Laser-multi-pass-narrow-gap-welding of nickel superalloy—Alloy 617OCC

Stringent requirements on creep strength and corrosion/oxidation resistance mean that nickel-based superalloys will be the material of choice for high-temperature and high-pressure (HT/HP) applications in the future. Components for these HT/HP processes in turbines, housings, or piping are often characterized by their large dimensions and wall thicknesses of ≥20 mm. Because of the high material costs and difficult machinability of Ni-based components in comparison to steel components, an efficient and reliable welding technology that produces crack-free weld seams is a necessary precondition for economic manufacturing. Conventional arc welding technologies require low welding speeds, large quantities of filler material, and large input energy per unit length, which can result in damages to microstructure and consequently diminished HT properties. Laser-multi-pass-narrow-gap-welding (Laser-MPNG) is the solution to this problem. This paper presents the technological approach of Laser-MPNG, which uses a brilliant fiber laser with a maximum laser power of 4 kW and remoweld^®MPNG, a welding head that was specifically developed to join the nickel superalloy Alloy 617OCC as a promising candidate for future industrial welding applications in pipe elements of up to 72.5 mm wall thickness in modern power stations.