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: FeOx 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.