High strength hot-rolled steel sheet having excellent formability, and manufacturing method therefor

A manufacturing method for a high-strength hot-rolled steel sheet having excellent formability, comprising operations of:

• reheating a steel slab including, by weight:
• carbon (C):
• 0.05 to 0.17%, silicon (Si):
• 0.01 to 1.5%, manganese (Mn):
• 1.5 to 3.0%, aluminum (Al):
• 0.01 to 0.1%, chromium (Cr):
• 2.0% or less (including 0%), molybdenum (Mo):
• 2.0% or less (including 0%), titanium (Ti):
• 0.01 to 0.15%, phosphorus (P):
• 0.001 to 0.05%, sulfur (S):
• 0.0001 to 0.05%, nitrogen (N):
• 0.0001 to 0.02%, with a balance of Fe and other unavoidable impurities, the steel slab satisfying the following Relational Expression 1 to a temperature within a range of 1100 to 1350° C.;
• hot rolling the reheated steel slab to manufacture a hot-rolled steel sheet;
• primarily cooling the hot-rolled steel sheet to a temperature of Bs or lower at a cooling rate of 70° C./s or more;
• secondarily cooling the steel sheet to a temperature of (Bs+Ms)/2 or higher at a cooling rate of 20° C./s or less after the primary cooling;
• tertiarily cooling the steel sheet to a temperature range of Ms−20° C. to 500° C. at a cooling rate of 30° C./s or more after the secondary cooling;
• and
• winding the steel sheet in the tertiarily-cooled temperature range,
• wherein finish hot rolling is performed to satisfy the following Relational Expression 2 within a temperature range of 750 to 1150° C. during the hot rolling, and a total reduction amount of two final passes is 10 to 40%,
• (
• 1.5
• ×
• [
• Si
• ]
• +
• 1.2
• ×
• [
• Cr
• ]
• +
• 0.7
• ×
• [
• Mo
• ]
• +
• 8.
• ×
• [
• Ti
• ]
• )
• ⁢
• ⁠
• /
• [
• C
• ]
• >
• 20
• [
• Relational
• ⁢
• Expression
• ⁢
• 1
• ]
• In Relational Expression 1, each element refers to a weight content,
• 800≤Du≤1106 [Relational Expression 2]
• In Relational Expression 2, Du is an indicator indicating an effective grain size of austenite immediately before primary cooling after hot rolling, expressed as Du=FDT+(7.35×[C])−(24.7×[Si])−(4.7×[Mn])−(3.9×[Cr])−(5.2×[Mo])−(560×[Ti])−(1110×[Nb]), where FDT refers to a rolling end temperature (° C.), and each element refers to a weight content.