Corrosion behaviour of MgO-based refractories by different existence states of manganese-containing volatile phases

Medium/high manganese steel is great interest because of its excellent energy absorption and strength. Further, it has emerged as a potential advanced high-strength steel in automobiles. In this study, the corrosion behaviour of MgO-based refractories by different existence states of manganese-containing volatile phases was systematically investigated via laboratory experiments of the vacuum treatment of medium/high manganese steel. The dissection of a magnesia crucible indicated that the manganese-containing volatile phases exist in three states: manganese vapour, liquid manganese and manganese oxides. The corrosion mechanism models of the MgO-based refractories were established as follows: (1) For the manganese vapour, the periclase was dissociated into the fine blocks when the magnesia-carbon brick was continuously exposed to the manganese vapour. (2) For the liquid manganese, a MnO layer was detected near the manganese metal, which was resulted from the MgO oxidation, and a further reaction took place to form a MnO·MgO solid solution layer at elevated temperatures, which led to the poor binding ability of the MgO crucibles. (3) For the manganese oxides, the Al2O3 crucibles were preferentially corroded by the molten manganese oxides, which are attributed to the superior thermodynamic driving force for the formation of MnAlO4. Moreover, a reaction layer composed of a MnO·MgO solid solution and a low-melting-point silicic acid phase was formed at the interface between the manganese oxides and the magnesia-carbon brick along the decarburized infiltrated zone. In addition, the molten manganese oxides infiltrated along the periclase grain boundaries into the magnesia-carbon brick and to form a reactive metamorphic layer. Consequently, under the attack of physical and chemical corrosion, the refractory particles were loosened and dropped into the corrosive manganese oxides, causing the irreversible damage of the refractory. This work provides a strong theoretical basis for the qualitative evaluating damage of MgO-based refractories by manganese-containing volatile phases.