Kinetics of Nitrogen Removal from Molten Steel under Vacuum and Gas-Blowing Conditions

The kinetics of nitrogen removal from molten steel under vacuum and gas-blowing conditions has been studied during the VIM process. The experimental results indicated that vacuum affected the kinetics of nitrogen removal in the range of 67~5 360 Pa. At 67 Pa, the rate of nitrogen removal is controlled by the liquid phase mass transfer of nitrogen in molten steel. At 2 680Pa, the limited step for nitrogen removal from molten steel is the chemical reaction at the metal/gas interface. Under the present experimental conditions, the type (Ar, CO, CO₂) and quantity of gas flowed have no evident influences on the rate of nitrogen removal. The ratio of nitrogen removal of gas bubbles is less than 3%. Based on the experimental results, the mechanism of nitrogen removal during the VD process with argon blowing and the other melting or secondary refining processes with carbon-oxygen reaction have been discussed. Some new viewpoints are proposed.