| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel tube having excellent formability suitable for hydroforming and to provide its production method. SOLUTION: This high strength steel tube excellent in formability has composite structure consisting of ferrite of >=60% by volume fractional ratio and a second phase containing martensite of 2 to 25% by volume fractional ratio, in which the hardness of martensite is >=1.4 times that of ferrite, the average of the X-ray random intensity ratios in the orientation groups of 110} <110> to 332} <110> in the sheet face at a sheet thickness of 1/2 in the steel sheet is >=2.0, and/or the X-ray random intensity ratio of 110} <110> in the sheet face at a sheet thickness of 1/2 in the steel sheet is >=3.0, and its production method.
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