Effect of initial base metal microstructure on weld hot cracking susceptibilities of Alloy 718 forgings

The effect of the base metal (BM) microstructure on the hot cracking susceptibilities of Alloy 718 during welding was investigated. A forged ring of Alloy 718 was subjected to a series of heat treatments to produce distinct initial BM microstructures with variations in grain size and precipitate distribution. The cracking susceptibilities in the fusion zone (FZ) and heat-affected zone (HAZ) were quantitatively assessed using Varestraint tests. The results revealed that the FZ cracking susceptibility increased with increasing BM grain size, owing to epitaxial grain growth during solidification that promoted the formation of coarser grains in the FZ. In the HAZ, cracking susceptibility was strongly influenced by Nb-rich precipitates formed during solution treatment, such as Laves and grain boundary δ phases, which promoted constitutional liquation and segregation-induced liquation along grain boundaries, respectively.