The ductile-to-brittle transition behavior of martensitic steels neutron irradiated to 26 dpa

Charpy impact tests were conducted on specimens made of HT-9 and 9CR-1Mo in various heat treatment conditions that were irradiated in EBR-II to 26 dpa at 390 to 5000C. The results are compared with previous results on specimens irradiated to 13 dpa. HT-9 base metal irradiated at low temperatures showed a small additional increase in ductile brittle transition temperature and a decrease in upper shelf energy from 13 to 26 dpa. No fluence effect was observed in 9Cr-1Mo base metal. The 9Cr-1Mo weldment showed degraded ductile-to-brittle transition temperature (DBTT) but improved upper shelf energy (USE) response compared to base metal, contrary to previous findings on HT-9. Significant differences were observed in HT-9 base metal between mill annealed material and normalized and tempered material. The highest DBTT for HT-9 alloys was 500C higher than for the worst case in 9Cr-1Mo alloys. Fractography and hardness measurements were also obtained. Significant differences in fracture appearance were observed in different product forms, although no dependence on fluence was observed. Failure was controlled by the preirradiation microstructure