This paper presents the results of a detailed microstructural evaluation of Linde 80 submerged arc weld metals typically found in Babcock and Wilcox 177FA Class reactor vessels. Optical metallography was performed on Linde 80 weld metals to characterize the grain structure, and scanning electron microscopy (SEM) was used to characterize the fracture surfaces. These weld metals have a tempered bainitic structure with large amounts of manganese rich inclusions.

Analytical transmission electron microscopy (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 electron diffraction (CBED) and energy dispersive X-ray (EDS) techniques were carried out to identify the particle chemical composition and crystal structure. These results are compared with published results from simulated reactor vessel welds found in the in-situ annealing program sponsored by the Electric Power Research Institute (EPRI).