The effect of process parameters on the morphology and hardness of nitride layers in plasma nitriding of H11 hot working steel

Plasma nitriding is one of the effective methods for the improvement of hardness, wear and corrosion resistance of iron alloys. In this research, AISI H11 steel was plasma nitrided with various gas mixtures, times and temperature The effect of process parameters on the morphology and hardness of nitride layers has been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness measurements. The results showed that by increasing the nitriding time, the depth of nitrogen diffusion into the sample and consequently, the size of nitride precipitates formed on the surface increased. therefore, the density of these particles and hence, the surface hardness decreased. By increasing the nitrogen percentage in the gas composition, the surface hardness increased due to the formation of more ε phase at the surface. Meanwhile, an increase in process time and/or temperature resulted in a decrease in the amount of ε phase which decreased the surface hardness.