Mass Transfer Model of Desulfurization in the Electroslag Remelting Process

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ELECTROSLAG remelting (ESR) has been widely employed in the production of special steels and alloys due to its specific advantages, such as efficient removal of non-metallic inclusions, effective slag refining, and excellent solidification structure of final products.[1,2] With the requirements for high-quality steel products becoming increasingly strict, the inert gas protection has been employed to reduce the level of oxygen inclusions, decrease the oxidation of alloying elements, and improve the steel cleanliness during the ESR process. However, as the oxidative desulfurization at the slag/air interface is restrained by the inert gas, the sulfur content in the ingot is likely to increase as a result of the accumulation of sulfur in the slag (S2) during remelting process. Therefore, for better control of sulfur content in steel, it is important to have a good understanding of the effect of slag on desulfurization as well as desulfurization kinetics during ESR process. Some studies on the control of sulfur content and sulfide inclusions in ingots during the ESR process have DONG HOU, ZHOU-HUA JIANG, YAN-WU DONG, YANG LI, WEI GONG and FU-BIN LIU are with the School of Metallurgy, Northeastern University, Shenyang, 110819, Liaoning, China. Contact e-mail: [email protected] Manuscript submitted July 27, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B

been reported. Shi et al.[3] investigated the effect of oxygen control on inclusion characteristics during the ESR of die steel, and assessed the evolution of (Cr, Mn)S inclusions in S136 die steel based on the thermodynamic analysis. Dong[4] studied the effect of slag on inclusions during electroslag remelting process of die steel, and obtained the excellent desulfurization during the ESR process. However, a very few works have been reported to study the effect of slag and remelting process on desulfurization during ESR on the basis of kinetics analysis, which is more important for practical operation. Here we thoroughly investigated the effect of slag on desulfurization during the ESR process through experimental study and theoretical calculations. Experiments of electroslag remelting were carried out with two different kinds of slags using a 50-kg ESR furnace. A new mass transfer model has been developed to reveal mechanism of desulfurization kinetics in ESR, which can also be used to elucidate the oxidation of active elements (such as Ti, Al, Si, Cr, and Mn) based on the kinetic analysis. The present work is expected to provide sulfur content in ingot control technique which can be applied to actual ESR operation by controlling the slag composition and sulfur in electrode. II.

EXPERIMENTAL

ESR experiments were carried out using a 50-kg lab-scale ESR furnace with a water-cooled copper mold

of 134 mm in inner diameter. The image and schematic diagram of ESR furnace are shown in Figure 1. The consumable electrode material used in experiments was stainless steel 1Cr21Ni5Ti with a diameter of 60 mm and a length of 2000 mm. The chemical composition of the electrode

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