THICK STEEL SHEET FOR LINEPIPE AND MANUFACTURING METHOD THEREFOR

摘要

To provide a thick steel sheet for linepipe excellent in DWTT property and HIC resistance and a manufacturing method therefor.SOLUTION: There is provided a thick steel sheet for linepipe having a chemical composition of a steel sheet containing, by mass%, C:0.03 to 0.08%, Si:0.10 to 0.50%, Mn:1.00 to 1.80%, P:0.020% or less, S:0.0010% or less, Cu:0.10 to 0.50%, Ni:0.10 to 0.50%, Nb:0.005 to 0.050%, Ti:0.005 to 0.030%, Al:0.010 to 0.040%, N:0.0010 to 0.0050%, B:0.001% or less, optional elements or the like, and the balance:Fe with impurities, and having Pcm of 0.15 to 0.23, and Ceq of 0.35 to 0.43, a metallic structure at a sheet thickness center part containing, by area percentage, 20 to 35% of ferrite, and 2.0% or less of a hard phase, and the balance bainite, average crystal particle diameter of ferrite at a sheet thickness center part of 20.0 μm or less, difference between area percentage of ferrite in a steel sheet surface layer and area percentage of ferrite at the sheet thickness center part of 5.0% or less, maximum longer diameter of an inclusion of 30.0 μm or less, and sheet thickness of 30 to 45 mm.SELECTED DRAWING: None