A spot welding monitoring method is configured to monitor a state of spot welding that holds a work including metal plates stacked on each other, between electrodes in a pair, and supplies electricity between electrodes. The spot welding monitoring method includes: by a converter disposed in a vicinity of a weld zone of the work, detecting a change in magnetic flux density of a magnetic field generated around the weld zone by the supplying of the electricity between electrodes, and converting the change in the magnetic flux density into a current; and calculating three-dimensional data on a melting zone of the work, based on a temporal change in a value of the current.

To enable welding in a state in which aluminum plating in a desired welding region is removed at a desired high accuracy, a plating layer (103) in a welding region (151) and a plating layer (104) in a welding region (152) are removed using an alkaline solution to form a preprocessed aluminum plated steel sheet (101a), and a plating layer (123) in a welding region (153) and a plating layer (124) in a welding region (154) are removed using an alkaline solution to form a preprocessed aluminum plated steel sheet (121a).

To enable welding in a state in which aluminum plating in a desired welding region is removed at a desired high accuracy, a plating layer (103) in a welding region (151) and a plating layer (104) in a welding region (152) are removed using an alkaline solution to form a preprocessed aluminum plated steel sheet (101a), and a plating layer (123) in a welding region (153) and a plating layer (124) in a welding region (154) are removed using an alkaline solution to form a preprocessed aluminum plated steel sheet (121a).

The present invention provides a resistance spot welding method. A resistance spot welding method according to the present invention in which a sheet combination of two or more overlapping steel sheets is sandwiched between a pair of electrodes and joined together by applying current while applying pressure, the method including a main current application step in which current application is performed with a current I.sub.w (kA), and subsequently, a post-tempering heat treatment step in which after cooling is performed for a cooling time t.sub.ct (ms) shown in formula (1) below, current application is performed with a current I.sub.t (kA) shown in formula (2) below for a current application time t.sub.t (ms) shown in formula (3) below: 800≤t.sub.ct . . . formula (1), 0.5×I.sub.w≤I.sub.t≤I.sub.w . . . formula (2), and 500≤t.sub.t . . . formula (3).

The present invention provides a resistance spot welding method. A resistance spot welding method according to the present invention in which a sheet combination of two or more overlapping steel sheets is sandwiched between a pair of electrodes and joined together by applying current while applying pressure, the method including a main current application step in which current application is performed with a current I.sub.w (kA), and subsequently, a post-tempering heat treatment step in which after cooling is performed for a cooling time t.sub.ct (ms) shown in formula (1) below, current application is performed with a current I.sub.t (kA) shown in formula (2) below for a current application time t.sub.t (ms) shown in formula (3) below: 800≤t.sub.ct . . . formula (1), 0.5×I.sub.w≤I.sub.t≤I.sub.w . . . formula (2), and 500≤t.sub.t . . . formula (3).

A localized annealing process and a part having localized areas with increased ductility produced by the process. The part is formed of hard material, tempered, and/or otherwise hardened such that it meets minimum hardness and ductility requirements. The part further includes localized areas that have increased ductility for workability, which could include various types of deformation. The localized annealing process includes providing a part with low levels of ductility and then annealing localized areas of the part for increased ductility that will need to be machined or attached to another formed part. The annealing process includes placing an electrode on either side of the localized area and generating electricity through the localized area. The material in the localized area is then heated from the electricity to form a more ductile physical structure.

A joint structure, includes: a first member including a high tensile strength steel; and a second member including a high tensile strength steel and superposed on the first member, the first member and the second member being resistance welded to each other, in which a gap between the first member and the second member is between 0 mm and 3 mm, a nugget is not formed at a joint portion between the first member and the second member, or when the nugget is formed at the joint portion between the first member and the second member, a diameter D1 of the nugget satisfies D1<5 mm, and a decarburized layer is provided on at least one of a superposition surface of the first member, on which the second member is superposed, and a superposition surface of the second member, on which the first member is superposed.

The present disclosure provides a method of resistance spot welding that can inhibit Liquid Metal Embrittlement-induced cracking in zinc-coated steel plates irrespective of the degrees of tensile strength. One aspect of the present disclosure provides a method of resistance spot welding. The method comprises welding a workpiece with a resistance spot welding apparatus. The workpiece includes two or more steel plates in an overlapping state. The two or more steel plates include at least one steel plate coated with zinc. The welding includes welding while compressing a high-tensile steel plate among the two or more steel plates in a direction intersecting a direction of a thickness of the high-tensile steel plate. The high-tensile steel plate has a tensile strength higher than a tensile strength of another steel plate among the two or more steel plates.

The present disclose provides a method of resistance spot welding that can inhibit Liquid Metal Embrittlement-induced cracking in zinc-coated steel plates irrespective of the plate thicknesses. One aspect of the present disclosure provides a method of resistance spot welding that includes welding a workpiece with a resistance spot welding apparatus. The workpiece includes two or more steel plates in an overlapping state. The two or more steel plates include at least one steel plate coated with zinc. The welding includes causing a cooling rate of a high-tensile steel plate among the two or more steel plates to be higher than a cooling rate of an other steel plate among the two or more steel plates. The high-tensile steel plate has a tensile strength higher than a tensile strength of the other steel plate.

A dual pass seam welding method for steels having a Ceq of greater than about 0.45. The first pass welds the immediately anneals the weld. On the second pass, the welder is disengaged, and the weld is subjected to a second anneal.