Effect of grain boundary ferrite morphologies on impact toughness of X80 girth weld

• The GBF in WMC and WME are network structure and layered structure. • The crack propagation energy of WME is nearly twice than WMC. • The strain localization is easy to occur at the network structure GBF. The X80 girth weld microstructure formed by high-strength acicular ferrite and low-strength grain boundary ferrite was studied to investigate the effect of grain boundary ferrite morphologies on impact toughness. The results show that due to the difference in direction of heat loss caused by the narrow groove, the grain boundary ferrite morphology of the weld metal center and the weld metal edge are continuous network structure and parallel layered structure, respectively. The continuous network structure grain boundary ferrite causes strain localization, resulting in the formation of a large number of secondary cracks in the crack propagation process, which seriously deteriorates the toughness.