Liquation cracking in Inconel 617 alloy by Laser and Laser-Arc Hybrid welding

Abstract

The present study investigates susceptibility of Inconel 617 to liquation cracking in laser-based welding techniques such as autogenous laser welding (ALW) and laser-MIG hybrid welding (LHW) with variation in heat input. Advanced characterization techniques such as high-speed Nano-Indentation testing and micro X-ray diffraction techniques were utilized to analyze microstructural variations in correlating mechanical behavior of low-melting eutectics formed in partially melted zone (PMZ). Results indicated that the liquation cracking in PMZ was associated with the constitutional liquation reaction between intermetallic carbides and austenite matrix. With increase in heat input, its susceptibility reduced, although with enhancement in grain-boundary liquid film formation and was associated with the constitutional liquation of (Cr, Mo)-rich M23C6 carbides and γ matrix. Combined effect of induced thermal stress with presence of low-melting eutectics in partially melted zone was found to greatly influence liquation-cracking susceptibility in both the welding processes. Indeed, ternary eutectic comprising metallic carbides of Cr and Mo and austenite-matrix with low nano-hardness values compared to that of hard carbides present in base metal and weld fusion zone re-confirmed their influence on cracking susceptibility. Increase in heat input enhanced dissolution of Mo-rich M6C carbides that attributed to stress-relaxation and thereby reduce cracking propensity.