Jfe Steel Corporation

Yasuaki Okita

Rinsei Ikeda

Chikaumi Sawanishi

Hiroshi Matsuda

Koichi Taniguchi

Yoshihiko Ono

Masaki Koba

Kenji Oi

Hiromi Yoshitomi

Koichi Nakagawa

Kohei Hasegawa

Seiji Nakajima

Shusaku Takagi

Muneo Matsushita

Michitaka Sakurai

Hidetaka Kawabe

Yasushi Kitani

Toshihiko Ooi

Provided is a resistance spot welding method wherein main current passage includes two or more electrode force application steps including a first electrode force application step and a second electrode force application step following the first electrode force application step, an electrode force Fin the first electrode force application step and an electrode force Fin the second electrode force application step in the main current passage satisfy a relationship F>F, and an electrode force switching point Tfrom the first electrode force application step to the second electrode force application step in the main current passage is set to satisfy predetermined relational formulas.

Resistance spot welding method and weld member production method

Provided is a resistance spot welding method wherein main current passage includes two or more electrode force application steps including a first electrode force application step and a second electrode force application step following the first electrode force application step, an electrode force Fin the first electrode force application step and an electrode force Fin the second electrode force application step in the main current passage satisfy a relationship F<F, and an electrode force switching point Tfrom the first electrode force application step to the second electrode force application step in the main current passage is set to satisfy predetermined relational formulas.

Provided is a resistance spot welding method by which a desired nugget diameter can be stably obtained without expulsion even when the effect of a disturbance is significant. An electrode force Fof a main current passage after an intermediate welding time Tis set based on an average value or time integration value Rof a resistance between electrodes from the start of main current passage to the intermediate welding time T.

A welding process used in a method of manufacturing a steel sheet assembly includes spot welding steel sheets performed for a heat time of 0.08 seconds or more using a convex electrode with a tip radius of curvature of 20 mm or more or a flat electrode such that the weld force F (kN) for initial 0.03 seconds of the heat time satisfies formula: F<0.00125×(1+0.75×t)+3 where TS (MPa) denotes an average strength of the steel sheets and represents a weighted mean value of a thickness of each of the steel sheets, and t(mm) denotes a total thickness of the steel sheets (the sum of the thicknesses of the steel sheets).

Steel sheet assembly, method of manufacturing steel sheet assembly, and spot welding process

Proposed is a resistance spot welding method to join parts to be welded which are a plurality of overlapping metal sheets, including: dividing a current pattern into two or more steps for welding; before actual welding, performing test welding; and subsequently, as actual welding, performing adaptive control welding, in which the two or more steps for welding include a step of securing a current path between the sheets directly below the electrodes and a subsequent step of forming a nugget having a predetermined diameter, and a welding interval time is provided between these steps. This method thus yields a good nugget without causing splashing even under special welding conditions.

Resistance spot welding method

A high-strength galvanized steel sheet is excellent in the external appearance of plating and the hydrogen brittleness resistance, and has a high yield ratio, and a method for manufacturing the same. The high-strength galvanized steel sheet including a steel sheet having a specific component composition and a specific steel structure, the amount of diffusible hydrogen in the steel sheet being 0.20 mass ppm or less; and a galvanizing layer provided on a surface of the steel sheet, the galvanizing layer having a content amount of Fe of 8 to 15% in mass %, and an attachment amount of plating per one surface of 20 to 120 g/m, wherein the amount of Mn oxides contained in the galvanizing layer is 0.050 g/mor less; and the high-strength galvanized steel sheet has a yield strength of 700 MPa or more and a yield strength ratio of 65% or more and less than 85%.

High-strength galvanized steel sheet and method for manufacturing same

A high-strength galvanized steel sheet includes a steel sheet having a steel composition having a specific component composition, a steel structure containing martensite and bainite at more than or equal to 70% (including 100%), ferrite at less than 20% (including 0%), and retained austenite at less than 5% (including 0%) in terms of area ratio, the amount of diffusible hydrogen in steel being less than or equal to 0.20 mass ppm; and a galvanizing layer provided on a surface of the steel sheet, having a content amount of Fe of 8 to 15% in mass %, and having an coating weight per one surface of 20 to 120 g/m, wherein the amount of Mn oxides contained in the galvanizing layer is less than or equal to 0.050 g/m, and a tensile strength is more than or equal to 1100 MPa and a yield ratio is more than or equal to 0.85.

A hot-pressed member is formed using a tailored blank material obtained by butt joining respective ends of two or more coated steel sheets. The hot-pressed member has two or more sites formed by the respective coated steel sheets and at least one joining portion between the sites. Depending on a type of a coated layer of each of the coated steel sheets, t/tis appropriately controlled where tis a thickness of a thinnest portion in the joining portion and tis a thickness of a thinnest site of the sites. A tensile strength of each of the sites is 1180 MPa or more.

Hot-pressed member and manufacturing method therefor

A resistance spot welding device for welding at least two overlapping steel sheets held between a pair of welding electrodes is provided. The resistance spot welding device includes the pair of electrodes, an electrode force gauge that measures an electrode force, and a controller that controls an electric current supply to the electrodes according to the electrode force measured by the electrode force gauge. The controller controls the electric current such that the electrode force F measured by the electrode force gauge after the start of the electric current supply is adjusted to a prescribed value.

Resistance spot welding device

Provided is a method for resistance spot-welding at least two overlapping steel sheets. When an electrode force F after an electric current supply is started changes from an initial electrode force Fi to an electrode force Fwhile a lapse from the start of the electric current supply is between 20 ms and 80 ms inclusive, a suspension of the electric current supply of from 20 ms to 60 ms inclusive is started. Then the electric current supply is resumed when the electrode force F reaches an electrode force F.

Resistance spot welding method and weld joint

The resistance spot welding method includes performing actual welding to squeeze, by a pair of electrodes (), a sheet combination with a sheet thickness ratio of more than 3 in which a thin sheet () is overlapped on at least one face of two or more overlapping thick sheets (), and passing a current while applying an electrode force to join the sheet combination, wherein in the actual welding, a pattern of the current and the electrode force is divided into two or more steps including a first step and a second step to perform welding, and an electrode force Fin the first step and an electrode force Fin the second step satisfy a relationship1&#x3e;2.

A method of resistance spot welding to join a plurality of overlapping metal sheets, including: dividing a current pattern into two or more steps for welding; before actual welding, performing test welding to store, for each step as a target value, a time variation of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume; and subsequently, as actual welding, starting welding using, as a standard, a time variation curve of the instantaneous amount of heat generated per unit volume obtained by the test welding, and when a time variation amount of an instantaneous amount of heat generated deviates during any step from the time variation curve by a difference, performing adaptive control welding to control a current passage amount in order to compensate for the difference during a remaining welding time in the step.

A resistance spot welding device that joins predetermined parts to be welded includes: a storage configured to store a time variation of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume in test welding that precedes actual welding; and an adaptive controller and an electrode force controller configured to, in the case where the time variation of the instantaneous amount of heat generated per unit volume in the actual welding differs from a time variation curve stored as the target value, respectively control the current or a voltage during current passage and the electrode force to the parts to be welded to compensate for the difference within a remaining welding time so that the cumulative amount of heat generated per unit volume in the actual welding matches the cumulative amount of heat generated per unit volume stored in the storage.

Resistance spot welding device and resistance spot welding method

Resistance spot welding is performed on a combination of overlapping steel sheets including at least one steel sheet that has, on a surface thereof, a coated layer with zinc as a main component, by (1) starting electric current passage in a state satisfying 0.9&#xd7;t&#x2266;L&#x2266;1.1&#xd7;t; and (2) dividing electric current into main current and initial current that precedes the main current and is two-step current, setting a current value Iduring current in a first step of the initial current to satisfy I&#xd7;1.1&#x2266;I&#x2266;15.0 kA with respect to a current value Iduring the main current, and setting a current value Iin the subsequent second step to no current or low current satisfying 0&#x2266;I&#x2266;I&#xd7;0.7.

A resistance spot welding system includes a calculation unit that calculate and store a time variation of an instantaneous amount of heat generated, a division unit that divides a current pattern into a plurality of steps and stores a time variation of the instantaneous amount of heat generated and a cumulative amount of heat generated for each step as a target value, and an adaptive control unit that starts welding upon subsequent actual welding using, as a standard, a time variation curve of the instantaneous amount of heat generated that is stored as the target value, and adjusts welding current and voltage during welding, when a time variation amount of an instantaneous amount of heat generated deviates during any step from the time variation curve by a difference, so as to compensate for the difference during a remaining welding time in the step.

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Tokyo, Japan

Yasuaki Okita