Fracture Toughness of Welded Thick Section High Strength Steels and Influencing Factors

One of the most significant problems associated with the implementation of high strength steels for offshore applications lies with the guarantee of welded joint reliability. An aspect of particular interest is the through thickness variation of heat affected zone toughness of thick section (above 60 mm) high strength steels. An experimental study combining microstructural investigations with a new adjusted sub-sized CTOD test was conducted in order to assess the fracture toughness in the heat affected zone (HAZ) of welds on high strength steels. The emphasis was placed on the coarse grain HAZ. The effects of variations in alloying and inclusion content on the microstructure and toughness properties have been studied. Results show that fracture toughness decreases in the mid-section of thick plates, which could be a result of non-uniform microstructure with local centerline segregation bands, larger grain sizes and inclusions, which act as crack initiation sites.