| 摘要 |
PROBLEM TO BE SOLVED: To provide a resistance welded tube excellent in workability and suitably used as resistance welded tubes for automobile and machine structural uses requiring excellent workability, and its manufacturing method. SOLUTION: The resistance welded tube excellent in workability has a composition consisting of, by weight, 0.0010-0.010% C, <=0.5% Si, <=1.5% Mn, <=0.08% P, <=0.02% S, 0.005-0.10% Al, <=0.0040% N, <=0.08% Ti, and the balance iron with inevitable impurities and satisfying Ti/(C+N)>4.0 and further containing, if necessary, 0.0005-0.0050% Ca and also has a structure composed of ferrite single phase having workability. The difference between hardness in a resistance weld zone and that in a base material part becomes <=Hv 50. This resistance welded tube can be manufactured by regulating heating temperature at hot rolling and finishing temperature to <=1200 deg.C and a value not lower than the Ar3 transformation point, respectively, starting cooling within one second, performing cooling at >=20 deg.C/s average cooling rate down to <=830 deg.C, successively coiling the resultant steel sheet at 500-800 deg.C coiling temperature, and subjecting this steel sheet to high frequency resistance welding to undergo tube making.
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