Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Seiji Furusako

Yasunobu Miyazaki

Fuminori Watanabe

Tohru Okada

Hatsuhiko Oikawa

Koichi Sato

Yoshiaki Nakazawa

Hiroyuki Kawata

Shinji Kodama

Hideki Hamatani

Chisato Wakabayashi

Chisato Yoshinaga

Sho Matsui

Masahiro Saito

Kengo Takeda

Yasuo Takahashi

Kunio Hayashi

Yuya Suzuki

Toyomitsu Nakamura

Tomohito Tanaka

Kazuhiko Fukutani

Yasuaki Naito

Hitomi Nishibata

Tasuku Zeniya

Provided is a steel sheet having a predetermined chemical composition and structure wherein (Fe, Mn)B precipitates having a circle equivalent diameter of 50 to 300 nm are present in a number density of 1/500 μmor more in a surface layer region down to a depth of 100 μm from the surface in the sheet thickness direction. Further, provided is a method for producing a steel sheet comprising continuously casting a molten steel having a predetermined chemical composition to form a steel slab, wherein the continuously casting includes introducing more than 10 ppm and less than 100 ppm of oxygen into the surface layer of the steel slab, hot rolling including finish rolling the steel slab, wherein a completion temperature of the finish rolling is 650 to 950° C., coiling the obtained hot rolled steel sheet at a coiling temperature of 400 to 700° C., and cold rolling the hot rolled steel sheet, then annealing it.

Steel sheet and method for producing same

Art for spot welding able to suppress penetration of hydrogen, one of the factors behind delayed fracture, at the time of spot welding, that is, a spot welding method in which at one or both of the surfaces of the steel sheets becoming the facing surfaces of the overlaid steel sheets, a location where the steel sheets contact each other to form a contact part at the time of initial squeezing of the spot welding is worked in advance to form a plurality of lines running through the contact part and connected to the outside of the contact part and the spot welding is performed at the location of the contact part and also a steel sheet in which the plurality of lines are formed in advance at the location becoming a contact part when steel sheets contact each other at the time of initial squeezing in the spot welding.

Method of manufacture of spot welded joint, steel sheet for spot welding use, and steel sheet member for spot welding use

By obtaining a spot-welded joint being a spot-welded joint formed by overlapping a plurality of pieces of steel plates (A,B) 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 (&#x3bc;m) or more exist in a square regionwithin a heat-affected zoneof a cross section that passes through a center of a welding mark, and is cut along a plate thickness direction of the steel plates (A,B), a cross tensile strength of the spot-welded joint to be formed is improved.

Spot-welded joint and spot welding method

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 jointincluding 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 Sarranged at an outermost side and another steel sheetB 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 Sside on the line Lin the sheet thickness direction and a crossing point O of the plane A and the line Land parallel to the plane A as the 'plane B', at a square area SA of sides of 30 &#x3bc;m centered about a crossing point X of a line L, which is separated by 250 &#x3bc;m to the heat affected zone side from a tangent at any position on a nugget end line NEL sandwiched between the plane A and plane B and parallel to that tangent, and a line Lvertical to Lincluded in a heat affected zonehaving a high strength steel sheet Sas a base material, an average value of widths of the blocks formed from lath martensite is 0.5 to 7.0 &#x3bc;m.

Spot welded joint and spot welding method

A resistance spot welding method able to form a welded joint having delayed fracture resistance, includes, in order, applying a pressing force P1 (kN) to the plurality of steel sheets by welding electrodes while supplying a supplied current I1 (kA), while applying the pressing force P1, supplying a current Ic (kA) during a cooling time tc (s), repeating two times or more a pressure force raising and lowering cycle of supplying a supplied current I2 (kA) to the welding electrodes while applying a pressing force P2 (kN) to the plurality of steel sheets by the welding electrodes during a pressing time tf (s), then immediately applying a pressing force P3 (kN) during a pressing time ti (s), applying the pressing force P2 during the pressing time tf, and releasing the pressing force and ending the supply of current, satisfying 0&#x2264;Ic&#x3c;I1, 0.3&#x2264;I2/I1&#x3c;1.0, P2/P1&#x2265;2, tf&#x2264;0.2, P3&#x3c;P2, and ti&#x2264;0.2.

Method of resistance spot welding

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.

Lap welding method of steel sheet and lap weld joint of steel sheet

The spot welding method of the present invention has steps of preliminary conduction, first conduction, second conduction, and third conduction:

Spot welding method

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.

Mechanical joining apparatus and mechanical joining method

A spot welding electrode of a donut-shaped electrode wherein even when a welded member of a steel sheet is slanted with respect a plane perpendicular to an axis of the spot welding electrode, a cross tensile strength (CTS) of the spot welded joint can be improved. The donut shape spot welding electrode according to the present invention has an electrode tip and an electrode support. The electrode tip contacts the electrode support to be able to move. Due to this, it is possible to strikingly raise the ability of the donut-shaped electrode to track a steel sheet and make the entire surface of the donut shape contact-and-conduction part contact the steel sheet, so it is possible to secure a high CTS value even if the steel sheet is slanted.

Spot welding electrode and welding apparatus and welding method using same

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.

There is provided a power supply device that supplies an output current to an electric processing device which performs electric processing on workpieces. The device includes: a first power supply; a magnetic energy recovery switch that receives a current supplied from the first power supply, and converts the received current into the output current; and a control unit that controls the magnetic energy recovery switch such that an electric current frequency of the output current includes a first electric current frequency and a second electric current frequency which are different from each other within a one-time electric processing time using the electric processing device.

Power supply device, joining system, and electric processing method

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. Steel sheets containing carbon in 0.2 mass % or more and having sheet thicknesses 't' or more are arranged overlaid. A backing plate including a non-contact part and a contact part maintaining the back surface of the lower side steel sheet is provided. An arc generation and short-circuit conduction where the welding voltage between the welding wire and upper side steel sheet becomes 10V or less are alternately repeated so that the time period of the short-circuit conduction becomes over 30% to less than 60% per cycle to thereby weld the steel sheets.

Arc spot welding method and welding apparatus for working the same

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.

Method of spot welding

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 (I/I) of a current Iof a second welding process to a current Iof 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&#xd7;tmin to 2.5&#xd7;tmin wherein tmin is calculated using the equation (0.2&#xd7;H) 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&#xd7;tmin to 2.5&#xd7;tmin, and setting a pressure from the cooling process onward to greater than a pressure until the first welding process.

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.

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Tokyo, Japan

Seiji Furusako