Physico-Chemical Study of Reactions between a Magnesia-Graphite Refractory and Liquid Steel

Immersion tests on magnesia-graphite refractory samples in liquid steel at 1600 C were carried out on a laboratory scale. They revealed the build up of a dense and continuous MgO-rich layer, at the interface between the refractory and steel, and the possible formation of inclusions as large clusters protruding from the refractory surface. The MgO-rich layer and the inclusions arise from the reduction of MgO by carbon from the refractory and the subsequent oxidation of the Mg vapour in contact with liquid steel. Microscopic observations and thermodynamic calculations suggest a formation mechanism for this MgO-rich layer, whose composition and thickness are related to the chemical composition of the metallic bath, particularly to the oxygen activity (at the interface between refractory and steel) and its evolution with time. 3 refs.