Embrittlement of reduced-activation ferritic/martensitic steels irradiatedin HFIR at 300 degrees C and 400 degrees C

Miniature tensile and Charpy specimens of four ferritic/martensitic steels were irradiated at 300 degreesC and 400 degreesC in the high flux isotope r eactor (HFIR) to a maximum dose of approximate to 12 dpa. The steels were s tandard F82H (F82H-Std), a modified F82H (F82H-Mod), ORNL 9Cr-2WVTa, and 9C r-2WVTa-2Ni, the 9Cr-2WVTa containing 2% Ni to produce helium by (n,alpha) reactions with thermal neutrons. More helium was produced in the F82H-Std t han the F82H-Mod because of the presence of boron. Irradiation embrittlemen t in the form of an increase in the ductile-brittle transition temperature (Delta DBTT) and a decrease in the upper-shelf energy (USE) occurred for al l the steels. The two F82H steels had similar Delta DBTTs after irradiation at 300 degreesC, but after irradiation at 400 degreesC, the Delta DBTT for F82H-Std was less than for F82H-Mod. Under these irradiation conditions, l ittle effect of the extra helium in the F82H-Std could be discerned. Less e mbrittlement was observed for 9Cr-2WVTa steel irradiated at 400 degreesC th an for the two F82H steels. The 9Cr-2WVTa-2Ni steel with approximate to 115 appm He had a larger Delta DBTT than the 9Cr-2WVTa with approximate to5 ap pm He, indicating a possible helium effect. (C) 2000 Elsevier Science B.V. All rights reserved.