| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a steel with high strength for a line pipe superior in HIC(hydrogen induced cracking) resistance. SOLUTION: This method comprises manufacturing a steel slab, which includes, by mass%, 0.03-0.06% C, 0.05-0.5% Si, 1.0-1.8% Mn, 0.01% or less P, 0.002% or less S, 0.02-0.05% Nb, 0.005-0.02% Ti, 0.01-0.07% Al, 0.0005-0.0025% Ca, 0.0001-0.0025% Mg, 0.003% or less O, and one or more of Cu, Ni, Mo, and Cr, and satisfies the expressions, 0.76([S]-0.8[Ca]+0.1[O])/[Mg]<=1, and 0.28<=Ceq<=0.45, from a molten steel having a slag oxidation degree of 0.5-3.0% during refinement in a ladle, heating it, then hot rolling, and acceleratingly cooling it to 600 deg.C or lower. |
