Abstract
High tensile strength steels are used in mobile crane as the material of telescopic booms for the purpose of lengthening and lightening the booms. The components of telescopic booms are produced by welding. However the fatigue strength of the welded joint is not proportion to the tensile strength of the base metal used. The improvement of fatigue strength of welded joints in high tensile strength steel is needed. In this study, ultrasonic impact treatment (UIT) , which is a peening method, was applied to welded joints as the post-weld treatment in order to introduce compressive residual stress and relax the stress concentration at the weld toes. As the result of fatigue tests, the fatigue strength of the welded joints treated by UIT was improved in about the double of fatigue strength of the as-weld joints.
