical and chemical properties of refining slags, including the melting temperature, viscosity, and MgO solubility, are estimated by FactSage7.2 calculation. The cleanliness of SWRS82B steel refined by slags with a basicity of 1 and C/A ratio in the range of 1.36–7.13 is studied systematically. The plasticity of inclusions is studied by phase diagram and Young modulus calculation. Deoxidizing capacity and desulfurization capacity of refining slags are discussed by kinetic calculation of steel–slag reactions based on FactSage7.2 macro-editing and the kungliga tekniska högskolan model. Slag with a composition of 42%CaO–47%SiO₂–4%Al₂O₃–7%MgO has the best refining effect, in which impurity elements are lowest and plastic inclusions with the smallest size and least quantity are obtained. The impurity elements oxygen and sulfur in steel can be controlled for 29 and 75 ppm, respectively. The average size of inclusions is 1.54 μm. The majority of inclusions are in a liquid state at 1600 °C and Young modulus of the inclusions ranges from 99.78 to 152.87 GPa.