(PS11047) The Influence of Solidification Conditions on the Quality of Remelting Electrodes

摘要

Commonly, in the production of nickel-based superalloys a remelting step follows primary vacuum induction melting (VIM). The remelting is usually carried out via electroslag remelting (ESR) or vacuum arc remelting (VAR) and improves the cleanliness, the compactness and to a certain extent the homogeneity of the metal. For selected highly stressed rotating components, even the combination of all three processes to the so-called triple melt route (VIM-ESR-VAR) is compulsory. Besides a thorough control of the remelting processes, a good electrode quality is essential to ensure the production of a defect-free and homogeneous ingot. Especially the VAR-process is prone to the presence of imperfections in the electrode like radial cracks or an extensive cavity pipe. The former can lead to undesired melt rate excursions, the latter to the formation of dendritic white spots, especially if the shrinking pipe contains dendrite clusters that can fall into the melt and sink to the bottom of the pool without melting. In the production of alloys that are susceptible to segregation, the attention has additionally to be turned to the homogeneous distribution of the alloying elements. The remelting processes are known to reduce microsegregation and radial macrosegregation, but as in the processes only a small volume of the metal is molten at a time, there is no possibility given to remove severe segregation over the height of the primary ingot that occurred during solidification.