The development of a thermodynamic model for Al2O3–MgO refractory castable corrosion by secondary metallurgy steel ladle slags

Alumina magnesia in situ spinel castables are used as ladle refractory lining in the steel industry. In contact with slag, they suffer degradations which limits their performance. The purpose of this article is to predict the thermochemical attack of a slag on alumina magnesia refractory using Factsage® thermodynamic modeling. To evaluate the reliability of the thermodynamic results, a validation step was carried out, which supported that the database was well adapted to the alumina magnesia spinel system. The corrosion phenomenon was then computed for a simple to a complete system to understand the mechanism and the influence of specific oxides. The model was also compared to corroded microstructures from a steel ladle to evaluate the contribution of each constituent in the castable. The aggregates of alumina react with slag to produce monomineral layers of lime aluminates (CA6 and CA2), while complex spinels (Mg, Fe, Mn)O (Fe2, Al2)O3 are formed from the reaction of the slag with the matrix of the castable. Several oxides (MnO, FeO, Fe2O3) from the slag contribute to the formation of the spinel structures. The microstructures of refractories used in steel ladles confirm the main conclusions and the thermodynamic approach.