| 摘要 |
A steel plate for linepipe is provided to improve deformability and secure high strength and high toughness at the same time by properly controlling internal structure and rolling conditions without performing an additional process of second cooling or tempering, and a method for manufacturing the steel plate for a linepipe is provided. A high strength and high toughness steel plate for linepipe excellent in deformability comprises, by weight percent, 0.04 to 0.1% of C, 0.1 to 0.4% of Si, 1.3 to 1.8% of Mn, 0.05 to 0.5% of Mo, 1.0% or less of Cr, 1.0% or less of Ni, 0.005 to 0.03% of Ti, 0.02 to 0.06% of Nb, 0.1% or less of V, 0.01 to 0.05% of Al, 1.0% or less of Cu, 0.006% or less of Ca, 0.001 to 0.006% of N, 0.02% or less of P, and 0.005% or less of S with the balance being Fe and other inevitable impurities, wherein the steel plate contains at least 20% in total of ferrite and bainitic in an internal structure by using polygonal ferrite as a matrix structure. A method for manufacturing a high strength and high toughness steel plate for linepipe excellent in deformability comprises the steps of: reheating at a temperature of 1050 to 1180 deg.C a steel slab comprising, by weight percent, 0.04 to 0.1% of C, 0.1 to 0.4% of Si, 1.3 to 1.8% of Mn, 0.05 to 0.5% of Mo, 1.0% or less of Cr, 1.0% or less of Ni, 0.005 to 0.03% of Ti, 0.02 to 0.06% of Nb, 0.1% or less of V, 0.01 to 0.05% of Al, 1.0% or less of Cu, 0.006% or less of Ca, 0.001 to 0.006% of N, 0.02% or less of P, and 0.005% or less of S with the balance being Fe and other inevitable impurities; subjecting the reheated slab to a first multistage rolling process of one or more of rolling operations at a reduction ratio of 20 to 80% in a temperature range of an austenite recrystallization temperature or higher; subjecting the first rolled slab to a second multistage rolling process of two or more of rolling operations at a reduction ratio of 60 to 80% in a temperature range of the austenite recrystallization temperature or lower; and cooling the rolled steel sheet to a temperature of 400 to 600 deg.C at a cooling rate of 5 to 10 deg.C/sec. |
