Abstract: A spot welded joint in which a high CTS is obtained even if including one or more high strength steel sheets and a method of welding of the same, that is, a spot welded joint 1 including a plurality of steel sheets, wherein one or more steel sheets is a tensile strength 750 to 2500 MPa high strength steel sheet and, at a cross-section in the sheet thickness direction of the steel sheets, when defining superposed surfaces of a high strength steel sheet S1 arranged at an outermost side and another steel sheet 1B as the “plane A” and defining a plane passing through a point of one-half of a distance between a nugget end position E of a high strength steel sheet S1 side on the line L1 in the sheet thickness direction and a crossing point O of the plane A and the line L1 and parallel to the plane A as the “plane B”, at a square area SA of sides of 30 ?m centered about a crossing point X of a line L2, which is separated by 250 ?m to the heat affected zone side from a tangent at any position on a nugget end line NEL

Abstract: A spot welding method is a method of performing spot welding to obtain a spot welded joint, the method including a spot welding with two-stage welding, setting a ratio (I2/I1) of a current I2 of a second welding process to a current I1 of a first welding process to from 0.5 to 0.8, setting a time tc of a cooling process within a range of from 0.8×tmin to 2.5×tmin wherein tmin is calculated using the equation (0.2×H2) according to a sheet thickness H of the steel sheets, setting an welding time t2 of a second welding process within a range of from 0.7×tmin to 2.5×tmin, and setting a pressure from the cooling process onward to greater than a pressure until the first welding process.

Abstract: In an arc spot welded joint manufacturing method in which two steel sheets configured by high strength steel having a component carbon content of 0.07% by mass or greater are overlapped, and the sheets are lap welded together in a spot pattern. The method includes a first welding pass in which a second steel sheet on the lower side is melted up to a back face side, and first weld metal is formed including a first reinforcement portion, and a second welding pass in which a second weld metal including a second reinforcement portion is formed over the first weld metal, such that the heights of the first reinforcement portion or the second reinforcement portion is formed at t/5 or greater with respect to the sheet thickness t of the steel sheets, and the average weld bead diameter is formed at from 3t to 10t.

Abstract: In a spot welded joint according to an aspect of the present invention, with respect to a rectangular planar region of 100 ?m×100 ?m which is perpendicular to a sheet surface of the plurality of the steel sheets and which centers around an inner point spaced away by 100 ?m in a direction parallel with the sheet surface from an edge of a nugget, in a case of measuring a P concentration at a pitch of 1 ?m to obtain measured values of the P concentration at 100×100 of measurement points, and in a case of repetitively calculating an average value of the measured values of the P concentration at 20 of the measurement points which are adjacent to each other and which are arranged in a row in the direction parallel with the sheet surface among the 100×100 of the measurement points while shifting each one point to obtain 81×100 of the average values, the number of the average values which are more than two times an average P concentration is 0 to 100.

Abstract: A welding method for obtaining a lap fillet welded joint excellent in tensile strength, without causing an increase in welding deformation, not fracturing at the weld metal when a tensile load is applied, that is, a method of overlaying at least scheduled welding locations of a first steel sheet with a tensile strength of 780 MPa or more and a second steel sheet and fillet welding an end part of the first steel sheet and a surface of the second steel sheet, characterized by providing a reinforcing part at a surface of the first steel sheet at the opposite side to the surface to be overlaid with the second steel sheet and fillet welding one end part of the reinforcing material and the surface of the first steel sheet and by fillet welding the end part of the reinforcing part, the end part of the first steel sheet, and the surface of the second steel sheet so as to be covered by the weld metal.

Abstract: 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 “0.015t2+0.020?Ht”.

Abstract: A lap welding method of a steel sheet includes spot welding in a state in which the flange portion of a second steel sheet member having the flange portion and a standing wall portion is overlapped with the first steel sheet member, thereby forming a nugget between a first steel sheet member and a flange portion; and, after the spot welding, laser welding a region between an R stop of the standing wall portion and the nugget, thereby forming a weld bead, and, in the weld bead, a length dimension is equal to or longer than a diameter of the nugget, and a width dimension is 0.5 to 3.0 mm.

Abstract: When two high-strength steel sheets (1A, 1B) whose sheet thickness ratio={the sum of sheet thicknesses of the steel sheets}/{the sheet thickness of the thinner steel sheet (when they have the same thickness, the sheet thickness per one sheet)} is within a range of not less than 2 nor more than 5 and which both have tensile strength of not less than 780 MPa nor more than 1850 MPa are stacked to be subjected to resistance spot welding, a first welding step being pre-welding with a pressurizing force P1 kN and a welding current I1 kA and a second welding step being main welding with a pressurizing force P2 kN and a welding current I2 kA are performed, the pressurizing forces P1, P2 are set to a fixed pressurizing force P=P1=P2 all through the first welding step and the second welding step and are set within a range expressed by {0.5?P?3.

Abstract: Provided is a mechanical joining apparatus enabling reduction of breakage of the area around a rivet of a joint obtained by riveting, the apparatus comprising a punch and die, blank holder, first power device, second power device and cooling device, wherein the first power device is configured to start supply of current through the holder and die so as to raise the temperature of the sheets before the punch drives in the rivet, the second power device is configured to start supply of current through the punch and die so as to supply current through and heat treat the rivet after the punch drives in the rivet, and the cooling device is connected to the punch and is configured to cool the rivet after the rivet is heat treated.

Abstract: Provided is a mechanical joining apparatus enabling stable riveting when joining metal sheets even when the sheets are large in deformation resistance, the apparatus comprising a punch and die, blank holder and power device, wherein the punch and die are arranged facing each other, the holder is configured by an electrode material able to push against and electrically heat the sheets by one end of the holder, the punch is comprised of a material able to drive in a rivet, the die is comprised of an electrode material able to support and electrically heat the sheets, and the power device is configured to start supply of current through the holder and die so as to raise the temperature of the sheets at the same time as the start of driving in of the rivet and to continue to supply current until the end of driving in of the rivet.

Abstract: A tailored blank for hot stamping includes a welded portion formed by butt-welding a first aluminum-plated steel sheet and a second aluminum-plated steel sheet, an Average Al concentration of a weld metal in the welded portion is in a range of 0.3 mass % to 1.5 mass %, an Ac3 point of the weld metal is 1250° C. or lower, and furthermore, an aluminum layer formed during the butt-welding is present on a surface of the welded portion.

Abstract: A spot welding method able to simply prevent liquid metal embrittlement cracks in spot welding of plated steel sheets, comprising, before spot welding, removing the plating at least in a zone including the inside of a circle centered at a scheduled location where the center of the nugget is formed and having an outer circumference of the inside of the outer edge of a weld affected zone or a zone at the mated surfaces of the steel sheets to be welded at the inside of a circle sharing a center of a scheduled location becoming the center of the nugget formed at the mated surfaces of the steel sheets and having an outer circumference of the inside of the outer edge of a weld affected zone

Abstract: A tailored blank for hot stamping includes a welded portion formed by butt-welding a first aluminum-plated steel sheet and a second aluminum-plated steel sheet, an Average Al concentration of a weld metal in the welded portion is in a range of 0.3 mass % to 1.5 mass %, an Ac3 point of the weld metal is 1250° C. or lower, and furthermore, an aluminum layer formed during the butt-welding is present on a surface of the welded portion.

Abstract: A laser welded joint has weld metal provided between a plurality of steel sheets. A chemical composition of the weld metal has predetermined components, and average hardness of the weld metal is 350 to 540 in Vickers hardness. In the weld metal, distribution density of porosities having a diameter of 2 ?m to 50 ?m is equal to or less than 5.0 pieces/mm2. In the weld metal, distribution density of oxide inclusions having a diameter of 3 ?m or more is 0.1 to 8.0 pieces/mm2.

Abstract: An arc spot welding method able to give a predetermined weld bead diameter or excess metal height in a back surface weld bead of arc spot welding and able to give a welded joint excellent in both strengths of TSS and CTS and a welding apparatus for working the same are provided. A steel sheet containing carbon in 0.2 mass % or more and having a sheet thickness “t” and at least one steel sheet containing carbon in 0.

Abstract: The present invention has as its object to provide a laser welded joint excellent in joint strength preventing a bead from cracking and comprised of exactly the number of weld beads required for joint strength and a laser welding method for the same in overlay laser welding of steel sheets forming multiple ring-shaped weld beads. The present invention is a laser welded joint excellent in joint strength preventing a bead from cracking and comprised of exactly the number of weld beads required for joint strength in overlay laser welding of steel sheets forming multiple ring-shaped weld beads, produced by a step of overlaying a plurality of metal sheets and forming a first weld bead and a step of firing a laser beam to successively form a further two or more weld beads at the outside of the first weld bead by laser irradiation, the surface hardness of the weld bead increasing from the inside bead to the outside bead.

Abstract: At a plurality of welding positions in an overlap portion of a plurality of members including a high-tensile steel sheet whose carbon content is 0.07 weight % or more, first beads (31 to 36) in a closed loop shape or a closed loop-like shape and second beads (41 to 46) in a closed loop shape or a closed loop-like shape on inner sides of the first bead (31 to 36) are formed by remote laser welding for joining. At this time, there are a procedure for successively forming the plural first beads (31 to 36) and a procedure for successively forming the plural second beads (41 to 46) for the plural formed first beads (31 to 36), and in both of the cases, the beads are each formed at a position except the closest welding position among the plural welding positions. Consequently, it is possible to enhance strength of a weld zone and to suppress welding deformation.

Abstract: The spot welding method of the present invention has steps of preliminary conduction, first conduction, second conduction, and third conduction: Preliminary conduction: Conduction method aimed at improving closeness of contact surfaces of steel sheets and reducing sheet gaps by gradually increasing the welding current (for example, upslope conduction). If rapidly applying current, current would be locally carried and that part would melt resulting in expulsion, so this is a conduction method gradually running current (for example upslope conduction) to avoid local heating. First conduction: Conduction method running a constant welding current and using the heat generated by the electrical contact resistance between steel sheets to cause the formation of a nugget when preliminary conduction results in close contact surfaces between the steel sheets.

Abstract: The present invention has as its object to provide a spot welded joint and spot welding method which raise the fracture toughness of spot welded metal to raise the strength of the spot welded joint. In the present invention, there is provided a spot welding method comprising a melt zone forming step forming a melt zone by conduction and, after the melt zone forming step, a solidification step of running a current lower than the current run in the melt zone forming step so as to cause the melt zone to solidify, wherein, in the solidification step, electromagnetic vibration is applied to the melt zone, and a frequency fV of the electromagnetic vibration, a solidification speed ?S when the melt zone solidifies, and an arm interval of dendrites ?D when the melt zone solidifies satisfy 0.2??S/(?D·fV)?4.0.

Abstract: In an arc spot welded joint manufacturing method in which two steel sheets configured by high strength steel having a component carbon content of 0.07% by mass or greater are overlapped, and the sheets are lap welded together in a spot pattern. The method includes a first welding pass in which a second steel sheet on the lower side is melted up to a back face side, and first weld metal is formed including a first reinforcement portion, and a second welding pass in which a second weld metal including a second reinforcement portion is formed over the first weld metal, such that the heights of the first reinforcement portion or the second reinforcement portion is formed at t/5 or greater with respect to the sheet thickness t of the steel sheets, and the average weld bead diameter is formed at from 3t to 10t.