Dresden 2006 – wissenschaftliches Programm
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MM: Metall- und Materialphysik
MM 34: Symposium Materials Modelling III
MM 34.1: Vortrag
Donnerstag, 30. März 2006, 17:00–17:15, IFW A
Material Modelling and Mathematical Simulation of Steel Carbonitriding — •Nicolas Bontems1, Taláat Al-Kassab1, Jürgen Gegner2, Reiner Kirchheim1, and Peter-J. Wilbrandt1 — 1Institut für Materialphysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany — 2SKF GmbH, Material Physics, Ernst-Sachs-Str. 5, D-97424 Schweinfurt, Germany
Carbonitriding of low-alloyed steels is performed in the austenitic region in gas mixtures offering high carbon and nitrogen potential at temperatures of about 850 ∘C. Inward diffusing nitrogen leads to a varying microstructure from the surface to the bulk. Such process is often applied to standard bearing steel 100Cr6. Since nitrogen increases the carbon activity, carbon will be released by carbide dissolution and chromium nitride precipitates will be formed. Carbon diffuses in the steel according to the activity gradient, which is acting as driving force. Two basic models have been developed to treat these two complex diffusion problems. The first model for nitrogen diffusion distinguishes atoms dissolved in the lattice and trapped in precipitates or at phase boundaries. The second model for carbon diffusion considers the varying gradient of the carbon activity. A numerical scheme enables the solution of Fick second laws. First results show the applicability of the models, which deliver a numerical evaluation of the variations of the carbon activity with the amount of nitrogen and support a special kinetic mechanism for nitrogen in-diffusion in presence of CrN precipitates.