STEEL PLATE FOR LINEPIPE HAVING ULTRA-HIGH STRENGTH AND EXCELLENT LOW TEMPERATURE TOUGHNESS AND MANUFACTURING METHOD OF THE SAME

摘要

A steel plate for linepipes having ultra-high strength and excellent low temperature toughness, and a method for manufacturing the same are disclosed . The steel plate has strength of 930 MPa or more and excellent toughness ev en with much smaller amounts of alloying elements than that of conventional steel plates, and a method for manufacturing the same. The steel comprises b y weight %: 0.03 ~ 0.10% C; 0 ~ 0.6% Si; 1.6 - 2.1% Mn; 0 ~ 1.0% Cu; 0-1.0% Ni; 0.02-0.06% Nb; 0-0.1% V; 0.1-0.5% Mo; 0-1.0% Cr; 0.005-0.03% Ti; 0.01-0. 06% Al; 0.0005 - 0.0025% B; 0.001 - 0.006% N; 0 - 0.006% Ca; 0.02% or less P ; 0.005% or less S; and the balance of Fe and unavoidable impurities. The mi crostructure comprises at least about 75 area percent of a mixture of bainit ic ferrite and acicular ferrite.