The nitriding of ferrous metals is primarily carried out to improve the surface hardness resulting from the formation of nitrogen compounds and diffused atomic nitrogen. In this study, we detail the achievements of the compound-layer-free nitriding of ferrous metallic surfaces using a low-power electron-beam-excited plasma in a nitrogen atmosphere. The X-ray diffraction and hardness results of our experiments indicate that the nitride layer consisting of CrN, Fe4N, and Fe3N compounds is drastically reduced when driving the system at 100 eV, while it maintains a hardness about 1.5 times that of the untreated surface. We have also confirmed that the present process can be applied to the nitriding of mechanical parts with narrow slit features.