| 摘要 |
PURPOSE: Provided is a process of preparing high-strength steel improved in mother material strength by using bainite and ferrite as a mother material while improving the toughness of a heat influencing part during welding using fine TiN precipitates and TiO. Whereby, the product can be effectively used in welded structures such as architecture, bridge, shipbuilding, marine structure, steel pipe, line pipe or the like. CONSTITUTION: A steel slab consisting of, by weight ratio, 0.03-0.17% C, 0.01-0.5% Si, 0.4-2.0% Mn, 0.005-0.2% Ti, 0.0005-0.1% Al, 0.008-0.030% N, 0.0003-0.01% B, 0.001-0.2% W, 0.03% or less P, 0.03% or less S, 0.002-0,03% O, and the balance Fe with inevitable impurities and satisfying 1.2<=Ti/N<=2.5, 10<=N/B<=40, 2.5<=Al/N<=7, 6.5<= (Ti+2Al+2B)/N<=14, 4<=Ti/O<=10 is heated at 1,100 to 1,250deg.C for 60 to 80 min, hot rolled in a rolling ratio of 40% or more and cooled at a speed of 5 to 20deg.C/sec at a bainite transformation temperature±10deg.C. The steel slab is obtained by pouring a deoxidizing element to molten metal, deoxidizing with a Ti deoxidizer and adding Ti.
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