Study on mechanism of grain boundary embrittlement of austenitic stainless steel after irradiation using in-situ monitoring system of grain boundary separation

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Helium embrittlement of austenitic stainless steel by tensile mode was investigated though grain boundary observation of solution-annealed and He-implanted Fe-15Cr-20Ni at high temperature. The following results were obtained. Grain boundary separation appeared during the elastic deformation area at 923 and 1023K. The separated grain boundaries were observed only after yielding tested at 823K, and these were not observed below 723K. These separated grain boundaries were random or higher grain boundaries and their direction was near perpendicularly to the stress direction. With increasing plastic strain, separated grain boundaries of lower sigma boundaries were observed. With increasing the applied strain, separated grain boundaries were linked and formed grain boundary cracks and before the specimen rupture. In-situ observation system for surface crack formation during tensile test was designed and manufactured, and the analysis of deformation mode is under investigated.