Desulfurization Behavior of FeNi-Based Expansion Alloy Melt Using CaO-SiO2-MgO-Al2O3-CaF2 Slag

The effects of slag components on the sulfur distribution ratio {(wt.%S)/[wt.%S]} were analyzed using thermodynamic calculations. On this basis, the effects of the slag with different binary basicities (wt.% CaO/wt.% SiO2 = 3.0, 5.0, 7.0, 9.0 and 11.0) and Al2O3 contents (wt.% Al2O3 = 12, 16, 20 and 24) on the desulfurization behavior were investigated. The results show that the binary basicity and Al2O3 content were the main factors that affected the desulfurization. And an increase in the binary basicity and a decrease in the content of Al2O3, increase the sulfide capacity of the slag. In the early stage of the smelting process, the desulfurization process was limited due to the high content of oxides, such as FeO and MnO in the slag, and the sulfur content in the alloy melt reached 35 ppm. After the final deoxidation of the Si-Ca alloy, the desulfurization rate was significantly increased, and the maximum desulfurization rate reached 44.12%. During the ladle standing, the sulfur content in the alloy melt changed little because of the limitation of kinetics. The rate-limiting step of the desulfurization process was the diffusion of sulfur in the alloy melt.