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 (Corresponding Author), Pentti Arffman, Jari Lydman, Pekka Nevasmaa, Ulla Ehrnstén, Pål Efsing

Research output: Contribution to journalArticleScientificpeer-review

1 Citation (Scopus)

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 de-bonded 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.

Original languageEnglish
Pages (from-to)867-876
Number of pages10
JournalInternational Journal of Minerals, Metallurgy and Materials
Volume28
Issue number5
DOIs
Publication statusPublished - 16 May 2021
MoE publication typeA1 Journal article-refereed

Keywords

  • brittle fracture
  • reactor pressure vessel
  • thermal aging
  • weld microstructure

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