MICROSTRUCTURAL EXAMINATION OF COMMERCIAL FERRITIC ALLOYS AT 200 DPA

Microstructures and density change measurements are reported for marte nsitic commercial steels HT-9 and modified 9Cr-1Mo (T91) and oxide dis persion strengthened ferritic alloys MA956 and MA957 following irradia tion in the FFTF/MOTA at 420 degrees C to 200 dpa. Swelling as determi ned by density change remains below 2% for all conditions. Microstruct ures are found to be stable except in recrystallized grains of MA957, which are fabrication artifacts, with only minor swelling in the marte nsitic steels and alpha' precipitation in alloys with 12% or more chro mium. These results further demonstrate the high swelling resistance a nd microstructural stability of the ferritic alloy class.