Note: Descriptions are shown in the official language in which they were submitted.
Description
Title of Invention: HOT-ROLLED STEEL PLATE AND STEEL TUBE
HAVING EXCELLENT ABRASION RESISTANCE, AND MANUFACTURING
METHOD THEREOF
Technical Field
[0001] The present disclosure relates to a hot-rolled steel
plate, a steel tube, and a manufacturing method thereof, and
more specifically, to a high-manganese hot-rolled steel
plate having excellent abrasion resistance, a steel tube
manufactured using the hot-rolled steel plate, and a
manufacturing method thereof.
Background Art
[0002] When dredging a route to secure a water depth and
water area of a sailing vessel or dredging landfill to create
a hinterland, a steel tube used for dredging is required to
have excellent abrasion resistance against gravel, sand, or
the like. In addition, in the case of a steel tube used in
the mining industry to extract and transport resources such
as minerals, abrasion resistance characteristics are closely
related to production costs, so excellent abrasion
resistance characteristics are required for efficient
production costs.
[0003] In the case of carbon steel of which a main structure
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is ferrite or martensite, which is used as an abrasion-
resistant steel tube, there is a need for substitute
materials that can overcome these disadvantages as
limitations in abrasion resistance have recently appeared.
[0004] Meanwhile, an austenitic steel material has excellent
abrasion resistance due to work hardenability
characteristics, which is used as abrasion-resistant parts
in various industries. In order to increase abrasion
resistance, high manganese steel contains a high content of
carbon and a large amount of manganese, and efforts have
been made to increase an austenite structure and resistance.
[0005] In addition, in the case of steel tubes for dredging
and mineral extraction/transport, as well as small and
medium-diameter steel tubes, ERW steel tubes are
manufactured and used using hot-rolled materials, and in the
case of large diameter steel tubes, spiral steel tubes using
hot-rolled materials and submerged arc welding (SAW) steel
tubes using thick plates are manufactured and used. In the
case of high manganese steel, much development has been
performed on steel tubes using thick plates, but the
development of high manganese hot-rolled steel and steel
tubes using the same is required.
Summary of Invention
Technical Problem
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[0006] An aspect of the present disclosure is to provide a
hot-rolled steel plate, a steel tube, having excellent
abrasion resistance, and a manufacturing method thereof.
[0007] The object of the present disclosure is not limited
to the above. A person skilled in the art would have no
difficulty in understanding the further subject matter of
the present disclosure from the general content of this
specification.
Solution to Problem
[0008] According to an aspect of the present disclosure,
provided is a hot-rolled steel plate, the hot-rolled steel
plate including, by weight: manganese (Mn): 10 to 20%, carbon
(C): 0.6 to 2.0%, chromium (Cr): 5.0% or less, aluminum (Al):
0.5% or less, silicon (Si): 1.0% or less, phosphorus (P):
0.1% or less, sulfur (S): 0.02% or less, with a remainder of
Fe, and other unavoidable impurities,
[0009] wherein the hot-rolled steel plate has
a
microstructure with austenite as a main phase, and includes
film-shaped precipitates formed along austenite grain
boundaries,
[0010] wherein hardness of the hot-rolled steel plate
increases by 1.1 times or more by work hardening after piping.
[0011] The precipitate may have a thickness of 0.1 to 2.0
um.
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[0012] The steel plate may have a tensile strength of 800
MPa or more and elongation of 30% or more.
[0013] The steel plate may have a Vickers hardness of 220Hv
or more.
[0014] The steel plate may have a thickness of 4 to 20 mm.
[0015]
[0016] According to another aspect of the present disclosure,
provided is a steel tube, the steel tube including, by weight:
manganese (Mn): 10 to 20%, carbon (C): 0.6 to 2.0%, chromium
(Cr): 5.0% or less, aluminum (Al): 0.5% or less, silicon
(Si): 1.0% or less, phosphorus (P): 0.1% or less, sulfur (S):
0.02% or less, with a remainder of Fe, and other unavoidable
impurities,
[0017] wherein the steel tube has a microstructure with
austenite as a main phase, and includes film-shaped
precipitates formed along austenite grain boundaries,
[0018] wherein hardness of the steel tube, as compared to
that of the steel plate, is 1.1 times or more.
[0019] The steel tube may have a Vickers hardness of 250Hv
or more.
[0020]
[0021] According to an aspect of the present disclosure,
provided is a manufacturing method of a hot-rolled steel
plate, the manufacturing method including operations of:
reheating a steel slab including, by weight: manganese (Mn):
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to 20%, carbon (C): 0.6 to 2.0%, chromium (Cr): 5.0% or
less, aluminum (Al): 0.5% or less, silicon (Si): 1.0% or
less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or
less, with a remainder of Fe, and other unavoidable
5 impurities,
[0022] hot rolling the reheated steel slab to obtain a hot-
rolled steel plate; and
[0023] cooling the hot-rolled steel plate to a temperature
range of less than 500 C and then coiled,
10 [0024] wherein a coiling start temperature is 500 C or lower,
and an average coiling temperature is less than 300 C.
[0025] The reheating may be performed at a temperature within
a range of 1000 to 1250 C.
[0026] The hot rolling may be performed at a finishing
temperature of 800 C or higher,
[0027] During the cooling, a cooling rate may be 5 C/s or
more.
[0028] The steel plate after the hot rolling may have a
thickness of 4 to 20 mm.
[0029]
[0030] Another aspect of the present disclosure may provide
a manufacturing method of a steel tube including the
operation of piping the hot-rolled steel plate to obtain a
steel tube.
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Advantageous Effects of Invention
[0031] As set forth above, according an aspect of the present
disclosure, a hot-rolled steel plate and a steel tube having
excellent abrasion resistance, and a manufacturing method
thereof may be provided.
Brief description of drawings
[0032] FIG. 1 is a photograph of a microstructure of
Inventive Example 1 according to an aspect of the present
disclosure observed with an optical microscope (200x
magnification).
Best Mode for Invention
[0033] Hereinafter, the present disclosure will be described
in detail. Embodiments of the present disclosure may be
modified in various forms, and the scope of the present
disclosure should not be construed as limited to the
embodiments described below. These embodiments are provided
to explain the present disclosure in more detail to those
skilled in the art.
[0034]
[0035] Hereinafter, the present disclosure will be described
in detail.
[0036]
[0037] Hereinafter, a steel composition of the present
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disclosure will be described in detail.
[0038] In the present disclosure, unless other specified, %
indicating a content of each element is based on weight.
[0039]
[0040] A hot-rolled steel plate may include, by weight:
manganese (Mn): 10 to 20%, carbon (C): 0.6 to 2.0%, chromium
(Cr): 5.0% or less, aluminum (Al): 0.5% or less, silicon
(Si): 1.0 % or less, phosphorus (P): 0.1% or less, sulfur
(S): 0.02% or less, with a remainder of Fe and other
unavoidable impurities.
[0041]
[0042] Manganese (Mn): 10 to 20%
[0043] Manganese (Mn) is a very important element that plays
a role in stabilizing austenite and may improve uniform
elongation. Manganese (Mn) is preferably included in an
amount of 10% or more in order to secure austenite as a main
structure. If a content of manganese (Mn) is less than 10%,
austenite stability may decrease and a martensite structure
may be formed during a rolling process in a manufacturing
process. As a result, an austenite structure may not be
sufficiently secured, making it difficult to secure
sufficiently uniform elongation. On the other hand, if the
content of manganese (Mn) exceeds 20%, manufacturing costs
may increase significantly, corrosion resistance may be
reduced due to excessive addition of manganese (Mn), and
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internal oxidation may occur severely when heated in the
manufacturing process, which may cause a problem such as
deterioration in surface quality. A more preferable lower
limit of the manganese (Mn) content may be 11.5%, and a more
preferable upper limit may be 19.5%.
[0044]
[0045] Carbon (C): 0.6 to 2.0%
[0046] Carbon (C) is an austenite stabilizing element that
only plays a role in improving uniform elongation, but is
also a very advantageous element in improving strength and
a work hardening rate. If a carbon (C) content is less than
0.6%, it may be difficult to form stable austenite at room
temperature, causing a problem in that it may be difficult
to secure sufficient strength and work hardening rate.
Meanwhile, if the carbon (C) content exceeds 2.0%, a large
amount of carbides are precipitated and the uniform
elongation is reduced, making it difficult to secure
excellent elongation, and premature fracturing may occur. In
order to increase abrasion resistance, it is advantageous to
increase the carbon (C) content as much as possible, but
even if precipitation of carbides is suppressed through heat
treatment, there is a limitation in solid solutioning of
carbon (C), since there are concerns about deterioration in
physical properties of the steel material, an upper limit of
the carbon (C) content is preferably limited to 2.0%. A more
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preferable lower limit of the carbon (C) content may be
0.75%, and a more preferable upper limit of the carbon (C)
content may be 1.85%.
[0047]
[0048] Chromium (Cr): 5.0% or less
[0049] Chromium (Cr) may serve to increase strength of a
steel material by being dissolved in austenite. In addition,
chromium (Cr) is an element for improving corrosion
resistance of the steel material, but it may reduce toughness
by forming carbides at austenite grain boundaries. Therefore,
a chromium (Cr) content added in the present disclosure is
preferably determined considering the relationship with C
and other elements added together, and in order to prevent
formation of carbides, chromium (Cr) is preferably included
in an amount of 5% or less. More preferably, chromium (Cr)
is preferably included in an amount of 4% or less. If the
chromium (Cr) content exceeds 5%, it may be difficult to
effectively suppress formation of chromium-based carbides at
austenite grain boundaries, which may reduce impact
toughness. In the present disclosure, the chromium (Cr)
content may be controlled as needed, and 0% may be included.
[0050]
[0051] Aluminum (Al): 0.5% or less
[0052] Aluminum (Al) is a component included as a deoxidizer
during a steelmaking process, and in the present disclosure,
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aluminum (Al) may be included in an amount of 0.5% or less.
In the present disclosure, 0% can be excluded as an aluminum
(Al) content.
[0053]
[0054] Silicon (Si): 1.0% or less
[0055] Silicon (Si) is a component included as a deoxidizer
during a steelmaking process along with Al, and in the
present disclosure, silicon (Si) may be included in an amount
of 1.0% or less, and 0% may be excluded.
[0056]
[0057] Phosphorus (P): 0.1% or less
[0058] Phosphorus (P) is a representative impurity that is
inevitably added to steel. If phosphorus (P) is added
excessively, it can cause quality deterioration, so an upper
limit thereof may be limited to 0.1%.
[0059]
[0060] Sulfur (S): 0.02% or less
[0061] Sulfur (S) is an impurity that is inevitably added to
steel along with P, and an upper limit thereof may be limited
to 0.02%.
[0062]
[0063] The steel of the present disclosure may include
remaining iron (Fe) and unavoidable impurities in addition
to the above-described composition. Since unavoidable
impurities may be unintentionally incorporated in a common
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manufacturing process, the component may not be excluded.
Since these impurities are known to any person skilled in
the common manufacturing process, the entire contents
thereof are not particularly mentioned in the present
specification.
[0064]
[0065] Hereinafter, a microstructure of steel of the present
disclosure will be described in detail.
[0066] In the present disclosure, unless specifically stated
otherwise, % indicating a fraction of microstructure is based
on area.
[0067]
[0068] The hot-rolled steel plate according to an aspect of
the present disclosure may have a microstructure with
austenite as a main phase.
[0069] In the present invention, the hot-rolled steel plate
may have a microstructure with austenite as the main phase
in order to secure abrasion resistance by increasing hardness
due to excellent work hardening of the material itself in an
abrasive environment. More preferably, the microstructure
may include 97 area% or more of austenite.
[0070]
[0071] A steel according to an aspect of the present
disclosure may include film-shaped precipitates formed along
austenite grain boundaries, and a thickness of the
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precipitates may be 0.1 to 2.0 pm.
[0072] In the present disclosure, it is intended to secure
sufficient strength and abrasion resistance by forming film-
shaped precipitates at austenite grain boundaries. The
precipitate according to the present disclosure may include
carbides, and may include carbides in which Cr is formed
together with C. If the thickness of the precipitates is
less than 0.1 pm, sufficient strength may not be secured,
causing a problem in that abrasion resistance may be reduced,
and if the thickness of the precipitates exceeds 2.0 pm,
there is a problem in that ductility and toughness are
reduced.
[0073]
[0074] A steel tube formed by piping a hot-rolled steel plate
according to an aspect of the present disclosure may have a
microstructure with austenite as a main phase, may include
film-shaped precipitates at grain boundaries, and a
thickness of the precipitates may be 0.1 to 2.0 pm.
[0075]
[0076] Hereinafter, a method of manufacturing steel of the
present disclosure will be described in detail.
[0077] The steel according to an aspect of the present
disclosure can be manufactured by reheating, hot rolling,
cooling, and coiling a steel slab satisfying the above-
described alloy composition.
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[0078]
[0079] Reheating
[0080] A steel slab satisfying the alloy composition of the
present disclosure may be reheated to a temperature within
a range of 1000 to 125000.
[0081] The slab maybe reheated before performing hot rolling.
In the slab operation, the slab may be reheated to solidify
and homonize a casting structure, segregation, and secondary
phases of the slab. If the reheating temperature is less
than 1000 C, it may be difficult to sufficiently secure the
reheating effect, and a heating furnace temperature may
become too low, causing a problem of increased deformation
resistance during hot rolling. On the other hand, if the
temperature exceeds 1250 C, partial melting and
deterioration of surface quality may occur in a segregation
zone within the casting structure.
[0082]
[0083] Hot rolling
[0084] The reheated slab can be hot rolled at a finishing
temperature of 800 C or higher to obtain a hot-rolled steel
plate with a thickness of 4 to 20 mm.
[0085] In the present disclosure, hot rolling may be
performed to produce a hot rolled steel plate with a
thickness of 4 to 20 mm. A finishing temperature is
preferably limited to be 800 C or higher for productivity,
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and more preferably, hot rolling can be performed at a
finishing temperature at a non-recrystallization temperature
(Tnr) or lower.
[0086]
[0087] Cooling and coiling
[0088] The hot-rolled steel plate may be cooled to a
temperature range of 500 C or lower at a cooling rate of
5 C/s or higher and then coiled. A coiling start temperature
may be 500 C or lower, and an average coiling temperature
may be 300 C or lower.
[0089] In the present disclosure, cooling may be performed
to a temperature within a range of less than 500 C to prevent
formation of coarse carbides. If a cooling end temperature
exceeds 500 C, coarse carbides may be formed during cooling
to room temperature after coiling to reduce uniform
elongation, and it may be difficult to secure excellent
elongation, and there may be a risk of premature fracturing.
A lower limit of the coiling temperature is not particularly
limited, and there is no problem even if the coiling is
performed at room temperature.
[0090] If a cooling rate is less than 5 C/s, coarse carbides
may be formed, which may cause a problem of a decrease in
strength and elongation. An upper limit of the average
cooling rate is not particularly limited, but may be
appropriately selected depending on equipment specifications.
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[0091] In addition, in the present invention, by controlling
the coiling start temperature and the average coiling
temperature, the formation of coarse carbides can be
prevented and the excellent strength and elongation, which
is unique to an austenite-based steel material can be secured,
and a work hardening rate may be improved to ensure excellent
abrasion resistance.
[0092] In the present disclosure, the coiling start
temperature represents the temperature of the steel plate
when coiling begins using a coiling equipment, and the
average coiling temperature refers to the average value of
the coiling temperature of an entire length of a coil. If
the coiling start temperature exceeds 500 C or the average
coiling temperature exceeds 300 C, there may be a problem of
reduced ductility and toughness due to excessive formation
of carbides.
[0093]
[0094] A steel tube according to an aspect of the present
disclosure may be manufactured by manufacturing the hot-
rolled steel plate satisfying the alloy composition and
manufacturing method described above.
[0095]
[0096] Piping
[0097] A steel tube can be obtained by piping a steel plate
according to an aspect of the present disclosure.
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[0098] In the present disclosure, the method
of
manufacturing a welded steel tube is not particularly limited,
and a typical ERW steel tube manufacturing method can be
used. However, due to a high Mn content, intrusion defects
may occur during ERW welding due to oxides generated during
a process of melting and solidifying a steel material. To
prevent this, molten metal and oxides in a narrow gap may be
completely discharged before entering a welding point, and
additional devices may be installed to prevent exposure from
the atmosphere and a coolant.
[0099]
[00100] The steel plate of the present disclosure
manufactured in this manner may have a thickness of 4 to 20
mm, a tensile strength of 800 MPa or more, an elongation of
30% or more, and a hardness after piping into a steel tube
of 1.1 times or more that of a hot-rolled steel plate, and
may have characteristics of excellent work hardening rate
and abrasion resistance.
[00101] In addition, the steel plate of the present
disclosure may have a hardness of 220Hv or more, and the
steel tube may have a hardness of 250Hv or more.
[00102]
[00103] Hereinafter,
the present disclosure will be
specifically described through the following Examples.
However, it should be noted that the following examples are
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only for describing the present disclosure by illustration,
and not intended to limit the scope of rights of the present
disclosure.
Mode for Invention
[00104] (Example)
[00105] A steel slab having the alloy composition shown in
Table 1 below was manufactured to form a hot-rolled steel
plate according to the conditions shown in Table 2 below,
and a steel plate was manufactured with the thickness shown
in Table 3. In this case, the same reheating temperature of
1150 C was applied.
[00106]
[00107] [Table 1]
Steel Alloy composition (wt%)
type Mn C Cr Al Si P
A 13.2 1.09 0 0.002 0.370
0.0127
B 14.2 1.13 3.9 0.002 0.365
0.0125
C 10.4 1.82 2.4 0.003 0.358
0.0128
D 15.3 1.93 1.5 0.002 0.376
0.0124
E 11.7 1.31 3.1 0.003 0.367
0.0123
F 18.1 0.79 0 0.003 0.006
0.0126
G 12.1 0.3 2.9 0.002 0.008
0.0128
H 1.1 0.12 0 0.003 0.007
0.0127
I 11.1 1.14 1.4 0.003 0.328
0.0124
[00108]
[00109] [Table 2]
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Sampl Steel Hot rolling Cooling Coiling
e No. type Finishing Temperat Rate Start
Average
temperature( C) ure ( C/s) temperature
temperature
( C) ( C) (
C)
1 A 950 454 7.3 430 180
2 B 950 478 6.5 370 180
3 C 910 493 8.4 460 160
4 D 970 467 7.8 380 160
E 890 484 5.6 370 170
6 F 910 490 18 480 220
7 G 880 470 21 470 250
8 H 950 480 22 480 260
9 I 890 490 17.1 560 420
[00110]
[00111] In Table 3 below, a microstructure and mechanical
properties were measured for the manufactured steel plate
and illustrated, and ERW welding steel tube was manufactured
5 from the steel plate, and then physical properties of the
steel tube were also shown. The microstructure was shown by
observing a 1/4 portion of a thickness of the steel plate
with an optical microscope at 200x magnification, and the
tensile strength and elongation were obtained by taking a
sample of API 5L standard from the 1/4 portion of the
thickness of the steel plate and performing a tensile test
and the results thereof were shown. In this case, if the
microstructure had 97% or more of austenite, it was indicated
as 0. In addition, when precipitates with a thickness of 0.1
to 2.0 pm were formed at austenite grain boundaries, 0 was
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indicated. Regarding the mechanical properties, a hardness
of the steel plate was measured using a Vickers hardness
test, and after piping, the hardness was measured and the
ratio thereof was calculated and shown.
[00112]
[00113] [Table 3]
Sam St Thic Microstructure
of Physical property of Physical Hardne Divis
pie ee knes steel plate steel plate property ss
ion
No. 1 s of steel
ratio
ty (mm) tube
pe Austenite Precipit Tensile Elonga Hardne Hardness
ate strengt tion ss (Hv)
(%) (Hv)
(MPa)
1 A 8 0 0 1097 52 229.3 264.8 1.15
Inven
tive
Examp
le 1
2 B 8 0 0 1086 52 231.5 269.4 1.16
Inven
tive
Examp
le 2
3 C 10 0 0 1133 58 232.3 267.5 1.15
'riven
tive
Examp
le 3
4 D 10 0 0 1159 51 233.9 271.4 1.14
Maven
tive
Examp
le 4
5 E 12 0 0 1140 57 236.1 269.3 1.14
Maven
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tive
Examp
le 5
6 F 8 0 0 1012 51
226.2 258.3 1.14 Inven
tive
Examp
le 6
7 G 8 0 0 981 49
216.2 234.1 1.08 Compa
rativ
e
Examp
le 1
8 H 8 X 0 501 27
168.7 171.5 1.01 Compa
rativ
e
Examp
le 2
9 I 8 0 X 898 29
239.1 261.1 1.09 Compa
rativ
e
Examp
le 3
[00114]
[00115] As shown in Table 3, in the case of the Invention
Example satisfying the alloy composition and manufacturing
conditions of the present disclosure, the microstructure
characteristics proposed in the present disclosure were
satisfied and the physical properties desired in the present
disclosure were secured.
[00116] FIG. 1 is a photograph of the microstructure of
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Inventive Example 1 according to an aspect of the present
disclosure observed with an optical microscope (200x
magnification).
[00117]
[00118] On the other hand, in Comparative Example 1 in which
a C content was below the range proposed in the present
disclosure, and compared to Invention Example, the strength
was insufficient and a work hardening rate after
manufacturing a steel tube was also insufficient.
[00119] In Comparative Example 2 in which contents of Mn and
C were outside of the range proposed in the present
disclosure, and the strength of the steel plate was inferior,
and the elongation was also not secured due to the inferior
austenite stability due to a lack of the Mn content.
[00120] In Comparative Example 3 in which a coiling start
temperature and average temperature exceeded the range of
the present disclosure, and coarse carbides were excessively
formed, resulting in poor ductility.
[00121]
[00122] While example embodiments have been illustrated and
described above, it will be apparent to those skilled in the
art that modifications and variations could be made without
departing from the scope of the present disclosure as defined
by the appended claims.
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