Corrosion mechanism of Al–MgO–MgAl2O4 refractories in RH refining furnace during production of rail steel

Abstract The corrosion behavior of Al–MgO–MgAl2O4 refractories by liquid rail steel was studied by analyzing the worn bricks used in an RH refining furnace of a steel mill in China. The corrosion mechanism of Al–MgO–MgAl2O4 refractories is expressed as follows: on one hand, during vacuum treatment, with the increasing temperature and declining oxygen partial pressure, a minor amount of Fe in the steel was oxidized into FeO at steel/refractory interface. Then FeO dissolved with MgO particles and fine powder, forming (Mg, Fe)O solid solution. During the refining interval, as the temperature decreased and the partial oxygen pressure increased, Fe2+ was oxidized into Fe3+ and MgO·Fe2O3 solid solution separated from (Mg, Fe)O solid solution. In the cyclic process of solid solution and desolution, MgO particles and fine powder were structurally weakened. On the other hand, the CaO–SiO-based slag infiltrated along the open pores and the grain boundaries into the Al–MgO–MgAl2O4 refractories, forming CaO·MgO·SiO2 and 3CaO·MgO·2SiO2 phases, which led to poor binding ability of refractories. At the same time, due to the Al–O reaction, the oxygen partial pressure in the system was further reduced, which provided conditions for the formation of MgAlON and MgO dense layers, improving the resistance to slag corrosion and slag permeability of Al–MgO–MgAl2O4 refractories. When the dense layer structure was completely destroyed, the interaction zones of the refractories were washed away into the liquid steel.