The relationship between the increase in tensile yield stress (YS) and the increase in the ductile-brittle transition temperature (DBTT) upon irradiation was studied for ASTM A 212-65 Grade B pressure vessel steel. Smooth tension specimens and Charpy V-notch impact specimens were irradiated in the same facility of the Oak Ridge Research Reactor under the same conditions of 60 C irradiation temperature and 1 × 1010 neutrons/cm2 (E > 1 MeV) fluence. The tension tests were carried out at temperatures from 20 to 473 K at two strain rates. The YS increased rapidly with decreasing test temperature, but the radiation-produced increment in YS was largely independent of test temperature. The impact specimens also were tested as a function of temperature and the increase in DBTT was determined based on absorbed energy and fracture appearance. To correlate the changes in YS and DBTT upon irradiation, strain-rate and triaxiality corrections were applied to the tensile yield stresses to approximate the corresponding stresses at the root of the notch of the impact specimens. The results of the tension and impact tests were found to be consistent, based on a critical cleavage stress deduced from the tension tests. No evidence for a decrease in the critical cleavage stress upon irradiation was noted.
The conclusion is that the radiation embrittlement is largely a consequence of radiation hardening and not a change in fracture properties as such.