Thermodynamic Evaluation and Optimization of the MnO–Al2O3 and MnO–Al2O3–SiO2 Systems and Applications to Inclusion Engineering

Abstract

THE MnO-Al2O3-SiO2 ternary system is of interest for inclusion control in Mn/Si-killed steel. Mn/Si complex deoxidation is indispensable for the production of high-value steels such as tire-cord steel and high-Ni steel (Fe-36 pct Ni Invar steel), in order to avoid the harmful effects of solid Al2O3 inclusions formed during Al deoxidation. Al2O3 inclusions usually cause wire breakage during tire-cord production, where inclusions should be deformable during the wiremaking process. Therefore, Mn/Si deoxidation, which results in MnO-SiO2(Al2O3) inclusions of low melting temperature, is usually preferred. In order to control inclusions precisely, inclusion engineering, based on the thermodynamic relations between inclusions and liquid steel, should be carried out during the secondary refining stage in the ladle and tundish. In the present study, a thermodynamic database of model parameters for the MnO-Al2O3-SiO2 system has been developed by evaluation/optimization of all available thermodynamic and phase-diagram data. This database, together with the previously developed database for molten steels, can be used to perform calculations of importance to inclusion engineering.