Electron beam welding of 2205 duplex stainless steel using pre-placed nickel-based filler material

Abstract

Duplex stainless steels are commonly used in the chemical as well as in the oil and gas industry due to their excellent mechanical properties and corrosion resistance. In this research, electron beam welded duplex stainless steel joints were investigated regarding their microstructure, mechanical and corrosion properties. Since the balance between austenite and ferrite is determined by the cooling rate and the chemical composition, a pre-placed nickel-based filler material was added to the weld joint in order to promote the austenite formation, which is suppressed by the rapid cooling. This is a common phenomenon in power beam welding processes. A suitable weld geometry was achieved by oscillating and defocusing the electron beam. Thereby, the process tolerates the diverse disturbances resulting from the production as well as an unexpected occurrence of a non-zero gap size. Using a nickel-based filler wire, the welds show an excellent austenite-ferrite balance, but with heterogeneous distribution over depth due to the insufficient dilution of filler wire and base material. As a result of a balanced microstructure, the post-welding heat treatment may become necessary solely in exceptional cases. The measured values of tensile strength as well as the impact energy meet all the requirements of the EN 10088-2 and EN ISO 17781, respectively. Furthermore, the critical pitting temperature values measured in the various regions of the seam are lower compared to the base material, although, they are above of the acceptance value according to EN ISO 17781.