Mechanical Properties and Stress Variations in Multipass Welded Joint of Low-Alloy High-Strength Steel after Layer-by-Layer Ultrasonic Impact Treatment

The layer-by-layer ultrasonic impact treatment (LUIT) was used to treat a multipass welded joint of low-alloy high-strength steel. The shear-punch strength of the weld metal (WM), heat-affected zone and base metal of the joint was measured using the shear-punch test, and the full two-dimensional maps of internal longitudinal and transverse stresses at different locations were obtained with the two-cut contour method. The hardness distribution across the joint was also measured. The measured results were compared with those in an untreated high-strength steel joint and those in the joints with different strength grades in references to investigate the effects of LUIT on the mechanical properties and stress distributions in welded joints with different strength grades. LUIT can induce higher and more uniform hardness distribution in the welded joints with different strength grades; it can increase the strength of the treated WM of low-alloy high-strength steel by 6 to 16% as compared with the untreated joint; it has no significant effect on the stress distribution in the interior of the weld zone, while UIT on the weld surface can induce compressive stress to 2-4 mm depth in welded joints with different strength grades.