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Effect of Thermomechanical Processing on the Transformation Kinetics, Microstructure and Mechanical Properties of a Continuously Cooled Cementite-free Bainitic Steel

  • P. J. de Castro EMAIL logo , A. Silveira , J. Dong , C. J. Turra , A. S. Rocha , R. Fechte-Heinen and J. Epp
Published/Copyright: July 5, 2024

Abstract

The combination of forming with continuous cooling bainitic steels offers a new path for reaching energy-efficient manufacturing chains. Improved energy efficiency is achievable thanks to the suppression of conventional, energy-intensive heat treatments. In the present paper, different thermomechanical processing strategies, including laboratory and industrial scale forgings, were assessed alongside their impact on the resulting microstructure. Firstly, phase transformation kinetics were assessed in precisely controlled environments via dilatometry coupled to in situ techniques. Secondly, the microstructure, mechanical properties, and forgeability of large-scale forged components were investigated in laboratory and industrial conditions. These investigations were also assisted by finite element method simulation. The comparison between controlled and industrial-scale conditions illustrates pitfalls in the transfer of knowledge to conditions approaching a real manufacturing chain. Nevertheless, alloy and process design is shown to be a key aspect to overcome the discussed challenges, allowing homogeneous bainite microstructures and mechanical properties to be achievable over a flexible range of processing conditions.

Kurzfassung

Die Kombination von Umformung mit kontinuierlicher Abkühlung bainitischer Stähle bietet einen neuen Weg zur Erreichung energieeffizienter Fertigungsketten. Durch den Verzicht auf konventionelle, energieintensive Wärmebehandlungen kann eine Verbesserung der Energieeffizienz erreicht werden. In der vorliegenden Arbeit wurden verschiedene thermomechanische Verarbeitungsstrategien, des Schmiedens im Labor- und Industriemaßstab bewertet. Zunächst wurde die Phasenumwandlungskinetik in genau kontrollierten Umgebungen mittels In-situ-Techniken bewertet. Anschließend wurden das Mikrogefüge, die mechanischen Eigenschaften und die Schmiedbarkeit von Großschmiedeteilen untersucht. Diese Untersuchungen wurden auch durch Finite-Elemente Simulationen unterstützt. Der Vergleich zwischen kontrollierten und industriellen Bedingungen verdeutlicht die Fallstricke bei der Übertragung von Erkenntnissen auf Bedingungen, die einer realen Fertigungskette nahekommen. Dennoch zeigt sich, dass die Legierungs- und Prozessgestaltung ein Schlüsselaspekt zur Überwindung der erörterten Herausforderungen ist, sodass homogene bainitische Gefüge und mechanische Eigenschaften über einen breiten und flexiblen Bereich von Verarbeitungsbedingungen erreicht werden können.


Note: Lecture held at the 27th International Federation for Heat Treatment and Surface Engineering Conference and European Conference on Heat Treatment, 5–8 September 2022 in Salzburg, Austria. Lecture title: Energy efficient manufacturing chain for advanced bainitic steels based on thermo-mechanical processing


Acknowledgments

The authors would like to acknowledge the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior –Brasil (CAPES) – Finance Code 001 number 1844/2017 and the Deutsche Forschungsgemeinschaft DFG (EP128-6-2-1) via Project number 327887503 for financial support.

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Published Online: 2024-07-05
Published in Print: 2024-05-29

© 2024 Walter de Gruyter GmbH, Berlin/Boston, Germany

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