Aiming at the problem that the nitrogen increases in LF refining process of Jingye Iron and Steel Co.,Ltd.and reaches 11.2 ppm,resulting in the nitrogen content of final product exceeding 45 ppm.The principle of nitrogen increase in liquid steel is analyzed,and it is found that the nitrogen increase rate of liquid steel is related to the contact area between liquid steel and air,the concentration of nitrogen in air,the temperature of liquid steel and other factors.A series of production tests are carried out in LF refining furnace to try to reduce the nitrogen increase in liquid steel during the refining process.By recovering liquid slag and reducing the contact area between liquid steel and air,nitrogen increase in LF refining process can be controlled from 4.2 ppm to 1.1 ppm.The nitrogen increase in the refining process can be controlled from 3.1 ppm to 2.1 ppm by reducing the power supply time and frequency to reduce the nitrogen increase in the molten steel at high temperature.The nitrogen increase in the process can be reduced by controlling the strong mixing time reasonably and reducing the exposure time of molten steel.By maintaining the micro-positive pressure in the furnace,the nitrogen concentration can be reduced even the nitrogen increase in the process can be reduced.After taking the above measures,the average nitrogen increase of large beam steel in the refining process decreased from 11.2 ppm to 5.5 ppm,and a good nitrogen control effect is achieved.
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