Tools and mechanics are subjected to stresses in short time periods and sometimes to corrosive atmospheres, which shortens their useful lifetime. Therefore it becomes necessary to improve the mechanical properties of the materials; one of those properties is hardness, which is a fundamental material property, related to mechanical resistance and wear resistance on tribologic applications. The industry is interested in solutions by means of new processes to improve properties such as fatigue and corrosion resistance. In the last decades there has been widespread use of techniques like Plasma Nitruration and Sputtering rf Magnetron (PVD, Physical Vapor Deposition), known as ecological techniques, to harden some tools. This work reports the results when some AISI 420 steel samples were ionically nitrurated, by dc plasma in an atmosphere of 20%N2+10%H2+70%Ar. The process conditions were: Temperature of 200 to 250 °C; nitruration time 1, 2 and 3 hours, at a pressure of 3 Torr. It was determined how these conditions influence the layer thickness as well as the micro-hardness, and how the nitruration influences the TiN film growth. Characterization by micro-hardness profiles, metallographic and XRD analysis was done. The highest hardness, 434 Knoop, was obtained in the 3 hour treated samples, with 115 µm nitrogen diffusion depth; with a TiN coating layer, the highest hardness was 3200 Knoop. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)