In Situ Investigation of Microstructure Evolution and Stress Generation During Low‐Pressure Carburizing and Quenching by Means of Synchrotron X‐Ray Diffraction

Low-pressure carburizing (LPC) is a thermochemical process that enriches steel surfaces with carbon. While LPC is already used in industry, there are still aspects that offer opportunities for optimization if the necessary basic process understanding is provided. The present study quantifies the effect of LPC process parameters on the material state of different steel grades. For this purpose, in situ carburizing and quenching experiments are performed in a custom-built chamber for synchrotron X-ray diffraction at the German Electron Synchrotron in Hamburg. During carbon enrichment, carbon saturation and carbide formation are observed, slowing acetylene decomposition. Carbides that initially form at the surface dissolve in later diffusion steps. The kinetics of carbide formation and dissolution strongly depend on steel grade and carbide size. Quenching experiments further enable systematic analysis of phase-specific stresses at the surface and subsurface. The influence of transformation temperature across the carbon gradient is tracked, revealing differences in maximum stresses in both austenite and martensite. A direct correlation is identified between the local martensite fraction and the generated stresses within the carburized layer. ... mehrThis work provides new experimental insights into carbon uptake, carbide evolution, and stress development during LPC, offering pathways for process optimization across different steel types.