IRRADIATION CREEP AND SWELLING OF THE US FUSION HEATS OF HT9-1MO AND 9CR-1MO TO 208-DPA AT SIMILAR-TO-400-DEGREES-C

The irradiation creep and swelling behaviors of the fusion heats of HT9 and 9Cr-1Mo at similar to 400 degrees C have been measured to exposures as large as 208 dpa, using both diametral and density measurements of helium-pressurized creep tubes. Void swelling was found in both alloys at 208 dpa to occur at rates of 0.012%/dpa or less, with the swelling of HT9 exhibiting a larger degree of stress enhancement than 9Cr-1Mo. The creep rate of HT9 is rather nonlinear in its response to hoop stress level in the range 0-200 MPa, but 9Cr-1Mo exhibits only slightly greater than linear behavior with stress level. The creep compliance and creep-swelling coupling coefficient for 9Cr-1Mo are consistent with values obtained for other steels.