<p>The refractory composition of submerged entry nozzles (SEN) critically governs interfacial reactions, which in turn determines the onset of clogging. The interfacial reactions between two Al₂O₃–C refractories with 8.7 and 1.7 Al₂O₃/SiO₂ ratios and Al-killed steel were studied through laboratory experiments. The flow of molten steel relative to the inner wall of the SEN was simulated by rotating a refractory rod in high-temperature molten steel. For the Al₂O₃–C refractory with an 8.7 Al₂O₃/SiO₂ ratio, an Al₂O₃ reaction layer was formed at the steel/refractory interface as the reaction progressed, which initially grew to 780&#xa0;μm before thinning to 470&#xa0;μm. Concurrently, the refractory surface became entirely coated with both clustered and plate-shaped Al₂O₃ inclusions following 120&#xa0;min of reaction. For the Al₂O₃–C refractory with a 1.7 Al₂O₃/SiO₂ ratio, a continuous Si–Al–Fe–O liquid reaction layer was generated at the steel/refractory interface, which significantly impeded the physicochemical interactions between the molten steel and refractory. The composition of the reaction layer evolved sequentially from the Si–Al–Fe–O liquid phase to the Si–Al–O solid phases with the increasing reaction time. After 120&#xa0;min, the refractory surface became fully coated with clustered Al₂O₃ inclusions. Compared to the Al₂O₃–C refractory with a 1.7 Al₂O₃/SiO₂ ratio, the Al₂O₃–C refractory with an 8.7 Al₂O₃/SiO₂ ratio was more likely to capture Al₂O₃ inclusions in the steel during its contact with Al-killed steel. The current experiment results indicate that in Al-killed steel continuous casting operations, Al₂O₃–C-based SEN with an 8.7 Al₂O₃/SiO₂ ratio should have a higher clogging potential than Al₂O₃–C-based SEN with a 1.7 Al₂O₃/SiO₂ ratio under equivalent casting conditions.</p>