Enhanced impact toughness of 316L stainless steel welded joint by ultrasonic impact

316 L welded structures have been widely used in the industrial field, but the weld defects seriously affect the reliability. The ultrasonic impact treatment (UIT) is used to improve the quality of welded joints and the effects of the UIT on the impact toughness, fracture morphology, microhardness and microstructure of the 316 L stainless steel welded joint were studied. Moreover, the coupled finite element model of the 316 L stainless steel welding-UIT was established to study the effects of the UIT on the residual stress. The results showed that the UIT could effectively improve the impact toughness of the 316 L stainless steel welded joint, and the impact toughness could be improved with the increasing of the UIT current. According to the fracture morphology, it was found that the fibrous region increased, and the radical region decreased. In addition, the dimple of the material tends to become deeper and larger, and the increase of dimple was accompanied by the increase of energy absorption. The microhardness of the welded joint was improved, and the grain was refined, which indicated that the 316 L stainless steel welded joint generated obvious plastic deformation. The simulation results show the welded joints can introduce the significant residual compressive stress under the action of the UIT. Based on the comprehensive analysis of the UIT on impact toughness, the generated plastic deformation, the reduced grain size, and the introduced residual compressive stress of the 316 L stainless steel welded joint were the main reasons for the improvement of the impact toughness.