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    Volume 6, Issue 3 (May 2017)

    Special Issue Paper

    Structural Investigation and Control of Multi-Pass Gas-Shielded Flux-Cored Arc Weldments

    (Received 30 March 2016; accepted 22 November 2016)

    Published Online: 26 May 2017

    CODEN: MPCACD

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    Abstract

    Structure–property relationships for multi-pass gas-shielded flux-cored arc welds of X70 grade pipeline steel have been evaluated. It is known that the optimum structure for these kinds of welds would consist mainly of acicular ferrite with a minimum of allotriomorphic ferrite along prior-austenite grain boundaries. Non-metallic inclusions based on Ti2O3 play an important role for intragranular nucleation of acicular ferrite. Fine non-metallic inclusions of more complex compositions, Al2O3-CaO-SiO2-MnO-MgO-TixOy-MnS, were detected within the microstructure of the investigated welds. These inclusions were the substrates for formation of intragranular acicular ferrite in the weld metal. The effective combination of the number and thickness of different structural zones guarantees high toughness of the weld metal. The influence of constructional and technological parameters of multi-pass welding (welding gap, welding torch tilt during layer filling, welding direction for a hot pass, different heat inputs) on the primary as-welded and secondary reheated zones of the lower layers of the weld was investigated. Allotriomorphic ferrite volume fraction was estimated using panoramic images of the lower layers of welds along with the fracture surfaces of Charpy V–notch impact test bars. A method for quantitative estimation of allotriomorphic ferrite volume fraction (VAF) by image analysis was developed. This allows formulation of the requirements for critical values of VAF that guarantee high-impact toughness of the lower layers of welds. All results have been used to improve the welding technology.


    Author Information:

    Kazakov, Alexander

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

    Karasev, Michael
    Peter the Great Saint Petersburg Polytechnic Univ., St. Petersburg,

    Lubochko, Dar'ya
    Peter the Great Saint Petersburg Polytechnic Univ., St. Petersburg,

    Lubochko, Dar'ya
    Peter the Great Saint Petersburg Polytechnic Univ., St. Petersburg,


    Stock #: MPC20160035

    ISSN:2165-3992

    DOI: 10.1520/MPC20160035

    Author
    Title Structural Investigation and Control of Multi-Pass Gas-Shielded Flux-Cored Arc Weldments
    Symposium ,
    Committee E04