Abstract: The effects of ultrasonic impact treatment (UIT) on fatigue performance of 22SiMn2TiB steel welded joint are investigated. Fatigue tests are carried out by using as-welded and UIT treated specimens. X-Ray diffraction stress measurements are performed on the distributions of residual stress of the specimens. With the aid of scanning electron microscopy (SEM), fractographic analyses are carried out on the fatigue specimens to determine the crack nucleating mechanism. The results indicate that the UIT can improve the fatigue life of 22SiMn2TiB steel welded joint. For the welded joint, the UIT changes the crack nucleating mechanism from surface cracking at welded toe to subsurface. As micro-defects are eliminated and residual compressive stresses are introduced by UIT at the welded toe, the surface cracking is constrained, which results in a much longer fatigue life of the welded joint.

Key words: Ultrasonic impact treatment　Welded toe　Fatigue performance　Residual stress