FIELD OF INVENTION
[0001] The invention relates to the field of steel rolling, particularly relates to a method
for rolling high-toughness high-strength low-alloy steel (rolling method for a high-toughness
high-strength low-alloy steel).
BACKGROUND OF THE INVENTION
[0002] With the economic development of society and progress of science and technology,
steel materials are already widely used in various fields, wherein, due to its high
strength, good plasticity and toughness, a high-strength low-alloy steel is already
widely used in high-end fields such as aerospace and ships, especially in infrastructures
such as oil pipes, bridges, large buildings, and engineering fields such as vehicles,
containers, and machinery, chemical, medical, light industrial devices, it is also
used broadly. The high-strength low-alloy steel is widely used in machinery devices,
vehicles, and tubulation fields and so on due to its high strength, superior formability,
and stable combination property.
[0003] At present, ways to increase strength of steel materials are solution strengthening,
dislocation strengthening, refined crystalline strengthening, and precipitation hardening
of a second-phase particle and so on; wherein, the effect of refined crystalline strengthening
is most obvious, the steel after refined crystalline strengthening has better strength
and toughness. With the increase of grain refinement resistance, crack propagation
resistance, the fatigue strength, toughness of the steel increases, temperature of
brittleness turning point decreases. A fine-grained steel has good coordination between
strength and toughness, and is broadly used in fields such as vehicles, ships, bridges,
and engineering machinery.
[0004] In prior art, there is a trade-off between strength and toughness of a high-strength
low-alloy steel, the prior art only relates to a rolling method of a steel plate and
strip, not relates to a rolling method of a round bar steel, and an off-line normalizing
step is necessary during the rolling, production cost is high, which is adverse to
energy saving and cost reduction and green manufacturing.
SUMMARY
[0005] With respect to deficiencies of the prior art, the purpose of the invention is to
provide a rolling method for a high-toughness high-strength low-alloy steel. It successfully
develops a rolling method for producing a high-toughness high-strength low-alloy steel
by making a reasonable production process control through micro-alloy elements and
control rolling and control cooling processes. During manufacturing of a production,
it eliminates the off-line normalizing step, reduces the manufacturing process, saves
manufacturing cost; for the high-strength low-alloy steel manufactured through this
process and method, its metallographic structure is fine ferrite and pearlite, its
tensile strength is more than 630MPa, its yield strength is more than 500MPa, its
grain size after rolling is fine and uniform, the grain size reaches 9.0 or above,
comprehensive mechanical properties are far superior to conventional rolling processes.
[0006] To achieve the above purpose, the invention provides the following technical solution:
A rolling method for high-toughness high-strength low-alloy steel, the rolling method
sequentially comprises the following steps: heating, descaling, rough rolling, continuous
rolling, first water cooling, finish rolling, second water cooling, and cold hearth
cooling.
[0007] Using a converter continuous casting billet as a raw material, the continuous casting
billet of the high-toughness high-strength low-alloy steel comprises the following
chemical components and contents in percentage by mass: C≤0.20, Si≤0.60, Mn:1.37∼1.70,
Cr≤0.30, P≤0.020, S≤0.020, V:0.05~0.10, Al≤0.03, N≤0.025, with others being Fe and
inevitable impurities.
[0008] In the above rolling method for high-toughness high-strength low-alloy steel, as
a preferable embodiment, the step of the heating is divided into four sections, which
are sequentially as follows: pre-heating zone, heating first zone, heating second
zone, and soaking zone.
[0009] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the temperature of the pre-heating zone is less than or equal
to 750°C.
[0010] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the temperature of the heating first zone is 900~1050°C.
[0011] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the temperature of the heating second zone is 1050∼ 1150°C.
[0012] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the temperature of the soaking zone is 1150~1210°C.
[0013] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the total heating time of the step of the heating is 3∼5h.
[0014] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the soaking time of the soaking zone is 30~80min.
[0015] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the step of the heating is performed in a four-section walking
beam heating furnace.
[0016] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, in the step of the rough rolling, the entry temperature of
the rough rolling is 950∼1050°C, the pass of the rough rolling is 5~7, preferably,
the number of rough-rolling mills provided in the step of the rough rolling is 6.
[0017] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the step of the continuous rolling includes intermediate
rolling and pre-finish rolling.
[0018] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the entry temperature of the rough rolling is 900∼1000°C.
[0019] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the number of intermediate-rolling mills provided in the
step of the intermediate rolling is 6, the pass of the intermediate rolling is 5~7,
preferably, the pass of the intermediate rolling is 6.
[0020] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, outlet temperature of the pre-finish rolling is 850~950°C.
[0021] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the number of pre-finish-rolling mills provided in the step
of the pre-finish rolling is 4, the pass of the pre-finish rolling is 3~5, preferably,
the pass of the pre-finish rolling is 4.
[0022] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, during the first water cooling, the first water cooling is
performed with incoming materials after the step of the continuous rolling, wherein,
the water cooling rate is 25~50°C/s, the hydraulic pressure is 0.2∼0.6MPa.
[0023] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, in the step of the finish rolling, rolling-start-temperature
at the entry of the finish rolling is 800∼850°C.
[0024] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, a reducing and sizing mill set is used for the finish rolling.
[0025] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the reducing and sizing mill set is a three-roller reducing
and sizing mill set.
[0026] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, during the second water cooling, the second water cooling
is performed with the steel after the step of the finish rolling, wherein, water cooling
rate is 25~100°C/s, hydraulic pressure is 0.2~0.6MPa.
[0027] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, in the step of the descaling, high-pressure water descaling
is used with the aim to descaling, the hydraulic pressure of the high-pressure water
is 15~20MPa.
[0028] Furthermore, preferably, the hydraulic pressure of the high-pressure water is 17~
20MPa.
[0029] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, a high-toughness high-strength low-alloy steel bar is obtained
by the rolling method, the specification of the steel bar is Ø60~120mm.
[0030] In the above rolling method for a high-toughness high-strength low-alloy steel, as
a preferable embodiment, the cold hearth cooling means the steel after the second
water cooling is cooled on the cold hearth.
[0031] Compared with the prior art, the beneficial effects of the invention are as follows:
- (1)adding the micro-alloy element vanadium V into the chemical components of the continuous
casting billet, in order to improve hardenability of the steel, reduce deformation
of the steel, avoid cracking, and to enhance the impact toughness; because the micro-alloy
element vanadium V has a delayed action on recrystallization only under 900°C, after
austenitic transformation, the micro-alloy element vanadium V almost dissolves completely,
at the same time, the micro-alloy element N further enhances the impact toughness
of micro-alloy elements, and precipitation strengthening effects of the micro-alloy
element vanadium V, nitrogen N are exploited to the full, by adding the content of
the micro-alloy element V to improve the impact toughness, at the meantime, it would
have a strengthening effect when the micro-alloy element vanadium V is dissolved into
the ferrite, thus forming stable carbon compounds and refining grains.
[0032] At this point, applying the on-line TMCP process, controlling the precipitation process
of nitrides, forming the ferrite and pearlite structure, grains are refined again
by exploiting the low end rolling temperature and cooling rate. During the refinement
of grains, the strength of the steel is improved, its plasticity and impact toughness
are also enhanced, thus achieving high-strength control to mechanical properties.
[0033] The actual grain size of the high-strength low-alloy steel can be refined by adopting
this rolling method, the comprehensive property of the obtained high-strength low-alloy
steel is excellent, the metallographic structure is fine ferrite and pearlite, the
tensile strength is more than 630MPa, the yield strength is more than 500MPa, the
grain size after rolling is fine and uniform, the grain size reaches 9.0 or above,
the impact energy at -20°C is greater than 100J, the impact energy at -40°C is greater
than 80J, its comprehensive mechanical properties are far superior to conventional
rolling processes.
[0034] (2)Without performing the off-line normalizing during the rolling, the mechanical
properties also can meet the utilizing requirements, this can not only save the machining
time, but also can reduce the cost and improve the effect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035]
Fig. 1 is a metallographic structure obtained by rolling Ø80mm specification in comparative
example 2;
Fig.2 is the grain size (7.5) obtained by rolling Ø80mm specification in comparative
example 2;
Fig.3 is a metallographic structure obtained by rolling Ø80mm specification in embodiment2
of the present invention;
Fig.4 is the grain size (9.0) obtained by rolling Ø80mm specification in embodiment2
of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0036] The technical solutions of embodiments of the invention will be described clearly
and fully in combination with drawings of embodiments of the invention below, obviously,
the described embodiments are only some of the embodiments of the invention, not the
all embodiments. Based on the embodiments of the invention, all the other embodiments
obtained by those skilled in the art without doing any creative work will fall in
the protection scope of the invention.
[0037] The rolling method disclosed in the invention results in a superior structural form
and excellent structural mechanical properties of a necessary product by designing
according to the process parameters of the continuous rolling, combining solid-state
phase transformation and plastic deformation of the rolling principle, plastic forming
through adopting the heating process system and the rolling reduction system of four-section
stepwise heating furnace, forming through the deformation system of the rough rolling,
the intermediate rolling, the finish rolling, finally controlling metal solid phase
transformation through the cooling process.
[0038] The technical solution of the invention is further detailed in combination with drawings
through the embodiments below.
[0039] A rolling method for a high-toughness high-strength low-alloy steel, the rolling
method sequentially comprises the following steps: heating, descaling, rough rolling,
continuous rolling, first water cooling, finish rolling, second water cooling, and
cold hearth cooling; and using a converter continuous casting billet as a raw material,
the continuous casting billet comprises the following chemical components and contents
in percentage by mass: C≤0.20, Si≤0.60, Mn:1.00~1.70, Cr≤0.30, P≤0.020, S≤0.020, V:0.05~0.10,
Al≤0.03, N≤0.025, with others being Fe and inevitable impurities.
[0040] By adding the micro-alloy element vanadium V into the chemical components of the
continuous casting billet to improve hardenability of the steel, reduce steel deformation
and cracks, and to enhance the impact toughness; because the micro-alloy element vanadium
V has a delayed action on recrystallization only under 900°C, after austenitic transformation,
the micro-alloy element vanadium V almost dissolves completely, the micro-alloy element
N further enhances the impact toughness of micro-alloy elements at the same time,
and precipitation strengthening effects of the micro-alloy element vanadium V, nitrogen
N are exploited to the full.
[0041] The reason that grain refinement can improve plasticity and toughness is the fine
grain provides a better condition for the occurrence and spread of plastic deformation.
Elements those make temperature Ar3 decrease all have a tendency of grain refinement,
temperature Ar3 causes austenite to transform into the ferrite. By adding the content
of the micro-alloy element V to improve the impact toughness, at the meantime, it
would have a strengthening effect when the micro-alloy element vanadium V is dissolved
into the ferrite, thus forming stable carbon compounds and refining grains.
[0042] The rolling method sequentially comprises the following steps:
(1) Heating
[0043] The step of the heating is performed in a four-section stepwise heating furnace;
the step of the heating is divided into four sections, which are sequentially as follows:
pre-heating zone, heating first zone, heating second zone, and soaking zone.
[0044] The temperature of the pre-heating zone is less than or equal to 750°C(for example.
600°C, 650°C, 665°C, 700°C, 750°C and interval zones or points between any two of
those temperatures); that is, if the temperature of the furnace exceeds 750°C, because
thermal conductivity of the billet is too fast, the temperature difference between
the billet and the heating furnace is too large, the surface of the casting billet
or the final rolled steel may be caused to crack.
[0045] The temperature of the heating first zone is 900~1050°C (for example. 900°C, 950°C,
980°C, 1000°C, 1010°C, 1050°C and interval zones or points between any two of those
temperatures). The temperature of the heating second zone is 1050~ 1150°C(for example.
1050°C, 1080°C, 1100°C, 1110°C, 1130°C, 1150°C and interval zones or points between
any two of those temperatures). The main roles of the heating first zone and the heating
second zone are to: reduce the energy consumption, reduce the oxidation burning loss
of the billet.
[0046] The temperature of the soaking zone is 1150 - 1210°C (for example. 1150°C, 1160°C,
1165°C, 1170°C, 1185°C, 1190°C, 1205°C, 1210°C and interval zones or points between
any two of those temperatures). The main role of the soaking heating section is to:
reduce the energy consumption, reduce the oxidation burning loss of the billet, reduce
the decarburization of the billet at the same time.
[0047] The total heating time of the step of the heating is 3~5h (for example. 3.5h, 4h,
4.5h, 4.8h and time points between any two of those times); the soaking time of the
soaking zone is 30~80min (for example. 30min, 35min, 40min, 45min, 50min, 55min, 60min,
70min, 75min, 80min and time points between any two of those time periods).
[0048] The step of the heating achieves the following four purposes: firstly, the energy
consumption may be reduced and the cost can be lowed when eliminating the step of
the off-line normalizing; secondly, the oxidation burning loss of the billet can be
reduced due to the four-zone heating process; thirdly, the decarburization of the
billet can be reduced; fourthly, the surface cracks of the final billet brought by
too long heating time can be reduced.
(2) Descaling
[0049] The billet after heating is descaled by employing the high-pressure water in order
to deoxidate the iron sheet, the pressure of the high-pressure water is 15~ 20MPa
(for example 15MPa, 16.5MPa, 17MPa, 18MPa, 20MPa and the pressure value between any
two of those pressure values); the pressure value of the high-pressure water is preferably
17~20MPa. The oxidized iron sheet on the surface of the steel is removed by the high-pressure
water. The oxidized iron sheet on the surface cannot be cleared cleanly and thoroughly
when the pressure is below 15MPa, thus affecting the rolling effect of the steel.
(3) Rough rolling
[0050] Preferably, 6 rough rolling mills are provided in the step of the rough rolling;
wherein, the entry temperature of the rough rolling is 950~ 1050°C(for example, 950°C,
980°C, 1000°C, 1020°C, 1035°C, 1050°C and interval zones or points between any two
of those temperatures), the pass of the rough rolling is 5~7; the pass of the rough
rolling is preferably 6. A method of continuous rolling is adopted in the step of
the rough rolling, the surface size of the steel billet is changed mainly through
plastic deformation, the pass design adopts a box pass design, the sectional shape
of the billet is changed and reduced through the high-pressure process.
(4) Continuous rolling
[0051] The step of the continuous rolling includes intermediate rolling and pre-finish rolling,
the entry temperature of the intermediate rolling is 900~1000°C(for example, 905°C,
920°C, 940°C, 950°C, 970°C, 1000°C and interval zones or points between any two of
those temperatures), 6 intermediate rolling mills are preferably provided in the step
of the intermediate rolling, the pass of the intermediate rolling is 5~7, the pass
of the intermediate rolling is preferably 6. The pass design mainly adopts an oval
and circle pass design, the sectional shape of the billet is made close to the finished
form through the rolling process.
[0052] The outlet temperature of the pre-finish rolling is 850~950°C(for example, 855°C,
870°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C and interval zones or points
between any two of those temperatures); 4 pre-finish rolling mills are preferably
provided in the step of the pre-finish rolling, the pass of the pre-finish rolling
is 3~5, the pass of the pre-finish rolling is preferably 4. The pass design mainly
adopts an oval and circle pass design, the sectional shape of the billet is made close
to the finished form through the rolling process.
(5) First water cooling
[0053] The first water cooling is performed with incoming materials after the step of the
continuous rolling, the temperature after the first water cooling is 750~800°C(for
example, 750°C, 765°C, 780°C, 795°C, 798°C, 800°C and interval zones or points between
any two of those temperatures), wherein, during the first water cooling, the water
cooling rate is 25~50°C/s, the hydraulic pressure is 0.2 -0.6MPa. The target temperature
as required in the finish rolling is obtained by controlling the temperature of the
first water cooling and the water cooling rate, controlling the temperature of the
steel before the pre-finish rolling.
(6) Finish rolling
[0054] The rolled steel obtained in the step (5) is rolled in a reducing and sizing finish
rolling mill set, the reducing and sizing finish rolling mill set is preferably a
three-roller reducing and sizing mill set, i.e. KOCKS reducing and sizing finish rolling
mill set, entry temperature of initial rolling is 800∼850°C (for example, 800°C, 810°C,
820°C, 824°C, 832°C, 850°Cand interval zones or points between any two of those temperatures).
Adopting the three-roller reducing and sizing mill set can achieve low-temperature
rolling better, thus improving non-quenched and tempered steel grain size, comprehensive
mechanical properties, providing its excellent performance for the production of the
non-quenched and tempered steel.
(7) Second water cooling
[0055] The second water cooling is performed with the steel after the finish rolling, the
temperature under which the steel performs the second water cooling after the step
of the finish rolling is 600~700°C (for example, 600°C, 625°C, 640°C, 662°C, 683°C,
700°Cand interval zones or points between any two of those temperatures), wherein,
the water cooling rate is 25~100°C/s, the hydraulic pressure is 0.2∼0.6MPa. The metallographic
structure and mechanical properties as finally required by the steel are obtained
by performing the second water cooling after the finish rolling and controlling the
temperature and the water cooling rate of the second water cooling, and controlling
the temperature of the steel.
(8) Cold hearth cooled is the cold hearth cooling
[0056] The steel obtained after the second water cooling is made to cool on the cold hearth,
the finish steel is finally obtained.
[0057] The technology of controlling rolling and controlling cooling as described in the
step (1) to the step (8) is the main steps of refining the grain size of the high-carbon
steel grade, by integrally controlling the heating temperature, deformation extent,
and cooling rate, the target of refining the actual grain size, improving stiffness
and roughness of the steel is reached.
[0058] At the same time, applying the on-line TMCP process (i.e. thermal mechanical control
process), controlling the precipitation process of nitrides, forming the uniform ferrite
and pearlite structure, grains are refined again by exploiting the low end rolling
temperature and cooling rate, during the refinement of grains, the strength of the
steel is improved, its plasticity and impact toughness are also enhanced, thus achieving
high-strength control to mechanical properties.
[0059] The invention provides a rolling method for a high-toughness high-strength low-alloy
steel, this method is unique, adopts the micro-alloy elements and the control rolling
and control cooling technology of the thermal mechanical control process to act collectively
so as to implement the on-line control, adopting this process method can refine the
actual grain size of the high-toughness high-strength low-alloy steel, the comprehensive
performance of the high-strength low-alloy steel is excellent; the metallographic
structure is fine ferrite and pearlite, the tensile strength is more than 630MPa,
the yield strength is more than 500MPa,the grain size after rolling is fine and uniform,
the grain size reaches 9.0 or above, Charpy V impact energy at -20°C is greater than
100J, and Charpy V impact energy at -40°C is greater than 80J, its comprehensive mechanical
properties are far superior to conventional rolling methods. The high-toughness high-strength
low-alloy steel is not performing the off-line normalizing during the manufacturing,
the mechanical properties also can meet the request for utilization, this can not
only save the machining time, but also can reduce the cost and improve the effect.
Embodiment 1
[0060] Embodiment 1 provides a rolling method for a high-toughness high-strength low-alloy
steel, the specification of the required finished form is Ø65mm, and 300×400mm sectional
continuous casting billet is selected; wherein, the continuous casting billet comprises
the chemical components in percentage by mass, as shown in Table 2, the mass percentage
is totally 100%, comprising the following steps:
- (1) Heating: the sectional continuous casting billet after being cut off is placed
into a four-zone stepwise heating furnace by the way of cold delivery to heat, the
temperature of the pre-heating section is 685°C, the temperature of the heating first
zone is 1005°C, the temperature of the heating second zone is 1086°C, and the temperature
of the soaking zone is 1175°C; the total heating time in the step of the heating is
3.8h, the soaking time of the soaking zone is 43min.
- (2) Descaling: The billet after heating is descaled by employing the high-pressure
water in order to descale the iron sheet, the pressure of the high-pressure water
is 18.0 MPa.
- (3) Rough rolling: the steel after being descaled is delivery into the high-stiffness
rough rolling mill (6 sets) to perform the rough rolling, so as to get the rough rolling
steel; the entry temperature of the rough rolling is 1015°C, the pass of the rough
rolling is 6.
- (4) Continuous rolling: the rough rolling steel obtained in the step (3) is delivered
into the continuous rolling mill set, the entry temperature of the intermediate rolling
is 925°C, the pass of the intermediate rolling is 6, the outlet temperature of the
pre-finish rolling steel is 910°C, the pass of the pre-finish rolling steel is 4.
- (5) First water cooling: the first water cooling is performed with the rolled steel
after the pre-finish rolling; the temperature is cooled to 790°C; the water cooling
rate is 40°C/s, the hydraulic pressure is 0.5MPa.
- (6) Finish rolling: the rolled steel of Ø80mm specification obtained after the pre-finish
rolling is rolled by KOCKS reducing and sizing mill set, the entry temperature of
the rolled steel is 845°C when the reducing and sizing mill set is performing rolling,
the steel bar of Ø65mm specification is obtained.
- (7) Second water cooling: the second water cooling is performed with the rolled steel
after the finish rolling; the temperature is cooled to 685°C; the water cooling rate
is 75°C/s, the hydraulic pressure is 0.6MPa.
- (8) Cold hearth cooled (cold hearth cooling): the steel bar of Ø65mm specification
obtained in the step (7) is cooled in the cold hearth, the finished steel bar is finally
obtained.
[0061] The hot-rolled structure of the high-toughness high-strength low-alloy steel obtained
in embodiment1 is a uniform ferrite and pearlite, the actual grain size is 9.0, its
mechanical properties of the steel product are as shown in Table 3. The hot-rolled
structure of the high-toughness high-strength low-alloy steel obtained in embodiment1
is a uniform ferrite and pearlite, the actual grain size is 9.0, as seen from Table
3, its mechanical properties of the steel product are excellent.
Embodiment 2
[0062] Embodiment 2 provides a rolling method for a high-toughness high-strength low-alloy
steel, the specification of the required finished form is Ø80mm, and 300×400mm sectional
continuous casting billet is selected; wherein, the continuous casting billet comprises
the chemical components in percentage by mass, as shown in Table 2, the mass percentage
is totally 100%; the rolling method sequentially comprises the following steps: (1)
heating, (2) descaling, (3) rough rolling, (4) continuous rolling, (5) first water
cooling, (6) finish rolling, (7) second water cooling, and (8) cold hearth cooled
(cold hearth cooling), the processing step of example 2 is the same as that of example
1, see Table 1 for its processing parameters of specific steps, its mechanical properties
of the steel product are as shown in Table 3.
[0063] The hot-rolled structure of the high-toughness high-strength low-alloy steel obtained
in example 2 is a uniform ferrite and pearlite, as shown in Fig. 3; the actual grain
size is 9.0, as shown in Fig. 4. As seen from Table 3, its mechanical properties of
the steel product are excellent.
Embodiments
[0064] Embodiment 3 provides a rolling method for a high-toughness high-strength low-alloy
steel, the specification of the required finished form is Qj 100mm; and 300×400mm
sectional continuous casting billet is selected; wherein, the continuous casting billet
comprises the chemical components in percentage by mass, as shown in Table 2, the
mass percentage is totally 100%; the rolling method sequentially comprises the following
steps: (1) heating, (2) descaling, (3) rough rolling, (4) continuous rolling, (5)
first water cooling, (6) finish rolling, (7) second water cooling, and (8) cold hearth
cooled (cold hearth cooling), the processing step of embodiments is the same as that
of embodiment1, see Table 1 for its processing parameters of specific steps, its mechanical
properties of the steel product are as shown in Table 3.
[0065] The hot-rolled structure of the high-toughness high-strength low-alloy steel obtained
in embodiment 3 is a uniform ferrite and pearlite, the actual grain size is 9.0, as
shown in Fig. 3, its mechanical properties of the steel product are excellent.
[0066] The specific parameters of the processing step in embodiments 1-3 is shown in Table
1.
Table 1 The specific parameters of the processing step in embodiments 1-3
Processing parameters |
Embodiment 1 |
Embodiment 2 |
Embodiments |
Size of the steel billet(mm×mm) |
300×400 |
300×400 |
300×400 |
Temperature of pre-heating (°C) |
685 |
705 |
732 |
Temperature of heating first zone (°C) |
1005 |
975 |
1015 |
Temperature of heating second zone (°C) |
1086 |
1055 |
1103 |
Temperature of soaking zone (°C) |
1175 |
1189 |
1178 |
Time of soaking zone (min) |
43 |
50 |
65 |
Total time of heating (h) |
3.8 |
4.1 |
4.5 |
Hydraulic pressure of descaling (MPa) |
18.0 |
18.5 |
18.3 |
Entry temperature of rough rolling (°C) |
1015 |
993 |
1002 |
Entry temperature of intermediate rolling (°C) |
925 |
965 |
950 |
Temperature of pre-finish rolling (°C) |
910 |
935 |
930 |
Temperature of first water cooling (°C) |
790 |
775 |
760 |
Water cooling rate(°C /s)/Hydraulic pressure (MPa) |
40/0.5 |
32/0.5 |
28/0.5 |
Entry temperature of finish rolling (°C) |
845 |
840 |
825 |
Temperature of second water cooling (°C) |
685 |
682 |
675 |
Water cooling rate (°C /s)/ Hydraulic pressure (MPa) |
75/0.6 |
68/0.5 |
60/0.5 |
Specification of the steel(mm) |
Ø65mm |
Ø80mm |
Ø100mm |
[0067] Chemical components of the continuous casting billet selected and used in embodiments1-3
are shown in Table 2.
Table 2 Chemical components of the continuous casting billet selected and used in
embodiments 1-3
Chemical components (percentage by mass %) |
Embodiment 1 |
Embodiment 2 |
Embodiment 3 |
C |
≤0.20 |
0.16 |
0.16 |
0.16 |
Si |
≤0.60 |
0.30 |
0.28 |
0.30 |
Mn |
1.00-1.70 |
1.40 |
1.37 |
1.41 |
Cr |
≤0.30 |
0.13 |
0.13 |
0.15 |
V |
0.05-0.10 |
0.06 |
0.07 |
0.06 |
N |
≤0.025 |
0.010 |
0.008 |
0.011 |
Al |
≤0.03 |
0.020 |
0.022 |
0.02 |
P |
≤0.020 |
<0.020 |
≤0.020 |
<0.020 |
s |
≤0.020 |
≤0.020 |
≤0.020 |
≤0.020 |
Fe |
the balance being Fe |
[0068] Each property of the high-toughness high-strength low-alloy steel obtained in embodiments
1-3 is shown in Table 3.
Table 3 Parameters of mechanical properties of the steel obtained in embodiments 1-3
Parameters of Properties |
Standar d value |
Embodiment 1 |
Embodiment 2 |
Embodiment 3 |
Yield strength (MPa) |
≥420 |
523 |
525 |
525 |
Tensile strength (MPa) |
≥520 |
648 |
654 |
654 |
Spread (%) |
≥19 |
32 |
28 |
28 |
Charpy V impact energy at -20°C(J) |
≥47 |
135 |
132 |
132 |
Charpy V impact energy at -40°C (J) |
≥31 |
103 |
105 |
105 |
Embodiments 4-7
[0069] Embodiments 4-7 provide a rolling method for a high-toughness high-strength low-alloy
steel, the rolling method sequentially comprises the following steps: (1) heating,
(2) descaling, (3) rough rolling, (4) continuous rolling, (5) first water cooling,
(6) finish rolling, (7) second water cooling, and (8) cold hearth cooled (cold hearth
cooling), the processing step and the mechanical parameters of embodiments 4-7 are
the same as those of embodiment 1; the continuous casting billet of embodiments 4-7
comprises the chemical components in percentage by mass, as shown in Table 4, the
mass percentage is totally 100%.
Table 4 Chemical components of the continuous casting billet selected and used in
examples 4-7
Chemical components of the continuous casting billet (%) |
Embodiment 4 |
Embodiment 5 |
Embodiment 6 |
Embodiment 7 |
C |
≤ 0.20 |
0.17 |
0.16 |
0.15 |
0.16 |
Si |
≤ 0.60 |
0.31 |
0.30 |
0.28 |
0.32 |
Mn |
1.00 -1.70 |
1.42 |
1.40 |
1.37 |
1.38 |
Cr |
≤ 0.30 |
0.15 |
0.15 |
0.16 |
0.14 |
V |
0.05 -0.10 |
0.07 |
0.07 |
0.06 |
0.06 |
N |
≤ 0.025 |
0.010 |
0.010 |
0.010 |
0.009 |
Al |
≤ 0.03 |
0.020 |
0.020 |
0.023 |
0.020 |
P |
≤ 0.020 |
≤0.020 |
≤0.020 |
≤0.020 |
≤0.020 |
S |
≤ 0.020 |
≤0,020 |
≤0.020 |
≤0.020 |
≤0.020 |
Fe |
The balance being Fe |
[0070] Each property of the high-toughness high-strength low-alloy steel obtained in embodiments
4-7 is shown in Table 5.
Table 5 Parameters of mechanical properties of the steel obtained in embodiments 4-7
Parameters of properties |
Standard Value |
Embodiment 4 |
Embodiment 5 |
Embodiment 6 |
Embodiment 7 |
Yield strength (MPa) |
≥420 |
530 |
537 |
528 |
525 |
Tensile strength (MPa) |
≥520 |
658 |
649 |
660 |
652 |
Spread (%) |
≥ 19 |
30 |
29 |
31 |
30 |
Charpy V impact energy at -20°C(J) |
≥47 |
129 |
135 |
130 |
132 |
Charpy V impact energy at -40°C(J) |
≥31 |
104 |
108 |
110 |
106 |
[0071] As known from Table 5, the hot-rolled structure of the high-toughness high-strength
low-alloy steel obtained in embodiments 4-7 is a uniform ferrite and pearlite, the
actual grain size is 9.0, its mechanical properties of the steel product are excellent.
Comparative example 1
[0072] The specification of the required finished form is Ø65mm, select 300×400mm sectional
continuous casting billet; the chemical components and contents of the continuous
casting billet are: C0.45, Si 0.28, Mn1.46, Cr 0.16, V0.06, N0.010, Al 0.020, P≤0.020,
S≤0.020, with the balance being Fe and inevitable impurities. The processing step
and parameters of the alloy steel are shown in Fig. 7.
As shown in Table 6, because the content of carbon C in the chemical components of
the continuous casting billet is 0.45%, i.e., C >0.20, as shown in Table 8, the ductility
of the rolled steel is 18%, Charpy V impact energy at -20°C is 32J; Charpy V impact
energy at -40°C is 17J.
Comparative example 2
[0073] The specification of the required finished form is Ø80mm, select 300×400mm sectional
continuous casting billet; the chemical components and contents of the continuous
casting billet are: C0.16, Si 0.30, Mn 0.8, Cr 0.15, V0.07, N0.012, Al 0.020, P≤0.020,
S≤0.020, with the balance being Fe and inevitable impurities. The processing step
and parameters of the alloy steel are shown in Fig. 7.
[0074] As shown in Table 6, because the content of manganese Mn in the chemical components
of the continuous casting billet is 0.8, i.e., Mn<1.0, as shown in Table 8, the ductility
of the rolled steel is 26%, Charpy V impact energy at -20°C is 54J; Charpy V impact
energy at -40°C is 25J.
Comparative example 3
[0075] The specification of the required finished form is Ø100mm, select 300×400mm sectional
continuous casting billet; the chemical components and contents of the continuous
casting billet are: C0.16, Si 0.30, Mn 1.40, Cr 0.15, N0.011, Al 0.022, P≤0.020, S≤0.020,
with the balance being Fe and inevitable impurities. The processing step and parameters
of the alloy steel are shown in Fig. 7.
[0076] As shown in Table 6, because vanadium V is not added into the chemical components
of the continuous casting billet, as shown in Table 8, the ductility of the rolled
steel is 25%, Charpy V impact energy at -20°C is 35J; Charpy V impact energy at -40°C
is 19J.
Comparative example 4
[0077] The specification of the required finished form is Ø90mm, select 300×400mm sectional
continuous casting billet; the chemical components and contents of the continuous
casting billet are: C0.16, Si 0.32, Mn 1.47, Cr 0.15, V0.06, N0.040, Al 0.020, P≤0.020,
S≤0.020, with the balance being Fe and inevitable impurities. The processing step
and parameters of the alloy steel are shown in Fig. 7.
[0078] As shown in Table 6, because the content of nitrogen N in the chemical components
of the continuous casting billet is 0.040, i.e., N>0.025, as shown in Table 8, the
ductility of the rolled steel is 27%, Charpy V impact energy at -20°C is 62J; Charpy
V impact energy at -40°C is 37J.
[0079] As known from Table 8, through comparison the rolling method of the comparative examples
1-4 with that disclosed in the application, for the mechanical properties of the obtained
steel, Charpy V impact energies at -20°C are all less than 100J, Charpy V impact energies
at -40°C are less than 80J, the grain sizes of the alloy steel after rolling do not
reach 9.0 or above.
Table 6 Chemical components of the continuous casting billet selected and used in
comparative examples 1-4
|
Chemical components |
Comparative |
Comparative |
Comparative |
Comparative |
of the continuous casting billet in the invention (percentage by mass %) |
example 1 |
example 2 |
example 3 |
example 4 |
C |
C≤0.20 |
0.45 |
0.16 |
0.6 |
0.16 |
Si |
Si≤0.60 |
0.28 |
0.30 |
0.30 |
0.32 |
Mn |
Mn1.00∼ 1.70 |
1.46 |
0.80 |
0.80 |
1.47 |
Cr |
Cr≤0.30 |
0.16 |
0.15 |
0.07 |
0.15 |
V |
V0.05∼ 0.10 |
0.06 |
0.07 |
0 |
0.06 |
N |
N≤0.025 |
0.010 |
0.012 |
0.008 |
0.040 |
Al |
Al≤0.03 |
0.020 |
0.020 |
0.022 |
0.020 |
P |
P≤0.020 |
P≤0.020 |
P≤0.020 |
P≤0.020 |
P≤0.020 |
S |
S≤0.020 |
S≤0.020 |
S≤0.020 |
S≤0.020 |
S≤0.020 |
Fe |
The balance being Fe |
[0080] The processing step and parameters of the alloy steel in comparative examples 1-4
are as shown in Table 7.
Table 7 the specific parameters of the processing step of the steel obtained in comparative
examples 1-4
Processing parameters |
Comparative example 1 |
Comparative example 2 |
Comparative example 3 |
Comparative example 4 |
Size of the steel (mm×mm) |
300×400 |
300×400 |
300×400 |
300×400 |
Temperature of pre-heating (°C) |
702 |
687 |
685 |
700 |
Temperature of heating one-section (°C) |
980 |
1001 |
995 |
1005 |
Temperature of heating two-section (°C) |
1068 |
1075 |
1098 |
1094 |
Temperature of soaking heating section (°C) |
1170 |
1180 |
1182 |
1191 |
Time of soaking heating section (min) |
53 |
47 |
56 |
62 |
Total time of heating (h) |
4.2 |
3.9 |
4.6 |
4.8 |
Hydraulic pressure of descaling (MPa) |
18.5 |
18.1 |
18.2 |
18.3 |
Entry temperature of rough rolling (°C) |
1002 |
1003 |
1011 |
1006 |
Entry temperature of intermediate rolling (°C) |
952 |
956 |
960 |
945 |
Temperature of pre-finish rolling (°C) |
922 |
930 |
933 |
935 |
Temperature of first water cooling (°C) |
785 |
/ |
780 |
782 |
Water cooling rate (°C/s) /Hydraulic pressure (MPa) |
38/0.5 |
/ |
33/0.5 |
32/0.5 |
Entry temperature of finish rolling (°C) |
835 |
880 |
820 |
821 |
Temperature of second water cooling (°C) |
680 |
/ |
670 |
675 |
Water cooling rate (°C/s) / Hydraulic pressure (MPa) |
72/0.6 |
/ |
65/0.5 |
62/0.5 |
[0081] Each property of the alloy steel obtained in comparative examples 1-4 are shown in
Table 8.
Table 8 Parameters of mechanical properties of the steel obtained in comparative examples
1-4
Specification of the steel bar (mm) |
∅65 |
∅80 |
Ø100 |
∅90 |
parameters of properties |
Standard values |
Comparative example 1 |
Comparative example 2 |
Comparative example 3 |
Comparative example 4 |
Yield strength (MPa) |
≥ 420 |
460 |
330 |
330 |
340 |
Tensile strength (MPa) |
≤ 520 |
657 |
445 |
445 |
498 |
Spread (%) |
≥19 |
is |
26 |
25 |
27 |
Charpy V impact energy at -20°C(J) |
≥47 |
32 |
54 |
35 |
62 |
Charpy V impact energy at -40°C(J) |
≥31 |
17 |
25 |
19 |
37 |
[0082] Although preferable examples of the invention are already described, the technical
engineering person in the art may make other changes and modifications to those examples.
Therefore, the attached claims should be interpreted as including preferable examples
and all changes and modifications falling in the scope of the invention.
[0083] The above contents are only preferable examples of the invention, and not limited
to the invention, for those skilled in the art, the invention may have various changes
and varieties. Any changes, equivalent substitutions, improvements that are made within
the spirit and principle of the invention should be included in the protection scope.
1. A rolling method for a high-toughness high-strength low-alloy steel, its characteristic
is that, the rolling method sequentially comprises the following steps:
Heating, descaling, rough rolling, continuous rolling, first water cooling, finish
rolling, second water cooling, and cold hearth cooling;
Using a converter continuous casting billet as a raw material, the continuous casting
billet comprises the following chemical components and contents in percentage by mass:
C≤0.20;Si≤0.60;Mn:1.37 ~ 1.70;Cr≤0.30;P≤.020;5≤0.020;V:0.07 ∼ 0.10;Al≤0.03;N.0.008~0.025;with
the balance being Fe and inevitable impurities;
After the first water cooling, the temperature is 765∼800°C;
In the step of the finish rolling, entry temperature of initial rolling during the
finish rolling is 832~850°C;
During the second water cooling, the temperature under which the steel performs the
second water cooling after the step of the finish rolling is 600°C~700°C, wherein,
water cooling rate is 25~100°C/s, hydraulic pressure is 0.2~0.6MPa;
The cold hearth cooling means the steel after the second water cooling is cooled on
the cold hearth.
2. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 1, its characteristic is that, the step of the heating is divided into four
zones, which are sequentially as follows: pre-heating zone, heating first zone, heating
second zone, and soaking zone,
The temperature of the pre-heating zoneis less than or equal to 750°C;
The temperature of the heating first zone is 900~1050°C;
The temperature of the heating second zone is 1050~1150°C;
The temperature of the soaking zone is 1150~1210°C.
3. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 2, its characteristic is that, the total heating time of the step of the
heating is 3~5h; the soaking time of the soaking zone is 30-80min.
4. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 2, its characteristic is that, the step of the heating is performed in a
four-section stepwise heating furnace.
5. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 1 or 2, its characteristic is that, the entry temperature of the rough rolling
is 950∼1050°C, the pass of the rough rolling is 5~7.
6. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 5, its characteristic is that, the number of rough-rolling mills provided
in the step of the rough rolling is 6; the pass of the rough rolling is 6.
7. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 6, its characteristic is that, the step of the continuous rolling includes
intermediate rolling and pre-finish rolling,
The entry temperature of the intermediate rolling is 900~1000°C, the pass of the intermediate
rolling is 5~7;
Outlet temperature of the pre-finish rolling is 850~950°C, the pass of the pre-finish
rolling is 3~5.
8. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 7, its characteristic is that, the number of intermediate-rolling mills provided
in the step of the intermediate rolling is 6; the pass of the intermediate rolling
is 6.
9. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 7, its characteristic is that, the number of pre-finish-rolling mills provided
in the step of the pre-finish rolling is 4; the pass of the pre-finish rolling is
4.
10. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 5, its characteristic is that, during the first water cooling, the first
water cooling is performed with incoming materials after the step of the continuous
rolling, wherein, the water cooling rate is 25~50°C/s, the hydraulic pressure is 0.2~0.6MPa.
11. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 5, its characteristic is that, a reducing and sizing mill set is used for
the finish rolling.
12. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 11, its characteristic is that, the reducing and sizing mill set is a three-roller
reducing and sizing mill set.
13. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 5, its characteristic is that, in the step of the descaling, high-pressure
water descaling is used with the aim to descale an iron sheet, the hydraulic pressure
of the high-pressure water is 15~20MPa.
14. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 13, its characteristic is that, the hydraulic pressure of the high-pressure
water is 17~20MPa.
15. According to the rolling method for a high-toughness high-strength low-alloy steel
in any one of claims 1-2, its characteristic is that, a high-toughness high-strength
low-alloy steel bar is obtained after the rolling method.
16. According to the rolling method for a high-toughness high-strength low-alloy steel
in claim 15, its characteristic is that, the specification of the steel bar is Ø060∼120mm.