THICK STEEL SHEET FOR SOUR RESISTANT LINEPIPE, AND MANUFACTURING METHOD THEREFOR

摘要

To provide a thick steel sheet for sour resistant linepipe excellent in HIC resistance, DWTT property and SSC resistance, and a manufacturing method therefor.SOLUTION: There is provided a thick steel sheet for sour resistant linepipe having a chemical composition containing, by mass%, C:0.03 to 0.06%, Si:0.10 to 0.60%, Mn:1.30 to 1.80%, P:0.010% or less, S:0.0010% or less, Nb:0.003 to 0.040%, Al:0.0010 to 0.050%, Ti:0.005 to 0.020%, N:0.002 to 0.006%, Ca:0.0010 to 0.0050%, O:0.0030% or less, B:0.0003% or less, other optional element and balance:Fe with impurities, and satisfying [0.05≤Cu+Ni+Cr+Mo+V≤0.80], a metallic structure on a surface layer having, by area percentage, ferrite:10 to 40%, a hard phase:3.0% or less, and the balance:bainite, and average crystal particle diameter of 15.0 μm or less, a metallic structure at a sheet thickness center part having, by area percentage, ferrite:30% or less, the hard phase:2.0% or less, and the balance:bainite, average crystal particle diameter of 20.0 μm or less, surface hardness of 200 HV or less, and sheet thickness of 25 to 40 mm.SELECTED DRAWING: None