Welding of invar Fe-36Ni alloy for tooling of composite materials

Abstract

Summary Invar alloy has traditionally been used almost exclusively in the manufacture of high-precision measuring instruments. Recently, however, new structural uses, such as the manufacture of bulky composite tooling for the aerospace industry, have forced us to reconsider all the welding procedures previously used. The aim of this research is to investigate some of the problems of welding Invar, proposing practical solutions based on experience. Several issues were considered: i.e. precautions regarding purity of inert shielding gas and the absence of surface residue, the role of titanium added to the filler metal, sensitivity of the alloy to reheat cracking and the existence of precipitates and inclusions, etc. The presence of characteristic banding in the weld pool, its origin and effects on joint properties, were also investigated.