• • Low-viscosity slag (viscosity below 2.5 Pa·s at tapping temperature) causes more severe refractory damage; safe tapping temperature range should be set as tICT−t2.5 when tICT > t25, ensuring slag remains fluid without crystallization.
• • Cracks in all corroded bricks arise from molten slag penetration and reaction; thermal expansion mismatch between newly formed phases and refractory material is the critical crack-driving factor, as confirmed by absence of zirconium spinel in XRD.
• • Reduction in Cr2O3 content is the earliest damage indicator at slag-aggregate and slag-matrix interfaces; early detection of Cr2O3 depletion is vital to prevent progressive refractory degradation.
• • Proposed damage mechanism: Cr2O3 reduction compromises matrix and aggregate integrity, enabling slag penetration and new phase formation, leading to crack-induced structural failure; preventing Cr2O3 loss is key to extending service life.