Abstract
Ductility-dip cracking (DDC) is an elevated temperature, solid-state cracking phenomenon that is observed in austenitic weld metals. In this study, the DDC susceptibility of several high-chromium, nickel-base filler metals was evaluated using the strain-to-fracture (STF) test technique. These filler metals were of the Ni-30Cr type and included INCONEL® Filler Metals 52 and 52M supplied by Special Metals Welding Products Company, and Sanicro 68HP® and Sanicro 69HP® supplied by Sandvik AB. In addition, two experimental Ni-30Cr filler metals were evaluated which contained variations in other alloy additions, including niobium additions up to 2.5 wt% and molybdenum additions of 4 wt%. A wide range in DDC susceptibility was observed with these filler metals, including large heat-to-heat variations in filler metals with similar compositions. The experimental filler metals containing Nb and Mo were found to be remarkably resistant to DDC. Cracking susceptibility is primarily associated with the type and form of precipitate that forms along the weld metal migrated grain boundaries. The formation of Nb-rich, M(C,N) at the end of solidification has the most profound effect on DDC, since these precipitates are most effective in pinning the boundaries. The formation of M23C6 carbides during weld cooling or subsequent reheating can also affect DDC susceptibility in these filler metals.
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