Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds

Pertti Aaltonen, Hannu Hänninen, Anssi Brederholm, Aki Toivonen, Ulla Ehrnsten

    Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

    Abstract

    Environment-assisted cracking (EAC) susceptibility of dissimilar metal mock-up welds of Alloy 182 and 82 as well as Alloy 152 and 52 were studied with four-point bending specimens in steam doped with hydrogen, chloride, sulfate and fluoride at 400 °C. The doped steam environment accelerated the crack initiation process and the susceptibility of the studied weld metals to EAC was obtained and ranked. High susceptibility to crack initiation and growth was observed with Alloy 182 and 82 weld metals, while Alloy 152 and 52 weld metals showed high resistance to crack initiation. No extension of the hot cracks was observed in the doped steam test in any of the studied materials. Fractography of the broken Alloy 182 and 82 samples showed both nickel deposition and presence of NiO in addition to the continuous spinel type Cr-rich oxide film on the fracture surface inside the crack. Fracture path was intergranular in all the studied samples. The same dissimilar metal welds were exposed to Varestraint hot cracking tests and their hot cracking susceptibility was also ranked and determined as a function of the amount of strain. The microstructures of the weld metals were fully characterized by optical metallography and a modern FE-SEM/EDS system. Hot cracking susceptibility was related to the solidification mechanism and segregation of Nb, Si, P and Mn in the weld metals. Fractography of the EAC and hot cracks was compared and their characteristic features are demonstrated. Finally, the mechanisms of hot cracking and EAC of nickel-base alloy dissimilar metal welds are identified and discussed.
    Original languageEnglish
    Title of host publicationBaltica VIII
    Subtitle of host publicationLife Management and Maintenance for Power Plants
    Place of PublicationEspoo
    PublisherVTT Technical Research Centre of Finland
    Pages384-400
    Volume1
    ISBN (Electronic)978-951-38-7592-3
    ISBN (Print)978-951-38-7591-6
    Publication statusPublished - 2010
    MoE publication typeB3 Non-refereed article in conference proceedings
    EventBALTICA VIII - International Conference on Life Management and Maintenance for Power Plants - Helsinki-Stockholm, Finland
    Duration: 18 May 201020 May 2010

    Publication series

    SeriesVTT Symposium
    Number264
    ISSN0357-9387

    Conference

    ConferenceBALTICA VIII - International Conference on Life Management and Maintenance for Power Plants
    CountryFinland
    CityHelsinki-Stockholm
    Period18/05/1020/05/10

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  • Cite this

    Aaltonen, P., Hänninen, H., Brederholm, A., Toivonen, A., & Ehrnsten, U. (2010). Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds. In Baltica VIII: Life Management and Maintenance for Power Plants (Vol. 1, pp. 384-400). VTT Technical Research Centre of Finland. VTT Symposium, No. 264 http://www.vtt.fi/inf/pdf/symposiums/2011/S264.pdf