Thermodynamic model-based design and optimization of Al-stabilized equilibrium slag for 16MnNiV steel electroslag remelting

Thermodynamic calculations investigated the effects of conventional electroslag systems based on CaF2–Al2O3-(CaO) on aluminum content in 16MnNiV steel. The results indicate that replacing Al2O3 with CaO in the slag significantly aggravates aluminum loss in the molten steel. The oxidation sequence of reactive elements (Al, Si, Mn, and Fe) in the steel was evaluated to elucidate the mechanisms of Al loss. The analysis shows that Al content in steel tends to increase when the temperature exceeds 1869 K, while it gradually decreases upon cooling, implying that Al oxidation intensifies during the cooling stage. A thermodynamic model based on the ion and molecule coexistence theory was developed to describe the equilibrium between the slag components and the consumable electrode during the electroslag remelting. This model quantitatively relates the slag composition, including CaO, FeO, CaF2, MnO, Al2O3, and SiO2, to the residual Al content in steel, thereby enabling optimized slag design for reducing Al loss during ESR. To minimize the oxidation of Al, Si, and Mn in the molten steel, the activity ratios of slag oxides should be controlled within the following ranges: α(Al2O3)/α(FeO) = 0.7∼1.2, α(SiO2)/α(FeO) = 0.3∼0.8, and α(MnO)/α(FeO) = 0.4∼0.9. The model-guided slag composition was screened and experimentally validated, demonstrating good agreement between predicted and observed results.