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    Volume 6, Issue 3 (May 2017)

    Special Issue Paper

    Investigation of the Origin of Coarse-Grained Bainite in X70 Pipeline Steels by EBSD Technique

    (Received 24 March 2016; accepted 6 September 2016)

    Published Online: 26 May 2017

    CODEN: MPCACD

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    Abstract

    Structural inhomogeneities that occurred in pipeline steels during controlled rolling and were identified as elongated regions of coarse-grained bainite were found to promote a tendency for brittle fracture of these steels. In particular, it was shown by tint etching, with subsequent analysis in polarized light with the light-optical microscope, that their volume fraction exhibited a perfect correspondence with the failure behavior. The aim of the present investigation was to comprehensively characterize the microstructure and the local texture of these regions using the EBSD technique and thereby clarify their origin. It was shown that, whereas the local texture of fine-grained regions corresponded well to the macroscopic texture of the steel band, the local texture of the structural inhomogeneities corresponds to certain minor components of the macroscopic texture. The grains of the parent austenite, from which these inhomogeneities have been produced, had orientations concentrated close to the brass component of austenite rolling texture. Hot deformation of the austenite leads to a strong variant selection (predominant realization of certain lattice orientations among plausible orientations of α-phase) during phase transformation of these grains, that result in a significant increase of the bainite packet size. Formation of bainite in the upper temperature range of bainite transformation, in its turn, leads to such a variant pairing that low-angle boundaries are formed predominantly both inside and between the packets. This further enlarges the effective grain size and correspondingly enhances the deteriorative effect of the structural inhomogeneity.


    Author Information:

    Zolotorevsky, N.
    Peter the Great Saint Petersburg Polytechnic Univ., St. Petersburg,

    Mechanical Engineering Research Inst. of the Russian Academy of Sciences, Nizhnii Novgorod,

    Kazakova, E.
    Peter the Great Saint Petersburg Polytechnic Univ., St. Petersburg,

    Kazakov, A.
    Peter the Great Saint Petersburg Polytechnic Univ., St. Petersburg,

    Petrov, S.
    Central Research Inst. of Structural Materials “Prometey”, St. Petersburg,

    Panpurin, S.
    Peter the Great Saint Petersburg Polytechnic Univ., St. Petersburg,


    Stock #: MPC20160031

    ISSN:2165-3992

    DOI: 10.1520/MPC20160031

    Author
    Title Investigation of the Origin of Coarse-Grained Bainite in X70 Pipeline Steels by EBSD Technique
    Symposium ,
    Committee E04