Trace element control in vacuum induction and consumable–electrode melted Ni superalloys

Abstract

Undesirable trace elements in Ni superalloys are classified, and the advanced methods of analytical detection described. The improvement in analytical techniques for these trace elements, together with more stringent user operating demands, has resulted in a progressive tightening of material specifications over the past decade. Control of these elements in Ni superalloy melting practice based on ‘state of the art’ producer experience is discussed, together with the importance of raw material selection. The levels of trace elements in virgin raw materials, as used for cast remelt bar and wrought alloy manufacture in the authors' company, are detailed, together with the problems associated with the recycling of scrap from foundries and end users. The effectiveness of secondary melting by vacuum arc remelting, electroslag remelting, and electron-beam remelting, in terms of chemical refinement, is discussed and contrasted with that of vacuum induction melting.