Influence of additives on corrosion resistance and corroded microstructures of MgO–C refractories

Corrosion resistance and corroded microstructures of MgO–C refractories containing various antioxidants in a model EAF slag (CaO/SiO2 weight ratio=1.38) were investigated after 30 h at 1650°C. Antioxidants influenced their corrosion resistance by affecting both carbon (C) oxidation and MgO dissolution in the slag. Al additions improved C oxidation resistance at 1650°C only a little, but accelerated MgO dissolution, resulting in a minor effect on corrosion resistance. Additions of Si or Al+Si improved C oxidation resistance slightly but accelerated MgO dissolution more than Al additions, resulting in worse corrosion resistance than Al addition and no addition. B4C conferred the worst corrosion resistance, since boron-containing liquid formed in the refractory, greatly accelerating MgO dissolution and resulting in C (mainly graphite) in the matrix being eroded easily by the slag. With double addition of Al+B4C, boron-containing liquid formed, which not only inhibited effectively C (mainly graphite) oxidation, but also accelerated formation and growth of MgAl2O4 spinel (MA) crystals between graphite in the matrix at the test temperature. In this case, even though MgO dissolution was accelerated to some extent, graphite was not easily washed away by the slag because it was effectively protected from oxidation and held in place by MA crystals. This maintained the integrity of the refractory texture, giving the Al+B4C containing refractory the best corrosion resistance.