The higher strength steels often show HEAT-AFFECTED ZONE (HAZ) softening. In the previous study, it was shown that CTOD toughness is much more important than strength matching to get higher welded joint performance in a stress concentrated region on the basis of the FEM analysis and wide plate test with through-thickness notch. This paper describes the further test results of the surface notched wide plate test with and without a stress concentrator. In conclusion, it shows that HAZ undermatching does not influence the deformability at the fracture of a welded joint in offshore structures. Moreover, it was shown that the local strain based CTOD approach can be applied to assess the fracture behavior of strength in an unevenly matched joint.


Offshore structures have been successfully used in cold and harsh environments such as the North Sea. This is partly due to the fact that high fracture toughness, especially CTOD toughness has been demanded in offshore structural steels as well as in welding consumables based on the fracture mechanics evaluation. Stringent CTOD testing is now carried out for weld HAZ of the steel. As offshore structures are going to be installed deeper and deeper in the sea, structures will become bigger and bigger. In order to save the weight of the topside structures from an economical viewpoint, there has been a trend toward using higher strength steels. Ih higher strength steels manufactured by either the thermo-mechanical control process (TMCP) or the quenching and tempering process (Q&T), HAZ softening (HAZ undermatching of strength) may occur, unlike normalized steel in which strength in the HAZ region is usually higher than the base plate, although the level and the width of HAZ softening depends on the chemistry of the base plate and the welding condition, especially heat input.

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