TS above 570MPa, the total elongation 25 or more and below fatigue crack propagation velocity 8.75x109m/cycle with K=15MPam, production methodological null mass of the thick steel sheet below board thickness 20mm which is superior in total elongation and fatigue crack

摘要

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thick steel plate that is as thin as the thickness of 20 mm or less, is superior in total elongation and fatigue crack propagation resistance, and is suitable for a welded structure such as a marine vessel, to which structural safety is strongly required.;SOLUTION: This manufacturing method includes the steps of: preparing a steel which comprises, by mass%, 0.03% or more but less than 0.10% C, 0.05-0.50% Si, 0.5-2.0% Mn, 0.05% or less P, 0.02% or less S and one or more of Cu, Ni, Cr, Mo, Nb, V, Ti, B and Ca as needed, while satisfying a value of Ceq={C}+{Mn}/6+{Cu+Ni}/15+{Cr+Mo+V}/5 to be 0.3-0.4, wherein each element represents its content (mass%), and the balance Fe with unavoidable impurities; heating the steel to 1,000-1,250C; rolling the steel at a rolling-finishing temperature of the Ar₃ point or higher so that the cumulative rolling reduction at the Ar₃ point or higher becomes 50% or more; and subsequently acceleratingly cooling the plate from the temperature range of the Ar₃ point or higher to 600-300C at 10C/s or more, on the line.;COPYRIGHT: (C)2010,JPO&INPIT