| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a high ductility electric resistance welded tube excellent in workability. SOLUTION: Steel contg., by weight, 0.05 to 0.25% C, 0.3 to 2.5% Si, 0.5 to 3.0% Mn, <=0.005% S, <=0.15% P, 0.005 to 0.10% Al and <=0.0050% N and, if required contg. 0.0002 to 0.0020% Ca is coiled at <=750 deg.C coiling temp. by hot rolling, the steel strip is performed to high frequency electric resistance welding in a welding atmosphere of <=100 ppm oxygen concn., the tube stock is heated to the AC1 transformation point temp. to the AC3 transformation point temp., is held for <=20 min, is thereafter cooled to the temp. range of the Ms transformation point temp. +100 deg.C to the Ms transformation point temp. at a cooling rate of >=0.5 deg.C/s, is held at the temp. for 30 to 300 s and is thereafter air-cooled to a room temp.
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