Welding Technology and Heat Treatment Butt-Welded Joints of Thin-Walled Inconel 718 Alloy Tubes

The subject of this research was the development of technology for welding and the heat treatment of butt-welded joints of thin-walled Inconel 718 alloy tubes, a process based on orbital TIG welding without a filler metal. The developed technology allows favorable conditions to obtain the appropriate hardness and mechanical properties in the weld area required by AMS 5589. In the tests, the microstructure and mechanical properties were evaluated. Compliance with the requirements was evaluated on the basis of metallographic and mechanical properties tests. The results obtained indicate that the weakest area of the joint is the base material of the thin-walled tube. The welded joints reveal elongation above 10% and tensile strength above 1400 MPa despite the dendritic structure of the weld. In the area of the welded joint, the occurrence of precipitates of the γ’ phase and mainly niobium carbide was revealed.