A Parametric Study of the Vacuum Arc Remelting (VAR) Process: Effects of Arc Radius, Side-Arcing, and Gas Cooling
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vacuum arc remelting (VAR) process is extensively used to purify numerous alloys such as stainless steel, Nickel-based, and Titanium-based alloys. It is a method of refining an impure alloy (electrode in VAR) through vacuum as heated by a DC arc. The tip of the electrode melts resulting in the formation of droplets. Afterward, droplets drip through the vacuum and reach the molten pool. The molten pool solidifies in a water-cooled mold to build the high-grade, ultraclean alloy as schematically shown in Figure 1(a). Droplets carry low-density oxide inclusions to the molten pool. Inclusions are transferred to the solidification rim (more precisely the surface of ingot) near the mold. Furthermore, unfavorable elements with high vapor pressure
E. KARIMI-SIBAKI and A. KHARICHA are with the Christian-Doppler Laboratory for Metallurgical Applications of Magnetohydrodynamics, Montanuniversitaet of Leoben, FranzJosef-Str. 18, 8700 Leoben, Austria. Contact e-mail: [email protected] M. WU, A. LUDWIG, and J. BOHACEK are with the Chair of Simulation and Modeling of Metallurgical Processes, Montanuniversitaet of Leoben, Franz-JosefStr. 18, 8700 Leoben, Austria. Manuscript submitted April 13, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
such as Pb, Sn, Bi, Te, As, and Cu are evaporated under vacuum conditions. Some of those elements may condensate on the mold wall. Modeling VAR process is very challenging and controversial as the process involves a wide range of physical phenomena and their interactions. Modeling activities are required to study each phenomenon including formation and movement of cathode spots at the tip of electrode,[1–7] the vacuum plasma,[4,5,8–20] the electric current transferred directly between the electrode and mold, known as ‘‘side-arcing,’’[12,18,21–24] the thermal radiation in the vacuum region,[21,25,26] melting of the electrode,[8,27–38] the influence of electromagnetic field on the flow known as magnetohydrodynamics (MHD) in the molten pool,[39–48] and the solidification of the ingot.[44,49–63] To attain a deeper understanding of modeling challenges, a brief description is given for each of those phenomena in the following. Cathode spots with the sizes in the range of 1 to 100 lm are the centers of plasma production from where electrons/ions are emitted to the vacuum plasma region. Each cathode spot carries a tremendous amount of electric current (~ 1010 to 1012 A m2), where the temperature is remarkably high (~ 1-1.2 eV corresponds to 11,000 K to 14,000 K).[4] Formation and movement of the cathode spots are described by self-similarity (Fractal) model in quantum mechanics. In this approach, the movement of the spots is assumed to be governed by a combination of the stochastic random
Fig. 1—(a) Schematic representation of VAR process and its main components, (b) A cross section of the VAR process is illustrated to indicate different regions and corresponding interfaces/boundaries. Calculations are carried out considering a 2D axisymmetric model.
motion and a drift in the retrograde di
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