HIC STEEL MATERIAL FOR HIGHLY-DEFORMABLE LINE PIPES HAVING SUPERIOR STRAIN AGING CHARACTERISTICS AND ANTI-HIC CHARACTERISTICS METHOD FOR MANUFACTURING SAME AND WELDED STEEL PIPE

摘要

for the purpose of providing an API 5L X60 to X70 grade high-deflection line pipe steel having excellent HIC characteristics in a humidified hydrogen sulfide environment of pH 5 or higher and having a lower yield ratio even after coating at 300 DEG C or lower, do. Wherein the ferrite and the bainite have a specific component composition and the metal structure has ferrite, bainite and island-shaped martensite, the island fraction of the island-shaped martensite is 0.5 to 5.0%, and the difference in hardness between the ferrite and the bainite is 60 or more And having a uniform elongation of 9% or more and a yield ratio of 90% or less with respect to each of the pre-strain aging treatment and the post-strain aging treatment at a temperature of 300 占 폚 or less.