Brittle fracture resistance of reactor pressure vessel steels in the initial state
The effect of chemical and structural inhomogeneity on the resistance to brittle fracture of VVER reactor pressure vessel materials in the initial state (without irradiation) was study in this article. The aim of this work is changing the estimate of brittle fracture resistance using the critical brittleness temperature TC to the estimate of brittle fracture resistance using the brittle viscous transition temperature TP. Also in this study the application of calibrating diagrams for studying the dependence of TP on the grain size and heat treatment is considered.
Comparison between TC and TP for experimental metal of standard 15H2NMFAA steel blanks indicates that TC values are significantly lower than TP values, namely – difference between Tc and TP at lower level of conservatism is 22°C; – difference between Tc and TP at upper level of conservatism is 24°C.
Statistical processing of impact test data array for VVER-1000 and VVER-1200 reactor vessel steels (15H2NMFAA and 15H2NMFA grade 1, respectively) was used. The industrial specimens of the Reactor Pressure Vessel Shells studied in the work were manufactured at the Public Joint Stock Company «Energomashspetsstal» (Kramatorsk, Ukraine).
It was found that when the content of copper in the metal of the surveillance specimens of VVER-1000 RPV is – less than 0.06 wt% heat treatment has a significant effect on the value of TP, which varies from –99°C to –28°C; – between 0.07 to 0.12 wt%, heat treatment does not significantly affect the value of TP, which varies from –60°C to –40°C.
The value of TP practically does not depend on conservatism level.
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