HIGH STRENGTH THICK STEEL PLATE FOR LINEPIPE HAVING EXCELLENT FRACTURE PROPAGATION ARRESTABILITY CHARACTERISTICS IN CENTER THEREOF AND METHOD FOR MANUFACTURING THE SAME

摘要

The present invention relates to a high strength afterglow steels for line pipes having excellent breakage and propagation stopping characteristics at the center and a method of manufacturing the same. An embodiment of the present invention is a steel sheet comprising, by weight%, 0.04 to 0.09% of C, 0.05 to 0.50% of Si, 0.5 to 2.0% of Mn, 0.01 to 0.05% of Al, 0.005 to 0.02% of Ti, 0.01 to 0.05% of Cr, 0.05 to 0.35% of Cr, 0.1 to 0.4% of Ni, 0.05 to 0.3% of Mo, 0.015% or less of P, 0.003% or less of S, , Ca: 0.0005 to 0.004%, balance Fe and other unavoidable impurities, and having an area fraction of 50 to 65% of needle ferrite, 30 to 45% of bainite, less than 10% of equiaxed ferrite and less than 5% of martensite Which is excellent in fracture propagation stopping characteristics at a center portion having a microstructure including a microstructure, and a method of manufacturing the same. According to the present invention, there is provided a backing steel sheet for a line pipe having a yield strength of not less than 555 MPa and a thickness of not less than 25 mm by securing a core DWTT ductile wavefront ratio of 85% or more at a guaranteed temperature of -30 캜 or lower .