The effect of initial microstructure on the final properties of press hardened 22MnB5 steels

Henri Järvinen, Matti Isakov, Tuomo Nyyssönen, Martti Järvenpää, Pasi Peura

    Research output: Contribution to journalArticleScientificpeer-review

    25 Citations (Scopus)

    Abstract

    This paper addresses the relationship between initial microstructure and final properties of press hardened 22MnB5 steels. Four commercial 22MnB5 steels having different initial microstructures were investigated. An experimental press hardening equipment with a flat-die was used to investigate material behavior in the direct press hardening process. Two austenitizing treatments, 450 s and 180 s at 900 °C, were examined. Microstructural characterization with optical and scanning electron microscopes revealed a mixture of martensite and auto-tempered martensite after press hardening. Electron backscatter diffraction data of the transformed martensite was used to reconstruct grain boundary maps of parent austenite. Grain sizes of parent austenite (mean linear intercept) were measured for each material. In addition to microstructural evaluation, quasistatic and high strain rate tensile tests at strain rates of 5×10−4 s−1 and 400 s−1, respectively, were performed for press hardened samples. The results show that strength and uniform elongation depend on the initial microstructure of the 22MnB5 steel, when parameters typical to the direct press hardening process are used. Parent austenite grain size was shown to influence the morphology of the transformed martensite, which in turn affects the strength and uniform elongation after press hardening. The tensile properties of the press hardened materials are almost strain rate independent in the studied strain rate range. The obtained results can be used to optimize the properties of 22MnB5 steels in the direct press hardening process. In addition, the here revealed connection between the parent austenite grain size and final steel properties should be taken into account in the development of new press hardening steel grades for automotive industry.

    Original languageEnglish
    Pages (from-to)109-120
    Number of pages12
    JournalMaterials Science and Engineering A: Structural Materials Properties Microstructure and Processing
    Volume676
    DOIs
    Publication statusPublished - 31 Oct 2016
    Publication typeA1 Journal article-refereed

    Keywords

    • EBSD
    • Grain boundaries
    • Grain growth
    • Hardening
    • Mechanical characterization
    • Steel

    Publication forum classification

    • Publication forum level 2

    ASJC Scopus subject areas

    • Materials Science(all)
    • Condensed Matter Physics
    • Mechanics of Materials
    • Mechanical Engineering

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