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A study of inclusion behaviour during electroslag remelting Burel, Bruno Charles

Abstract

Different mechanisms are proposed in the literature to describe the formation and behaviour of inclusions during electroslag remelting: - dissolution in the liquid metal of the inclusions already present in the electrode and then renucleation in the freezing ingot. - total or partial dissolution in the slag. - exchange reactions between inclusions in the metal and the slag. - entrapment in the freezing ingot of pieces of slag skin or droplets of slag. The mechanism of dissolution of alumina inclusions in a 70/30 CaF₂/Al₂0₃ slag has been studied in detail. For this a new equilibrium diagram for the system CaF₂/Al₂0₃ has been proposed and the diffusion coefficient of alumina in the slag has been determined by the rotating disk system. In a 70/30 CaF₂/Al₂0₃ slag at 1518°C the diffusion coefficient was estimated as D = 8.5 10⁻⁹ m² sec⁻¹. Calculations of the extent of the dissolution of alumina particles in the slag predicted that big particles (800 μ) might dissolve only partially in the slag. Particles of this size were introduced artificially in electrodes, but after electroslag remelting a much larger number of relatively small (15 μ max) alumina, iron aluminates and iron oxide inclusions were found in the ingot. The same types of inclusions could also be observed in ingots obtained after remelting a Ferro Vac-E electrode. The presence of these inclusions cannot be explained by one the mechanisms proposed precedently (dissolution in the liquid metal and then renucleation or partial dissolution in the slag), but only by an electrolytic oxidation and electrolytic aluminum dissolution on the electrodes and then nucleation of deoxidation products in the freezing ingot.

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