| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength steel pipe having excellent expandability for oil well use. SOLUTION: The steel pipe having a composition consisting of C: 0.04-0.30%, Si: 0.5-2.0%, Mn: 2.0-4.0%, P:≤0.07%, S:≤0.01%, and Al:≤0.05% is subjected to the first heat treatment in which the steel pipe is heated at the heating temperature in the range of 800-1,050°C, and cooled at the cooling rate equal to or higher than natural cooling, and the second heat treatment in which the steel pipe is heated at the heating temperature in the range of 650-750°C, kept for≥300s, and cooled at the average cooling rate of <5°C/s. Thus, the high-strength steel tube is obtained, which can deposit a stable residual austenitic phase of an adequate amount, and has the excellent expandability withstanding the expansion processing under a severe condition of the expansion ratio being≥40%, and has the high strength of≥600 MPa in tensile strength. COPYRIGHT: (C)2011,JPO&INPIT
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