低放射化マルテンサイト鋼における高濃度ヘリウムによる自己修復機能の発現

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The experimental results were summarized as follows :1. Helium effects : 1) Martensitic steels does not suffer embrittlement by helium implantation up to 600 atppm at 423K. Post-implantation annealing results in the formation of helium bubbles but no helium-induced intergranular facture was observed.2. Mechanism of suppression of helium embritlement : Martensitic structure that consists of high density dislocation, solid solutioning elements and a number of precipitates traps helium and vacancies, which results in the wide distribution of helium and vacancies in the martensitic structure and prevent the helium atoms from segregation at grain bondaries.3. Mechanism of retardation of the recovery of irradiation hardening : Helium stabilizes vacancy cluster at higher temperature and suppress the decomposition of V-clusters. Consequently, mutual annihilation of dislocation loops and vacancies was retarded.Conclusion : Helium trapping and irradiation-induced dislocation loop formation shifts the transition temperature of hardening/softening. It is considered that the high temperature creep properties will be improved by the simultaneous introduction of the displacement damage and helium atoms.