| 摘要 |
PURPOSE: To refine the structure by dispersing fine particles such as oxide and nitride also in the vicinity of the shorter side so as to prevent the toughness from being deteriorated through the coarsening of the crystal particles of a HAZ part in welding the steel. CONSTITUTION: Steel having the composition consisting of, by weight, 0.01-025% C, <=0.6% Si, 0.3-3.0% Mn, <=0.03% P, <=0.01% S, 0.0010-0.0070% O, <=1.5% Cr, Mo and Cu respectively, <=3.0% Ni, <=0.5% one or more kinds of Nb and V respectively, <=0.00005-0.002% B, and the balance Fe with inevitable impurities, and where 4-1000 disperse particles containing Ti of 02-20μm in diameter are present per unit mm<2> of the steel section is manufactured. The preliminary deoxidation is achieved by adding Si and Mn in advance, and after the concentration of dissolved oxygen is controlled to be 20-100ppm and the concentration of Al is controlled below 0.01%, Ti is added in the range of 0.005-0.05%, and the continuous casting is achieved while the braking is applied to the discharged flow of the molten steel 2 to be fed from a dipped nozzle 1 to a mold 3.
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