| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel tube in which both of a Young's modulus in a tube-axial direction and that in a tube-circumferential direction are≥230 GPa, respectively, and its manufacturing method. SOLUTION: Twisting at≥0.35 shearing strain is applied to a steel tube in a temperature region not higher than the Ac<SB>3</SB>transformation point to form a crystalline texture where the average value of the respective X-ray random intensity ratios of orientation groups ä110}<557>, ä227}<212> and ä332}<10 49> in the wall thickness central plane becomes≥3.5, and hereby a high rigidity of≥230 GPa Young's modulus both in a tube-longitudinal direction and in a tube-circumferential direction can be attained. A step of applying local twisting at a temperature ranging from 400°C and the Ac<SB>3</SB>transformation point can be sequentially applied along the tube-axial direction. Moreover, either of the following treatments can be applied to the steel tube: holding treatment where, after the twisting, reheating is applied and the steel tube is heated and held in a temperature region between 500°C and [(Ac<SB>1</SB>transformation point)+20°C]; holding treatment where, in the course of cooling after the twisting, the steel tube is held in a temperature region between 500°C and [(Ar<SB>1</SB>transformation point)+20°C]. COPYRIGHT: (C)2007,JPO&INPIT
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