Influence of Material, Environment and Strain Rate on Environmentally Assisted Cracking of Austenitic Nuclear Materials (DEFSPEED): Deformation localisation and EAC in inhomogeneous microstructures of austenitic stainless steels

Ulla Ehrnsten, Wade Karlsen, Janne Pakarinen, Tapio Saukkonen, Hannu Hänninen

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

    Abstract

    Inhomogeneous microstructures, e.g. grain size, dislocation density etc., always occur in welded structures. Varying manufacturing methods leading to complex strain paths result in highly varying cold work and consequent residual strains. The role of strain localisation is probably playing a key role as a precursor for crack initiation but its mechanisms are still not fully known. If strain localisation occurs by a creep mechanism, the incubation time for crack initiation can be very long, as frequently observed in NPPs. EBSD employed to measure strain distributions in a Type 304 austenitic stainless steel weld shows a high variation in residual strain distribution, which was verified by hardness measurements as well as with residual stress measurements. Strain localisation investigations were also performed on specimens from Super Slow Strain Rate Test (SSSRT) using a very slow strain rate of 1 o 10-8 s-1. This is in the creep strain rate range, where diffusion along dislocation cores and grain boundaries occur together with grain boundary sliding. SSSRT's were performed in simulated BWR environment on sensitized Type 304 and non-sensitised Type 316L austenitic stainless steel either with or without cold deformation. Local variation in the amount of surface cold-work affects crack initiation. Local variations of grain size also affect strain localisation. During crack growth, strain localisation occurs at grain boundaries ahead of the crack tips.
    Original languageEnglish
    Title of host publicationSAFIR2010
    Subtitle of host publicationThe Finnish Research Programme on Safety 2007-2010: Final Report
    Place of PublicationEspoo
    PublisherVTT Technical Research Centre of Finland
    Chapter27.2
    Pages453-463
    ISBN (Electronic)978-951-38-7690-6
    ISBN (Print)978-951-38-7689-0
    Publication statusPublished - 2011
    MoE publication typeNot Eligible

    Publication series

    SeriesVTT Tiedotteita - Research Notes
    Number2571
    ISSN1235-0605

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    Ehrnsten, U., Karlsen, W., Pakarinen, J., Saukkonen, T., & Hänninen, H. (2011). Influence of Material, Environment and Strain Rate on Environmentally Assisted Cracking of Austenitic Nuclear Materials (DEFSPEED): Deformation localisation and EAC in inhomogeneous microstructures of austenitic stainless steels. In SAFIR2010: The Finnish Research Programme on Safety 2007-2010: Final Report (pp. 453-463). VTT Technical Research Centre of Finland. VTT Tiedotteita - Research Notes, No. 2571