Prediction of deoxidation and inclusion precipitation in semikilled steel

A generalized thermodynamic calculation procedure for the prediction of oxide inclusion precipitation of desired compositions for Mn-Si-Al deoxidation has been developed. The procedure directly uses established tertiary iso-activity diagrams in the MnO2-SiO2-AlO3 system, and does not assume any slag model. The thermodynamic data required for calculation, such as deoxidation constants, interaction coefficients, and activity vs composition relations in the oxide phase, reported in the literature, were examined and the ones considered to be most satisfactory were accepted. On the basis of the computed results for inclusions in the spessartite phase field of the MnO-SiO2-AlO2 system, discussions have been presented on the applicability of the regular solution model as well as an empirical model reported in the literature. Some predictions for plain carbon steels have also been included.