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US 2025/0051870 A1Published application
Ultrahigh-strength hot-rolled steel sheet having excellent formability and manufacturing method therefor
AssigneePosco
InventorsTae-Jin Song, Joo-Hyun Ryu, Je-Woong Lee
Life of this patent
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Abstract
The present invention relates to a hot-rolled steel sheet that can be suitably applied to an automobile chassis structure member or the like and, more specifically, to an ultrahigh-strength hot-rolled steel sheet having tensile strength of 1180 MPa or more, excellent formability, and uniform material distribution in the steel sheet, and a manufacturing method therefor.
Claims13
An ultrahigh-strength hot-rolled steel sheet, comprising:
- by wt %, carbon ( ):
- 0.06 to 0.18%, silicon (Si):
- 0.01 to 1.8%, manganese (Mn):
- 1.6 to 3.5%, aluminum (Al):
- 0.001 to 0.1%, chromium (Cr):
- 2.5% or less (including 0%), molybdenum (Mo):
- 2.0% or less (including 0%), titanium (Ti):
- 0.01 to 0.15%, boron (B):
- 0.0005 to 0.003%, phosphorus (P):
- 0.0001 to 0.05%, sulfur(S):
- 0.0001 to 0.05%, nitrogen (N):
- 0.0001 to 0.02%, and a balance of Fe and other inevitable impurity elements,
- wherein a microstructure comprises, in area fraction, one or more selected from low-temperature bainite and martensite:
- 75 to 90%, one or more selected from acicular ferrite and bainitic ferrite:
- 10 to 25%, and other phases:
- 5% or less (including 0%).
13 more elements
A method for manufacturing an ultrahigh-strength hot-rolled steel sheet, the method comprising:
- reheating a steel slab at a temperature range of 1100 to 1350° C., the steel slab comprising, by wt %, carbon (C):
- 0.06 to 0.18%, silicon (Si):
- 0.01 to 1.8%, manganese (Mn):
- 1.6 to 3.5%, aluminum (Al):
- 0.001 to 0.1%, chromium (Cr):
- 2.5% or less (including 0%), molybdenum (Mo):
- 2.0% or less (including 0%), titanium (Ti):
- 0.01 to 0.15%, boron (B):
- 0.0005 to 0.003%, phosphorus (P):
- 0.0001 to 0.05%, sulfur (S):
- 0.0001 to 0.05%, nitrogen (N):
- 0.0001 to 0.02%, and a balance of Fe and other inevitable impurity elements,
- manufacturing a hot-rolled steel sheet by hot rolling the reheated steel slab;
- primarily cooling the hot-rolled steel sheet to a temperature equal to or less than Bs at an average cooling rate of 50° C./s or more;
- after the primary cooling, performing secondary cooling for ts time (seconds) at an average cooling rate of 25° C./s or less to a temperature equal to or higher than (Bs+Ms)/2;
- after the secondary cooling, performing tertiary cooling at an average cooling rate of 30° C./s or more to a temperature range of Ms° C. to 500° C.;
- and
- coiling in a tertiary cooling temperature range,
- wherein during the hot rolling, finish hot rolling is performed so that a value of Du, defined by the following relational expression 1, satisfies a range of 2 to 10 in a temperature range of 750 to 1150° C.,
- 〈
- Relational
-
- Expression
-
- 1
- 〉
- Du
- =
- {
- FDT
- +
- (
- 7.4
- ×
- [
- C
- ]
- )
- -
- (
- 24.7
- ×
- [
- Si
- ]
- )
- -
- (
- 4.7
- ×
- [
- Mn
- ]
- )
- -
- (
- 3.9
- ×
- [
- Cr
- ]
- )
- -
- (
- 5.2
- ×
- [
- Mo
- ]
- )
- -
- (
- 560
- ×
- [
- Ti
- ]
- )
- -
- (
- 1110
- ×
- [
- Nb
- ]
- )
- }
- ×
- 0.049
- -
- 34.2
- ,
- where FDT refers to a rolling end temperature (° C.), and each of [C], [Si], [Mn], [Cr], [Mo], [Ti] and [Nb] represents a weight percent content of an element in parentheses.
90 more elements
Dependencies are inferred from the claim text.