Phase stability of long term creep tested F82H and its correlation with irradiation resistance

谷川 博康*; 中島 基樹*; 酒瀬川 英雄   ; 安堂 正己*; 渡辺 淑之*; 野澤 貴史*; 加藤 雄大*; 中田 隼矢*

Tanigawa, Hiroyasu*; Nakajima, Motoki*; Sakasegawa, Hideo; Ando, Masami*; Watanabe, Yoshiyuki*; Nozawa, Takashi*; Kato, Yutai*; Nakata, Toshiya*

Reduced activation ferritic/martensitic (RAFM) steels have been developed as the candidate structural material of fusion reactor breeding blanket system, since fast reactor (FBR) irradiation experiments on commercial heat-resistant ferritic steels, which showed high swelling resistance, opened up the possibility of their application in fusion reactors. Phase stability, which is the key to creep properties in heat-resistant ferritic steels by preventing dislocation glide, was considered to be a key property for achieving high defect absorption strength, which is the key to irradiation resistance. One of RAFM steels intensively developed in Japan is F82H (Fe-8Cr-2W-0.2V-0.04~0.10Ta-0.1C). The 5-ton F82H melted in 1994 and 1995, together with their welded materials, were subjected to round-robin tests under the international cooperation of the International Energy Agency (IEA). As a part of IEA collaboration, the creep test campaign for these F82H IEA heat was initiated around 1997, and the world's longest creep test on RAFM steel, over 20 years, was completed with creep fracture times of 176019.5 hours (20.1 years) at 226 MPa/500 degree Celsius and 213475.0 hours (24.4 years) at 26.5 MPa /650 degree Celsius. In this study, detailed microstructure analyses concerning phase stability, especially the stability of precipitates, were carried out on the gage and grip section of fractured specimens of F82H after long-term creep testing. The phase stability of crept F82H was compared with that observed in aged and irradiated F82H, and the correlation between the two was discussed.