Study on the Effect of Ultrasonic Impact Treatment on the Impact Toughness of S355J2 Steel Welded Joints

This study thoroughly investigates the effect of Ultrasonic Impact Treatment (UIT) on the impact toughness of S355J2 steel welded joints prepared using gas tungsten arc welding (GTAW). The study systematically analyzes the mechanisms by which UIT affects impact toughness through Charpy impact tests, optical microscopy, scanning electron microscopy (SEM) analysis, and microhardness measurements. The experimental results indicate that the average impact toughness of the welded joints significantly increased to 66.02 J/cm² after UIT, representing a 45.39% improvement. Regular UIT significantly improved the surface quality of the samples, reducing surface roughness, enhancing surface uniformity, and effectively minimizing stress concentration, thereby inhibiting crack propagation. Additionally, by refining the surface grain size, UIT enhanced the surface hardness of the material. Observations from SEM revealed the mechanisms by which UIT strengthens and toughens the impact toughness of the welded joints, showing significant plastic deformation in the impact fracture zone, enlarged void areas, and a transformation in the fracture characteristics of the radiative zone. These changes suggest that UIT enhances the material’s resistance to crack propagation, increases energy consumption during crack growth, raises fracture stress, effectively slows down material degradation, and even achieves crack suppression.