A Mathematical Model for Dehydrogenation of Molten Steel in the Vacuum Degasser

This paper presents a mathematical model of VD dehydrogenation aimed at predicting hydrogen removal during the VD vacuum refining process and investigating the effect of controllable parameters on the dehydrogenation process. Taking into account the behavior of argon bubbles during their uplifting, the model considers that the dehydrogenation reaction occurs at three sites, the surface of the Ar bubbles, the bath surface of the molten steel, and the bulk steel. The calculated results are in good agreement with the industrial production data. The hydrogen content of the molten steel during VD dehydrogenation is observed to vary as an inversely proportional function with the vacuum holding time, decreasing rapidly in the early stage and slowing down in the later stage. Using the model, the contribution of different reaction sites to the dehydrogenation process was investigated. It was found that the internal spontaneous nucleation of the molten steel dominated the dehydrogenation process at the beginning. Then, the internal spontaneous nucleation gradually weakened to disappear as the hydrogen content of the molten steel decreased, followed by the dominance of dehydrogenation on the surface of the Ar bubble. The model also investigated the effect of vacuum pressure and argon flow rate on the VD dehydrogenation process. It was found that the vacuum pressure significantly influenced the dehydrogenation rate on the Ar bubble surface and the bath surface mainly by affecting the equilibrium hydrogen concentration in the gas phase and by influencing the critical nucleation depth, which affected the internal spontaneous dehydrogenation. Moreover, the increase of the argon flow rate not only increases the reaction area of the Ar bubble but also the reaction area at the activation zone on the bath surface. Additionally, the increase of the initial hydrogen content in the molten steel significantly promotes the spontaneous dehydrogenation of the internal nucleation in the bulk steel.