ABSTRACT
Pure charge materials are melted in a ceramic-lined vacuum induction furnace, in the so-called VIM (vacuum induction melting) process. Superalloys to be used for the production of castings are solidified in the form of cylindrical “sticks”, corresponding to a typical foundry furnace charge weight of about 50 kg. The sticks show a classical ingot structure, with columnar and equiaxed regions and a central shrinkage pipe (Figure 5.1-1). Since they are remelted in the foundry, the grain structure (Figure 5.1-2) is of little importance, the essential requirement being to control contamination in the form of oxide films, inclusions etc.
