US2024141454A1PendingUtilityA1
Ultra high strength steel sheet having high yield ratio and excellent bendability and method of manufacturing same
Est. expiryJun 18, 2041(~14.9 yrs left)· nominal 20-yr term from priority
C21D 8/02C21D 2211/008C21D 1/26C21D 1/19C23G 1/08C21D 8/0263C21D 8/0226C21D 8/0236C21D 9/46C21D 1/18C21D 1/84C21D 6/002C21D 6/005C21D 6/008C21D 8/0205C21D 8/0278C22C 38/001C22C 38/002C22C 38/02C22C 38/04C22C 38/06C22C 38/12C22C 38/14C22C 38/26C22C 38/28C22C 38/32C22C 38/38C22C 38/22B21C 47/02C23G 1/02
66
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Claims
Abstract
Provided is an ultra high strength steel sheet having a high yield ratio, and a method for manufacturing same and, more specifically, to a steel sheet having ultra high strength, a high yield ratio and excellent bendability, and a method for manufacturing same.
Claims
exact text as granted — not AI-modified1 . A steel sheet comprising, by weight:
carbon (C): 0.1 to 0.3%, manganese (Mn): 1.0 to 2.3%, silicon (Si): 0.05 to 1 0%, phosphorous (P): 0.1% or less, sulfur 0.03% or less, aluminum (Al): 0.01 to 0.5%, with a balance of Fe and inevitable impurities, wherein an R value defined by the following Relational Expression 1 is 0.12 to 0.27, an average number of carbides per 1 μm 2 area is 40 or less, and an average length of a major axis of carbides is 300 nm or less, and a yield ratio is greater than 0.73,
R
=
{
(
Ceq
1
)
2
+
(
Ceq
2
)
2
}
2
[
Relational
Expression
1
]
Ceq
1
=
[
C
]
+
[
Mn
]
20
+
[
Si
]
30
+
2
[
P
]
+
4
[
S
]
Ceq
2
=
[
C
]
+
[
Mn
]
6
+
[
Si
]
30
+
(
[
Cr
]
+
[
Mo
]
+
[
V
]
+
[
Nb
]
)
5
+
(
[
Cu
]
+
[
Ni
]
)
15
where [C], [Mn], [Si], [P], [S], [Cr], [Mo], [V], [Nb], [Cu] and [Ni] are weight % of respective elements.
2 . The steel sheet of claim 1 , wherein the steel sheet further comprises two or more of chromium (Cr): 0.01 to 0.2%, molybdenum (Mo): 0.01 to 0.2%, and boron (B): 0.005% or less (excluding 0%).
3 . The steel sheet of claim 1 , wherein the steel sheet further comprises one or more of titanium (Ti): 0.1% or less (excluding 0%), and niobium (Nb): 0.1% or less (excluding 0%).
4 . The steel sheet of claim 1 , wherein the steel sheet comprises 99 area% or more of martensite or tempered martensite as a microstructure.
5 . The steel sheet of claim 1 , wherein the steel sheet has a tensile strength (TS) of 1300 MPa or more, a bending property (R/t) of less than 4, where R is a minimum bending radius at which cracks do not occur in a bent portion after a 90° bending test, and is a thickness of the steel sheet.
6 . A method for manufacturing a steel sheet, comprising operations of:
preparing a cold-rolled steel sheet including, by weight: carbon (C): 0.1 to 0.3%, manganese (Mn): 1.0 to 2.3%, silicon (Si): 0.05 to 1.0%, phosphorous (P): 0.1% or less, sulfur (S): 0.03% or less, aluminum (Al): 0.01 to 0.5%, with a balance of Fe and inevitable impurities, wherein an R value defined by the following Relational Expression 1 is 0.12 to 0.27, heat treating the cold-rolled steel sheet at a temperature of Ac3 or higher for 30 seconds or more; primarily cooling the cold-rolled steel sheet to a temperature within a range of 500 to 750° C. at an average cooling rate of 1 to 10° C./s after the heat treatment; secondarily cooling the primarily-cooled steel sheet to a temperature of Ms-190° C. or lower at an average cooling rate of 20 to 80° C./sec; and reheating and overaging by heating the secondarily-cooled steel sheet to a temperature within a range of greater than secondary cooling end temperature+30° C. and less than 270° C., and holding the same for 1 to 20 minutes,
R
=
{
(
Ceq
1
)
2
+
(
Ceq
2
)
2
}
2
[
Relational
Expression
1
]
Ceq
1
=
[
C
]
+
[
Mn
]
20
+
[
Si
]
30
+
2
[
P
]
+
4
[
S
]
Ceq
2
=
[
C
]
+
[
Mn
]
6
+
[
Si
]
30
+
(
[
Cr
]
+
[
Mo
]
+
[
V
]
+
[
Nb
]
)
5
+
(
[
Cu
]
+
[
Ni
]
)
15
where [C], [Mn], [Si], [P], [S], [Cr], [Mo], [V], [Nb], [Cu] and [Ni] are weight percent (%) of respective elements.
7 . The steel sheet of claim 6 , wherein the cold-rolled steel sheet further comprises two or more of chromium (Cr): 0.01 to 0.2%, molybdenum (Mo): 0.01 to 0.2%, and boron (B): 0.005% or less (excluding 0%).
8 . The steel sheet of claim 6 , wherein the cold-rolled steel sheet further comprises one or more of titanium (Ti): 0.1% or less (excluding 0%), and niobium (Nb): 0.1% or less (excluding 0%).
9 . The method for manufacturing a steel sheet of claim 6 , wherein the operation of preparing the cold-rolled steel sheet comprises operations of:
reheating a steel slab to a temperature within a range of 1100 to 1300° C.; hot rolling the reheated steel slab at a finish hot rolling temperature of Ar3 or higher; cooling and winding the hot-rolled steel sheet to a temperature within a range of 700° C. or lower; and cold rolling the cooled and wound steel sheet at a reduction ratio of 30 to 80%.
10 . The method for manufacturing a steel sheet of claim 9 , further comprising
pickling the cooled and wound steel sheet with hydrochloric acid.Join the waitlist — get patent alerts
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