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Multipass weld HAZs in structural steel exhibit a high level of heterogeneity. High-toughness and low-toughness microstructures can exist within 1 or 2 mm of each other. Low-HAZ crack-tip opening displacement (CTOD) results in some structural steels have been attributed to local brittle zones (LBZs), which exist in the coarse-grain heat-affected zone (HAZ) region (CGHAZ). Fracture initiation in an LBZ occurs by a weak-link process, which is described in this paper. If a particular weld contains LBZs, before a low CTOD result will occur, the precrack must be located close enough to the weak link that the crack-tip process zone can initiate fracture. HAZ CTOD precrack placement for welds containing LBZs is discussed, and the importance of posttest sectioning techniques is also explained. The line fraction of CGHAZ that was sampled by the crack tip was calculated for 485 HAZ CTOD tests (22 structural steels). These data are statistically analyzed to show that for welds containing LBZs, a low CTOD result becomes more probable if the crack samples more CGHAZ.
weldments, structural steels, heat-affected zone, fracture toughness, crack-tip opening displacement, local brittle zones, microstructure, weak link
Senior research engineer, Exxon Production Research Co., Houston, TX