RADIATION-INDUCED MICROSTRUCTURAL EVOLUTION IN FERRITIC MARTENSITIC STEELS

R & D of ferritic/martensitic steels as structural materials for fusio n reactor is one of the most important issues of fusion technology. Th e efforts to characterize microstructural evolution under irradiation in the conventional Fe-Cr-Mo steels as well as newly developed Fe-Cr-M n or Fe-Cr-W low activation ferritic/martensitic steels have been cont inued. This paper provides some of the recent results of heavy irradia tion effects on the microstructural evolution of ferritic/martensitic steels neutron irradiated in the FFTF/MOTA (Fast Flux Test Facility/ M aterials Open Test Assembly). Materials examined are Fe-10Cr-2Mo dual phase steel (JFMS: Japanese Ferritic/Martensitic Steel), Fe-12Cr-XMn-1 Mo manganese stabilized martensitic steels and Fe-8Cr-2W tungsten stab ilized low activation martensitic steel (F82H). JFMS showed excellent void swelling resistance similar to 12Cr martensitic steel such as HT- 9, while the manganese stabilized steels and F82H showed less void swe lling resistance with small amount of void swelling at 640-700 K (F82H : 0.14% at 678 K). As for irradiation response of precipitate behavior , significant formation of intermetallic chi phase was observed in the manganese stabilized steels along grain boundaries which is thought t o cause mechanical property degradation. On the other hand, precipitat es identified were the same type as those in unirradiated condition in F82H with no recognition of irradiation induced precipitates, which s uggested satisfactory mechanical properties of F82H after the irradiat ion.