Abstract
In situ X-ray diffraction investigations during low pressure carburizing (LPC) processes were performed with a specially developed process chamber at the German Electron Synchrotron Facility (DESY) in Hamburg, Germany. Carbon saturation in austenite was reached in less than 20 seconds for all processes with different parameters and carbides formed at the surface. Therefore, the direct contribution of carbon donor gas to the carbon profile after 20 seconds was reduced to very low levels. After that point, further supply of carbon donor gas increased the amount of carbides formed at the surface, which will contribute to the carbon profile indirectly by dissolution in the following diffusion steps. During quenching, martensite at higher temperatures had a lower c/a ratio than later formed ones. This difference is credited to self-tempering effects and reordering of carbon atoms within the martensite lattice.
Kurzfassung
In-situ-Röntgenbeugungsuntersuchungen während des Niederdruckaufkohlungsprozesses wurden mit einer speziell entwickelten Prozesskammer am Deutschen Elektronen-Synchrotron (DESY) in Hamburg, Deutschland, durchgeführt. Die Kohlenstoffsättigung im Austenit wurde bei allen Prozessen mit unterschiedlichen Parametern in weniger als 20 Sekunden erreicht und Karbide bildeten sich an der Oberfläche. Daher war der direkte Beitrag des Kohlenstoffspendergases zum Kohlenstoffprofil nach 20 Sekunden auf ein sehr niedriges Niveau reduziert. Nach diesem Zeitpunkt erhöhte die weitere Zufuhr von Kohlenstoffspendergas die Menge der an der Oberfläche gebildeten Karbide, die in den folgenden Diffusionsschritten indirekt durch Auflösung zum Kohlenstoffprofil beitragen. Während des Abschreckens wiesen Martensite bei höheren Temperaturen ein niedrigeres c/a-Verhältnis auf als später gebildete Martensite. Dieser Unterschied wird auf Selbstanlasseffekte und auf eine Umordnung der Kohlenstoffatome im martensitischen Gitter zurückgeführt.
Acknowledgement
The authors gratefully acknowledge the support from the Deutsche Forschungsgemeinschaft (DFG) for funding this research under the collaborative project EP-128/2-1- | GI-376/15-1 (DFG project no. 399551201), Deutsches Elektronen-Synchrotron (DESY) for granting beam time. Furthermore, the authors would like to thank Alexander Kohl and Sebastian Ohneseit for their participation in the measuring campaign at DESY and in particular Alexander Kohl for his engagement in the planning and realization of the process chamber.
Danksagung
Die Autoren bedanken sich bei der Deutschen Forschungsgemeinschaft (DFG) für die Förderung dieser Forschungsarbeit im Rahmen des Verbundprojekts EP-128/2-1- | GI-376/15-1 (DFG-Projekt Nr. 399551201) und beim Deutschen Elektronen-Synchrotron (DESY) für die Bereitstellung von Strahlzeit. Darüber hinaus danken die Autoren Alexander Kohl und Sebastian Ohneseit für ihre Teilnahme an der Messkampagne bei DESY und insbesondere Alexander Kohl für sein Engagement bei der Planung und Realisierung der Prozesskammer.
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