Vacuum denitrification and nitrogen absorption of molten steel under ultra-low nitrogen conditions

Vacuum smelting experiments were conducted to investigate the effects of different initial nitrogen content and surface active elements on nitrogen denitrification and nitrogen absorption in molten steel. Thermodynamic calculations show that the pressure corresponding to 10 ppm of [N] should be less than 45 Pa; at 30 Pa and 1600°C, the nitrogen content in the steel reduced from 18 to 10 ppm in 50 min. Furthermore, denitrification can be described as a 1.5th order reaction model. In addition, the mean parameters of nitrogen absorption between the ultra-low and common-nitrogen steels are different: for ultra-low nitrogen molten steel exposed to air, even if [S] ≥ 200 ppm and [O] ≥ 300 ppm, [N] can increase from 10 to over 40 ppm in 20 min.