DECARBURIZATION OF LOW CARBON STEEL MELTS WITH CO_2 - O_2 UNDER VACUUM

摘要

1. In the present experiments with little nitrogen and hydrogen in the steel, and a low freeboard temperature, CO_2 reactivity can be calculated from the off-gas composition. 2. Decarburization and oxidation occurred simultaneously; C-O equilibrium was virtually achieved. The efficiency of decarburization decreased with increasing oxygen content. 3. For pure CO_2 injection, it was proposed that the kinetics were controlled by dissociative chemisorption of CO_2 that was impeded by oxygen adsorption at higher oxygen content. The rate was also limited by carbon diffusion to the bubble interface. 4. For mixtures of CO_2-O_2 the rate of decarburization was faster. It was proposed that the oxygen reaction with the steel raises the bubble interface temperature, so that CO_2 dissociates, obviating the need for chemisorption, and providing a more rapid mechanism for decarburization. 5. An analysis was performed to account for decarburization and oxidation. 6. In the present experiments, CO_2 efficiency was low due to shallow injection. 7. No influence on CO_2 reactivity was observed for the experimentally investigated range of vessel pressure and steel temperature. 8. CO_2 is not practical for carbon removal above 200 ppm O; however, CO_2 may be used in vacuum applications with large submerged injection rates, such as RH-degassing, and the VOD and VODC processes for stainless steel refining. Mixtures of CO_2 and O_2 may provide even better performance.