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 bainite have an area fraction of 90% or more in total, a difference in hardness between the ferrite and the bainite is 70 or more in terms of Vickers hardness, A steel material for a high-strain line pipe excellent in deformation aging characteristics and HIC resistance before and after deformation aging treatment at a temperature of 300 占 폚 or less and having a uniform elongation of 9% or more and a yield ratio of 90% or less.