| 摘要 |
PROBLEM TO BE SOLVED: To obtain a high strength electric resistance welded tube in which the softening and hardening of a welding heat-affected part are suppressed and excellent in fatigue durability. SOLUTION: A slab contg. 0.03 to 0.10% C, 0.20 to 1.0% Si, 1.0 to 2.5% Mn, <=0.03% P, <=0.005% S, <=150 ppm (N+O), 0.02 to 0.20% Ti, 0.02 to 0.10% Nb, 0.01 to 0.1% total Al, 0 to 0.0050% B, 0 to 0.3% Cr and 0 to 0.0050% Ca is heated at 1,150 to 1,300 deg.C, is thereafter hot-rolled in the state that the total rolling ratio in finish rolling is controlled to >=90% and the finishing temp. in controlled to the Ar transformation point to the Ar3 transformation point +100 deg.C, is cooled at a cooling rate of 10 to 50 deg.C/sec and is coiled at 450 to 550 deg.C coiling temp. to form it into a hot rolled coil. In the case of producing an electric ressitance welded tube after pickling, after cooling an electric resistance weld part, continuously, by high frequency heating, the electric resistance weld part is tempered in the temp. range of the Ac1 transformation point to the Ac1 transformation point -70 deg.C. It is preferable that, at the time of the hot rolling, descaling under >=200 kgf/cm2 descaler discharging pressure is executed in the temp. range of 900 to 1,100 deg.C for at least one or more passes.
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