| 摘要 |
<p>A line pipe suitable as a heavy wall, high-strength line pipe for sour gas service having a wall thickness of 20 mm or more and a tensile strength of 560 MPa or more and a production method therefor are provided. According to this line pipe, the base metal portion contains particular amounts of C, Si, Mn, P, S, Al, Nb, Ca, N, and O, one or more component selected from Cu, Ni, Cr, Mo, V, and Ti as optional components, and the balance being Fe and unavoidable impurities. The microstructure in the pipe thickness direction contains 90% or more bainite and 1% or less of MA in a region that extends from a position 2 mm from an inner surface to a position 2 mm from an outer surface. In a hardness distribution in the pipe thickness direction, the hardness in a region other than a center segregation area is 220 Hv10 or less and the hardness in the center segregation area is 250 Hv10 or less. The major axes of pores, inclusions, and inclusion clusters that are present in a portion that extends from a position 1 mm from the inner surface to a 3/16 position of the tube thickness and in a portion that extends from a position 1 mm from the outer surface to a 13/16 position of the tube thickness in the tube thickness direction are 1.5 mm or less. A continuous casting slab having the above-described composition is hot-rolled under particular conditions, subjected to accelerated cooling, and then subjected to reheating.</p> |
