Effect of Changes in Sulfur and Oxygen Concentration on Change in Nitrogen Concentration in Liquid Steel During CaO Powder Blowing under Reduced Pressure

Abstract

To examine the change of the rate of nitrogen desorption with sulfur concentration and low oxygen concentration change, the rates of nitrogen desorption from molten steel were measured with the blow of CaO powder or argon gas onto the molten steel through a top lance under the reduced pressure. 15 kg of electrolytic iron was melted molten in a MgO crucible by a high frequency induction furnace and the temperature of the melt was held at 1873K. Aluminum, FeS and other alloying elements were added and composition of molten steel was kept at 0.001–0.19%Al, 0.0007–0.0064%S, 0.002–0.006%N, 0.5%Mn and 0.2%Si. CaO powder was blown onto molten steel with argon gas for 20 min under the reduced pressure of about 670 Pa and metal samples were taken during CaO powder blowing in order to clarified the removal rate of sulfur and nitrogen. The rate constant of desulfurization was maintained during CaO powder blowing, however, the apparent rate constant of nitrogen desorption increased gradually. A mathematical model of nitrogen desorption was presented with the consideration of the chemical reaction of aluminum and sulfur in molten steel with CaO flux, respectively. The calculated nitrogen concentration by the model were in good agreement with the experimental values. It was estimated that the apparent rate constant of nitrogen desorption was increased as a result of decrease of oxygen and sulfur concentration in moleten steel by the reaction between aluminum in molten steel and CaO flux.