Crack formation and propagation mechanism in the punching process of high tensile strength steel sheet

Takehiro Okano, Kota Sakumoto, Kazuhiko Yamazaki, Shunsuke Toyoda, Shinsuke Suzuki

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    2 Citations (Scopus)

    Abstract

    The microstructure (crystal grain and the center segregation of Mn) around the voids and cracks in punching process was investigated using Hot-rolled 780 MPa-grade high tensile strength steel sheets. Steel sheets without center segregation were prepared by grinding only one side, while ones with center segregation were prepared by grinding both side. Punching tests were conducted with these two kind of steel sheets. Crack length and number of cracks on the punched surface were measured and counted by an optical microscope. Steel sheets with center segregation had more cracks in total and longer average crack length than that without center segregation. The Mn mapping and the crystal orientation mapping around the crack obtained through EPMA and EBSD showed that the range larger than 70 μm in crack length tend to cause intergranular fracture along Mn segregated area. Also in the range between 10 μm and 70 μm in crack length, cracks forming both along and away from Mn segregated area were observed. Concentration of Mn around the grain boundary of the center segregation area measured by TEM/EDS revealed that grain boundary contains high Mn concentration. The calculation on distribution of equivalent stress just before the onset of crack for steel sheets with and without center segregation using finite element model showed that equivalent stress concentrates at both edges of the punch and die and the center segregation part. Next, interrupted punching tests were conducted with two kind of steel sheets. The observation around voids through SEM, EPMA, and EBSD showed that voids initiate at the ferrite-Ti precipitate interface. From these results, following tendencies were found, within and near Mn center segregated area, voids initiate at the ferrite-Ti precipitate interface, and crack propagates along Mn center segregation. Moreover, Mn segregates at the grain boundary, and Mn weakens grain boundary cohesion which leads to an intergranular fracture. However, without Mn center segregated area, voids initiate at the ferrite-Ti precipitate interface, and crack propagates easily into the ferrite matrix by cleavage which leads to cause a transgranular fracture.

    Original languageEnglish
    Title of host publicationMetal Forming 2016
    PublisherTrans Tech Publications Ltd
    Pages643-651
    Number of pages9
    Volume716
    ISBN (Print)9783038357049
    DOIs
    Publication statusPublished - 2016
    Event16th Metal Forming International Conference, 2016 - Krakow, Poland
    Duration: 2016 Sep 182016 Sep 21

    Publication series

    NameKey Engineering Materials
    Volume716
    ISSN (Print)10139826

    Other

    Other16th Metal Forming International Conference, 2016
    CountryPoland
    CityKrakow
    Period16/9/1816/9/21

    Fingerprint

    Punching
    Steel sheet
    Crack initiation
    Crack propagation
    Tensile strength
    Cracks
    Ferrite
    Grain boundaries
    Precipitates
    Electron probe microanalysis
    Crystal microstructure
    Crystal orientation
    Energy dispersive spectroscopy
    Microscopes

    Keywords

    • Center Segregation
    • Crack
    • High Tensile Steel Sheet
    • Punching
    • Ti Precipitate.

    ASJC Scopus subject areas

    • Materials Science(all)
    • Mechanics of Materials
    • Mechanical Engineering

    Cite this

    Okano, T., Sakumoto, K., Yamazaki, K., Toyoda, S., & Suzuki, S. (2016). Crack formation and propagation mechanism in the punching process of high tensile strength steel sheet. In Metal Forming 2016 (Vol. 716, pp. 643-651). (Key Engineering Materials; Vol. 716). Trans Tech Publications Ltd. https://doi.org/10.4028/www.scientific.net/KEM.716.643

    Crack formation and propagation mechanism in the punching process of high tensile strength steel sheet. / Okano, Takehiro; Sakumoto, Kota; Yamazaki, Kazuhiko; Toyoda, Shunsuke; Suzuki, Shinsuke.

    Metal Forming 2016. Vol. 716 Trans Tech Publications Ltd, 2016. p. 643-651 (Key Engineering Materials; Vol. 716).

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    Okano, T, Sakumoto, K, Yamazaki, K, Toyoda, S & Suzuki, S 2016, Crack formation and propagation mechanism in the punching process of high tensile strength steel sheet. in Metal Forming 2016. vol. 716, Key Engineering Materials, vol. 716, Trans Tech Publications Ltd, pp. 643-651, 16th Metal Forming International Conference, 2016, Krakow, Poland, 16/9/18. https://doi.org/10.4028/www.scientific.net/KEM.716.643
    Okano T, Sakumoto K, Yamazaki K, Toyoda S, Suzuki S. Crack formation and propagation mechanism in the punching process of high tensile strength steel sheet. In Metal Forming 2016. Vol. 716. Trans Tech Publications Ltd. 2016. p. 643-651. (Key Engineering Materials). https://doi.org/10.4028/www.scientific.net/KEM.716.643
    Okano, Takehiro ; Sakumoto, Kota ; Yamazaki, Kazuhiko ; Toyoda, Shunsuke ; Suzuki, Shinsuke. / Crack formation and propagation mechanism in the punching process of high tensile strength steel sheet. Metal Forming 2016. Vol. 716 Trans Tech Publications Ltd, 2016. pp. 643-651 (Key Engineering Materials).
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