ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Managing Both Strength and Ductility in Ultrafine Grained Steels
Nobuhiro TsujiNaoya KamikawaRintaro UejiNaoki TakataHirofumi KoyamaDaisuke Terada
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2008 Volume 48 Issue 8 Pages 1114-1121


Ultrafine grained (UFG) steels provide surprisingly high strength but sometimes show limited tensile ductility. In the present paper, systematic experimental results on mechanical properties of UFG steel with ferrite single phase are shown first. The limited tensile ductility of the UFG ferritic steel was due to very small uniform elongation, which was attributed to the early plastic instability in the UFG microstructures. This basic understanding suggested a way to overcome the low tensile ductility: if the strain-hardening of the matrix is enhanced by any means, both high strength and adequate ductility can be managed even in UFG structures. Actual examples of the UFG steels that could achieve good strength–ductility balance are also presented. Dispersing fine carbides within the UFG ferrite matrix, and making the UFG dual-phase structure composed of ferrite and martensite were both effective to manage high strength and large uniform elongation. It was clearly shown that the future studies on the UFG steels from practical viewpoint should be directed to make the UFG structures multi-phased.

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© 2008 by The Iron and Steel Institute of Japan
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