University of Oulu

J. Hannula et al 2019 IOP Conf. Ser.: Mater. Sci. Eng. 651 012072.

The effect of microalloying on the sheared edge ductility of ferritic steels

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Author: Hannula, J.1; Kaijalainen, A.1; Porter, D.1;
Organizations: 1Materials and Mechanical Engineering,Centrefor Advanced Steels Research, FI-90014 University of Oulu, Finland
2SSAB, Raahe Research Centre, Rautaruukintie 155, POB 93, FI-92101 Raahe, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 9.5 MB)
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Language: English
Published: IOP Publishing, 2019
Publish Date: 2019-12-02


Sheared edge ductility plays a critical role in many automotive and structural applications. The effect of microalloying elements on the microstructure, mechanical properties, sheared edge quality and hole expansion properties of six thermomechanically laboratory hot rolled and coiled, approximately 4 mm thick, precipitation hardened ferritic steels have been investigated. The studied V-microalloyed steels had low carbon contents, 0.05 and 0.09 wt.%, and, in some cases, microalloying additions of either Nb or Nb+Ti. Yield strengths were in the range 500 MPa to 750 MPa and hardness values between 176 and 260 HV10 depending on the carbon content and level of precipitation strengthening. Detailed microstructural analysis using laser scanning confocal microscopy (LCSM), FESEM and FESEM-EBSD revealed that all the steels consisted of mainly single-phase ferrite. FESEM analysis revealed the presence of relatively coarse precipitates at grain boundaries and inside some of the ferrite grains, but the number density of visible precipitates varied greatly between grains. The addition of Nb or Nb+Ti reduced the ferrite grain size, especially the size of the largest grains as defined by the 90th percentile in the cumulative grain area distribution (d90%). Mean hole expansion (HE) ratios varied from 39 % to 76 % with the highest values associated with the lowest carbon contents. Despite raising the strength, microalloying with Nb or Nb+Ti had little if any detrimental effect on HE ratios compared to the V-microalloyed variants without Nb or Ti, presumably as a result of the grain refinement. Titanium nitrides acted as void nucleation sites close to the sheared edge. Microalloying with Nb and Nb+Ti led to a decrease in the depth of the shear affected zone (SAZ) and a smaller difference in hardness between the base material and the SAZ.

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Series: IOP conference series. Materials science and engineering
ISSN: 1757-8981
ISSN-E: 1757-899X
ISSN-L: 1757-8981
Volume: 651
Article number: 012072
DOI: 10.1088/1757-899X/651/1/012072
Host publication: 38th International Deep Drawing Research Group Annual Conference (IDDRG 2019) 3–7 June 2019, Enschede, Netherlands
Conference: International Deep Drawing Research Group Conference
Type of Publication: A4 Article in conference proceedings
Field of Science: 216 Materials engineering
Funding: The financial support of CBMM (Companhia Brasileira de Metalurgia e Mineracao) and SSAB Europe Oy 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