ZrO2-C refractory used as slag band of submerged entry nozzle (SEN) in continuous casting of steel. In service ZG-refractory contact with molten steel and aggressive fluorine-containing slag. Microstructure of refractories (A and B) was studied after using at 6 hours. ZG-refractory A has most wear 2,8 mm/charge by comparison with ZG-refractory B 2,0 mm/charge. Besides solution of refractory in slag occur change of microstructure in refractory under the influence of high temperature and CO. Observed destabilization of zirconia and formation zirconium carbide (ZrC) in refractory A.