Fatigue property of the fillet lap joint using arc welding is lower than that of as-received material, which is affected by the various factors such as the stress concentration on the toe due to its own shape and the residual stress retained astension in the vicinity of the toe. The TIG arc was applied to the local heat treatment in the vicinity of the welded joint parallel to the bead after the MAG welding for sheet steels. The effects of the distance from the bead and the speed of TIG torchon the residual stress perpendicular to the bead were investigated in case of the 310 to 590 MPa class hot rolled steel sheets. This heat treatment in the condition of the distance, 15 mm, and the torch speed, 150 cm/min., changed the residual stressperpendicular to the bead in the vicinity of the toe from tension to zero. As the result, the fatigue strength of the fillet lap joint in the out-of-plane bending mode for each material successfully increased and the improvement in the fatigue strengthincresed with increase of the strength of material. The endurance limit for the specimen without residual stress was estimated using the modified Goodman's diagram. The mechanism of the improvement in the fatigue strength by this heat treatment isdiscussed in view of the release of the residual stress induced by the arc welding.
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