| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a steel pipe having superior electromagnetic properties, and to provide a manufacturing method therefor. <P>SOLUTION: This steel pipe has a composition including, by mass%, 0.5% or less C and 85% or more Fe. The manufacturing method comprises: heating the base steel pipe having the above composition; and rolling it to reduce a diameter at a diameter reduction rate of 15% or more and at a rolling-finishing temperature of (Ar<SB>3</SB>transformation temperature -10)°C or lower. Thereby, the steel pipe acquires a structure having the three-dimensional random intensity ratio of crystals having the orientation of <100> in a circumferential direction and of <110> in a rolling direction in an amount of 3.0 or larger, when measured with an X-ray diffraction method; an enhanced r-value; and improved electromagnetic properties. Annealing treatment at 550°C or higher but the Ac<SB>1</SB>transformation temperature or lower after rolling for diameter reduction increases the grain size and further improves the electromagnetic properties. The steel pipe may be cold-drawn before being annealed. The electromagnetic properties are further improved by using a steel pipe having the high-purity composition including less than 0.01% C and 95% or more Fe, for the base steel pipe. It is preferable to contain a proper amount of Si and Al for further improving the electromagnetic properties. The electromagnetic properties in a high-frequency area are improved by containing the proper amount of Cr. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
