This paper reports the results of a numerical study concerning the influence of local brittle zones intersecting the crack front on the fracture behaviour of welded joints. This work was performed using the numerical simulation of the three point bending test of weld samples with different amount of brittle structures at the crack front. Using 3D finite element discretization it was possible to simulate welded samples with very small fractions of brittle zone at the crack front, such as 5 %. Comparing the results of samples with increasing proportion of brittle zone it was observed a significant decrease in the crack growth resistance with increasing amounts of brittle material. This decrease in crack growth resistance was obtained even for samples with very small amounts of brittle material at the crack front.