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Metals 2018, 8(8), 646; https://doi.org/10.3390/met8080646

Study of Carbide Dissolution and Austenite Formation during Ultra-Fast Heating in Medium Carbon Chromium Molybdenum Steel

1
Laboratory of Physical Metallurgy, Division of Metallurgy and Materials, School of Mining & Metallurgical Engineering, National Technical University of Athens, 9, Her. Polytechniou str., Zografos, 15780 Athens, Greece
2
Department of Physical Metallurgy and Forming, Hellenic Research Centre for Metals S.A. -ELKEME S.A., 61st km Athens-Lamia Nat. Road, 32011 Oinofyta, Viotia, Greece
3
Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628CD Delft, The Netherlands
4
Department of Electrical Energy, Metals, Mechanical constructions & Systems, Ghent University, Technologiepark 903, 9052 Gent, Belgium
*
Author to whom correspondence should be addressed.
Received: 24 July 2018 / Revised: 9 August 2018 / Accepted: 9 August 2018 / Published: 16 August 2018
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Abstract

In this study, UltraFast Heat Treatment (UFHT) was applied to a soft annealed medium carbon chromium molybdenum steel. The specimens were rapidly heated and subsequently quenched in a dilatometer. The resulting microstructure consists of chromium-enriched cementite and chromium carbides (in sizes between 5–500 nm) within fine (nano-sized) martensitic and bainitic laths. The dissolution of carbides in austenite (γ) during ferrite to austenite phase transformation in conditions of rapid heating were simulated with DICTRA. The results indicate that fine (5 nm) and coarse (200 nm) carbides dissolve only partially, even at peak (austenitization) temperature. Alloying elements, especially chromium (Cr), segregate at austenite/carbide interfaces, retarding the dissolution of carbides and subsequently austenite formation. The sluggish movement of the austenite/carbide interface towards austenite during carbide dissolution was attributed to the partitioning of Cr nearby the interface. Moreover, the undissolved carbides prevent austenite grain growth at peak temperature, resulting in a fine-grained microstructure. Finally, the simulation results suggest that ultrafast heating creates conditions that lead to chemical heterogeneity in austenite and may lead to an extremely refined microstructure consisting of martensite and bainite laths and partially dissolved carbides during quenching. View Full-Text
Keywords: Ultra-Fast heating; simulation; dissolution; microstructure; martensite; bainitic ferrite Ultra-Fast heating; simulation; dissolution; microstructure; martensite; bainitic ferrite
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Papaefthymiou, S.; Bouzouni, M.; Petrov, R.H. Study of Carbide Dissolution and Austenite Formation during Ultra-Fast Heating in Medium Carbon Chromium Molybdenum Steel. Metals 2018, 8, 646.

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