CHARACTERIZATION OF IRRADIATED A533B PRESSURE VESSEL STEEL WELD

The microstructure of a neutron irradiated A533B pressure vessel steel weld has been characterized by atom probe field-ion microscopy.Many fine scale features including roughly spherical copper precipitates and clusters, spherical and rod-shaped molybdenum carbide and discshaped molybdenum nitride precipitates were observed inhomogeneously distributed in the ferrite matrix.The copper content of the ferrite was substantially reduced from the nominal level.A thin brightly-imaging film of molybdenum carbide and nitride was observed on grain boundaries.A large darkly-imaging copper-manganese precipitate was also observed on a boundary.Composition profiles indicated substantial enrichments of manganese and nickel a t the precipitate-ferrite interface and that the enrichment extended into the ferrite.Enrichments of nickel, manganese and phosphorus were also measured a t grain boundaries.