The Sub-Entry Nozzle (SEN) is one of the most critical refractory components used in continuous casting of steel. Installed between the tundish and the mold, the SEN performs essential metallurgical and operational functions: stabilizing molten steel flow, minimizing reoxidation, reducing heat loss, suppressing surface turbulence, and preventing mold powder entrapment. To meet these functional requirements under severe conditions—including temperatures above 1,550°C, corrosive slag atmosphere, high levels of argon injection, and erosive molten steel flow—the SEN must be manufactured from highly engineered refractory compositions.