| 摘要 |
<p>PURPOSE: A steel sheet with high strength and low yield ratio and a manufacturing method thereof are provided to obtain a steel sheet suitable for a line pipe requiring moldability and vibration resistance. CONSTITUTION: A steel sheet with high strength and low yield ratio comprises C of 0.04-0.08 weight%, Si of 0.01-0.5 weight%, Mn of 1.5-2.5 weight%, Ni of 0.3-0.6 weight%, Cu of 0.5 weight% or less, Cr of 0.8 weight% or less, Mo of 0.1-0.5 weight%, Nb of 0.03-0.07 weight%, V of 0.01-0.1 weight%, Ti of 0.1-0.2 weight%, Al of 0.05 weight% or less, and Fe and inevitable impurities of the remaining amount. The steel sheet comprises a bainite ferrite structure of 40-60 area% and a martensite structure of 40-60 area%. The steel sheet has a yield ratio of 0.75 or less, a tensile strength of 950MPa or greater, and an elongation ratio of 18% or greater.</p> |
