| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a low yield ratio high tensile strength thick steel plate (with a plate thickness of≤100 mm) which is used in the fields of civil engineering, building, bridges or the like. SOLUTION: The low yield ratio high tensile strength thick steel plate having excellent toughness in a super-large heat input weld heat-affected zone has a composition which contains C, Si, Mn, P, S, Al, B, Ti and N of the prescribed contents, and contains one or more selected from among Cr, Mo, Nb and V, and further contains one or more selected from among Cu and Ni in such an amount that the value of ([%Mn]/6+[Cu]/15+[%Ni]/15) becomes 0.20 to 0.38, wherein Ceq satisfies 0.46 to 0.60, Pcm satisfies≤0.28 and P<SB>SR</SB>satisfies≤0.30, and the balance comprising Fe and inevitable impurities. The steel plate has a microstructure including a rich region in which the contents of Mn, Cu and Ni are higher than those of the average in the steel, and a lean region in which the contents of Mn, Cu and Ni are lower than those of the average, wherein the fraction of the lean region in which the value of ([%Mn]/6+[%Cu]/15+[%Ni]/15) is≤85% of the average of the steel is≥15%. COPYRIGHT: (C)2011,JPO&INPIT |
