Effect of Calcium Treatment of Molten Steel on Alumina Buildup on Submerged Entry Nozzles

摘要

A submerged entry nozzle that clogged during the continuous casting of calcium-treated molten steel was investigated to discover the actual condition of inclusion buildup. At the same time, an alumina adhesion model experiment was conducted. Based on the results, a study was made of the mechanism of inclusion buildup in a submerged entry nozzle used with calcium treatment of molten steel. It was found that solid CaO-6Al_2O_3 attaches together with molten TiO_2-CaO-Al_2O_3 to the inner wall of a submerged entry nozzle that clogs rapidly during continuous casting of calcium-treated molten steel and that its source is CaO-6Al_2O_3 preexisting in the molten steel. In the alumina adhesion model experiment, when the Al_2O_3 particles were not modified into a liquid oxide by CaO they rapidly adhered and coalesced forming a liquid bridge bond of TiO_2-CaO-Al_2O_3 between themselves. The adhesion force due to the liquid bridge of molten TiO_2-CaO-Al_2O_3 is greater than the adhesion force due to the van der Waals force or the surface tension of the molten steel. When the inclusions are not fully modified by calcium treatment, CaO-6Al_2O_3 is considered to adhere rapidly to the nozzle interface by the binding action of molten TiO_2-CaO-Al_2O_3 formed in the molten steel and this adhesion condition is maintained without being removed by the flow of the molten steel in the submerged entry nozzle.