Modeling of Vacuum Arc Remelting of Alloy 718 Ingots

Abstract

Vacuum Arc Remelting (VAR) is typically the final melting process in the production of a wide range of alloys including superalloys, titanium, zirconium and specialty steels. During this process, a DC arc is struck under vacuum between a consumable electrode and a water-cooled copper crucible. The heat from the arc melts the electrode and molten metal droplets from the electrode solidify in the crucible to form an ingot. The purpose of VAR is to cast a sound, segregation free ingot. The soundness of the final structure and tendency for defect formation are determined by the pool profile and ingot solidification patterns during the process. These, in turn, depend on the melting parameters, which change as the ingot freezes. A carefully developed physics-based numerical model is useful in analyzing a priori the effect of melt parameters on the molten metal pool in the ingot. The purpose of this paper is to discuss the key features of such a model, and examine the effect of melting parameters on the pool profile. In addition, the effect of a molten metal pool perturbation during a power interruption and a melt rate cycle is examined for a 0.5m (20-inch) diameter ingot. Finally, the computed temperature distribution and flow field is used to predict the melting time for particles that fall into the molten pool and the likelihood of freckle formation in an alloy 718 VAR ingot.