Patent ID: 8776564

Claim:
An impact treatment method for improving welded joint fatigue characteristics, the welded joint having a weld line, the method comprising: pressing an impact pin against the surface of a base metal material near a toe of a weld bead, moving the impact pin relative to the direction of the weld line, and applying a hammer peening treatment or ultrasonic impact treatment with the impact pin, wherein the impact pin has a tip curvature radius of ½ or less of the metal material thickness and the tip curvature radius is between 2 to 10 mm, and the hammer peening or ultrasonic impact treatment is applied on a surface of the base metal material to generate impact dents on the surface of the base metal material in a direction intersecting with the weld line direction within a range of 90% or more of the length of the weld line based on a toe of the weld line so that a distance from the toe of the weld bead to the center of the impact dents is no more than 2.5 times the tip curvature radius of the impact pin, and the impact pin does not contact weld metal during the impact treatment, wherein the impact pin produces residual plastic deformation on the surface of the base metal material by providing an impact dent groove having a depth satisfying all of the following: 0.1 to 2 mm, not more than the tip curvature radius of the impact pin, and 1/10 or less of the thickness of the metal material, and a width satisfying both of the following: 1.5 to 15 mm and five times or more of the impact dent groove depth.