Plasma Nitriding of Hard Chromium Electroplated Low Alloy AISI 4340 Steel in Pure Nitrogen Gas Atmosphere

Duplex treatments are surface modification techniques used to enhance the surface properties of steels. In this study, hard chromium electroplated AISI 4340 steel was plasma nitrided in pure nitrogen gas at 600°C for 90 min. The structural and morphological properties were analysed by an X-ray diffractometer and a scanning electron microscope (SEM), respectively. The hardness profile was obtained by a multicycle nanoindentation test and the tribological properties by a ball-on-disk test at room temperature. The results showed that the duplex layer was composed mainly of Cr2N and it had a rough surface morphology with a network of micro-cracks. The highest values of hardness were registered in the nitrogen diffusion layer beneath the outer porous thin layer. The friction coefficient and the specific wear rate after plasma nitriding were reduced by 3 and 5 factors, respectively.