Effect of weld microstructure on brittle fracture initiation in the thermally-aged boiling water reactor pressure vessel head weld metal

Noora Hytönen; Zai-qing Que; Pentti Arffman; Jari Lydman; Pekka Nevasmaa; Ulla Ehrnstén; Pål Efsing

doi:10.1007/s12613-020-2226-6

Volume 28 Issue 5

May 2021

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Article Navigation > International Journal of Minerals, Metallurgy and Materials > 2021 > 28(5): 867-876

Noora Hytönen, Zai-qing Que, Pentti Arffman, Jari Lydman, Pekka Nevasmaa, Ulla Ehrnstén, and Pål Efsing, Effect of weld microstructure on brittle fracture initiation in the thermally-aged boiling water reactor pressure vessel head weld metal, Int. J. Miner. Metall. Mater., 28(2021), No. 5, pp. 867-876. https://doi.org/10.1007/s12613-020-2226-6

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Noora Hytönen, Zai-qing Que, Pentti Arffman, Jari Lydman, Pekka Nevasmaa, Ulla Ehrnstén, and Pål Efsing, Effect of weld microstructure on brittle fracture initiation in the thermally-aged boiling water reactor pressure vessel head weld metal, Int. J. Miner. Metall. Mater., 28(2021), No. 5, pp. 867-876. https://doi.org/10.1007/s12613-020-2226-6

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Effect of weld microstructure on brittle fracture initiation in the thermally-aged boiling water reactor pressure vessel head weld metal

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Corresponding author:
Zai-qing Que E-mail: Zaiqing.Que@vtt.fi
Received: 9 September 2020; Revised: 20 October 2020; Accepted: 18 November 2020; Available online: 26 November 2020

Abstract

Abstract

Effects of the weld microstructure and inclusions on brittle fracture initiation are investigated in a thermally aged ferritic high-nickel weld of a reactor pressure vessel head from a decommissioned nuclear power plant. As-welded and reheated regions mainly consist of acicular and polygonal ferrite, respectively. Fractographic examination of Charpy V-notch impact toughness specimens reveals large inclusions (0.5–2.5 μm) at the brittle fracture primary initiation sites. High impact energies were measured for the specimens in which brittle fracture was initiated from a small inclusion or an inclusion away from the V-notch. The density, geometry, and chemical composition of the primary initiation inclusions were investigated. A brittle fracture crack initiates as a microcrack either within the multiphase oxide inclusions or from the debonded interfaces between the uncracked inclusions and weld metal matrix. Primary fracture sites can be determined in all the specimens tested in the lower part of the transition curve at and below the 41-J reference impact toughness energy but not above the mentioned value because of the changes in the fracture mechanism and resulting changes in the fracture appearance.
- reactor pressure vessel;
- brittle fracture;
- weld microstructure;
- thermal aging

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