Irradiation creep and swelling of the US fusion heats of HT9 and 9Cr-1Mo to 208 dpa at similar 400 C

The irradiation creep and swelling behaviors of the fusion heats of HT9 and 9Cr-1Mo at similar 400 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. ((orig.))