JPWO2018069955A1 - Steel wire and coated steel wire - Google Patents

Abstract

This steel wire has a chemical composition of mass%, C: 0.40 to 1.10%, Si: 0.005 to 0.350%, Mn: 0.05 to 0.90%, Cr: 0 to 0%. 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: containing 0 to 0.0030%, the balance being Fe and impurities, and the metallographic structure in the cross section contains 80 area% or more of pearlite structure having lamellar cementite, and the average lamellar which is the interval between the lamellar cementite A pearlite structure having a spacing of 28 to 80 nm, an average length of the lamellar cementite of 22.0 μm or less, and the lamellar cementite having an inclination of 15 ° or less with respect to the longitudinal direction of the steel wire in the pearlite structure. 40 It is area% or more, the integration degree of the {110} plane of the ferrite with respect to the longitudinal direction is in the range of 2.0 to 8.0, and has a diameter of 1.4 mm or more.

Description

The present invention relates to a steel wire and a coated steel wire.
The present invention particularly relates to a steel wire excellent in conductivity and strength suitably used for a power transmission line, and a coated steel wire in which a coating layer is formed on the surface of the steel wire.

  Conventionally, a steel core aluminum stranded wire (Aluminum Conductor Steel-Reinforced cable, hereinafter "ACSR") is used as a power transmission line for transmitting electric power, in which an aluminum wire is twisted around an iron core (steel core) made of steel wire. There is. The steel wire used for the core of this ACSR has a strong role as a tension member of aluminum wire. The core of the steel core aluminum stranded wire is a galvanized steel wire obtained by subjecting drawn pearlite steel to zinc plating, or an aluminum clad wire coated with aluminum as a surface layer to improve the corrosion resistance of the wire. A drawn aluminum-clad steel wire is used.

The ACSR used as a transmission line is required to have strength and high transmission efficiency. In order to improve the power transmission efficiency of ACSR, it has been considered to reduce the weight of the core to increase the aluminum cross-sectional area, and to reduce the electrical resistance of the steel wire itself, which serves as the core. .
For example, Patent Document 1 discloses a method of reducing the specific gravity of a power transmission line by making the core a composite wire of carbon fiber and aluminum or an aluminum alloy instead of a steel wire for the purpose of reducing the weight of the core. ing. Further, Patent Document 2 discloses a method of limiting the content of C, Si and Mn in the steel wire to the necessary minimum for the purpose of reducing the electric resistance of the steel wire itself.

  However, since the technology disclosed in Patent Document 1 uses carbon fiber, which has a higher unit cost than steel, the cost is high. Moreover, since the technique disclosed by patent document 2 reduces content of an alloy element, it is difficult for a steel wire to ensure the intensity | strength as a tension member.

  In addition, according to Non-Patent Document 1, a wire rod of 5.5 mm diameter having a high carbon content of 0.92% is once drawn to 1.75 mm diameter and then patented to an extremely thin 0.26 mm diameter. It is reported that the conductivity is improved by making the condition of a true strain of about 1.5 as a peak by largely performing cold drawing.

  However, it is processed into such an extra-fine steel wire, and further plating of zinc etc. is performed around the extra-fine steel wire (core part), or an aluminum wire is twisted around the extra-fine steel wire to be fed. It is extremely difficult to manufacture the wire and the cost is significantly increased.

Japanese Patent Application Publication No. 2001-176333 Japanese Patent Application Laid-Open No. 2003-226938

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”

  The present invention was made in view of the above circumstances. An object of the present invention is to provide a coated steel wire having a wire diameter suitable for power transmission line applications and having excellent conductivity and tensile strength, and a coating layer covering the steel wire and the steel wire. I assume.

The present inventors examined the relationship between the chemical composition of steel materials and the form of the structure and conductivity. As a result, it has been found that by controlling the chemical components and the form of cementite, the conductivity of the wire serving as the material of the steel wire is improved. As a result of further investigation focusing on the form of ferrite and cementite, the present inventors found that the conductivity is further improved by applying strain to the wire to change the orientation of the ferrite and cementite. Furthermore, in addition to the excellent conductivity and tensile strength, the present inventors can obtain a steel wire having a wire diameter suitable for transmission line applications by devising the conditions of the cooling step and the wire drawing step after rolling. I found out.
That is, the present inventors carry out a cooling process under specific conditions after hot rolling, and perform wire drawing processing under specific conditions on a wire that has enhanced conductivity by controlling chemical components and structure. It has been found that a steel wire having a wire diameter suitable for transmission line applications, excellent in conductivity and high in tensile strength can be obtained.
The present invention has been made based on the above findings, and the summary thereof is as follows.

(1) The steel wire according to an aspect of the present invention is a steel wire, and the chemical composition is, 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 It contains ~ 0.050%, Mo: 0 to 0.20%, B: 0 to 0.0030%, the balance being Fe and impurities, and the metallographic structure in the cross section has a pearlite structure having lamellar cementite. The average lamellar spacing, which is 80 area% or more and which is the spacing between the lamellar cementite, is 28 to 80 nm, the average length of the lamellar cementite is 22.0 μm or less, and the length of the steel wire in the pearlite structure The lamella above has an inclination of less than 15 ° with respect to the direction The pearlite structure having a menthite is 40 area% or more, and the degree of accumulation of {110} plane of ferrite with respect to the longitudinal direction obtained by X-ray diffraction method is in the range of 2.0 to 8.0, 1 .4 mm or more in diameter.
(2) In the steel wire described in (1) above, the chemical composition is, by mass%, 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%, B: 0.0003 to 0.0030% You may contain 1 type, or 2 or more types selected from the group.
(3) A coated steel wire according to another aspect of the present invention includes the steel wire according to the above (1) or (2), and a metal coating layer coating the steel wire.
(4) In the coated steel wire according to (3), the metal coating layer may contain any one or more of zinc, zinc alloy, aluminum, aluminum alloy, copper, copper alloy, nickel and nickel alloy Good.

According to the above aspect of the present invention, a coated steel wire having a wire diameter suitable for transmission line applications and having excellent conductivity and tensile strength, and a coating layer coating the steel wire and the steel wire Can provide a line.
The steel wire and the coated steel wire according to the above aspect of the present invention can be suitably used for power transmission lines because the wire diameter of the steel wire as the core material is large and the conductivity and the tensile strength are excellent.

It is a figure which shows the cross section (L cross section) parallel to the longitudinal direction of a steel wire, Comprising: It is a schematic diagram explaining the measuring method of the average length of lamella cementite in the pearlite structure which has lamella cementite. It is a figure explaining the measuring method of the area ratio of pearlite structure which has lamellar cementite with inclination (angle difference) with respect to the longitudinal direction of a steel wire within 15 degrees, and the photograph which shows an example of lamellar cementite which inclination is within 15 degrees It is. It is a figure explaining the measuring method of the area ratio of pearlite structure which has lamellar cementite with inclination (angle difference) with respect to the longitudinal direction of a steel wire within 15 degrees, and the photograph which shows an example of lamellar cementite which inclination is not within 15 degrees It is. It is a figure which shows L cross section of a steel wire, Comprising: It is a schematic diagram which shows TD direction and RD direction. It is a figure which shows L cross section of a steel wire, Comprising: It is a schematic diagram for demonstrating the measuring method of the integration degree of a ferrite.

  A steel wire according to an embodiment of the present invention (a steel wire according to the present embodiment) and a coated steel wire according to an embodiment of the present invention (coated steel wire according to the present embodiment) will be described below.

  The steel wire according to the present embodiment has a steel component (chemical composition) described below, and has a pearlite structure having lamellar cementite in the metal structure (hereinafter sometimes referred to simply as "pearlite structure"). Contains. Moreover, in the steel wire according to the present embodiment, the average lamellar spacing of lamellar cementite contained in the pearlite structure is 28 to 80 nm, and the average length of lamellar cementite is 22.0 μm or less. The pearlite structure having lamellar cementite having an inclination of 15 ° or less with respect to the longitudinal direction of the line is 40 area% or more, and the degree of accumulation of {110} plane of ferrite with respect to the longitudinal direction obtained by X-ray diffraction method is 1. It is the range of 0-8.0. Furthermore, the steel wire according to the present embodiment has a diameter of 1.4 mm or more.

  First, the chemical composition of the steel wire according to the present embodiment will be described. Hereinafter, the unit of the content of each element is mass% unless otherwise noted.

(C: 0.40 to 1.10%)
C increases the pearlite fraction in steel and has the effect of reducing the lamellar spacing in the pearlite structure. As the lamellar spacing is reduced, the strength is improved. If the C content is less than 0.40%, it becomes difficult to secure 80% by area or more of pearlite structure. In this case, sufficient strength of the steel wire can not be secured. Therefore, the C content is 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 conductivity of the steel wire is lowered, and the ductility is lowered by increasing the amount of proeutectoid cementite. Therefore, the C content is made 1.10% or less. 1.05% or less is preferable, as for C content, 1.00% or less is more preferable, and 0.95% or less is still more preferable.

(Si: 0.005 to 0.350%)
Si is an effective component for enhancing the strength of the steel by solid solution strengthening, and is also a component necessary as a deoxidizer. If the Si content is less than 0.005%, these effects can not be sufficiently obtained, so the Si content is made 0.005% or more. In order to further improve the hardenability and to facilitate the heat treatment, the Si content is preferably 0.010% or more, more preferably 0.020% or more. On the other hand, Si is an element which increases electrical resistivity when distributed in ferrite in the pearlite structure. If the Si content exceeds 0.350%, the electrical resistivity significantly increases, so the Si content is made 0.350% or less. In order to obtain lower electrical resistivity (that is, high conductivity), the Si content is preferably 0.250% or less, more preferably 0.150% or less.
In addition, when forming zinc plating or zinc alloy plating on a steel wire, if the Si content is small, the growth of the alloy layer during plating is promoted, and the fatigue characteristics of the steel wire are degraded. Therefore, on the premise that the steel wire is subjected to zinc plating or zinc alloy plating and used, it is preferable to set the Si content to 0.050% or more.

(Mn: 0.05 to 0.90%)
Mn is a deoxidizing element and is an element having the function of fixing S in steel as MnS to prevent hot shortness. Further, Mn is an element which improves the hardenability, reduces the ferrite structure fraction at the time of patenting, and contributes to the improvement of the strength. However, if the Mn content is less than 0.05%, the above effect can not be sufficiently obtained. Therefore, the Mn content is set to 0.05% or more. On the other hand, when the Mn content is excessive, the conductivity of the steel is reduced. Therefore, the Mn content is made 0.90% or less. In order to further enhance the conductivity, the Mn content is preferably 0.75% or less, more preferably 0.60% or less.

  The steel wire according to the present embodiment is based on including the above-mentioned elements, with the balance being Fe and impurities. In the steel wire according to the present embodiment, it is preferable to limit the contents of N, P and S among the impurities as follows. The content of impurities is preferably as low as possible, so it may be 0%. The impurities are elements which are inevitably mixed from raw materials or the like or from the manufacturing process of steel.

(N: 0.0100% or less)
N is an element that reduces ductility and also reduces conductivity by strain aging during cold working. In particular, when the N content exceeds 0.0100%, the ductility and the conductivity decrease significantly, so it is preferable to limit the N content to 0.0100% or less. The N content is more preferably 0.0080% or less, still more preferably 0.0050% or less.

(P: 0.030% or less)
P is an element that contributes to the solid solution strengthening of ferrite but significantly reduces the ductility. In particular, when the P content exceeds 0.030%, the wire drawability declines significantly when drawing from a wire rod to a steel wire. Therefore, it is preferable to limit the P content to 0.030% or less. The P content is more preferably 0.020% or less, still more preferably 0.012% or less.

(S: 0.030% or less)
S is an element that causes red shortness and lowers ductility. When the S content exceeds 0.030%, the decrease in ductility becomes remarkable. Therefore, it is preferable to limit the S content to 0.030% or less. The S content is more preferably 0.020% or less, still more preferably 0.010% or less.

  As described above, the steel wire according to the present embodiment is based on the fact that the above element is contained and the balance is made of Fe and impurities. However, in place of the above elements, one or more elements selected from the group consisting of Cr, Al, Ti, V, Nb, Mo, and B, in place of the above elements, in the range described later You may make it contain. However, the lower limit is 0% because these elements do not necessarily have to be contained. In addition, even if the content of these optional elements is less than the range described later, it is acceptable because the properties of the steel wire are not impaired.

(Cr: 0.01 to 0.70%)
Cr is an element that improves the hardenability of the steel, and is an element that reduces the lamellar spacing of lamellar cementite in the pearlite structure to enhance the tensile strength. In order to obtain this effect, the Cr content is preferably 0.01% or more. More preferably, it is 0.02% or more. On the other hand, when the Cr content exceeds 0.70%, the conductivity is lowered depending on the patenting conditions. Therefore, even when Cr is contained, it is preferable to set the upper limit of the Cr content to 0.70%.

(Al: 0.001 to 0.070%)
Al is a deoxidizing element and is an element that fixes nitrogen as a nitride and contributes to the refinement of the austenite grain size. If the Al content is less than 0.001%, it is difficult to obtain the above-mentioned effect. Therefore, in order to obtain the effect, it is preferable to set the Al content to 0.001% or more. On the other hand, Al is an element which lowers the conductivity when it is not fixed as a nitride in ferrite but exists as free Al. Therefore, even when it is contained, it is preferable to set the upper limit of the Al content to 0.070%. A more preferred upper limit is 0.050%.

(Ti: 0.002 to 0.050%)
Ti is a deoxidizing element and is an element which forms carbonitrides and contributes to the refinement of the austenite grain size. In order to obtain this effect, it is preferable to make the Ti content 0.002% or more. On the other hand, when the Ti content exceeds 0.050%, coarse nitrides may be formed in the steel making stage, and carbides are precipitated during the patenting treatment, and the ductility is lowered. Therefore, even when it is contained, it is preferable to set the upper limit of the Ti content to 0.050%. The more preferred Ti content is less than 0.030%.

(V: 0.002 to 0.10%)
V is an element that improves the hardenability of the steel and is an element that precipitates as a carbonitride and contributes to the improvement of the strength of the steel. In order to acquire this effect, it is preferable to make V content into 0.002% or more. On the other hand, when the V content is excessive, the time until completion of transformation at the time of patenting becomes long, and the ductility is lowered due to the precipitation of coarse carbonitrides. Therefore, even when it is contained, it is preferable to set the upper limit of the V content to 0.10%. A more preferred upper limit is 0.08%.

(Nb: 0.002 to 0.050%)
Nb is an element that improves the hardenability of the steel, and is an element that precipitates as a carbide and contributes to the refinement of the austenite grain size. In order to obtain this effect, the Nb content is preferably made 0.002% or more. On the other hand, when the Nb content exceeds 0.050%, the time to completion of transformation at the time of patenting becomes long. Therefore, even when it is contained, it is preferable to make the Nb content 0.050% or less. More preferably, it is 0.020% or less.

(Mo: 0.02 to 0.20%)
Mo is an element that improves the hardenability of steel and reduces the area ratio of ferrite in the structure. In order to obtain this effect, the Mo content is preferably 0.02% or more. However, when the Mo content is excessive, the time to completion of transformation at the time of patenting becomes long. Therefore, even when it is contained, it is preferable to make the Mo content 0.20% or less. More preferably, it is 0.10% or less.

(B: 0.0003 to 0.0030%)
B is an element that improves the hardenability of steel and is an element that suppresses the formation of ferrite to increase the pearlite area ratio. In order to obtain this effect, the B content is preferably made 0.0003% or more. On the other hand, when the B content exceeds 0.0030%, M ₂₃ (C, B) ₆ precipitates on the austenite grain boundary in the supercooled austenite state in the patenting step, and the ductility decreases. Therefore, even when it is contained, it is preferable to make B content into 0.0030% or less. More preferably, it is 0.0020% or less.

Next, the metallographic structure of the steel wire according to the present embodiment will be described.
The steel wire according to the present embodiment aims to have a tensile strength of 1500 MPa or more, preferably 1600 MPa or more, more preferably 2000 MPa or more, in consideration of application to a steel core of ACSR constituting a power transmission line. . In order to realize such tensile strength and to improve conductivity, the steel wire according to the present embodiment needs to have the metal structure described below. Unless otherwise specified, the cross-section is a so-called L-section parallel to the longitudinal direction of the steel wire and passing through the longitudinal central axis of the steel wire.

<Contains 80% or more of perlite structure with lamellar cementite>
The steel wire according to the present embodiment includes 80 area% or more of pearlite structure having lamellar cementite in the metallographic structure in the cross section. When the pearlite structure is less than 80% by area, sufficient tensile strength can not be obtained. 95 area% or more is preferable, 97 area% or more is more preferable, and 100% may be sufficient as the pearlite structure which has lamellar cementite. In this embodiment, the pearlite structure having lamellar cementite is a structure derived from pearlite or pseudo-pearlite present in the wire before wire drawing, and the cementite phase (lamella cementite) and the ferrite phase are alternately formed in layers. It is an organization that repeatedly overlaps. In other words, the pearlite structure having lamellar cementite in the present embodiment is a structure including cementite which exists linearly, in a curvilinear shape or in pieces, and a ferrite phase which exists between cementite.
The steel wire according to the present embodiment may include a ferrite structure in addition to the pearlite structure. However, if the ferrite structure exceeds 20 area%, the area ratio of the pearlite structure decreases and the tensile strength decreases, so the ferrite structure needs to be limited to 20 area% or less. The ferrite structure referred to here is not the ferrite phase contained in the pearlite structure.
The steel wire according to the present embodiment may include a small amount of bainite structure or martensitic structure in addition to the above-described pearlite structure and ferrite structure. However, bainite or martensite, which is a non-diffusion transformation type structure, is a structure in which the diffusion of the solid solution element is inhibited, so the conductivity of the steel wire is reduced when the structure fraction of these structures is increased. Therefore, it is preferable that the bainite structure and the martensitic structure be less than 3 area% in total.
The structure fraction in the steel wire is obtained by taking a photograph of a metallographic structure at a magnification of 2000 times with respect to the observation position of the average lamellar spacing of the cut surface of the steel wire described later, marking the region of each structure, and image analysis It is obtained by calculating the average value of the area ratio of each tissue.

<Average Lamellar Spacing: 28 to 80 nm>
The average lamellar spacing, which is the spacing between adjacent lamellar cementites in the pearlite texture, is in the range of 28-80 nm. When the average lamellar spacing is less than 28 nm, the conductivity of the steel wire decreases. On the other hand, if the average lamellar spacing is more than 80 nm, the conductivity and the tensile strength can not be sufficiently improved.

  The average lamellar spacing is measured by the following method. That is, the L cross section of the steel wire is embedded in a resin, polished to a mirror surface, then corroded with picral, and an optional region of 5000 to 10000 times containing five or more pearlite blocks using FE-SEM is 10 Take a digital image for the field of view. For each picture taken, the image analyzer measures the average lamellar spacing. The lamellar spacing is the distance from the center of lamellar cementite to the center of the nearest lamellar cementite.

<Average length of lamellar cementite is 22.0 μm or less>
The average length of lamellar cementite in pearlite is less than 22.0 μm. When the average length of lamellar cementite exceeds 22.0 μm, the conductivity of the steel wire decreases. From the viewpoint of improving the conductivity, the average length of lamellar cementite is preferably 12.0 μm or less, more preferably 10.0 μm or less. On the other hand, from the viewpoint of tensile strength, the average length of lamellar cementite is preferably 1.0 μm or more, more preferably 2.0 μm or more, and still more preferably 5.0 μm or more.

  The average length of lamellar cementite in pearlite tissue is measured by the following method. That is, mirror-polished and then etched with picral to the cut surface (L section) in the longitudinal direction (wire drawing direction) of the steel wire, and the structure is observed by FE-SEM, and the result of the structure observation is shown Analyze and find. Specifically, as shown in FIG. 1, in the cross section of the steel wire, a region (D is the diameter of the steel wire) is set from the axial center position (D / 2) of the steel wire to the D / 4 position. The set area is a rectangular area in which each side has a length of D / 2. This rectangular area is further divided into nine equal meshes, and the apexes (16 locations) of each divided mesh are used as observation positions. At each observation position, the imaging region is set so that the drawing direction is horizontal to the image at a magnification of 10000 and the surface of the cross section is imaged by FE-SEM. The image of the imaging region is subjected to image analysis to binarize the cementite portion and the other portion (ferrite portion), and the length of cementite on the long side is determined. And the obtained cementite length is averaged and the average length of cementite is calculated.

<Perlite structure of pearlite structure having lamellar cementite having inclination with respect to the longitudinal direction of the steel wire within 15 ° among the pearlite structure is 40 area% or more>
Among pearlite structures, pearlite structures having lamellar cementite having an inclination (angular difference) with respect to the longitudinal direction of the steel wire within 15 ° are 40% or more in area ratio. When the area ratio of the pearlite structure having lamellar cementite having the inclination of 15 ° or less is less than 40 area%, the conductivity is lowered. From the viewpoint of conductivity, the area ratio of pearlite structure having lamellar cementite having an inclination of 15 ° or less with respect to the longitudinal direction of the steel wire (hereinafter, may simply be referred to as “lamellar cementite having an inclination of 15 ° or less”) is 55 It is preferable that it is area% or more, and it is more preferable that it is 60 area% or more.
The higher the proportion of lamellar cementite with an inclination of 15 ° or less with respect to the longitudinal direction of the steel wire, the more preferable from the viewpoint of conductivity, so the upper limit of the area ratio of pearlite structure having lamellar cementite with an inclination of 15 ° or less is 100 area% .

The area ratio of pearlite structure having lamellar cementite having an inclination of 15 ° or less with respect to the longitudinal direction of the steel wire is measured by the following method. That is, using each image taken in measurement of the average length of lamella cementite, both ends of one lamella cementite are line segments in an area (perlite colony) of drawn pearlite structure having the same orientation of lamella cementite in the center of the image. Measure the angle difference from the horizontal direction and check if it is within the range of 15 ° or less. If it is within 15 °, the region is judged to be a pearlite structure having lamellar cementite having an inclination of 15 ° or less with respect to the longitudinal direction of the steel wire. If the orientation of lamellar cementite is irregular or unclear in the drawn pearlite structure, it is judged to be lamellar cementite whose inclination is not within 15 °, and the region is It is not included in "perlite organization".
Longitudinal length of steel wire when total area of perlite structure whose inclination of lamellar cementite with respect to the longitudinal direction of the steel wire is within 15 ° is 40 area% or more with respect to the total area of pearlite structure in the total field of view It is judged that a pearlite structure having lamellar cementite having an inclination of 15 degrees or less with respect to the direction is present at an area ratio of 40% or more. FIG. 2A is an example of an image showing a pearlite structure in a range of inclination of 15 ° or less in a region of drawn pearlite structure in which the orientation of lamellar cementite in the central portion is equal, and FIG. 2B is a pearlite whose inclination is not 15 ° or less It is an example of the picture which shows organization.

<The degree of integration of {110} plane of ferrite with respect to the longitudinal direction is in the range of 2.0 to 8.0>
The degree of integration of the {110} plane of ferrite with respect to the longitudinal direction of the steel wire is in the range of 2.0 to 8.0. When the degree of integration of the {110} plane of ferrite is less than 2.0 or more than 8.0, the conductivity of the steel wire is unfavorably reduced. From the viewpoint of conductivity and tensile strength, the degree of integration of the {110} plane of ferrite is preferably 2.2 to 5.5, and more preferably 3.0 to 4.5.

The degree of integration of ferrite is measured by the following method. That is, in the region from the central portion to D / 4 (D is the diameter of the steel wire) in the radial direction of the cut surface in the longitudinal direction (drawing direction) of the steel wire shown in FIG. 3B, {110} by X-ray diffraction method A pole figure is created, and the maximum value of the pole density (ratio to the random orientation) of the spots observed in the RD direction (longitudinal direction of the steel wire) is taken as the degree of integration of the {110} plane of ferrite.
Here, the degree of integration of the {110} plane of ferrite obtained by X-ray diffraction is the degree of integration calculated from information obtained from both the ferrite phase contained in the pearlite structure and ferrite structures other than the pearlite structure. It is.
In addition, the measurement conditions of X-ray diffraction in this embodiment are as follows.
X-ray diffractometer: manufactured by RIGAKU, trade name: RINT 2200 (tube) (RINT 2000 / PC series)
X-ray source: MoKα
Divergence slit: 1/4 ° (0.43 mm)

<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. If the wire diameter is 1.4 mm or more, wire drawing from the wire and production of a coated steel wire in which a metal coating layer of aluminum, zinc or the like is formed around the steel wire are easy. Therefore, the steel wire according to the present embodiment is excellent in terms of ease of processing and manufacturing cost as well as conductivity and 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.
However, if the diameter of the steel wire is too large, it becomes difficult to shorten the length of the lamellar cementite, so the diameter of the steel wire according to this embodiment is preferably 4.2 mm or less, and 4.0 mm or less It is more preferable that

<Electric resistivity and tensile strength>
The steel wire according to the present embodiment is excellent in both conductivity and tensile strength.
In the steel wire according to the present embodiment, the electrical resistivity which is an indicator of conductivity is preferably less than 19.0 μΩ · cm, more preferably less than 18.0 μΩ · cm, still more preferably less than 17.0 μΩ · cm It is.
The tensile strength of the steel wire according to the present embodiment is preferably 1500 MPa or more, more preferably 1600 MPa or more, and still more preferably 2000 MPa or more.
As seen in a part of the examples described later, the electrical resistivity is less than 18.0 μΩ · cm, the tensile strength is 2000 MPa or more, and the electrical resistivity is less than 17.0 μΩ · cm, and the tensile strength A steel wire having a pressure of 2000 MPa or more is also feasible.

The coated steel wire according to the present embodiment includes the steel wire according to the present embodiment described above and a metal coating layer that covers the steel wire. That is, the coated steel wire according to the present embodiment is a metal coated steel wire.
The metal coating layer contains, for example, any one or more 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 plating layer or a cladding layer. The plating layer may be an electroplating layer or a hot-dip plating layer. In the metal coating layer formed by hot-dip plating, an alloy layer may be formed at the interface between the steel wire and the metal coating layer. Examples of the alloy layer include a ZnFe alloy layer, an AlFe alloy layer, a NiFe alloy layer, and a CuFe alloy layer. By having the metal coating layer, the conductivity of the entire coated steel wire can be enhanced.

  Next, the steel wire which concerns on this embodiment, and the preferable manufacturing method of the coated steel wire which concerns on this embodiment are demonstrated. The manufacturing method described below is an example, and if a steel wire or a coated steel wire satisfying the scope of the present invention is obtained, the steel wire according to the present embodiment and the method for manufacturing a coated steel wire according to the present embodiment Is not limited to the following manufacturing conditions.

<Fusing process, casting process, hot rolling process>
After the steel having the components described above is melted, a billet is manufactured by continuous casting or the like, and hot rolling is performed. After casting, mass rolling may be performed. When hot-rolling a steel piece, it is preferable to heat so that the center part of a steel piece may be 1000-1100 degreeC, and to hot-roll at a finishing temperature of 900-1000 degreeC to obtain a wire rod.

<Cooling process>
The wire rod after the hot rolling step is cooled by water cooling, air cooling, furnace cooling, and / or immersion in a melting bath. Under the present circumstances, it is preferable to set a cooling pattern according to C content.
When the C content is 0.40 to 0.70%, after finish rolling, it is cooled to a temperature range of 800 to 920 ° C. (first cooling) at an average cooling rate of 20 ° C./s or more, and then 800 to 600 It is cooled so that the average cooling rate to 5 ° C. is 5 to 20 ° C./s (second cooling), and then it is cooled so that the average cooling rate to 600 to 500 ° C. is 5 ° C./s or less (the third cooling).
If the cooling rate of the first cooling is less than 20 ° C./s, pro-eutectoid ferrite is likely to be generated, and the pearlite structure fraction is reduced. In addition, when the first cooling stop temperature is less than 800 ° C., the austenite grain size is refined and sufficient hardenability can not be obtained. On the other hand, when the stop temperature of the first cooling is over 920 ° C., pro-eutectoid ferrite is easily generated in the subsequent cooling process, and the pearlite structure fraction is lowered.
Further, if the cooling rate of the second cooling is less than 5 ° C./s, the formation of proeutectoid ferrite tends to lower the pearlite structure fraction. On the other hand, if the cooling rate of the second cooling exceeds 20 ° C./s, the pearlite transformation and the distribution of the alloying elements during the second to third cooling become insufficient. In addition, when the cooling rate of the third cooling exceeds 5 ° C./s, distribution of alloying elements is less likely to occur, and the conductivity is lowered.
However, if the residence time at 600 to 500 ° C is as long as 33 seconds or more (about 3.0 ° C / s or less in terms of average cooling rate) in the above cooling, distribution of alloying elements proceeds sufficiently, so 800 to 600 The average cooling rate up to ° C. may be 20 ° C./s or more. Also, after transformation is completed using, for example, a lead bath, a salt bath, or a fluidized bed furnace, heating may be performed again to a temperature range of 600 to 400 ° C.
When the C content is more than 0.70 to 1.10%, after finish rolling, it is cooled to 800 to 920 ° C. at an average cooling rate of 20 ° C./s or more and 30 to 500 to 600 ° C. molten salt Perlite transformation by immersion for more than a second.

  In the present embodiment, the finishing temperature of rolling refers to the surface temperature of the wire rod immediately after finish rolling, and the average cooling rate in the cooling step after finish rolling refers to the cooling rate of the central portion of the wire rod.

  In the wire obtained through the above-mentioned manufacturing process, for example, 80% or more of the metallographic structure in the cross section is a pearlite structure, the average lamellar spacing of the pearlite structure is 50 to 170 nm, and the average length of lamella cementite in the pearlite structure Becomes 1.5 μm or less. In addition, it is preferable that the wire diameter of the wire manufactured by said manufacturing process is 3.0-14.0 mm from a viewpoint of obtaining the steel wire which concerns on this embodiment by the following wire-drawing processes.

Wire drawing process
Next, the wire rod is subjected to wire drawing to obtain a steel wire. In wire drawing, it is preferable to perform wire drawing so as to give a true strain of 1.5 to 2.4 to the wire. Preferably, the true strain is 1.7 to 2.1. When wire drawing is performed under the above conditions, the electrical resistivity of the steel wire after wire drawing is reduced by about 1.0 to 1.5 μΩ · cm (that is, the conductivity is improved) with respect to the wire before wire drawing ). In addition, depending on the steel type (for example, steel type K used in the examples described later), even if the true strain is less than 1.5 or more than 2.4, a steel wire having a low electric resistivity and a high tensile strength. Is obtained. However, even with such a steel type, by applying a true strain of 1.5 to 2.4, it is easy to obtain a steel wire having a high tensile strength and a lower electrical resistivity.
As the reduction in area during wire drawing increases and strain increases, the average lamellar spacing decreases, the average length of lamellar cementite increases, and the inclination of the lamellar cementite relative to the longitudinal direction decreases and the angle difference The proportion of pearlite structure having cementite within 15 ° increases, and the degree of accumulation of {110} planes of ferrite increases. When wire drawing is performed under the condition that the true strain is less than 1.5, the proportion of cementite having an angle difference of 15 ° or less runs short and the conductivity decreases. On the other hand, when wire drawing is performed under the condition that the true strain exceeds 2.4, the amount of solid solution C in the ferrite increases and the conductivity is lowered.

  According to the manufacturing method including the above-described steps, the steel wire according to the present embodiment is manufactured.

<Coating process>
Next, a metal coating layer is formed on the obtained steel wire. The means for forming the metal coating layer may be any of electroplating, hot-dip plating and cladding. The thickness of the metal coating layer at this point is preferably about 0.7% to 20% of the diameter of the wire or steel wire.
Thereby, the coated steel wire which concerns on this embodiment is manufactured.
This coating step may be performed between the cooling step and the wire drawing step. That is, the coated steel wire according to the present embodiment can be obtained even if wire drawing is performed after forming the metal coating layer on the wire.

  Next, examples of the present invention will be described. The conditions in the examples are one condition example adopted to confirm the practicability and effects of the present invention, and the present invention is not limited to the one condition example. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the scope of the present invention.

  Molten steel melted to chemical components shown in Table 1 (with the balance being Fe and impurities) in a 50 kg vacuum melting furnace was cast into an ingot. The respective ingots were heated at 1250 ° C. for 1 hour, hot forged so as to be a rod wire having a diameter of 15 mm so that the finishing temperature would be 950 ° C. or more, and allowed to cool to room temperature. The hot forged material was cut to a diameter of 10 mm and cut to a length of 1500 mm. The cut material was heated at 1050 ° C. for 15 minutes in a nitrogen atmosphere, and then hot rolled so that the finishing temperature was 900 ° C. or higher, to obtain a rolled material with a diameter of 7 mm.

Thereafter, for some rolled materials, after finish rolling, air-cooling to 900 ° C. with an electric fan in the atmosphere after atmosphere rolling, and then enclosing in a heating furnace heated at low temperature within 10 seconds, average cooling rate to 600 ° C. The average cooling rate to 6 ° C./s and 400 ° C. was furnace cooled at 1 ° C./s, and further cooled to 400 ° C., taken out and allowed to cool to room temperature to obtain steel wire (conditions of cooling step in Table 2) Number 5).
Moreover, about another rolled material, after finish rolling, it air-cools to 850 ° C or 900 ° C with an electric fan in the atmosphere in air, and then immerses in a lead bath under condition numbers 2 to 4 of the cooling process shown in Table 2 within 10 seconds. Then, it was taken out and allowed to cool to room temperature to obtain a steel wire rod. The average cooling rates in each temperature range are as shown in Table 2.
Further, another rolled material was hot-rolled to a diameter of 7 mm and cooled to room temperature by air-cooling with a fan in the atmosphere (Condition No. 6 of the cooling step in Table 2). The average cooling rates in each temperature range are as shown in Table 2.
Further, some of the rolled materials were finish-rolled and dipped in a lead bath at 640 ° C., and then immediately cooled at 100 ° C./s to 400 ° C. or less (condition number 1 in the cooling step of Table 2). The average cooling rates in each temperature range are as shown in Table 2.

  The metal coating layer was formed with the hot dip galvanizing method or the aluminum clad method with respect to the test numbers 1-31 among the obtained wire.

  Thereafter, the steel portion included in the wire was drawn to give a true strain shown in Table 3 to obtain a steel wire or a coated steel wire having a diameter of 2.0 mm to 3.5 mm of the steel portion.

  Then, the metal coating layer which consists of zinc was formed with the hot dip galvanization method with respect to the steel wire of the test number 32 which did not form the coating layer before wire-drawing.

The metal coating layer was removed from the coated steel wire obtained as described above with hydrochloric acid, sodium hydroxide or the like, the steel wire was taken out, and the tensile strength and conductivity of the steel wire were evaluated.
<Tensile strength>
Three tensile test pieces of 350 mm in length were taken from the steel wire as the wire. This tensile test piece is subjected to a tensile test at normal temperature at a tensile speed of 10 mm / min with a distance between chucks of 200 mm and 200 mm to measure the tensile strength (TS), and the average value is taken as the tensile strength of the test material did.

<Conductive property>
A test piece for conductivity measurement having a length of 60 mm was cut out of the steel wire, and the electrical resistivity was measured by a four-terminal method at a temperature of 20 ° C.

In addition, the obtained steel wire, pearlite having lamellar cementite having each structure fraction, average lamellar spacing of lamellar cementite, average length of lamellar cementite, and inclination (angular difference) to the longitudinal direction of the steel wire within 15 °. The area ratio of the structure and the degree of integration of the {110} plane of the ferrite were measured.
<Average Lamellar Interval>
For each steel wire, the L cross section is embedded in the resin, polished to a mirror surface, corroded with picral, and an optional region including five or more perlite blocks at 5000 to 10000 times using FE-SEM. I took a digital image for the field of view. For each picture, the average lamellar spacing was measured using an image analyzer.
<Area rate of each organization>
Photograph metallographic photograph with magnification of 2000 times with respect to observation point of average lamellar spacing of cut surface of each steel wire, mark area of each tissue and calculate average value of area ratio of each tissue by image analysis did. In addition, although the area ratio of a pearlite structure and a ferrite structure is shown in Table 3, in the steel wire in which the sum total of these structures is not 100%, a bainite structure and / or a martensitic structure were observed as another structure.

<Average length of lamellar cementite>
The average length of the lamellar cementite in the pearlite tissue was determined by analyzing the tissue observation result by performing the tissue observation with FE-SEM, using the sample provided for the measurement of the average lamellar spacing. As shown in FIG. 1, in the L section of the steel wire, a region (D is the diameter of the steel wire) from the axial center position (D / 2) of the steel wire to the D / 4 position was set. The set area was a rectangular area having a length of D / 2 on each side. The rectangular area is further divided into nine equal meshes, and the apex of each divided mesh is used as the observation position. At each observation position, the imaging region was set so that the drawing direction is horizontal to the image at a magnification of 10000 times, and the surface of the cross section was imaged by FE-SEM. The image of the photographed area was image-analyzed and the cementite portion and the other portion (ferrite portion) were binarized to obtain the length of cementite on the long side. And the average length of cementite was computed by averaging the obtained cementite length.

<Area ratio of pearlite structure having lamellar cementite having an inclination of 15 ° or less with respect to the longitudinal direction of the steel wire>
Next, using each image taken in the measurement of the average length of lamellar cementite, in a region of drawn pearlite structure in which the orientation of lamellar cementite in the center of the image is equal, both ends of one lamellar cementite are connected by line segments The angle difference from the horizontal direction was measured, and it was confirmed whether it was within the range of 15 ° or less. The inclination to the longitudinal direction of the steel wire is 15 when the total of the pearlite structure whose inclination of the lamellar cementite with respect to the longitudinal direction of the steel wire is within 15 ° is 40 area% or more with respect to the total area of the pearlite structure in the total number of photographs. It was determined that a pearlite structure having lamellar cementite, which is within °°, was present at 40% or more in area ratio.

<Intensity of {110} face of ferrite>
Next, the degree of integration of the {110} plane of ferrite is, as shown in FIGS. 3A to 3B, with respect to the cut surface in the wire drawing direction (RD direction) of the steel wire, the central portion in the radial direction to D / 4 (D Create a {110} pole figure by X-ray diffraction in the region up to the diameter of the steel wire, and maximize the pole density (ratio to the random orientation) of the spots observed in the RD direction The degree of accumulation of the surface is used. The measurement conditions for X-ray diffraction are as described above.

  The results are shown in Tables 1 to 3.

  From Table 3, in the case of Test Nos. 19 to 22 and 28 to 30 out of the conditions defined in the present invention, target values (tensile strength: 1500 MPa or more, electrical resistivity: 19) of at least one property described above Less than 0 μΩ · cm, diameter: 1.4 mm or more). On the other hand, in Test Nos. 3 to 18, 23, 26, 27, 31, and 32 satisfying all the conditions defined in the present invention, all the above-mentioned characteristics reached the target values. In addition, although the steel type K is used in all of test numbers 11 to 14, 26, 27 and 32, particularly in test numbers 11 to 14 and 32 whose true strain at the time of wire drawing is 1.5 to 2.4. The electrical resistivity was kept low.

According to the present invention, it is possible to provide a coated steel wire having a wire diameter suitable for power transmission line applications and having excellent conductivity and tensile strength, and a coating layer covering the steel wire and the steel wire. .
Since the steel wire and the coated steel wire of the present invention have a large wire diameter and are excellent in conductivity and tensile strength, they can be suitably used for applications of power transmission lines.

Claims (4)

Steel wire,
The chemical composition is in 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%,
Contains
The balance consists of Fe and impurities,
The metallographic structure in the cross section contains 80% by area or more of pearlite structure having lamellar cementite,
The average lamellar spacing, which is the spacing between the lamellar cementite, is 28 to 80 nm,
The average length of the lamellar cementite is 22.0 μm or less,
Among the pearlite structures, the pearlite structure having the lamellar cementite having an inclination of 15 ° or less with respect to the longitudinal direction of the steel wire is 40 area% or more.
The degree of integration of the {110} plane of the ferrite with respect to the longitudinal direction obtained by the X-ray diffraction method is in the range of 2.0 to 8.0,
A steel wire characterized by having a diameter of 1.4 mm or more. The chemical composition is in mass%,
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%,
B: 0.0003 to 0.0030%
The steel wire according to claim 1, containing one or more selected from the group consisting of: A steel wire according to claim 1 or 2;
A metal coating layer coating the steel wire;
A coated steel wire comprising:   The coated steel wire according to claim 3, wherein the metal coating layer contains any one or more of zinc, zinc alloy, aluminum, aluminum alloy, copper, copper alloy, nickel, and nickel alloy.