Zirconia graphite refractory is used as a core-nozzle in the thin-strip casting of steel. Post-mortem analysis of used refractory was performed in an effort to establish the failure mechanism. Corrosion behavior was studied against molten steel with MnO-SiO₂ based liquid inclusions. Corrosion of these materials involves dissolution and oxidation of graphite in the matrix followed by penetration of liquid slag leading to degradation of ZrO₂ particles. Thermodynamic equilibrium calculations were performed to study this corrosion mechanism.