| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a strength member for an automobile, having high bending reaction force at the initial stage of collision and having a cross section shape enabling the reduction of its manufacturing cost and weight. SOLUTION: The method is for manufacturing a square steel tube having a square cross section, wherein a square steel tube having a tensile strength of≥690 MPa and a square cross section is manufactured by cold-drawing a round steel tube. In the method, a round steel tube having a tensile strength of≥590 MPa is used, and the outer peripheral length reduction Or is 10-40%, as shown in the formula (1) as follows: 10≤Or=[(L<SB>0</SB>-L)/L<SB>0</SB>]×100≤40 (wherein, L<SB>0</SB>is the outer peripheral length (mm) of the round steel tube before cold drawing; and L is the outer peripheral length (mm) of the square steel tube after cold drawing). COPYRIGHT: (C)2007,JPO&INPIT
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