Note: Descriptions are shown in the official language in which they were submitted.
Abstract
Disclosed is a cold-rolled and annealed dual-phase steel having a tensile
strength of greater
than 780 MPa. A matrix structure thereof is fine and uniform martensite +
ferrite. The cold-rolled
and annealed dual-phase steel contains the following chemical elements in the
following mass
percentages: C: 0.1%-0.13%, Si: 0.4%-0.8%, Mn: 1.65%-1.9%, Al: 0.01%-0.05%,
Nb:
0.01-0.03%, and Ti: 0.01-0.03%. Furthermore, the cold-rolled annealed dual-
phase steel does not
contain the elements Cr or Mo. In addition, also disclosed is a method for
manufacturing the
cold-rolled and annealed dual-phase steel, comprising smelting and continuous
casting, hot rolling,
cold rolling, annealing, tempering and flattening. The cold-rolled and
annealed dual-phase steel of
the present invention is not only economical, but also has the characteristics
of high strength,
excellent elongation and cold bending properties.
CA 03180469 2022- 11- 25
780 MPA-CLASS COLD-ROLLED AND ANNEALED DUAL-PHASE STEELAND
MANUFACTURING METHOD THEREFOR
Technical Field
The present disclosure relates to a metallic material and a method for
manufacturing the
same, particularly to a cold-rolled and annealed dual-phase steel and a method
for manufacturing
the same.
Background Art
As the global energy crisis and environmental problems are becoming more and
more severe,
energy conservation and safety have become the main direction of the
development of the
automobile manufacturing industry. One of the measures for energy saving and
emission
reduction is to reduce vehicle weight. High-strength dual-phase steel has good
mechanical
properties and usability, and can be effectively used to produce vehicle
structural parts.
Along with the development of ultra-high strength steel and current market
changes, it is
desirable that ultra-high strength steel is economical and has better
performances. At present, 780
DP steel is still the mainstream steel in applications. It accounts for 60% of
the total amount of DP
steel, and it is widely used for various types of structural members and
safety members. Along
with the ongoing trend of weight reduction and energy saving in the automobile
industry, and the
rapid advancement of the technical level of the steel makers around the globe,
especially those in
China, the main concerns in the development of dual-phase steel in the future
must be low cost
and high performances in combination.
Canadian Patent Application No. CA2526488 published on December 2, 2004 and
entitled
"A COLD-ROLLED STEEL SHEET HAVING A TENSILE STRENGTH OF 780 MPA OR
MORE, AN EXCELLENT LOCAL FORMABILITY AND A SUPPRESSED INCREASE IN
WELD HARDNESS" discloses a cold-rolled steel sheet having a chemical
composition of: C:
0.05-0.09%; Si: 0.4-1.3%; Mn: 2.5-3.2%; optional Mo: 0.05-0.5% or Ni: 0.05-2%;
P:
0.001-0.05%; S<0.08*Ti-3.43*N+0.004; N<0.006%; Al: 0.005-0.10%; Ti: 0.001-
0.045%;
optional Nb < 0.04% or B: 0.0002-0.0015%; optional Ca for treatment, with the
balance of Fe and
unavoidable impurities. It requires a bainite content of greater than 7%;
Pcm<0.3; hot rolling at a
temperature equal to or higher than Ar3; coiling at 700 C or lower; cold
rolling; annealing at a
temperature of 700-900 C; and rapid cooling from a temperature of 550-700 C.
Finally, a
high-strength steel having a minimum strength of 780 Mpa is obtained. The
steel has the
characteristics of strong local deformation ability and low hardness in the
welding area. However,
1
CA 03180469 2022- 11- 25
the high Mn content used in the design of this steel will inevitably result in
a severe banded
structure which will lead to nonuniform mechanical properties. In addition,
while a high content
of Mn is added, a relatively large amount of Si is added. This is detrimental
to both the surface
quality and welding performance of the steel.
United States Patent Publication No. US20050167007 published on August 4, 2005
discloses
a method for manufacturing a high-strength steel sheet comprising the
following chemical
composition: 0.05-0.13% C, 0.5-2.5% Si, 0.5-3.5% Mn, 0.05-1% Cr, 0.05-0.6% Mo,
<0.1% Al,
<0.005% S, <0.01% N, <0.03% P, with addition of 0.005-0.05% Ti or 0.005-0.05%
Nb or
0.005-0.2% V. The steel is hot rolled at a temperature equal to or higher than
Ar3, coiled at
450-700 C, annealed, quenched from 700-600 C by cooling at a cooling rate of
100 C/s, and
then tempered at 180-450 C. Finally, a high-strength steel having a tensile
strength of 780 Mpa
and a hole expansion rate of higher than 50% is obtained. The main problem of
this steel is that
the total amount of alloy is too high and the Si content is high, which is
detrimental to the
weldability or phosphatability of the steel.
Chinese Patent Publication No. CN101363099A published on February 11, 2009
entitled
"COLD-ROLLED DUAL-PHASE STEEL SHEET WITH TENSILE STRENGTH OF 1000 MPA
AND METHOD FOR PREPARING SAME" discloses an ultra-high-strength dual-phase
steel
comprising C: 0.14-0.21%, Si: 0.4-0.9%, Mn: 1.5-2.1%, P: <0.02%, S<0.01%, Nb:
0.001-0.05%,
V: 0.001-0.02%. After hot rolling and cold rolling, it is held at 760-820 C,
cooled at a cooling
rate of 40-50 C/s, and overaged at 240-320 C for 180-300 s. The carbon
equivalent is high in
the design of this steel, and the steel is not characterized by balanced
performances.
As it can be seen, although the 780 M pa dual-phase steels designed according
to some of the
existing patent technologies exhibit good formability, they have either high
contents of C and Si,
or high contents of alloy elements such as Cr, Ni, and Mo. This is detrimental
to the weldability,
surface quality or phosphatability of the steels, and the cost is also high.
In addition, for some
steels with high Si contents, although the hole expansion rate is very high
and the bendability is
good, the yield ratio is high, and the stamping performance is degraded.
Summary
One of the objects of the present disclosure is to provide an economical 780
MPa grade
cold-rolled and annealed dual-phase steel. By reasonably designing the alloy
elements and the
manufacturing process for the cold-rolled and annealed dual-phase steel, the
resulting steel plate
has a strength of 780MPa grade with no addition of Mo and Cr, and a fine and
uniform martensite
+ ferrite dual-phase structure is obtained to ensure excellent performances of
elongation and cold
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CA 03180469 2022- 11- 25
bending, so that the steel has good formability. The cold-rolled and annealed
dual-phase steel has
a yield strength of >420MPa; a tensile strength of >780MPa; an elongation at
break with A50
gauge length of >18%; a 90-degree cold bending parameter Rit<1, where R
represents bending
radius in mm, and t represents plate thickness in mm.
In order to achieve the above object, the present disclosure provides a 780MPa
grade
cold-rolled and annealed dual-phase steel having a matrix structure of fine
and uniform martensite
+ ferrite, wherein the cold-rolled and annealed dual-phase steel comprises the
following chemical
elements in mass percentages, in addition to Fe:
C: 0.1%-0.13%, Si: 0.4%-0.8%, Mn: 1.65%-1.9%, Al: 0.01%-0.05%, Nb: 0.01-0.03%,
Ti:
0.01-0.03%;
wherein the cold-rolled and annealed dual-phase steel is free of Cr and Mo
elements.
Further, the cold-rolled and annealed dual-phase steel in the present
disclosure comprises the
following chemical elements in mass percentages:
C: 0.1%-0.13%, Si: 0.4%-0.8%, Mn: 1.65%-1.9%, Al: 0.01%-0.05%, Nb: 0.01-0.03%,
Ti:
0.01-0.03%, and a balance of Fe and other unavoidable impurities.
In the cold-rolled and annealed dual-phase steel according to the present
disclosure, a
composition system with C and Mn as the dominant additive elements is designed
for the
composition of the cold-rolled and annealed dual-phase steel according to the
present disclosure,
so as to ensure that the cold-rolled and annealed dual-phase steel can reach a
strength of 780 MPa
grade. The absence of precious alloy elements such as Mo and Cr can
effectively guarantee the
economic efficiency. The addition of Nb and Ti in trace amounts can achieve
the effect of
inhibiting growth of austenite grains, and can effectively refine the grains.
In addition, due to the
special design of the composition with no addition of Mo or Cr, the strength
of the hot rolled coil
is not too high, which can guarantee the processability in cold rolling. The
principles for
designing the various chemical elements are described as follows:
C: In the cold-rolled and annealed dual-phase steel according to the present
disclosure, the
addition of the C element can improve the strength of the steel and the
hardness of martensite. If
the mass percentage of C in the steel is lower than 0.1%, the strength of the
steel plate will be
affected, and it is detrimental to formation and stability of austenite. If
the mass percentage of C
in the steel is higher than 0.13%, the hardness of martensitic will be too
high, and the grain size
will be large, which is detrimental to the formability of the steel plate. At
the same time, an
unduly high carbon equivalent is detrimental to welding in use. Therefore, in
the cold-rolled and
annealed dual-phase steel according to the present disclosure, the mass
percentage of C is
controlled at 0.1%-0.13%.
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CA 03180469 2022- 11- 25
In some preferred embodiments, the mass percentage of C may be controlled at
0.11-0.125%.
Si: In the cold-rolled and annealed dual-phase steel according to the present
disclosure, the
addition of the Si element to the steel can improve hardenability. In
addition, the solid dissolved
Si in the steel may have an effect on the interaction of dislocations, thereby
increasing the work
hardening rate. This may increase the elongation of the dual-phase steel
suitably, which is
beneficial to obtain better formability. However, it should be noted that if
the mass percentage of
Si in the steel is too high, it will be detrimental to the control of the
surface quality. Therefore, in
the cold-rolled and annealed dual-phase steel according to the present
disclosure, the mass
percentage of Si is controlled at 0.4%-0.8%.
In some preferred embodiments, the mass percentage of Si may be controlled at
0.5-0.7%.
Mn: In the cold-rolled and annealed dual-phase steel according to the present
disclosure, the
addition of the Mn element is beneficial to improve the hardenability of the
steel, and can
effectively improve the strength of the steel plate. However, it should be
noted that when the mass
percentage of Mn in the steel is lower than 1.65%, the strength of the steel
plate will be
insufficient; when the mass percentage of Mn in the steel is higher than 1.9%,
the strength of the
steel plate will be too high to reduce its formability. Therefore, in the cold-
rolled and annealed
dual-phase steel according to the present disclosure, the mass percentage of
Mn is controlled at
1.65%-1.9%.
In some preferred embodiments, the mass percentage of Mn may be controlled at
1.7-1.8%.
Al: In the cold-rolled and annealed dual-phase steel according to the present
disclosure, the
addition of Al may have the effect of removing oxygen and refining grains.
Therefore, in the
cold-rolled and annealed dual-phase steel according to the present disclosure,
the mass percentage
of Al is controlled at 0.01%-0.05%.
In some preferred embodiments, the mass percentage of Al may be controlled at
0.015-0.045%.
Nb: In the cold-rolled and annealed dual-phase steel according to the present
disclosure, the
Nb element is an important element for grain refinement. With the addition of
a small amount of
the strong carbide forming element Nb to the micro-alloy steel, a strain-
induced precipitation
phase can be formed in the controlled rolling process. The strain-induced
precipitation phase can
significantly reduce the recrystallization temperature of deformed austenite
by means of the action
of particle pinning and subgrain boundaries, provide nucleation particles, and
thus have a
significant effect of refining grains. In the process of austenization by
continuous annealing, the
soaked undissolved carbide and nitride particles will prevent coarsening of
soaked austenite
grains by the mechanism of pinning grain boundaries by particles, thereby
refining the grains
4
CA 03180469 2022- 11- 25
effectively. Therefore, in the cold-rolled and annealed dual-phase steel
according to the present
disclosure, the mass percentage of Nb is controlled at 0.01-0.03%.
In some preferred embodiments, the mass percentage of Nb may be controlled at
0.015-0.025%.
Ti: The strong carbide forming element Ti added to the cold-rolled and
annealed dual-phase
steel according to the present disclosure also exhibits a strong effect of
inhibiting growth of
austenite grains at high temperatures. At the same time, the addition of Ti
helps to refine grains.
Therefore, in the cold-rolled and annealed dual-phase steel according to the
present disclosure, the
mass percentage of Ti is controlled at 0.01-0.03%.
In some preferred embodiments, the mass percentage of Ti may be controlled at
0.015-0.025%.
In the above composition design, precious alloy elements such as Mo and Cr are
not added to
the cold-rolled and annealed dual-phase steel, so as to ensure economy. At the
same time, in order
to ensure obtainment of a tensile strength of 780MPa grade at a gas cooling
rate of 40-100 C/s in
normal continuous annealing, the amounts of the alloy elements C and Mn in the
composition
should be guaranteed to provide sufficient hardenability. Nevertheless, the
upper limits of the
contents of the alloy elements C and Mn need to be controlled so as to
guarantee excellent
welding performance and formability, and to prevent the strength from
exceeding its upper limit.
Because the precipitation of Al nitrides and the precipitation of Nb, Ti
carbonitrides are
competitive in the steel production process, in view of the contents of Al and
N in the composition
system according to the present disclosure, the effect of refining grains can
be achieved only when
certain amounts of Nb and Ti to be added are guaranteed. Therefore, the mass
percentage contents
of Nb and Ti in the cold-rolled and annealed dual-phase steel may further
satisfy the following
formula: Nb%+Ti%x3>0.047%, preferably >0.06%. In the above formula, Nb and Ti
each
represent the mass percentage content of the corresponding element, that is,
the value in front of
the percent sign in the formula. In some embodiments, 0.047%<Nb%+Ti%x3<0.10%;
preferably,
0.06%<Nb%+Ti%x3<0.10%.
Further, in the cold-rolled and annealed dual-phase steel according to the
present disclosure,
the mass percentage contents of the chemical elements satisfy at least one of
the following:
C: 0.11%-0.125%,
Si: 0.5%-0.7%,
Mn: 1.7%-1.8%,
Al: 0.015%-0.045%,
Nb: 0.015-0.025%,
CA 03180469 2022- 11- 25
Ti: 0.015-0.025%.
Further, in the cold-rolled and annealed dual-phase steel according to the
present disclosure,
the unavoidable impurities include the P, S and N elements, and the contents
thereof are
controlled to be at least one of the following: P <0.015%, S<0.003%, N<0.005%.
In the above technical solution, in the cold-rolled and annealed dual-phase
steel according to
the present disclosure, the P, N and S elements are all unavoidable impurity
elements in the steel.
It's better to lower the contents of the P, N and S elements in the steel as
far as possible. MnS
formed from S seriously affects the formability, and N tends to incur cracks
or bubbles on the
surface of the slab. Therefore, in the cold-rolled and annealed dual-phase
steel according to the
present disclosure, the mass percentage of P is controlled at P<0.015%; the
mass percentage of S
is controlled at S<0.003%; and the mass percentage of N is controlled at N
<0.005%.
Further, in the cold-rolled and annealed dual-phase steel according to the
present disclosure,
the phase proportion (by volume) of martensite is >55%.
Further, in the cold-rolled and annealed dual-phase steel according to the
present disclosure,
the grain diameter of martensite is not greater than 5 microns, and the grain
diameter of ferrite is
not greater than 5 microns.
Further, the performances of the cold-rolled and annealed dual-phase steel
according to the
present disclosure satisfy at least one of the following: yield strength>420
MPa, preferably>430
MPa; tensile strength>780 MPa, preferably>800 MPa; elongation at break with
A50 gauge length
218%; a 90-degree cold bending parameter Rit<1, where R represents bending
radius in mm, t
represents plate thickness in mm.
Further, the performances of the cold-rolled and annealed dual-phase steel
according to the
present disclosure satisfy the following: yield strength2420 MPa,
preferab1y2430 MPa; tensile
strength>780 MPa, preferab1y2800 MPa; elongation at break with A50 gauge
length 218%; 90
degree cold bending parameter Rit<1, where R represents bending radius in mm,
t represents plate
thickness in mm.
Further, the yield ratio of the cold-rolled and annealed dual-phase steel
according to the
present disclosure is 0.53-0.57.
Accordingly, another object of the present disclosure is to provide a method
for
manufacturing a cold-rolled and annealed dual-phase steel. The cold-rolled and
annealed
dual-phase steel made by the manufacturing method has the characteristics of
high strength,
excellent elongation and cold bending performance. It has a yield strength of
2420MPa; a tensile
strength of >780MPa; an elongation at break with A50 gauge length of 218%; a
90-degree cold
bending parameter Rit<1, where R represents bending radius in mm, and t
represents plate
6
CA 03180469 2022- 11- 25
thickness in mm.
To achieve the above object, the present disclosure proposes a method for
manufacturing the
above cold-rolled and annealed dual-phase steel, comprising steps of:
(1) Smelting and continuous casting;
(2) Hot rolling;
(3) Cold rolling;
(4) Annealing: annealing soaking temperature: 770-820 C; annealing time: 40-
200 s;
cooling at a rate of 3-5 C/s to a starting temperature of rapid cooling;
rapid cooling at a rate of
30-80 C/s, wherein the starting temperature of rapid cooling is 650-730 C,
and the rapid cooling
is ended at a temperature of 200-270 C;
(5) Tempering;
(6) Temper rolling.
In the method for manufacturing the cold-rolled and annealed dual-phase steel
according to
the present disclosure, in step (4), the reason for controlling the annealing
soaking temperature at
770-820 C is as follows: when the annealing soaking temperature is lower than
770 C, the steel
having a strength of 780 MPa grade cannot be obtained; while if the annealing
soaking
temperature is higher than 820 C, the grain size will be large, which will
greatly degrade the
formability. Therefore, controlling the annealing soaking temperature at 770-
820 C can ensure
obtainment of both the tensile strength of 780MPa and the small grain size, so
that the cold-rolled
and annealed dual-phase steel has better formability.
In some preferred embodiments, the annealing soaking temperature may be
controlled in the
range of 790-810 C in order to obtain better implementation effects, i.e. to
obtain a smaller grain
size, moderate mechanical properties of the steel obtained, and better
formability.
Further, in the manufacturing method according to the present disclosure, in
step (2), the slab
is first heated to 1160-1220 C, preferably 1165-1215 C; held for 0.6 hours
or longer, preferably
0.6-1.5 hours; hot rolled at a temperature of 850-900 C; rapidly cooled at a
rate of 30-80 C/s
after the rolling; coiled with the coiling temperature being controlled at 500-
600 C, preferably
520-600 C; and air cooled after the coiling.
Further, in the manufacturing method according to the present disclosure, in
step (3), a cold
rolling reduction rate is controlled at 50-70%.
Further, in the manufacturing method according to the present disclosure, in
step (5), a
tempering temperature is controlled at 200-270 C, and a tempering time is 100-
400 s, preferably
150-400 s.
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CA 03180469 2022- 11- 25
Further, in the manufacturing method according to the present disclosure, in
step (6), a
temper rolling reduction rate is controlled at <0.3%.
Further, in the manufacturing method according to the present disclosure, in
step (4), the
annealing soaking temperature is 790-810 C.
Compared with the prior art, the cold-rolled and annealed dual-phase steel and
the
manufacturing method therefor according to the present disclosure have the
following advantages
and beneficial effects:
The alloy chemical composition in the cold-rolled and annealed dual-phase
steel is designed
reasonably, so that a steel plate having a strength of more than 780M Pa grade
and a martensite +
ferrite dual-phase structure is obtained without addition of Mo and Cr. The
steel plate has a yield
strength of >420MPa; a tensile strength of >780MPa; an elongation at break
with A50 gauge
length of 218%; a 90-degree cold bending parameter R/t<1, where R represents
bending radius in
mm, and t represents plate thickness in mm. While good economy is achieved,
the steel plate has
the characteristics of high strength, excellent elongation and cold bending
performance.
Accordingly, by reasonably designing and controlling the specific process
parameters in the
manufacturing method according to the present disclosure, the cold-rolled and
annealed
dual-phase steel obtained by the manufacturing method according to the present
disclosure not
only has good economy, but also has the characteristics of high strength,
excellent elongation and
cold bending performance.
Description of the Drawing
Figure 1 shows the structure of the cold-rolled and annealed dual-phase steel
of Example 1.
Detailed Description
The economical 780 MPa grade cold-rolled and annealed dual-phase steel and the
method
for manufacturing the same according to the disclosure will be further
explained and illustrated
with reference to the specific Examples. Nonetheless, the explanation and
illustration are not
intended to unduly limit the technical solution of the disclosure.
Examples 1-7 and Comparative Examples 1-14
Table 1 lists the mass percentages of various chemical elements in the steel
grades
corresponding to the cold-rolled and annealed dual-phase steels in Examples 1-
7 and the steels in
Comparative Examples 1-14.
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CA 03180469 2022- 11- 25
Table 1 (wt%, the balance is Fe and unavoidable impurities other than P, S and
N)
Steel Chemical elements
grade C Si Mn Al P S N Nb Ti Nb%+Ti%x3
Ex. 1 A 0.103 0.45 1.74
0.012 0.014 0.0015 0.0035 0.012 0.021 0.075
Ex. 2 B 0.106 0.52 1.68
0.032 0.013 0.0016 0.0033 0.017 0.015 0.062
Ex. 3 C 0.110 0.55 1.85
0.022 0.009 0.0018 0.0045 0.015 0.026 0.093
Ex. 4 D 0.115 0.43 1.82
0.028 0.011 0.0020 0.0042 0.024 0.024 0.096
Ex. 5 E 0.118 0.61 1.69
0.018 0.012 0.0022 0.0038 0.029 0.023 0.098
Ex. 6 F 0.123 0.66 1.76
0.025 0.011 0.0024 0.0045 0.021 0.021 0.084
Ex. 7 G 0.129
0.72 1.80 0.045 0.009 0.0012 0.0027 0.0195 0.014 0.0615
Comp. Ex. 1 H 0.091
0.63 1.77 0.044 0.011 0.0022 0.0037 0.015 0.018 0.069
Comp. Ex. 2 I 0.138 0.64 1.81
0.047 0.009 0.0022 0.0033 0.018 0.022 0.084
Comp. Ex. 3 J 0.121 0.58 1.62
0.033 0.012 0.0015 0.0028 0.026 0.021 0.089
Comp. Ex. 4 K 0.124
0.63 1.99 0.038 0.013 0.0015 0.0035 0.026 0.019 0.083
Comp. Ex. 5 L 0.118
0.62 1.69 0.035 0.011 0.0017 0.0034 0.005 0.024 0.077
Comp. Ex. 6 M 0.117
0.57 1.72 0.026 0.008 0.0012 0.0029 0.020 0.004 0.032
Comp. Ex. 7-14 N 0.109
0.72 1.75 0.024 0.010 0.0014 0.0043 0.023 0.027 0.104
The cold-rolled and annealed dual-phase steels in Examples 1-7 according to
the present
disclosure and the steels in Comparative Examples 1-14 were all prepared by
the following steps:
(1) Smelting and continuous casting: the required alloy components were
obtained, and the
contents of S and P were minimized;
(2) Hot rolling: a slab was first heated to 1160-1220 C which was held for
0.6 hours or more;
then hot-rolling at a temperature of 850-900 C was conducted; after the
rolling, rapid cooling
was conducted at a rate of 30-80 C/s; the coiling temperature was controlled
at 500-600 C; air
cooling was conducted after coiling;
(3) Cold rolling: the cold rolling reduction rate was controlled at 50-70%;
(4) Annealing: the annealing soaking temperature was controlled at 770-820 C,
alternatively
and preferably at 790-810 C; the annealing time was controlled at 40-200 s;
the temperature was
decreased to a starting temperature of rapid cooling by cooling at a rate of 3-
5 C/s; rapid cooling
was conducted at a rate of 30-80 C/s, wherein the starting temperature of the
rapid cooling was
650-730 C, and the rapid cooling was ended at a temperature of 200-270 C;
(5) Tempering: the tempering temperature was controlled at 200-270 C, and the
tempering
time was 100-400 s;
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CA 03180469 2022- 11- 25
(6) Temper rolling: the temper rolling reduction rate was controlled at <0.3%.
It should be noted that the chemical compositions of the cold-rolled and
annealed dual-phase
steel in Examples 1-7 and the related process parameters all met the control
requirements of the
design specification according to the present disclosure. The chemical
compositions of the steels
in Comparative Examples 1-6 all included parameters that failed to meet the
requirements of the
design according to the present disclosure. Although the chemical composition
of steel grade N in
Comparative Examples 7-14 met the requirements of the design according to the
present
disclosure, the related process parameters all included parameters that failed
to meet the
requirements of the design according to the present disclosure.
Tables 2-1 and 2-2 list the specific process parameters for the cold-rolled
and annealed
dual-phase steels in Examples 1-7 and the steels in Comparative Examples 1-14.
Table 2-1
Step (2)
Step (3)
Finishing
Steel Heating Holding Coiling
Cold rolling
No. hot rolling Cooling
rate
grade temperature time
temperature reduction
temperature ( C/s)
( C) (h) ( C)
rate (%)
( C)
Ex. 1 A 1210 0.75 855 32 585
52
Ex. 2 B 1205 0.65 870 30 525
67
Ex. 3 C 1195 1.2 890 47 545
58
Ex. 4 D 1187 1.5 886 54 575
50
Ex. 5 E 1169 0.8 864 68 590
55
Ex. 6 F 1211 1.1 895 74 588
62
Ex. 7 G 1191 0.9 885 44 600
48
Comp. Ex.
H 1187 0.7 875 50 548
50
1
Comp. Ex.
I 1175 1.1 850 62 566
56
2
Comp. Ex.
3 J 1200 0.95 890 68 535
55
Comp. Ex.
K 1213 1.3 900 76 505
52
4
Comp. Ex.
L 1178 1.4 895 46 586
67
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CA 03180469 2022- 11- 25
Comp. Ex.
M 1194 0.8 890 38 533 48
6
Comp. Ex.
N 1153 1.6 866 55
564 62
7
Comp. Ex.
N 1237 1.5 885 60
592 50
8
Comp. Ex.
N 1195 1.4 886 70
480 55
9
Comp. Ex.
N 1186 0.9 895 75
622 58
Comp. Ex.
N 1209 1.1 858 49
578 56
11
Comp. Ex.
N 1193 1.3 864 55
555 60
12
Comp. Ex.
N 1169 1.5 877 62
511 52
13
Comp. Ex.
N 1178 0.9 855 48
548 54
14
Table 2-2
Step (4) Step
(5) Step (6)
Ending Temperin
Annealing Starting
Temper
Annealing Cooling Rapid temperature g
Temperin
No. soaking temperature of
rolling
time rate cooling rate of rapid
temperatu g time
temperature rapid cooling
reduction
(s) ( C/s) ( C/s) cooling re
(s)
( C) ( C)
rate (%)
( C) ( C)
Ex. 1 815 150 5 705 55 200 200
220 0.3
Ex. 2 785 90 4 715 44 250 250
300 0.2
Ex. 3 796 105 5 670 65 265 265
210 0.3
Ex. 4 784 180 3 720 70 270 270
250 0.2
Ex. 5 810 60 4 680 66 235 235
175 0.1
Ex. 6 808 175 5 725 58 240 240
205 0.2
Ex. 7 777 85 3 695 57 266 266
380 0.1
Comp. 790 150 3 675 48 216 216
330 0.1
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CA 03180469 2022- 11- 25
Ex. 1
Comp.
796 90 3 670 36 208 208
205 0.3
Ex. 2
Comp.
800 120 4 705 48 262 262
190 0.1
Ex. 3
Comp.
811 180 5 720 62 225 225
210 0.3
Ex. 4
Comp.
789 60 5 725 58 239 239
250 0.2
Ex. 5
Comp.
812 75 5 700 80 252 252
120 0.1
Ex. 6
Comp.
786 140 4 655 70 227 227
300 0.3
Ex. 7
Comp.
793 135 4 700 62 264 264
125 0.3
Ex. 8
Comp.
811 95 3 680 48 240 240
175 0.2
Ex. 9
Comp.
806 165 5 685 80 215 215
205 0.1
Ex. 10
Comp.
758 125 4 675 35 235 235
380 0.1
Ex. 11 ¨
Comp.
835 65 4 705 56 242 242
280 0.3
Ex. 12 ¨
Comp.
810 75 3 710 48 178 178
300 0.2
Ex. 13
Comp.
795 120 3 695 72 292 292
280 0.1
Ex. 14
It should be noted that, as shown in Table 2-2, the ending temperature of
rapid cooling and
the tempering temperature in each Example and in each Comparative Example are
the same. The
reason is that, in the actual process operation, the tempering operation was
performed right after
the rapid cooling operation was ended.
A variety of performance tests were performed on the cold-rolled and annealed
dual-phase
steels in Examples 1-7 and the steels in Comparative Examples 1-14. The test
results obtained are
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CA 03180469 2022- 11- 25
listed in Table 3. As to the performance test method, GB/T 13239-2006 Metallic
Materials -
Tensile Testing at Low Temperature was referred to. A standard sample was
prepared, and
subjected to static stretching on a tensile testing machine to obtain a
corresponding stress-strain
curve. After data processing, the parameters of yield strength, tensile
strength and elongation at
break were obtained finally.
Table 3 lists the performance test results for the cold-rolled and annealed
dual-phase steels in
Examples 1-7 and the steels in Comparative Examples 1-14.
Table 3
Elongation at break 900 bending radius Plate thickness
Yield strength Tensile
No. A50 R t
R/t
(MPa) strength (MPa)
(%) (mm) (mm)
Ex. 1 454 800 22.3 1.0 1.1
0.91
Ex. 2 435 812 21.5 1.0 1.1
0.91
Ex. 3 474 856 19.5 1.0 1.1
0.91
Ex. 4 449 832 20.5 1.0 1.2
0.83
Ex. 5 458 827 20.8 1.0 1.2
0.83
Ex. 6 476 872 19.7 1.0 1.2
0.83
Ex. 7 489 884 18.4 1.0 1.1
0.91
Comp. Ex. 1 386 768 25.2 1.0 1.2
0.83
Comp. Ex. 2 525 934 14.6 1.5 1.0
1.50
Comp. Ex. 3 393 777 24.3 1.0 1.0
1.00
Comp. Ex. 4 518 941 15.1 1.5 1.1
1.36
Comp. Ex. 5 404 835 19.6 1.0 1.0
1.00
Comp. Ex. 6 408 828 20.1 1.0 1.1
0.91
Comp. Ex. 7 383 765 24.7 1.0 1.1
0.91
Comp. Ex. 8 525 936 16.6 1.5 1.3
1.15
Comp. Ex. 9 543 952 15.8 1.5 1.0
1.50
Comp. Ex. 10 394 774 24.5 1.0 1.0
1.00
Comp. Ex. 11 390 772 24.5 1.0 1.0
1.00
Comp. Ex. 12 537 947 15.5 1.5 1.2
1.25
Comp. Ex. 13 534 942 15.3 1.5 1.1
1.36
Comp. Ex. 14 385 774 24.5 1.0 1.0
1.00
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As it can be seen from Table 3, Examples 1-7 meeting the control requirements
of the design
specification according to the present disclosure have excellent performances,
including yield
strength>420 MPa; tensile strength>780 MPa; elongation at break with A50 gauge
length >18%; a
90-degree cold bending parameter R/t<1 (R represents bending radius in mm, t
represents plate
thickness in mm). The various performances of the cold-rolled and annealed
dual-phase steels of
the various Examples are quite excellent. With no addition of precious alloy
elements such as Mo
and Cr, the steels achieve a tensile strength of greater than 780 MPa, and
exhibit good elongation
and superior cold bending performance.
It's to be noted that the prior art portions in the protection scope of the
present disclosure are
not limited to the examples set forth in the present application file. All the
prior art contents not
contradictory to the technical solution of the present disclosure, including
but not limited to prior
patent literature, prior publications, prior public uses and the like, may all
be incorporated into the
protection scope of the present disclosure. In addition, the ways in which the
various technical
features of the present disclosure are combined are not limited to the ways
recited in the claims of
the present disclosure or the ways described in the specific examples. All the
technical features
recited in the present disclosure may be combined or integrated freely in any
manner, unless
contradictions are resulted.
It should also be noted that the Examples set forth above are only specific
examples
according to the present disclosure. Obviously, the present disclosure is not
limited to the above
Examples. Similar variations or modifications made thereto can be directly
derived or easily
contemplated from the present disclosure by those skilled in the art. They all
fall in the protection
scope of the present disclosure.
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