scope:

This review encompasses a very large body of data obtained both from the open technical literature and privately sponsored research programs on the topic of underclad cracking, that is, cracking underneath weld cladding in pressure-vessel components. The purpose of the review was to determine what factors contribute to this condition, and to outline means by which it could be either alleviated or eliminated. In the course of the review, a substantial data bank was created on the manufacture, heat treatment, and cladding of heavy-section pressure vessel steels for nuclear service. Underclad cracks were defined as intergranular separations no less than about 3 mm (0.12 in.) deep and 3 mm (0.12 in.) long found in the coarse-grained heat-affected zone of low-alloy steels underneath the weld-cladding overlay. Grain-boundary decohesions of sizes less than this were also included in the investigation. They are generally produced during postweld heat treatment. The combination of three factors that promote underclad cracking are a susceptible micro structure, a favorable residual-stress pattern, and a thermal treatment bringing the steel into a critical temperature region, usually between 600 and 650C (1112 and 1202°F) were creep ductility is low. Weld-overlay cladding with high-heat-input processes provides the susceptible micro structure and residual-stress pattern, particularly where weld passes overlap, and postweld heat treatment provides the critical temperature