Application of phase equilibrium studies of CaO-SiO2-Al2O3-MgO system for oxide inclusions in Si-deoxidized steels

In the steelmaking process, the compositions of the oxide inclusions could be modified by refining slags to a large extent. The chemistries of the oxide inclusions and refining slags can be described by the system CaO-SiO2-Al2O3-MgO. Phase equilibria and liquidus temperatures in this system have been experimentally investigated in the composition and temperature ranges related to the oxide inclusions and refining slags by means of high-temperature equilibration, quenching and electron probe X-ray microanalysis. Isotherms in the interval of 20 degrees C between 1260 and 1560 degrees C were determined in the primary phase fields of wollastonite, anorthite, spinel, and melilite. Effects of the mass ratio of (Al2O3+SiO2)/((Al2O3+SiO2)+(CaO+SiO2)) and MgO content on the liquidus temperatures have been discussed to assist inclusion control. To obtain the lowest liquidus temperature of Al2O3-SiO2-CaO-MgO system inclusions, refining time ought to be properly controlled.