Effect of heat treatment and irradiation temperature on impact properties of Cr-W-V ferritic steels

Charpy impact tests were conducted on eight normalized-and-tempered ferriti c and martensitic steels irradiated in two different normalized conditions. Irradiation was conducted in the Fast Flux Test Facility (FFTF) at 393 deg rees C to approximate to 14 dpa on eight steels with 2.25%, 5%, 9%, and 12% Cr (0.1% C) with varying amounts of W, V, and Ta. The different normalizat ion treatments involved changing the cooling rate after austenitization. Th e faster cooling rate produced 100% bainite in the 2.25Cr steels, compared to duplex structures of bainite and polygonal ferrite for the slower coolin g rate. For both cooling rates, martensite formed in the 5% and 9% Cr steel s, and martensite with approximate to 25% delta-ferrite formed in the 12% C r steel. Irradiation caused an increase in the ductile-brittle transition t emperature (DBTT) and a decrease in the upper-shelf energy (USE). The diffe rence in microstructure in the low-chromium steels due to the different hea t treatments had little effect on properties. For the high-chromium martens itic steels, only the 5Cr steel was affected by heat treatment. When the re sults at 393 degrees C were compared with previous results at 365 degrees C , all but a 5Cr and a 9Cr steel showed the expected decrease in the shift i n DBTT with increasing temperature. (C) 1999 Elsevier Science B.V. All righ ts reserved.