Method of resistance spot welding of high tensile strength steel sheet and welding joint manufactured by the method

摘要

Provided is a method of resistance spot welding of welding a sheet set including a high strength steel sheet with which a high joint strength can be achieved even for a high Ceq material. A method of resistance spot welding a sheet set of two or more lapped steel sheets by weld the sheet set while clamping and pressing the sheet set between a pair of welding electrodes includes a first welding step of applying an weld current Im (kA) and forming a nugget having a nugget diameter d (mm) that satisfies the following inequality (1); a cooling step, subsequent to the foregoing first welding, of cooling the sheet set while continuing to press the sheet set; and a second welding step of performing two-step welding,
3×√tm≦d≦6×√tm  (1),
where tm is the thickness (mm) of the thinnest one of the foregoing two or more steel sheets.

主权项

1. A method of resistance spot welding a sheet set of two or more lapped steel sheets by welding the sheet set while clamping and pressing the sheet set between a pair of welding electrodes, the method sequentially comprising:
a first welding step of applying an weld current Im (kA) and forming a nugget having a nugget diameter d (mm) that satisfies the following inequality (1); a cooling step (A), subsequent to the first welding step, of cooling the sheet set while continuing to press the sheet set; and a second welding step of performing two-step welding of applying weld currents that satisfy the following inequalities (2) and (3),
3×√tm≦d≦6×√tm  (1), where tm is the thickness (mm) of the thinnest one of the two or more steel sheets,
Im