Influence of process parameters during secondary melting of nickel based superalloys

Abstract

The superalloys are characterised by a strong tendency to form segregation defects during solidification and consequently have been the subject of much attention in the development of suitable melting and casting techniques. Processes such as vacuum arc remelting and electroslag remelting are now mature technologies and have well developed strategies for minimising segregation defects in the ingots produced. However, as the process control systems have gradually become more complex and automated, the need for control logic and a good understanding of it has become pronounced. Here, the underlying technical reasons for adopting particular process control methodologies are considered. The role of process parameters in controlling slag temperature and flow patterns in the electroslag remelting process and the metal pool thermal regime in the vacuum arc remelting process is reviewed in the context of ingot solidification, with particular attention being paid to electrode position, dimensions and the need for parameter stability. It is concluded that the equipment designs presently available for these processes are fundamentally correct, but that the control systems must be instructed carefully in order to produce the desired results.