| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a steel pipe, in which the decrease in yield stress caused by the Bauschinger effect is inhibited by optimizing chemical components and metal structure of a steel sheet, and which has high compressive strength and superior weld HAZ toughness and shows an API-X80 grade or higher. <P>SOLUTION: The steel pipe for a sour resistant line pipe of high compressive strength of a tensile strength of ≥630 MPa includes, by mass, C, Si, Mn, P, S, Al, 0.003-0.070% of Nb, 0.005-0.035% of Ti, and 0.01-0.5% of Mo, wherein C(%)-0.065Nb(%)-0.025Mo(%) is 0.025 to 0.060, C(%)+0.67Nb(%) is ≤0.10, and Pcm value is ≤0.20. The steel pipe is characterized in that in its metal structure, the total area fraction of bainite is ≥95%, fine precipitates containing Nb are precipitated in a dispersed state in bainite, and the area fraction of island martensite is ≤3%. <P>COPYRIGHT: (C)2013,JPO&INPIT |
