Electrochemical Corrosion and Tribological Behaviors of Q345B Steel after Ultrasonic Shot Peening Treatment

The microstructure of Q345B steel after ultrasonic shot peening (USSP) treatment was investigated through microstructural observations, while the electrochemical corrosion and tribological behaviors along the depth of the USSP-treated layers were studied using electrochemical corrosion and wear tests. The USSP treatment resulted in the formation of a 50 nm nanocrystalline layer and a gradient nanostructure (nearly 330 μm) along depth. This gradient nanostructure comprised a large deforming region (less than 150 μm), a transition region (from 150 to 330 μm) and an undeformed region (beyond 330 μm). While USSP treatment reduced the corrosion resistance of Q345B steel, it enhanced the wear resistance. When the surface of the steel after USSP treatment was polished to match the roughness of the as-received steel, both corrosion and wear resistance improved. The polished top surface exhibited the best corrosion and wear resistance. However, both corrosion and wear resistance gradually decreased with increasing depth in the USSP-treated layers. The grain refinement, residual stress, and gradient nanostructure induced by USSP treatment all contributed to the improvement in corrosion and wear resistance.