超低碳铝镇静钢冶炼过程氮含量的控制

Nitrogen control of ultra-low-carbon Al-killed steel in a smelting process

针对企业冶炼超低碳铝镇静钢过程中增氮量高、波动大及控制不稳定的问题,采用工艺数据统计和现场取样的手段,系统梳理了冶炼过程钢液脱氮和增氮的主要环节和影响因素.转炉脱碳期和真空处理是脱氮的主要环节,碳氧期的总脱碳量高则终点氮含量低;转炉底吹N2/Ar切换点在吹炼70%以前对终点氮含量影响不大;VD在无氧条件下脱氮有利,RH则在有氧条件下脱氮有利.控制钢中溶解氧>200×10-6则出钢过程增氮可控制在5×10^(-6)以下;炉料的氮带入是真空精炼环节增氮的重要因素,最高达11×10^(-6);采用密封垫+吹Ar的保护方式,增氮量最低为1×10^(-6).

Based on the fact of high nitrogen pick-up, large nitrogen fluctuation and poor control in some steel works, the main aspects of nitrogen removal and nitrogen pick-up in an ultra-low-carbon Al-killed steel smelting process were summarized by analyzing the process data and sampling. The main sections for nitrogen removal are BOF decarburization period and vacuum treatment. High decarburization amount can lower the nitrogen content at the BOF endpoint. There is just a limited effect of switching between nitrogen and argon on the final nitrogen content at the BOF endpoint before the point of 70% oxygen blowing. Free oxygen is favorable for deni-trification by promoting the reaction of carbon and oxygen under the RH mode, in contrast under the VD mode. When free oxygen in liquid steel is controlled above 200 í10 -6 , the nitrogen absorption during tapping can be controlled within 5 í10 -6 . The nitrogen introduction of furnace charge is the important factor of nitrogen pick-up during the vacuum refining process, and it is up to 11í10 -6 . The minimum of nitrogen pick-up can reduce to 1í10 -6 by adopting gasket sealing and argon blowing protection simultaneously.