In this paper, the ferritic nitrocarburizing process (fluidized bed and gaseous ferritic nitrocarburizing) is explored as a means to increase the rolling contact fatigue (RCF) life and sliding wear resistance of M-50 and M-50 NiL under simulated high stress, marginally lubricated conditions. Test results confirmed the detrimental quality of the surface iron carbonitride compound layer and the beneficial aspect of the diffusion zone below the surface. Test specimens with the compound layer ground off gave substantial improvement in RCF life over the baseline M-50 and M-50 NiL steels. The ferritic nitrocarburizing process had little effect on the sliding wear performance of M-50, which was far superior to the ferritic nitrocarburized M-50 NiL or untreated M-50 NiL. The hardness of the diffusion zone and the generation of large compressive residual stresses contribute to the prominent enhancement of mechanical properties by this surface modification.