High strength hot-rolled steel sheet having excellent workability, and method for manufacturing the same

A high strength hot-rolled steel sheet having excellent formability, comprising:

• by weight %, 0.1-0.15% of C, 2.0-3.0% of Si, 0.8-1.5% of Mn, 0.001-0.05% of P, 0.001-0.01% of S, 0.01-0.1% of Al, 0.7-1.7% of Cr, 0.0001-0.2% of Mo, 0.02-0.1% of Ti, 0.01-0.03% of Nb, 0.001-0.005% of B, 0.1-0.3% of V, 0.001-0.01% of N, and a balance of Fe and inevitable impurities,
• wherein [relational expression 1] and [relational expression 2] are satisfied,
• wherein a microstructure of the hot-rolled steel sheet includes, by an area fraction, 5-15% of ferrite, 5-20% of retained austenite, and 10% or less of inevitable structure, in addition to a bainite matrix structure, and
• wherein tensile strength (TS) is 1180 MPa or more, a product (TS×El) of tensile strength and elongation is 20,000 MPa % or more, and a product (TS×HER) of tensile strength and hole expandability is 30,000 MPa % or more,
• 20≤Hγ≤50
• Hγ=194.5−(428[C]+11[Si]+45[Mn]+35[Cr]−10[Mo]−107[Ti]−56[Nb]−70[V]) [Relational expression 1]
• where [elemental symbol] indicates a content (weight %) of each element
• 0.7≤ap≤3.5
• ap=([Mo]+[Ti]+[Nb]+[V])×[C]−1 [Relational expression 2]
• where [elemental symbol] indicates a content (weight %) of each element.