| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing steel tubes for a steel tower with less change in the mechanical properties when manufacturing a steel tube having the diameter/thickness ratio of ≤20 and the tensile strength of ≥780 MPa by press-bending a steel plate. SOLUTION: In the method for manufacturing steel tubes for the steel tower having the diameter/thickness ratio of ≤20 and the tensile strength of ≥780 MPa, a slab having a composition containing, by mass, 0.05-0.20% C, 0.03-0.40% Si, 0.5-2.0% Mn, ≤0.02% P, ≤0.005% S, 0.03-0.10% Al, ≤0.005% N, and the balance Fe with inevitable impurities is heated to ≥1,100°C, hot-rolled, and cooled down to ≤100°C, and then, re-heated and hardened, tempered at 500-650°C to manufacture a thick steel plate, which is re-heated at ≥500°C to the temperature equal to or lower than [the tempering temperature when manufacturing the thick steel plate -30°C], and then, subjected to the press-bending, and welded. One or two or more kinds of Cu, Cr, Mo, V, Nb, Ni, B and Ti may be contained in place of a part of Fe. COPYRIGHT: (C)2011,JPO&INPIT
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