# US 11,027,361 B2 · Spot-welded joint and spot welding method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,027,361 B2 - Document ID: US11027361B2 - Status: Granted - Kind: B2 - Application number: 16/145,696 - Filed: 2018-09-28 - Published: 2019-01-31 - Granted: 2021-06-08 - Earliest claimed: 2013-06-05 - Assignees: Nippon Steel Corporation - Applicants: Nippon Steel & Sumitomo Metal Corporation - Inventors: Chisato Wakabayashi; Fuminori Watanabe; Seiji Furusako; Yasunobu Miyazaki; Hiroyuki Kawata; Tohru Okada; Hideki Hamatani - Web page: https://patentgrep.com/patent/US11027361B2 ## CPC - B23K 11/115: {by means of two electrodes placed opposite one another on both sides of the welded parts} - B23K 11/16: taking account of the properties of the material to be welded - B23K 2103/04: Steel {or steel} alloys - B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM ## Abstract 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. ## Claims ### Claim 1 A spot welding method of overlapping a plurality of pieces of steel plates and performing spot welding on the steel plates, wherein at least one piece of steel plate out of the plurality of pieces of steel plates is a high-strength steel plate whose tensile strength is 750 MPa to 2500 MPa, wherein a carbon equivalent Ceq of the high-strength steel plate represented by the following expression (A) is 0.20 mass% to 0.55 mass%, the spot welding method comprising: performing pre-energization of energizing welding electrodes with a pre-energization current If (kA) satisfying the following expression (C) for a pre-energization time tf (msec) satisfying the following expression (D), in a state where the overlapped plurality of pieces of steel plates are pressurized by the welding electrodes at a pressurizing force FE (N) satisfying the following expression (B); performing, after the pre-energization is finished, cooling after pre-energization of cooling the plurality of pieces of steel plates for a cooling time after pre-energization tc (msec) satisfying the following expression (E) while retaining the pressurizing force FE (N) satisfying the following expression (B); performing, after the cooling after pre-energization is finished, main welding of energizing the welding electrodes with a main welding current IW (kA) while retaining the pressurizing force FE (N) satisfying the following expression (B); performing, after the main welding is finished, cooling after main welding of cooling the plurality of pieces of steel plates for a cooling time after main welding ts (msec) satisfying the following expression (F) while retaining the pressurizing force FE (N) satisfying the following expression (B); performing, after the cooling after main welding is finished, post-energization of energizing the welding electrodes with a post-energization current IP (kA) satisfying the following expression (G) for a post-energization time tP (msec) satisfying the following expression (H) while retaining the pressurizing force FE (N) satisfying the following expression (B); and retaining, after the post-energization is finished, the pressurizing force FE (N) satisfying the above expression (B) for a retention time tH (msec) satisfying the following expression (I), and then releasing the pressurizing at the pressurizing force FE (N), Ceq=[C]+[Si]/30+[Mn]/20+2[P]+4[S] (A) 1960×h≤FE≤3920×h (B) 0.40+IW≤If