US2026028706A1PendingUtilityA1
Thick composite-phase steel having excellent durability and manufacturing method therefor
Est. expiryDec 2, 2039(~13.3 yrs left)· nominal 20-yr term from priority
C21D 2211/005C21D 2211/002C23C 2/06C22C 38/38C22C 38/28C21D 8/0226C22C 38/26C21D 8/0273C21D 8/02C23C 30/00C23C 2/12C23C 2/02C22C 38/04C22C 38/02C21D 2221/01C21D 8/0263C21D 1/02C21D 2211/008C21D 9/46
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Claims
Abstract
Provided is a manufacturing method of composite-phase steel. The method includes: reheating a steel slab including, by wt %, 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.; finish hot rolling the reheated steel slab; primarily cooling the hot-rolled steel sheet to a mid-temperature range of 550 to 650° C.; and secondarily cooling a region of the head part and the tail part corresponding to an outer wound portion of a coil during winding to a temperature range from 450 to 550° C., and secondarily cooling a region of the mid part corresponding to an inner wound portion of the coil to the temperature range from 400 to 500° C., and coiling the secondly cooled steel sheet.
Claims
exact text as granted — not AI-modified1 . A manufacturing method of composite-phase steel having excellent material and durability uniformity and a thickness of 5 mm or more, the manufacturing method comprising:
reheating a steel slab including, by wt %, 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.; manufacturing a hot-rolled steel sheet by finish hot rolling the reheated steel slab at a finish hot rolling (FDT) satisfying the following [Relational Expression 1] of steel; primarily cooling the hot-rolled steel sheet to a mid-temperature (MT) range of 550 to 650° C. to satisfy the following [Relational Expression 2]; and when the primarily cooled steel sheet is divided, in a lengthwise direction, into three parts: HEAD, MID, and TAIL parts, secondarily cooling a region of the HEAD part and the TAIL part corresponding to an outer wound portion of a coil during winding to a temperature range from 450 to 550° C. to satisfy the following [Relational Expression 3], and secondarily cooling a region of the MID part corresponding to an inner wound portion of the coil to the temperature range from 400 to 500° C. to satisfy the following [Relational Expression 4], and then coiling the secondly cooled steel sheet;
Tn
-
60
≤
FDT
≤
Tn
[
Relational
Expression
1
]
Tn
=
740
+
92
[
C
]
-
80
[
Si
]
+
70
[
Mn
]
+
45
[
Cr
]
+
650
[
Nb
]
+
410
[
Ti
]
-
1
.
4
(
t
-
5
)
the FDT of the above Relational Expression 1 is a finish hot-rolling temperature (° C.),
[C], [Si], [Mn], [Cr], [Nb], and [Ti] in the above Relational Expression 1 are wt % of the corresponding alloy element,
t of the above Relational Expression 1 is a thickness of a final hot-rolled sheet (mm)
CR
1
min
<
CR
1
<
CR
1
max
[
Relational
Expression
2
]
CR
1
min
=
210
-
850
[
C
]
+
1.5
[
Si
]
-
67.2
[
Mn
]
-
59.6
[
Cr
]
+
187
[
Ti
]
+
852
[
Nb
]
CR
1
max
=
240
-
850
[
C
]
+
1.5
[
Si
]
-
67.2
[
Mn
]
-
59.6
[
Cr
]
+
187
[
Ti
]
+
852
[
Nb
]
CR 1 of the above Relational Expression 2 is a primary cooling rate (° C./sec) in an FDT to MT (550 to 650° C.) section,
[C], [Si], [Mn], [Cr], [Ti], and [Nb] in the above Relational Expression 2 are wt % of the corresponding alloy element
CR
2
OUT
-
min
<
CR
2
OUT
<
CR
2
OUT
-
max
[
Relational
Expression
3
]
CR
2
OUT
-
min
=
14.5
[
C
]
+
18.75
[
Si
]
+
8.75
[
Mn
]
+
8.5
[
Cr
]
+
35.25
[
Ti
]
+
42.5
[
Nb
]
-
14
CR
2
OUT
-
max
=
38.7
[
C
]
+
50
[
Si
]
+
23.3
[
Mn
]
+
22.7
[
Cr
]
+
94
[
Ti
]
+
113.3
[
Nb
]
-
37.4
CR 2 OUT of the above Relational Expression 3 is the secondary cooling rate (° C./sec) in MT to coiling temperature section of the HEAD part and the TAIL part,
[C], [Si], [Mn], [Cr], [Ti], and [Nb] in the above Relational Expression 3 are wt % of the corresponding alloy element
CR
2
IN
-
min
<
CR
2
IN
<
CR
2
IN
-
max
[
Relational
Expression
4
]
CR
2
IN
-
min
=
29
[
C
]
+
37.5
[
Si
]
+
17.5
[
Mn
]
+
17
[
Cr
]
+
20.5
[
Ti
]
+
25
[
Nb
]
-
28
CR
2
IN
-
max
=
211.5
[
C
]
+
5.5
[
Si
]
+
15
[
Mn
]
+
6
[
Cr
]
+
30.5
[
Ti
]
+
41
[
Nb
]
+
30.5
CR 2 IN of the above Relational Expression 4 is the secondary cooling rate (° C./sec) in MT to coiling temperature section of the MID part,
[C], [Si], [Mn], [Cr], [Ti], and [Nb] in the above Relational Expression 4 are wt % structure of the corresponding alloy element.
2 . The manufacturing method of claim 1 , wherein the composite-phase steel has a mixed phase of ferrite and bainite as a base structure, in the base structure, an area fraction of each of a pearlite phase and a martensite and austenite (MA) phase is less than 5%, and an area fraction of a martensite phase is less than 10%, and a product of tensile strength, elongation, and fatigue strength of the outer wound portion of the coil, which is the region of the HEAD part and the TAIL part, is 25×10 5 % or greater, and a product of tensile strength, elongation, and fatigue strength of the inner wound portion of the coil, which is the region of the MID part, is 24×10 5 % or greater.
3 . The manufacturing method of claim 1 , wherein the wound steel sheet is air-cooled to a temperature range from room temperature to 200° C.
4 . The manufacturing method of claim 1 , further comprising pickling and oiling the coiled steel sheet after the secondary cooling.
5 . The manufacturing method of claim 4 , further comprising heating the pickled or oiled steel sheet to a temperature range from 450 to 740° C., and then hot-dip galvanizing the steel sheet.
6 . The manufacturing method of claim 5 , wherein the hot-dip galvanizing is formed using a plating bath including, by wt %, magnesium (Mg): 0.01 to 30%, Al: 0.01 to 50%, the remaining of Zn, and inevitable impurities.Join the waitlist — get patent alerts
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