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      FEM simulation of local heat treatment on dual phase and TRIP steel parts∗

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          Abstract

          The optimization of crash relevant automotive parts made of a Fe-0.13 C-1.4 Mn-1.2 Al dual phase (DP) steel and a Fe-0.22 C-1.6 Mn-1.3 Al transformation induced plasticity assisted (TRIP) steel by local hardening is investigated. The goal is to combine energy absorbing ductile regions in the front of the part with a high strength region near the passenger area within one part. To this end, sheet samples of DP 600 and TRIP 700 are locally hardened in a salt bath at an optimized annealing temperature and different annealing times. The results are compared to accompanying FEM simulations. Both steel grades are characterized not only by heterogeneous microstructures but also by gradients in the carbon distribution on a microscopic scale. Accordingly, the heat treatment is described by a model consisting of both phase transformation based on Johnson-Mehl-Avrami (JMA) kinetics as well as carbon diffusion depending on the phase proportions. Parameters are taken from earlier studies [1]. Comparison of simulated hardness profiles and measurements reveals that the model used in this study is suitable to predict the transition from the base material to the hardened region.

          Kurzfassung

          Die Optimierung crash-relevanter Automobilteile aus einem Fe-0.13 C-1.4 Mn-1.2 Al Dualphasen (DP)-Stahl sowie einem Fe-0.22 C-1.6 Mn-1.3 Al TRIP-Stahl (TRIP = transformation induced plasticity assisted) durch eine lokale Wärmebehandlung wurde untersucht. Die Idee ist, zähere Zonen im vorderen Teil, welche mehr Energie absorbieren können, mit härteren und festeren Bereichen im hinteren Teil, welche Verformungen im Bereich der Fahrgastzelle verhindern sollen, in einem Bauteil zu vereinen. Zu diesem Zweck wird die lokale Härtbarkeit von Proben der Werkstoffe DP 600 sowie TRIP 700 im Salzbad bei einer optimalen Glühtemperatur und verschiedenen Glühzeiten untersucht und die Ergebnisse mit begleitenden FEM-Simulationen verglichen. Beide Stahlsorten weisen nicht nur ein heterogenes Gefüge, sondern auch Mikroskalen-Gradienten im Kohlenstoffgehalt auf. Die Wärmebehandlung wird deswegen durch eine Kombination aus kohlenstoffabhängiger Phasenumwandlung nach dem Johnson-Mehl-Avrami-Ansatz (JMA) und phasenabhängiger Kohlenstoffdiffusion modelliert. Die Parameter wurden in einer früheren Untersuchung [1] auf der Basis von Dilatometerversuchen bestimmt. Härteprofile an den lokal gehärteten Proben, insbesondere im Übergangsbereich zwischen Ausgangsmaterial und gehärteter Zone, werden mit begleitenden FEM-Simulationen verglichen.

          Most cited references1

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          Reaction kinetics in process of nucleation and growth

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            Author and article information

            Journal
            htmd
            HTM Härtereitechnische Mitteilungen
            Carl Hanser Verlag
            0341-101X
            2194-1831
            2006
            : 61
            : 5
            : 249-253
            Author notes

            Dr. Jörn Lütjens, born in 1971, studied Physics at the Universities of Bremen, Gießen, and Nantes. He graduated to PhD at the University of Surrey, Guildford/UK, in 2002. Since 2003 he works as postdoctoral research fellow in the Foundation Institute for Materials Science (IWT) in Bremen.

            Dr.-Ing. Martin Hunkel, born in 1966, studied Physics at the University Karlsruhe (TH). He received his PhD. in Physical Metallurgy at the Technical University Bergakademie Freiberg. Since 1998 he is with the Heat Treatment Department of the Foundation Institute for Materials Science (IWT) in Bremen.

            Apl. Prof. Dr.-Ing. habil. Franz Hoffmann, born in 1950, studied Mechanical Engineering at the University Karlsruhe. Since 1975 he operates at the Foundation Institute for Material Science (IWT) in Bremen and there he is the Head of the Heat Treatment Department.

            Prof. Dr.-Ing. Hans-Werner Zoch, born in 1953, is Professor for Materials Science / Metals at the faculty of Production Engineering at the University Bremen. Since 2004 he is the Managing Director of the Foundation Institute for Materials Science (IWT) in Bremen.

            [∗]

            The lecture was held by J. Lütjens at the 15 th Int. Conf. IFHTSE, 26–29 September 2006 in Vienna/Austria.

            Article
            HT100388
            10.3139/105.100388
            da6b1909-f4b6-4c4d-a241-fa3cf2067ce8
            © 2006, Carl Hanser Verlag, München
            History
            Page count
            References: 10, Pages: 5
            Categories
            Fachbeiträge/Technical Contributions

            Materials technology,Materials characterization,General engineering,Mechanical engineering,Materials science

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