Note: Descriptions are shown in the official language in which they were submitted.
THIN GAUGE AR450 STEEL PLATE AND MANUFACTURING METHOD THEREOF
TECHNICAL FIELD
[01] The present invention relates to a thin gauge AR450 steel plate and a
manufacturing method thereof. The present invention belongs to the technical
field of special
steel smelting.
BACKGROUND ART
[02] As a steel material with high abrasion resistance, low-alloy abrasion-
resistant steel
plates have been widely used in workplaces with harsh environments, such as
mines, railways
and metallurgy. In addition to abrasion resistance, the low-alloy abrasion-
resistant steel plates
also have high strength, good toughness, strong weldability and other
characteristics. At
present, the low-alloy abrasion-resistant steel plates produced in China are
mainly
concentrated in AR500 and below grades, among which the use of AR450 steel
plates occupies
a considerable market share.
[03] The main using thickness of the AR450 steel plates is concentrated
below 50 mm,
especially the thickness of 8-30 mm, with parts of mechanical equipment as
thin as 4 mm.
[04] At present, for wide and thick plate enterprises in the domestic and
overseas,
except for steel enterprises with continuous rolling equipment, the thinnest
limit thickness of
steel plates produced by steel plate enterprises is generally 6 mm. However,
even 6 mm steel
plates are only rolled by rolling mills with furnace coiler equipment because
coiling furnaces at
both ends of the rolling mill can keep the temperature of the steel plates and
even heat the steel
plates to ensure the rolling temperature, while the thinnest rolling thickness
of the rolling mill
without such equipment is only about 8 mm. When the thickness is further
reduced, slabs cool
rapidly, and the rolling torque force is too large, which affects the life of
the equipment; and the
rolled steel plates have a poor shape, and it is difficult to control the
thickness accuracy,
especially for the high-strength steel plates.
[05] Chinese Patent Publication No. CN1121444A discloses a new process for
multi-stand tandem pack-rolled sheet production, in which multiple single-roll
rolling mills are
arranged in tandem. After being heated, a thin slab enters the first rolling
mill for single-sheet
rolling, the second rolling mill performs two-in-one rolling, and the third
rolling mill performs
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four-in-one rolling. The temperature of each stand is controlled during the
rolling process, and
the temperature of the third stand and the fourth stand is controlled at 400-
500 C. This method
is to stack semi-finished products together for rolling in the rolling
process, which is only
suitable for production of materials with a small unit weight.
[06] The patents such as Chinese Patent Publication No. CN101439348A "A
production process for producing extra-thick plates" and CN101590596A "A
method of
producing and manufacturing extra-thick slabs by accumulative pack rolling and
welding" all
mention a plate compounding manner, that is, two or more continuous casting
slabs are
adopted for joint rolling. However, the production of thick gauge steel plates
is all realized by
welding two or more original materials together in the rolling process.
SUMMARY OF THE INVENTION
[07] The technical problem to be solved by the present invention is to
provide a 4-8 mm
thick AR450 wide plate and a manufacturing method of the same with respect to
the above prior
art. The maximum width is up to 3200 mm. Not only does the product width
exceed the
conventional width of hot continuous rolled sheets, but also the problem that
some of wide and
thick plate enterprises without rolling equipment cannot produce such thin
steel plates is solved,
the product supply specifications are completed, and market competitiveness is
improved.
[08] The technical solution adopted by the present invention to solve the
above
problems is a 4-8 mm thin gauge AR450 steel plate, chemical compositions of
the steel plate
include, by weight percentage, C: 0.15-0.30, Si: 0.25-0.45, Mn: 0.80-1.20, Cr:
0.20-0.60, Mo:
0.10-0.50, Ni: 0.10-0.50, Al: 0.02-0.08, B: 0.0010-0.0030, P 5 0.020, S 5
0.010, and the balance
being Fe and unavoidable impurities. The carbon equivalent of the finished
final steel plate is
not more than 0.52%.
[09] The present invention also provides a method of making the above thin
gauge
AR450 steel plate. The main working procedures of the manufacturing method
include:
determining a low carbon-equivalent chemical composition for a 4-8 mm steel
plate, and
obtaining 150-400 mm thick continuous casting slabs through steelmaking,
refining and vacuum
continuous casting; compound welding the edges of two slabs of the same
dimensions or
intermediate slabs having a selected thickness obtained by cogging and
rolling, wherein a
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middle portion of the compounded slab is maintained in a non-vacuum condition;
heating and
then rolling the compounded slabs to a selected thickness, wherein the middle
portion of the
rolled compounded slab is not welded due to the non-vacuum condition, and
cutting off the
welded edges of the rolled compounded slab to obtain two steel plates; and
subjecting each
one of the steel plates to heat treatment, and straightening each steel plate
before quenching if
the each steel plate has a relatively low flatness. The final delivery state
of the steel plate
produced by the manufacturing method is Q + T, the thickness of the finished
product is 4-8 mm,
and the maximum width of the steel plate is 3200 mm. The product performance
and
appearance quality of the steel plates meet GB/T 24186-2009 standards.
[010] The manufacturing method specifically includes the following steps:
[011] I. Slab preparation
[012] (1) Steelmaking: precisely controlling alloying elements in steel to
ensure that a
carbon equivalent deviation between different heats is not more than 0.02%,
wherein precise
control of compositions helps to stabilize the performance of large batches of
steel plates;
performing LF furnace refining to fully deoxidize and desulfurize; keeping the
RH limit vacuum
time to be longer than 20 min so as to reduce contents of H and N in the
steel; and performing
calcium treatment operation to promote modification and floating of
inclusions;
[013] (2) Continuous casting of slabs: performing continuous casting on 150-
400 mm
thick slabs by a straight arc continuous casting machine, realizing low
superheat and constant
casting speed operation by using a tundish induction heating technology, and
realizing
production of high-quality continuous casting slabs by adopting technologies
such as argon
protection and dynamic soft reduction, wherein low-power quality of the
casting slabs meets: a
center segregation is not greater than Level 1.0 of Class C; a center porosity
is not greater than
Level 1.0; and there are no other defects such as cracks in triangular areas.
[014] (3) Prefabricating of intermediate slabs, wherein thinner prefabricated
intermediate
slabs need to be used for production of the 4-5 mm thick steel plate through
compound rolling.
The prefabricated intermediate slabs are rolled when the 150-400 mm continuous
casting slabs
are heated to about 1220 C, and a thickness of the prefabricated intermediate
slabs is
controlled at 60-100 mm. For steel plates with a thickness > 5-8 mm, 150 mm
thick slabs can be
used for direct compound rolling, without needing compounding after rolling
into the
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prefabricated intermediate slabs. When a width of the finished steel plates
exceeds a width of
the continuous casting slabs, it is necessary to roll the slabs and widen them
to the
prefabricated intermediate slabs with a width larger than that of the finished
products, and the
maximum width of the prefabricated intermediate slabs is not greater than 3400
mm.
[015] II. Slab finishing and compounding
[016] The appearance quality of the continuous casting slabs or the
prefabricated
intermediate slabs is inspected according to YB/T 2012, and the slabs with
qualified
appearance quality are cut into sections according to size requirements of a
production plan,
surfaces of two slabs with the same size are milled and then welded on the
periphery, the
middles are subjected to non-vacuum treatment, and a welding width from edges
of the slabs is
controlled at 50-80 mm. On one hand, it is ensured that the peripheries of the
slabs cannot be
layered when the slabs are rolled, and on the other hand, the yield of the
steel plates must be
considered.
[017] III. Compound slab heating and rolling
[018] (1) Compound slab heating: in a low-temperature section, the temperature
rises to
850 20 C at a rate of 60-100 C/h, and the temperature is kept for 2-3 hours;
in an
intermediate-temperature section, the temperature rises to 1000 20 C at a
rate of not more
than 120 C/h, and the temperature is kept for 2-3 h; and in a high-temperature
section, the
temperature rises to 1200-1250 C at a rate of not more than 100 C/h, and the
temperature is
kept for 5-9 hours. Appropriately reducing the heating rate in the high-
temperature section and
prolonging the holding time after reaching the required temperature are
beneficial to bonding of
metal in welding areas.
[019] (2) Compound slab rolling: on a wide and thick plate rolling mill,
rolling is
performed by 10-15 passes until a thickness is twice a target thickness of the
finished single
steel plate, and a thickness tolerance of the compound steel plates is
controlled at 0-0.6 mm.
During the rolling process, there is no widening rolling, but all longitudinal
rolling. During rolling
in the first 2 passes, a small rolling reduction is used, and in the middle
pass, there are 2-3
passes with a rolling reduction of 30-50 mm, so as to realize welding of the
welding area. After
passing through a hot straightening machine, the steel plates are cooled on a
cooling bed.
When cooled to about 300 C, the steel plate can be straightened on a cold
straightening
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machine if there is a warp.
[020] IV. Steel plate heat treatment
[021] (1) Quenching: the 4-5 mm thick compound steel plate is quenched by a
quenching machine. After quenching, the four side edges of the compound steel
plate are cut
off, and the upper and lower plates are split to obtain two steel plates with
the same thickness;
due to the limitations to material hardenability of the compound steel plates
with a thickness >
5-8 mm, it is necessary to cut off the four side edges of the compound steel
plate and split the
upper and lower plates before quenching the single steel plate. A quenching
process of the
steel plate includes: a heating temperature of 900-940 C, a holding time of
(20-25) min + 3
min/mm x steel plate thickness (calculating according to a total thickness of
the upper and
lower plates for the compound steel plate), and water cooling after furnace
discharge.
[022] (2) Tempering: low temperature tempering and furnace discharge are
performed
on the steel plate by using a continuous furnace. The tempering process
includes: the heating
temperature of 180-220 C, the holding time of 1-2 hours, and air cooling after
furnace discharge.
The warped steel plate can be subjected to strong straightening treatment with
temperature
after furnace discharge, so that the unevenness of the steel plate is not
greater than 5 mm/m.
V. Inspection and examination
[023] The finished AR450 steel plate is inspected for appearance quality
according to
GB/T 24186-2009, sampled for various performance inspections, and judged
according to GB/T
24186-2009 standards.
[024] Compared with the prior art, the present invention has the advantages
that:
the present invention provides a manufacturing method of a 4-8 mm AR450 wide
plate, and
the maximum width is up to 3200 mm; not only the product width exceeds the
conventional
width of hot continuous rolled sheets, but also the problem that parts of wide
and thick plate
enterprises without rolling equipment cannot produce such thin steel plates is
solved; the
product supply specifications are completed; and market competitiveness is
improved.
DETAILED DESCRIPTION OF EMBODIMENTS
[025] The present invention will be further described in detail below in
conjunction with
embodiments and comparative examples.
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[026] Embodiment 1
[027] A thin gauge AR450 wide plate involved in this embodiment has a
thickness of 4
mm and a width of 3200 mm, and chemical compositions of the plate include, by
mass
percentage: C: 0.20, Si: 0.35, Mn: 1.10, Cr: 0.30, Mo: 0.20, Ni: 0.20, Al:
0.03, B: 0.0020, P:
0.005, 5: 0.002, and the balance being Fe and unavoidable impurities, and the
carbon
equivalent is 0.50%.
[028] A manufacturing process of the steel plate is as follows:
Steelmaking ¨> continuous casting ¨> prefabrication of intermediate slabs ¨>
compounding ¨>
rolling ¨> quenching ¨> splitting of upper and lower plates ¨> tempering ¨>
finishing ¨>
inspection ¨> storage.
[029] Specific operation of the main working procedures is as follows:
[030] Steelmaking: five harmful elements in steel are strictly controlled
during the
steelmaking process, wherein N is not more than 25 ppm, 0 is not more than 8
ppm, and H is
not more than 1.2 ppm; and calcium treatment is required in the refining and
degassing process
to control the size and composition of inclusions.
[031] Continuous casting: molten steel is continuously cast into continuous
casting slabs
with a thickness of 300 mm and a width of 2500 mm by a straight arc continuous
casting
machine; the low-power quality of the slabs is: a center segregation is Level
1.0 of Class C; a
center porosity is Level 0.5; and there are no other defects such as cracks in
triangular areas.
[032] Rolling and compounding of prefabricated intermediate slabs: after being
heated,
the continuous casting slabs are first subject to widening rolling to 3350 mm
and then
longitudinal rolling to 65 mm, the hot-rolled steel plate enters a hot
straightening machine to be
straightened and then cooled in a cooling bed to ensure the flatness of the
prefabricated
intermediate slabs. The hot-rolled steel plate is cut into two prefabricated
intermediate slabs of
the same size for surface milling, then four sides of the prefabricated
intermediate slabs are
subject to compound welding, the middles are in a non-vacuum state, the
compound welding
positions are within 50-80 mm from the edges of the slabs, and the thickness
of the slabs after
compounding is 124 2 mm.
[033] Compound slab heating and rolling: the compound slabs are heated in
stages, in a
low-temperature section, the temperature rises to 850 20 C at a rate of 70
C/h, and the
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temperature is kept for 2 hours; in an intermediate-temperature section, the
temperature rises
to 1000 20 C at a rate of 100 C/h, and the temperature is kept for 2 h; and
in a
high-temperature section, the temperature rises to 1220 20 C at a rate of 80
C/h, and the
temperature is kept for 5.5 hours. During the compound slab rolling process,
there is no
widening rolling, but all longitudinal rolling, and a total of 12 rolling
passes, of which the rolling
reductions in the first two passes are 5 mm and 8 mm, and the rolling
reductions in the fifth pass
and the sixth pass are respectively 35 mm and 32 mm; and after passing through
a hot
straightening machine, the rolled steel plate is cooled on a cooling bed, and
there is no obvious
warp. The thickness of the rolled compound steel plate is 8.2 mm
[034] Heat treatment: the compound steel plate is heated to 920 C in a
continuous
furnace, is subjected to heat holding for 48 min, and then enters a quenching
machine for water
cooling; after the steel plate is cooled, four-side welding areas of the steel
plate are cut off, and
the upper and lower plates are split to obtain quenched steel plates with a
width of 3200 mm;
the quenched steel plates are subjected to tempering heat treatment by the
continuous furnace
in time, the steel plates are heated to 200 C and subject to heat holding for
1 hour, and then
discharged from the furnace; and the steel plates are subjected to strong
straightening
treatment with the temperature, and an AR450 thin plate with the unevenness
not greater than
mm/m is obtained.
[035] The AR450 steel plate with a thickness of 4 mm and a width of 3200 mm
manufactured by the above manufacturing process has a good shape and uniform
hardness,
and its main properties are shown in Table 1.
[036] Embodiment 2
[037] A thin gauge AR450 wide plate involved in this embodiment has a
thickness of 6
mm and a width of 2500 mm, and chemical compositions of the plate include, by
mass
percentage: C: 0.19, Si: 0.29, Mn: 1.15, Cr: 0.25, Mo: 0.21, Ni: 0.18, Al:
0.03, B: 0.0018, P:
0.006, 5: 0.002, and the balance being Fe and unavoidable impurities, and the
carbon
equivalent is 0.49%.
[038] A manufacturing process of the steel plate is as follows:
Steelmaking ¨> continuous casting ¨> compounding ¨> rolling ¨> splitting of
upper and lower
plates ¨> quenching ¨> tempering ¨> finishing ¨> inspection ¨> storage.
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[039] Specific operation of the main working procedures is as follows:
[040] Steelmaking: five harmful elements in steel are strictly controlled
during the
steelmaking process, wherein N is not more than 25 ppm, 0 is not more than 8
ppm, and H is
not more than 1.2 ppm; and calcium treatment is required in the refining and
degassing process
to control the size and composition of inclusions.
[041] Continuous casting: molten steel is continuously cast into the
continuous casting
slabs with a thickness of 150 mm and a width of 2600 mm by a straight arc
continuous casting
machine; the low-power quality of the slabs is: a center segregation is Level
0.5 of Class C; a
center porosity is Level 0.5; and there are no other defects such as cracks in
triangular areas.
[042] Slab compounding: two continuous casting slabs of the same size are
subject to
surface milling, and then compound welding is carried out on the peripheries,
and the middles
are in a non-vacuum state. The compound welding positions are within 50-80 mm
from edges of
the slabs, and a thickness of the slabs after compounding is 294 2 mm.
[043] Compound slab heating and rolling: the compound slabs are heated in
stages, in a
low-temperature section, the temperature rises to 850 20 C at a rate of 70
C/h, and the
temperature is kept for 3 hours; in an intermediate-temperature section, the
temperature rises
to 1000 20 C at a rate of 100 C/h, and the temperature is kept for 3 h; and
in a
high-temperature section, the temperature rises to 1220 20 C at a rate of 80
C/h, and the
temperature is kept for 9 hours. There is no widening rolling in the compound
slab rolling
process, but all longitudinal rolling, and a total of 14 rolling passes, of
which the rolling
reductions in the first two passes are 5 mm and 8 mm, and the rolling
reductions in the fifth pass,
the sixth pass and the seventh pass are respectively 50 mm, 50 mm and 45 mm,
the rolled steel
plate is cooled by a cooling bed after passing through a hot straightening
machine, and there is
no obvious warp. The thickness of the rolled compound steel plate is 12.3 mm
[044] Heat treatment: before the heat treatment of the compound steel plate,
the
four-side welded areas are cut off, and the upper and lower plates are split
to obtain hot-rolled
steel plates with a width of 2500 mm. The split steel plates are heated to 920
C in a continuous
furnace, subject to heat holding for 40 min, and then enters a quenching
machine for water
cooling; tempering heat treatment is performed on the quenched steel plates in
time by the
continuous furnace, the steel plates are heated to 190 C, subject to heat
holding for 1.2 hours,
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and then discharged from the furnace; and the steel plates are subject to
strong straightening
treatment with the temperature, and an AR450 thin plate with the unevenness
not greater than
mm/m is obtained.
[045] The AR450 steel plate with a thickness of 6 mm and a width of 2500 mm
manufactured by the above manufacturing process has a good shape and uniform
hardness,
and its main properties are shown in Table 1.
[046] Embodiment 3
[047] A thin gauge AR450 wide plate involved in this embodiment has a
thickness of 8
mm and a width of 3000 mm, and chemical compositions of the plate include, by
mass
percentage: C: 0.21, Si: 0.25, Mn: 1.11, Cr: 0.25, Mo: 0.23, Ni: 0.17, Al:
0.03, B: 0.0016, P:
0.005, 5: 0.003, and the balance being Fe and unavoidable impurities, and the
carbon
equivalent is 0.50%.
[048] A manufacturing process of the steel plate is as follows:
Steelmaking ¨> continuous casting ¨> prefabrication of intermediate slabs ¨>
compounding ¨>
rolling ¨> splitting of upper and lower plates ¨> quenching ¨> tempering ¨>
finishing ¨>
inspection ¨> storage.
[049] Specific operation of the main working procedures is as follows:
[050] Steelmaking: five harmful elements in steel are strictly controlled
during the
steelmaking process, wherein N is not more than 25 ppm, 0 is not more than 8
ppm, and H is
not more than 1.2 ppm; and calcium treatment is required in the refining and
degassing process
to control the size and composition of inclusions.
[051] Continuous casting: molten steel is continuously cast into the
continuous casting
slabs with a thickness of 370 mm and a width of 2200 mm by a straight arc
continuous casting
machine; the low-power quality of the slabs is: a center segregation is Level
1.0 of Class C; a
center porosity is Level 0.5; and there are no other defects such as cracks in
triangular areas.
[052] Rolling and compounding of prefabricated intermediate slabs: after being
heated,
the continuous casting slabs are first subject to widening rolling to 3150 mm
and then
longitudinal rolling to 80 mm, the hot-rolled steel plate enters a hot
straightening machine to be
straightened and then cooled in a cooling bed to ensure the flatness of the
prefabricated
intermediate slabs. The hot-rolled steel plate is cut into two prefabricated
intermediate slabs of
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the same size for surface milling, then four sides of the prefabricated
intermediate slabs are
subject to compound welding, the middles are in a non-vacuum state, the
compound welding
positions are within 50-80 mm from the edges of the slabs, and the thickness
of the slabs after
compounding is 154 2 mm.
[053] Compound slab heating and rolling: the compound slabs are heated in
stages, in a
low-temperature section, the temperature rises to 850 20 C at a rate of 70
C/h, and the
temperature is kept for 2.5 hours; in an intermediate-temperature section, the
temperature rises
to 1000 20 C at a rate of 100 C/h, and the temperature is kept for 2.5 h;
and in a
high-temperature section, the temperature rises to 1220 20 C at a rate of 85
C/h, and the
temperature is kept for 6.5 hours. During the compound slab rolling process,
there is no
widening rolling, but all longitudinal rolling, and a total of 12 rolling
passes, of which the rolling
reductions in the first two passes are 5 mm and 8 mm, and the rolling
reductions in the fifth pass
and the sixth pass are 50 mm and 45 mm respectively, after passing through a
hot straightening
machine, the rolled steel plate is cooled by a cooling bed , and there is no
obvious warp. The
thickness of the rolled compound steel plate is 16.3 mm.
[054] Heat treatment: before the heat treatment of the compound steel plate,
the
four-side welded areas are cut off, and the upper and lower plates are split
to obtain hot-rolled
steel plates with a width of 3000mm. The split steel plates are heated to 910
C in a continuous
furnace, subjected to heat holding for 46min, and then enters a quenching
machine for water
cooling; tempering heat treatment is performed on the quenched steel plates in
time by the
continuous furnace, the steel plates are heated to 200 C, heat holding is
performed for 1.5
hours, and then discharged from the furnace; and the steel plates are subject
to strong
straightening treatment with the temperature, and an AR450 thin plate with the
unevenness not
greater than 5 mm/m is obtained.
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Table 1 Mechanical properties and unevenness conditions of AR450 steel plates
produced in
each embodiment
Surface
Tensile Elongation
Brinell
Unevenness
Embodiment Thickness/mm strength after breaking
Hardness mm/m
Rrn/M Pa Asornm/%
H BW
1 4 1472 9 450 3
2 6 1480 10 456
2.5
3 8 1465 9.5 448
2.5
[055] In addition to the above embodiments, the present invention also
includes other
implementations, and all technical solutions formed by equivalent
transformation or equivalent
replacement shall fall within the protection scope of the claims of the
present invention.
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