Mechanism and Effect of Carbon–Oxygen Reaction on Nitrogen Content in Molten Steel During BOF Process
摘要
In the current study, the mechanism and effect of COx gases (CO and CO2 from carbon–oxygen reaction) on the nitrogen content was studied by industrial trials and nitrogen removal model. Four groups of trials with scrap ratios ranging from 15 to 50 pct were designed to analyze the relationship between the nitrogen content, carbon content, and COx gas generation. The results indicate that the nitrogen content exhibits a characteristic ‘decrease followed by increase’ trend throughout the converter process. When the carbon content was above 0.4 pct, the nitrogen content decreases with an increasing total volume of COx gases, reaching its minimum within the carbon content range of 0.1 to 0.4 pct. However, in the low‑carbon region below approximately 0.1 pct, nitrogen content increases slowly as carbon content decreases, and rises sharply when carbon content falls below 0.03 pct. Furthermore, a quantitative model correlating COx characteristics with nitrogen content was established. The denitrification mechanism during the converter process is divided into three stages: (1) Si–Mn reaction stage: the high carbon content enhances the denitrification efficiency of COx. The overall denitrification efficiency remains good due to the gradual increase in COx production and the reduced nitrogen input from entrained air. (2) High-speed decarburization stage: the volume of entrained air is the least, leading to minimal nitrogen input from the air. With the maximum volume of COx generated, this stage retains good denitrification capacity. (3) Final decarburization stage: the COx generation decrease to minimum, and the low carbon content results in weak denitrification efficiency of COx. Meanwhile, the increased nitrogen input from entrained air causes this stage to exhibit nitrogen increment.