| 摘要 |
PURPOSE:To produce a steel sheet having excellent strength and toughness and a small difference in the sectional hardness in the thickness direction thereof by subjecting steel having a specific compsn. contg. C, Si, Mn, Al, N, and Fe to heating and hot rolling after continuous casting then to controlled cooling. CONSTITUTION:The steel which contains over 0.09-<0.18wt.% C, 0.05-<0.50% Si, 0.7-<1.8% Mn, 0.005-<0.1% Al, and <0.006% N, is added with >=1 kinds of <=1.0% Ti, Zr, Nb, V, Ta, <=1.0% Ni, Cr, Mo, Cu, and <=0.003% B, has <=0.36% carbon equiv. C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15 and consists of the balance Fe and unavoidable impurities is continuously cast. The resultant ingot is heated to 1,000-1,200 deg.C and is rolled at >=60% in the recrystallization region of austenite. The hot rolling is ended in the recrystallization region. The steel sheet is thereafter cooled at >=15 deg.C/sec cooling rate from the Ar3 temp. or above down to 500-650 deg.C. The desired steel sheet is thereby obtd. with high efficiency.
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