PURPOSE: To produce shape steel excellent in strength and toughness at a low cost by subjecting molten steel having a specified compsn. consisting of C, Si, Mn, N, Al and Fe to deoxidation, thereafter subjecting it to continuous casting, executing specified rolling and gradually cooling it.
CONSTITUTION: Molten steel contg., by weight, 0.04 to 0.20% C, 0.05 to 0.50% Si, 0.4 to 2.0% Mn, 0.003 to 0.015% N and ≤0.005% Al, furthermore contg., at need, prescribed amounts of V, Cr, Nb, Ni, Cu and Mo, and the balance Fe with inevitable impurities is subjected to preliminary deoxidation treatment to regulate the content of dissolved oxygen [O] into 0.003 to 0.025%, and furthermore, it is subjected to Ti deoxidation and continuous casting. The obtd. slab contg. 0.005 to 0.025% Ti and satisfying -0.006≤(Ti-2[O])≤0.008 is reheated to 1100 to 1300°C, and after that, rolling is started. If required, water-cooling treatment is executed in the process of intermediate rolling, and it is completed at 750 to 1050°C. After that, the rolled sheet is cooled to 650 to 400°C at 0.01 to 0.30°C/S cooling rate.
YAMAMOTO KOICHI
EDA KAZUHIKO
SHIBATA MASAFUMI
