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.
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ACKNOWLEDGMENTS
The authors would like to acknowledge the technical and scientific support of the Center for Electron Microscopy at Monash University. One of the authors (I.T.) acknowledges the support of Outside Study Program from Deakin University. One of the authors (P.D.H.) also acknowledges the support of the ARC Laureate Fellowship scheme. Atom probe tomography (M.K.M.) was supported through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
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Timokhina, I.B., Miller, M.K., Beladi, H. et al. The influence of fine ferrite formation on the γ/α interface, fine bainite and retained austenite in a thermomechanically-processed transformation induced plasticity steel. Journal of Materials Research 31, 806–818 (2016). https://doi.org/10.1557/jmr.2016.73
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DOI: https://doi.org/10.1557/jmr.2016.73