Micro-Focused X-ray Diffraction Imaging Analysis of Fe Nitrides and Carbides in the Compound Layer of Nitrocarburized and Gas Nitrided Steel Surfaces

Thermochemical treatments like nitrocarburizing and gas nitriding form hardened surface layers of iron nitrides and carbides, improving wear, fatigue, and corrosion resistance in loaded components made of steel. This study employs micro-focused X-ray diffraction (µXRD) imaging at a synchrotron facility to characterize the microstructure of nitrocarburized and gas-nitrided steel surfaces in three steel grades (46MnVS3, 34CrNiMo6, 16CrMnNiMo9–5–2). Through line profile analysis with fine-step mesh grid scanning, we spatially resolve phase distributions and elastic strains in the compound layer. The ε-phase exhibits isotropic residual strain, transitioning from expansion to compression with depth, while the γ’-phase displays anisotropic strain, expanding perpendicular to the surface and compressing parallel to it. These findings highlight µXRD’s potential for detailed structural analysis, enabling optimization of surface hardening processes.