Interaction of a Nonstick Corundum Coating with Iron–Carbon Melts under Lost-Foam Casting Conditions

Abstract

The interaction of iron–carbon melts with a corundum-based nonstick coating at the steelmaking temperatures (1600–1700°C) is thermodynamically calculated with allowance for the specific features of lost-foam casting (LFC). The melts of St10 and U8 steels and SCh15 cast iron with oxygen and aluminum contents [O] = 0.001% and [Al] = 0.02%, respectively, are studied. To estimate the interaction of corundum with the iron–carbon melt, we consider the dissolution of the coating in a metal, its reduction by the melt components (carbon, silicon), and its interaction with dissolved oxygen. As a result, of calculations, the boundary aluminum concentration in a melt [Al] above which corundum can be dissolved and reduced is determined. At a high degree of melt oxidation ([O] > 0.05% at 1600°C), oxygen can pass from a metal to the nonstick coating in the form of FeO and form hercynite and liquid FeO–Al₂O₃ slags. During LFC, casting molds of foamed polystyrene undergo destruction induced by the heat energy of the melt; as a result, a gas–vapor phase forms and is removed through pores in the nonstick coating to the base material. The reactions of interaction of corundum with the gas–vapor phase components are analyzed to estimate the influence of this phase on the nonstick coating.