In this study, a three-dimensional transient electromagnetic-thermal-component multi-physical field model has been developed to investigate the processes of electromagnetic induction, electrothermal conversion, dynamic thermal characteristics, and component reactions during the smelting of a ferronickel submerged arc furnace. The model also considered the influences of component reactions on porosity change, as well as the feedback effects of porosity on the heat and mass transfer and multi-physical field distribution. On this basis, the transient alternating characteristics of the electric field, magnetic field, and Joule heat field were analyzed on a fast timescale. Subsequently, the transient solutions on the slow timescale were obtained to further reveal the coupling mechanisms among the multi-physical fields. The results show that under the effect of periodically alternating electric potentials, polarity reversal occurs between different electrodes, resulting in transient variations in the electric field, magnetic field, and Joule heat on a fast timescale, with corresponding peak values reaching 2.05 × 105 A·m−2, 0.026 T, and 4.23 × 108 W/m3, respectively. Meanwhile, the multi-physical fields are also strongly coupled on a slow timescale, jointly influencing the temperature distribution, component reactions, and porosity change in the furnace. When t = 50 minutes, the maximum temperature in the molten pool reaches 4325 K. As the smelting time increases from 20 to 50 minutes, the average conversion rates of nickel oxide, iron oxides, and silicon oxide on the cross-section Z = 1.67 m increase from 14.3 to 37.2 pct, 2.2 to 25.6 pct, and 0 to 9.8 pct, respectively. Meanwhile, the porosity change corresponds to the component reactions and the maximum porosity along Line D increases correspondingly from 0.512 to 0.731.
