| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel pipe in which elongation suitable for hydroform forming is secured by forming an extra low C material having a specified C content into an electroseamed steel pipe and subjecting the electroseamed weld zone to heat treatment at a specified temp. SOLUTION: An extra low C material having <=0.01 wt.% C content is formed into an electroseamed steel pipe, and the electroseamed weld zone of this electroseamed steel pipe tube is subjected to heat treatment at 600 to 850 deg.C. By using the extra low C material, the elongation of the base material part can be secured to about 50%, and by subjecting the electroseamed weld zone to heat treatment at 600 to 850 deg.C, the elongation value in the base material part and the electroseamed weld zone can be made approximately equal. Moreover, the difference in the hardness by Vickers between the electroseamed weld zone and the base material part of about 30 to 80 which is the former value can be reduced to about 10 to 20. In this way, the electroseamed steel pipe excellent in hydroform formability and furthermore small in the risk of buckling, wrinkles and rupture can be obtd.
|
