Importance

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Abstract

A line pipe and a production method therefor are provided. The microstructure in the pipe thickness direction contains 90% or more bainite 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 Hv0.05 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 and then subjected to accelerated cooling.

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First Claim