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The influence of fine ferrite formation on the γ/α interface, fine bainite and retained austenite in a thermomechanically-processed transformation induced plasticity steel

Published online by Cambridge University Press:  03 March 2016

Ilana B. Timokhina ,
Michael K. Miller ,
Hossein Beladi  and
Peter D. Hodgson
Ilana B. Timokhina*
Affiliation:
Institute for Frontier Materials, Deakin University, Geelong, Victoria 3217, Australia
Michael K. Miller
Affiliation:
Oak Ridge National Laboratory, Center for Nanophase Materials Sciences, Oak Ridge, Tennessee 37831-6139, USA
Hossein Beladi
Affiliation:
Institute for Frontier Materials, Deakin University, Geelong, Victoria 3217, Australia
Peter D. Hodgson
Affiliation:
Institute for Frontier Materials, Deakin University, Geelong, Victoria 3217, Australia
*
a)Address all correspondence to this author. e-mail: ilana.timokhina@deakin.edu.au
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Abstract

An Fe–0.26C–1.96Si–2Mn with 0.31Mo (wt%) steel was subjected to a novel thermomechanical processing route to produce fine ferrite with different volume fractions, bainite, and retained austenite. Two types of fine ferrites were found to be: (i) formed along prior austenite grain boundaries, and (ii) formed intragranularly in the interior of austenite grains. An increase in the volume fraction of fine ferrite led to the preferential formation of blocky retained austenite with low stability, and to a decrease in the volume fraction of bainite with stable layers of retained austenite. The difference in the morphology of the bainitic ferrite and the retained austenite after different isothermal ferrite times was found to be responsible for the deterioration of the mechanical properties. The segregation of Mn, Mo, and C at distances of 2–2.5 nm from the ferrite and retained austenite/martensite interface on the retained austenite/martensite site was observed after 2700 s of isothermal hold. It was suggested that the segregation occurred during the austenite-to-ferrite transformation, and that this would decrease the interface mobility, which affects the austenite-to-ferrite transformation and ferrite grain size.

Keywords

fine ferritefine bainiteretained austeniteγ/α interfaceatom probe tomographytransmission electron microscopy
Type
Articles
Information
Journal of Materials Research , Volume 31 , Issue 6 , 28 March 2016 , pp. 806 - 818
Copyright
Copyright © Materials Research Society 2016 

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