Correction of the Phase Balance on Nd:YAG Pulsed Laser Welded Super Duplex Stainless Steel by Nickel and Cobalt Electroplating

With a volume fraction of austenite and ferrite that is roughly equal, super duplex stainless steels (SDSS) have good mechanical characteristics and a high level of corrosion resistance. Achieving an equilibrium microstructure in the fusion zone, and ensuring its qualities and uses, is the difficulty in SDSS laser welding. In general, when SDSS is welded with a technique inherently associated with high cooling rates, a mostly ferritic micro structure results. To maintain the alloy's mechanical properties and corrosion resistance, ferrite and austenite must remain in roughly equal quantities. To balance the microstructure, the addition of austenite stabilizing elements or heat treatments is indicated. The addition of alloying materials is challenging due to the Nd:YAG pulsed laser welding properties. An approach is to use metal electroplating to prepare the surfaces of the mechanical SDSS components that will be welded, therefore promoting the phase balance in the fusion zone. This work examined the use of metals electroplating techniques to encourage the enrichment of nickel and cobalt in the bead of UNS S32750 to be welded by pulsed Nd:YAG laser source and, as a result, prevent the phase imbalance. This was done because phase balance is important to the SDSS's characteristics and applications. Prior to butt-welding, two UNS S32750 SDSS sheets with a pulsed Nd:YAG laser, a nickel and cobalt layer, were electrodeposited onto the edge of one of them with a Watts bath procedure. By adjusting the deposition periods, different thicknesses of nickel and cobalt were utilized, and the microstructure of the weld bead was assessed. As the volume fractions of austenite clearly increased, the results demonstrated that the nickel and cobalt added in the fusion zone were effective in resolving the unwanted unbalanced microstructure that resulted from autogenous laser welding of the SDSS