Method of resistance spot welding and resistance spot welding apparatus

A resistance spot welding apparatus configured to weld a workpiece including two or more steel plates in an overlapping state in a thickness direction, the resistance spot welding apparatus comprising:

• a first electrode configured to move in up-and-down directions, to thereby be downwardly in contact with a high-tensile steel plate having a tensile strength higher than a tensile strength of another steel plate among the two or more steel plates;
• a second electrode configured to be upwardly in contact with the workpiece, to thereby interpose such that the workpiece is interposed between the second electrode and the first electrode and the second electrode, and
• a bending device including a jig configured to hold all of the two or more steel plates in a bent manner in a direction so that a weld portion of the high-tensile steel plate, which is to be in contact with the first electrode, is positioned inside of a bend,
• the two or more steel plates including at least one steel plate coated with zinc, and
• the resistance spot welding apparatus being configured to:
• in a state where the first electrode is in contact with the high-tensile steel plate arranged furthest above the workpiece and the second electrode is not in contact with the other steel plate, move the first electrode downwards with the second electrode remaining fixed, to thereby place all of the two or more steel plates in a bent state in a direction so that a weld portion of the high-tensile steel plate, which is to be in contact with the first electrode, is positioned inside of a bend;
• and
• hold the bend state maintain the bent manner all the two or more steel plates by the jig, to thereby compress the high-tensile steel plate in a direction intersecting a direction of a thickness of the high-tensile steel plate while welding, to thereby cancel a tensile stress generated in the high-tensile steel plate while welding, and
• the jig including a first jig and a second jig that are arranged so as to interpose an imaginary line connecting a leading end of the first electrode and a leading end of the second electrode.