Abstract: A resistance spot welded joint is formed by resistance-spot-welding two or more steel sheets including at least one high strength steel sheet. The high strength steel sheet has a chemical composition containing, in mass %, C: 0.05 to 0.6%, Si: 0.1 to 2.0%, Mn: 1.5 to 4.0%, and P: 0.10% or less, with the balance being Fe and incidental impurities. The hardness of a softest nugget region is 90% or less of the hardness of the heat-affected zone. The softest nugget region has a microstructure including tempered martensite. The average number density of carbide particles having a diameter of 100 nm or more in the softest nugget region is 10 or more per 5 ?m2 in a cross section of the steel sheets.

Abstract: Provided is a coated aluminum material for joining having an adhesion layer on a surface, and can exert excellent adhesion strength and corrosion resistance performance even under severe use conditions while being chromium-free. Provided is a coated aluminum material capable of producing the coated aluminum material for joining, and an aluminum resin composite material using the coated aluminum material for joining. Disclosed are a coated aluminum material for joining having an adhesion layer on a surface thereof and including a coated aluminum material and a silica-containing film formed on a surface of the aluminum material, the silica-containing film including 0.5 to 35 mass % of a silane coupling agent and having Si and P contents of 2 to 60, and 0.1 to 6.0 mg/m2, respectively, and P/Si mass ratio of P content and Si content of 0.02 to 0.

Abstract: An automotive member and a resistance spot welding method. The automotive member includes a resistance spot weld formed by resistance-spot-welding a plurality of steel sheets including at least one high strength steel sheet. The high strength steel sheet has a specific chemical composition. The microstructure in the vicinity of the edge of the nugget of the resistance spot weld is a composite microstructure containing ferrite at a volume fraction of 1 to 30%, martensite at a volume fraction of 1 to 50%, and tempered martensite at a volume fraction of 20% or more. The average number density of Nb-based precipitate grains having a grain diameter less than 0.09 ?m and Ti-based precipitate grains having a grain diameter less than 0.09 ?m is 10 or more grains per 100 ?m2 in a sheet cross section.

Abstract: 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 Iw (kA), and subsequently, a post-tempering heat treatment step in which after cooling is performed for a cooling time tct (ms) shown in formula (1) below, current application is performed with a current It (kA) shown in formula (2) below for a current application time tt (ms) shown in formula (3) below: 800?tct . . . formula (1), 0.5×Iw?It?Iw . . . formula (2), and 500?tt . . . formula (3).

Abstract: Provided are a resistance spot welding method and a method for manufacturing a resistance spot welded joint. At least one of the steel sheets used is a high strength steel sheet. The method includes a main current application step in which current is applied with a current Iw and a tempering post-heat treatment step. The tempering post-heat treatment step includes a cooling process and a heating process and can include at least one of a transition process and a holding process. In the heating process, a current is applied at a current value It, shown in formula (2), for a current application time tt. 0.8×Iw?It?1.

Abstract: Main current passage and subsequent current passage are performed, with a cooling time of 0.01 s or more being provided between the main current passage and the subsequent current passage. Ip/I which is a ratio of a current value of the subsequent current passage to a current value of the main current passage is controlled to satisfy a predetermined relationship depending on a constant A defined by Mn content and P content of a steel sheet as a part to be welded, in relation to a welding time Tp of the subsequent current passage, a cooling time T, and the constant A.

Abstract: This application relates to a resistance spot weld, a resistance spot welding method, a resistance spot welded joint, and a method for manufacturing the resistance spot welded joint. In the resistance spot weld, at least one of steel sheets is a high-strength steel sheet having a prescribed chemical composition. In at least one of a nugget edge region corresponding to a faying interface, the nugget edge region has a metal microstructure including tempered martensite as a main phase. The hardness Hv of the nugget edge region and the hardness Hmw of martensite in the nugget as a whole satisfy formula (4). In at least one of a strong HAZ region corresponding to the faying interface, the hardness Hh of the strong HAZ region and the hardness Hmh of martensite in a prescribed steel sheet satisfy formula (8).

Abstract: 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 Iw (kA), and subsequently, a post-tempering heat treatment step in which after cooling is performed for a cooling time tct (ms) shown in formula (1) below, current application is performed with a current It (kA) shown in formula (2) below for a current application time tt (ms) shown in formula (3) below: 800?tct . . . formula (1), 0.5×Iw?It?Iw . . . formula (2), and 500?tt . . . formula (3).

Abstract: Main current passage and subsequent current passage are performed, with a cooling time of 0.01 s or more being provided between the main current passage and the subsequent current passage. Ip/I which is a ratio of a current value of the subsequent current passage to a current value of the main current passage is controlled to satisfy a predetermined relationship depending on a constant A defined by Mn content and P content of a steel sheet as a part to be welded, in relation to a welding time Tp of the subsequent current passage, a cooling time T, and the constant A.