Effect of Slag Compositions on Change Behavior of Nitrogen in Molten Steel

Abstract

The problem of nitrogen pickup in the smelting process of the electric arc furnace (EAF) has not been solved well. Using seven slag–steel equilibrium experiments and theoretical analysis, the relation of the foaming index and optical basicity with the nitrogen capacity of slag was clarified. Meanwhile, the effect of slag composition on the equilibrium distribution ratio of nitrogen and the mass transfer coefficient of nitrogen pickup was also studied. The results show that, with the increase in slag basicity, the nitrogen pickup amount, nitrogen pickup rate, and nitrogen equilibrium distribution ratio LN increase. Increasing the foaming index of slag and reducing its optical basicity will increase the nitrogen capacity of slag, which is conducive to hindering the nitrogen pickup of molten steel. The relationship between slag optical basicity and nitrogen capacity can be expressed as lgCN = −5.59lgΛ − 12.41. With the increase in the Al2 O3 content of slag, the nitrogen pickup amount of molten steel decreases and the nitrogen pickup rate decreases. The test with MgO = 7.5% showed the highest nitrogen pickup rate and the highest nitrogen pickup mass transfer coefficient, which were 0.21 × 10−4 %/min and 1.97 × 10−4 cm/s, respectively. The test with Al2 O3 = 7.5% in slag showed the lowest nitrogen pickup rate and the lowest nitrogen pickup mass transfer coefficient, which were 0.08 × 10−4 %/min and 1.35 × 10−4 cm/s, respectively.