To investigate the effect of swelling upon mechanical properties of irradiated austenitic steel the investigations were conducted with steel 18Cr-10Ni-Ti and its weld irradiated up to same damage doses in two different temperature ranges: at the irradiation temperature of 330÷340°C when swelling is practically absent and at 400÷450°C when a considerable swelling level of 3÷13% is observed. Basing on the investigation results the temperature dependences of tensile properties of irradiated metal were constructed and analyzed. Fracture surfaces for ruptured specimens were examined by SEM. Comparative investigations of magnetization of irradiated metal at different irradiation temperatures were performed. It was concluded from the performed analysis of the results that in highly irradiated austenitic steel with considerable swelling a ductile to brittle transition is observed, which is caused of the Feγ→Feα phase transformation. The investigations of magnetization of metals with different swelling, as well as on the available literature data confirm a possibility of the Feγ→Feα phase transformation under considerable radiation swelling. The criterion is proposed allowing one to determine the radiation conditions under which the Feγ→Feα transformation make it possible a brittle fracture. The mechanism resulting in a sharp decrease of the ultimate tensile strength of highly irradiated metal is considered.

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