Heterogeneity of ion irradiation-induced hardening in A533B reactor pressure vessel model alloys

Reactor pressure vessels comprise bainitic steel structures, and are heterogeneous on the mesoscale. Nanoindentation techniques were used to evaluate the hardness of these structures on the micrometer scale, and to evaluate the heterogeneity in a specimen using the distribution of the hardness. Three A533B model alloys were irradiated by 2.8 MeV Fe2+ ions at 563 K, and the effects of ion fluence, ion flux, and chemical composition on the change in the hardness distribution were examined. Heterogeneity of the hardening is observed in high-copper specimens irradiated up to (2-10) x 10(14) ions/cm(2), where the average hardness increases the most. In these specimens, the hardness distribution broadens, and demonstrates that the hardening in certain positions (possibly where the initial hardness is high) is greater than in other positions. Variation in initial chemical composition (especially copper and carbon) or sink strength may cause a difference in the curing behavior.