Bubble Growth and Floating Behavior during Degassing Process of Molten Steel/(N₂, H₂) System

摘要

Dissolved gas flotation method has been developed to remove inclusions in molten steel. The principle is that bubbles formed on inclusions by vacuum treatment of nitrogen or hydrogen supersaturated molten steel can carry the inclusions to slag. A kinetic model was constructed to analyze the bubble growth and floating behavior during the degassing process of the method, and its accuracy was verified by related experiments. The results show that pretreatment pressure, bubble nucleation depth and gas type have significant effects on bubble growth and floating, while vacuum treatment pressure and inclusion radius have little effects on it. The growth rate and floating velocity of bubbles increase with the increase of pretreatment pressure or the decrease of bubble nucleation depth. The growth rate and floating velocity of hydrogen bubbles are much larger than those of nitrogen bubbles. Calculation results indicate that the diameters of the bubbles are mostly 0.2–10 mm during floating process via this method. Moreover, the distribution of the bubbles nucleating on the inclusions is dispersive. In addition to the bubbles carrying inclusions to slag directly, these dispersive fine bubbles have a high probability of inclusion adhesion resulting in an improvement of the inclusion removal.