Steel plate for high-strength line pipe and steel pipe for high-strength line pipe with excellent low-temperature toughness

摘要

In order to provide steel pipes for line pipes and line pipe steel pipes excellent in low temperature toughness, which are optimal for steel pipes used for transportation pipes for oil, natural gas, etc., C: 0.03-0 0.08%, Si: 0.01 to 0.5%, Mn: 1.5 to 2.3%, Nb: 0.001 to 0.05%, N: 0.0010 to 0.0050%, Ca: Including 0.0001 to 0.0050%, P: 0.015% or less, S: 0.0020% or less, Ti: 0.030% or less, Al: 0.030% or less, O: 0.0035% or less The balance is made of Fe and inevitable impurity elements, S / Ca 0.5 is satisfied, the maximum hardness of the center segregation part is 400 Hv or less, and the length of the uncompressed part is 0.1 mm or less. Restrict.