WO2018069955A1

WO2018069955A1 - Steel wire and coated steel wire

Info

Publication number: WO2018069955A1
Application number: PCT/JP2016/080066
Authority: WO
Inventors: 敏之真鍋; 俊彦手島
Original assignee: 新日鐵住金株式会社
Priority date: 2016-10-11
Filing date: 2016-10-11
Publication date: 2018-04-19
Also published as: JP6575691B2; EP3527682A1; CN109906283A; BR112019006010A2; US20190316238A1; EP3527682A4; KR20190045309A; MX2019004147A; CA3039025A1; JPWO2018069955A1

Abstract

This steel wire has a chemical composition containing, in % by mass, 0.40%–1.10% C, 0.005%–0.350% Si, 0.05%–0.90% Mn, 0%–0.70% Cr, 0%–0.070% Al, 0%–0.050% Ti, 0%–0.10% V, 0%–0.050% Nb, 0%–0.20% Mo, and 0%–0.0030% B, with the remainder being Fe and impurities. A metal structure inside a cross-section includes at least 80 area% of a pearlite structure having lamellar cementite. The average lamellar spacing between lamellar cementite is 28–80 nm. The average length of the lamellar cementite is no more than 22.0 µm. At least 40 area% of the pearlite structure has lamellar cementite having an inclination of no more than 15° relative to the longitudinal direction of the steel wire. The degree of integration in the ferrite {110} plane relative to said longitudinal direction is 2.0–8.0 and the diameter is at least 1.4 mm.

Description

Steel wire and coated steel wire

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 that is 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, as a power transmission line for transmitting electric power, a steel core aluminum stranded wire (Aluminum Conductor Steel-Reinforced cable, hereinafter referred to as “ACSR”) in which an aluminum wire is twisted around a core portion (steel core) made of a steel wire has been used. Yes. The steel wire used for the core part of this ACSR has a strong role as an aluminum wire tension member. The steel wire that forms the core of the steel core aluminum wire is made of galvanized steel wire that has been galvanized on drawn pearlite steel or aluminum clad wire that has been 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 power transmission line is required to have strength and high power transmission efficiency. In response to such demands, with regard to improving the power transmission efficiency of the ACSR, it has been studied to reduce the electrical resistance of the steel wire itself that becomes the core part by reducing the weight of the core part and increasing the aluminum cross-sectional area accordingly. .
For example, Patent Document 1 discloses a method for reducing the specific gravity of a transmission line by using 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. Patent Document 2 discloses a method for limiting the contents of C, Si, and Mn in a steel wire to the minimum necessary for the purpose of reducing the electrical resistance of the steel wire itself.

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

In Non-Patent Document 1, a wire with a diameter of 5.5 mm having a high carbon content of 0.92% is once drawn to a diameter of 1.75 mm, and after further patenting, it is further reduced to a diameter of 0.26 mm. It has been reported that the electrical conductivity is improved by performing a cold drawing process with a peak at a condition where the true strain is about 1.5.

However, it is processed into such an extremely fine steel wire and further plated with zinc or the like around the ultrafine steel wire (core part), or the aluminum wire is further aligned around the ultrafine steel wire and sent. It is extremely difficult to manufacture an electric wire, and the cost is greatly increased.

Japanese Unexamined Patent Publication No. 2001-176333 Japanese Unexamined Patent Publication No. 2003-226938

The present invention was made paying attention to the above situation. It is an object of the present invention to provide a coated steel wire having a wire diameter suitable for use as a power transmission line and having excellent conductivity and tensile strength, and a steel wire and a coating layer covering the steel wire. And

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

(1) The steel wire according to one embodiment of the present invention is a steel wire, and the chemical composition is 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 -0.050%, Mo: 0-0.20%, B: 0-0.0030%, the balance is made of Fe and impurities, and the metal structure in the cross section is a pearlite structure having lamellar cementite. The lamellar cementite is contained in an area of 80% by area or more, an average lamellar interval between the lamellar cementites is 28 to 80 nm, an average length of the lamellar cementite is 22.0 μm or less, and the length of the steel wire in the pearlite structure The lamellar case whose inclination with respect to the direction is within 15 ° The pearlite structure having mentite is 40% by area or more, and the degree of integration of {110} faces of ferrite with respect to the longitudinal direction obtained by X-ray diffraction is in the range of 2.0 to 8.0. It has a diameter of 4 mm or more.
(2) The steel wire according to the above (1) has a chemical composition of 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) The coated steel wire which concerns on another aspect of this invention is equipped with the steel wire as described in said (1) or (2), and the metal coating layer which coat | covers the said steel wire.
(4) In the coated steel wire according to (3), the metal coating layer may include any one or more of zinc, zinc alloy, aluminum, aluminum alloy, copper, copper alloy, nickel, or nickel alloy. Good.

According to the above aspect of the present invention, a steel wire having a wire diameter suitable for use in power transmission lines and excellent in conductivity and tensile strength, and a coated steel having the steel wire and a coating layer covering 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 a power transmission line because the diameter of the steel wire as the core material is large and excellent in conductivity and tensile strength.

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 lamellar cementite in the pearlite structure | tissue which has lamellar cementite. It is a figure explaining the measuring method of the area rate of the pearlite structure | tissue which has the lamellar cementite whose inclination (angle difference) with respect to the longitudinal direction of a steel wire is 15 degrees or less, Comprising: The photograph which shows an example of the lamellar cementite whose inclination is 15 degrees or less It is. It is a figure explaining the measuring method of the area rate of the pearlite structure | tissue which has the lamellar cementite whose inclination (angle difference) with respect to the longitudinal direction of a steel wire is 15 degrees or less, Comprising: The photograph which shows an example of the lamellar cementite whose inclination is not less than 15 degrees It is. It is a figure which shows the 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 the 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 (a 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 a pearlite structure having lamellar cementite in the metal structure (hereinafter sometimes simply referred to as “pearlite structure”). Is included. In the steel wire according to the present embodiment, the average lamellar interval of lamellar cementite contained in the pearlite structure is 28 to 80 nm, the average length of lamellar cementite is 22.0 μm or less, The pearlite structure having lamellar cementite whose inclination with respect to the longitudinal direction of the line is within 15 ° is 40 area% or more, and the degree of integration of {110} planes of ferrite with respect to the longitudinal direction obtained by X-ray diffraction method is 2. The range is from 0 to 8.0. Furthermore, the steel wire which concerns on this embodiment has a diameter of 1.4 mm or more.

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

(C: 0.40 to 1.10%)
C has the effect of increasing the pearlite fraction in the steel and reducing the lamellar spacing in the pearlite structure. When the lamellar spacing is reduced, the strength is improved. If the C content is less than 0.40%, it is difficult to secure a pearlite structure of 80 area% or more. In this case, sufficient strength of the steel wire cannot be ensured. Therefore, the C content is set to 0.40% or more. The C content is preferably 0.60% or more. On the other hand, if 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 1.10% or less. The C content is preferably 1.05% or less, more preferably 1.00% or less, and even more preferably 0.95% or less.

(Si: 0.005-0.350%)
Si is an effective component for increasing the strength of steel by solid solution strengthening, and is also a necessary component as a deoxidizer. If the Si content is less than 0.005%, these effects cannot be obtained sufficiently, so the Si content is set to 0.005% or more. In order to further improve the hardenability and facilitate heat treatment, the Si content is preferably 0.010% or more, and more preferably 0.020% or more. On the other hand, Si is an element that increases electrical resistivity when distributed in ferrite in a pearlite structure. If the Si content exceeds 0.350%, the electrical resistivity increases remarkably, so the Si content is set to 0.350% or less. In order to obtain a lower electric resistivity (that is, higher conductivity), the Si content is preferably 0.250% or less, and more preferably 0.150% or less.
Moreover, 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 reduced. Accordingly, when it is assumed that the steel wire is used after being subjected to galvanization or zinc alloy plating, the Si content is preferably 0.050% or more.

(Mn: 0.05-0.90%)
Mn is a deoxidizing element and is an element having an action of fixing S in steel as MnS to prevent hot brittleness. Mn is an element that improves hardenability, reduces the ferrite structure fraction during patenting, and contributes to improvement in strength. However, if the Mn content is less than 0.05%, the above effect cannot be obtained sufficiently. 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 lowered. Therefore, the Mn content is set to 0.90% or less. In order to further increase 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 basically includes the above 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 impurities as follows. The impurity content is preferably as low as possible, and may be 0%. Impurities are elements that are inevitably mixed from raw materials and the like or from the manufacturing process of steel.

(N: 0.0100% or less)
N is an element that lowers the ductility and lowers the conductivity due to strain aging during cold working. In particular, when the N content exceeds 0.0100%, the ductility and conductivity are significantly lowered. Therefore, it is preferable to limit the N content to 0.0100% or less. The N content is more preferably 0.0080% or less, and still more preferably 0.0050% or less.

(P: 0.030% or less)
P contributes to the solid solution strengthening of ferrite, but is an element that greatly reduces the ductility. In particular, when the P content exceeds 0.030%, the wire drawing workability is markedly lowered when wire drawing is performed from a wire 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 hot brittleness and decreases ductility. When the S content exceeds 0.030%, the ductility is significantly lowered. 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 basically includes the above elements and the balance is made of Fe and impurities. However, instead of a part of Fe, in addition to the above elements, one or more elements selected from the group consisting of Cr, Al, Ti, V, Nb, Mo, and B are included in a range described later. You may make it contain. However, since these elements are not necessarily contained, the lower limit is 0%. Moreover, even if these arbitrary elements are contained in less than the range described later, they are allowed because they do not hinder the properties of the steel wire.

(Cr: 0.01-0.70%)
Cr is an element that improves the hardenability of steel and is an element that increases the tensile strength by reducing the lamellar spacing of lamellar cementite in the pearlite structure. When obtaining this effect, the Cr content is preferably 0.01% or more. More preferably, it is 0.02% or more. On the other hand, if the Cr content exceeds 0.70%, the conductivity is lowered depending on the patenting conditions. Therefore, even when Cr is contained, the upper limit of the Cr content is preferably 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 effect. Therefore, when obtaining the effect, the Al content is preferably set to 0.001% or more. On the other hand, Al is an element that lowers conductivity when it is present as free Al but not fixed as a nitride in ferrite. Therefore, even when contained, the upper limit of the Al content is preferably 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 that forms carbonitrides and contributes to refinement of the austenite grain size. When obtaining this effect, the Ti content is preferably 0.002% or more. On the other hand, if the Ti content exceeds 0.050%, coarse nitrides may be formed in the steelmaking stage, and carbides precipitate during the patenting process, resulting in a decrease in ductility. Therefore, even when contained, the upper limit of the Ti content is preferably 0.050%. A more preferable 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 an improvement in the strength of the steel. In order to obtain this effect, the V content is preferably 0.002% or more. On the other hand, when the V content is excessive, the time until the end of transformation at the time of patenting becomes longer, and the ductility decreases due to precipitation of coarse carbonitrides. Therefore, even when it is contained, the upper limit of the V content is preferably 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. When obtaining this effect, the Nb content is preferably 0.002% or more. On the other hand, if the Nb content exceeds 0.050%, the time until the end of transformation during patenting becomes longer. Therefore, even when it contains, it is preferable to make 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 the steel and reduces the area ratio of ferrite in the structure. When obtaining this effect, the Mo content is preferably 0.02% or more. However, if the Mo content is excessive, the time until the end of transformation during patenting becomes longer. Therefore, even when it contains, it is preferable to make Mo content into 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 the steel and is an element that suppresses the formation of ferrite and increases the pearlite area ratio. When obtaining this effect, the B content is preferably 0.0003% or more. On the other hand, if the B content exceeds 0.0030%, M ₂₃ (C, B) ₆ precipitates on the austenite grain boundaries in the supercooled austenite state in the patenting step, and the ductility decreases. Therefore, even when it contains, it is preferable that B content shall be 0.0030% or less. More preferably, it is 0.0020% or less.

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

<Including 80% by area or more of pearlite structure having lamellar cementite>
The steel wire according to the present embodiment includes 80% by area or more of a pearlite structure having lamellar cementite in the metal structure in the cross section. When the pearlite structure is less than 80% by area, sufficient tensile strength cannot be obtained. The pearlite structure having lamellar cementite is preferably 95 area% or more, more preferably 97 area% or more, and may be 100%. In the present embodiment, the pearlite structure having lamellar cementite is a structure derived from pearlite or pseudo pearlite present in the wire before drawing, and the cementite phase (lamellar cementite) and the ferrite phase are alternately arranged in layers. It is a repeated organization. In other words, the pearlite structure having lamellar cementite in the present embodiment is a structure including cementite existing linearly, curvilinearly or fragmentarily, and a ferrite phase existing between the cementites.
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 mentioned here is not a ferrite phase contained in the pearlite structure.
Moreover, the steel wire which concerns on this embodiment may contain a small amount of bainite structure and a martensitic structure other than said pearlite structure and a ferrite structure. However, bainite and martensite, which are non-diffusive transformation structures, are structures in which the diffusion of solid solution elements is inhibited. Therefore, when the structure fraction of these structures increases, the conductivity of the steel wire decreases. Therefore, the total of the bainite structure and the martensite structure is preferably less than 3 area%.
The structural fraction in the steel wire was measured by taking a metal structure photograph at a magnification of 2000 times, marking the region of each structure, and analyzing the image by analyzing the average lamellar spacing of the cut surface of the steel wire described later. It is obtained by calculating the average value of the area ratio of each tissue.

<Average lamellar spacing is 28 to 80 nm>
The average lamellar spacing, which is the spacing between adjacent lamellar cementites in the pearlite structure, is in the range of 28 to 80 nm. When the average lamellar spacing is less than 28 nm, the conductivity of the steel wire is lowered. On the other hand, if the average lamellar spacing exceeds 80 nm, the conductivity and tensile strength cannot be sufficiently increased.

The average lamellar interval is measured by the following method. In other words, after embedding the L cross-section of the steel wire in a resin and polishing the mirror surface, it is corroded with picral, and an FE-SEM is used to create an arbitrary region of 5000 to 10,000 times containing 5 or more pearlite blocks. Take digital images for the field of view. For each photograph taken, the average lamellar spacing is measured using an image analyzer. The lamellar interval is a distance from the center of the lamellar cementite to the center of the nearest lamellar cementite.

<The average length of lamellar cementite is 22.0 μm or less>
The average length of lamellar cementite in the pearlite structure is 22.0 μm or less. When the average length of lamellar cementite exceeds 22.0 μm, the conductivity of the steel wire is lowered. From the viewpoint of improving conductivity, the average length of lamellar cementite is preferably 12.0 μm or less, and 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 further preferably 5.0 μm or more.

The average length of lamellar cementite in the pearlite structure is measured by the following method. That is, the cut surface (L cross section) in the longitudinal direction (drawing direction) of the steel wire is mirror-polished and then etched with picral, and the structure is observed with FE-SEM. Determine by analysis. Specifically, as shown in FIG. 1, in the cross section of the steel wire, a region from the axial center position (D / 2) to the D / 4 position of the steel wire (D is the diameter of the steel wire) is set. The set area is a rectangular area in which the length of each side is D / 2. This rectangular area is further divided into nine equal meshes, and the vertexes (16 places) of each divided mesh are taken as observation positions. At each observation position, an imaging region is set at a magnification of 10,000 times so that the drawing direction is in the horizontal direction with the image, and the surface of the cross section is imaged with the FE-SEM. Image analysis of the image of the imaging region is performed to binarize the cementite portion and the other portion (ferrite portion), and the length of the long side cementite is obtained. Then, the average length of the cementite is calculated by averaging the obtained cementite lengths.

<Of the pearlite structure, the pearlite structure having lamellar cementite with an inclination with respect to the longitudinal direction of the steel wire within 15 ° is 40 area% or more>
Among the pearlite structures, the pearlite structure having lamellar cementite whose inclination (angle difference) with respect to the longitudinal direction of the steel wire is within 15 ° is 40% or more in terms of area ratio. When the area ratio of the pearlite structure having lamellar cementite having an inclination of 15 ° or less is less than 40% by area, the conductivity is lowered. From the viewpoint of conductivity, the area ratio of the pearlite structure having lamellar cementite having an inclination with respect to the longitudinal direction of the steel wire of 15 ° or less (hereinafter sometimes simply referred to as “lamellar cementite having an inclination of 15 ° or less”) is 55 It is preferably area% or more, and more preferably 60 area% or more.
The higher the ratio of lamellar cementite whose inclination with respect to the longitudinal direction of the steel wire is within 15 °, the better from the viewpoint of conductivity. Therefore, the upper limit of the area ratio of the pearlite structure having lamellar cementite whose inclination is within 15 ° is 100 area%. .

The area ratio of the pearlite structure having lamellar cementite whose inclination with respect to the longitudinal direction of the steel wire is within 15 ° is measured by the following method. That is, using each image taken in the measurement of the average length of lamellar cementite, both ends of one lamellar cementite are segmented in a stretched pearlite structure region (perlite colony) with the same orientation of lamellar cementite in the center of the image. And measure the angle difference from the horizontal direction to check if it is within 15 ° or less. If it is within 15 °, it is determined that the region is a pearlite structure having lamellar cementite whose inclination with respect to the longitudinal direction of the steel wire is within 15 °. When the orientation of lamellar cementite is irregular or unclear in the drawn pearlite structure, it is determined that the lamellar cementite is not within 15 °, and the region is “the inclination of lamellar cementite with respect to the longitudinal direction of the steel wire is within 15 °. Is not included in "Perlite organization".
When the total area of the pearlite structure in which the inclination of the lamellar cementite with respect to the longitudinal direction of the steel wire is within 15 ° with respect to the total area of the pearlite structure in the field of view of the total number of shots is 40% by area or more, It is judged that a pearlite structure having lamellar cementite whose inclination with respect to the direction is within 15 ° exists in an area ratio of 40% or more. FIG. 2A is an example of an image showing a pearlite structure having an inclination of 15 ° or less in a region of a drawn pearlite structure having the same orientation of lamellar cementite in the center, and FIG. 2B is a pearlite having an inclination of 15 ° or less. It is an example of the image which shows a structure | tissue.

<The degree of integration of the {110} face of the ferrite in the longitudinal direction is in the range of 2.0 to 8.0>
The degree of integration of the {110} face 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 lowered, which is not preferable. From the viewpoint of conductivity and tensile strength, the integration degree of the {110} face of the ferrite is preferably 2.2 to 5.5, and more preferably 3.0 to 4.5.

The degree of ferrite integration is measured by the following method. That is, in the region from the central part 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} A pole figure is created, and the maximum value of the pole density (ratio with the random orientation) of the spot observed in the RD direction (longitudinal direction of the steel wire) is defined as the degree of integration of the {110} plane of the ferrite.
Here, the {110} plane integration degree of ferrite obtained by X-ray diffraction is the integration degree calculated from information obtained from both the ferrite phase contained in the pearlite structure and the ferrite structure other than the pearlite structure. It is.
In addition, the measurement conditions of the X-ray diffraction in this embodiment are as follows.
X-ray diffractometer: Rigaku Corporation product name: RINT2200 (tube) (RINT2000 / PC series)
X-ray source: MoKα
Divergent slit: 1/4 ° (0.43mm)

<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, it is easy to draw a wire from a wire and to manufacture a coated steel wire in which a metal coating layer such as aluminum or zinc is formed around the steel wire. Therefore, the steel wire according to the present embodiment is excellent in terms of workability and manufacturing cost in addition to conductivity and tensile strength. The diameter of the steel wire according to this 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 thick, it is difficult to shorten the length of the lamellar cementite. Therefore, 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 this embodiment is excellent in both conductivity and tensile strength.
In the steel wire according to this embodiment, the electrical resistivity, which is an index of conductivity, is preferably less than 19.0 μΩ · cm, more preferably less than 18.0 μΩ · cm, and even more preferably less than 17.0 μΩ · cm. It is.
Further, 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 further preferably 2000 MPa or more.
As can be seen in some 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 thickness 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 includes, for example, any one or more of zinc, zinc alloy, aluminum, aluminum alloy, copper, copper alloy, nickel, or nickel alloy. The metal coating layer may be a plating layer or a clad layer. The plating layer may be an electroplating layer or a hot dipping layer. In the metal coating layer formed by hot dipping, 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 a metal coating layer, the conductivity of the entire coated steel wire can be increased.

Next, the preferable manufacturing method of the steel wire which concerns on this embodiment, and the covering steel wire which concerns on this embodiment is 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 can be obtained, the steel wire according to the present embodiment and the method for manufacturing the coated steel wire according to the present embodiment Is not limited to the following production conditions.

<Melting process, casting process, hot rolling process>
After melting the steel having the components described above, a billet is manufactured by continuous casting or the like, and hot rolling is performed. After the casting, you may perform partial rolling. When hot-rolling a steel slab, it is preferable to heat the steel slab so that the center of the steel slab is 1000 to 1100 ° C., and perform hot rolling at a finishing temperature of 900 to 1000 ° C. to obtain a wire.

<Cooling process>
The wire rod after the hot rolling step is cooled by water cooling, air cooling, furnace cooling, and / or immersion in a molten bath. At this time, it is preferable to set a cooling pattern according to the 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. at an average cooling rate of 20 ° C./s or more (first cooling), and then 800 to 600 Cooling is performed so that the average cooling rate to 5 ° C. is 5 to 20 ° C./s (second cooling), and then cooling is performed so that the average cooling rate from 600 to 500 ° C. is 5 ° C./s or less. cooling).
When the cooling rate of the first cooling is less than 20 ° C./s, pro-eutectoid ferrite is easily 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 becomes fine and sufficient hardenability cannot be obtained. On the other hand, when the stop temperature of the first cooling is higher than 920 ° C., proeutectoid ferrite is easily generated in the subsequent cooling process, and the pearlite structure fraction is lowered.
Further, when the cooling rate of the second cooling is less than 5 ° C./s, the pearlite structure fraction tends to decrease due to the formation of proeutectoid ferrite. On the other hand, if the cooling rate of the second cooling exceeds 20 ° C./s, the pearlite transformation and the distribution of the alloy elements during the second to third coolings are insufficient. Further, when the cooling rate of the third cooling exceeds 5 ° C./s, distribution of the alloy element is difficult to occur, so that the conductivity is lowered.
However, in the above cooling, if the residence time at 600 to 500 ° C. is as long as 33 seconds or more (approximately 3.0 ° C./s or less in terms of average cooling rate), the alloy element distribution proceeds sufficiently, so that the 800 to 600 ° C. The average cooling rate up to 20 ° C. may be 20 ° C./s or more. Further, for example, after the transformation is completed using a lead bath, a salt bath, or a fluidized bed furnace, it may be heated again to a temperature range of 600 to 400 ° C.
In addition, when the C content is more than 0.70 to 1.10%, after finish rolling, the steel 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 is performed by immersion for more than 2 seconds.

In this embodiment, the finishing temperature of rolling refers to the surface temperature of the wire immediately after finish rolling, and the average cooling rate in the cooling step after finish rolling refers to the cooling rate of the center of the wire.

The wire rod obtained through the above manufacturing process has, for example, a pearlite structure in which 80% or more of the metal structure in the cross section is 50 to 170 nm, and the average length of lamellar cementite in the pearlite structure. Becomes 1.5 μm or less. From the viewpoint of obtaining the steel wire according to the present embodiment by the following wire drawing process, the wire diameter of the wire manufactured in the above manufacturing process is preferably 3.0 to 14.0 mm.

<Wire drawing process>
Next, the wire rod is subjected to wire drawing to obtain a steel wire. In the wire drawing, the wire drawing is preferably performed so as to impart a true strain of 1.5 to 2.4 to the wire. Preferably, the true strain is 1.7 to 2.1. When the wire is drawn under the above conditions, the electrical resistivity of the steel wire after drawing is reduced by about 1.0 to 1.5 μΩ · cm with respect to the wire before drawing (that is, conductivity is improved). ). Depending on the steel type (for example, steel type K used in the examples described later), a steel wire having a low electrical resistivity and a high tensile strength even if the true strain is less than 1.5 or more than 2.4. Is obtained. However, even with such steel types, it is easy to obtain a steel wire having a high tensile strength and a lower electrical resistivity by imparting a true strain of 1.5 to 2.4.
As the area reduction ratio during wire drawing increases and the strain increases, the average lamellar spacing decreases, the average length of lamellar cementite increases, and the inclination of the lamellar cementite with respect to the longitudinal direction decreases, resulting in an angular difference. However, the proportion of pearlite structure having cementite within 15 ° increases, and the degree of integration of {110} faces of ferrite increases. When wire drawing is performed under conditions where the true strain is less than 1.5, the proportion of cementite having an angle difference of 15 ° or less is insufficient, resulting in a decrease in conductivity. On the other hand, when the wire drawing is performed under a condition where the true strain exceeds 2.4, the amount of solid solution C in the ferrite increases, and the conductivity decreases.

According to the manufacturing method including the steps described above, 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 metal coating layer may be formed by any of electroplating, hot dipping, and cladding. The thickness of the metal coating layer at this point is preferably about 0.7% to 20% with respect to the diameter of the wire or steel wire.
Thereby, the coated steel wire which concerns on this embodiment is manufactured.
This covering 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 by performing a wire drawing process after forming a 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 feasibility and effects of the present invention, and the present invention is not limited to this 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 gist of the present invention.

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

After that, for some rolled materials, after finish rolling, air-cooled to 900 ° C with an electric fan in the atmosphere, and then sealed in a heating furnace heated at a low temperature within 10 seconds, and the average cooling rate to 600 ° C was set. The furnace was cooled at an average cooling rate of 6 ° C./s to 400 ° C. at 1 ° C./s, further cooled to 400 ° C., taken out and allowed to cool to room temperature to obtain a steel wire (conditions for cooling step in Table 2). Number 5).
As for another rolled material, after finish rolling, it is cooled to 850 ° C. or 900 ° C. with an electric fan in the atmosphere, and then immersed in a lead bath under the 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. Table 2 shows the average cooling rate in each temperature range.
Further, another rolled material was hot-rolled to a diameter of 7 mm, and then cooled to room temperature by air cooling with an electric fan in the atmosphere (condition number 6 of the cooling step in Table 2). Table 2 shows the average cooling rate in each temperature range.
Further, some of the rolled materials were immersed in a 640 ° C. lead bath after finish rolling, and then immediately cooled to 100 ° C./s to 400 ° C. or lower (condition number 1 of the cooling step in Table 2). Table 2 shows the average cooling rate in each temperature range.

Among the obtained wires, a metal coating layer was formed on the test numbers 1 to 31 by a zinc hot dipping method or an aluminum clad method.

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

Thereafter, a metal coating layer made of zinc was formed by hot dip galvanizing on the steel wire of test number 32 in which the coating layer was not formed before wire drawing.

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

<Conductivity>
A test piece for measuring conductivity having a length of 60 mm was cut out from 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 has pearlite having lamellar cementite whose structural fraction, average lamellar cementite interval, average length of lamellar cementite, and inclination (angle difference) with respect to the longitudinal direction of the steel wire is within 15 °. The area ratio of the structure and the degree of integration of the {110} face of the ferrite were measured.
<Average lamellar spacing>
For each steel wire, after embedding the L cross-section in resin and polishing the mirror surface, the steel wire is corroded with picral, and an arbitrary region containing 5 or more pearlite blocks at 5000 to 10000 times is used with FE-SEM. Digital images were taken for the field of view. About each photograph, the average lamellar space | interval was measured using the image analyzer.
<Area ratio of each organization>
For each observation point of the average lamellar spacing on the cut surface of each steel wire, take a metal structure photograph at a magnification of 2000 times, mark the area of each structure, and calculate the average value of the area ratio of each structure by image analysis did. Table 3 shows the area ratios of the pearlite structure and the ferrite structure. In the steel wire in which the total of these structures is not 100%, a bainite structure and / or a martensite structure were observed as other structures.

<Average length of lamellar cementite>
The average length of lamellar cementite in the pearlite structure was determined by using a sample subjected to measurement of the average lamellar spacing, observing the structure with FE-SEM, and analyzing the result of the structure observation. As shown in FIG. 1, in the L cross section of the steel wire, a region from the axial center position (D / 2) to the D / 4 position (D is the diameter of the steel wire) of the steel wire was set. The set area is a rectangular area in which the length of each side is D / 2. This rectangular area was further divided into nine equal meshes, and the vertex of each divided mesh was taken as the observation position. At each observation position, an imaging region was set at a magnification of 10,000 times so that the drawing direction was in the horizontal direction with the image, and the surface of the cross section was imaged with FE-SEM. The image of the imaging region was image-analyzed to binarize the cementite portion and the other portion (ferrite portion), and the length of the long side cementite was determined. And the average length of cementite was computed by averaging the obtained cementite length.

<Area ratio of pearlite structure having lamellar cementite whose inclination with respect to the longitudinal direction of the steel wire is within 15 °>
Next, using each image taken in the measurement of the average length of lamellar cementite, in the region of drawn pearlite structure with the same orientation of lamellar cementite in the center of the image, connect both ends of one lamellar cementite with 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. When the total pearlite structure inclination of the lamellar cementite with respect to the longitudinal direction of the steel wire is within 15 ° relative to the total area of the pearlite structure in the total number of shots, the inclination with respect to the longitudinal direction of the steel wire is 15% or more. It was judged that a pearlite structure having lamellar cementite within an angle of 40 ° C. or more was present in area ratio.

<Degree of integration of {110} face of ferrite>
Next, as shown in FIGS. 3A to 3B, the degree of integration of the {110} plane of the ferrite is from the center to D / 4 (D / 4) in the radial direction with respect to the cut surface in the drawing direction (RD direction) of the steel wire. {110} pole figure is created by X-ray diffraction method in the region up to the diameter of the steel wire), and the maximum value of the pole density (ratio with random orientation) of the spot observed in the RD direction is set to {110 } The degree of surface integration. 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 numbers 19 to 22 and 28 to 30 that deviate from the conditions specified in the present invention, at least one characteristic described above is a target value (tensile strength: 1500 MPa or more, electrical resistivity: 19 Less than 0.0 μΩ · cm, diameter: 1.4 mm or more). On the other hand, in test numbers 3 to 18, 23, 26, 27, 31, and 32 that satisfy all the conditions defined in the present invention, all the above-mentioned characteristics reached the target values. In all of the test numbers 11 to 14, 26, 27, and 32, the steel type K is used, but in the test numbers 11 to 14, and 32, in which the true strain at the time of wire drawing is 1.5 to 2.4. The electrical resistivity was kept low.

ADVANTAGE OF THE INVENTION According to this invention, the coated steel wire which has a wire diameter suitable for a power transmission line use, and was excellent in electroconductivity and tensile strength, and this steel wire and the coating layer which coat | covers a steel wire can be provided. .
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 transmission lines.

Claims

A steel wire,
Chemical composition is mass%,
C: 0.40 to 1.10%,
Si: 0.005 to 0.350%,
Mn: 0.05-0.90%
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%,
Containing
The balance consists of Fe and impurities,
The metal structure in the cross section contains pearlite structure having lamellar cementite of 80 area% or more,
The average lamellar spacing that is the spacing between the lamellar cementites is 28 to 80 nm,
An average length of the lamellar cementite is 22.0 μm or less,
Of the pearlite structure, the pearlite structure having the lamellar cementite with an inclination with respect to the longitudinal direction of the steel wire being within 15 ° 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 having a diameter of 1.4 mm or more.
Chemical composition is 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, comprising one or more selected from the group consisting of:
A steel wire according to claim 1 or 2,
A metal coating layer covering the steel wire;
A coated steel wire comprising:
The coated steel wire according to claim 3, wherein the metal coating layer contains at least one of zinc, zinc alloy, aluminum, aluminum alloy, copper, copper alloy, nickel, and nickel alloy.