Fracture behaviour of specimens with surface notch tip in the heat affected zone (HAZ) of strength mis-matched welded joints

The generally accepted conditions for the strength overmatched welded joints of high strength steel are not clearly defined. In this paper, the fracture mechanics analysis of specimens, with surface notch tips completely embedded in the heat affected zones was conducted. The results showed that the strength of mismatching of a welded joint caused a redirection of the crack propagation towards the low strength region of the welded joint. This redirection of the crack propagation affected the values of the critical CTOD. In the cases of the overmatched welded joints containing a soft root layer it is possible to achieve a comparable fracture behaviour related to the homogeneous overmatched welded joint if the impact toughness of the soft root layer is higher than the impact toughness of the overmatched weld metal. Such a type of welded joint is therefore preferable for the welding of high strength low alloy steels, because it enables the manufacturing of a welded joint without preheating.