Low-temperature glow discharge nitriding of nanobainitic X37CrMoV5-1 steel: Surface and core properties

This study presents the first investigation of low-temperature glow discharge nitriding of nanobainitic X37CrMoV5-1 (AISI H11) steel. The main aim was to produce hard and wear-resistant diffusion layers while preserving the carbide-free nanobainitic core. Nitriding was performed at 420 °C for 6 hours, producing thin diffusion layers primarily composed of ε-Fe 3 N nitrides. For comparison, quenched-and-tempered martensitic steel was also nitrided under identical conditions. The thickness and nitrogen distribution of the layers depended on the substrate microstructure, with the martensitic steel showing a slightly thicker layer and more gradual nitrogen profile than the nanobainitic steel. Despite lower surface hardness, the nitrided nanobainitic steel exhibited approximately 30 % higher wear resistance compared to the nitrided martensitic reference. This improvement is attributed to the refined nanobainitic microstructure and the transformation-induced plasticity (TRIP) effect of retained austenite, which increased local surface hardness, suppressed further plastic deformation, and reduced debris accumulation in the wear track. The nanobainitic microstructure of X37CrMoV5-1 steel also demonstrated high thermal stability up to 425 °C, allowing low-temperature nitriding without significant microstructural degradation. Overall, the results show that low-temperature glow discharge nitriding is a promising surface engineering method for enhancing the tribological performance of nanobainitic steels, combining a hard nitrided layer with the superior properties of the nanobainitic core.