In-beam fatigue behavior of F82H steel at 500 °C

Stress-controlled fatigue tests were conducted for side-notched small specimens of F82H steel under in-beam and unirradiated conditions with 17 MeV protons at 500 °C. The environment for the fatigue tests was impure He gas containing 10–3000 ppm oxygen. The number of cycles to fracture (Nf) was slightly reduced under irradiation. SEM examination of fracture surfaces indicated the formation of an oxide film in the vicinity of notch tip only for the in-beam specimens. Optical microscopic observation demonstrated oxidation not only along the grain boundaries but also on the crystallographic slip planes on the specimen surfaces of both in-beam and unirradiated specimens. The oxidation appeared to be enhanced to form numerous oxidation pits on the surface, especially for the in-beam specimens. In this study, the in-beam fatigue behavior at 500 °C is discussed with respect to the dynamic irradiation effect in the low oxygen potential atmosphere.