| 摘要 |
PURPOSE: To provide a manufacturing method of high tensile strength plate for line pipes with high tensile strength and excellent corrosion resistance as well as superior impact toughness even in a ultra-low temperature environment by reducing content of Mn in a composition for steel, properly adding Cu and Ni to the composition and properly controlling manufacturing conditions. CONSTITUTION: The manufacturing method comprises the steps in spheroidizing CaS inclusion by dividingly injecting molten steel comprising 0.07 to 0.11 wt.% of C, 0.20 to 0.30 wt.% of Si, 1.00 to 1.30 wt.% of Mn, 0.020 wt.% or less of P, 0.003 wt.% or less of S, 0.10 to 0.30 wt.% of Cu, 0.10 to 0.25 wt.% of Ni, 0.040 to 0.060 wt.% of Nb, 0.060 to 0.080 wt.% of V, 0.005 to 0.020 wt.% of Ti, 0.020 to 0.040 wt.% of soluble Al and a balance of Fe and other inevitable impurities and having 0.262 to 0.379% of carbon equivalent(Ceq) twice in a Ca-Si shape during powder injection treatment and in a Ca-wire shape during vacuum degassing treatment in secondary refining; reheating a spheroidized slab; rough rolling the reheated slab to a remaining reduction ratio of 80±5% in a temperature range of 980±20 deg.C; completing the finish rolling on the rough rolled steel in a temperature range of 760±20 deg.C by starting finish rolling on a rough rolled steel from a temperature of 900±20 deg.C that is a non-crystallization temperature range in the state that a remaining reduction ratio is 75±5%; and accelerated cooling the finish rolled steel to a temperature range of 480±20 deg.C in a cooling rate of 8 to 12 deg.C/second.
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