Proton irradiation effects on tensile and bend-fatigue properties of welded F82H specimens

In several institutes, research and development for an accelerator-driven transmutation system (ADS) have been progressed. Ferritic/martensitic (FM) steels are the candidate materials for the beam window of ADS. To evaluate of the mechanical properties of the irradiated materials, the post irradiation examination (PIE) work of the SINQ (Swiss spallation neutron source) target irradiation program (STIP) specimens was carried out at JAEA. In present study, the results of PIE on FM steel F82H and its welded joint have been reported. The present irradiation conditions of the specimens were as follows: proton energy was 580 MeV. Irradiation temperatures were ranged from 130 to 380 °C, and displacement damage level was ranged from 5.7 to 11.8 dpa. The results of tensile tests performed at 22 °C indicated that the irradiation hardening occurred with increasing the displacement damage up to 10.1 dpa at 320 °C irradiation. At higher dose (11.8 dpa) and higher temperature (380 °C), irradiation hardening was observed, but degradation of ductility was relaxed in F82H welded joint. In present study, all specimens kept its ductility after irradiation and fractured in ductile manner. The results on bend-fatigue tests showed that the fatigue life (Nf) of F82H base metal irradiated up to 6.3 dpa was almost the same with that of unirradiated specimens. The Nf of the specimens irradiated up to 9.1 dpa was smaller than that of unirradiated specimens. Though the number of specimen was limited, the Nf of F82H EB (15 mm) and EB (3.3 mm) welded joints seemed to increase after irradiation and the fracture surfaces of the specimens showed transgranular morphology. While F82H TIG welded specimens were not fractured by 107 cycles.