Numerical Study on the Effect of Electrode Polarity on Desulfurization in Direct Current Electroslag Remelting Process
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RODUCTION
ELECTROSLAG remelting processes have been widely employed to increase the production of special steels for applications in ocean, aeronautics, and nuclear industries.[1] Figure 1 displays a schematic of the ESR process with DC power supply. During this process, a DC is passed from the consumable electrode to the baseplate, creating Joule heating in the highly resistive calcium fluoride-based molten slag, whose large amount is enough to melt the electrode. A film of the molten metal is then created at the anode tip, while a droplet is gradually formed within QIANG WANG, YU LIU, and GUANGQIANG LI are with the The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081 Hubei, China, and also with the Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081 Hubei, China. Contact e-mail: [email protected] FANG WANG and BAOKUAN LI are with the School of Metallurgy, Northeastern University, Shenyang 110819, Liaoning, China. WENWEI QIAO is with the Jiangsu Huaneng Cable Company Limited, Yangzhou 225613 Jiangsu, China. Manuscript submitted November 16, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
the continuous melting process. The dense metal droplet sinks through the less dense slag, forming a liquid metal pool in a water-cooled mold.[2] Due to the chemical reaction, sulfur dissolved in the metal would be transferred into the slag. The desulfurization behavior could be expressed as follows: ½1 ½S þ 2e ¼ S2 ; where [ ] and ( ) indicated the matter dissolved in the metal and slag, respectively. The movement of sulfur ions or atoms during remelting has been found to be the rate-limiting step when compared with reaction rate,[3] and the transfer of sulfur ions or atoms is dramatically affected by coupled physical fields, including the electromagnetic field, flow pattern, and thermal history.[4,5] The DC power supply type has been proved to have great influence on the thermal behavior of the ESR furnace.[6] Generally, the DC ESR furnace could be supplied with the DCSP, i.e., the electrode is fed by an anodic current, and the DCRP, i.e., the electrode is imposed by a cathodic current. Kato et al. experimentally investigated the electric power consumption and the desulfurization rate in DC ESR process.[6] The melt rate of the DCRP remelting was found to be higher than
Fig. 1—Schematic of electroslag remelting process.
that of the DCSP remelting when the electrode diameter was 10 mm. However, the melt rate of the DCRP remelting decreased if the electrode diameter increased to 50 mm, and was smaller than that of the DCSP remelting. Besides, the desulfurization rate of the DCRP remelting with the 50 mm electrode is much larger than that of the DCSP remelting. The desulfurization of the remelting process with the 10-mm electrode was not studied. Paar et al. studied the effect of the polarity on the oxygen content and the inclusion type in the ESR ingot by using a labo
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