| 摘要 |
PROBLEM TO BE SOLVED: To provide a low yield ratio high tensile strength thick steel plate having excellent toughness in a super-large heat input weld affected zone, which has a tensile strength of≥590 MPa and a yield ratio of≤80%, can obtain a high toughness HAZ by super-large heat input welding, and used in the fields of civil engineering, building, bridges or the like, and to provide a method for producing the same. SOLUTION: A steel stock having a composition comprising prescribed amounts of C, Si, Mn, P, S, Al, Cr, Nb, Mo, V, B, Ti, Ca, N and O, and further comprising one or more kinds selected from Cu and Ni, and in which Ceq satisfies 0.44 to 0.50, Pcm satisfies≤0.21 and ACR satisfies 0.2 to 0.8, and the balance Fe with inevitable impurities is subjected to hot rolling, so as to be a thick steel plate. The thick steel plate is then reheated at 900 to 1,000°C, is held for≥20 min, is thereafter subjected to reheat quenching treatment, is further heated to the two phase region temperature of (Ac1+20°C) to (Ac1+80°C), is held for≥30 min, is subsequently subjected to two phase region quenching treatment, and is further subjected to tempering treatment at 400 to 600°C. COPYRIGHT: (C)2010,JPO&INPIT
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