| 摘要 |
PURPOSE: To produce a high tensile strength steel plate excellent in toughness by applying controlled rolling to a low carbon/low alloy steel of specific composition. CONSTITUTION: A steel, having a composition consisting of, by weight ratio, 0.10-0.20% C, 0.03-0.60% Si, 0.50-2.00% Mn, 0.10-0.80% Mo, 0.008-0.100% Nb, 0.005-0.060% sol. Al, 0.0005-0.0015% B, and the balance Fe with inevitable impurities, is used. It is preferable to further incorporate one or >=2 kinds among <=0.50% Cu, <=1.50% Ni, <=1.00% Cr, <=0.10% V, and <=0.05% Ti. A steel slab of this composition is heated to 1100-1250 deg.C and rolled. At this time, the cumulative rolling reduction in the temp. range between (Ar1 +30) and (Ar3 -10) deg.C and finishing temp. are regulated to 16-30% and (Ar1 +10)±20 deg.C, respectively, and, after rolling, tempering treatment is applied at a temp. not higher than the Ac1 point. By this method, the mechanical properties of 780N/mm<2> tensile strength, 685N/mm<2> yield strength, 16% elongation, and >=471vE-20 value can be obtained.
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