Abstract: Low-carbon MgO-C refractories are key refractories employed in the refining of high-quality special steels. Free radical reactions between such refractories and molten slags lead to service failure. A weak static magnetic field shows considerable potential for regulating interfacial reaction rates between high-temperature molten slags and refractory materials. Using a high-temperature electromagnetic visualization apparatus and introducing the corrosion severity index, the effects of a weak static magnetic field (0-1.5 mT) on wetting, penetration andcorrosion of low-carbon MgO-C refractories by high-alumina CaO-Al₂O₃-based molten slag were investigated and evaluated under air, argon and vacuum atmospheres. Results show that magnesia and carbon sources generate superoxide free radicals and graphite σ dangling bonds, respectively, at elevated temperatures. Under vacuum at 1 600 ℃, application of a 1.5 mT weak static magnetic field reduces the corrosion severity index from 54.25 to 16.35 after 30 min of reaction between S1 slag and low-carbon MgO-C refractory containing5%(mass fraction) carbon. The reduction is attributed to altered spin-state distributions of radical pairs, which lowers the probability of oxidation reactions between superoxide free radicals and σ dangling bonds. Therefore, resistance of low-carbon MgO-C refractories to slag attack is improved by weak static magnetic fields through suppression of free radical reactions and deceleration of MgO dissolution. Findings provide an important theoretical basis for performance optimization of low-carbon MgO-C refractories used in high-quality special steel refining and development of magnetic field-assistedcorrosion-resistant technologies.