Steel material for high deformability line pipe excellent in strain aging resistance and HIC resistance, manufacturing method thereof, and welded steel pipe

摘要

API 5L X60-X70 grade high-deformability line pipe steel, which exhibits excellent HIC resistance in a wet hydrogen sulfide environment of pH 5 or higher and has a low yield ratio even after coating treatment at 300 ° C. or lower, and a method for producing the same It aims at providing a welded steel pipe. It has a specific component composition, the metal structure has ferrite, bainite, and island martensite, the area fraction of the island martensite is 0.5 to 5.0%, and the ferrite and bainite Difference in hardness with respect to Vickers hardness is 60 or more, and the uniform elongation is 9% or more and the yield ratio is 90% or less before and after the strain aging treatment at a temperature of 300 ° C. or less. High deformability steel for pipes with excellent strain aging characteristics and HIC resistance.