RESISTANCE SPOT-WELDING METHOD AND WELDING CONDITION DETERMINATION METHOD FOR RESISTANCE SPOT WELDING

摘要

PROBLEM TO BE SOLVED: To provide a resistance spot-welding method capable of forming a weld zone having superior delayed fracture resistance properties even when a high-strength galvanized steel plate is joined with a small-diameter nugget formed.SOLUTION: A resistance spot-welding method is characterized in that at least one steel plate is a high-strength galvanized steel plate of 980-1,770 MPa in tensile strength which has a galvanizing layer on a surface on a weld face side, and also comprises a preliminary energization process and a main energization process energizing with a current value higher than that of the preliminary energization process after the preliminary energization process. The preliminary energization process is performed under welding conditions that a weld zone 22 has a diameter of 2√t [mm] or smaller and a region 23 where galvanizing of 3√t [mm] or larger in diameter is discharged is formed, a plate thickness of a steel plate which is less in plate thickness between two adjacent steel plates to be joined together being t [mm] at a stage where the preliminary energization process is completed. The main energization process is performed under a welding condition that a nugget of 3√t [mm] or larger is formed.SELECTED DRAWING: Figure 2