Low-cycles fatigue properties of structural materials exposed in flowing sodium at high temperature (I); Test results of sodium exposed materials for 10000 hours

not registered; not registered; Koakutsu, Toru; not registered; not registered

For the purpose of the verification of the evaluation method on the sodium environmental effect on the mechanical properties of the structural materials used for the prototype LMFBR "MONJU" and the rationalization of the evaluation method for large scale LMFBRs, SUS 304 and 316 austenitic stainless steels and 2.25Cr-1Mo steel (NT) were carried out. Test specimens were exposed to a sodium loop for 10,000 hours at 400 600C simulating the primary and secondary coolant systems of the prototype LMFBR "MONJU". After the exposure, fatigue tests were performed in sodium environment. Fatigue tests were also performed on the thermal aged material for 10.000 hours in inert gas. The results obtaind were as follows. (1)The difference between the fatigue lives of sodium exposed materials and thermal aged materials was very small for both kinds of steels and these lives were almost the same as these of as - received materials. (2)Caburization was recognized on the surface of SUS 304 and SUS 316 austenitic stainless steels in the cage tested in sodium after sodium exposed. In the case of 2.25Cr-1Mo steel (NT), some decarburization was observed at 500 C. (3)The fatigue lives didnot depend on the exposure history such as sodium exposed materials and thermal aged materials for 10,000 hours. The carburization and decarburization effects were very small on fatigue life. The fatigue lives were affected by the environment in which fatigue tests are conducted.