Izvestiya vuzov. Yadernaya Energetika

The peer-reviewed scientific and technology journal. ISSN: 0204-3327

Thermal Resistance of Steels with Increased Strength Properties for Pressure Vessels of Advanced VVER Reactors of Various Designs

6/22/2023 2023 - #02 Nuclear materials

Kuleshova E.A. Fedotov I.V. Maltsev D.A. Isaenkova M.G. Krymskaya O.A. Minushkin R.A.

DOI: https://doi.org/10.26583/npe.2023.2.08

UDC: 621.039.53

The paper considers the results of structural studies and mechanical tests after a long-term thermal exposure of laboratory heats of the metallurgically improved 15Kh2NMFA steel and steel with an increased content of nickel viewed as materials for the pressure vessels of advanced VVER-type reactors of various designs. It has been shown that, both for the improved 15Kh2NMFA steel and the high-nickel steel, there are no signs of grain boundary embrittlement after a thermal treatment that provokes embrittlement. This is explained by the extremely low grain boundary segregation of phosphorus in the initial state caused by a high degree of the structure dispersion as well as by rather a low content of impurities. Besides, no changes have been found in the yield strength value for the improved 15Kh2NMFA steel, which agrees with the structure investigation results. For the high-nickel steel, a tendency has been revealed towards a minor yield strength decrease by 5 to 10- and a regular reduction in the critical brittle temperature. A decrease in the mechanical performance has been caused by a relatively low temperature of the high-nickel steel temper and, accordingly, by the potential occurrence of the structure after-temper processes during long-term thermal exposure, as evidenced by results of an X-ray diffraction analysis. Despite the after-temper processes in the high-nickel steel in the course of the long-term heat exposure, the basic strengthening carbide phases remain stable. Due to this, the yield strength value remains at a relatively high level that exceeds the values for the currently employed VVER-type vessel steels, even in the case of a thermal exposure much in excess of the expected operating conditions of advanced VVER reactors. And the critical brittle temperature decrease in the course of the heat exposure just contributes to an increase in the steel resistance to brittle fracture in the process of service.

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reactor vessel steels high-nickel steel mechanical performance structure properties temper brittleness thermal resistance

Link for citing the article: Kuleshova E.A., Fedotov I.V., Maltsev D.A., Isaenkova M.G., Krymskaya O.A., Minushkin R.A. Thermal Resistance of Steels with Increased Strength Properties for Pressure Vessels of Advanced VVER Reactors of Various Designs. Izvestiya vuzov. Yadernaya Energetika. 2023, no. 2, pp. 93-106; DOI: https://doi.org/10.26583/npe.2023.2.08 (in Russian).

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