Degradation mechanisms of magnesia-chromite refractories by high-alumina stainless steel slags under vacuum conditions

The corrosion behaviour of magnesia-chromite refractory by an alumina-rich (15–20 wt.%) stainless steelmaking slag is investigated by rotating finger tests in a vacuum induction furnace. The influence on the refractory wear, of the process temperature, corrosion time and, in particular, the high Al₂O₃ content in the slag, is discussed. Two distinct mechanisms cause primary chromite degradation: FeO_x and Cr₂O₃ decomposition because of low oxygen potentials and dissolution by infiltrated slag due to the high Al₂O₃ slag content. Upon decomposition, small metallic particles and pores are homogeneously generated inside the primary chromite. At the refractory/slag interface, a relatively continuous solid (Mg,Mn)[Al,Cr]₂O₄ spinel layer is formed. Its density and stability decreases with higher temperatures and more turbulent conditions. The spinel formation arises through heterogeneous in situ precipitation from a slag rich in spinel forming compounds. Higher Al₂O₃ levels in the slag promote the spinel layer formation, which may limit slag infiltration. Finally, it is shown that the present experimental procedure is an excellent tool to simulate refractory wear in industrial processes, diminishing the risks associated with plant trials.