Fracture characteristics of new ultra-high-strength steel with yield strengths 900-960 MPa

Pekka Nevasmaa, Päivi Karjalainen-Roikonen, Anssi Laukkanen, T. Nykänen, A. Ameri, T. Björk, T. Limnell, J. Kuoppala

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

    Abstract

    The fracture behaviour of S960 steel in different conditions, i.e as-delivered, cold strained, cold strained and artificially aged, has been studied using small-scale fracture mechanics and Charpy V testing as well as tests on large-scale U-beams and cold-formed rectangular hollow sections. At room temperature and -40 deg C, fracture resistance testing indicated overall ductile behaviour. Regarding brittle fracture, the T0 reference temperature for the as-received material was around -50 deg C. Artificial ageing alone increased this temperature only slightly, but cold-straining and artificial ageing together raised T0 (and T28J) by almost 50 deg C. For the strength level studied, the FITNET correlation between T0 and T28J leads to severely un-conservative KJC estimates, indicating that KJC needs to be measured directly. T0 estimates based on fracture mechanics tests using small-scale 3-point bend specimens were clearly conservative in relation to the large-scale U-beam behaviour due to different constraints. Shear fracture occurred in the U-beam tests as a result of the small plate thickness; however, this led to only a 10 % decrease in the load-bearing capacity from the theoretical maximum load. Quasi-static bending tests on welded fatigue-cracked cold-formed rectangular hollow sections at -40 deg C showed good agreement with nonlinear FEA calculations using the J-integral approach. Both large-scale test variants showed that brittle cleavage fracture will not become the dominant fracture mode in the welded beam constructions studied, provided the service temperature does not fall below -50 deg C.
    Original languageEnglish
    Title of host publicationProceedings
    Subtitle of host publication2nd International Conference Super-High Strength Steels (SHSS), Peschiera del Garda, 17-20 October 2010
    Place of PublicationMilano
    PublisherAssociazione Italiana di Metallurgia AIM
    Number of pages14
    ISBN (Print)978-88-85298-79-8
    Publication statusPublished - 2010
    MoE publication typeB3 Non-refereed article in conference proceedings

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