Carbon supersaturation of ferrite in a nanocrystalline bainitic steel

The extremely slow transformation kinetics of a nanocrystalline bainitic steel allows the carbon content of the bainitic ferrite away from any carbon-enriched regions such as dislocations and boundaries to be determined by atom probe tomography as the bainite transformation progresses at 200 C. A high level of carbon, well above that expected from para-equilibrium with austenite, has been detected in solid solution in bainitic ferrite at the early stage of transformation. Results provide strong evidence that bainite transformation is essentially displacive in nature so that the newly formed bainitic ferrite retains much of the carbon content of the parent austenite. 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.The authors gratefully acknowledge the support of the Research Fund for Coal and Steel and the Spanish Ministry of Science and Innovation for funding this research under the contracts RFSR-CT-2008-00022 and MAT2007- 63873, respectively. Research at the Oak Ridge National Laboratory SHaRE User Facility was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.Peer reviewe