Abstract: Surface ultrasonic rolling treatment (SURT) was applied to ER8 wheel steel to create a ~ 250 lm gradient nanostructured (GNS) surface layer. SURT induced severe plastic deformation, grain refinement, increased dislocation density, and continuous dynamic recrystallization. The GNS layer enhanced surface hardness to 728 HV (~ 2.4 × substrate) and improved yield and tensile strength to 680 and 1015 MPa, respectively, while maintaining satisfactory ductility. Under dry sliding, wear rates decreased by 79%–88% compared to coarse-grained samples, with lower friction coefficients and improved wear resistance in deionized water and NaCl solution. High-cycle fatigue tests showed a fatigue strength of 350 MPa at 1 × 10⁷ cycles, with residual compressive stress delaying crack initiation and shifting crack sites inward. These performance enhancements are primarily attributed to the formation of a gradient nanostructured surface layer with refined grains, high dislocation density, and abundant high-angle grain boundaries, together with deep residual compressive stress, which jointly suppress plastic deformation and delay crack initiation. These findings demonstrate that SURT effectively strengthens wheel steel surfaces, improving mechanical, tribological, and fatigue performance, and offers significant potential for extending the service life of high-speed railway wheels.