Deoxidation mechanism of Al-killed steel during industrial refining process

Abstract

Deoxidation is a key step for steel refining, and it would influence the cleanliness of final product. In present study, the measured and calculated oxygen activities in Al-killed bulk steel were compared according to industrial trails, and the Fe-O equilibrium at the interface between slag and steel was also concerned by thermodynamic analysis. Finally, the deoxidation mechanism of Al-killed during industrial refining was proposed. It is found that the activity of oxygen in bulk steel is controlled by Al content, since the activity of oxygen in bulk steel is very close to the equilibrium value as the activity of Al2O3 is treated as unity. In order to keep low oxygen in molten steel, a certain Al content needs to be guaranteed. At slag-steel interface, the activity of oxygen is controlled by FeO, which is much larger than that of bulk steel, so the oxygen would transfer from slag into bulk steel. Slagging therefore presents its importance for deoxidation to reduce the oxygen transfer. Besides, the essence of SiO2 supplying oxygen is Al consumption in bulk steel, which gives rise to the increase of dissolved oxygen. So, stable refining slag is also very important to obtain low oxygen steel, and the slag basicity needs to be no smaller than 3 to reduce the Al consumption caused by SiO2 reduction. In present study, the basicity of 3-4 is recommended to refine low oxygen Al-killed steel. © 2014 ISIJ.