Ultra high strength hot-rolled steel and method of fabricating the same

The present invention provides hot-rolled ultra high strength steel setting ingredient design and a manufacture condition to satisfy not only strength/formability/shape which are demanded quality but also deviation reduction of material quality, and a manufacturing method for the same. According to an embodiment of the present invention, the manufacturing method for the same includes: a first step of reheating a slab material at the temperature of 1200C or greater; a second step of hot-rolling the slab material in the condition of a finishing delivery temperature (FDT) of 880-920C; a third step of slowly cooling the slab material at a cooling speed of 30 C/s or less; and a fourth step of winding the slab material at the temperature of 600-640C. The slab material is composed of: 0.04-0.07 wt% of carbon (C); 0.03 wt% or less (exceeding 0 wt%) of silicon (Si): 1.3-1.5 wt% of manganese (Mn); 0.02 wt% or less (exceeding 0 wt%) of phosphorous (P); 0.03 wt% or less (exceeding 0 wt%) of sulfur (S); 0.065-0.075 wt% of titanium (Ti); 0.055-0.065 wt% of niobium (Nb); and residues composed of Fe and inevitable impurities. 본 발명의 일 실시예에 따른 열연 초고강도강의 제조 방법은 탄소(C): 0.04~0.07 중량%, 실리콘(Si): 0.03 중량% 이하(0 중량% 초과), 망간(Mn): 1.3~1.5 중량%, 인(P) : 0.02 중량% 이하(0 중량% 초과), 황(S) : 0.03 중량% 이하(0 중량% 초과), 티타늄(Ti) : 0.065~0.075 중량%, 니오븀(Nb) : 0.055~0.065 중량% 및 나머지가 철(Fe)과 불가피한 불순물로 이루어진 슬라브재를 1200℃ 이상에서 재가열하는 제 1 단계; 상기 슬라브재를 마무리압연온도(Finishing Delivery Temperature, FDT): 880~920℃ 조건으로 열간 압연하는 제 2 단계; 상기 슬라브재를 30℃/s 이하의 냉각속도로 서냉하는 제 3 단계; 및 상기 슬라브재를 600~640℃의 온도에서 권취하는 제 4 단계;를 포함한다.