Fracture toughness evaluation of multipass weld HAZ considering the strength mismatch effect. (MITS WP 1761)

The paper describes heat affected zone-notched crack tip opening displacement tests of multipass welds in yield strength = 420-460 MPa class high strength steels for offshore structural applications. The weld metal strength overmatch causes different fracture behaviour depending on the actual coarse-grained (CG) HAZ toughness. When the CGHAZ is completely embrittled, the weld metal strength overmatch leads to the lower bound critical CTOD value. This is due to elevation of the local stress in the CGHAZ caused by the restraint effect of the overmatched weld metal. [From Japanese].