17-4PH stainless steel was plasma nitrocarburized at 430 degrees C for different time with rare earths (RE) addition. Plasma RE nitrocarburized layers were studied by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction, microhardness tests, pin-on-disc tribometer and anodic polarization tests. The results show that rare earths atoms can diffuse into the surface of 17-4PH steel. The modified layer depths increase with increasing process time and the layer growth conforms approximately to the parabolic law. The phases in the modified layer are mainly of gamma'-Fe4N, nitrogen and carbon expanded martensite (alpha'(N)) as well as some incipient CrN at short time (2 h). With increasing of process time, the phases of CrN and gamma'-Fe4N increase but alpha'(N) decomposes gradually. Interestingly, the peaks of gamma'-Fe4N display a high (2 0 0) plane preferred orientation. The hardness of the modified specimen is more than 1340 HV, which is about 3.7 times higher than that of untreated one. The friction coefficients and wear rates of specimens can be dramatically decreased by plasma RE nitrocarburizing. The surface hardness and the friction coefficients decrease gradually with increasing process time. The corrosion test shows that the 8 h treated specimen has the best corrosion resistance with the characterization of lower corrosion current density, a higher corrosion potential and a large passive region as compared with those of untreated one. (C) 2010 Elsevier B.V. All rights reserved.