WELDING JOINT HAVING EXCELLENT FATIGUE CHARACTERISTICS AND METHOD FOR MANUFACTURING SAME
A welding joint having excellent fatigue characteristics and a method for manufacturing the same are disclosed. The welding joint having the excellent fatigue characteristics, according to an embodiment of the present disclosure, may include a welded metal formed by welding between a plurality of steel sheets arranged in such a way to overlap each other at a connecting portion between the plurality of steel sheets, and a remolten portion which is formed at an end of the welded metal and whose surface layer has a Vickers hardness value of 200 Hv or greater.
1 . A welding joint having excellent fatigue characteristics, comprising:
a welded metal 20 formed by welding between a plurality of steel sheets 10 arranged in such a way to overlap each other at a connecting portion between the plurality of steel sheets 10 ; and
a remolten portion 30 which is formed at an end of the welded metal 20 and whose surface layer has a Vickers hardness value of 200 Hv or greater.
2 . The welding joint of claim 1 , wherein the remolten portion 30 is formed by irradiating a defocused laser 1 on the end of the welded metal 20 to remelt the end of the welded metal 20 .
3 . The welding joint of claim 1 , wherein the surface layer of the remolten portion 30 has a bainite or martensite structure.
4 . The welding joint of claim 1 , wherein a toe angle θ of the remolten portion 30 is 30° or smaller.
5 . The welding joint of claim 1 , wherein fatigue strength of the welding joint is 260 MPa or greater.
6 . The welding joint of claim 1 , wherein fatigue strength of the welding joint is 70% or more of fatigue strength of the steel sheets 10 .
7 . A method for manufacturing a welding joint, comprising operation of irradiating a defocused laser 1 on an end of a welded metal 20 formed by welding a connection portion between a plurality of steel sheets 10 arranged in such a way to overlap each other at the connecting portion to remelt the end of the welded metal 20 .
8 . The method of claim 7 , wherein an output of the defocused laser 1 is 6 kW, and movement speed of the defocused laser 1 is 4 to 6 m/min.
9 . The method of claim 7 , wherein a defocus length L of the defocused laser 1 is 15 to 20 mm.
10 . The method of claim 9 , wherein the defocus of the defocused laser 1 covers the end of the welded metal 20 and a part of a heat affected zone (HAZ) 11 of the steel sheets 10 adjacent to the end of the welded metal 20 .
11 . The method of claim 7 , wherein an irradiation angle of the defocused laser 1 is 30 to 45°.