Fracture behavior in a pressure vessel steel weld

The fracture behavior of pressure vessel steel weld, with notch pre-crack tip completely located in the heat-affected zone (HAZ) is investigated. It is shown that the ductile fracture occurs by the redirection of the crack propagation from the HAZ to the weld metal. Analysis by optical microcopy, SEM and energy-dispersive X-ray spectrometry has revealed that the improvement in the toughness, and thus the higher resistance to crack propagation in the HAZ, is due to the presence of a large proportion of fine acicular ferrite. The size and distribution of inclusions seems to influence the formation of fine acicular ferrite. The effect of the hardness distribution on the fracture behavior of the weld is also analyzed.