Resistance spot welding method and weld member production method

A resistance spot welding method of squeezing, by a pair of electrodes, parts to be welded which are a plurality of overlapping metal sheets, and passing a current while applying an electrode force to join the parts to be welded, the resistance spot welding method comprising:

• performing test welding;
• and
• performing actual welding after the test welding,
• wherein
• (a) in the test welding, main current passage for nugget formation and subsequent current passage for subsequent heat treatment are performed,
• in the main current passage in the test welding, a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume that are calculated from an electrical property between the electrodes in forming an appropriate nugget by performing current passage by constant current control are stored, and
• in the subsequent current passage in the test welding, current passage is performed by constant current control under a condition:
• 0.5≤Vtp/Vtm≤2.0 when tc<800 ms;
• 0.5−0.3×(tc−800)/800≤Vtp/Vtm≤2.0−0.5×(tc−800)/800 when 800 ms≤tc<1600 ms;
• and
• 0.2≤Vtp/Vtm≤1.5 when tc≥1600 ms,
• where Vtm is an average value of a voltage between the electrodes in the main current passage in the test welding, Vtp is an average value of a voltage between the electrodes in the subsequent current passage in the test welding, and tc is a cooling time between the main current passage and the subsequent current passage in the test welding, and
• (b) thereafter, in the actual welding, main current passage for nugget formation and subsequent current passage for subsequent heat treatment are performed, in the main current passage in the actual welding, the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated per unit volume that are stored in the main current passage in the test welding are set as a target, and adaptive control welding is performed to control a current passage amount according to the target, and
• in the subsequent current passage in the actual welding, current passage is performed by constant current control under a condition:
• 0.8×Itp≤Imp≤1.2×Itp,
• where Itp is a current in the subsequent current passage in the test welding, and Imp is a current in the subsequent current passage in the actual welding.