Efthymiadis, Panagiotis, Hazra, S. K. , Clough, Andrew Richard, Lakshmi, R., Alamoudi, A., Dashwood, R. J. and Shollock, Barbara A. (2017) Revealing the mechanical and microstructural performance of multiphase steels during tensile, forming and flanging operations. Materials Science and Engineering: A, 701 . pp. 174-186. doi:10.1016/j.msea.2017.06.056

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Abstract

The mechanical performance of Dual Phase (DP) and Complex Phase (CP) steels was investigated by SEM analysis, tensile testing, Forming Limit Curve investigation and flange formability testing. The alloys of interest were Dual Phase (DP) untempered, Dual Phase (DP) tempered and Complex Phase (CP) steels. Phase content analysis showed that the distribution of the ferrite and martensite phases was the same for the two DP alloys, but the grain size and condition (tempered/untempered) for the martensite islands was much different in the two alloys. In the tempered DP steel, the smaller grain size for the martensite and the tempering process resulted in increased elongation, more formability and ability to form a flange (flangeability). In CP steels the soft ferrite phase is replaced by harder bainite, yielding a bainitic-martensitic microstructure. Bainite reduced the total elongation of the alloy during tensile testing, reduced the formability (especially under plane strain conditions) of the alloy but improved the flangeability of the alloy. Under flanging conditions, CP steels deformed to higher strains, at tighter radii with minimum springback. Microstructural inspections at the outer radius of the flanged specimens revealed that in CP steels bainite deforms similarly to martensite, therefore the strain partitioning is smaller in CP steels in comparison to DP steels. Plastic deformation in CP steels upon flanging occurs with the formation of strong slip bands in both martensite and bainite. In contrast, the martensite and ferrite grains in DP steels deform quite differently leading to strong strain localisations. Void nucleation and cracking occurred at the martensite islands or within the soft ferrite phase next to the martensite islands. In CP steels no voids or damage was observed within the matrix. A special case study was done with a thicker and stronger alloy, a Martensitic 1400 steel to reveal the flangeability limits for advanced high strength steels. Neither cracks nor damage were observed visually on the flanged specimens. However SEM observations at the outer radius of the flanged samples revealed significant void growth at inclusion sites and cracks nucleating within the matrix adjacent to the inclusions.

Item Type:	Journal Article
Subjects:	T Technology > TN Mining engineering. Metallurgy
Divisions:	Faculty of Science > WMG (Formerly the Warwick Manufacturing Group)
Library of Congress Subject Headings (LCSH):	Steel alloys -- Analysis
Journal or Publication Title:	Materials Science and Engineering: A
Publisher:	Elsevier S. A.
ISSN:	0921-5093
Official Date:	31 July 2017
Dates:	Date Event 31 July 2017 Published 22 July 2017 Available 13 June 2017 Accepted
Date of first compliant deposit:	27 June 2017
Volume:	701
Page Range:	pp. 174-186
DOI:	10.1016/j.msea.2017.06.056
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access
Funder:	Engineering and Physical Sciences Research Council (EPSRC)
Grant number:	EP/M014096/1

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