Resistance spot welding method and resistance spot welding joint of high strength steel plate

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 (A), 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 × ˆšt m ‰¤ d ‰¤ 6 × ˆšt m where t m is the thickness (mm) of the thinnest one of the foregoing two or more steel sheets.