Thermodynamic analysis of aluminum and titanium content control in electroslag remelting of monel K500

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.