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. https://doi.org/10.1007/s12613-020-2226-6
Cite this article as:
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. https://doi.org/10.1007/s12613-020-2226-6
Research Article

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 2020Revised: 20 October 2020Accepted: 18 November 2020Available online: 26 November 2020
  • 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.
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