Reduction of Cracks During Punching Process by Cementite in High Tensile Strength Steel Sheets

Takehiro Okano, Chikara Inoue, Shinsuke Suzuki, Kazuhiko Yamazaki, Shunsuke Toyoda

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    Abstract

    An experimental study on high tensile strength steel sheets with ferritic and ferrite–cementite microstructures was performed with the objective of determining the crack formation and propagation mechanism in the punching process. In addition, the effect of dispersed cementites was also investigated. SEM, EPMA, and EBSD analyses confirmed that voids initiate at the ferrite-inclusion/precipitate (TiN, TiS, and cementite) interface, and the voids then propagate into the ferrite matrix by cleavage. EPMA, EBSD, and TEM/EDS demonstrated that cracks which formed within and near a center segregation area propagate along the Mn center segregation by intergranular fracture due to Mn segregation at the grain boundary. In addition to TiN and TiS, observation of the number of cracks, the length of cracks in the punched surface, and the number density of voids in tensile fracture parts indicated that dispersed cementites are also void formation factors, and cementites decrease the number of cracks and average crack length in the punched surface of ferrite–cementite steel sheets by reducing the stress applied to the voids.

    Original languageEnglish
    JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
    DOIs
    Publication statusAccepted/In press - 2018 Jan 1

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    ASJC Scopus subject areas

    • Condensed Matter Physics
    • Mechanics of Materials
    • Metals and Alloys

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