Weld Zone Characterization of Dissimilar SS UNS S43000/UNS S32304 Joined through Laser Beam Welding: EBSD Study, Phase E
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Weld Zone Characterization of Dissimilar SS UNS S43000/ UNS S32304 Joined through Laser Beam Welding: EBSD Study, Phase Evolutions, and Fractography Hossein Mostaan, Morteza Shmanian, Reza Moradi, Fardin Nematzadeh, Ali Sonboli, and Jerzy A. Szpunar Submitted: 22 May 2020 / Revised: 4 August 2020 / Accepted: 5 September 2020 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., a (with bcc crystal structure), c (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 a (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 c (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 Widmansta¨tten austenite, was seen mainly at ferrite grain boundaries and ferrite grain interior, respectively. Keywords
dissimilar welding, EBSD, laser welding, UNS S43000, UNS S32304
1. Introduction Ferritic stainless steel containing 10-30% of chromium in solid solution along with other alloying elements (with or without nickel) has excellent properties, such as high resistance to stress corrosion cracking and high pitting resistance, especially in chloride media (Ref. 1-5). It is also less expensive as it contains no nickel. The ferritic stainless steel has a great advantage—i.e., lower expansion coefficient—over austenitic stainless steel, so it can be used in applications in which resistance to temperature cycling is necessary (Ref. 3, 6). Also, ferritic stainless steel has found some important applications such as in the upstream part of exhaust lines, coal carriages, mufflers, and catalytic converters (Ref. 3, 7, 8). On the other side, duplex (dual-phase) stainless steel contains austenite (c) and ferrite (a) phases in its microstructure designed to represent an outstanding combination of beneficial aspects of austenitic and ferritic stainless steel, so they have generally high strength Hossein Mostaan, Reza Moradi, Fardin N
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