Direct deposition of diamond thin films upon ferrous substrates is dramatically restrained by the catalytic capability of Fe to enhance the formation of a soft carbon soot rather than diamond, and the rapid diffusion of carbon species from substrate surface into the bulk material. In this paper, AL-N thin layers were synthesized on a steel surface with high power Al/N plasma streams generated from a Plasma-Focus device, operated with Aluminum electrodes and Nitrogen filling gas, The diamond layer deposition was then performed on this surface within a separate hot -filament CVD system. Auger electron spectra X-ray photoelectron spectra, scanning electron microscope pictures, and Raman scattering measurements, were used to investigate the samples characteristics. It seems that the AL-N compound layer, obtained as described above, can work well as an interlayer for the diamond growth on steel substrates.