THICK STEEL PLATE FOR HIGH TOUGHNESS LINE PIPE IN WHICH LOWERING OF YIELD STRESS CAUSED BY BAUSCHINGER EFFECT IS REDUCED AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide a steel plate in which the lowering of yield stress caused by Bauschinger effect is reduced, which can be produced at high productivity without reducing its weldability and deformability and has excellent brittle crack propagation arresting performance, and to provide its production method.;SOLUTION: The steel plate has a composition containing, by mass, 0.03 to 0.08% C, 0.01 to 0.50% Si, 1.0 to 2.0% Mn, ≤0.015% P, ≤0.005% S, ≤0.08% Al, 0.005 to 0.060% Nb, 0.005 to 0.040% Ti and 0.001 to 0.010% N, and further one or more kinds selected from Cu, Ni, Cr, Mo and V, wherein the total of the volume fractions of a ferrite phase and a bainite phase is ≥80%, the average hardness difference between the two phases is 50 to 150, the volume fraction of an insular martensite phase included in the balance is ≤2%, and the gathering degree of the (100) plane in the rolling face at the central position of the sheet thickness obtained by X-ray diffraction is ≥1.5.;COPYRIGHT: (C)2010,JPO&INPIT