Effect of reaction time on interaction between steel with and without La and MgO–C refractory

Laboratory experiments and thermodynamic calculations were performed to investigate the interfacial reactions between the MgO–C refractory and the steel with and without the lanthanum (La) addition. Following a reaction time of 50 min, a reaction layer comprised MgO and CaS with a thickness of 30 μm was observed at the interface between the La-free steel and refractory. The MgO layer was observed in La-bearing steel after just 10 min of reaction. The addition of La to the steel accelerated the formation of the MgO layer. As the reaction time increased, a La-containing layer was formed at the La-bearing steel/refractory interface. This La-containing layer progressed through stages from La₂O₂S + La₂O₃ → La–Ca–O–S → La–Ca–O → La–Ca–Al–O. Furthermore, the evolution of oxide inclusions in the La-free steel followed the sequence of MgO⋅Al₂O₃, Ti–Ca–Al–O and Ti–Mg–Al–O → MgO·Al₂O₃ and MgO with increasing the reaction time. In contrast, the sequence for the La-bearing steel was: La₂O₂S and La₂O₃ → La₂O₂S and La–Ti–Al–Mg–O → La–Ti–Al–Mg–O, MgO and MgO·Al₂O₃. The average penetration depth of the La-bearing steel into the refractory was notably lower than that of the La-free steel, revealing that the incorporation of rare earth element La in steel exhibits a significant inhibitory effect on the penetration of molten steel into the MgO–C refractory.