Square steel pipe, method for manufacturing same, and building structure

Abstract

Provided are: a square steel pipe in which the mechanical characteristics of a flat plate section are excellent, the function of scale formed on the inner and outer surfaces of the pipe is sufficiently ensured, and the work hardening is suppressed while sufficiently ensuring toughness at corners; a method for manufacturing the square steel pipe; and a building structure using the square steel pipe. A plurality of flat plate sections (101) and corner sections (102) are alternately formed in the circumferential direction of the tube, the yield strength (YS) of the flat plate sections (101) is 295 MPa or more, the tensile strength (TS) of the flat plate sections (101) is 400 MPa or more, the yield ratio (YR) of the flat plate sections (101) is 0.80 or less, the Charpy absorption energy at 0 DEG C of the corner sections (102) is 70 J or more, the thickness of scales on the inner and outer surfaces of the tube is 1-20 [mu] m, and the thickness of the scales on the inner and outer surfaces of the tube is 1-20 [mu] m. The difference between the average Vickers hardness at a predetermined position from the apex of the corner section (102) in the thickness direction of the inner surface and the average Vickers hardness at a predetermined position from the central section of the flat plate section (101) in the thickness direction of the outer surface is from 5 HV to 60 HV (inclusive).

Description

technical field [0001] The present invention relates to a square steel pipe that is used as a column material of a building structure, has excellent deformability, and has little influence of work hardening at a corner, a manufacturing method thereof, and a building structure. Background technique [0002] Conventionally, square steel pipes used as pillars of buildings have been manufactured by a method (BCP method) in which thick steel plates are punched into a square shape by a press machine and then welded. On the other hand, in recent years, instead of the BCP method with low productivity, from the viewpoint of cost reduction, the method (BCR method) to obtain square steel pipes by welding after roll forming and square forming has been carried out to manufacture square steel pipes. try. [0003] The BCR method is to form a hot-rolled steel sheet into a cylindrical open pipe shape by roll forming, and then perform resistance welding on the butt joints, and then use rolle...

AI Technical Summary

Problems solved by technology

[0016] However, the technologies described in the above-mentioned Patent Documents 1 to 3 are not yet sufficient for obtaining square steel pipes satisfying these requirements.

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