HIGH STRENGTH LINEPIPE STEEL PLATE FOR LARGE DIAMETER PIPE WITH HIGH LOW-TEMPERATURE DUCTILITY AND HIC RESISTANCE AT THE H2S CONTAINING ENVIRONMENT AND MANUFACTURING METHOD THEREOF

摘要

A high strength steel for large diameter linepipe with excellent hydrogen induced cracking resistance and low-temperature toughness is provided to obtain a steel with high hydrogen induced cracking resistance by optimizing a steel composition and controlling rolling conditions and cooling conditions, thereby properly controlling fraction of the entire second phase, fraction of acicular ferrite and hardness of a central part in the microstructure, and a manufacturing method thereof is provided. A manufacturing method of a high strength steel for large diameter linepipe with excellent hydrogen induced cracking resistance and low-temperature toughness comprises the steps of: reheating a steel slab in a temperature range of 1100 to 1200 deg.C, the steel slab having a composition comprising 0.01 to 0.06 wt.% of C, 0.1 to 0.4 wt.% of Si, 1.0 to 1.5 wt.% of Mn, 0.05 to 0.3 wt.% of Ni, 0.05 to 0.3 wt.% of Cu, 0.005 to 0.1 wt.% of Al, 0.015 wt.% or less of P, 0.002 wt.% or less of S, 0.0005 to 0.004 wt.% of Ca, 0.01 to 0.08 wt.% of Nb, 0.002 to 0.007 wt.% of N, and at least one component selected from the group consisting of 0.5 wt.% or less of Cr, 0.5 wt.% or less of Mo, and 0.003 wt.% or less of B with the balance of Fe and other inevitable impurities, the Ca and the S satisfying the relation of 1.2