Hot-rolled steel plate for square steel tube for use as building structural member and process for producing same
A technology for square steel pipes and building structures, which is applied to square steel pipes manufactured by roll forming, further improves toughness and reduces yield ratio, and can solve problems such as reduced productivity, high manufacturing costs, and complicated procedures.
Active Publication Date: 2014-12-17
JFE STEEL CORP
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Problems solved by technology
In addition, in the technology described in Patent Document 2, it is necessary to perform two heat treatments of rapid cooling and tempering after heating in the two-phase zone, and there are problems in that the process is complicated, the productivity is lowered, and the manufacturing cost is high.
Method used
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[0142] Molten steel having the composition shown in Table 1 was melted in a converter, and a slab was produced by continuous casting (steel raw material: wall thickness: 215 mm). These slabs (steel raw materials) were heated to the heating temperatures shown in Table 2 and Table 3, and then passed through the hot rolling process, cooling process, and coiling process shown in Table 2 and Table 3, and the plate thickness: 12 ~25mm thick-walled hot-rolled steel plate. The obtained hot-rolled steel sheet is used as a raw material, and rolled into a circular steel pipe in a cold state, and then formed into a square steel pipe (250-550 mm square) by roll forming in a cold state.
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Abstract
Provided is a hot-rolled steel plate suitable as a raw material for a square steel tube for use as a building structural member. This hot-rolled steel plate contains, in mass%, 0.07 to 0.18% of C, 0.3 to 1.5% of Mn, 0.01 to 0.06% of Al and at most 0.006% of N with the balance being Fe and unavoidable impurities, and comprises a primary phase consisting of ferrite and a secondary phase consisting of pearlite or both pearlite and bainite. The frequency of the second phase is 0.20 to 0.42, and the mean grain diameter of the primary and secondary phases is 7 to 15 [mu]m. A square steel tube which combines a low yield ratio and high toughness can be produced by subjecting the hot-rolled steel plate to cold forming.
Description
technical field [0001] The present invention relates to a hot-rolled steel plate used for square steel pipes for building structural members, and in particular to low yield ratio and toughness of square steel pipes (square columns) produced by roll forming in a cold state using hot-rolled steel plates as raw materials further improvement. It should be noted that hot-rolled steel sheets include hot-rolled steel sheets and hot-rolled steel strips. Background technique [0002] Square steel pipes are usually produced by cold forming using hot-rolled steel sheets (hot-rolled steel strips) or thick plates as raw materials. When producing square steel pipes, there are press forming and roll forming as the cold forming used. When a hot-rolled steel strip is used as a raw material to manufacture square steel pipes by roll forming, the hot-rolled steel strip is usually first formed into a circular steel pipe, and then the circular steel pipe is subjected to cold forming to form a s...
Claims
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Login to View More IPC IPC(8): C22C38/00C21D8/02C22C38/06C22C38/14
CPCC21D6/005C21D6/008C21D8/0226C21D8/0263C21D9/46C21D2211/005C21D2211/009C22C38/00C22C38/001C22C38/002C22C38/02C22C38/04C22C38/06C22C38/12C22C38/14E04C3/32
Inventor 上力田村雄太玉井崇登川村修司
Owner JFE STEEL CORP