Nitrocarburising of annealed and severe plastically deformed 16MnCr5 steel

The microstructure resulting from a gaseous multistage nitrocarburising treatment applied to a 16MnCr5 steel has been investigated to study the microstructural evolution during the process and the effects of severe plastic deformation. The depth of the compound layer and the porous zone has been measured by optical microscopy. The microstructure has been investigated by means of a scanning electron microscope equipped with both an electron backscatter diffraction detector, to assess the amount and the distribution of nitrogen nitrides, and an energy-dispersive X-ray microanalysis to reveal the N diffusion depth. Finally, microhardness investigations have been carried out. The results indicate that severe plastic deformation influences the microstructure of the compound layer, the N concentration trends and the hardness profiles. The effects of severe plastic deformation lead to a greater initial diffusivity of nitrogen, a subsequent premature N saturation in the diffusion zone and an increased porous/compact-layer thickness ratio.