Effect of Variation in Process Parameters on the Formation of Freckle in INCONEL 718 by Vacuum Arc Remelting

In order to study the effect of variation in process parameters on the final ingot of INCONEL 718 during vacuum arc remelting, a 508-mm-diameter vacuum arc remelting (VAR) ingot of INCONEL 718 was produced under conditions of variation in electrode diameter and arc gap. It was sectioned and analyzed in the as-cast state. Freckle was found in the midradius and center regions when the electrode diameter and arc gap changed. The experimental results were discussed in relation to composition, current distribution, and fluid flow. Freckle formation was found to be associated with large changes in melting conditions probably resulting in significant perturbation of the fluid flow in the melt pool and mushy zone. Instability in the solidification process may contribute to the initiation and formation of freckle defects in INCONEL 718 ingot.