The Formation of Surface Nanoparticles Enhances the Vacuum Carburizing Efficiency of 20CrMnTi Steel

The effect of a pre-nitriding treatment, applied prior to vacuum carburizing, on the carburizing efficiency of 20CrMnTi steel is investigated. The results demonstrate that pre-nitriding significantly enhances the vacuum carburizing efficiency of 20CrMnTi steel, refines the martensitic microstructure of the carburized layer, and promotes carbide precipitation. At the same carburized layer depth, the hardness and carbon content of the pre-nitriding samples are markedly higher than those of the without pre-nitriding samples. Specifically, the effective hardened depth and the surface hardness increase by approximately 0.15 mm and 75 HV500gf, respectively. These improvements are attributed to the formation of loose, porous nano-sized nitride particles on the surface during the pre-nitriding process, which substantially increases the surface roughness and pore volume. This surface morphology facilitates the adsorption and inward diffusion of carbon atoms during carburizing, and the presence of nitrogen in solid solution further enhances carbon diffusion.