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780 mpa low yield ratio round steel pipe for building structure with excellent shock resistance and production process

A steel pipe and round technology, applied in the field of round steel pipes and their manufacturing, can solve the problems of unconsidered hardness of round steel pipes and difficult manufacturing management, and achieve the effects of improving shock resistance, crack resistance and ensuring ductility.

Active Publication Date: 2009-09-30
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0016] However, there is a problem with this technology that the surface layer may be softened more than the inside of the plate, and it is difficult to manage the production in the mass production direction to obtain a stable material.
In addition, in this technology, the hardness after processing into a round steel pipe is not considered

Method used

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  • 780 mpa low yield ratio round steel pipe for building structure with excellent shock resistance and production process
  • 780 mpa low yield ratio round steel pipe for building structure with excellent shock resistance and production process
  • 780 mpa low yield ratio round steel pipe for building structure with excellent shock resistance and production process

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Experimental program
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Effect test

Embodiment 1

[0089] Steels with the chemical compositions shown in the following Tables 1 and 2 were smelted by a common melting method to form steel slabs, followed by hot rolling, accelerated cooling (cooling after rolling), dual-phase domain quenching, and tempering to manufacture steel sheets. Using the obtained steel sheet, it was formed into a circular steel pipe by a press bending method. In addition, Tables 1 and 2 also show the PCM values ​​defined by the aforementioned formula (1). The production conditions at this time are as follows.

[0090] (manufacturing conditions)

[0091] In steel No.1-60, after heating the ingot to 1150±50°C, hot rolling is carried out at the finish rolling temperature (surface temperature) in the range of 900±30°C to a plate thickness of 60 mm, followed by t / 4(t : The cooling rate at the position of plate thickness) is controlled at 5 to 25°C / sec, so that the surface temperature when the cooling stops is below 250°C. In addition, the two-phase region...

Embodiment 2

[0119] Using steel Nos. 1 to 11 shown in Table 1 (the chemical composition satisfies the range specified in the present invention), steel sheets were produced according to various manufacturing conditions (DQ-Q'-T) shown in Table 7 below (experimental No.1~20). Using the obtained steel sheet, it was formed into a circular steel pipe by a press bending method. Same as embodiment for the circular steel pipe obtained, to material (yield stress YS, tensile strength TS, yield ratio YR and toughness vE -20 ) and weldability were evaluated.

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Abstract

The steel pipe not only satisfies predetermined expression, but also regulates chemical composition, and satisfies following conditions (A)-(C): (A) the central portion for removing the surface portion 2mm from the front and the back face of the steel pipe has an average Vickers hardness from 230 to 310; (B) in microscopic constitution of steel pipe, bainitic ferrite structure is over 80% in area, martensitic phase is below 5% in area; (C) average Vickers hardness Hv of the surface portion 2mm from the front and the back face of the steel pipe is below 1.3 times of the average hardness Hv of the central portion. According to the construction, high strength and low yield ratio can be realized in the mean time, tractility can be ensured by reducing hardness on external surface of the steel pipe due to bending machining in steel pipe forming, cracking resistance in welding can be improved because of improved shock resistance for steel pipes with highest tensile strength at 780MPa for building reinforcement.

Description

technical field [0001] The present invention mainly relates to circular steel pipes for building steel bar applications requiring earthquake resistance and a manufacturing method thereof, in particular to high-strength low-yield-ratio circular steel pipes with a tensile strength of more than 780 MPa (grade 780) and a yield ratio of less than 90%. shaped steel pipes, and useful methods for making such round steel pipes. Background technique [0002] In order to ensure the earthquake resistance of building structures, steel used in construction absorbs earthquake energy by using plastic deformation after elastic deformation. Under this idea, the ratio of yield stress YS to tensile strength TS (YS / TS) represents The upper limit of the yield ratio YR is specified. [0003] The circular steel pipes used in the above-mentioned building structures are formed by extruding and bending steel plates, so the material changes due to work hardening, and the yield ratio YR and the hardnes...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/58C21D8/10
Inventor 盐饱丰明小林克壮
Owner KOBE STEEL LTD
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