| 摘要 |
PURPOSE: A process for preparing steel is provided, which is medium carbon steel being useful for marine structures, to give the removal of the occurrence for the crack generally inducing from over the steel in manufacturing. CONSTITUTION: The ingot steel composition used in the process is intended to be comprised of 0.12 to 0.17% of C, 0.30 to 0.40% of Si, 1.30 to 1.55% of Mn, 0.025% of less of P, 0.005% or less of S, 0.020 to 0.050% of soluble Al, 0.020 to 0.040% of Nb, 0.20 to 0.30% of Cu, 0.10 to 0.20% of Ni, the remaining being Fe and other evitable impurities, based on the weight of the total composition. The process is sharply characterized in that the content of B is intended to be 1ppm or less, the refined ingot steel to be treated at 10¬-1 torr or less for at least 20 min, the temperature of a tundish is continued to be 13 to 18°C, the taper in a continuous casting mold is imparted to be 1.05 to 1.15% to the mold, the speed in casting is within 0.95 to 1.05 m/min, and 0.45 to 0.50 L/Kg of the cooling water is spreaded on the casting fraction.
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