Oxidation of molten steel by the air permeated through a refractory tube

Abstract

Refractory tubes such as a shrouding nozzle and a submerged entry nozzle are employed for molten steel transferring from a ladle to a tundish, and a tundish to a mold, respectively, to prevent molten steel from being oxidized. When the cross-sectional area in the molten steel flow channel is suddenly contracted and subsequently enlarged, a negative pressure is generated at the area. Thereby air is permeated into the molten steel flow through the refractory tube and oxidizes the molten steel. The permeability of a submerged entry nozzle was predicted from measurement of the gas permeated through the refractory tube by a dipping test. Using the predicted permeability and the pressure analysis in fluid flow, we calculated the oxidation rate by the permeated air during molten steel transferring. As a result, the concentration decrease rate of aluminum in molten steel is estimated 0.35 ppm per hour and this oxidation formed by the permeated air does not attribute to alumina build-up in the submerged entry nozzle.