| 摘要 |
<p>PURPOSE: An ultrahigh-strength steel sheet and a manufacturing method thereof are provided to improve strength thereof over 1180 MPa through controlling a precipitate type alloy element and a hardenability element, and through controlling a hot-rolling process. CONSTITUTION: A manufacturing method of an ultrahigh-strength steel sheet includes: a step (S110) of reheating a slab sheet material; a step (S120) of hot-rolling the reheated sheet material at a finish rolling temperature of 750 to 950°C; and a step (S130) of cooling the hot-rolled sheet material to a martensitic temperature range at an average cooling rate of 200 to 400°C/sec, and then coiling the sheet material. The sheet material includes 0.03 to 0.2 wt% of C, 0.01 to 0.5 wt% of Si, 0.8 to 2.5 wt% of Mn, 0.002 to 0.1 wt% of Al, below 0.02 wt% of P, below 0.003 wt% of S, and below 0.01 wt% of N, and further includes at least one of 0.01 to 0.1 wt% of Ti, 0.01 to 0.1 wt% of Nb, and 0.01 to 0.1 wt% of V, and further includes at least one of 0.01 to 0.1 wt% of Ni, 0.01 to 0.1 wt% of Cr, and 0.0005 to 0.004 wt% of B, and remnants Fe and inevitable impurities. [Reference numerals] (AA) Start; (BB) End; (S110) Reheat a slab (SRT: 1150-1300°C); (S120) Hot-rolling (FDT: 850±100°C); (S130) Cooling/winding (200-400°C/sec, CT: 50-350°C)</p> |
