(PS11078) Metallurgical Characterisation of Failed Dissimilar Metal Weld-Interface Between a UNS S32760 Superduplex Stainless Steel and an Alloy 686CPT TIG Weld

摘要

The welded joint under investigation comprised of an Alloy 686CPT TIG closure weld between Alloy 625 buttering layers on ASTM A182 Grade F22 low alloy steel forging and a UNS S32760 superduplex stainless steel (SDSS) pipe. During 180° side-bend testing, failures were observed at the dissimilar metal interface between the 686 TIG closure weld and the UNS S32760 superduplex stainless steel. The interface was critically analysed in terms of fracture morphology, microstructure development, intermetallic phase distribution, and strain distribution. Even though side-wall lack of fusion and porosity were observed, failures were actually shown to have occurred from the combined effects of exhaustion of the plastic deformation capacity due to strain concentration on the weld metal as a result of a slight undermatching in strength compared to the parent material combined with decreased ductility due to the presence of Sigma and Mu intermetallic phases.