Probe Pulse Conditions and Solidification Parameters for the Dissimilar Welding of Inconel 718 and AISI 316L Stainless S
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DING and joining of dissimilar materials significantly reduce component costs by diminishing the volume of expensive materials without sacrificing their service condition. The bimetallic combination of Inconel 718, a Ni-Cr-based superalloy, and AISI 316L austenitic stainless steel has applications in the aerospace, chemical processing and oil industries in addition to nuclear and gas power stations for the fabrication of various hot section components.[1] In a compressor rotor, the high-pressure and low-pressure stages are made of Inconel 718 and AISI 316L austenitic stainless steel, respectively.[2] Inconel 718 is a precipitation-hardened superalloy that is strengthened primarily by c¢¢ (Ni3Nb) precipitates and has a complicated microstructure.[3] It has excellent mechanical properties along with extensive corrosion and oxidation resistance up to a temperature of 650 C. Hence, it is suitable for various high-temperature applications, even those in extreme
A.K. SAHU and S. BAG are with the Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India. Contact e-mail: [email protected]. Manuscript submitted July 15, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
environments.[4] AISI 316L stainless steel also exhibits excellent mechanical properties along with excellent oxidation and corrosion resistance at elevated temperatures. A low amount of carbon in the alloy makes it immune to sensitization at elevated temperatures.[5] AISI 316L stainless steel possesses excellent toughness at cryogenic temperatures, which makes it distinct from other chromium-nickel-based austenitic stainless steels. Dissimilar welding is always a challenging task since the variability in composition and thermophysical properties may result in metallurgical incompatibility between the metals. Various intermetallic phases lead to the incompatibility of joining Inconel 718 and AISI 316L stainless steel with fusion welding processes and influence the solidification cracking and/or liquidation cracking in the fusion zone and heat-affected zone (HAZ).[6,7] The time-temperature profile of the welding technique influences the formation of various Nb-based brittle intermetallic phases, such as NbC and Laves [(Ni, Cr, Fe)2 (Nb, Ti, Mo)], in the interdendritic regions. These intermetallic phases are mainly responsible for the hot cracking of the weld or microfissuring during solidification. Microfissuring is related to the presence of the d-phase at the boundaries of fine grains. It forms due to the presence of NbC in coarse-grained materials.[3] In AISI 316L stainless steels, d-ferrite that forms in the range from 3 to 9 pct diminishes the hot cracking
tendency, but a higher percentage of d-ferrite reduces the creep life and corrosion resistance.[5] Dissimilar welding of Ni-based superalloys and austenitic stainless steels are not completely free from metallurgical issues. The segregation of the Nb-rich phase may occur at the HAZ and fusion zone. The formation of intermetallics that are enriched with Nb, M
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