Ultrafine grained multi-phase steel sheets based on low-carbon steels containing 0.15 % C and 3-5 % Mn were developed. The mechanical properties and dynamic collapse properties are shown in this paper. Hot-rolled sheets 5 or 3.5 mm thick, having microstructure composed of ferrite and hard second phases were rolled to 1.0 or 1.2 mm in thickness. The sheets were annealed at intercritical region of ferrite and austenite, and some were followed by subsequent annealing at 400 deg C. The microstructures of the fabricated steel sheets were composed of sub-micrometer grains of ferrite and second phases. The amounts of retained austenite varied from 12 to 35% according to Mn content. In spite of the ultrafine grain size, the present microstructures showed significant work hardening after yielding, which resulted in large uniform elongation. The work hardening was brought by strain induced martensitic transformation of the retained austenite. Rectangular columns were prepared using the fabricated ultrafine grained multi-phase steel sheets by bending and spot-welding, and dynamically deformed along the axial direction using a free-fall type dynamic collapse test machine. The columns made of ultrafine grained multi-phase steel sheets were deformed in 'compact-mode' and showed larger absorbed energy compared with the steels having other microstructures.


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    Title :

    Mechanical properties of ultrafine grained multi-phase steel sheets aiming for automobile body applications


    Additional title:

    Mechanische Eigenschaften ultrafeinkörniger Mehrphasenstahlbleche für den Einsatz in Automobilkarosserien


    Contributors:


    Publication date :

    2009


    Size :

    4 Seiten, 8 Bilder, 3 Tabellen, 11 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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