One aspect of the present invention provides a method for preventing spot welding crack of a galvanized steel plate, which can reduce crack occurring due molten zinc having a low melting point when a galvanized advanced high strength steel (AHSS) plate is spot-welded, and can thus improve welding strength and fatigue life.

One aspect of the present invention provides a method for preventing spot welding crack of a galvanized steel plate, which can reduce crack occurring due molten zinc having a low melting point when a galvanized advanced high strength steel (AHSS) plate is spot-welded, and can thus improve welding strength and fatigue life.

An automotive framework member 1 includes a first steel sheet 10, a second steel sheet 20, and a first weld metal part 40 joining an interface between the first steel sheet 10 and the second steel sheet 20, in which tensile strength of the first steel sheet 10 is 1.0 GPa or more and 1.6 GPa or less, tensile strength of the second steel sheet 20 is 1.8 GPa or more and 2.5 GPa or less, the first steel sheet 10 includes a groove part 18, the second steel sheet 20 is overlapped with the groove part 18, and a minimum Vickers hardness of a region within 4 mm of a periphery of the first weld metal part 40 of the second steel sheet 20 is 80% or more of a hardness of an outside of the region of the second steel sheet 20.

A method of producing a secondary battery includes an electrode body forming process and a resistance welding process. In the electrode body forming process, a sheet-like positive electrode and negative electrode are wound in an overlapping manner with a separator therebetween to form a flat wound electrode body. In the resistance welding process, a current collector terminal is bonded to at least one of a pair of uncoated parts which are positioned at both ends of the wound electrode body in a winding axis direction and to which no electrode mixture is applied by resistance welding. The resistance welding process is performed while metal members are brought into contact with the uncoated parts.

By obtaining a spot-welded joint being a spot-welded joint formed by overlapping a plurality of pieces of steel plates (1A, 1B) and performing spot welding on the steel plates, including a high-strength steel plate whose tensile strength is 750 (MPa) to 2500 (MPa), being at least one piece of steel plate out of the plurality of pieces of steel plates, in which a carbon equivalent Ceq of the high-strength steel plate is 0.20 mass % to 0.55 mass %, and ten or more of iron-based carbides in each of which a length of a longest portion is 0.1 (μm) or more exist in a square region 103 within a heat-affected zone 4 of a cross section that passes through a center of a welding mark, and is cut along a plate thickness direction of the steel plates (1A, 1B), a cross tensile strength of the spot-welded joint to be formed is improved.

By obtaining a spot-welded joint being a spot-welded joint formed by overlapping a plurality of pieces of steel plates (1A, 1B) and performing spot welding on the steel plates, including a high-strength steel plate whose tensile strength is 750 (MPa) to 2500 (MPa), being at least one piece of steel plate out of the plurality of pieces of steel plates, in which a carbon equivalent Ceq of the high-strength steel plate is 0.20 mass % to 0.55 mass %, and ten or more of iron-based carbides in each of which a length of a longest portion is 0.1 (μm) or more exist in a square region 103 within a heat-affected zone 4 of a cross section that passes through a center of a welding mark, and is cut along a plate thickness direction of the steel plates (1A, 1B), a cross tensile strength of the spot-welded joint to be formed is improved.

An automotive framework member 1 includes a first steel sheet 10, a second steel sheet 20, and a first weld metal part 40 joining an interface between the first steel sheet 10 and the second steel sheet 20, in which tensile strength of the first steel sheet 10 is 1.0 GPa or more and 1.6 GPa or less, tensile strength of the second steel sheet 20 is 1.8 GPa or more and 2.5 GPa or less, the first steel sheet 10 includes a groove part 18, the second steel sheet 20 is overlapped with the groove part 18, and a minimum Vickers hardness of a region within 4 mm of a periphery of the first weld metal part 40 of the second steel sheet 20 is 80% or more of a hardness of an outside of the region of the second steel sheet 20.

A resistance spot welding electrode cap contains a groove at the center of the welding contact interface. During welding, because of the groove, the area of contact between the electrode cap and a metal workpiece to be soldered is reduced. In the initial stage, the overall heat generation is concentrated on the outer ring of the weld point and heat dissipation becomes slower, helping a weld nugget to form from the outside to the inside. Due to the presence of the groove, the metal workpiece expands toward the groove at the center of the electrode, thereby increasing the size of the weld nugget and reducing splash and deformation. In comparison with conventional electrode caps, the welding current required to form weld points of the same size is lower, saving on electricity costs, and weld points obtained using the same current have higher strength and stability with fewer welding defects.

The present invention provides a spot welding method for a member to be welded constituted of a plurality of steel sheets that are overlapped with each other at at least a welding zone, in which at least an overlapped face of at least one of the plurality of steel sheets at the welding zone is coated with zinc plating, a total sheet thickness t (mm) of the plurality of steel sheets is 1.35 mm or more, a squeeze time St (seconds) from the time when welding electrodes are brought into contact with the member to be welded to the time when electric current flow for welding starts satisfies “0.020≤St”, and a hold time Ht( seconds) after welding from the time when electric current flow for welding between the welding electrodes ends to the time when the welding electrodes and the member to be welded are brought out of contact satisfies “0.015t.sup.2+0.020≤Ht”.

The present invention provides a spot welding method for a member to be welded constituted of a plurality of steel sheets that are overlapped with each other at at least a welding zone, in which at least an overlapped face of at least one of the plurality of steel sheets at the welding zone is coated with zinc plating, a total sheet thickness t (mm) of the plurality of steel sheets is 1.35 mm or more, a squeeze time St (seconds) from the time when welding electrodes are brought into contact with the member to be welded to the time when electric current flow for welding starts satisfies “0.020≤St”, and a hold time Ht( seconds) after welding from the time when electric current flow for welding between the welding electrodes ends to the time when the welding electrodes and the member to be welded are brought out of contact satisfies “0.015t.sup.2+0.020≤Ht”.