In Situ Synchrotron X-Ray Diffraction Analyses of the Low-Pressure Carburizing Process on Steel AISI 5120 Using a Reflection Setup

Abstract Low-pressure carburizing (LPC) is a recipe-controlled heat treatment process for surface layer hardening. The combination of the process parameters determines the chemical gradients established within the case, the local microstructure and the depth distribution of the resulting process-induced residual stresses. Here, the objective was to quantify the influence of the process parameters on the resulting material state of the case hardening steel AISI 5120 (EN 20MnCr5). Therefore, the carburizing and quenching processes were examined using a self-built process chamber specially designed for in situ synchrotron X-ray diffraction experiments. A method for synchrotron X-ray diffraction in reflection geometry was developed to investigate the LPC process. It could be demonstrated that such experiments enable the analysis of microstructural changes, phase transformations and stress evolution at the immediate surface layer with high temporal resolutions. From a material science perspective, the investigations showed, among others, a carbon saturation of the austenite phase within 10 seconds during the boost segments of the LPC process and the formation of compressive residual stresses below -180 MPa after subsequent quenching.