Note: Descriptions are shown in the official language in which they were submitted.
CA 02785318 2012-06-21
[DESCRIPTION]
[Invention Title]
AUSTENITE STEEL MATERIAL HAVING SUPERIOR DUCTILITY
[Technical Field]
[0001] The present invention relates to austenite steels
having excellent wear resistance, corrosion resistance, or
non-magnetic performance as well as ductility, as steels used
for industrial machines and in structures requiring ductility
and wear resistance, superconducting application devices and
general electric devices requiring non-magnetic properties, in
the mining, transportation, and storage sectors as well as in
oil and gas industries such as steel for a expansion pipe,
steel for a slurry pipe, or sour resistant steel.
[Background Art]
[0002] Recently, demand for austenitic steels (non-magnetic
steels) for use as structural materials in superconducting
application devices, such as a linear motor car track and a
fusion reactor, and general electric devices, has increased. A
typical example of non-magnetic steel is AISI 304 (18Cr-8Ni
base) austenitic stainless steel. However, AISI 304 austenitic
stainless steel may be uneconomical because the yield strength
thereof is low and large amounts of expensive elements, such
as Cr and Ni, are included therein. In particular, with
respect to a structural material requiring stable non-magnetic
properties according to a load, such austenitic steels may
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CA 02785318 2012-06-21
exhibit magnetic properties due to a ferromagnetic ferrite
phase induced by deformation-induced transformation and thus,
there may be limitations in the uses and applications thereof.
[0003] High-manganese austenitic steels have been continuously
developed, in which expensive nickel in the austenitic
stainless steels is replaced by manganese. With respect to the
high-manganese austenitic steels, it is essential to secure
stability of an austenite structure through appropriate
changes in contents of manganese and carbon. In the case that
the content of manganese is high, a stable austenite structure
may be obtained even with a low content of carbon. However, in
the case that the content of manganese is low, a large amount
of carbon must be added for austenitization. As a result,
carbides are precipitated by forming a network along austenite
grain boundaries at high temperatures and the precipitates may
rapidly decrease physical properties of the steel, in
particular, ductility.
[0004] In order to inhibit the precipitation of carbides
having a network form, a method of performing a solution
treatment at a high temperature or manufacturing high-
manganese steel by rapid cooling to room temperature after hot
working has been suggested. However, in the case that the
steel is thick or changes in manufacturing conditions are not
facilitated as in the case in which welding is essentially
accompanied, the precipitation of carbides having a network
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. CA 02785318 2012-06-21
form may not be inhibited and as a result, physical properties
of the steel may rapidly deteriorate. Also, segregation due to
alloying elements, such as manganese and carbon, inevitably
occurs during solidification of an ingot or billet of high-
manganese steel and segregation becomes severe during post-
processing such as hot rolling. Eventually, partial
precipitation of carbides occurs in a network form along an
intensified segregation zone in a final product, thereby
promoting non-uniformity of a microstructure and deteriorating
physical properties.
[0005] In order to inhibit the precipitation of carbides in
the segregation zone, increasing the content of manganese may
be a method generally used. However, this may eventually cause
increases in an alloy amount and manufacturing costs, and thus,
research into the addition of elements effective in inhibiting
carbide formation with respect to manganese has been required
for resolving the foregoing limitations. Also, since a level
of corrosion resistance of high-manganese steel may decrease
in comparison to that of a general carbon steel due to the
addition of manganese, applications in fields requiring
corrosion resistance may be limited, and thus, research into
improving corrosion resistance of high-manganese steel has
also been required.
[Disclosure]
[Technical Problem]
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CA 02785318 2013-12-03
[0006] An aspect of the present invention provides an alloy
having improved ductility and wear resistance by stabilizing
austenite through appropriate control of contents of carbon
and manganese and economically inhibiting generation of
carbides in a network form that may be formed at austenite
grain boundaries.
[Technical Solution]
[0007] According to an aspect of the present invention, there
is provided an austenite steel comprising: 8wt% to 15wt% of
manganese(Mn); 0.26wt% to 3wt% of copper(Cu); a content of
carbon(C) satisfying relationships of 33.5C+Mn25 and 33.5C-Mn
23; and iron(Fe) as well as unavoidable impurities as a
remainder, wherein magnetic permeability of the austenite
steel is 1.012 or less at a tensile strain of 20%.
[0008] At this time, the steel may further include 8 wt% or
less (excluding 0 wt%) of chromium (Cr).
[0009] Also, the steel may further include 0.05 wt% or less
(excluding 0 wt%) of titanium (Ti) and 0.1 wt% or less
(excluding 0 wt%) of niobium (Nb).
[0010] Yield strength of the steel may be 500 MPa or more.
[0011] The steel may further include 0.002 wt% to 0.2 wt% of
nitrogen (N).
[0012] A microstructure of the steel may include austenite
having an area fraction of 95% or more.
[0013] Magnetic permeability of the steel may be 1.01 or less
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at a tensile strain of 20%.
[Advantageous Effects]
[0014] According to an aspect of the present invention,
austenite is stabilized and generation of carbides in a
network form at austenite grain boundaries is inhibited by
adding copper (Cu) favorable to inhibition of carbide
formation with respect to manganese and appropriately
controlling contents of carbon and manganese, and thus,
ductility and wear resistance may be improved and corrosion
resistance of steel may also be improved through the addition
of chromium (Cr).
[Description of Drawings]
[0015] The above and other aspects, features and other
advantages of the present invention will be more clearly
understood from the following detailed description taken in
conjunction with the accompanying drawings, in which:
[0016] FIG. 1 is a graph showing composition ranges of carbon
and manganese of the present invention;
[0017] FIG. 2 is a photograph showing an example of a
microstructure of a steel sheet according to the present
invention; and
[0018] FIG. 3 is a photograph showing another example of a
microstructure of a steel sheet according to the present
invention.
[Best Mode]
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CA 02785318 2012-06-21
[0019] The present invention may provide an austenite steel
having excellent ductility by stabilizing austenite and
inhibiting generation of carbides in a network form at
austenite grain boundaries through controlling contents of
carbon, manganese, and copper in a component system.
[0020] According to an aspect of the present invention, there
is provided a steel having excellent ductility including 8 wt%
to 15 wt% of manganese (Mn), 3 wt% or less (excluding 0 wt%)
of copper (Cu), a content of carbon (C) satisfying
relationships of 33.5C + Mn 25 and 33.5C - Mn 23, and
iron
(Fe) as well as unavoidable impurities as a remainder.
[0021] Manganese (Mn): 8 wt% to 15 wt%
[0022] Mn, as the most important element added to a high-
manganese steel as in the present invention, is an element
acting to stabilize austenite. In consideration of a content
of carbon controlled for improving non-magnetic properties in
the present invention, Mn may be included in an amount of 8%
or more so as to stabilize austenite. That is, in the case
that a content of Mn is 8 wt% or less, an austenite structure
may not be sufficiently obtained because ferrite, a
ferromagnetic phase, becomes a main structure. Also, in the
case that the content of Mn is greater than 15 wt%, a stable
austenite structure may not be maintained because unstable c-
martensite is formed and easily transformed into ferrite
according to deformation. As a result, magnetic properties may
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CA 02785318 2012-06-21
increase and fatigue properties may deteriorate, and also, a
decrease in corrosion resistance, difficulty in a
manufacturing process, and increases in manufacturing costs
may be obtained due to the excessive addition of manganese.
[0023] Carbon (C): 33.5C + Mn 25 and 33.5C - Mn 23
[0024] C is an element that allows an austenite structure to
be obtained at room temperature by stabilizing austenite and
has an effect of increasing strength and wear resistance of
steel. In particular, carbon functions to decrease Ms or Md, a
transformation point from austenite to martensite by a cooling
process or working.
[0025] A content of C in the present invention may
simultaneously satisfy relationships of 33.5C + Mn 25 and
33.5C - Mn 23 and
content ranges of carbon and manganese
controlled in the present invention may be confirmed in FIG. 1.
In the case that a value of 33.5C + Mn is less than 25, an
alpha-martensite structure, a ferromagnetic phase, may be
formed because stabilization of austenite is insufficient, and
thus, a sufficient amount of an austenite structure may not be
In the case that a value of 33.5C - Mn is greater
than 23, carbides are excessively formed at grain boundaries
because the content of C becomes excessively high, and thus,
physical properties of a material may rapidly deteriorate.
Therefore, the contents of carbon and manganese are required
to be controlled in the foregoing ranges and as a result,
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CA 02785318 2012-06-21
sufficient austenite may be secured and the inhibition of
carbide formation may be possible. Therefore, ductility and
non-magnetic properties may be improved.
[0026] Copper (Cu): 3 wt% or less (excluding 0 wt%)
[0027] Cu has very low solubility in carbide and low
diffusivity in austenite, and thus, is concentrated at an
interface between the austenite and the nucleated carbide. As
a result, Cu effectively delays growth of the carbide by
inhibiting diffusion of carbon and eventually, has an effect
of inhibiting carbide formation. However, since hot
workability of steel may be decreased in the case that a
content of Cu is greater than 3 wt%, an upper limit thereof
may be limited to 3 wt%. In particular, in order to
sufficiently obtain the effect of inhibiting carbide formation,
Cu may be added to an amount of 0.3 wt% or more, and for
example, it is more effective to maximize the foregoing effect
in the case that Cu is added in an amount of 2 wt% or more.
[0028] At this time, corrosion resistance of the steel may be
additionally improved by further including 8 wt% or less
(excluding 0 wt%) of r.hr^m-Him
[0029] Chromium (Cr): 8 wt% or less (excluding 0 wt%)
[0030] In general, manganese is an element decreasing
corrosion resistance of steel and corrosion resistance of the
steel having the foregoing range of Mn may be lower than that
of a general carbon steel. However, in the present invention,
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corrosion resistance may be improved by the addition of Cr.
Also, ductility may be increased by stabilizing austenite
through the addition of Cr having the foregoing range and
strength may also be increased by solution strengthening.
[0031] In the case that a content of Cr is greater than 8 wt%,
manufacturing costs may not only increase, but also,
resistance to sulfide stress corrosion cracking may be
decreased by forming carbides along grain boundaries as well
as carbon dissolved in a material and a sufficient fraction of
austenite may not be obtained due to formation of ferrites.
Therefore, an upper limit thereof may be limited to 8 wt%. In
particular, in order to maximize the effect of improving
corrosion resistance, Cr may be added in an amount of 2 wt% or
more. Corrosion resistance is improved by the addition of Cr
and thus, the steel of the present invention may be widely
used in a steel for a slurry pipe or sour resistance steel.
[0032] Also, yield strength of the steel may be further
improved by including 0.05 wt% or less (excluding 0 wt%) of
titanium (Ti) and 0.1 wt% or less (excluding 0 wt%) of niobium
(Nb) and thus, the steel having a yield strength of 500 MPa or
more may be obtained.
[0033] Titanium (Ti): 0.05 wt% or less (excluding 0 wt%)
[0034] Ti combines with nitrogen to form TiN and thus,
exhibits an effect of increasing yield strength of steel by
inhibiting growth of austenite grains at high temperatures.
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However, in the case that Ti is added excessively, physical
properties of the steel may be deteriorated due to coarsening
of titanium precipitates. Therefore, an upper limit thereof
may be limited to 0.05 wt%.
[0035] Niobium (Nb): 0.1 wt% or less (excluding 0 wt%)
[0036] Nb is an element increasing strength through
dissolution and precipitation hardening effects, and in
particular, may improve yield strength through grain
refinement during low-temperature rolling by increasing a
recrystallization stop temperature (Tnr) of steel. However, in
the case that Nb is added in an amount of greater than 0.1 wt%,
physical properties of the steel may be rather deteriorated
due to formation of coarse precipitates. Therefore, an upper
limit thereof may be limited to 0.1 wt%.
[0037] Also, in the case that the steel further includes 0.002
wt% to 0.2 wt% of nitrogen (N), the effect of the present
invention may be further improved.
[0038] Nitrogen (N): 0.002 wt% to 0.2 wt%
[0039] Nitrogen is an element stabilizing austenite with
carbon and also, may improve strength of steel through
solution strengthening. In the case that unstable austenites
are formed, N greatly deteriorates physical properties and
non-magnetic properties by inducing deformation induced
transformation into E-martensite and a-martensite according to
deformation. Therefore, physical properties and non-magnetic
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,
properties of the steel may be improved by stabilizing
austenite through appropriate addition of nitrogen.
[0040] In the case that a content of N is less than 0.002 wt%,
the effect of stabilization may not be anticipated, and in the
case that the content of N is greater than 0.2 wt%, physical
properties of the steel may be deteriorated due to formation
of coarse nitrides.
[0041] Therefore, the content of N may be limited to a range
of 0.002 wt% to 0.2 wt%. For example, in the case that N is
added to an amount of 0.05 wt% or more, non-magnetic
properties may be more effectively improved through the
stabilization of austenite.
[0042] In the present invention, iron (Fe) and other
unavoidable impurities are included as a remainder. However,
since unintended impurities may be inevitably incorporated
from raw materials or a surrounding environment during a
typical steelmaking process, the unintended impurities may not
be excluded. Since the unintended impurities are obvious to
those skilled in the art, detailed descriptions thereof are
not particularly provided in the present specification.
[0043] Austenite is a main phase in the steel of the present
invention having the foregoing composition and austenite may
be included in an area fraction of 95% or more. In the case
that the foregoing composition is satisfied, a targeted
fraction of an austenite structure may be obtained without
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performing rapid cooling (water cooling) in order to inhibit
grain boundary carbide precipitation, a limitation in a
typical steel. That is, a targeted microstructure may be
formed in the steel almost without dependency on a cooling
rate and as a result, high ductility and wear resistance may
be obtained. Also,
corrosion resistance may be improved
through the addition of Cr having the foregoing range and
strength may be improved through solution strengthening.
[0044] Further, the steel may have a magnetic pearmeability of
1.01 or less at a tensile strain of 20%. In the present
invention, non-magnetic properties are improved by stably
securing austenite, and in particular, excellent non-magnetic
properties may be obtained by allowing very low magnetic
permeability to be obtained even at a tensile strain of 20%
through the addition of nitrogen. For example, non-magnetic
properties may be further improved by controlling magnetic
permeability to have a value of 1.005 or less at a tensile
strain of 20%.
[0045] In the present invention, a slab satisfying the
foregoing component system may be manufactured according to a
typical method of manufacturing steel, and for example, the
slab of the present invention may be manufactured by rough
rolling and finishing rolling after reheating the slab and
then cooling.
[Mode for Invention]
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21
,
[0046] Hereinafter, the present invention will be described in
detail, according to an embodiment. However, the following
individual examples are merely provided to allow for a clearer
understanding of the present invention, rather than to limit
the scope thereof.
[0047] (Embodiment)
[0048] Slabs satisfying component systems and composition
ranges described in Tables 1 and 4 were manufactured through a
series of hot rolling and cooling processes, and
microstructures, elongations, strengths, and magnetic
permeabilities thereof were then measured, and the results
thereof are presented in the following Table 2. The results of
corrosion rate tests according to dipping experimentations are
presented in Table 3 below and weight losses of samples in
accordance with wear experimentations (ASTM 065) are presented
in Table 4 below.
[Table 1]
,
Category C Mn Cu Cr Ti Nb N
35.5C+Mn35.5C-Mn
(wt) ,
Inventive
0.66 10 1.06 - - - 32
12
Example 1
Inventive
0.83 9.98 1.08 - - - 38
10
Example 2
Inventive
0.5 14 0.37 - - - - 31
3
Example 3
Inventive
0.79 10.84 1.21 - 0.017 0.021 -
37 16
Example 4
Inventive
0.63 10.25 1.12 1.5 - - - 31
11
Example 5
Inventive
0.93 11.05 1.34 1.47 - - -
42 20
Example 6
Inventive
0.83 9.92 1.28 0.98 - - - 38
18
Example 7
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4 CA 02785318 2012-06-21
b
Inventive
0.92 12.01 0.71 1.23 - - - 43 19
Example 8
Inventive
0.6 14.25 0.26 5.07 - - 34 6
Example 9
Inventive
0.72 12.54 2.35 2.07 - - - 37 12
Example 10
Inventive
0.79 11.2 1.38 2.53 0.014 0.02 38 15
Example 11
Inventive
0.82 10.95 0.95 3.15 0.016 0.02 - 38 17
Example 12
Inventive
0.64 12.12 1.37 1.85 0.015 0.018 0.13 34 9
Example 13
Comparative
0.39 9.94 - - - - - 23 3
Example 1
Comparative
0.9 10 - - - - 40 20
Example 2
Comparative
0.2 17 - - - - - 24 -10.3
Example 3
Comparative
1.2 10 - - - - - 50 30
Example 4
Comparative
0.9 10 3.5 - - - - 40 20
Example 5
,
Comparative
0.9 10.1 1.25 10 - - - 40 20
Example 6
Comparative
0.05 19 - - - - 21 -17
Example 7
Comparative
0.02 17 0.5 1.2 - - - 18 -16
Example 8
[Table 2]
[ I I I 1
1,L=gnti,-. I
Magnetic
Austenite Yield permeability
Elongation permeability
Category fraction (%) (before strength
(after 20%
(area%) (MPa)
tensile
deformation)
strain)
Inventive
98 22.5 376 1.002 1.012
Example 1
Inventive
99 25.6 357 1.002 1.01
Example 2
Inventive
99 27.3 362 1.001 1.009
Example 3
Inventive
99 26.4 574 1.001 1.002
Example 4
Inventive
99 25.7 395 1.002 1.01
Example 5
Inventive
99 28.7 402 1.002 1.01
Example 6
Inventive
99 28.4 386 1.002 1.01
Example 7
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Inventive
99 27.6 392 1.001 1.009
Example 8
Inventive
99 35.6 472 1.001 1.009
Example 9
Inventive
100 37.2 630 1.002 1.002
Example 10
Inventive
99 28.1 592 1.002 1.01
Example 11
Inventive
99 30.6 605 1.002 1.01
Example 12
Inventive
99 32.2 577 1.001 1.003
Example 13
Comparative Non
65 4 336 5 or more
Example 1
measurable
Comparative Non
78 4.6 352 1.001
Example 2 measurable
,
Comparative
68 32 303 1.002 5 or more
Example 3
Comparative Non
72 4.3 358 1.002
Example 4
measurable
Comparative Non Non Non Non Non
Example 5 measurable measurable measurable
measurable measurable
Comparative Non
72 3.8 520 1.002
Example 6
measurable
Comparative
41 31 297 1.002 5 or more
Example 7
Comparative
38 27 312 1.002 5 or more
Example 8
[Table 3]
I I I
Corrosion rate (mm/year)
Category
3.5% NaC1, 50 C, 2 weeks 0.05 M H2SO4, 2 weeks
Inventive Example 5 0.12 0.42
Inventive Example 6 0.11 0.41
Inventive Example 7 0.12 0.42
Inventive Example 8 0.12 0.42
Inventive Example 9 0.06 0.33
Inventive Example 10 0.06 0.35
_ ________________________________________________________________________
Inventive Example 11 0.09 0.40
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Inventive Example 12 0.07 0.37
Inventive Example 13 0.11 0.43
Comparative Example 1 0.14 0.48
Comparative Example 2 0.16 0.48
Comparative Example 3 0.15 0.47
Comparative Example 4 0.16 0.48
Comparative Example 5 Non measurable Non measurable
Comparative Example 6 0.03 0.27
Comparative Example 7 0.15 0.45
Comparative Example 8 0.14 0.43
[Table 4]
Category
Weight
C Mn Si Ni Cu Cr Ti Nb N
(wt%) loss
(g)
Inventive
0.66 10 1.06 - - - 0.59
Example 1
Inventive
0.83 9.98 1.08 - - - 0.61
Example 2
Inventive
0.5 14 0.37 - - - - 0.65
Example 3
Inventive
0.79 10.84 1.21 - 0.017
0.021 - 0.63
Example 4
Inventive
0.63 10.25 - - 1.12 1.5 - - -
0.65
Example 5
Inventive
0.93 11.05 - - 1.34 1.47 - - -
0.59
Example 6
Inventive
0.83 9.92 - - 1.28 0.98 0.58
Example 7
Inventive
0.92 12.01 - - 0.71 1.23 - - 0.57
Example 8
Inventive
0.6 14.25 - - 0.26 5.07 - -
0.61
Example 9
Inventive
0.72 12.54 - - 2.35 2.07 - - -
0.54
Example 10
Inventive
0.79 11.2 - - 1.38 2.53
0.014 0.02 - 0.57
Example 11
Inventive
0.82 10.95 - - 0.95 3.15
0.016 0.02 - 0.58
Example 12
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Inventive
0.64 12.12 1.37 1.85 0.015 0.018 0.13 0.62
Example 13
Comparative
0.45 0.6 0.25 0.75
Example 9
Comparative
0.066 1.5 0.2 0.15 0.1 0.012 0.04 1.32
Example 10
Comparative
0.36 1.5 0.26 0.2 0.011 0.012 0.9
Example 11
Comparative
0.9 12 0.5 0.59
Example 12
[0049] Inventive Examples 1 to 13 were steels satisfying the
component systems and composition ranges controlled in the
present invention and it may be understood that deterioration
of physical properties due to grain boundary carbide formation
were not obtained even by slow cooling. Specifically, since
area fractions of austenite were 95% or more and magnetic
permeabilities were stably maintained even at a tensile strain
of 20%, non-magnetic properties as well as elongations and
yield strengths were excellent. Also, since weight losses of
the samples were low, wear resistance may be secured.
[0050] In particular, in Inventive Examples 5 to 13, it may be
understood that corrosion resistances were also improved
because corrosion rates were slow in the corrosion evaluation
tests according to additional addition of Cr. That is, it may
be confirmed that Inventive Examples 5 to 13 had effects of
improving corrosion resistance better than those of Inventive
Examples 1 to 4 in which Cr was not added. Further, it may be
understood that Inventive Example 10 had a better effect of
improving corrosion resistance, because Cu was added to an
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amount of 2 wt% or more, a more desirable amount. Also, in
Inventive Examples 4 and 11 to 13, yield strengths were
improved by further additions of Ti and Nb, and thus, were 500
MPa or more.
[0051] In contrast, Comparative Example 1 had a value of
33.5C+Mn of 23, which did not correspond to the range
controlled in the present invention. A content of carbon as an
austenite-stabilizing element was insufficient and as a result,
targeted austenite structure and elongation were not obtained
due to formation of a large amount of martensites.
[0052] Also, in Comparative Example 2, contents of manganese
and carbon corresponded to the ranges controlled in the
present invention. However, since a large amount of carbides
were formed along gain boundaries due to copper not being
added, austenite was formed in an area fraction of less than
95%. Thus, it may be confirmed that targeted microstructure
and elongation may not be obtained.
[0053] Further, Comparative Example 3 had a value of 33.5C+Mn
of 24, which did not correspond to the range controlled in the
present invention. In particular, since E-martensite, a semi-
stable phase, was formed due to a high manganese content, an
austenite structure having a targeted area fraction may not be
obtained. Since the semi-stable c-martensite phase was easily
transformed into deformation-induced martensite during
subsequent deformation, very high magnetic permeability may be
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obtained at a tensile strain of 20%. Thus, it may be confirmed
that non-magnetic properties were poor.
[0054] Comparative Example 4 had a value of 33.5C-Mn of 30,
which did not correspond to the range controlled in the
present invention. In particular, since carbides having a
network form formed at grain boundaries due to excessive
addition of carbon, austenite was formed in an amount of less
than 95%. Thus, a targeted microstructure may not be obtained
and as a result, elongation was very low.
[0055] In Comparative Example 5, contents of manganese and
carbon corresponded to the ranges controlled in the present
invention. However, since hot workability was rapidly
deteriorated due to the addition of Cu in an amount above the
range controlled in the present invention, severe cracks were
generated during hot working, and thus, a sound rolled
material may not be obtained. As a result, measurements were
not possible through experimentations.
[0056] In Comparative Example 6, contents of manganese and
carbon also corresponded to the ranges controlled in the
present invention. However, since Cr carbides precipitdLed
along grain boundaries due to addition of Cr in an amount
above the range controlled in the present invention, a
targeted fraction of austenite may not be obtained, and as a
result, it may be confirmed that ductility was deteriorated.
[0057] In Comparative Examples 7 and 8, values of 33.5C+Mn
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were respectively 21 and 18, which deviated from the range of
the present invention. In particular, since c-martensite, a
semi-stable phase, was excessively formed due to a high
manganese content and a low C content, a fraction of austenite
was very low. As a result, the semi-stable c-martensite was
easily transformed into deformation-induced a-martensite, a
ferromagnetic structure, during deformation to increase
magnetic permeability and thus, it may be confirmed that non-
magnetic properties were poor.
[0058] Comparative Example 9 had a composition of AISI 1045
steel, a general carbon steel for machine structural use.
Since a content of Mn was very low and Cu was not added, a
weight loss of the sample according to the wear test was 0.75
g, and it may be confirmed that a wear amount was relatively
larger than those of Inventive Examples.
[0059] Comparative Example 10 had a composition of API X70
grade steel. Likewise, since a content of Mn was very low and
Cu was not added, a weight loss of the sample was greater than
1 g, and it may be confirmed that wear resistance was very
poor.
[0060] Comparative Example 11 had a composition of API K55
grade steel. Likewise, since a content of Mn was very low and
Cu was not added, a weight loss of the sample was 0.9 g, and
it may be confirmed that wear resistance was very poor.
[0061] Comparative Example 12 was a high-manganese austenitic
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Hadfield steel widely used as a wear resistant steel. Since
contents of C and Mn were sufficient, weight loss according to
the wear test was 0.59 g, and thus, excellent wear resistance
properties were obtained. However, since the inhibition of
carbide formation was not facilitated due to no addition of Cu
and water cooling must be performed after a long
austenitization treatment at a high temperature in order to
inhibit the carbide formation, there may be a limitation in a
thickness of applied steel and there may have many constraints
in manufacturing steel such as difficulty in using in a weld
structure. Also, since Cr was not added, corrosion resistance
targeted in the present invention may not be secured.
[0062] FIG. 2 is a micrograph of a steel sheet manufactured
according to Inventive Example 1 and FIG. 3 is a micrograph of
a steel sheet manufactured according to Inventive Example 5.
Since almost all structures were austenitic, it may be
confirmed that stabilization of austenite may be effectively
achieved by control of the component system and the
composition range of the present invention.
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