Cr8 steel should be Steel containing ~8 wt.% of chromium is widely used in demanding die applications due to its excellent wear resistance; however, conventional shot peening, while enhancing strength, inevitably increases surface roughness, thereby compromising overall performance. To address this limitation, this study systematically investigates the influence of ultrasonic surface rolling (USR) step size—comparing 0.06 mm and 0.12 mm—on mitigating surface degradation and improving surface integrity. Friction wear and electrochemical corrosion tests demonstrate that USR effectively reduces surface roughness and enhances microhardness. The 0.06 mm step size achieves superior results, yielding the lowest surface roughness (0.8317 μm), highest microhardness (647.47 HV), lowest friction coefficient (0.655), and optimal corrosion resistance (minimum corrosion rate reduction: 3.472 µA·cm⁻², corresponding to an inhibition efficiency of 37.05%). These performance improvements are attributed to the synergistic effects of surface smoothing and work hardening, resulting from more uniform processing achieved under a smaller step size. Consequently, a 0.06 mm step size is determined to be optimal, establishing the integrated shot peening–USR process as a highly effective strategy for enhancing surface properties and extending the service life of critical Cr8 steel components in industrial applications.

The effect of post-rolling annealing time on the microstructural evolution and room-temperature mechanical properties of a hot-rolled Cu–Zn–Sn alloy was systematically investigated. The alloy was isothermally annealed at 500 °C for 4, 5, and 6 h. Results reveal that annealing time non-monotonically governs the recrystallization of the α and β phases and the final content of the Sn-rich intergranular phase, coupled with the α/β phase transformation and Sn partitioning. The as-hot-rolled microstructure comprises a dual α + β structure without the Sn-rich intergranular phase. After 4 h, the α phase recrystallizes completely, and the β phase fraction decreases, leading to Sn rejection and Sn-rich intergranular phase formation after furnace cooling; hardness and strength are minimum, while ductility is high. At 5 h, the β phase fraction recovers and Sn partitions into the β phase, decreasing the final Sn-rich intergranular phase content. The β phase transforms into fine short-rod and lath-like morphologies, refining grains and yielding optimal strength–ductility synergy, with an ultimate tensile strength (UTS) of 451.6 MPa and an elongation of 41.7%. At 6 h, the β phase fraction decreases and grains coarsen, leading to re-formation of the Sn-rich intergranular phase and degraded strength. Quantitative analysis reveals that solid-solution strengthening provides a stable baseline, while variations in yield strength are dominated by dislocation and grain-boundary strengthening. The β phase provides load-transfer strengthening, and the Sn-rich intergranular phase acts primarily as a damage source. Fracture changes from ductile dimples to mixed ductile–brittle with local flat features, depending on the Sn-rich intergranular phase distribution. This study links processing, microstructure, and properties for optimizing tin brass heat treatment.