US 2026/0028706 A1 · THICK COMPOSITE-PHASE STEEL HAVING EXCELLENT DURABILITY AND MANUFACTURING METHOD THEREFOR

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.

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
]
CR1 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
CR2OUT 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
CR2IN 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.

372 more elements

Thick composite-phase steel having excellent durability and manufacturing method therefor

Life of this patent

Thick composite-phase steel having excellent durability and manufacturing method therefor

Life of this patent

Abstract

Claims6