Effects of ultrasonic impact treatment on the residual stress and fatigue performance of ultrahigh strength steel weld joint

Using special ultrasonic impact treatment(UIT) equipment treated butt welded joint of ultrahigh strength steel(σb= 1600MPa). The surface residual stress test of the butt welded joint of ultrahigh strength steel both in the as-welded conditions and ultrasonic impact treated conditions were performed by X-ray diffraction instrument. And the fatigue performance tests of the butt welded joint both in the as-welded conditions and UIT conditions were performed, too. The test results are as follows: (1) In as-welded condition, there is 180Mpa residual tension stress near the weld toe. While in ultrasonic impact treated condition, there is −350Mpa residual compression stress near the weld toe. The residual stress of the welded joint specimen treated by UIT reduced 300%. (2) The geometry of weld toe is rounded off by UIT, and the stress concentration level was reduced near the weld toe. (3) In as-welded condition, the fatigue strength Δσ(2×10⁶) of welded specimen is about 141MPa, and that of specimen in UIT condition is about 188MPa. The fatigue strength of welded specimen treated by UIT increases by 33.3%. Fatigue performance of ultrahigh strength steel welded joint was improved by ultrasonic impact treatment.