| 摘要 |
PURPOSE:To manufacture steel sheet superior in toughness and stopping characteristic for brittle crack propagation at low cost, by hot rolling a steel having a specified compsn. contg. C, Si, Mn, Al and Ti under a specified condition, then controlledly cooling, further rolling the plate under particular light rolling reduction. CONSTITUTION:Steel slab composed of, by weight 0.02-0.10% C, 0.03-0.60% Si, 0.7-2.0% Mn, 0.005-0.08% Al, 0.005-0.03% Ti, further if necessary, one kind or more among <=0.05% Nb, <=0.1% V, <=0.5% Cu, <=1.0% Ni, <=0.5% Cr, <=0.5% Mo, <=0.003% B, 0.0005-0.005% Ca, 0.0005-0.01% REM and the balance Fe with inevitable impurity is heated to 900-1,150 deg.C. Thereafter, the steel slab is pressed down by >=50% accumulative draft at unrecrystallization temp. range, to finish the rolling at Ar3-Ar3+40 deg.C range. Thereafter, immediately the plate is cooled to <=600 deg.C by 2-20 deg.C/sec rate. Next, rolling of 1-5% accumulative draft is applied by 0.5-2% draft per one time at <600-200 deg.C range.
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