| 摘要 |
PROBLEM TO BE SOLVED: To produce a tempered high tensile strength steel plate excellent in homogeneity in the plate thickness direction and small in the anisotropy of toughness by composing it of the one having a specified componental compsn. contg. C, Si, Mn, Cu, Ni or the like, and the balance Fe, and in which carbon equivalent, the index of weld crack sensitivity, the quantity of alloy elements to enter into solid solutions or the like. SOLUTION: This 950 N/mm<2> class tempered high tensile strength steel plate having a compsn. contg., by mass, 0.07 to 0.18% C, 0.05 to 0.30% Si, 0.40 to 1.30% Mn, 0.01 to 0.50% Cu, 0.8 to 3.5% Ni, 0.10 to 1.20% Cr, 0.05 to 0.80% Mo and 0.005 to 0.1005 V, contg. Al, Nb and B, in which the contents of N, P and S are regulated, and the balance Fe, in which carbon equivalent Ceq (formula I) is regulated to 0.52 to 0.61%, the index of weld crack sensitivity PcM (formula II) is regulated to 0.25 to 0.31%, the solid solution quantity (formula III) of alloy elements is regulated to >=0.88%, the average grain size of Nb compounds is regulated to <=8 nm, the volume fractional rate is regulated to 1.5×10<-4> to 5.0×10<-4> , the average size No. of old austenitic grains is regulated to >=8, and the degree of elongation AI1 is regulated to <=1.5 is produced.
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