Study of Nitrogen Diffusion in Aluminum Containing Plasma-Nitrided Air-Hardening Medium Manganese Steels

This study explores the effects of plasma nitriding on the surface hardness and nitride compound layer thickness of AHD steels containing 4% manganese, with a focus on aluminium content and treatment temperature. A temperature range from 500-700°C was studied. Chemical analysis and nitrogen diffusion profiles were obtained via Electron Probe Micro-Analysis (EPMA). Results showed nitrogen diffusion during plasma nitriding is highly temperature-dependent. At 500°C, a compound layer comprising γ'-Fe4N or γ'/ɛ- phases was observed across all three investigated alloys. Elevated aluminum levels promote thicker nitride layers and higher diffusivity, whereas treatment duration has a comparatively minor influence on layer growth. Additionally, nitrogen diffusion induces a displacement effect on carbon within the alloys interior, affecting overall microstructural evolution. The nitrogen diffusion coefficient was calculated, revealing an increase with rising temperature. These findings underscore the significant roles of process temperature and alloy composition in tailoring microstructural modifications and enhancing mechanical properties through plasma nitriding of AHD steels.