| 摘要 |
PURPOSE:To manufacture a steel plate having superior strength and toughness in the weld zone by properly controlling conditions during the hot rolling and normalizing of a low free-nitrogen steel. CONSTITUTION:A steel slab contg. 0.03-0.20% C, 0.05-0.60% Si, 0.60-2.50% Mn, <0.0030% [N] (free nitrogen in the steel), <0.080% Sol. Al and <0.035% Ti or further contg. one or more among <0.80% Cu, <1.00% Cr, <1.00% Ni, <0.080% Nb, <0.15% V and <0.80% Mo is subjected to controlled rolling at 680-800 deg.C finishing temp. and cooled to room temp. The resulting steel plate is normalized at a temp. between the Ar3 point of the steel and the Ar3 point + 30 deg.C to make the austenite and ferrite grains fine. A steel plate having superior strength and toughness is manufactured.
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