| 摘要 |
PROBLEM TO BE SOLVED: To produce a high tensile strength steel having >=70 kgf/mm2 tensile strength and high in productivity. SOLUTION: This steel has a compsn. contg., by weight, 0.20 to 0.30% C, 0.01 to 0.50% Si, 1.00 to 3.00% Mn, <=0.030% P, 0.001 to 0.020% S, 0.03 to 0.20% V, 0.005 to 0.017% Ti, 0.005 to 0.070% Al, 0.007 to 0.030% N, and the balance Fe with inevitable impurities and has <=70 kgf/mm2 tensile strength. If required, the steel furthermore contains one or more kinds among <=1.5% Cu, <=3.0% Ni, <=1.0% Cr and <=1.0% Mo in the range satisfying Cu+Ni+3×Cr+3 Mo<=3.0%. The steel moreover contains <=0.10% Nb and 0.0005 to 0.010% Mg if necessary as well. The steel is subjected to hot rolling preferably at 1150 to 1300 deg.C heating temp. and also at >=900 deg.C finishing temp.
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