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US 2023/0416860 A1Published application
High yield ratio and high strength steel sheet having excellent thermal stability, and manufacturing method therefor
AssigneePosco
InventorsSung-Il KIM, Hyun-Taek NA
Life of this patent
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Abstract
Provided is a high strength steel sheet and a manufacturing method therefor, and, more specifically, to a steel sheet and a manufacturing method therefor, the steel sheet having excellent thermal stability to have high yield ratio and high strength even after heat treatment at a relatively low temperature.
Claims10
A high strength steel sheet, comprising:
- by wt %, C:
- 0.02 to 0.08%, Si:
- 0.01 to 0.5%, Mn:
- 0.8 to 1.8%, Al:
- 0.01 to 0.1%, P:
- 0.001 to 0.02%, S:
- 0.001 to 0.01%, N:
- 0.001 to 0.01%, Ti:
- 0.0005 to 0.13%, Nb:
- 0.005 to 0.06%, Mo:
- 0.001 to 0.2%, the balance, and unavoidable impurities,
- wherein a |K| value is 0.8 or less defined in the following Relational Expression 1,
- an RA value is 5 to 9.2 defined in the following Relational Expression 2,
- a microstructure includes ferrite of 95 area % or more and the remaining pearlite, and
- a CN value is 1.5 or more defined in the following Relational Expression 3.
- |K|=−0.555−1.27[C]+0.043[Si]−0.113[Mn]+0.08[Ti]+0.086[Nb]2 [Relational Expression 1]
- (where [C], [Si], [Mn], [Ti], and [Nb] are wt % of the corresponding alloy element.)
- RA=([Ti]/48+[Mo]/96+[V]/51)/([Nb]/93) [Relational Expression 2]
- (where [Ti], [Mo], [V], and [Nb] are wt % of the corresponding alloy element.)
- CN=NGB×103×NG−1 [Relational Expression 3]
- (where NGB and NG each are the number of precipitates having a diameter of 50 nm or less formed within a grain boundary and a crystal grain of ferrite within a unit area (1 mm2).)
18 more elements
A method of manufacturing a high strength steel sheet, comprising:
- reheating a steel slab in a temperature range of 1100 to 1350° C., the steel slab including, by wt %, C:
- 0.02 to 0.08%, Si:
- 0.01 to 0.5%, Mn:
- 0.8 to 1.8%, Al:
- 0.01 to 0.1%, P:
- 0.001 to 0.02%, S:
- 0.001 to 0.01%, N:
- 0.001 to 0.01%, Ti:
- 0.0005 to 0.13%, Nb:
- 0.005 to 0.06%, Mo:
- 0.001 to 0.2%, the balance, and unavoidable impurities, a |K| value of 0.8 or less defined in the following Relational Expression 1, and an RA value of 5 to 9.2 defined in the following Relational Expression 2;
- hot rolling the reheated steel slab at a rolling end temperature of 850 to 1150° C.;
- cooling the hot-rolled steel sheet to a temperature range of 550 to 700° C. at a cooling rate of 10 to 70° C./s and then coiling the steel sheet;
- and
- cooling the coiled steel sheet to a temperature of 500° C. or less at a cooling rate of 10 to 50° C./h.
- |K|=−0.555−1.27[C]+0.043[Si]−0.113[Mn]+0.08[Ti]+0.086[Nb]2 [Relational Expression 1]
- (where [C], [Si], [Mn], [Ti], and [Nb] are wt % of the corresponding alloy element.)
- RA=([Ti]/48+[Mo]/96+[V]/51)/([Nb]/93) [Relational Expression 2]
- (where [Ti], [Mo], [V], and [Nb] are wt % of the corresponding alloy element.)
16 more elements
Dependencies are inferred from the claim text.