Mechanism of crack formation of the butt joint between UMCo50A and Inconel 600

The burner nozzle serves as the core component in pressurized coal-water slurry gasification systems . During the butt welding process between the nozzle and a nickel-based alloy cooling water coil, cracks were observed in the Heat Affected Zone (HAZ) of the welded joint. To address technical and safety concerns in industrial applications, this study systematically investigated the crack formation mechanism through microstructural characterization. Results indicate that liquation cracks originate from partial liquefaction of M 23 C 6 carbides along grain boundaries during the welding thermal cycle. The liquefied carbides combine with low-melting eutectic phases to form discontinuous liquid films at grain boundaries. As the material approaches its solidification temperature, these viscous liquid films exhibit limited fluidity. Subsequent welding tensile stresses induce liquid film decohesion from grain boundaries, ultimately generating microvoids that coalesce into macroscopic cracks. • The crack at the butt joint of the UMCo50 burner and the Inconel 1600 cooling water coil is a liquation crack. • The M 23 C 6 Carbides production is a key factor in crack initiation. • Complete revelation of intergranular product production and crack formation processes.