| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a steel pipe for a sour resistant line pipe which has high compressive strength and superior weld HAZ toughness by optimizing the chemical composition and metallographic structure of a steel plate so that the decrease of yield stress by the Bauschinger effect is suppressed. <P>SOLUTION: The steel pipe for the sour resistant line pipe having high compressive strength with tensile strength of 570 MPa or more is a steel pipe containing, by mass%, C, Si, Mn, P, S, Al, 0.030-0.08% Nb, 0.010-0.04% Ti, Ca, N, wherein C(%)-0.065Nb(%) is 0.025 or more, C(%)+0.67Nb(%) is 0.08 or less, CP value is 0.98 or less, and P<SB POS="POST">CM</SB>value is 0.170 or less. The steel pipe has a metallographic structure in which the total of the area fraction of bainite and ferrite is 95% or more, fine precipitates containing Nb and Ti with average grain diameter of 20 nm or less are dispersedly precipitated in the ferrite, and the area fraction of insular martensite is 3% or less. <P>COPYRIGHT: (C)2013,JPO&INPIT</p> |
