Microstructure evolution and mechanical properties of flash butt-welded Inconel718 joints

Microstructural evolution and mechanical properties of the Inconel718 alloy subjected to flash butt welding are investigated in this work. A gradient structure without welding defaults in a heat-affected zone (HAZ) is formed on the base material (BM) because of a thermal gradient and strain gradient. A gradient of the grain size results from a decrease in the recrystallization degree from the welding seam (WS) to the coarse-grained zone (CGZ). In addition, dissolution of the γ″ and γ′ phases occurred after temporary flashing, and this is mainly responsible for the lower ductility and strength (hardness) in the HAZ. However, formation of GB carbides and their coarsening account for the decrease in impact toughness in WS and adjacent zones. Meanwhile, a double-necking phenomenon during loading is attributed to the coarse carbides in WS and to large grains in the CGZ. Despite a decrease in ductility, the welding joint exhibits sufficient formability during roundness correction and bulging deformation. This work provides a new understanding of the good properties that the flash butt-welded Inconel718 alloy has, and this is expected to be applicable for other superalloys.