Weld Zone Characterization of Dissimilar SS UNS S43000/UNS S32304 Joined through Laser Beam Welding: EBSD Study, Phase Evolutions, and Fractography

Abstract

Dissimilar joints are growingly prevailing modern design of a wide range of equipment, especially in petrochemical, oil, and gas industries. In this research, UNS 43000 ferritic stainless steel and UNS 32304 duplex stainless steel were welded by a laser beam welding process in butt joint configuration, and microstructural evolutions and phase formation during laser welding were investigated using electron backscatter diffraction. The effect of heat input on the tensile properties and fracture behavior of the welded joint was also studied. It was observed that irregular grain orientations implied a relatively weak texture in the laser-welded joint. It was also found that three different phases, i.e., α (with bcc crystal structure), γ (with fcc crystal structure), and Cr7C3 (with hcp crystal structure), appeared in different areas of the welded joint. The predominant phase in the welded metal and the heat-affected zone was α (bcc). Also, despite the concentrated heat source on laser beam welding and the associated short cooling times, no martensitic structure was formed in these areas. By moving toward UNS 32304 base metal, more γ (fcc) phase was formed in the welded metal, which could be attributed to the higher concentration of austenite stabilizer elements, e.g., Ni and N, at UNS 32304 side. The presence of distinguished forms of austenite with fcc crystal structure, namely grain boundary allotriomorphic austenite and wedge-shaped Widmanstatten austenite, was seen mainly at ferrite grain boundaries and ferrite grain interior, respectively.