HIGH-STRENGTH THICK STEEL PLATE FOR LINE PIPE HAVING EXCELLENT LOW-TEMPERATURE TOUGHNESS AND ELONGATION AND LOW YIELD RATIO AND MANUFACTURING METHOD THEREOF

摘要

The present invention relates to a high-strength thick steel plate for a line pipe having excellent low-temperature toughness and elongation and a low yield ratio and a manufacturing method thereof. According to an embodiment of the present invention, the high-strength thick steel plate for a line pipe having excellent low-temperature toughness and elongation and a low yield ratio comprises 0.03-0.055 wt% of C, 0.1-0.35 wt% of Si, 1.7-2.2 wt% of Mn, 0.01-0.04 wt% of Al, 0.005-0.025 wt% of Ti, 0.008 wt% or lower of N, 0.08-0.12 wt% of Nb, 0.2-0.45 wt% of Cr, 0.2-0.35 wt% of Ni, 0.05-0.3 wt% of Cu, 0.2-0.4 wt% of Mo, 0.02 wt% or lower of P, 0.002 wt% or lower of S, 0.0005-0.004 wt% of Ca, 0.01-0.04 wt% of V, 0.0005 wt% or lower of B, and the remainder consisting of Fe and inevitable impurities, and satisfies the following relation formulas 1-4. The microstructure includes 1-5 area% of polygonal ferrite, 60-75 area% of acicular ferrite, 20-30 area% of bainitic ferrite, and 5 area% or lower of a martensite-austenite constituent. [Relation formula 1] 19 = (Mo/96)/(P/31) = 30 [Relation formula 2] 1.42 = Cr+2Mo+Cu+Ni+1000B = 1.75 [Relation formula 3] 4 {3C/12+Mn/55} 100 = 4.9 [Relation formula 4] 600 = 400C+6800Nb+600V+800Ti+300Al = 820. The contents of the alloy elements written in the relation formulas 1-4 are in wt%.;COPYRIGHT KIPO 2020