| 摘要 |
<p>PURPOSE: A steel plate is provided to have excellent impact toughness at a low temperature, and to have 490-630 MPa of a tensile strength (TS) and more than 21% of an elongation ratio (El), and to have 200-400 J of impact absorption energy at -60°C. CONSTITUTION: A method of manufacturing a steel sheet comprises the following steps: a slab board comprises 0.05-0.10% of C, 0.2-0.4% of Si, 1.0-1.7% of Mn, less than 0.05% of Al, less than 0.012% of P, less than 0.003% of S, 0.01-0.03% of Nb, less than 0.0005% of B, 0.01-0.02% of Ti, less than 0.03% of Ca, less than 0.005% of N, and a rest iron (Fe) and an unavoidable impurity as a weight%; the slab board is re-heated at 1150-1200°C of a slab reheating temperature (SRT) (S110); the re-heated slab board is primary-rolled in an austenite re-crystallization area (S120); the board is secondary-rolled in an austenite non re-crystallization area (S130); and the board is cooled at 5-9°C/sec of a speed until 400-550°C (S140). [Reference numerals] (AA) Start; (BB) End; (S110) Reheat a slab; (S120) First rolling; (S130) Second rolling; (S140) Cooling</p> |
