Jfe Steel Corporation

Kenji Oi

Koji Yano

Akihide Nagao

Naoya Hayakawa

Atsushi Ishigami

Kenji Hayashi

Rinsei Ikeda

Yasuaki Okita

Hiroshi Matsuda

Chikaumi Sawanishi

Kenji Shimada

Koichi Yasuda

Muneo Matsushita

Masahito Suzuki

Toshifumi Kodama

Hiroyuki Sumi

Yasushi Kitani

Shigeto Sakashita

Nobuo Shikanai

Masahiro Odaka

Tokihiko Kataoka

Shohei Kozuki

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

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.

Resistance spot welding method

A steel strip is formed into a cylinder so that opposite ends of the steel strip face each other, while continuously conveying the steel strip. The opposite ends are melted across the entire thickness by irradiating the opposite ends with a high-energy-density beam while applying a pressure with squeeze rolls. A seam is formed by joining the opposite ends, and excess weld metal of the seam on the outer and inner sides of the obtained welded steel pipe is removed by cutting. A repaired seam is then formed by remelting and solidifying a region on the inner side of the welded steel pipe, the region having a depth of 0.5 mm or more from the surface and a width of double or more the width of the seam, and in addition, the center line of the seam is made to coincide with the center line of the repaired seam.

Welded steel pipe joined with high-energy-density beam and method for producing the same

A method of manufacturing a laser welded steel pipe by forming a steel strip into a cylindrical open pipe and performing laser welding on edges that includes: emitting two laser beams along the edges from an upper surface side of the open pipe, the two laser beams being transmitted through different optical fibers with in-focus spot diameters exceeding 0.3 mm; emitting leading and trailing laser beams each inclined toward a direction in which welding proceeds at an incident angle with respect to a direction perpendicular to an upper surface of the open pipe; setting the incident angle of the leading laser beam to be larger than the incident angle of the trailing laser beam; and setting a gap between a center point of the leading laser beam and a center point of the trailing laser beam on a back surface of the open pipe to 1 mm or larger.

Method of manufacturing laser welded steel pipe

Provided are a combination welding method and a combination arc welding machine thereof having excellent construction efficiency and preventing a deterioration of toughness of a HAZ by maintaining the current density of each of gas metal arc welding and submerged-arc welding within an appropriate range at the time of welding a steel plate by the combination of the gas metal arc welding using multielectrodes and the submerged-arc welding using multielectrodes. The gas metal arc welding is performed using two or more electrodes, a wire for welding having a wire diameter of 1.4 mm or more is used in the first electrode of the gas metal arc welding, and a current density of the first electrode is set to 320 A/mmor more.

Combination welding method using combination of gas metal arc welding and submerged-arc welding and combination arc welding machine

Method for producing a steel pipe using a high energy density beam

Provided is a submerged arc welding method for a steel plate. In welding the steel plate from an internal surface or an external surface by a submerged arc welding, welding condition is set such that, a cross-sectional area of internal weld metal Sand a cross-sectional area of external weld metal Ssatisfy the formula (1), the formula (2), and the formula (3), that is, 0.40&#x2266;(S+S)/t&#x2266;0.80 . . . (1), S/t&#x2266;0.35 . . . (2), and S/t&#x2266;0.45 . . . (3), wherein t is a plate thickness of the steel plate (mm), Sis a cross-sectional area of the internal weld metal (mm) excluding the cross-sectional area of a portion of the internal weld metal overlapping with the external weld metal after external welding, and Sis a cross-sectional area of the external weld metal (mm).

Submerged arc welding method for steel plate

Steel is subjected to multiple-electrode submerged arc welding with three or more electrodes in which a direct-current power source is used to supply current to a first electrode, the welding by the first electrode is carried out at a current density of 250 A/mmor more, preferably with a wire diameter of 3.2 mm or less and a weld current of 1,000 A or more, the welding by the second electrode is carried out at a current density of 150 A/mmor more, preferably with a weld current of 600 A or more, one of the interelectrode spacings is 23 mm or more on a surface of the steel, and the remaining interelectrode spacings are 20 mm or less.

Submerged arc welding method with multiple electrodes for steel material

The invention provides a high tensile strength steel material having a tensile strength of 600 MPa, which is excellent in delayed fracture resistance property, and a method of manufacturing the steel material. As means for this, a steel material contains, in mass percent, C of 0.02 to 0.25%, Si of 0.01 to 0.8%, Mn of 0.5 to 2.0%, Al of 0.005 to 0.1%, N of 0.0005 to 0.008%, P of 0.03% or less, and S of 0.03% or less. In addition, the steel material contains at least one element selected from Mo, Nb, V, and Ti, and contains at least one of Cu, Ni, Cr, W, B, Ca, REM and Mg, as needed. The remainder includes Fe and inevitable impurities. In addition, in the steel material, precipitates having an average grain size of 20 nm or less, which contains at least one of Mo, Nb, V and Ti, are contained in steel in the number of at least 5 per 250000 nm, and a microstructure includes residual austenite in a volume fraction of 0.5 to 5%. When Ca to be added is specified to be 0.0010% to 0.0020%, it is specified that S is 0.0005% to 0.0020% and O is 0.0008% to 0.0025%. ACR is specified to be 0.2&#x2266;ACR(=(Ca&#x2212;(0.18+130*Ca)*O)/1.25/S)&#x2266;1.0.

High tensile strength steel material having excellent delayed fracture resistance property, and method of manufacturing the same

There is provided a method for manufacturing a laser welded steel pipe in which the status of laser welding is accurately assessed, and the assessment is used to modify welding conditions, so that laser welded steel pipes can be manufactured at a high yield rate and in a stable manner. Irradiation point(s) of laser beam(s), with which the longitudinal edges are irradiated from the side of the outer surface, are monitored from the side of the inner surface of an open pipe, and then conditions of welding with the laser beam(s) are assessed to be kept unchanged if any keyhole is found penetrating out of the inner surface of the open pipe, or modified if no keyhole is found penetrating out of the inner surface of the open pipe.

Method for manufacturing a laser welded steel pipe

High tensile strength steels that have both favorable delayed fracture resistance and a tensile strength of 600 MPa or higher and are suitably used in construction machinery, tanks, penstocks, and pipelines, as well as methods for manufacturing such steels are provided. The safety index of delayed fracture resistance (%) is 100&#xd7;(X/X), where X: reduction of area of a specimen substantially free from diffusible hydrogen, and X: reduction of area of a specimen containing diffusible hydrogen.

High tensile strength steel having favorable delayed fracture resistance and method for manufacturing the same

The present invention provides a method for manufacturing high tensile strength steel plate having 570 MPa (N/mm) or larger tensile strength and having also extremely superior balance of strength and toughness both before PWHT and after PWHT to that of the conventional steel plates, by specifically specifying the temperature-rising rate at the plate thickness center portion of a quenched and tempered material during tempering, and to be concrete, the method has the steps of: casting a steel consisting essentially of 0.02 to 0.18% C, 0.05 to 0.5% Si, 0.5 to 2.0% Mn, 0.005 to 0.1% Al, 0.0005 to 0.008% N, 0.03% or less P, 0.03% or less S, by mass, and balance of Fe and inevitable impurities; hot-rolling the cast steel without cooling the steel to the Artransformation point or lower temperature, or after reheating the steel to the Actransformation point or higher temperature, to a specified plate thickness; cooling the steel by direct quenching from the Artransformation point or higher temperature, or by accelerated cooling, to 400&#xb0; C. or lower temperature; and then tempering the steel, using a heating apparatus being installed directly connecting the manufacturing line containing a rolling mill and a direct-quenching apparatus or an accelerated cooling apparatus, to 520&#xb0; C. or above of the maximum ultimate temperature at the plate thickness center portion at an average temperature-rising rate of 1&#xb0; C./s or larger at the plate thickness center portion up to a specified tempering temperature between 460&#xb0; C. and the Actransformation point.

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Tokyo, Japan

Kenji Oi