what's the effect of Ultrasonic stress relief

what's the effect of Ultrasonic stress relief 

For joints using the arc welding process, weld toe defects are inevitable. The weld toe defect is parallel to the weld and is located between the weld and the base metal. This stress-concentrated defect and the coarse-grained zone of the HAZ and the lateral residual stress constitute a high-risk zone where the joint is laterally cracked. The US AWSD1.1 steel structure specification has been clarified: hammering and rolling can be used to reduce residual stress, and smooth toe, machining or Tig remelting process can be used to remove weld toe defects to reduce the cracking probability of the weld toe. The project team used the ultrasonic impact process proposed by the Patong Welding Research Institute of Ukraine to perform ultrasonic shock treatment on the outer surface of the weld. On the one hand, it can change the stress concentration defects of the weld toe, and on the other hand, the tensile stress of the surface is caused by impact yielding. Becomes a compressive stress. For joints without internal defects, under the condition of tensile stress, the defects of the surface are firstly generated under residual stress, working stress, stress concentration and corrosive environment, causing the crack to expand to the inside and cause failure failure. Ultrasonic impact can "kill" surface defects through the point impact of the frequency of 30,000 times / sec, and then generate compressive stress due to the yield of the impacted surface, thereby effectively improving the ability to suppress tensile stress damage. The effect of ultrasonic shock on the A105 steel test cylinder is shown in Table 1. The test site is shown in Figure 1.

Figure1   A105 The welding residual stress of steel welded cylinder body is eliminated by ultrasonic impact [30]

Figure 2 Stress of the measuring point after impact

Estimated curve of change

The analysis shows that the effect of the stress relief >20% can be obtained within 4 mm from the surface by ultrasonic shock. From the perspective of the stress level, the average thickness can also be reduced by about 3%.