Ultrafine grained structure formation in steels using dynamic strain induced transformation processing

Beladi, Hossein, Kelly, Georgina and Hodgson, Peter 2007, Ultrafine grained structure formation in steels using dynamic strain induced transformation processing, International materials reviews, vol. 52, no. 1, pp. 14-28, doi: 10.1179/174328006X102538.

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Title Ultrafine grained structure formation in steels using dynamic strain induced transformation processing
Author(s) Beladi, HosseinORCID iD for Beladi, Hossein orcid.org/0000-0003-0131-707X
Kelly, Georgina
Hodgson, Peter
Journal name International materials reviews
Volume number 52
Issue number 1
Start page 14
End page 28
Publisher Maney Publishing
Place of publication London, England
Publication date 2007-01
ISSN 1743-2804
Keyword(s) ferrite refinement
ultrafine ferrite
steel
dynamic strain induced
transformation
thermomechancial processing
Summary The refinement of ferrite grain size is the most generally accepted approach to simultaneously improve the strength and toughness in steels. Historically, the level of ferrite refinement is limited to 5-10 μm using conventional industrial approaches. Nowadays, though, several thermomechanical processes have been developed to produce ferrite grain sizes of 1-3 μm or less, ranging from extreme thermal and deformation cycles to more typical thermomechanical processes. The present paper reviews the status of the production of ultrafine grained steels through relatively simple thermomechanical processing. This requires deformation within the Ae3 to Ar3 temperature range for a given alloy. Here, the formation of ultrafine ferrite (UFF) involves the dynamic transformation of a significant volume fraction of the austenite to ferrite. This dynamic strain induced transformation (DSIT) arises from the introduction of extensive intragranular nucleation sites that are not present in conventional controlled rolling. The DSIT route has the potential to be adjusted to suit current industrial infrastructure. However, there are a number of significant issues that have been raised, both as gaps in our understanding and as obstacles to industrial implementation. One of the critical issues is that it appears that very large strains are required. Combined with this concern is the issue of whether a combination of dynamic and static transformation can be used to achieve an adequate level of refinement. Another issue that has also become apparent is that grain sizes of 1 μm can lead to low levels of ductility and hence many workers are attempting to obtain 2-3 μm grains, or to introduce a second phase to provide the required ductility. There are also a number of areas of disagreement between authors including the role of dynamic recrystallisation of ferrite in the production of UFF by DSIT, the reasons for the low coarsening rate of UFF grains, the role of microalloying elements and the effects of austenite grain size and strain rate. The present review discusses these areas of controversy and highlights cases where experimental results do not agree.
Language eng
DOI 10.1179/174328006X102538
Field of Research 091207 Metals and Alloy Materials
HERDC Research category C1 Refereed article in a scholarly journal
Copyright notice ©W.S. Maney & Son Ltd
Persistent URL http://hdl.handle.net/10536/DRO/DU:30007078

Document type: Journal Article
Collections: Centre for Material and Fibre Innovation
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