Cold-rolled steel sheet having excellent strength and elongation and method for manufacturing same
AssigneePosco
InventorsMinho Jo, Young-Kwang Hong
Life of this patent
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Abstract
A cold-rolled steel sheet having improved strength and elongation, according to one embodiment of the present invention, comprises, in weight %: 0.04-0.08% of C; 0.05% or less (excluding 0%) of Si; 0.1-0.6% of Mn; 0.02-0.06% of Al; 0.015% or less (excluding 0%) of P; 0.015% or less (excluding 0%) of S; 0.006% or less (excluding 0%) of N; 0.02-0.04% of Nb; and the remainder of Fe and other inevitable impurities, wherein the cold-rolled steel sheet has a component reinforcement index defined by expression 1 of 470 or less, a crystal grain aspect ratio defined by expression 2 of 2.15 or less, and a composite reinforcement index defined by expression 3 of 500 to 600.
Claims11
A cold-rolled steel sheet having excellent strength and elongation comprising, by weight:
- 0.04 to 0.08% of C;
- 0.05% or less (excluding 0%) of Si;
- 0.1 to 0.6% of Mn;
- 0.02 to 0.06% of Al;
- 0.015% or less (excluding 0%) of P;
- 0.015% or less (excluding 0%) of S;
- 0.006% or less (excluding 0%) of N;
- 0.02 to 0.04% of Nb;
- and the remainder of Fe and other inevitable impurities,
- wherein the cold-rolled steel sheet has a component reinforcement index defined by the following [Expression 1] of 470 or less,
- a crystal grain aspect ratio defined by the following [Expression 2] of 2.15 or less, and
- a composite reinforcement index defined by the following [Expression 3] of 500 to 600:
- Component
-
- reinforcement
-
- index
- =
- 160
- +
- 1
- ,
- 000
-
- C
- +
- 100
-
- Mn
- +
- 5
- ,
- 000
-
- Nb
-
- wherein
-
- C
- ,
- Mn
- ,
- and
-
- Nb
-
- denote
-
- wt
-
- %
-
- of
-
- each
-
- component
- ,
- [
- Expression
-
- 1
- ]
- Crystal
-
- grain
-
- aspect
-
- ratio
- =
- average
-
- value
-
- of
- [
- (
- crystal
-
- grain
-
- major
-
- axis
-
- length
- )
- /
- (
- crystal
-
- grain
-
- minor
-
- axis
-
- length
- )
- ]
- [
- Expression
-
- 2
- ]
- Composite
-
- reinforcement
-
- index
- =
- [
- Expression
-
- 1
- ]
- +
- (
- [
- Expression
-
- 2
- ]
- -
- 1.8
- )
- ×
- 600.
- [
- Expression
-
- 3
- ]
A method for manufacturing a cold-rolled steel sheet having excellent strength and elongation, the method comprising:
- slab preparation of preparing a slab which includes, by weight:
- 0.04 to 0.08% of C;
- 0.05% or less (excluding 0%) of Si;
- 0.1 to 0.6% of Mn;
- 0.02 to 0.06% of Al;
- 0.015% or less (excluding 0%) of P;
- 0.015% or less (excluding 0%) of S;
- 0.006% or less (excluding 0%) of N;
- 0.02 to 0.04% of Nb;
- and the remainder of Fe and other inevitable impurities, and has a component reinforcement index defined by the following [Expression 1] of 470 or less and reheating the slab;
- hot rolling the slab and finish hot rolling the slab at Ar3 or higher to manufacture a hot rolled steel sheet;
- winding the hot rolled steel sheet at 560 to 700° C.;
- cold rolling the wound hot rolled steel sheet at a reduction rate of 80 to 95% to manufacture a cold-rolled steel sheet;
- annealing the cold-rolled steel sheet at a temperature of 720 to 800° C.;
- and
- secondary rolling the annealed cold-rolled steel sheet:
- Component
-
- reinforcement
-
- index
- =
- 160
- +
- 1
- ,
- 000
-
- C
- +
- 100
-
- Mn
- +
- 5
- ,
- 000
-
- Nb
- [
- Expression
-
- 1
- ]
- wherein C, Mn, and Nb denote wt % of each component.
11-12. (canceled)
Dependencies are inferred from the claim text.