FIM/atom probe study of irradiated pressure vessel steels

Copper and phosphorus have a deleterious effect on the impact properties of pressure vessel steels that have been exposed to high doses of neutron irradiation. Field-ion microscopy (FIM)/ atom probe studies of irradiated A302B steel showed that these elements are concentrated in small regions within the ferrite matrix. Such regions were not detected in the unirradiated control samples. Analysis of the ferrite-ferrite and ferrite-cementite interfaces in the irradiated material indicated the segregation of various solute elements but not of copper or phosphorus. The irradiation also produces ultrafine molybdenum-rich carbides. These carbides may contribute to the small amount of matrix hardening left after 450 deg C temperature annealing. (author)