US2024337003A1PendingUtilityA1
High-strength steel having high yield ratio and excellent durability, and method for manufacturing same
Est. expiryNov 4, 2039(~13.3 yrs left)· nominal 20-yr term from priority
C21D 8/02Y10T428/12799C23G 1/00C23C 2/40C23C 2/12C23C 2/06C22C 38/26C22C 38/06C22C 38/04C22C 38/02C22C 38/002C22C 38/001C21D 2211/009C21D 2211/008C21D 2211/005C21D 2211/002C21D 2211/001C21D 9/46C21D 8/0226C21D 8/0263C21D 1/02C23C 2/02C22C 38/28C22C 38/38
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Claims
Abstract
Thick high-strength steel having a high yield ratio and excellent durability, and a method for manufacturing same are provided. The thick high-strength steel having a high yield ratio and excellent durability of the present invention comprises, in percentage by weight, C: 0.05 to 0.15%, Si: 0.01 to 1.0%, Mn: 1.0 to 2.3%, Al: 0.01 to 0.1%, Cr: 0.005 to 1.0%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.07%, Ti 0.005 to 0.11%, Fe and unavoidable impurities.
Claims
exact text as granted — not AI-modified1 . A method for producing a thick high-strength steel having a high yield ratio and excellent durability, comprising:
reheating a steel slab comprising, in percentage by weight, C: 0.05 to 0.15%, Si: 0.01 to 1.0%, Mn: 1.0 to 2.3%, Al: 0.01 to 0.1%, Cr: 0.005 to 1.0%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.07%, Ti 0.005 to 0.11%, Fe and unavoidable impurities at a temperature of 1200 to 1350° C.; and producing a hot-rolled steel sheet by performing finish hot rolling on the reheated steel slab at a finish hot rolling temperature (FDT) satisfying the following [Relational Expression 1]; and cooling the hot-rolled steel sheet at a cooling rate (CR) that satisfies the following [Relational Expression 2] to a cooling termination temperature in a range of 450 to 650° C., and then coiling the hot-rolled steel sheet, wherein, when a length of the hot-rolled steel sheet constituting a coiled coil is L, an average cooling termination temperature range for a corresponding portion of the hot-rolled steel sheet to a 0 to L/5 region of a head portion of the coiled coil is controlled to A1 (550 to 650° C.), the average cooling termination temperature range for the corresponding portion of the hot-rolled steel sheet to a L/5 to 2L/3 region of the coiled coil is controlled to A2 (450 to 550° C.), the average cooling termination temperature range for the corresponding portion of the hot-rolled steel sheet to a 2L/3 to L region of the coiled coil is controlled to A3 (550 to 650° C.), and the A1-A2 and A3-A2 values are controlled at 100° C. or higher, respectively.
Tn
-
50
≤
FDT
≤
Tn
[
Relational
Expression
1
]
Tn
=
730
+
92
×
[
C
]
+
70
×
[
Mn
]
+
45
×
[
Cr
]
+
780
×
[
Nb
]
+
520
×
[
Ti
]
-
80
×
[
Si
]
-
1.4
×
(
t
-
5
)
C, Mn, Cr, Nb, Ti, and Si in the above Relational Expression 1 are % by weight of the corresponding alloy element,
the FDT of the above Relational Expression 1 is a temperature (° C.) of a hot-rolled sheet at a termination time point of hot rolling,
t of the Relational Expression 1 is a thickness of a final rolled sheet material (mm),
CR
≥
196
-
300
×
[
C
]
+
4.5
×
[
Si
]
-
71.8
×
[
Mn
]
-
59.6
×
[
Cr
]
+
187
×
[
Ti
]
+
852
×
[
Nb
]
[
Relational
Expression
2
]
in the above Relational Expression 2, the CR is a cooling rate (° C./sec) during cooling to an A2 average cooling termination temperature after the FDT, and
C, Si, Mn, Cr, Ti, and Nb in the above Relational Expression 2 are % by weight of the corresponding alloy element.
2 . The method of claim 1 , wherein the high-strength steel has a microstructure comprising, in percentage by area, less than 5% of a pearlite phase including nitrides and coarse carbides having a diameter of 1 μm or more, less than 10% of a bainite phase, and less than 5% of a martensite and austenite (MA) phase, and the remaining of a ferrite phase, and has a ratio of fatigue limit and yield strength of 0.15 or more and a yield ratio of 0.8 or more.
3 . The method of claim 1 , wherein the coiled steel sheet is air-cooled to a temperature ranging from room temperature to 200° C.
4 . The method of claim 1 , further comprising: pickling and oiling the coiled steel sheet after the cooling.
5 . The method of claim 4 , further comprising: heating the pickled and oiled steel sheet to a temperature in a range of 450 to 740° C., followed by hot-dip galvanizing.
6 . The method of claim 5 , wherein the hot-dip galvanizing is formed using a plating bath comprising 0.01 to 30% by weight of magnesium (Mg), 0.01 to 50% by weight of aluminum (Al), the remaining of Zn, and unavoidable impurities.Cited by (0)
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