Jfe Steel Corporation

Muneo Matsushita

Rinsei Ikeda

Koichi Taniguchi

Hiroshi Matsuda

Reiko Endo

Shohei Iwata

Yasuaki Okita

Kenji Oi

Yasushi Kitani

Akihide Yoshitake

Daiki Yamagishi

Kai Tomita

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).

Resistance spot weld, resistance spot welding method, resistance spot welded joint, and method for manufacturing resistance spot welded joint

Provided is an electrical steel strip friction stir welding method that is able to inhibit the occurrence of coil joint fractures on a production line caused by deterioration of mechanical properties and shape of the coil joint while maintaining high work efficiency and that is also advantageous in terms of rotating tool durability. In the method, preheated double-sided friction stir welding is performed, diameter D (mm) of shoulders of rotating tools satisfies the relationship of the following Expression (7), and rotation speed RS (r/min) of the rotating tools, the diameter D (mm) of shoulders of the rotating tools, and joining speed JS (mm/min), expressed as RS×D/JS, satisfy the relationship of the following Expression (8), 4×TJ≤D≤10×TJ . . . (7), and 180×TJ≤RS×D/JS≤1500×TJ . . . (8).

Electrical steel strip friction stir welding method and method of producing electrical steel strip

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

Disclosed are rotating tools for double-sided friction stir welding that are applied to double-sided friction stir welding, which is a technique for welding two metal plates by rotating a pair of rotating tools, which oppose each other, in opposite directions, a double-sided friction stir welding apparatus that uses the rotating tools, and a double-sided friction stir welding method. A pair of rotating tools for double-sided friction stir welding that are used in double-sided friction stir welding, which is a technique for welding metal plates by using a pair of rotating tools that are each disposed on one of first and second surfaces of an unwelded portion of the metal plates such that the rotating tools rotate in opposite directions, include end portions each of which is formed in a circular and planar shape. The end portions are each made of a material harder than the metal plates.

Rotating tool for double-sided friction stir welding, double-sided friction stir welding apparatus, and double-sided friction stir welding method

A double-sided friction stir welding method, methods for producing a cold-rolled steel strip and a coated steel strip, a double-sided friction stir welding apparatus, and facilities for producing a cold-rolled steel strip and a coated steel strip. The double-sided friction stir welding method includes pressing two rotating tools, which are disposed on a first surface and a second surface of a butt portion or overlap portion of the steel strips, against the butt portion or overlap portion of steel strips and moving the rotating tools in the welding direction while rotating the rotating tools in opposite directions to each other, so that an unwelded portion of the steel strips is softened by frictional heat generated between the rotating tools and the unwelded portion of the steel strips, and the softened portion is stirred with the rotating tools to generate plastic flow so as to weld the steel strips together.

Double-sided friction stir welding method, methods for producing cold-rolled steel strip and coated steel strip, double-sided friction stir welding apparatus, and facilities for producing cold-rolled steel strip and coated steel strip

Provided is a double-side friction stir welding method of metal sheets or metal plates to each other, and a double-side friction stir device for performing the double-side friction stir welding. According to the present invention, a pair of rotating tools facing each other is respectively arranged on a top-surface side and a bottom-surface side of a butted portion or an overlapping portion, which comprises a joint portion of two metal sheets or two metal plates, the pair of rotating tools is moved in a welding direction while being rotated at the butted portion or the overlapping portion, and while the metal sheets or the metal plates are softened by frictional heat generated between the rotating tools and the metal sheets or the metal plates, softened parts are stirred by the rotating tools to produce a plastic flow to join the metal sheets or the metal plates to each other.

Double-side friction stir welding method and double-side friction stir welding device for metal sheets or metal plates

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

Resistance spot welding method and method for producing resistance spot welded joint

There is provided a friction stir welding method in which, when double-sided friction stir welding is performed, enough plastic flow to obtain a welded state uniform in the thickness direction of metal sheets can be obtained, in which an increase in welding speed is achieved while the occurrence of defects during welding is prevented, and in which sufficient strength and improvement in welding workability can be achieved. There is also provided a friction stir welding device suitable for the friction stir welding.

Double-sided friction stir welding method for metal sheets and double-sided friction stir welding device

An object is to provide a friction stir welding method and apparatus that provide sufficient strength and good welding workability by advantageously eliminating plastic flow deficiency generated as a result of insufficient heating of workpieces. In friction stir welding for steel sheets () as workpieces, a pair of facing rotary tools () are inserted into a non-welded part from both one surface side and the other surface side of the steel sheets (), the rotary tools move in a welding direction while rotating, and in addition, a preheating process for heating steel sheets () is performed by heating means () provided in front of the rotary tools (). The configuration of the pair of facing rotary tools () and the surface temperature, area, position, and so forth of a heated region in the preheating process are strictly controlled.

Friction stir welding method and apparatus for structural steel

A friction stir welding apparatus that includes a rotary tool and a heating device. The heating device is placed in front of the rotary tool to heat steel sheets that are used as a workpiece. The rotary tool is moved in the welding direction so that steel sheet is softened by frictional heat. Additionally, the surface temperature, the area, and the position of the heated region during the heating process are strictly controlled. The heating of the steel sheets by the welding apparatus provides sufficient strength and good welding workability by advantageously eliminating plastic flow defects generated due to insufficient heating of workpieces.

Friction stir welding apparatus for structural steel

In the indirect spot welding apparatus, a lower limit in a stable pressing force region where the pressing force of the spot welding electrode against the metal sheets can be controlled within a tolerance of &#xb1;10% ranges from 70 N to 200 N and an upper limit in the stable pressing force region ranges from 800 N to 2000 N, and an overshoot OS(%)=(PL&#x2212;AL)/AL&#xd7;100 of the pressing force occurring when the spot welding electrode is pressed against the metal sheets is controlled to be 10% or less.

Indirect spot welding apparatus

An oval nugget can reliably be obtained with this indirect spot welding method. In this indirect spot welding method, an electrode end portion of a welding electrode includes a tip of the welding electrode, and as viewed from the tip, the electrode end portion has a two-step dome shape formed by a first curved surface with a curvature radius r(mm) located within a range of a circle of radius R (mm) centering on the tip and a second curved surface with a curvature radius r(mm). 2&#x221a;t&#x2264;R&#x2264;6&#x221a;t (1), 30&#x2264;r(2), and 6&#x2264;r&#x2264;12 (3), where t is the sheet thickness (mm) of a thinner metal sheet.

Indirect spot welding method

This indirect spot welding is for welding members including at least two overlapping steel sheets that have a ferrite phase as a main phase by holding a welding electrode () against a steel sheet () from one side while applying pressure with the electrode (), attaching a feeding point () to a steel sheet () at the other side at a location remote from the electrode (), and allowing current to flow between the electrode () and the feeding point (). This welding includes contacting magnetic rigid bodies (--) to a peripheral area of the electrode () from the one side against which the electrode () is held and securing an overlapping region in the peripheral area of the electrode () by a magnetic force produced by the rigid bodies (--), thereby obtaining a weld having fully satisfactory strength, regardless of the rigidity of the members.

A friction stir welding method for steel sheets includes inserting a rotating tool into an unwelded portion where two or more steel sheets are overlapped or butted together; moving the rotating tool along portions to be welded while rotating the tool so that a softened portion is formed in the steel sheets by friction heat generated between the rotating tool and the steel sheets, and the steel sheets are welded together by utilizing a plastic flow generated by the softened portion being stirred; and preheating the unwelded portion before welding by the rotating tool by a pair of heating devices disposed over and under the unwelded portion and ahead of the rotating tool in the advancing direction to enable high speed welding without the risk of generation of welding defects and damage to the welding tool.

Friction stir welding method for steel sheets and method of manufacturing joint

A friction stir welding method for welding steel sheets together includes a heating device disposed ahead of a rotating tool in an advancing direction that preheats an unwelded portion before the welding thereof by the rotating tool and at the time of preheating, the surface temperature distribution in a direction perpendicular to the advancing direction in a position at which the welding by the rotating tool is initiated is set such that given that Tis the Acpoint of a steel sheet, the maximum temperature (T) thereof is 0.6&#xd7;T&#x3c;T&#x3c;1.8&#xd7;T, and given that L is the width of the heating region exceeding a temperature (T)=0.6&#xd7;T, 0.3&#xd7;d&#x2266;L&#x2266;2.0&#xd7;d is satisfied with a diameter (d) of the shoulder.

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Tokyo, Japan

Muneo Matsushita