PURPOSE: To manufacture high-strength and high-toughness steel with superior weldability by heating a low C steel slab having a specified composition contg. a very small amount of added Ti to a medium temp., rolling the heated slab at a sufficient draft, and slowly cooling the rolled slab after restoring the austenite.
CONSTITUTION: A steel slab consisting of 0.005W0.14% C, ≤0.6% Si, 0.7W2.2% Mn, ≤0.008% S, 0.005W0.08% Al, 0.004W0.03% Ti, ≤0.007% N and the balance Fe with inevitable impurities or further contg. one or more among 0.01W0.10% Nb, 0.01W0.10% V, 0.1W4.0% Ni, 0.1W1.0% Cu, 0.1W1.0% Cr, 0.05W0.30% Mo, 0.0005W0.005% Ca and 0.003W0.03% REM is heated to 1,000W1,200°C and rolled so as to regulate the draft at ≤900°C to ≥60% and the finishing temp. to 640W 850°C. After the passage of 30W180sec, the rolled slab is cooled to an arbitrary temp. below 500°C at 10W40°C/sec cooling rate.
ONOUE YASUMITSU
OOHASHI MAMORU
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