Administering hot rolling process, cold rolling process and annealing process

摘要

PROBLEM TO BE SOLVED: To provide a thin high strength welded steel tube excellent in formability, and torsion-proof fatigue characteristics after cross-sectional forming processing.;SOLUTION: A steel material which contains C: 0.08-0.24%, Si: 0.001-1.5%, Mn: 0.8-2.8%, Al: 0.01-0.08%, and has composition in which P, S, N, O are adjusted to a predetermined value or less is heated, hot rolling which uses finish rolling finishing temperature as A_r3 transformation point or more is performed, then, winding hot-rolled steel strip is made at winding temperature: 650-500°C, then, annealing treatment for performing cooling to temperature equal to or less than that of Ms transformation point at average cooling temperature: 81-500°C/s after cold rolling at draft of 41-76% and heating soaking to 750-950°C by a continuous annealing furnace, and then, the annealing treatment is performed by (Ms transformation point - 150°C)-(Ms transformation point - 350°C).;COPYRIGHT: (C)2011,JPO&INPIT