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The aim of this study is to compare the frictional and wear behaviour of 35NCD6 steel in three different states: as received, heat-treated, and duplex coated by Cr/CrN multilayer. The samples of the second state were maintained at 850 C for 15 min, and then they were quenched in oil. After that, they were tempered at 180 C. The samples in the third state were surface coated in two steps. Firstly, a thin layer of chromium (about 200 m) was electrodeposited using a plating bath consisting of chromic acid (250 g/L) and sulphuric acid (2.5 g/L) at about 57C. Then, the electroplated samples were gas nitrided in NH3+N2 atmosphere at 750C for 6 hours.Characterization of frictional behaviour of the three different types of samples was performed using a ball-on-disk tribometer, then, the sliding wear track was analysed using an optical microscopy.
The results showed that friction coefficient at constant sliding velocity and normal load of the duplex-coated 35NCD6 steel was the lowest (0.272 compared to 0.387 and 0.359 for asreceived and heat-treated steels respectively). It showed also that the sliding wear track of duplexcoated steel was less profound than that in as received and heat-treated steel specimens, which means better wear resistance. The main cause of these results may be the high hardness of the chromium nitride layer formed at the surface of the duplex-coated steel specimens as confirmed by many researchers [1-3].