Dissimilar welding of duplex stainless steel with Ni alloys: A review

This review article presents an overview of the dissimilar welded joint's microstructure and mechanical behavior. Dissimilar metal weldings are generally employed in high-pressure tubing/tubing-coupler assembly generally functional in subsea oil-gas production instruments and a wide range of geothermal plants and piping systems for subsea manifolds. Thus, dissimilar metal welding has an essential role in enhancing the subsea oil-gas drilling system's structural integrity. Dual-phase super duplex stainless steel 2507 (super DSS 2507) comprises a balanced phase of austenite and ferrite, establishing great attention of manufacturers and researchers due to its mechanical strength and corrosion resistance properties in several hostile surroundings like marine, offshore, petrochemical, and nuclear power plant. The other most frequently used material in the marine application is nitronic steel (N50), primarily used in subsea oil and gas developments in tube and couplers for its corrosion resistance, high strength, and resistance to galling. Nickel-based superalloy Inconel 625 has significant application in the aviation, petrochemical, and marine industry due to its high tensile, yield, and creep strength with excellent corrosion properties in an unfavorable environment. The dissimilar joining of these materials is repeatedly required in marine and offshore industries. This review focuses on the significant difficulties related to the dissimilar welding of super DSS 2507 with nitronic steel (N50) and Inconel 625. Unlike chemical composition, metallurgical properties, mechanical and physical properties of these steel and nickel alloys lead to the problem like stress corrosion cracking, hydrogen embrittlement, ductility dip cracking and migration of carbon. The other metallurgical problems are deleterious secondary phase formation, carbon diffusion-related problem, d-ferrite phase present in the fusion zone, and residual stresses are required to be removed or decrease their intensity for the qualification of the weld. The effect of intermetallic phases such as sigma phase, FCC carbides like (M23C6, M6C, and M7C3), laves phase, R and chi-phase, Z-phase on the mechanical property of dissimilar welded joints of each material are reviewed in detail. After the extensive literature review, proper selection of filler metal has also been covered in this article because it plays an essential role in decreasing some of the dissimilar welded joint problems. Heterogeneity across the weldment, unmixed zone formation including peninsula, island, beaches, and filler deficient region, grain boundaries related problems during the dissimilar welded joint of these materials is also discussed thoroughly in this article. The effect of residual stresses in the dissimilar welded joint's distinct condition has also been discussed in detail.

Automated summary

This review article provides an overview of the microstructure and mechanical behavior of dissimilar welded joints, with a focus on the challenges related to the dissimilar welding of super DSS 2507 with nitronic steel (N50) and Inconel 625.