University of Oulu

A Kaijalainen et al 2017 J. Phys.: Conf. Ser. 896 012103

The effect of microstructure on the sheared edge quality and hole expansion ratio of hot-rolled 700 MPa steel

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Author: Kaijalainen, Antti1; Kesti, V2; Vierelä, R3;
Organizations: 1Materials and Production Engineering, University of Oulu, Finland
2SSAB Europe, Raahe, Finland
3Lapland University of Applied Sciences, Kemi, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 5.6 MB)
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Language: English
Published: IOP Publishing, 2017
Publish Date: 2017-10-04


The effects of microstructure on the cutting and hole expansion properties of three thermomechanically rolled steels have been investigated. The yield strength of the studied 3 mm thick strip steels was approximately 700 MPa. Detailed microstructural studies using laser scanning confocal microscopy (LCSM), FESEM and FESEM-EBSD revealed that the three investigated materials consist of 1) single-phase polygonal ferrite, 2) polygonal ferrite with precipitates and 3) granular bainite. The quality of mechanically sheared edges were evaluated using visual inspection and LSCM, while hole expansion properties were characterised according to the methods described in ISO 16630. Roughness values (Ra and Rz) of the sheet edge with different cutting clearances varied between 12 µm to 21 µm and 133 µm to 225 µm, respectively. Mean hole expansion ratios varied from 28.4% to 40.5%. It was shown that granular bainite produced the finest cutting edge, but the hole expansion ratio remained at the same level as in the steel comprising single-phase ferrite. This indicates that a single-phase ferritic matrix enhances hole expansion properties even with low quality edges. A brief discussion of the microstructural features controlling the cutting quality and hole expansion properties is given.

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Series: Journal of physics. Conference series
ISSN: 1742-6588
ISSN-E: 1742-6596
ISSN-L: 1742-6588
Volume: 896
Article number: 012103
DOI: 10.1088/1742-6596/896/1/012103
Conference: 36th IDDRG Conference – Materials Modelling and Testing for Sheet Metal Forming
Type of Publication: A4 Article in conference proceedings
Field of Science: 216 Materials engineering
Funding: This work was made as a part of the Breakthrough Steels and Applications program coordinated by DIMECC Oy (Digital, Internet, Materials & Engineering Co-Creation). The financial support of the Finnish Funding Agency for Technology and Innovation (Tekes) is gratefully acknowledged.
Copyright information: Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd