WELDED JOINT

摘要

Provided is a welded joint which is excellent for steel structures such as steel bridges that require a superior fatigue property, and which improves fatigue strength by introducing compressive residual stress without imparting to the weld portion deformation that becomes a new stress concentration zone. Specifically, this is a welded joint of steel material having an impact mark that is formed continuously on a steel material surface along a weld bead by means of an oscillation element of hammer peening or an ultrasonic shock process, with the tip of the oscillation element having a length of 1 mm - 10 mm in the direction of advance, and the crowning of the tip of the oscillation element in a cross section perpendicular to the direction of advance being in the shape of an arc with a curvature radius of 1 mm - 10 mm, or the crowning in a cross section perpendicular to the direction of advance having chamfered parts with a curvature radius of 0.1 mm - 2 mm at either end of a 0.1 mm or less linear part, or the crowning in a cross section perpendicular to the direction of advance being in the shape of an arc on the major-axis side of an ellipse having a minor axis of 1 mm or greater. The impact mark is formed by the oscillation element 4 mm from the weld toe to the base material side, and preferably in a region of 0.5-4 mm, with a maximum depth of 0.03 mm or greater, but less than 0.50 mm.