Mechanical and microstructural evaluation of SAF 2507 and incoloy 825 dissimilar welds

Abstract

This research work articulated a comparative study on Incoloy 825 Ni-based alloy and SAF 2507 super duplex stainless steel dissimilar joints. Welding was accomplished by ER2594 and ERNiFeCr-1 filler wires, pulsed current (PCGTAW) and continuous current gas tungsten arc welding (CCGTAW) techniques. Characterizations were conducted by optical microscopy, scanning electron microscopy equipped with an energy dispersive spectroscopy and X-ray diffraction. In order to investigate the evolution of mechanical properties of the weld joints’ micro-hardness, impact and tensile tests were employed. The results showed that Ti-rich phase was formed in weld zones employing ERNiFeCr-1 filler metal. On the other hand, Cr-rich phase was characterized in the weld zone of ER2594 sample employing CCGTAW. The welds of PCGTAW method displayed finer microstructure, lower ferrite contents and lack of Cr-rich phase formation. In tensile tests, fracture occurred at weaker base metals (Incoloy 825) in all cases. The use of ER2594 caused higher hardness and lower toughness than ERNiFeCr-1 filler metal. Based upon comparative investigations, ERNiFeCr-1 filler metal and PCGTAW technique were recommended to improve dissimilar joint efficiency.