Investigation of the Effects of Low-Pressure Carburizing Process Parameters on Microstructural Evolution by Means of In Situ Synchrotron X-Ray Diffraction

Abstract

In situ X-ray diffraction experiments during low-pressure carburizing processes are performed at the German Electron Synchrotron Facility, Beamline P07, in Hamburg, Germany, with a specially developed process chamber. Microstructural evolution is precisely analyzed based on diffraction data, and several process parameters are varied. The investigations focus on boost and diffusion steps in which carbon donor gas interacts with the hot steel surface and carbon atoms diffuse through the sample. An increased process temperature leads to higher carbon absorption during the boost step, especially at the early stages of the process. Regardless of process parameters, austenite saturation is reached in a few seconds. Therefore, longer boost step duration and/or a higher acetylene amount does not directly increase the carbon profile; instead, this would only increase the amount of carbides formed on the surface, which would contribute to the carbon profile by dissolution in the following steps. Therefore, shorter and a high number of boost steps are recommended for high efficiency. The cementite formation rate shows a similar trend with austenite saturation. It is very fast at the beginning and then stays almost constant. Therefore, introducing acetylene to the furnace after that point has no positive effect on the carburization.