CA 03039025 2019-04-01
[Document Type] Specification
[Title of the Invention] STEEL WIRE AND COATED STEEL WIRE
[Technical Field of the Invention]
[0001]
The present invention relates to a steel wire and a coated steel wire.
The present invention particularly relates to a steel wire having excellent
electrical conductivity and excellent strength which is preferably used for
power
transmission lines and a coated steel wire having a coating layer formed on
the surface of
the steel wire.
[Related Art]
[0002]
In the related art, as power transmission lines that transmit power, aluminum
conductor steel-reinforced cables (hereinafter, abbreviated as "ACSR")
obtained by
twisting aluminum wires around a core portion made of a steel wire (steel
core) have been
used. The steel wire that is used for the core portion of ACSR plays an
important role as
a tension member of the aluminum wires. As steel wires that serve as the core
portion of
aluminum conductor steel-reinforced cables, galvanized steel wires obtained by
galvanizing drawn pearlitic steels or aluminum clad steel wires obtained by
wire drawing
aluminum clad wire rods covered with aluminum as a surface layer in order to
improve
the corrosion resistance of the wires are used.
[0003]
ACSR that is used as power transmission lines is demanded to have strength and
a high power transmission efficiency. In response to the above described
demand,
regarding the improvement of the power transmission efficiency of ACSR, an
increase in
the aluminum cross-sectional area by reducing the weight of the core portion,
a decrease
in the electrical resistance of the steel wire that serves as the core
portion, and the like are
being studied.
For example, Patent Document 1 discloses a method for reducing the specific
weight of a power transmission line by using not a steel wire but a composite
wire rod of
a carbon fiber and aluminum or an aluminum alloy for the core portion for the
purpose of
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reducing the weight of the core portion. In addition, Patent Document 2
discloses a
method in which the amounts of C, Si, and Mn in a steel wire are limited to
minimum
necessary amounts for the purpose of decreasing the electrical resistance of
the steel wire.
[0004]
However, in the technique disclosed by Patent Document 1, since a carbon fiber
having a higher unit price than steel is used, the cost is increased. In
addition, in the
technique disclosed by Patent Document 2, the amounts of the alloying elements
are
decreased, and thus it is difficult for the steel wire to ensure strength
suitable for a tension
member.
[0005]
In addition, in Non Patent Document 1, it is reported that, when first wire
drawing is performed on a wire rod having a diameter of 5.5 mm in which C
content is as
high as 0.92% so that a diameter is 1.75 mm, furthermore after patenting is
performed,
and then cold wire drawing is significantly performed so that the diameter is
as ultrafine
as 0.26 mm, the electrical conductivity improves most under a condition of a
true strain
being approximately 1.5.
[0006]
However, it is extremely difficult to manufacture a power transmission line by
working a wire rod to the above described ultrafine steel wire and,
furthermore, plating
the surrounding of the ultrafine steel wire (core portion) with zinc or the
like or twisting
aluminum wires around the ultrafine steel wire, and thus the cost
significantly is
increased.
[Prior Art Document]
[Patent Document]
[0007]
[Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. 2001-176333
[Patent Document 2] Japanese Unexamined Patent Application, First
Publication No. 2003-226938
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[Non Patent Document]
[0008]
[Non Patent Document 1] Materials Science & Engineering A 644 (2015) 105-
113, A. Lamontagne et al., "Comparative study and quantification of cementite
decomposition in heavily drawn pearlitic steel wires"
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0009]
The present invention has been made with attention paid to the above described
circumstance. An object of the present invention is to provide a steel wire
which has a
wire diameter preferable for the use of power transmission lines and has
excellent
electrical conductivity and tensile strength and a coated steel wire having
the above
described steel wire and a coating layer which coats the steel wire.
[Means for Solving the Problem]
[0010]
The present inventors studied a relationship among the chemical composition of
steel, the form of the structure, and the electrical conductivity. As a
result, it was found
that the electrical conductivity of a wire rod which serves as a material of a
steel wire is
improved by controlling the chemical composition and the form of cementite. As
a
result of additionally repeating studies with attention paid to the forms of
ferrite and
cementite, the present inventors found that the electrical conductivity is
further improved
by imparting strain to the wire rod and changing the orientations of ferrite
and cementite.
Furthermore, the present inventors found that a steel wire having not only
excellent
- electrical conductivity and excellent tensile strength but also a wire
diameter preferable
for the use of power transmission lines can be obtained by devising the
conditions of
cooling and wire drawing after rolling.
That is, the present inventors found that a steel wire having a wire diameter
preferable for the use of power transmission lines, excellent electrical
conductivity, and
high tensile strength can be obtained by wire drawing a wire rod, which has an
electrical
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conductivity increased by cooling under specific conditions after hot rolling
and
controlling the chemical composition and the structure, under specific
conditions.
The present invention has been made on the basis of the above described
finding,
and the gist is as described below.
[0011]
(1) A steel wire according to an aspect of the present invention includes, as
a
chemical composition, by mass%, C: 0.40% to 1.10%, Si: 0.005% to 0.350%, Mn:
0.05%
to 0.90%, Cr: 0% to 0.70%, Al: 0% to 0.070%, Ti: 0% to 0.050%, V: 0% to 0.10%,
Nb:
0% to 0.050%, Mo: 0% to 0.20%, B: 0% to 0.0030%, and a remainder including Fe
and
impurities; in which a metallographic structure in a cross section includes 80
area% or
more of a pearlite structure having a lamellar cementite; an average lamellar
spacing
which is a spacing between the lamellar cementites is 28 nm to 80 nm; an
average length
of the lamellar cementite is 22.0 pm or less; among the pearlite structure, a
pearlite
structure having the lamellar cementite of which an inclination with respect
to a
longitudinal direction of the steel wire is 15 or less is 40 area% or more;
an integration
degree of a {110} plane of a ferrite with respect to the longitudinal
direction, which is
obtained using an X-ray diffraction method, is in a range of 2.0 to 8.0, and a
diameter of
the steel wire is 1.4 mm or more.
(2) The steel wire according to (1) may include, as the chemical composition,
by
mass%, one or more selected from the group consisting of Cr: 0.01% to 0.70%,
Al:
0.001% to 0.070%, Ti: 0.002% to 0.050%, V: 0.002% to 0.10%, Nb: 0.002% to
0.050%,
Mo: 0.02% to 0.20%, and B: 0.0003% to 0.0030%.
(3) A coated steel wire according to another aspect of the present invention
includes the steel wire according to (1) or (2) and a metal coating layer
which coats the
steel wire.
(4) In the coated steel wire according to (3), the metal coating layer may
include
at least one of the group consisting of zinc, zinc alloy, aluminum, aluminum
alloy, copper,
copper alloy, nickel, and nickel alloy.
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[Effects of the Invention]
[0012]
According to the above described aspects of the present invention, it is
possible
to provide a steel wire which has a wire diameter preferable for the use of
power
transmission lines and is excellent for electrical conductivity and tensile
strength, and a
coated steel wire having the steel wire and a coating layer which coats the
steel wire.
In the steel wire and the coated steel wire according to the above described
aspects of the present invention, the wire diameter of the steel wire that
serves as a core
material is large, and the electrical conductivity and the tensile strength
are excellent.
Therefore, the steel wire and the coated steel wire can be preferably used for
the use of
power transmission lines.
[Brief Description of the Drawings]
[0013]
FIG. 1 is a view showing a cross section parallel to a longitudinal direction
of a
steel wire (L cross section) and a schematic view that shows a method for
measuring an
average length of lamellar cementite in a pearlite structure having lamellar
cementite.
FIG. 2A is a view that shows a method for measuring an area ratio of a
pearlite
structure having lamellar cementite of which an inclination with respect to a
longitudinal
direction of the steel wire (angular difference) is 150 or less and a
photograph showing an
example of lamellar cementite having an inclination being 150 or less.
FIG. 2B is a view that shows the method for measuring the area ratio of the
pearlite structure having the lamellar cementite of which the inclination with
respect to
the longitudinal direction of the steel wire (angular difference) is 150 or
less and a
photograph showing an example of lamellar cementite having an inclination
being not 15
or less.
FIG. 3A is a view showing an L cross section of the steel wire and a schematic
view showing a TD direction and an RD direction.
FIG. 3B is a view showing the L cross section of the steel wire and a
schematic
view that shows a method for measuring an integration degree of ferrite.
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[Embodiments of the Invention]
[0014]
A steel wire according to an embodiment of the present invention (the steel
wire
according to the present embodiment) and a coated steel wire according to an
embodiment of the present invention (the coated steel wire according to the
present
embodiment) will be described below.
[0015]
The steel wire according to the present embodiment has steel composition
described below (chemical composition) and includes a pearlite structure
having lamellar
cementite in a metallographic structure (hereinafter, simply referred to as
"the pearlite
structure" in some cases). In addition, in the steel wire according to the
present
embodiment, an average lamellar spacing between the lamellar cementites in the
pearlite
structure is 28 nm to 80 nm, an average length of the lamellar cementite is
22.0 pm or
less, among the pearlite structure, a pearlite structure having the lamellar
cementite of
which an inclination with respect to a longitudinal direction of the steel
wire is 15 or less
is 40 area% or more, and an integration degree of a {110} plane of ferrite
with respect to
the longitudinal direction, which is obtained using an X-ray diffraction
method, is in a
range of 2.0 to 8Ø Furthermore, the steel wire according to the present
embodiment has
a diameter of 1.4 mm or more.
[0016]
First, the chemical composition of the steel wire according to the present
embodiment will be described. Hereinafter, the unit of the contents of
individual
elements is "mass%" unless particularly otherwise described.
[0017]
(C: 0.40% to 1.10%)
C has an effect of increasing the pearlite fraction in steel and refining the
lamellar spacing in the pearlite structure. When the lamellar spacing is
refined, the
strength is improved. When the C content is less than 0.40%, it becomes
difficult to
ensure 80 area% or more of the pearlite structure. In this case, it becomes
impossible to
sufficiently ensure the strength of the steel wire. Therefore, the C content
is set to
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0.40% or more. The C content is preferably 0.60% or more. On the other hand,
when
the C content exceeds 1.10%, the electrical conductivity of the steel wire is
decreased,
and the amount of proeutectoid cementite is increased. Therefore, the
ductility is
degraded. Therefore, the C content is set to 1.10% or less. The C content is
preferably
1.05% or less, more preferably 1.00% or less, and still more preferably 0,95%
or less.
[0018]
(Si: 0.005% to 0.350%)
Si is an effective element for increasing the strength of steel by solid
solution
strengthening and is also an element necessary as a deoxidizing agent. When
the Si
content is less than 0.005%, the above described effects cannot be
sufficiently obtained,
and thus the Si content is set to 0.005% or more. In order to further enhance
hardenability and facilitate a heat treatment, the Si content is preferably
set to 0.010% or
more and more preferably set to 0.020% or more. On the other hand, Si is an
element
that increases the electrical resistivity when distributed in ferrite in the
pearlite structure.
When the Si content exceeds 0.350%, the electrical resistivity is
significantly increased,
and thus the Si content is set to 0.350% or less. In order to obtain a lower
electrical
resistivity (that is, a higher electrical conductivity), the Si content is
preferably set to
0.250% or less and more preferably set to 0.150% or less.
In addition, in a case where a zinc plating or a zinc alloy plating is formed
on the
steel wire, when the Si content is small, the growth of an alloying layer
during plating is
accelerated, and the fatigue properties of the steel wire is degraded.
Therefore, in a case
where it is assumed that the steel wire is used after a zinc plating or a zinc
alloy plating is
performed thereon, the Si content is preferably set to 0.050% or more.
[0019]
(Mn: 0.05% to 0.90%)
Mn is a deoxidizing element and an element having an action of preventing hot
brittleness by fixing S in steel as MnS. In addition, Mn is an element that
improves
hardenability, decreases the microstructure fraction of ferrite during
patenting, and
contributes to the improvement of strength. However, when the Mn content is
less than
0.05%, the above described effects cannot be sufficiently obtained. Therefore,
the Mn
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content is set to 0.05% or more. On the other hand, when the Mn content
becomes
excessive, the electrical conductivity of steel is decreased. Therefore, the
Mn content is
set to 0.90% or less. In order to further increase the electrical
conductivity, the Mn
content is preferably 0.75% or less and more preferably 0.60% or less.
[0020]
The steel wire according to the present embodiment basically includes the
above
described elements and the remainder including Fe and impurities. In the steel
wire
according to the present embodiment, among the impurities, the amounts of N,
P, and S
are preferably limited as described below. With respect to impurities, it is
preferable that
contents thereof are small and may be 0%. The impurities refer to elements
that are
inevitably mixed into the steel wire from a raw material or the like or during
manufacturing steel.
[0021]
(N: 0.0100% or less)
N is an element that degrades ductility by strain aging during cold working
and
also decreases electrical conductivity. Particularly, when the N content
exceeds
0.0100%, the ductility and the electrical conductivity significantly are
decreased, and thus
the N content is preferably limited to 0.0100% or less. The N content is more
preferably
0.0080% or less and still more preferably 0.0050% or less.
[0022]
(P: 0.030% or less)
P is an element that contributes to the solid solution strengthening of
ferrite but
significantly degrades ductility. Particularly, when the P content exceeds
0.030%, the
degradation in wire drawability during the wire drawing of a wire rod to a
steel wire
becomes significant. Therefore, the P content is preferably limited to 0.030%
or less.
The P content is more preferably 0.020% or less and still more preferably
0.012% or less.
[0023]
(S: 0.030% or less)
S is an element that causes red brittleness and degrades ductility. When the S
content exceeds 0.030%, the degradation in ductility becomes significant.
Therefore,
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the S content is preferably limited to 0.030% or less. The S content is more
preferably
0.020% or less and still more preferably 0.010% or less.
[0024]
As described above, the steel wire according to the present embodiment
basically
includes the above described elements and the remainder including Fe and
impurities.
However, besides the above elements, the steel wire may contain one or more
elements
selected from the group consisting of Cr, Al, Ti, V, Nb, Mo, and B in a range
described
below instead of some of Fe. Since it is not necessary that these elements
need to be
contained, and the lower limits thereof are 0%. In addition, since the
properties of the
steel wire are not impaired even in a case where these arbitrary elements are
contained in
an amount less than the range described below, the case is acceptable.
[0025]
(Cr: 0.01% to 0.70%)
Cr is an element that improves the hardenability of steel and an element that
increases the tensile strength by decreasing the lamellar spacing of the
lamellar cementite
in the pearlite structure. In a case where the effects are obtained, the Cr
content is
preferably set to 0.01% or more. The Cr content is more preferably 0.02% or
more.
On the other hand, when the Cr content exceeds 0.70%, the electrical
conductivity is
decreased depending on patenting conditions. Therefore, even in a case where
Cr is
contained, the upper limit of the Cr content is preferably set to 0.70%.
[0026]
(Al: 0.001% to 0.070%)
Al is a deoxidizing element and an element that contributes to the refining of
austenite grain size by fixing nitrogen as a nitride. When the Al content is
less than
0.001%, it is difficult to obtain the above described effects, and thus, in a
case where the
effects are obtained, the Al content is preferably set to 0.001% or more. On
the other
hand, when Ails not fixed in ferrite as a nitride and is present as free Al,
Al is an element
that decreases the electrical conductivity. Therefore, even in a case where Al
is
contained, the upper limit of the Al content is preferably set to 0.070%. A
more
preferred upper limit is 0.050%.
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[0027]
(Ti: 0.002% to 0.050%)
Ti is a deoxidizing element and an element that contributes to the refining of
austenite grain size by forming a carbonitride. In a case where the effects
are obtained,
the Ti content is preferably set to 0.002% or more. On the other hand, when
the Ti
content exceeds 0.050%, there is a possibility that a coarse nitride may be
formed during
steelmaking, a carbide is precipitated during a patenting treatment, and
ductility is
degraded. Therefore, even in a case where Ti is contained, the upper limit of
the Ti
content is preferably set to 0.050%. A more preferred Ti content is less than
0.030%.
[0028]
(V: 0.002% to 0.10%)
V is an element that improves the hardenability of steel and an element that
contributes to the improvement of the strength of steel by being precipitated
as a
carbonitride. In order to obtain the effects, the V content is preferably set
to 0.002% or
more. On the other hand, when the V content becomes excessive, the time until
ending
the transformation during patenting becomes long, and ductility is degraded
due to the
precipitation of a coarse carbonitride. Therefore, even in a case where V is
contained,
the upper limit of the V content is preferably set to 0.10%. A more preferred
upper limit
is 0.08%.
[0029]
(Nb: 0.002% to 0.050%)
Nb is an element that improves the hardenability of steel and an element that
contributes to the refining of austenite grain size by being precipitated as a
carbide. In a
case where the effects are obtained, the Nb content is preferably set to
0.002% or more.
On the other hand, when the Nb content exceeds 0.050%, the time until ending
the
transformation during patenting becomes long. Therefore, even in a case where
Nb is
contained, the Nb content is preferably set to 0.050% or less. The Nb content
is more
preferably 0.020% or less.
[0030]
(Mo: 0.02% to 0.20%)
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MO is an element that improves the hardenability of steel and decreases the
area
ratio of ferrite in the structure. In a case where the effects are obtained,
the Mo content
is preferably set to 0.02% or more. However, when the Mo content becomes
excessive,
the time until ending the transformation during patenting becomes long.
Therefore, even
in a case where Mo is contained, the Mo content is preferably set to 0.20% or
less. The
Mo content is more preferably 0.10% or less.
[0031]
(B: 0.0003% to 0.0030%)
B is an element that improves the hardenability of steel and an element that
increases the pearlite area ratio by suppressing the generation of ferrite. In
a case where
the effects are obtained, the B content is preferably set to 0.0003% or more.
On the
other hand, when the B content exceeds 0.0030%, M23(C, B)6 is precipitated on
austenite
grain boundaries in a supercooled austenite state during patenting, and
ductility is
degraded. Therefore, even in a case where B is contained, the B content is
preferably set
to 0.0030% or less. The B content is more preferably 0.0020% or less.
[0032]
Next, the metallographic structure of the steel wire according to the present
embodiment will be described.
The steel wire according to the present embodiment intends to provide a
tensile
strength of 1,500 MPa or more, preferably 1,600 MPa or more, and more
preferably 2,000
MPa or more in consideration of the application to steel cores of ACSR that
constitutes
power transmission lines. In order to realize the above described tensile
strength and
increase the electrical conductivity, the steel wire according to the present
embodiment
needs to include a metallographic structure described below. Unless
particularly
otherwise described, a cross section refers to a so-called L cross section
that is parallel to
the longitudinal direction of the steel wire and passes through the
longitudinal-direction
central axis of the steel wire.
[0033]
<80 area% or more of pearlite structure having lamellar cementite is included>
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The steel wire according to the present embodiment includes 80 area% or more
of a pearlite structure having lamellar cementite in the metallographic
structure of a cross
section. When the area ratio of the pearlite structure is less than 80 area%,
it becomes
impossible to obtain a sufficient tensile strength. The area ratio of the
pearlite structure
having lamellar cementite is preferably 95 area% or more, more preferably 97
area% or
more, and may be 100area%. In the present embodiment, the pearlite structure
having
lamellar cementite refers to a structure that is derived from pearlite or
pseudo pearlite
present in a wire rod before wire drawing and a structure in which cementite
phase
(lamellar cementite) and ferrite phase are alternately repeated and overlaid.
In other
words, the pearlite structure having lamellar cementite in the present
embodiment is a
structure including cementites that are present linearly, in a curved shape,
or
fragmentarily and ferrite phase present between the cementites.
The steel wire according to the present embodiment may include a ferrite
structure in addition to the pearlite structure. However, when the ferrite
structure
exceeds 20 area%, the area ratio of the pearlite structure is decreased, and
the tensile
strength is decreased. Therefore, the ferrite structure needs to be limited to
20 area% or
less. The ferrite structure mentioned herein is not the ferrite phase that is
included in the
pearlite structure.
In addition, there is a case that the steel wire according to the present
embodiment includes a small amount of a bainite structure or a martensite
structure in
addition to the pearlite structure and the ferrite structure. However, bainite
or martensite
that is a diffusionless transformation-type structure is a structure in which
the diffusion of
a solid solute element is staggered. Thus, when the microstructure fraction of
these
structures increases, the electrical conductivity of the steel wire is
decreased. Therefore,
the bainite structure and the martensite structure are preferably set to less
than 3 area% in
total.
The microstructure fractions in the steel wire are obtained by capturing a
metallographic structure photograph from an observation place of the average
lamellar
spacing on a cut surface of the steel wire described below at a magnification
of 2,000
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times, marking the regions of the respective structures, and computing the
average values
of the area ratios of the respective structures by an image analysis.
[0034]
<Average lamellar spacing is 28 nm to 80 nm>
The average lamellar spacing that is a spacing between lamellar cementites
adjacent to each other in the pearlite structure is in a range of 28 nm to 80
nm. When
the average lamellar spacing reaches less than 28 nm, the electrical
conductivity of the
steel wire is decreased. On the other hand, when the average lamellar spacing
is more
than 80 nm, it is not possible to sufficiently increase the electrical
conductivity and the
tensile strength.
[0035]
The average lamellar spacing is measured using the following method. That is,
the L cross section of the steel wire is implanted into a resin, polished to a
mirror surface,
and then etched with picral, and digital images of 10 views of arbitrary
regions including
five or more pearlite blocks are captured using FE-SEM at a magnification of
5,000 times
to 10,000 times. From the respective captured photographs, the average
lamellar
spacings are measured using an image analyzer. The lamellar spacing refers to
the
distance from the center of a lamellar cementite to the center of the closest
lamellar
cementite.
[0036]
<Average length of lamellar cementite is 22.0 pm or less>
The average length of the lamellar cementite in the pearlite structure is 22.0
pm
or less. When the average length of the lamellar cementite exceeds 22.0 m,
the
electrical conductivity of the steel wire is decreased. From the viewpoint of
improving
the electrical conductivity, the average length of the lamellar cementite is
preferably 12.0
i_un or less and more preferably 10.0 jim or less. On the other hand, from the
viewpoint
of the tensile strength, the average length of the lamellar cementite is
preferably 1.0 gm or
more, more preferably 2.0 gm or more, and still more preferably 5.0 pm or
more.
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[0037]
The average length of the lamellar cementite in the pearlite structure is
measured
using the following method. That is, a cut surface of the steel wire in the
longitudinal
direction (wire drawing direction) (the L cross section) is mirror-polished
and then etched
with picral, the structure is observed using FE-SEM, and the results of the
structural
observation are analyzed, thereby obtaining the average length of the lamellar
cementite.
Specifically, as shown in FIG. 1, on a cross section of the steel wire, a
region from the
axial-direction central location (D/2) of the steel wire to D/4 locations (D
represents the
diameter of the steel wire) is set. The set region is a rectangular region in
which the
lengths of individual sides reach D/2. This rectangular region is further
divided into
nine equal meshes, and the vertices (16 places) of the respective divided
meshes are used
as observation locations. At the respective observation locations, capture
regions are set
at a magnification of 10,000 times so that the wire drawing direction becomes
parallel to
images, and the surface of the cross section is captured using FE-SEM. The
images of
the capture regions are analyzed, cementite portions and the other portions
(ferrite
portions) are binarized, and the lengths of cementite along the long side are
obtained. In
addition, the obtained cementite lengths are averaged, thereby computing the
average
length of cementite.
[0038]
< Among pearlite structure, pearlite structure having lamellar cementite of
which
inclination with respect to longitudinal direction of steel wire is 150 or
less is 40 area% or
more >
Among the pearlite structure, a pearlite structure having lamellar cementite
of
which the inclination (angular difference) with respect to the longitudinal
direction of the
steel wire is 150 or less is 40 area% or more by the area ratio. When the area
ratio of the
pearlite structure having the lamellar cementite of which the inclination is
150 or less is
less than 40 area%, the electrical conductivity is decreased. From the
viewpoint of the
electrical conductivity, the area ratio of the pearlite structure having the
lamellar
cementite of which the inclination with respect to the longitudinal direction
of the steel
wire is 15 or less (hereinafter, simply referred to as "the lamellar
cementite of which an
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inclination of 150 or less") is preferably 55 area% or more and more
preferably 60 area%
or more.
It is preferable that the proportion of the lamellar cementite of which the
inclination with respect to the longitudinal direction of the steel wire is
150 or less is high
from the viewpoint of the electrical conductivity, and thus the upper limit of
the area ratio
of the pearlite structure having the lamellar cementite of which the
inclination is 150 or
less is 100 area%.
[0039]
The area ratio of the pearlite structure having the lamellar cementite of
which the
inclination with respect to the longitudinal direction of the steel wire is
150 or less is
measured using the following method. That is, each of the images captured in
the
measurement of the average length of the lamellar cementite is used, in a
region of a
drawn pearlite structure in which the orientations of lamellar cementites in
the image
central part (pearlite colony) are equal to one another, both terminals of one
lamellar
cementite are connected with a line segment, the angular difference from the
horizontal
direction is measured, and whether or not the angular difference is 15 or
less is
confirmed. When the angular difference is 150 or less, the region is
determined as the
pearlite structure having lamellar cementite of which the inclination with
respect to the
longitudinal direction of the steel wire is 150 or less. In a case where the
orientations of
lamellar cementites are irregular or unclear in the drawn pearlite structure,
the lamellar
cementite is determined as lamellar cementite of which the inclination is not
15 or less,
and the region is not included as "the pearlite structure in which the
inclination of
lamellar cementite with respect to the longitudinal direction of the steel
wire is 150 or
less".
In a case where the total area of the pearlite structures in which the
inclination of
lamellar cementite with respect to the longitudinal direction of the steel
wire is 15 or less
is 40 area% or more with respect to the total area of the pearlite structures
present in the
field of views of the total number of captured sheets, it is determined that
40% or more of
the pearlite structures having lamellar cementite of which the inclination
with respect to
the longitudinal direction of the steel wire is 15 or less are present by the
area ratio.
- 15 -
CA 03039025 2019-04-01
FIG. 2A is an example of an image showing a pearlite structure in which the
inclination is
in a range of 150 or less in the region of the drawn pearlite structure in
which the
orientations of lamellar cementites in the central part are equal to one
another, and FIG.
2B is an example of an image showing a pearlite structure in which the
inclination is not
150 or less.
[0040]
<Integration degree of {110} plane of ferrite with respect to longitudinal
direction is in a range of 2.0 to 8.0>
The integration degree of a {110} plane of ferrite with respect to the
longitudinal
direction of the steel wire is in a range of 2.0 to 8Ø In a case where the
integration
degree of the {110} plane of ferrite is less than 2.0 or more than 8.0, the
electrical
conductivity of the steel wire is decreased, which is not preferable.
Meanwhile, from
the viewpoint of the electrical conductivity and the tensile strength, the
integration degree
of the {110} plane of ferrite is preferably 2.2 to 5.5 and more preferably 3.0
to 4.5.
[0041]
The integration degree of ferrite is measured using the following method. That
is, in a region from the central part to D/4 (D represents the diameter of the
steel wire) in
a radial direction of a cut surface in the longitudinal direction (the wire
drawing direction)
of the steel wire shown in FIG. 3B, a {110} pole figure is produced using an X-
ray
diffraction method, and the absolute maximum value of the pole densities
(ratios to a
random orientation) of spots observed in an RD direction (the longitudinal
direction of
the steel wire) is considered as the integration degree of the {110} plane of
ferrite.
Here, the integration degree of the {110} plane of ferrite that is obtained by
X-
ray diffraction refers to the integration degree being computed from
information obtained
from both ferrite phase included in the pearlite structure and ferrite that is
not the pearlite
structure.
Meanwhile, the measurement conditions of the X-ray diffraction in the present
embodiment are as described below.
X-ray diffraction device: manufactured by Rigaku Corporation
Trade name: RINT2200 (tube) (RINT2000/PC series)
- 16 -
CA 03039025 2019-04-01
X-ray source: MoKa
Diffusion slit: 1/4 (0.43 mm)
[0042]
<Wire diameter (diameter): 1.4 mm or more>
The steel wire according to the present embodiment has a wire diameter of
1.4 mm or more. When the wire diameter is 1.4 mm or more, the wire drawing of
wire
rods and the manufacturing of coated steel wires having a metal coating layer
of
aluminum, zinc, or the like formed around the steel wire are easy. Therefore,
the steel
wire according to the present embodiment is also excellent in views of the
drawnability
and the manufacturing costs in addition to the electrical conductivity and the
tensile
strength. The diameter of the steel wire according to the present embodiment
is
preferably 1.5 mm or more and more preferably 1.6 mm or more.
Here, when the diameter of the steel wire is too large, it becomes difficult
to
shorten the length of lamellar cementite, and thus the diameter of the steel
wire according
to the present embodiment is preferably 4.2 mm or less and more preferably 4.0
mm or
less.
[0043]
<Electrical resistivity and tensile strength>
The steel wire according to the present embodiment is excellent for both the
electrical conductivity and the tensile strength.
In the steel wire according to the present embodiment, the electrical
resistivity
that is an index of the electrical conductivity is preferably less than 19.0
[tn.cm, more
preferably less than 18.0 12.cm, and still more preferably less than 17.0
[tf2. cm.
In addition, the tensile strength of the steel wire according to the present
embodiment is preferably 1,500 MPa or more, more preferably 1,600 MPa or more,
and
still more preferably 2,000 MPa or more.
As shown in parts of examples described below, it is possible to realize a
steel
wire having an electrical resistivity of less than 18.0 ttS2.cm and a tensile
strength of
2,000 MPa or more, preferably, an electrical resistivity of less than 17.0
[10.cm and a
tensile strength of 2,000 MPa or more.
- 17 -
CA 03039025 2019-04-01
[0044]
A coated steel wire according to the present embodiment includes the steel
wire
according to the present embodiment and a metal coating layer that coats the
steel wire.
That is, the coated steel wire according to the present embodiment is a metal-
coated steel
wire.
The metal coating layer includes, for example, at least one of the group
consisting of zinc, a zinc alloy, aluminum, an aluminum alloy, copper, a
copper alloy,
nickel, and a nickel alloy. The metal coating layer may be a plated layer or a
clad layer.
The plated layer may be an electroplated layer or a hot-dipped layer. In a
metal coating
layer formed by hot dipping, there is a case in which an alloying layer is
formed in the
interface between the steel wire and the metal coating layer. As the alloying
layer, a
ZnFe alloying layer, an AlFe alloying layer, a NiFe alloying layer, and a CuFe
alloying
layer can be exemplified. When the coated steel wire has the metal coating
layer, it is
possible to increase the electrical conductivity of the entire coated steel
wire.
[0045]
Next, a preferred method for manufacturing the steel wire according to the
present embodiment and the coated steel wire according to the present
embodiment will
be described. The manufacturing method described below is an example, and the
method for manufacturing the steel wire according to the present embodiment
and the
coated steel wire according to the present embodiment is not limited to
manufacturing
conditions described below as long as steel wires or coated steel wires
satisfying the
scope of the present invention can be obtained.
[0046]
<Melting, casting, and hot rolling>
After steel having the composition described above is melted, a steel piece
(billet) is manufactured by continuous casting or the like, and hot rolling is
carried out.
After the casting, blooming may be carried out. When the hot rolling is
performed on
the steel piece, it is preferable that the steel piece is heated so that the
central part of the
steel piece is reached 1,000 C to 1,100 C, hot rolling in which the finish
temperature is
set to 900 C to 1,000 C is carried out, and thus a wire rod is obtained.
- 18 -
CA 03039025 2019-04-01
[0047]
<Cooling>
On the hot-rolled wire rod, cooling is carried out by water cooling, air
cooling,
furnace cooling, and/or immersion in a melting bath. At this time, the cooling
pattern is
preferably set depending on the C content.
In a case where the C content is 0.40% to 0.70%, after finish rolling, the
wire rod
is cooled to a temperature range of 800 C to 920 C at an average cooling rate
of 20 C/s
or more (first cooling), then, cooled so that the average cooling rate in a
temperature
range of 800 C to 600 C reaches 5 C/s to 20 C/s (second cooling), and then
cooled so
that the average cooling rate in a temperature range of 600 C to 500 C reaches
5 C/s or
less (third cooling).
When the cooling rate of the first cooling is less than 20 C/s, proeutectoid
ferrite
is likely to be generated, and the microstructure fraction of pearlite is
decreased. In
addition, when the first cooling stop temperature is less than 800 C,
austenite grain size
are refined, and sufficient hardenability cannot be obtained. On the other
hand, when
the first cooling stop temperature is more than 920 C, proeutectoid ferrite is
likely to be
generated in the subsequent cooling, and the microstructure fraction of
pearlite is
decreased.
In addition, when the cooling rate of the second cooling is less than 5 C/s,
the
microstructure fraction of pearlite is likely to be decreased by the
generation of
proeutectoid ferrite. On the other hand, when the cooling rate of the second
cooling is
more than 20 C/s, pearlitic transformation and the distribution of alloying
elements
become insufficient throughout the second and third cooling. In addition, when
the
cooling rate of the third cooling is more than 5 C/s, the distribution of the
alloying
element does not easily occur, and thus the electrical conductivity is
decreased.
However, in the above described cooling, when the retention time at 600 C to
500 C is as long as 33 seconds or longer (approximately 3.0 C/s or less in
terms of the
average cooling rate), the distribution of the alloying elements sufficiently
is proceeded,
and thus the average cooling rate in a temperature range of 800 C to 600 C may
be 20
C/s or more. In addition, for example, after the completion of transformation
using a
- 19 -
CA 03039025 2019-04-01
lead bath, a salt bath, or a fluid bed bath, the wire rod may be heated again
to a
temperature range of 600 C to 400 C.
In addition, In a case where the C content is more than 0.70% and 1.10% or
less,
after the finish rolling, the wire rod is cooled to 800 C to 920 C at an
average cooling rate
of 20 C/s or more and immersed in a molten salt of 500 C to 600 C for 30
seconds or
more, and thus pearlitic transformation is caused.
[0048]
In the present embodiment, the finish temperature of rolling refers to the
surface
temperature of the wire rod immediately after the finish rolling, and the
average cooling
rate in the cooling after the finish rolling refers to the cooling rate of the
central part of
the wire rod.
[0049]
In the wire rod obtained through the above described manufacturing process,
for
example, 80% or more of the metallographic structure in a cross section is a
pearlite
structure, the average lamellar spacing of the pearlite structure is 50 nm to
170 nm, and
the average length of lamellar cementite in the pearlite structure becomes
1.51AM or less.
Meanwhile, from the viewpoint of obtaining the steel wire according to the
present
embodiment by wire drawing described below, the wire diameter of the wire rod
manufactured by the above described manufacturing process is preferably 3.0 mm
to 14.0
mm.
[0050]
<Wire drawing>
Next, wire drawing is performed on the wire rod, so that a steel wire is
obtained.
In the wire drawing, it is preferable that the wire drawing is performed on
the wire rod as
to impart a true strain of 1.5 to 2.4. The true strain is preferably 1.7 to
2.1. When the
wire drawing is carried out under the above described condition, the
electrical resistivity
of the steel wire after the wire drawing is decreased by approximately 1.0
[tC2.cm to 1.5
cm relative to the wire rod before the wire drawing (that is, the electrical
conductivity
is increased). Meanwhile, depending on the kind of steel (for example, a kind
of steel K
that is used in examples described below), steel wires having a low electrical
resistivity
- 20 -
CA 03039025 2019-04-01
and a high tensile strength can be obtained even when the true strain is less
than 1.5 or
more than 2.4. However, when a true strain of 1.5 to 2.4 is imparted to the
above
described kind of steel, it is easy to obtain steel wires having a high
tensile strength and
an electrical resistivity that is suppressed to be lower.
As the reduction of area during the wire drawing of the wire rod increases,
and
the strain increases, the average lamellar spacing is decreased, the average
length of
lamellar cementites is increased, the inclination of lamellar cementite with
respect to the
longitudinal direction is decreased, the proportion of the pearlite structure
having
cementite of which the angular difference is 150 or less is increased, and the
integration
degree of the {110} plane of ferrite is increased. When the wire drawing is
carried out
under a condition in which the true strain is less than 1.5, the proportion of
cementite of
which the angular difference is 150 or less is insufficient, and the
electrical conductivity is
decreased. On the other hand, when the wire drawing is carried out under a
condition in
which the true strain exceeds 2.4, the amount of solid solute C in ferrite is
increased, and
thus the electrical conductivity is decreased.
[0051]
According to the manufacturing method including the above described
processes, the steel wire according to the present embodiment is manufactured.
[0052]
<Coating>
Next, the metal coating layer is formed on the obtained steel wire. A method
for forming the metal coating layer may be any of an electroplating method, a
hot dipping
method, and a cladding method. The thickness of the metal coating layer at
this time is
preferably as thick as approximately 0.7% to 20% of the diameter of the wire
rod or the
steel wire.
In this manner, the coated steel wire according to the present embodiment is
manufactured.
The coating may be carried out between the cooling and the wire drawing.
That is, the coated steel wire according to the present embodiment can be
obtained even
- 21 -
CA 03039025 2019-04-01
when the wire drawing is carried out after forming the metal coating layer on
the wire
rod.
[Examples]
[0053]
Next, examples of the present invention will be described. Conditions in the
examples are one of the examples employed to confirm the feasibility and
effect of the
present invention, and the present invention is not limited to these condition
examples.
The present invention is capable of employing a variety of conditions within
the scope of
the present invention as long as the object of the present invention is
achieved.
[0054]
Molten steel melted to chemical composition shown in Table 1 (here, the
remainder was Fe and impurities) in a 50 kg vacuum melting furnace was cast to
ingots.
The respective ingots were heated at 1,250 C for one hour and then hot-forged
so as to
become bar wire rods having a diameter of 15 mm so that the finish temperature
was
950 C or more, and then cooled in the air to room temperature. These hot-
forged
materials were machined to a diameter of 10 mm and cut to a length of 1,500
mm.
These machined materials were heated in a nitrogen atmosphere at 1,050 C for
15
minutes and then hot-rolled so that the finish temperature was 900 C or more,
thereby
obtaining rolled materials having a diameter of 7 mm.
[0055]
After that, some of the rolled materials were finish-rolled, then, cooled to
900 C
in the atmosphere by wind using a fan, then within 10 seconds, sealed in a
heating furnace
that had been heated at a low temperature, cooled to 600 C in the furnace at
an average
cooling rate of 6 C/s and cooled to 400 C in the furnace at an average
cooling rate of 1
C/s, then, removed after further cooling to 400 C, and cooled in the air to
room
temperature, thereby obtaining steel wire materials (the condition number 5 of
the cooling
in Table 2).
In addition, some of the rest of the rolled materials were finish-rolled,
then,
cooled to 850 C or 900 C in the atmosphere by wind using a fan, then within 10
seconds,
immersed in a lead bath under the condition numbers 2 to 4 of the cooling
shown in
- 22 -
CA 03039025 2019-04-01
Table 2, then, removed and cooled in the air to room temperature, thereby
obtaining steel
wire materials. The average cooling rates in the respective temperature ranges
were as
shown in Table 2.
Some of the rest of the rolled materials were hot-rolled to a diameter of 7 mm
and then cooled to room temperature in the atmosphere by wind using a fan (the
condition
number 6 of the cooling in Table 2). The average cooling rates in the
respective
temperature ranges were as shown in Table 2.
Furthermore, some of the rest of the rolled materials were finish-rolled,
then,
immersed in a lead bath at 640 C, then, immediately cooled to 400 C or less at
100 C/s
(the condition number 1 of the cooling in Table 2). The average cooling rates
in the
respective temperature ranges were as shown in Table 2.
[0056]
Among the obtained wire rods, on test numbers 1 to 31, metal coating layers
were formed using a hot dip galvanizing method or an aluminum cladding method.
[0057]
After that, wire drawing was performed on the wire rods so as to impart true
strains shown in Table 3 to steel portions included in the wire rods, thereby
obtaining
steel wires or coated steel wires in which the diameters of the steel portions
were 2.0 mm
to 3.5 mm.
[0058]
After that, a metal coating layer made of zinc was formed on the steel wire of
test number 32 on which no coating layer had been formed before the wire
drawing using
a hot dip galvanizing method.
[0059]
The metal coating layers were removed from the coated steel wires obtained in
the above described manner using hydrochloric acid, sodium hydroxide, or the
like to
take out steel wires, and the tensile strengths and the electrical
conductivities of these
steel wires were evaluated.
- 23 -
CA 03039025 2019-04-01
<Tensile strength>
Three tensile test pieces having a length of 350 mm were sampled in a wire
form
from the steel wire. A tensile test was carried out at normal temperature on
these tensile
test pieces with an inter-chuck distance of 200 mm at a tensile rate of 10
mm/min, tensile
strengths (TS) were measured, and the average value thereof was considered as
the tensile
strength of this test specimen.
[0060]
<Electrical conductivity>
A test piece for electrical conductivity measurement having a length of 60 mm
was cut out from the steel wire, and the electrical resistivity was measured
at a
temperature of 20 C using a four-terminal method.
[0061]
In addition, from the obtained steel wires, individual microstructure
fractions,
the average lamellar spacings of lamellar cementite, the average lengths of
the lamellar
cementite, the area ratios of pearlite structures having lamellar cementite of
which the
inclination with respect to the longitudinal direction of the steel wires
(angular
differences) was 150 or less, and the intengration degrees of {110} planes of
ferrite were
measured.
<Average lamellar spacing>
For each of the steel wires, the L cross section was implanted into a resin,
polished to a mirror surface, and then etched with picral, and digital images
of 10 views
of arbitrary regions including five or more pearlite blocks were captured
using FE-SEM
at a magnification of 5,000 times to 10,000 times. From the respective
photographs, the
average lamellar spacings were measured using an image analyzer.
<Area ratio of individual structures>
A metallographic structure photograph was captured at a magnification of 2,000
times at the observation place of the average lamellar spacing of the cut
surface of each of
the steel wires, the regions of individual structures were marked, and the
average values
of the area ratios of the individual structures were computed by an image
analysis.
Meanwhile, Table 3 shows the area ratios of a pearlite structure and a ferrite
structure;
- 24 -
CA 03039025 2019-04-01
however, for steel wires in which the total of these structures was not 100%,
a bainite
structure and/or a martensite structure were observed as other structures.
[0062]
<Average length of lamellar cementite>
The average length of lamellar cementite in the pearlite structure was
obtained
by using the sample provided for the measurement of the average lamellar
spacing,
carrying out structural observation using FE-SEM, and analyzing the results of
the
structural observation. As shown in FIG. 1, on an L cross section of the steel
wire, a
region from the axial-direction central location (D/2) of the steel wire to
D/4 locations (D
represents the diameter of the steel wire) was set. The set region was a
rectangular
region in which the lengths of individual sides reached D/2. This rectangular
region was
further divided into nine equal meshes, and the vertices of the respective
divided meshes
were used as observation locations. At the respective observation locations,
capture
regions were set at a magnification of 10,000 times so that the wire drawing
direction
became parallel to images, and the surface of the cross section was captured
using FE-
SEM. The images of the capture regions were analyzed, cementite portions and
the
other portions (ferrite portions) were binarized, and the lengths of cementite
along the
long side were obtained. In addition, the obtained cementite lengths were
averaged,
thereby computing the average length of cementite.
[0063]
<Area ratio of pearlite structure having lamellar cementite of which
inclination
with respect to longitudinal direction of steel wire was 150 or less>
Next, each of the images captured in the measurement of the average length of
the lamellar cementite was used, in a region of a drawn pearlite structure in
which the
orientations of lamellar cementites in the image central part were equal to
one another,
both terminals of one lamellar cementite were connected with a line segment,
the angular
difference from the horizontal direction was measured, and whether or not the
angular
difference is 15 or less was confirmed. In a case where the total of the
pearlite
structures in which the inclination of lamellar cementite with respect to the
longitudinal
direction of the steel wire was 15 or less was 40 area% or more with respect
to the total
- 25 -
CA 03039025 2019-04-01
area of the pearlite structures in the total captured images, it was
determined that 40% or
more of the pearlite structures having lamellar cementite of which the
inclination with
respect to the longitudinal direction of the steel wire was 15 or less were
present by the
area ratio.
[0064]
<Integration degree of {110} plane of ferrite>
Next, the integration degree of a {110} plane of ferrite was measured as
described below. In a region from the central part to D/4 (D represents the
diameter of
the steel wire) in a radial direction of a cut surface in the wire drawing
direction (RD
direction) of the steel wire as shown in FIGS. 3A and 3B, a {110} pole figure
was
produced using an X-ray diffraction method, and the maximum value of the pole
densities
(ratios to a random orientation) of spots observed in the RD direction was
considered as
the integration degree of the {110} plane of ferrite. The measurement
conditions of the
X-ray diffraction are as described above.
[0065]
The results are shown in Table 1 to Table 3.
- 26 -
[0066]
[Table 1]
mass%
Kind
C Si Mn P S N Cr Al
Ti V Nb Mo B
of steel
A 0.38 0.150 0.45 0.013 0.004 0.0039 - -
- - - -
B 0.45 0.320 _ 0.15 0.004 0.005 0.0041 - - 0.045
- - - -
C 0.58 0.015 0.42 0.004 0.009 0.0024 0.35 - -
- - -
D 0.62 0.220 0.35 0.010 0.005 0.0037 - - -
- -
-
E 0.76 0.330 0.12 0.006 0.005 0.0040 - - -
- - 0.0012
-
F 0.79 0.140 0.32 0.010 0.006 0.0031 - - -
0.06 - - -
P
G 0.82 0.200 0.38 0.005 0.009 0.0036 - - -
- 0.022 - - o
. H 0.83 0.220 0.33 0.010 0.009 0.0033 - -
0.06 -
u,
--4 I 0.87 0.120 0.60 0.008 0.007 0.0037 0.25
0.049 0.003 0.03 0.005 0.05 0.0009
.
,
K 0.92 0.006 0.42 0.007 0.009 0.0027 0.23 0.055
0.013 0.01 0.01 0.03 0.0008 - .
,
L 0.92 0.030 0.45 0.013 0.009 0.0037 0.55 0.035
- - - - - ..
,
,
M 0.93 0.140 0.33 0.011 0.005 0.0036 0.032 -
- - - -
_ N 0.93 0.200 0.98 _ 0.006 0.005 0.0027 0.15
0.033 0.012 0.05 0.005 0.03 0.0015
0 0.98 0.200 0.35 0.010 0.008 0.0032 0.029
- - - -
P 1.05 0.140 0.40 0.010 0.005 0.0024 0.19 0.062
- - - -
Q 1.07 0.010 0.31 , 0.011 0.006 0.0036
0.21 - 0.015 - - - -
R 1.12 0.200 0.42 0.009 0.005 0.0041 - - -
- - -
S 0.82 0.500 0.40 0.010 0.010 0.0035 0.030 -
- - - -
T 0.82 0.150 0.05 0.012 0.008 0.0040 0.045 -
- - - -
[0067]
[Table 21
First cooling Second cooling Third
cooling Bath
Condition
Retention time Bath
immersion
number of Cooling stop temperature Average cooling Average cooling
Average cooling at 600 C to temperature
time
cooling [ C] rate [ C/s] rate ['Cis] rate
[ C/s 500 C [s] [ C]
[Seconds]
1 900 45 20
100 1 640 45
2 900 45 30
1.82 55 600 35
3 850 50 40
1.33 75 560 60
4 850 50 50
0.54 186 520 180
_
Wind cooling¨furnace
900 45 6 1 100
cooling-cooling in air
p
6 900 45 10
10 10 Wind cooling using fan 0
`0;
.
w
00
u,
N)
1
I
[0068]
[Table 3]
True A verage Average Lamellar
Integration
Kind Condition strain Pearlite Ferrite length of
cementite degree of Electrical Tensile .
Test lamellar
Diameter
of number of during structure structure lamellar having
angular ferrite resistivity strength Note
Number spacing
[mm]
steel cooling wire [area%] [area%1 cementite
difference of {110} [uS1.cm] [MPa]
[nm]
drawing [um] 15 or
less [%] plane
3 C 2 2.06 85 13 45 14.6 58
3.8 15.9 1598 2.5 Example
4 D 3 2.31 82 16 40 13.8 71
5.2 16.9 1788 2.2 Example
D 4 2.31 86 12 38 12.3 75 6.0
17.0 1812 2.2 Example
6 E 2 2.31 83 15 41 13.7 69
5.1 17.8 1994 2.2 Example
7 F 2 2.31 94 4 36 13.0 72
4.2 16.4 2091 2.2 Example
8 G 2 2.06 96 2 40 12.0 61
4.0 17.5 2034 2.5 Example
9 H 2 2.06 96 2 40 11.2 64
4.4 17.6 2074 2.5 Example P
I 2 2.06 97 1 35 13.4 66 4.1
17.9 2199 2.5 Example
11 K 2 2.06 96 2 34 12.6 63
3.9 16.7 2244 2.5 Example
t\.)
r.,
vo 12 K 3 1.57 100 0 45 8.2 54
3.2 16.1 2000 3.2 Example
r.,
.
.
13 K 3 2.06 100 0 34 12.5 67
4.2 16.7 2274 2.5 Example ,
,
14 K 4 2.06 97 1 35 13.6 73
4.4 16.6 2220 2.5 Example .
,
M 3 2.06 96 2 36 10.1 68 3.9
16.9 2261 2.5 Example ,
16 0 3 2.06 96 2 35 10.8 69
4.1 18.2 2348 2.5 Example
17 P 2 2.06 96 2 33 14.9 60
3.8 18.9 2499 2.5 Example
18 Q 3 2.06 97 1 32 10.9 66
3.7 16.6 2508 2.5 Example
19 A 2 2.31 33 65 50 15.9 65
4.8 15.4 1290 2.2 Comparative
Example
B 1 2.31 50 48 60 15.5 60 4.4
16.3 1349 2.2 Comparative
Example
21 B 5 1.39 52 46 82 5.5 28
2.2 16.5 1144 3.5 Comparative
Example
22 C 6 1.69 76 22 84 12.2 42
3.1 15.3 1461 3.0 Comparative
Example
23 D 5 2.06 82 16 66 12.8 48
4.1 16.6 1674 2.5 Example
26 K 3 2.51 97 2 28 21.8 82
5.8 17.3 2466 2.0 Example
True Average Lamellar
Integration
Kind Condition strain Pearlite Ferrite
Averagelength of cementite degree of Electrical Tensile
Test lamellar Diameter
of number of during structure structure lamellar having
angular ferrite resistivity strength Note
Number spacing
[mm]
steel cooling wire [area%] [area%] cementite
difference of {110} [pil=cm] [MPa]
[nm]
drawing [gm] 150 or
less [%] plane
27 K 3 1.39 97 1 50 7.0 43
2.0 17.0 1920 3.5 Example
28 N 2 2.06 97 1 31 28.0 63
4.3 22.1 2359 2.5 Comparative
Example
29 R 2 2.06 97 1 31 11.9 42
3.5 19.5 2627 2.5 Comparative
Example _
Comparative
30 S 3 2.06 89 8 35 10.8 61
4.1 22.3 2195 2.5
Example
31 T 2 2.06 98 1 46 13.0 66
4.3 15.6 1890 2.5 Example
_
_
32 K 3 2.06 100 0 36 10.5 60
4.0 16.3 2025 2.5 Example
P
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r.,
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.
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.
,
CA 03039025 2019-04-01
[0069]
Table 3 shows that, in the case of the test numbers 19 to 22 and 28 to 30 not
satisfying the conditions regulated by the present invention, at least one of
the above
described properties failed to reach the target values (tensile strength:
1,500 MPa or more,
electrical resistivity: less than 19.0 [t.O.cm, and diameter: 1.4 mm or more).
In contrast,
in the test numbers 3 to 18, 23, 26, 27, 31, and 32 satisfying all of the
conditions
regulated by the present invention, all of the above described properties
reached the target
values. Meanwhile, for all of the test numbers 11 to 14, 26, 27, and 32, a
kind of steel K
was used; however, in the test number 11 to 14 and 32 in which the true strain
during the
wire drawing was 1.5 to 2.4, particularly, the electrical resistivity was
suppressed to be
low.
[Industrial Applicability]
[0070]
According to the present invention, it is possible to provide a steel wire
which
has a wire diameter preferable for the use of power transmission lines and is
excellent for
electrical conductivity and tensile strength and a coated steel wire having
the above
described steel wire and a coating layer that coats the steel wire.
The steel wire and the coated steel wire of the present invention have a large
wire diameter and is excellent for the electrical conductivity and the tensile
strength and
thus can be preferably used for the use of power transmission lines.
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