In this study, plasma nitrocarburizing at various temperatures in the range of 460-540 degrees C were carried out on M50NiL steel in order to improve wear properties. The nitrocarburizing temperature was optimized to obtain the best wear properties. The phase composition, microstucture and microhardness profiles of nitrocarburized layers of M50NiL steel were characterized by XRD, optical microscope and Vickers microhardness measurements, respectively. Pin-on-disc tribometer and SEM equipped with EDS were applied to measure friction and wear properties and analyze wear mechanisms involved. XRD results show that the amount of epsilon-Fe2-3(N,C) phase increased as the nitrocarburizing temperature rose form 460 degrees C to 500 degrees C and then decreased at 540 degrees C, while the amount of gamma'-Fe-4(N,C) phase increased as the treatment temperature rose. The hardness of the nitrocarburized layers showed an obvious improvement accompanied with the increasing nitrocarburizing temperature, and obtained the maximum surface hardness of 1287 HV at 540 degrees C. The results of wear tests carried out at various sliding speeds indicated that the wear mechanism depends on sliding speed rather than the nitrocarburizing temperature. With the increase of the sliding speed, the wear mechanism transfers from oxidation mode to abrasive mode. The gradually deceased wear rate of the specimen nitrocarburized at 500 degrees C with the increase of the sliding speed indicated the excellent wear resistance under high sliding speed condition. Therefore, 500 degrees C can be selected as an optimized nitrocarburizing temperature for M50NiL steel. (C) 2014 Elsevier B.V. All rights reserved.