Effect of surface modification on corrosion fatigue fracture behavior and mechanisms of Q235 steel

To significantly enhance the service reliability of electric power connection fittings in coastal and other corrosive environments, this study systematically investigates the effects of shot peening (SP) and ultrasonic surface rolling process (USRP) on the corrosion fatigue behavior of Q235 steel. The results show that in a 3.5 wt.% NaCl solution, the corrosion fatigue limit of the as-received Q235 steel decreased by approximately 37.50% compared to that in air, while after SP and USRP treatments, the corrosion fatigue limits increased by 7.50% and 12.50%, respectively. Surface performance analysis revealed that SP and USRP introduced gradient nanostructured layers with depths of about 213.61 μm and 373.81 μm, respectively, and generated near-surface compressive residual stresses of approximately -170.47 MPa and -306.91 MPa. The core innovation of this study lies in conducting a systematic comparative investigation of the corrosion fatigue behavior of SP and USRP-treated Q235 steel within the same corrosive medium, quantitatively revealing the competitive mechanisms by which these two distinct surface modifications inhibit Cl - -induced crack initiation and propagation. Comprehensive analysis indicates that USRP outperforms SP in delaying pit initiation and fatigue crack growth due to its ability to form a deeper gradient structure, higher surface compressive stress, and superior surface smoothness. This research elucidates the micro-mechanisms through which different surface strengthening technologies influence corrosion fatigue performance, providing direct theoretical basis and data support for selecting and optimizing surface protection processes for electric power connection fittings and other critical steel components in harsh corrosive environments.