Ultra-high strength sheet having excellent hole expansion ratio, and method for manufacturing same

A method for manufacturing a steel sheet comprising:

• reheating a steel slab including by weight %, 0.1 to 0.3% of carbon (C), 0.5% or less (excluding 0%) of silicon (Si), 1.0 to 3.0% of manganese (Mn), 0.0005 to 0.003% of boron (B), 0.01% or less (excluding 0%) of phosphorus (P), 0.01% or less (excluding 0%) of sulfur(S), 0.01% or less (excluding 0%) of nitrogen (N), 0.01 to 0.1% of aluminum (Al), with a remainder of Fe and other inevitable impurities, at a temperature within a range of 1100 to 1300° C.;
• hot rolling the reheated slab to manufacture a hot-rolled steel sheet;
• coiling the hot-rolled steel sheet at a temperature within a range of 400 to 600° C.;
• cold rolling the coiled hot-rolled steel sheet at a reduction ratio of 30 to 80%;
• annealing the cold-rolled steel sheet by heat treatment at a temperature within a range of Ac3+10° C. to Ac3+80° C.,
• wherein in the annealing operation, a dew point temperature is controlled to be −40° C. or lower at a temperature of Ac3+10° C. or lower, and a dew point temperature is controlled to be from −30° C. to +30° C. at a temperature within a range of Ac3+10° C. to Ac3+80° C.