Crack growth resistance of MAG butt-welded joints of S355JR construction steel

Fatigue crack growth resistance and elastic–plastic fracture toughness were measured on MAG (Metal Active Gas) butt-welded joints made of S355JR construction steel. For this purpose, C(T) specimens were extracted from virgin and welded 15 mm thick rolled plates. Tests were conducted on the base material (BM), the heat affected zone (HAZ) and weld metal (WM). The analyses showed that compressive residual stresses due to welding increased the fatigue crack growth resistance of WM and HAZ owing to crack closure effects. The WM displayed the lowest elastic–plastic fracture toughness with respect to HAZ and BM. The highest value was exhibited by the HAZ because stable tearing crack extension is forced along an unfavourable crack path. Therefore, particular care must be taken in evaluating the crack path in welded joints in order to correctly estimate their resistance to crack advance.