Influence of material, environment and strain rate on environmentally assisted cracking of austenitic nuclear materials (DEFSPEED). Strain localisation in sensitised Type 304 stainless steel in simulated BWR-environment

Ulla Ehrnsten, Tapio Saukkonen, Hannu Hänninen

    Research output: Chapter in Book/Report/Conference proceedingChapter or book articleProfessional

    Abstract

    Intergranular, environmentally assisted cracking (EAC) has been observed, not only in sensitised austenitic stainless steels in oxidising BWR conditions, but also in non-sensitised, cold deformed stainless steels. Further, EAC has recently been reported also in PWR plants, in connection to local non-specified water chemistry conditions. Environmentally assisted cracking in nickel-based weld metals is considered to be one of the most challenging issues for operating power plants today. Mechanistic understanding of the effects of main factors affecting environmentally assisted cracking of austenitic materials is important, especially as the trend in the NDE inspection strategy is moving towards risk-informed inspection. In the SAFIR 2010 DEFSPEED project (Influence of material, environment and strain rate on environmentally assisted cracking of austenitic nuclear materials), investigations are performed using super slow strain rate tests (SSSRT) in LWR environments and the deformation is characterised using versatile methods such as FE-SEM EBSD and TEM. The investigations aim to increase the mechanistic understanding of precursors to crack initiation as well as factors affecting crack growth in austenitic nuclear materials. The results achieved from the SSSRT's on deformed and sensitised austenitic stainless steel of Type 304 and from EBSD characterisation of a Type 304 nuclear pipe weld show non-uniform distribution of micro-strains in the material, being higher in the vicinity of grain boundaries than inside the grains. The results indicate that several phenomena can occur during extremely slow deformation, such as heterogeneous creep, dynamic recovery and relaxation leading to grain boundary sliding, dynamic strain ageing and short range ordering. The results also show that non-homogeneous microstructures, e.g. local changes in the grain size, affect strain localisation.
    Original languageEnglish
    Title of host publicationSAFIR2010. The Finnish Research Programme on Nuclear Power Plant Safety 2007-2010
    Subtitle of host publicationInterim Report
    Place of PublicationEspoo
    PublisherVTT Technical Research Centre of Finland
    Pages418-429
    ISBN (Electronic)978-951-38-7267-0
    ISBN (Print)978-951-38-7266-3
    Publication statusPublished - 2009
    MoE publication typeD2 Article in professional manuals or guides or professional information systems or text book material

    Publication series

    SeriesVTT Tiedotteita - Meddelanden - Research Notes
    Number2466
    ISSN1235-0605

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