METHOD FOR JOINING HIGH-STRENGTH STEEL SHEET HAVING EXCELLENT JOINING STRENGTH PROPERTY

摘要

PROBLEM TO BE SOLVED: To provide a method for joining high-strength steel sheets having excellent joining strength properties which can provide sufficiently high cross tensile strength even when an automotive body or chassis or the parts thereof or the like to which high strength steel sheets particularly having a high carbon equivalent are applied are subjected to spot joining by friction stir spot welding method.;SOLUTION: The method is provided for joining high-strength steel sheets 10, 20 which has a tensile strength of 320 to 1,550 MPa, a sheet thickness of 0.6 to 2.0 mm and a carbon equivalent lying in the range expressed by inequality of {C+Si/30+Mn/20+2P+4S0.24(mass%)}. The method uses the friction stir spot welding method in which a rotor 5 rotating at high speed is pressed against the high-strength steel sheets 10, 20, by the frictional heat between the rotor 5 and the high-strength steel sheets 10, 20, the high-strength steel sheets are partially softened, and the softened parts are stirred to join the high-strength steel sheets. In the method, the pressurizing force between the rotor and the high-strength steel sheets is controlled to the range of 5.0 to 8,0 kN, the speed of rotation of the rotor is controlled to the range of 2,750 to 3,250 rpm, and pressurizing time is controlled to the range of 1.0 to 3.0 sec.;COPYRIGHT: (C)2010,JPO&INPIT