Study On Nitrogen Control Technology For IF Steel

With the development of automobile industry, automotive sheet steel requires quality increasingly, especially for deep-punching performance, while nitrogen content has a direct impact on this performance. So controlling the nitrogen content in steel is the key technology for automotive sheet production. In order to control the nitrogen content in IF steel better, Steelmaking Plant No.2of Ansteel Corporation was related in practice, the effect of relevant factors on controlling nitrogen content in the BOF converter, refining and casting processes was studied, and nitrogen control technology of low nitrogen steel was summed up in this paper. From the study, the following conclusions were obtained:(1) Tapping and LF refining process are the main processes for nitrogen increase in IF steel. Aluminum deoxidation enhances nitrogen absorption of tapping and later process. By improving deoxidation method, shortening the sedation time, adjusting fluidity of slag, enhancing the slag protection for liquid steel and controlling the pressure of argon blowing, nitrogen absorption could be reduced when tapping. The longer treatment time by LF refining, the more nitrogen content absorbed, and nitrogen absorption could be controlled in LF refining by controlling refining time and making good foam slag.(2) By increasing hot metal ratio, controlling slag returning to dry, reducing reblowing times and time and using iron ore to slagging, nitrogen content could be reduced obviously with nitrogen content less than12×10-6.(3) Deep denitrogenation result could be improved in RH-TB refining process by increasing decarburization speed at the early stage, increasing vacuum degree quickly, increasing argon gas flow rate and circulation of liquid steel at the middle stage, and controlling oxygen content and low sulfur content at the end stage. When nitrogen content of low nitrogen steel is less than20×10-6, the maximum denitrogenation result can be obtained with5×10-6nitrogen content reduced.(4) According to controlling long nozzle argon blowing volume, adding new packing seal between long nozzle and ladle, strengthening the seal of tundish,enhancing casting beginning operation control, using big amount slag with continuous casting optimized and developing protection slag, nitrogen content could be controlled effectively with less than5×10-6increased.