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.

Reaction of Al‐Killed Manganese Steel with Ladle Slag

“…To improve the yield of Mn in liquid steel, high‐basicity refining slag is recommended in this case. On the other hand, the reduction of SiO 2 by dissolved Al (Equation ) is not profound as discussed, therefore the reoxidation of steel led by this reaction can be ignored to a certain extent, which is different from conventional Al‐killed steel grades . From this aspect, it seems that low‐basicity slag does not have an evident impact on steel cleanliness.…”

Study on Desulfurization Ability of CaO-Al2O3-SiO2and CaO-CaF2Slags at 1600 °C

“…During the secondary refining process of low sulfur steel, it is necessary to control the top slag composition close to the CaO saturation line as much as possible to achieve best thermodynamic condition. Furthermore, it should be mentioned that even if the FeO content in slag is less than 1 mass%, the FeO would still supply oxygen to molten steel, as reported by Deng et al . So, it is necessary to decrease the FeO content in slag as much as possible and maintain a relative high level of acid‐soluble Al content in steel to promote desulfurization.…”

The role of process control on the steel cleanliness

“…This could indicate that some sort of equilibrium between the top slag and the steel is being approached [13,25] and/or that the top slag has been dispersed into the slag during the intense stirring. Thus, it is not strange that similar aluminium contents are reached in the different heats after a completed vacuum treatment, since these contents most likely are controlled by a steel/slag equilibrium that has been reached [41]. A recent investigation [40] has shown that less aluminium is maintained in the steel when a poor deslagging has been made.…”