Carbon Clustering in Low-Temperature Bainite
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INTRODUCTION
LOW-TEMPERATURE bainite is obtained in high-carbon high-silicon steels after transformation at temperatures below 573 K (300 C). Once a bainitic ferrite plate grows, carbon is mobile enough to partition rapidly from supersaturated bainitic ferrite to austenite,
ROSALIA REMENTERIA is with the Department of Physical Metallurgy, Spanish National Center for Metallurgical Research (CENIM-CSIC) Avda. Gregorio del Amo 8, 28040, Madrid, Spain, and is now with the Additive Manufacturing New Frontier, ArcelorMittal Global R&D calle Marineros 4, 33490, Avile´s, Asturias, Spain. CARLOS CAPDEVILA, CARLOS GARCIAMATEO, and FRANCISCA G. CABALLERO are with the Department of Physical Metallurgy, Spanish National Center for Metallurgical Research (CENIM-CSIC). Contact e-mail: [email protected] RICARDO DOMI´NGUEZ-REYES is with the Departamento de Fı´ sica, Universidad Carlos III de Madrid, Avda. de la Universidad 30, E-28911, Legane´s, Madrid, Spain. JONATHAN D. POPLAWSKY and WEI GUO are with the Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, PO Box 2008 MS6064, Oak Ridge, TN 37831-6064. ESTEBAN URONESGARROTE is with the Spanish National Centre for Electron Microscopy (CNME), Facultad de Ciencias Quı´ micas, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040, Madrid, Spain. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/dow nloads/doe-public-access-plan). Manuscript submitted May 21, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
simultaneously with other competing reactions such as carbon segregation to linear defects. As bainitic transformation proceeds, the residual austenite is enriched in carbon and further stabilized at ambient temperature. The resulting structure primarily consists of nanoscaled plates of bainitic ferrite embedded in carbon-enriched regions of austenite.[1] In these steels, silicon additions (over 1.50 wt pct, ~ 2.95 at. pct) prevent the precipitation of cementite between subunits of bainitic ferrite, but are not effective in retarding the precipitation of carbides from ferrite plates at low temperatures.[2] In the last decade, a significant amount of atom probe tomography (APT) observations have been performed in low-temperature bainite, showing that large quantities of excess carbon remain in ‘‘defect-free’’ solid solution in the bainitic ferrite matrix,[3–6] even after prolonged heat treatment.[7] However, the term ‘‘defect-free’’ would imply that bainitic ferrite would contain
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