Full length article Investigation of solute/interphase interaction during ferrite growth H.P. Van Landeghem a, b, * , B. Langelier a , B. Gault c , D. Panahi a, 1 , A. Korinek d , G.R. Purdy a , H.S. Zurob a a McMaster University, Faculty of Engineering, Department of Materials Science and Engineering, 1280 Main St. W., Hamilton, ON, Canada b SIMaP, UMR 5622, Grenoble INP e CNRS e UGA, 1130 rue de la piscine, BP75, F-38420, St Martin d’H eres, France c Max-Planck Institut für Eisenforschung, Max-Planck Str 1, 40237, Düsseldorf, Germany d McMaster University, Brockhouse Institute for Materials Research, Canadian Centre for Electron Microscopy,1280 Main St. W., Hamilton, ON, Canada article info Article history: Received 11 July 2016 Received in revised form 26 October 2016 Accepted 12 November 2016 Keywords: Segregation Interface Atom probe tomography Ferrite Austenite abstract Knowledge of solute interaction with the interface during the transformation of austenite into ferrite is fundamental in predicting its kinetics in multicomponent steel. This interaction notably translates in segregation, or depletion, of the solutes at the transformation interface. Here, this segregation was successfully quantified by atom probe tomography (APT) in four ternary Fe-X-C systems involving substitutional solutes commonly found in modern steel grades (X ¼ Cr, Mn, Ni, Mo). Controlled decar- burization was used to grow a uniform, planar and incoherent ferrite layer at the surface of fully austenitic samples. In the case of Fe-Cr-C and Fe-Mo-C, the interfacial concentrations permitted the evaluation of the binding energy of each substitutional solute to the interface, which was found to be comparable to its respective grain boundary binding energy. In the case of Fe-Mn-C and Fe-Ni-C, un- desirable motion of the interface during the quench of the samples could not be avoided, preventing a reliable estimation of their binding energy since temperature and interface velocity were unknown. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. 1. Introduction The decomposition of austenite is a key reaction in steel pro- cessing. Predicting the decomposition kinetics is particularly important in modern steel grades such as dual phase (DP) and transformation-induced plasticity (TRIP) steels; the properties of these advanced grades can vary dramatically as a function of the amount of ferrite formed [1,2]. Reliable and accurate predictions of ferrite volume fraction as a function of time and temperature are highly desirable for efficient alloy design. The steel grades in question typically contain many substitutional solutes (e.g. Mn, Cr, Mo etc.). The presence of these solutes alters the kinetics of the decomposition, which renders it difficult to predict accurately. Major aspects contributing to this complexity include the interac- tion of solutes with the moving interface and solute-solute in- teractions within the interface. A number of ferrite growth models have been devised in order to account for this interaction in ternary Fe-X-C systems [3]. In these models, the interaction is solely attributed to the substitutional solute X through a parameter referred to as the binding energy, which captures the affinity of the element for the interface. In practical situations where a value is required for this binding energy, such as transformation kinetics modeling, it is usually kept as a fitting parameter [4] or estimated using ab-initio calculations [5]. However, the interaction of the solutes with the interface also leads to segregation at the trans- formation interface, with the amount of segregation being a func- tion of the binding energy. Thus, if this segregation can be accurately quantified, then an estimate for the binding energy can also be determined. This approach has been extensively utilized to quantify solute interaction with grain boundaries [6]. Applying the same technique to solute segregation at ferrite/ austenite interface boundaries has proven much more challenging. Earlier attempts [7,8] showed great variations in the segregation from one interface boundary to another, which were attributed to varying crystallography between interfaces, as well as differences in the velocity of the interfaces prior to quenching. It can therefore be expected that variations in segregation at the interface would be minimized if the velocity of the interface boundary and its crys- tallography were well defined. * Corresponding author. SIMaP, UMR 5622, Grenoble INP e CNRS e UGA, 1130 rue de la piscine, BP75, F-38420, St Martin d’H eres, France. E-mail address: Hugo.VanLandeghem@simap.grenoble-inp.fr (H.P. Van Landeghem). 1 Dr. D. Panahi is now with ArcelorMittal Global R&D East Chicago, 3001 E Co- lumbus Drive, 9-000 East Chicago, IN 46312, USA. Contents lists available at ScienceDirect Acta Materialia journal homepage: www.elsevier.com/locate/actamat http://dx.doi.org/10.1016/j.actamat.2016.11.035 1359-6454/© 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Acta Materialia 124 (2017) 536e543