Note: Descriptions are shown in the official language in which they were submitted.
CA 031.13056 2021-03-16
[DESCRIPTION]
[Invention Title]
ABRASION RESISTANT STEEL HAVING EXCELLENT HARDNESS AND
IMPACT TOUGHNESS AND MANUFACTURING METHOD THEREFOR
[Technical Field]
[0001] The present disclosure relates to a high hardness
abrasion resistant steel and a manufacturing method therefor,
and more particularly, to a high hardness abrasion resistant
steel which may be used for construction machinery, and the like,
and a manufacturing method therefor.
[Background Art]
[0002] As for construction machinery and industrial machinery
used in many industrial fields such as construction, civil
engineering, mining, and cement industries, since abrasion may
occur severely due to friction in operation, it may be necessary
to apply a material exhibiting abrasion resistance properties.
[0003] Generally, as abrasion resistance and hardness of a
thick steel sheet maybe correlated with each other, it maybe
necessary to increase hardness in the thick steel sheet
concerned, to be worn down. To secure stable abrasion resistance,
it may be necessary to have uniform hardness from the surface
of the thick steel sheet to the inside (around t/2, t = thickness)
of the sheet thickness (that is, having the same degree of
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hardness on the surface of the thick steel sheet and inside).
[0004] Generally, to obtain high hardness in a thick steel
sheet, a method of reheating to an Ac3 temperature or higher
after rolling and quenching may be widely used. For example,
cited references 1 and 2 disclose a method of increasing a
content of C and adding a large amount of hardenability
enhancing elements such as Cr and Mo, thereby increasing surface
hardness. However, to manufacture an extremely thick steel
sheet, it may be necessary to add a greater amount of
hardenability elements to secure hardenability in the center
of the steel sheet, and as C and hardenability alloys are added
in large amounts, manufacturing costs may increase, and
weldability and low-temperature toughness may degrade, which
may be problematic.
[0005] Therefore, while it is inevitable to add hardenability
alloys to secure hardenability, it has been necessary to devise
a measure for obtaining excellent abrasion resistance by
securing high hardness, and securing high strength and high
impact toughness.
[Reference]
(Reference 1) Japanese Laid-Open Patent Publication No.
1996-041535
(Reference 2) Japanese Laid-Open Patent Publication No.
1986-166954
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[Disclosure]
[Technical Problem]
[0006] An aspect of the present disclosure may be to provide
a high hardness abrasion resistant steel which may have
excellent abrasion resistance and also high strength and high
impact toughness, and a manufacturing method therefor.
[Technical Solution]
[0007] An example embodiment of the present disclosure
provides an abrasion resistant steel having excellent hardness
and impact toughness including, by weight%, 0.33-0.42% of
carbon (C), 0.1-0.7% of silicon (Si), 0 . 6-1 . 6% of manganese (Mn),
0.05% or less of phosphorus (P) (excluding 0), 0.02% or less
of sulfur (S) (excluding 0), 0.07% or less of aluminum (Al)
(excluding 0), 0.55-5.0% of nickel (Ni), 0.01-1.5% of copper
(Cu), 0. 01-0 . 8% of chromium (Cr), 0 . 01-0 . 8% of molybdenum (Mo),
50 ppm or less of boron (B) (excluding 0), and 0.02% or less
of cobalt (Co) (excluding 0) and further comprising one or more
selected from a group consisting of 0.02% or less of titanium
(Ti) (excluding 0), 0.05% or less of niobium (Nb) (excluding
0), 0.05% or less of vanadium (V) (excluding 0) and 2-100 ppm
of calcium (Ca), with a balance of Fe and other inevitable
impurities, wherein C and Ni satisfy relational expression 1
as below, and wherein a microstructure includes 95 area% or more
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of martensite and 5% or less of bainite (including 0%).
[Relational Expression 1] [C]x[Ni] 0.231
[0008] Another example embodiment of the present disclosure
provides a method of manufacturing an abrasion resistant steel
having excellent hardness and impact toughness including
heating a steel slab including, byweight%, 0 .33-0 .42% of carbon
(C), 0.1-0.7% of silicon (Si), 0 . 6-1. 6% ofmanganese (Mn), 0.05%
or less of phosphorus (P) (excluding 0), 0.02% or less of sulfur
(8) (excluding 0), 0.07% or less of aluminum (Al) (excluding
0), 0.55-5.0% of nickel (Ni), 0.01-1.5% of copper (Cu),
0.01-0.8% of chromium (Cr), 0.01-0.8% of molybdenum (Mo), 50
ppm or less of boron (B) (excluding 0), and 0.02% or less of
cobalt (Co) (excluding 0) and further comprising one or more
selected from a group consisting of 0.02% or less of titanium
(Ti) (excluding 0), 0.05% or less of niobium (Nb) (excluding
0), 0.05% or less of vanadium (V) (excluding 0) and 2-100 ppm
of calcium (Ca), with a balance of Fe and other inevitable
impurities, where C and Ni satisfy relational expression 1 as
below, in a temperature range of 1050-1250 C; obtaining a
rough-rolled bar by rough-rolling the reheated steel slab in
a temperature range of 950-1050 C; obtaining a hot-rolled steel
sheet by finishing-hot-rolling the rough-rolled bar in a
temperature range of 850-950 C; air-cooling the hot-rolled
steel sheet to room temperature and reheating the steel sheet
for a residence time of 1.3t+10min-1.3t+60min (t: sheet
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thickness) in a temperature range of 860-950 C; and
water-cooling the reheated hot-rolled steel sheet to 150 C or
less.
[Relational Expression 1] [C] x [Ni] 0.231
[Advantageous Effects]
[0009] According to an aspect of the present disclosure, an
effect of providing an abrasion resistant steel having a
thickness of 60mm or less and having high hardness and excellent
low-temperature toughness may be obtained.
[Best Mode for Invention]
[0010] In the description below, the present disclosure will
be described in detail. The alloy composition of the present
disclosure will be described first. The content of the alloy
composition described below may be represented by weight%.
Carbon (C): 0.33-0.42%
[0011] Carbon (C) may be effective in increasing strength and
hardness in a steel having a martensite structure and may be
effective for improving hardenability. To sufficiently secure
the above-described effect, it may be preferable to add C by
0.33% or more. However, when the content thereof exceeds 0.42%,
weldability and toughness may degrade, such that an additional
heat treatment such as tempering may be inevitable. Therefore,
in the present disclosure, it may be preferable to control the
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content of C to be 0.33-0.42%. A lower limit of the content of
C may more preferably be 0.34%, even more preferably 0.35%, and
most preferably 0.36%. An upper limit of the content of C may
more preferably be 0.40%, even more preferably 0.39%, and most
preferably 0.38%.
Silicon (Si) : 0.1-0.7%
[0012] Silicon (Si) may be effective in improving strength
according to deoxidation and solid solution strengthening. To
obtain the above effect, it may be preferable to add Si by 0.1%
or more. However, when the content thereof exceeds 0.7%,
weldability may deteriorate, which may not be preferable.
Therefore, in the present disclosure, it may be preferable to
control the content of Si to be 0.1-0.7%. A lower limit of the
content of Si may more preferably be 0.12%, even more preferably
0.15%, and most preferably 0.2%. An upper limit of the Si content
may more preferably be 0.5%, even more preferably 0.45%, and
most preferably 0.4%.
Manganese (Mn) : 0.6-1.6%
[0013] Manganese (Mn) may suppress ferrite formation and may
effectively improve hardenability by decreasing Ar3
temperature, thereby improving strength and toughness of steel.
In the present disclosure, to secure hardness of the thick steel
material, it may be preferable to include Mn in an amount of
0.6% or more. When the content exceeds 1.6%, weldability may
degrade. Therefore, in the present disclosure, it may be
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preferable to control the content of Mn to be 0.6-1.6%. A lower
limit of the content of Mn may more preferably be 0.65%, even
more preferably 0 . 70%, and most preferably 0 . 75% . An upper limit
of the content of Mn may more preferably be 1.55%, even more
preferably 1.50%, and most preferably 1.45%.
Phosphorus (P): 0.05% or less (excluding 0)
[0014] Phosphorus (P) maybe inevitably included in steel, and
may degrade toughness of steel. Therefore, it may be preferable
to control the content of P to be less than 0.05% by lowering
the content as much as possible, but 0% may be excluded in
consideration of the inevitably included amount. The content
of P may more preferably be 0.03% or less, even more preferably
0.02% or less, and most preferably 0.01% or less.
Sulfur (S): 0.02% or less (excluding 0)
[0015] Sulfur (S) may deteriorate toughness of steel by forming
an MnS inclusion in steel. Therefore, it may be preferable to
control the content of S to be 0.02% or less by lowering the
content as much as possible, but 0% may be excluded in
consideration of the inevitably included amount. The content
of S may more preferably be 0.01% or less, even more preferably
0.005% or less, and most preferably 0.003% or less.
Aluminum (Al): 0.07% or less (excluding 0)
[0016] Aluminum (Al) may be effective in lowering an oxygen
content in molten steel as a deoxidizing agent for steel. When
the content of Al exceeds 0.07%, cleanliness of the steel may
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be impaired, which may not be preferable. Therefore, in the
present disclosure, it may be preferable to control the content
of Al to be 0.07% or less, and 0% may be excluded in consideration
of load and an increase in manufacturing costs in the
steelmaking process. The content of Al may more preferably be
0.05% or less, even more preferably 0.04% or less, and most
preferably 0.03% or less.
Nickel (Ni): 0.55-5.0%
[0017] Nickel (Ni) may be generally effective in improving
toughness along with strength of steel. To obtain the
above-described effect, it may be preferable to add Ni in an
amount of 0.55% or more. However, when the content thereof
exceeds 5.0%, the manufacturing costs may increase as Ni is an
expensive element. Therefore, in the present disclosure, it may
be preferable to control the content of Ni to be 0.55-5.0%. A
lower limit of the content of Ni may more preferably be 0.6%,
even more preferably 0.7%, and most preferably 0.8%. An upper
limit of the content of Ni may more preferably be 4.5%, even
more preferably 4.0%, and most preferably 3.5%.
Copper (Cu): 0.01-1.5%
[0018] Copper (Cu) may simultaneously increase strength and
toughness of steel along with Ni. To obtain the above effect,
it may be preferable to add Cu in an amount of 0.01% or more.
However, when the content of Cu exceeds 1.5%, possibility of
surface defects may increase, and hot workability may be
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deteriorated. Therefore, in the present disclosure, it maybe
preferable to control the content of Cu to be 0.01-1.5%. A lower
limit of the content of Cu may more preferably be 0.05%, even
more preferably 0 . 10%, andmost preferably 0 . 15% . An upper limit
of the Cu content may more preferably be 1.2%, even more
preferably 1.0%, and most preferably 0.8%.
Chrome (Cr): 0.01-0.8%
[0019] Chromium (Cr) may increase strength of steel by
increasing hardenability, and may be advantageous in securing
hardness. To obtain the above-described effect, it may be
preferable to add Cr in an amount of 0.01% or more, but when
the content thereof exceeds 0.8%, weldability may be
deteriorated and the manufacturing costs may increase.
Therefore, in the present disclosure, it may be preferable to
control the content of Cr to be 0.01-0.8%. A lower limit of the
Cr content may more preferably be 0.1%, even more preferably
0.15%, and most preferably 0.2%. An upper limit of the content
of Cr may more preferably be 0.75%, even more preferably 0.70%,
and most preferably 0.65%.
Molybdenum (Mo): 0.01-0.8%
[0020] Molybdenum (Mo) may increase hardenability of steel,
and may be effective in improving hardness of a thick steel
material. To sufficiently obtain the above-described effect,
it may be preferable to add Mo in an amount of 0.01% or more.
However, as Mo is also an expensive element, when the content
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thereof exceeds 0.8%, the manufacturing costs may increase, and
weldability may degrade. Therefore, in the present disclosure,
it may be preferable to control the content of Mo to be 0.01-0.8%.
A lower limit of the content of Mo may more preferably be 0.1%,
even more preferably 0.12%, and most preferably 0.15%. An upper
limit of the Mo content may more preferably be 0.75%, even more
preferably 0.72%, and most preferably 0.70%.
Boron (B) : 50ppm or less (excluding 0)
[0021] Boron (B) may be effective in improving strength by
effectively increasing hardenability of steel even by adding
a small amount of B. When the content thereof is excessive,
however, toughness and weldability of steel may be deteriorated,
and thus, it may be preferable to control the content to be 50
ppm or less. A lower limit of the content of B may more preferably
be 2 ppm, even more preferably 3 ppm, and most preferably 5 ppm.
An upper limit of the content of B may more preferably be 40
ppm, even more preferably 35 ppm, and most preferably 30 ppm.
Cobalt (Co) : 0.02% or less (excluding 0)
[0022] Cobalt (Co) may be advantageous in securing hardness
as well as strength of steel by increasing hardenability of
steel. When the content thereof exceeds 0.02%, hardenability
of the steel may decrease, and may increase the manufacturing
costs as Co is an expensive element. Therefore, in the present
disclosure, it may be preferable to add Co by 0.02% or less.
A lower limit of the Co content may more preferably be 0.001%,
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even more preferably 0.002% or less, and most preferably 0.003%
or less. An upper limit of the Co content may more preferably
be 0.018%, even more preferably 0.015%, and most preferably
0.013%.
[0023] In addition to the above-described alloy composition,
the abrasion-resistant steel in the present disclosure may
further include elements advantageous for securing physical
properties aimed in the present disclosure. For example, the
abrasion-resistant steel may further include one or more
selected from a group consisting of 0.02% or less of titanium
(Ti) (excluding 0), 0.05% or less of niobium (Nb) (excluding
0), 0.05% or less of vanadium (V) (excluding 0) and 2-100 ppm
of calcium (Ca).
Titanium (Ti): 0.02% or less (excluding 0)
[0024] Titanium (Ti) may maximize the effect of B, an element
effective in improving hardenability of steel. Specifically,
Ti may form a TIN precipitate by being combined with nitrogen
(N), such that formation of BN may be prevented. Accordingly,
solid solute B may increase, such that improvement of
hardenability may be maximized. When the content of Ti exceeds
0.02%, a coarse TiN precipitate may be formed, such that
toughness of the steel may deteriorate. Therefore, in the
present disclosure, it may be preferable to add Ti by 0.02% or
less. A lower limit of the content of Ti may more preferably
be 0.005%, even more preferably 0.007%, and most preferably
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0.010%. An upper limit of the content of Ti may more preferably
be 0.019%, even more preferably 0.017%, and most preferably
0.015%.
Niobium (Nb): 0.05% or less (excluding 0)
[0025] Niobium (Nb) may be solid-solute in austenite and may
increase hardenability of austenite, and may form carbonitride
such as Nb (C,N) such that Nb may be effective for increasing
strength of steel and inhibiting austenite grain growth. When
the content of Nb exceeds 0.05%, a coarse precipitate may be
formed, which becomes a starting point of brittle fracture, such
that toughness may degrade. Therefore, in the present
disclosure, it may be preferable to add Nb by 0.05% or less.
A lower limit of the content of Nb may more preferably be 0.002%,
even more preferably 0.003%, and most preferably 0.005%. An
upper limit of the content of Nb may more preferably be 0.040%,
even more preferably 0.035%, and most preferably 0.030%.
Vanadium (V): 0.05% or less (excluding 0)
[0026] Vanadium (V) may form a VC carbide during reheating
after hot-rolling, such that growth of austenite grains maybe
inhibited, and V may be advantageous to securing strength and
toughness by improving hardenability of steel. As V is an
expensive element, when the content thereof exceeds 0.05%, V
may become a factor increasing the manufacturing costs.
Therefore, in the present disclosure, it may be preferable to
control the content thereof to be 0.05% or less. A lower limit
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of the content of V may more preferably be 0.002%, even more
preferably 0.003%, and most preferably 0.005%. An upper limit
of the content of V may more preferably be 0.045%, even more
preferably 0.042%, and most preferably 0.040%.
Calcium (Ca) : 2-100ppm
[0027] Calcium (Ca) may have good bonding strength with S such
that Ca may have an effect of inhibiting formation of MnS
segregated in a center of a thickness of a steel material by
generating CaS. Also, CaS created by adding Ca may have an effect
of increasing corrosion resistance in a humid external
environment. To obtain the above-described effect, it may be
preferable to add Ca in an amount of 2 ppm or more. However,
when the content thereof exceeds 100 ppm, it may not be
preferable as Ca may cause clogging of a nozzle in steelmaking.
Therefore, in the present disclosure, it may be preferable to
control the content of Ca to be 2-100 ppm. A lower limit of the
content of Ca may more preferably be 3 ppm, even more preferably
4 ppm, and most preferably 5 ppm. An upper limit of the content
of Ca may more preferably be 80 ppm, even more preferably 60
ppm, and most preferably 40 ppm.
[0028] Also, the abrasion resistant steel in the present
disclosure may further include one or more selected from a group
consisting of 0.05% or less of arsenic (As) (excluding 0) , 0.05%
or less of tin (Sn) (excluding 0) , and 0.05% or less of tungsten
(W) (excluding 0) .
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[0029] As may be effective in improving toughness of steel,
and Sn may be effective in improving strength and corrosion
resistance of steel. Also, W may increase hardenability such
that W may be effective in improving strength and also improving
hardness at high temperature. When each content of As, Sn, and
W exceeds 0.05%, the manufacturing costs may increase, and
physical properties of steel may rather be deteriorated.
Therefore, in the present disclosure, when As, Sn and W are
additionally included, it may be preferable to control each
content thereof to be 0.05% or less . A lower limit of each content
of As, Sn, and W may more preferably be 0.001%, even more
preferably 0.002%, and most preferably 0.003%. An upper limit
of each content of As, Sn and W may more preferably be 0.04%,
even more preferably 0.03%, and most preferably 0.02%.
[0030] A remainder of the present disclosure may be iron (Fe) .
However, in a general manufacturing process, inevitable
impurities may be inevitably added from raw materials or an
ambient environment, and thus, impurities may not be excluded.
A person skilled in the art of a general manufacturing process
may be aware of the impurities, and thus, the descriptions of
the impurities may not be provided in the present disclosure.
[0031] In the abrasion resistant steel in the present
disclosure, it may be preferable for C and Ni of the
above-described alloy composition to satisfy relational
expression 1 as below. In the present disclosure, ultra-high
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hardness and also excellent low-temperature toughness may be
secured, and to this end, relational expression 1 should be
satisfied preferably. When relational expression 1 is not
satisfied, it may be difficult to improve both hardness and low
temperature toughness to an excellent level. Therefore, a value
of [C] x [Ni] may preferably be 0 .231 or more. A value of [C] x [Ni]
may more preferably be 0.396 or more, even more preferably 0.792
or more, and most preferably 1 or more. The higher the value
of [C] [Ni] , the more advantageous the effect may be implemented,
and thus, an upper limit of the value of [C] x [Ni] may not be
particularly limited in the present disclosure.
[0032] [Relational Expression 1] [C] x [Ni] 0.231
[0033] It may be preferable for a microstructure of the
abrasion resistant steel in the present disclosure to include
martensite as a matrix structure. More specifically, the
abrasion resistant steel in the present disclosure may include
95% or more (including 100%) of martensite by an area fraction.
When the fraction of martensite is less than 95%, it may be
difficult to secure a target level of strength and hardness.
The microstructure of the abrasion resistant steel in the
present disclosure may further include bainite by 5 area% or
less, and accordingly, low-temperature impact toughness may
further improve. A fraction of martensite may more preferably
be 96% or more, and even more preferably 97% or more. A fraction
of bainite may more preferably be 4% or less, and even more
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preferably 3% or less.
[0034] The abrasion resistant steel in the present disclosure
provided as above may an effect of securing surface hardness
of 550-650HB and also having an impact absorption energy of 21J
or more at a low temperature of -40 C. HB indicates surface
hardness of the steel measured by the Brinell hardness tester.
[0035] Also, it may be preferable that hardness (HB) and impact
absorption energy (J) of the abrasion resistant steel in the
present disclosure satisfy relational expression 2 as below.
In the present disclosure, low-temperature toughness
properties may improve in addition to high hardness, and to this
end, it may be preferable to satisfy relational expression 2
as below. In other words, when only surface hardness is high
and impact toughness is degraded such that relational
expression 2 is not satisfied, or when impact toughness is
excellent but surface hardness does not reach a target value
such that relational expression 2 is not satisfied, final target
high hardness and low temperature toughness properties may not
be guaranteed.
[0036] [Relational Expression 2] HB+J 31.0 (HE
indicates
surface hardness of the steel measured by the Brinell hardness
tester, and J indicates an impact absorption energy value at
-40 C)
[0037] Hereinafter, a method of manufacturing the abrasion
resistant steel will be described in detail.
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[0038] First, a steel slab may be heated in the temperature
range of 1050-1250 C. When the slab heating temperature is less
than 1050 C, re-solid solution of Nb may not be sufficient,
whereas when the temperature exceeds 1250 C, austenite crystal
grains may be coarsen such that a non-uniform structure may be
formed. Therefore, in the present disclosure, the heating
temperature of the steel slab may have a range of 1050-1250 C
preferably. A lower limit of the heating temperature of the
steel slab may more preferably be 1060 C, even more preferably
1070 C, and most preferably 1080 C. An upper limit of the
heating temperature of the steel slab may more preferably be
1230 C, even more preferably 1200 C, and most preferably
1180 C.
[0039] The reheated steel slab may be roughly rolled in a
temperature range of 950-1050 C to obtain a rough-rolled bar.
When the temperature is less than 950 C during the rough-rolling,
a rolling load may increase and the pressure may be relatively
weakened, such that deformation may not be sufficiently
transmitted to a center of the slab in a thickness direction,
and defects such as voids may not be removed. When the
temperature exceeds 1050 C, recrystallization may
simultaneously occur while rolling, and grains may grow, such
that initial austenite grains may become excessively coarse.
Therefore, in the present disclosure, the rough-rolling
temperature may preferably be 950-1050 C. A lower limit of the
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rough-rolling temperature may more preferably be 960 C, even
more preferably 970 C, and most preferably 980 C. An upper limit
of the rough-rolling temperature may more preferably be 1040 C,
even more preferably 1020 C, and most preferably 1000 C.
[0040] The rough-rolled bar may be finishing hot-rolled in a
temperature range of 850-950 C to obtain a hot-rolled steel
sheet. When the finishing hot-rolling temperature is less than
850 C, the rolling may become two-phase rolling, such that
ferrite may be formed in the microstructure. When the
temperature exceeds 950 C, a grain size of the final structure
may become coarse such that low-temperature toughness may be
deteriorated. Therefore, in the present disclosure, the
finishing hot-rolling temperature may be 850-950 C preferably.
A lower limit of the finishing hot-rolling temperature may more
preferably be 860 C, even more preferably 870 C, and most
preferably 880 C. An upper limit of the finish hot-rolling
temperature may more preferably be 940 C, even more preferably
930 C, and most preferably 920 C.
[0041] Thereafter, the hot-rolled steel sheet may be
air-cooled to room temperature, and may be reheated in a
temperature range of 860-950 C for a residence time of
1.3t+10min-1.3t+60m1n (t: sheet thickness) . The reheating may
be performed for reverse transformation of the hot-rolled steel
sheet including ferrite and pearlite into austenite single
phase. When the reheating temperature is less than 860 C,
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austenitization may not be sufficiently performed and coarse
soft ferrites may be mixed, such that hardness of the final
product may degrade. When the temperature exceeds 950 C,
austenite grains may become coarse, such that hardenability may
increase, but low temperature toughness of the steel may be
deteriorated. Therefore, in the present disclosure, the
reheating temperature may preferably be 860-950 C. A lower
limit of the reheating temperature may more preferably be 870 C,
even more preferably 880 C, and most preferably 890 C. An upper
limit of the reheating temperature may more preferably be 940 C,
even more preferably 930 C, and most preferably 920 C.
[0042] When the residence time during the reheating is less
than 1.3t+10 minutes (t: sheet thickness) , austenitization may
not occur sufficiently, such that a phase transformation by
rapid cooling subsequently performed, a martensitic structure,
may not be sufficiently obtained. When the residence time during
the reheating exceeds 1.3t+60 minutes (t: sheet thickness) ,
austenite crystal grains may become coarse such that
hardenability may increase, but low temperature toughness may
deteriorate. Therefore, in the present disclosure, the
residence time during the reheating may preferably be
1.3t+10min-1.3t+60m1n (t: sheet thickness) . A lower limit of
the residence time during reheating may more preferably be
1.3t+12 minutes, even more preferably 1.3t+15 minutes, and most
preferably 1.3t+20 minutes. An upper limit of the residence time
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during reheating may more preferably be 1.3t+50min, even more
preferably 1.3t+45min, and most preferably 1.3t+40m1n.
[0043] Thereafter, the reheated hot-rolled steel sheet may be
water-cooled to 150 C or less with reference to a surface layer
portion (e.g., the area from the surface to 1/8t (t: sheet
thickness (mm) ) of the sheet. The water-cooling stop
temperature exceeds 150 C, a ferrite phase may be formed during
cooling or a bainite phase may be excessively formed. Therefore,
the water-cooling stop temperature may preferably be 150 C or
less. The water-cooling stop temperature may more preferably
be 100 C or less, even more preferably 70 C or less, and most
preferably 40 C or less.
[0044] The water-cooling rate may preferably be 10 C/s or more.
When the cooling rate is less than 1 0 C/s, a ferrite phase may
be formed during cooling or a bainite phase may be excessively
formed. A cooling rate during the water-cooling may more
preferably be 15 C/s or more, and even more preferably 20 C/s
or more. In the present disclosure, the higher the cooling rate,
the more advantageous it may be, and thus, an upper limit of
the cooling rate may not be particularly limited, and may be
determined in consideration of facility limitations by a person
skilled in the art.
[0045] The hot-rolled steel sheet in the present disclosure
having gone through the above process conditions may be a thick
steel sheet having a thickness of 60mm or less, and may have
Page 20
Date Recue/Date Received 2021-03-16
CA 031.13056 2021-03-16
a thickness of 8-50mm more preferably, and 12-40mm even more
preferably. In the present disclosure, it may be preferable to
not perform a tempering process on the thick steel sheet.
Node for Invention]
[0046] Hereinafter, the present disclosure will be described
in greater detail with reference to an embodiment. However, it
should be noted that the following embodiment are provided to
describe the present disclosure in greater detail, and to not
limit the scope of the present disclosure. The scope of the
present disclosure may be determined by matters described in
the claims and matters reasonably inferred therefrom.
(Embodiment)
[0047] A steel slab having alloy compositions as in Tables 1
and 2 below was prepared, and the steel slab
heating-rough-rolling-hot-rolling-cooling (room
temperature)-reheating-water cooling was performed on the
steel slab under the conditions as in Table 3 below to
manufacture a hot-rolled steel sheet. A microstructure and
mechanical properties of the hot-rolled steel sheet were
measured, and results thereof are listed in Table 4 below.
[0048] In this case, as for the microstructure, the sample was
cut out in an arbitrary size to manufacture a mirror surface,
the surface was corroded using a nital etching solution, and
a 1/2t position, a center of the thickness, was observed using
an optical microscope and an electron scanning microscope.
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Date Recue/Date Received 2021-03-16
CA 03113056 2021-03-16
[0049] Hardness and toughness were measured using the Brinell
hardness tester (load 3000kgf, lOmm tungsten indentation) and
the Charpy impact tester, respectively. As for surface hardness,
an average value of values obtained by milling the sheet surface
by 2 mm and measuring surface hardness three times therefrom
was used. As for the Charpy impact test result, an average value
of values obtained by taking a sample from a 1/4t position and
measuring toughness three times therefrom at -40 C was used.
[0050] [Table 1
ALLOY COMPOSITION (WEIGHT%)
CLASSIFICATION
Si Mn P S Al Cr Ni Mo B Co
COUPARATIVE
0.346 0.35 3,07 0.013 0.0031 0.031 0.05 0,05 0,01 0,0011 -
STEEL1
361FApRAT2IVE 0.287 0.38 0.85 0.009 0.0018 0.025 0.12 1,21 0.13 0.0002 -
C0FA'Ar;tIVE 0.440 0.31 1.51 0.015 0.0016 0= .036 0.45
0.09 0.19 0.0015 - 0.01
C0N2EtIVE 0.385 0,25 0.85 0.007 0.0021 0.036 0.78 0.37 0.56 0.0017 0.01
IrlailrE 0.370 0.34 1.36 0.007 0.0010 0.023 0.58 0.92 0.25 0.0022 0.01
.77E-
INsIE'.\E[ Dirf 0.401 0:31 1.23 0.008 - 0.0021 0.022 0.31
2:91 6.56 6.0020 0.01 -
fliC1rC/E 0.383 0.21 1.47 0.008 0.0009 0.031 0,31 1.74 0.33 0.0020 0,01
STFEP3
[0051] [Table 2]
ALLOY COMPOSITION (WEIGHT%)
CLASSIFICATION
Cu Ti Nb V Ca As - Sn w RELATIONAL
EXPRESSI0N1
CITPFW,TIRE 0.05 0.013 0.021 0.03 0.0002 -
0.017
COILI,PV2IVE 6.45 -- 0.018 0.037 0.01 - 0=
.0004 0.347
Ciihrr - 0.02 0.017 0.026 0.02 0= .0009 0.003
0.003 - 0.040
a 7 V7k. fiVE 0.21 0.002 0.023 0.03 0.0005 0.003 0.004
0.01 0.142
&EEL 1
1SENTIVE 0.31 0.016 0,035 0.04 0.0012 - 0.01
0.340
Igc.rpgpI\i2E 0.15 0.012 0.024 - 0.0006 0.003 0.003
0.01 1.167
IrI 0,22 0.013 - 0.04 0= .0004 0,003
0.003 0.666
FIEF 3
[RELATIONAL EXPRESSION 1] [C] x[Ni]
[0052] [Table 3]
Page 22
Date Recue/Date Received 2021-03-16
CA 031.13056 2021-03-16
STEEL TYPE SLAB ROUGH- FINISHING- REHEATING REHEATING
COOLING CMG - THICKNESS
No, HEATING ROLLING HOT- TEMPERATURE RESIDENCE RATE
TERMINATION
TEMPERATURE TEMPERATURE ROLLING TIME TEMPERATURE ( mm)
CLASSIFICATION
( C) (.0 TEMPERATURE (CC) (MIN) (T/s)
( C) ( C)
,
COMPARA FIVE - 1121 1048 ' 901 908 32 52 42 12
EXAMPLE 1
COMPARATIVE COMPARATIVE 1137 1050 923 915 75 41
126 ' 40 '
EXAMPLE 2 ,3TEEL I
COMPARATIVE 1117 1023 940 912 90 38 23 60
EXAMPLE 3 , .
COMPARATIVE . 1= 133 - 1045 ' 903 921, 45 49 176
20
CgAAPU1/4FTE COMPARATIVE 1125 1021 911 921 52 48 52 30
EXAMPLE 5 STEEL 2
COMPARATIVE 1140 1030 920 909 100 31 25 50
EXAMPLE 6 ,
COMPARATIVE - 1= 123 1049 882 911 32 65 24 8
EXAMPLE 7 , ,
COMPARATIVE' COMPARATIVE 1097 ' 1038 - 901 ' 917 ' 71
47 40 25
EXAMPLE 8 STEEL 3
COMPARATIVE 1145 1019 934 915 93 40 ' 123 50 '
EXAMPLE 9
COMPARATIVE 1130 1028 922 931 60 51 36 15
EXAMPLE 10
COMPARATIVE COMPARATIVE 1112 1039 ¨ 930 ' 927 ' 77 ' 47
'135 ' 30 '
EXAMPLE 11 STEEL 4
COMPARATIVE 1127 1044 947 928 ' 1.13 25 27 60
EXAMPLE 12
INVENTIVE 1124 1031 ' 888 918 52 53 126 12
EXAMPLE
' INVENTIVE 1131 1039 915 915 61 ' 50 53 20 '
EXAMPLE 2 STEEL 1 ,
COMPARATIVE 1126 1042 939 850 110 32 29 60
EXAMPLE 13
COMPARATIVE - 1= 129 ' 1045 . 920 910 78 50 200
25
EXAMPLE 14 ,
INVENTIVE ' INVENTIVE 1137 1042 931 913 93 44 25 40
EgD-I STEEL 2 ,
1102 1041 946 920 88 33 36 50 '
EXAMPLE 4 .
INVENTIVE 1126 1040 890 914 59 46 22 20
EXAMPLE 5
COMPARATIVE INVENTIVE 1120 1053 913 925 104 6 29 40
EXAMPLE 15 STEEL 3
INVENTIVE 1105 1044 932 916 116 28 141 ' 60
EXAMPLE 6
[0053] [Table 4]
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Date Recue/Date Received 2021-03-16
CA 03113056 2021-03-16
MICROSTRUCTURE (AREA%) SURFACE IMPACT TOUGHNESS RELATIONAL
__________________________________________________________________ HARDNESS
EXPRESSION 2
CLASSIFICATION M THE OTHERS (HB) (J, @-40 C)
COMPARATIVE 100 - 589 7 84.1
EXAMPLE 1
COMPARATIVE 95 B:5% 592 5 118.4
CRAVE 100 - 574 8 71.8
CgAPMAPRIAET1E 94 B:6% 541 34 15.9
EXAMPLE 4
COMPARATIVE 97 B:3% 529 38 13.9
C8 '"WE 98 B:2% 545 31 17.6
CV\WRIAckE 100 - 670 6 111.7
CRipmAiUrkE 100 - 667 _______ 5 133.4
HARE 99 R:1% 662 5 132.4
AMWE 100 - 619 11 ________ 56.3
CfbiSPWE 96 B:4% 609 19 32.1
EXAMPLE 11
COMPARATIVE 100 - 623 12 51.9
Ep_D,IIIV2
99 B:1% 608 25 24.3
WrhU 100 - 605 27 ________ 22,4
EXAMPLE 2
COMPARATIVE 85 B:10%, PF:5% 516 48 10.8
OikrkTP E 90 B:6%, RA:4% 531 75 7.1
E4
100 - 625 35 17.9
VITIQ 100 - 630 33 ________ 19.1
EXAMPLE 4
INVENTIVE 98 B:2% 618 42 14.7
CRAr-ijAi& 75 B:25% 411 63 6.5
EalAt5
96 B:4% 604 45 13.4
EXAMPLE 6
[ RELATIONAL EXPRESSION 2] 11B J (HB INDICATES SURFACE HARDNESS OF THE STEEL
MEASURED BY
THE BRINELL HARDNESS TESTER, AND J INDICATES AN IMPACT ABSORPTION ENERGY VALUE
AT -40 C.)
IC MARTENSITE , B: BAINITE , PF: POLYGONAL FERRITE, RA: RETAINED AUSTENITE
[0054] As indicated in Tables 1 to 4, inventive examples 1 to
6 satisfying the alloy composition, relational expression 1,
and the manufacturing conditions suggested in the present
disclosure satisfied the microstructure fraction of the present
disclosure, and secured excellent hardness and low-temperature
impact toughness.
[0055] It is indicated that comparative examples 1 to 12, which
Page 24
Date Recue/Date Received 2021-03-16
satisfied the manufacturing conditions suggested in the present
disclosure but did not satisfy the alloy composition or
relational expression 1, did not satisfy hardness and
low-temperature impact toughness aimed in the present
disclosure.
[0056] It is indicated that comparative example 13 satisfying
the alloy composition and relational expression 1 suggested in
the present disclosure but not satisfying the reheating
temperature among the manufacturing conditions did not secure
the microstructure type and fraction suggested in the present
disclosure, and surface hardness was low.
[0057] It is indicated that comparative example 14 satisfying
the alloy composition and relational expression 1 suggested in
the present disclosure but not satisfying the cooling
termination temperature among the manufacturing conditions
secured the martensite fraction suggested in the present
disclosure, but retained austenite was formed, and accordingly,
surface hardness was low.
[0058] It is indicated that comparative example 15 satisfying
the alloy composition and relational expression 1 suggested in
the present disclosure but not satisfying the cooling rate among
the manufacturing conditions did not secure the martensite
fraction suggested in the present disclosure, and accordingly,
surface hardness was low.
***
[0059] In some aspects, embodiments of the present invention
as described herein include the following items:
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Date Regue/Date Received 2022-08-23
[Item 1]
An abrasion resistant steel having excellent hardness and
impact toughness, consisting of:
by weight%, 0.33-0.42% of carbon (C), 0.1-0.7% of silicon
(Si), 0.6-1.6% of manganese (Mn), 0.05% or less of phosphorus
(P) (excluding 0), 0.02% or less of sulfur (S) (excluding 0),
0.022-0.07% of aluminum (Al), 0.55-5.0% of nickel (Ni),
0 .01-1 .5% of copper (Cu), 0 .01-0 .8% of chromium (Cr), 0.01-0.8%
of molybdenum (Mo), 2-50 ppm of boron (B), . 001-0 .02% of cobalt
(Co), 0.005-0.02% of titanium (Ti), 2-100 ppm of calcium (Ca)
and further comprising one or two of 0.002-0.05% niobium (Nb)
and 0.002-0.05% of vanadium (V), optionally further comprising
one or more selected from the group consisting of 0.05% or less
of arsenic (As) (excluding 0), 0.05% or less of tin (Sn)
(excluding 0) , and 0.05% or less of tungsten (W) (excluding 0) ,
with a balance of Fe and other inevitable impurities,
wherein C and Ni satisfy relational expression 1 as below,
wherein a microstructure includes 95-99 area% of
martensite and 1-5% of bainite, and
wherein the abrasion resistant steel secures hardness of
550-650HB, and has 21J or more at a low temperature of -40 C,
where HB is surface hardness of the steel measured by the
Brinell hardness tester,
[Relational Expression 1] [C]x [Ni] 0.231.
[Item 2]
The abrasion resistant steel of item 1, wherein the
Page 26
Date Recue/Date Received 2023-05-30
abrasion resistant steel has hardness (HB) and impact
absorption energy (J) satisfying relational expression 2 as
below,
[Relational Expression 2] HB+J 31.0,
where HR is surface hardness of the steel measured by the
Brinell hardness tester, and J is an impact absorption energy
value at -40 C.
[Item 3]
The abrasion resistant steel of item 1 or 2, wherein the
abrasion resistant steel has a thickness of 60 mm or less.
[Item 4]
A method of manufacturing the abrasion resistant steel
of item 1 having excellent hardness and impact toughness, the
method comprising:
heating a steel slab consisting of, by weight%, 0.33-0.42%
of carbon (C), 0.1-0.7% of silicon (Si), 0.6-1.6% of manganese
(Mn), 0.05% or less of phosphorus (P) (excluding 0) , 0.02% or
less of sulfur (S) (excluding 0) , 0.022-0.07% of aluminum (Al),
0.55-5.0% of nickel (Ni), 0.01-1.5% of copper (Cu), 0.01-0.8%
of chromium (Cr), 0.01-0.8% of molybdenum (Mo), 2-50 ppm of
boron (B), 0.001-0.02% of cobalt (Co), 0.005-0.02% of titanium
(Ti), 2-100 ppm of calcium (Ca) and further comprising one or
two of 0.002-0.05% of niobium (Nb) and 0.002-0.05% of vanadium
(V), optionally further comprising one or more selected from
the group consisting of 0.05% or less of arsenic (As) (excluding
Page 27
Date Recue/Date Received 2023-05-30
0), 0.05% or less of tin (Sn) (excluding 0), and 0.05% or less
of tungsten (W) (excluding 0), with a balance of Fe and other
inevitable impurities, where C and Ni satisfy relational
expression 1 as below, in a temperature range of 1050-1250 C;
obtaining a rough-rolled bar by rough-rolling the heated
steel slab in a temperature range of 950-1050 C;
obtaining a hot-rolled steel sheet by
finishing-hot-rolling the rough-rolled bar in a temperature
range of 850-950 C;
air-cooling the hot-rolled steel sheet to room
temperature and reheating the steel sheet for a maintaining time
of 1.3t+10min-1.3t+60min (t: sheet thickness) in a temperature
range of 860-950 C; and
water-cooling the reheated hot-rolled steel sheet to
150 C or less,
[Relational Expression 1] [C]x[Ni] 0.231.
[Item 5]
The method of item 4, wherein a cooling rate is 10 C/s
or more in the water-cooling.
Page 28
Date Recue/Date Received 2023-05-30
