Steel sheet and manufacturing method thereof
AssigneePosco
InventorsSeong-Ho Han, Yu-Mi Ha
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Abstract
A steel sheet according to the present invention comprises, in weight %: 0.008-0.015% of C, 0.200% or less of Si; 1.30-2.00% of Mn; 0.5-1.0% of Cr; 0.030% or less of P; 0.010% or less of S; 0.0020-0.0080% of N; and 0.010-0.060% of Al, the remainder being Fe and inevitable impurities, wherein the value of K defined in relational expression 1 is 0 to 15.000, and the microstructure may include, by area %, 0.30-0.80% of a transformed structure, the remainder being ferrite. [Relational expression 1] K=−651[C]−2.42[Mn]+25.7[Cr]−220[N] (In the formula, [C], [Mn], [Cr] and [N] are the weight % of the respective elements.)
Claims11
A steel sheet comprising, by wt %, 0.008 to 0.015% of C, 0.200% or less of Si, 1.30 to 2.00% of Mn, 0.5 to 1.0% of Cr, 0.030% or less of P, 0.010% or less of S, 0.0020 to 0.0080% of N, 0.010 to 0.060% of Al, and the balance of Fe and inevitable impurities,
- wherein a K value defined by the following Relational Expression 1 is 0 to 15.000, and
- a microstructure includes, by area %, 0.30 to 0.80% of a transformed structure and a balance of ferrite:
- K
- =
- -
- 6
-
- 51
- [
- C
- ]
- -
- 2.42
- [
- Mn
- ]
- +
- 25.7
- [
- Cr
- ]
- -
- 220
- [
- N
- ]
- [
- Relational
-
- Expression
-
- 1
- ]
- wherein [C], [Mn], [Cr], and [N] represent wt % of the respective elements.
A method for manufacturing a steel sheet, the method comprising:
- reheating a steel slab including, by wt %, 0.008 to 0.015% of C, 0.200% or less of Si, 1.30 to 2.00% of Mn, 0.5 to 1.0% of Cr, 0.030% or less of P, 0.010% or less of S, 0.0020 to 0.0080% of N, 0.010 to 0.060% of Al, and the balance of Fe and inevitable impurities, the steel slab having a K value of 0 to 15.000 defined by the following Relational Expression 1;
- performing finish hot rolling on the reheated steel slab;
- cooling the finish hot-rolled steel sheet to a temperature range of 550 to 700° C. and then coiling the cooled steel sheet;
- cold rolling the coiled steel sheet;
- and
- continuously annealing the cold-rolled steel sheet in a temperature range of 760 to 830° C.:
- K
- =
- -
- 6
-
- 51
- [
- C
- ]
- -
- 2.42
- [
- Mn
- ]
- +
- 25.7
- [
- Cr
- ]
- -
- 220
- [
- N
- ]
- [
- Relational
-
- Expression
-
- 1
- ]
- wherein [C], [Mn], [Cr], and [N] represent wt % of the respective elements.
Dependencies are inferred from the claim text.