To address the challenge of precisely controlling the active elements Al and Ti during the electroslag remelting of Monel K500 alloy, a thermodynamic model of the CaO-CaF 2 -Al 2 O 3 -MgO-TiO 2 slag system was developed using the Ion-Molecule Coexistence Theory. A thermodynamic model with interfacial equilibrium reactions was further developed to predict the competitive oxidation behavior of Al and Ti quantitatively. An equilibrium calculation method applicable to TiO 2 -free initial slag systems was established to optimize slag composition. The effects of slag composition and melting temperature on the Al 2 O 3 /TiO 2 activity ratio and the equilibrium concentrations of Al and Ti were quantitatively analyzed. Increasing the CaO or Al 2 O 3 content and melting temperature favored Al retention but intensified Ti oxidation, whereas a higher CaO/Al 2 O 3 ratio reduced the oxidation driving force of Ti. In contrast, SiO 2 and FeO exhibited opposite effects on the equilibrium Al content, although their influences were relatively weak. Based on the model calculations, the optimized slag composition was determined to be 18∼22 wt.% CaO, 16.5∼21 wt.% Al 2 O 3 , 0.1∼0.6 wt.% SiO 2 , 0.1∼0.3 wt.% FeO, 2∼3 wt.% MgO, and 50∼55 wt.% CaF 2 . Industrial electroslag remelting experiments were subsequently conducted using the optimized slag system for validation. The relative burn-off of Al decreased from 5.08% to as low as-1.36%, while that of Ti decreased from 3.70% to 0.93%, showing good agreement with the model predictions. This study provides a theoretical basis for slag design and the precise control of Al and Ti during the electroslag remelting of Monel K500 alloy.
Zhang et al. (Fri,) studied this question.