Simultaneous Desulfurization and Deoxidation of Molten Steel with in Situ Produced Magnesium Vapor

Abstract

A new simultaneous desulfurization and deoxidation process of molten steel with magnesium vapor produced in situ by aluminothermic reduction of magnesium oxide is proposed. The pellets composed of MgO and Al are charged into an immersion tube and the magnesium vapor produced in situ by aluminothermic reduction of magnesium oxide is injected directly into molten steel to react with the dissolved sulfur and oxygen in it. Effects of various operating parameters on desulfurization and deoxidation are discussed.In the case of the high initial oxygen concentration, deoxidation of molten steel proceeds preferentially, and desulfurization does not take place. When the oxygen concentration in the melt is low enough, desulfurization of molten steel with magnesium vapor can proceed.A higher initial sulfur concentration increases the desufurization ratio of molten steel. The sulfur concentration in the melt tends to be in equilibrium with the magnesium partial pressure in the Mg–Ar bubble rather than the dissolved magnesium concentration in the melt. Increasing pellet mass promoted desulfurization of molten steel. The maximum desulfurization ratio of molten steel can be obtained at a relatively low argon carrier gas flow rate. In both cases of the porous magnesia and the dense alumina immersion tubes with injecting holes, addition of lime onto the melt surface increases the desulfurization ratio. The desulfurization using the dense alumina tube is accompanied by resulfurization more significantly at the later stage than that using the porous magnesia tube.