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This paper presents the results of additional microstructural evaluations of Mn-Mo-Ni wire/Linde 80 flux submerged-arc weld metals typically found in Babcock & Wilcox fabricated reactor vessels. Optical metallography was performed on four Mn-Mo-Ni wire/Linde 80 surveillance weld metals to study the grain structure and to characterize the size and distribution of macroinclusions (>0.26 μm). These weld metals have a tempered bainitic structure with large amounts of manganese-rich inclusions.
Analytical TEM was used to characterize the carbides, coarse (0.1 to 2.0 μm) inclusions, and fine (2 to 50 nm) precipitates. Thin foil and extraction techniques were used to characterize particle morphology, while convergent beam diffraction and energy dispersive X-ray techniques were carried out to identify the crystal structural and chemical composition. The results are compared with previously evaluated Mn-Mo-Ni wire/Linde 80 flux submerged-arc weld metals. The data suggest that the initial Charpy impact properties may be related to the size and distribution of inclusions and not to their composition.
transmission electron microscopy, optical microscopy, scanning electron microscopy, convergent beam diffraction, energy dispersive X-ray technique, thin foil technique, extraction technique, submerged arc weld, reactor vessel, inclusion, copper precipitation, carbides
Professor, University of Virginia, Charlottesville, VA
Advisory engineer (Materials), B&W Nuclear Service Co., Lynchburg, VA