TWI635186B - Steel wire and coated steel wire - Google Patents

Abstract

The steel wire of the present invention has a chemical composition of, 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%, and Al: 0 to 0.070%. , Ti: 0~0.050%, V: 0~0.10%, Nb: 0~0.050%, Mo: 0~0.20%, B: 0~0.0030%, the rest is composed of Fe and impurities; the metal in the cross section The structure comprises 80% by area or more of a ferritic carbon-iron-bearing iron structure; the layered stellites are spaced apart from each other, that is, an average layered interval of 28 to 80 nm; and the average of the layered stellites a length of 22.0 μm or less; the wave-forming iron structure having a layered ferritic carbon iron having an inclination of 15° or less with respect to the longitudinal direction of the steel wire, and an iron structure of 40% by area or more; and the longitudinal direction The accumulation degree of the {110} plane of the ferrite iron is in the range of 2.0 to 8.0; the diameter is 1.4 mm or more.

Description

Steel wire and coated steel wire

The present invention relates to a steel wire and a coated steel wire. In particular, the present invention relates to a steel wire which is excellent in electrical conductivity and strength applied to a power transmission line, and a coated steel wire in which a coating layer is formed on the surface of the steel wire.

Conventionally, an electric power transmission line uses an Aluminum Conductor Steel-Reinforced Cable (hereinafter referred to as "ACSR") around a core (steel core) composed of a steel wire by an aluminum wire. The steel wire used in the core of the ACSR mainly functions as a tensile member of the aluminum wire. The steel wire that becomes the core of the steel core aluminum stranded wire is galvanized steel wire which is galvanized after the wire is pulled by the iron wire, or the aluminum wire is used as the surface layer to improve the corrosion resistance of the wire material. Aluminum-clad steel wire made of wire.

The ACSR used as a power transmission line is required to have strength and high power transmission efficiency. In response to such a request, in order to improve the transmission efficiency of the ACSR, it is being reviewed to increase the aluminum cross-sectional area of the core portion which is lightened, and to reduce the electric resistance of the steel wire itself which becomes the core. For example, Patent Document 1 discloses a method of reducing the specific gravity of a power transmission line by using a composite wire of carbon fiber and aluminum or aluminum alloy as a core portion for the purpose of weight reduction of the core portion. Further, Patent Document 2 discloses a method for limiting the content of C, Si, and Mn in a steel wire to a minimum necessary for reducing the electric resistance of the steel wire itself.

However, the technique disclosed in Patent Document 1 is costly because it uses a carbon fiber having a higher unit price than steel. Further, the technique disclosed in Patent Document 2 is difficult to secure the strength of the steel wire as the tensile member because the alloy element content is lowered.

Further, Non-Patent Document 1 reports that a 5.5 mm diameter wire having a high carbon content of 0.92% is first drawn to a diameter of 1.75 mm, and then toughened and then worked by a large cold drawing wire to a very fine diameter of 0.26 mm. The true strain is about 1.5 conditions as a peak to improve conductivity.

However, after processing such a very thin steel wire, it is extremely difficult to manufacture a power transmission line by plating a zinc wire or the like around a very thin steel wire (core) or by twisting such a thin steel wire with an aluminum wire. Increased substantially. Prior Technical Literature Patent Literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2001-176333. Patent Document 2: Japanese Patent Laid-Open Publication No. 2003-226938

Non-Patent Document 1: Materials Science & Engineering A 644 (2015) 105-113, A. Lamontagne et al., "Comparative study and quantification of cementite decomposition in heavily drawn pearlitic steel wires"

Disclosure of the Invention Problems to be Solved by the Invention The present invention has been made in view of the foregoing circumstances. An object of the present invention is to provide a steel wire having a wire diameter suitable for a power transmission application and having excellent electrical conductivity and tensile strength, and a coated steel wire having a coating layer of the steel wire and the coated steel wire. Means to solve the problem

The present inventors reviewed the relationship between the chemical composition, the microstructure, and the electrical conductivity of steel materials. As a result, it was found that the electrical conductivity of the wire material of the steel wire material was improved by controlling the chemical composition and the form of the ferritic carbon iron. The inventors of the present invention have focused on the form of ferrite iron and ferritic carbon iron, and have repeatedly reviewed the results. It has been found that by imparting strain to the wire, the alignment of the ferrite iron and the ferritic carbon iron is changed, and the electrical conductivity is further enhanced. Further, the inventors of the present invention have found that a steel wire having excellent electrical conductivity and tensile strength and having a wire diameter suitable for a power transmission line can be obtained by focusing on the conditions of the cooling step and the wire drawing step after rolling. In other words, the inventors of the present invention have found that the hot rolling is delayed by a specific condition, and the chemical composition and the structure are controlled to improve the conductive wire, and the wire is processed by a specific condition to obtain a wire diameter suitable for the use of the power transmission line. Steel wire with excellent electrical conductivity and high tensile strength. The present invention has been made in view of the above-observed knowledge, and the gist thereof is as follows.

(1) A steel wire according to one aspect of the present invention has a chemical composition of, in mass%, C: 0.40 to 1.10%, Si: 0.005 to 0.350%, Mn: 0.05 to 0.90%, and Cr: 0 to 0.70%. , Al: 0~0.070%, Ti: 0~0.050%, V: 0~0.10%, Nb: 0~0.050%, Mo: 0~0.20%, B: 0~0.0030%, the rest is made of Fe and impurities The metal structure in the cross section includes 80% by area or more of a ferritic carbon iron having a layered ferritic carbon iron; the layered stellite carbon iron is spaced apart from each other, that is, an average layered interval of 28 to 80 nm; The average length of the stellite carbon iron is 22.0 mm or less; and the wave-like iron structure has a wave-like structure of the layered ferritic carbon iron within a range of 15° or less with respect to the longitudinal direction of the steel wire. The above-mentioned accumulation degree of the {110} plane of the ferrite iron with respect to the longitudinal direction obtained by the X-ray diffraction method is in the range of 2.0 to 8.0; and has a diameter of 1.4 mm or more. (2) The steel wire according to the above (1), which may have one or more selected from the group consisting of: Cr: 0.01 to 0.70%, Al, in terms of the chemical composition. : 0.001 to 0.070%, Ti: 0.002 to 0.050%, V: 0.002 to 0.10%, Nb: 0.002 to 0.050%, Mo: 0.02 to 0.20%, and B: 0.0003 to 0.0030%. (3) A coated steel wire according to another aspect of the invention, comprising the steel wire according to the above (1) or (2), and a metal coating layer covering the steel wire. (4) The coated steel wire according to the above (3), wherein the metal coating layer may include at least one of zinc, a zinc alloy, aluminum, an aluminum alloy, copper, a copper alloy, nickel, or a nickel alloy. Effect of the invention

According to the above aspect of the present invention, it is possible to provide a steel wire having a wire diameter suitable for a power transmission use and having excellent electrical conductivity and tensile strength, and a coated steel wire having a coating layer of the steel wire and the coated steel wire. The steel wire and the coated steel wire according to the above aspect of the present invention are suitable for use in a power transmission line because the steel wire as the core material has a large wire diameter and excellent electrical conductivity and tensile strength.

MODE FOR CARRYING OUT THE INVENTION A steel wire (a steel wire according to the present embodiment) according to an embodiment of the present invention 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 of the present embodiment has a steel component (chemical composition) described below, and the metal structure includes a wave-like iron structure having a layered stellite carbon iron (hereinafter, simply referred to as "Bordonite structure"). Further, in the steel wire of the present embodiment, the average layered interval of the layered stellite carbon contained in the ferritic structure is 28 to 80 nm, and the average length of the layered stellite carbon is 22.0 μm or less. 40% or more of the Bronze structure of the layered ferritic carbon iron having a inclination of 15° or less with respect to the longitudinal direction of the steel wire in the structure, and the ferrite-grained iron obtained by the X-ray diffraction method with respect to the longitudinal direction The accumulation degree of the {110} plane is in the range of 2.0 to 8.0. Further, the steel wire of the present embodiment has a diameter of 1.4 mm or more.

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

(C: 0.40 to 1.10%) C has an effect of increasing the iron fraction of the wave in the steel and making the layered interval in the ferrite structure fine. When the layered interval is refined, the strength is increased. When the C content is less than 0.40%, it is difficult to ensure that the ferrite structure is 80 area% or more. At this time, the strength of the steel wire will not be sufficiently ensured. Therefore, the C content is made 0.40% or more. The C content is preferably 0.60% or more. On the other hand, when the C content is more than 1.10%, the electrical conductivity of the steel wire is lowered, and the amount of the precipitated ferritic carbon iron is increased, resulting in a decrease in ductility. Therefore, the C content is made 1.10% or less. The C content is preferably 1.05% or less, more preferably 1.00% or less, and still more preferably 0.95% or less.

(Si: 0.005 to 0.350%) The Si system is a component which contributes to the strength of the steel by solid solution strengthening, and is also a component necessary for the deoxidizer. When the Si content is less than 0.005%, the effects are not sufficiently obtained, so the Si content is made 0.005% or more. In order to further improve the hardenability and to easily perform the heat treatment, the Si content is preferably 0.010% or more, and preferably 0.020% or more. On the other hand, an element which increases the specific resistance when Si is dispersed in the ferrite iron in the Borne iron structure. When the Si content is more than 0.350%, the resistivity is remarkably increased, so the Si content is made 0.350% or less. In order to obtain a low resistivity (i.e., high conductivity), the Si content is preferably 0.250% or less, and preferably 0.150% or less. Further, when a galvanized or galvannealed alloy is formed on the steel wire, when the Si content is small, the alloy layer during plating is helped to grow, and the fatigue properties of the steel wire are lowered. Therefore, it is preferable to set the Si content to 0.050% or more on the premise that the steel wire is used after galvanization or zinc alloy.

(Mn: 0.05 to 0.90%) The Mn-based deoxidizing element is also an element which has an effect of fixing S in steel to MnS to prevent hot brittleness. Moreover, Mn is an element which contributes to the improvement of hardenability, reduces the iron fraction of the ferrite grain during toughening, and enhances the strength. However, when the Mn content is less than 0.05%, the aforementioned effects are not sufficiently obtained. Therefore, the Mn content is set to 0.05% or more. On the other hand, when the Mn content is excessive, the electrical conductivity of steel is lowered. Therefore, the Mn content is made 0.90% or less. In order to further improve conductivity, the Mn content is preferably 0.75% or less, more preferably 0.60% or less.

The steel wire of the present embodiment is mainly composed of the above-mentioned elements, and the remainder is composed of Fe and impurities. In the steel wire of the present embodiment, the impurities are particularly preferably limited to N, P, and S contents as follows. The content of impurities is preferably as small as 0%. The impurities are elements which are inevitably mixed from a raw material or the like or a manufacturing step of steel.

(N: 0.0100% or less) N is an element which reduces ductility by strain aging during cold working and lowers conductivity. In particular, when the N content is more than 0.0100%, the ductility and conductivity are remarkably lowered. Therefore, it is preferred to limit the N content to 0.0100% or less. The N content is preferably 0.0080% or less, more preferably 0.0050% or less.

(P: 0.030% or less) P contributes to the solid solution strengthening of the ferrite iron, but it is an element which greatly reduces the ductility. In particular, when the P content is more than 0.030%, the wire drawability when the wire is drawn into a steel wire is remarkably lowered. Therefore, it is preferred to limit the P content to 0.030% or less. The P content is preferably 0.020% or less, more preferably 0.012% or less.

(S: 0.030% or less) S is an element which causes red hot brittleness and decreases ductility. A decrease in the ductility of the S content of more than 0.030% will become remarkable. Therefore, it is preferred to limit the S content to 0.030% or less. The S content is preferably 0.020% or less, more preferably 0.010% or less.

As described above, the steel wire of the present embodiment is basically composed of the above-mentioned elements and the remainder consisting of Fe and impurities. However, in addition to the one of the above-mentioned elements, one or two or more selected from the group consisting of Cr, Al, Ti, V, Nb, Mo, and B may be contained in a range as described below. element. However, since these elements are not necessarily contained, the lower limit is 0%. Further, even if any of the arbitrary elements smaller than the range described later is contained, the steel wire characteristics are not inhibited, so that it is allowed.

(Cr: 0.01 to 0.70%) Cr is an element which enhances the hardenability of steel, and is an element which reduces the laminar spacing of the layered stellite in the ferrite structure to increase the tensile strength. In order to obtain this effect, the Cr content is preferably 0.01% or more. Preferably, it is 0.02% or more. On the other hand, when the Cr content is more than 0.70%, the conductivity will decrease depending on the toughening 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%) The Al-based deoxidizing element is also an element which fixes nitrogen to a nitride and contributes to the finer grain size of the Worthite iron. When the Al content is less than 0.001%, the above effects are not easily obtained. Therefore, in order to obtain an effect, the Al content is preferably 0.001% or more. On the other hand, Al is an element which does not act as a nitride and is present as free Al in the ferrite iron, and which lowers the conductivity. Therefore, it is preferable to set the upper limit of the Al content to 0.070% when it is contained. A preferred upper limit is 0.050%.

(Ti: 0.002 to 0.050%) The Ti-based deoxidizing element is also an element which forms a carbonitride and contributes to the refinement of the particle size of the Worthite iron. In order to obtain this effect, it is preferable to set the Ti content to 0.002% or more. On the other hand, when the Ti content is more than 0.050%, there is a possibility that coarse nitrides are formed in the steel making stage, and carbides are precipitated in the toughening treatment, and ductility is lowered. Therefore, it is preferable to set the upper limit of the Ti content to 0.050% when it is contained. Preferably, the Ti content is less than 0.030%.

(V: 0.002 to 0.10%) V is an element which enhances the hardenability of steel and is an element which precipitates as a carbonitride and contributes to the strength of steel. In order to obtain this effect, it is preferable to set the V content to 0.002% or more. On the other hand, when the V content is excessive, the time until the end of the metamorphism at the time of toughening becomes long, and the ductility is lowered due to precipitation of coarse carbonitride. Therefore, it is preferable to set the upper limit of the V content to 0.10% when it is contained. A preferred upper limit is 0.08%.

(Nb: 0.002 to 0.050%) Nb is an element which improves the hardenability of steel and precipitates as a carbonitride, contributing to the refinement of the particle size of the Worthite iron. In order to obtain this effect, it is preferable to set the Nb content to 0.002% or more. On the other hand, when the Nb content is more than 0.050%, the time until the end of the metamorphosis at the time of toughening becomes long. Therefore, it is preferable to set the Nb content to 0.050% or less when it is contained. Preferably, it is 0.020% or less.

(Mo: 0.02 to 0.20%) Mo is an element which improves the hardenability of steel and reduces the area ratio of ferrite and iron in the structure. In order to obtain this effect, it is preferable to set the Mo content to 0.02% or more. However, when the Mo content is excessive, the time until the end of the metamorphosis at the time of toughening becomes long. Therefore, it is preferable to set the Mo content to 0.20% or less when it is contained. Preferably, it is 0.10% or less.

(B: 0.0003 to 0.0030%) B is an element that enhances the hardenability of steel, and is an element that suppresses the formation of ferrite iron and increases the area ratio of the ferrite. In order to obtain this effect, it is preferable to set the B content to 0.0003% or more. On the other hand, when the B content is more than 0.0030%, in the toughening step, M ₂₃ (C, B) ₆ is precipitated on the Worthfield iron grain boundary in the state of the supercooled Worth iron, and the ductility is lowered. Therefore, it is preferable to set the B content to 0.0030% or less when it is contained. Preferably, it is 0.0020% or less.

Next, the metal structure of the steel wire of the present embodiment will be described. The steel wire of the present embodiment has a tensile strength of 1500 MPa or more, preferably 1600 MPa or more, and more preferably 2000 MPa or more. In order to achieve such tensile strength and improve electrical conductivity, the steel wire of the present embodiment needs to have a metal structure as described below. Unless otherwise specified, the cross section refers to a so-called L cross section which is parallel to the longitudinal direction of the steel wire and passes through the central axis of the longitudinal direction of the steel wire.

<Wave structure containing layered stellite carbon of 80% by area or more> The steel wire of the present embodiment contains 80% by area or more of a layered ferritic carbon iron in a metal structure in a cross section. Iron organization. When the Borne iron structure is less than 80% by area, sufficient tensile strength is not obtained. The ferritic carbon-iron-iron structure is preferably 95% by area or more, more preferably 97% by area or more, and may be 100%. In the present embodiment, the ferritic carbon-iron-based iron structure is derived from the structure of the ferritic or pseudo-wave iron present in the wire before the wire drawing process, and is a stellite carbon-iron phase (layered swarf Carbon iron) is a layered interaction with the fertilized iron phase. In other words, the ferritic carbon-based iron structure of the present embodiment comprises a linear, curved, or fragmented swarf carbon iron, and a ferrite phase iron phase existing between the swarf carbon and iron. organization. The steel wire of the present embodiment may contain a ferrite iron structure in addition to the ferrite structure. However, when the ferrite iron structure is larger than 20% by area, since the area ratio of the Borne iron structure is lowered and the tensile strength is lowered, it is necessary to limit the ferrite iron structure to 20 area% or less. The ferrite iron structure referred to herein is not the ferrite phase contained in the Borne iron structure. Further, the steel wire according to the present embodiment may contain a small amount of a toughened iron structure or a granulated iron structure in addition to the above-described Bourne structure and the ferrite structure. However, the ductile iron or the granulated iron of the non-diffusing metamorphic structure is a structure that hinders the diffusion of the solid solution element, so that the electrical conductivity of the steel wire decreases when the tissue fraction of the tissues increases. Therefore, it is preferable that the toughened iron structure and the granulated iron structure are less than 3 area% in total. The tissue fraction in the steel wire can be obtained by taking a photograph of the metal structure at a magnification of 2000 times for the observation of the average layered interval of the cross section of the steel wire described later, and dividing the area of each tissue by image The average value of the area ratios of the respective tissues was calculated and analyzed.

<Average layered spacer 28 to 80 nm> The interval between adjacent layered stellites in the ferritic structure, that is, the average layered interval is in the range of 28 to 80 nm. When the average lamellar spacing is less than 28 nm, the electrical conductivity of the steel wire is lowered. On the other hand, when the average layer interval is more than 80 nm, the conductivity and the tensile strength are not sufficiently improved.

The average layered interval was measured by the following method. In other words, after the L-section of the steel wire is filled into the resin and polished into a mirror surface, it is etched with a bitter etchant, and then an FE-SEM is used to shoot 10 or more fields of the wave-forming iron block at 5,000 to 10,000 times. Digital image of any area. The average layered interval in each of the photographs taken was measured using an image analysis device. The lamellar spacing is from the center of the layered stellite carbon iron to the closest to the center of the layered stellite carbon iron.

<The average length of the layered stellite carbon iron is 22.0 μm or less> The average length of the layered stellite carbon in the Borne iron structure is 22.0 μm or less. When the average length of the layered stellite carbon iron is more than 22.0 μm, the electrical conductivity of the steel wire is lowered. The average length of the layered stellite carbon iron is preferably 12.0 μm or less, and preferably 10.0 μm or less from the viewpoint of improving conductivity. On the other hand, from the viewpoint of tensile strength, the average length of the layered stellite carbon 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 the layered stellite carbon in the Borne iron structure is measured by the following method. In other words, the cross section (L section) in the longitudinal direction of the steel wire (the wire drawing direction) was mirror-polished, and then etching was performed by a bitter etching agent, and the structure was observed by FE-SEM, and the result of the structure observation was analyzed. Specifically, as shown in FIG. 1, in the steel wire cross section, the axial center position (D/2) of the steel wire is set to the D/4 position (D system steel wire diameter). The set area is a rectangular area with a length of D/2 on each side. Further, the rectangular area is divided into nine equal-divided meshes, and the vertices (16 places) of the divided meshes are taken as observation positions. The imaging area was set at a magnification of 10000 times at each observation position, and the drawing direction was horizontally aligned with the image, and the surface of the cross section was taken by FE-SEM. After image analysis of the image of the shooting area, the binarized carbon-carbon portion and other parts (fertilizer iron portion) are binarized to determine the length of the long-side snow-capped carbon iron. Further, after the average length of the obtained simon carbon, the average length of the ferritic carbon iron was calculated.

In the case of a ferritic structure, the ferritic structure of the ferritic carbon iron having a thickness of 15° or less with respect to the longitudinal direction of the steel wire is 40% by area or more > in the wave-iron structure, with respect to the longitudinal direction of the steel wire The ferritic carbon-iron structure having a slope (angle difference) of 15 or less is 40% or more in area ratio. When the area ratio of the iron-containing iron structure having the layered stellite carbon iron having an inclination of 15 or less is less than 40 area%, the electrical conductivity is lowered. From the viewpoint of the conductivity, the layered stellite carbon iron having a gradient of 15° or less with respect to the longitudinal direction of the steel wire (hereinafter, simply referred to as “layered stellite carbon iron having an inclination of 15° or less”) The area ratio of the iron structure is preferably 55 area% or more, and more preferably 60 area% or more. The higher the proportion of the layered stellite carbon iron which is inclined within 15° with respect to the longitudinal direction of the steel wire, the better from the viewpoint of conductivity, and therefore the layered stellite carbon wave having a inclination of 15° or less The upper limit of the area ratio of the iron structure is 100 area%.

The area ratio of the ferritic structure having the layered stellite carbon iron which is inclined within 15° with respect to the longitudinal direction of the steel wire is measured by the following method. In other words, each of the images captured in the measurement of the average length of the layered stellite carbon iron is in the iron-and-wire region (Bolaite Group) in which the alignment of the layered ferritic carbon iron in the center of the image is equal. The two ends of one layer of stellite carbon iron are connected by a line segment, and the difference in angle from the horizontal direction is measured to confirm whether it is within a range of 15 or less. If it is within 15°, it is judged that this region has a Borne iron structure of layered stellite which is inclined within 15° with respect to the longitudinal direction of the steel wire. When the alignment of the layered ferritic carbon iron in the pull-wired iron structure is irregular or unclear, it is judged to be a layered stellite carbon iron which is not inclined within 15°, and this area is not included in the "relative to the length of the steel wire." The direction of the layered stellite carbon iron is inclined to be within 15° of iron. The total area of the iron-and-iron structure in the field of view with respect to the total number of shots is 40% of the total area of the wave-iron structure with an inclination of the layered ferritic carbon iron in the longitudinal direction of the steel wire of 15° or less. In the above, it is judged that the proportion of the Bronze structure having the layered stellite carbon having a inclination of 15 or less with respect to the longitudinal direction of the steel wire is 40% or more in terms of the area ratio. Fig. 2A is a view showing an example of a wave-like iron image in a range of an inclination of 15° or less in the aligned iron-wave-organized iron region of the layered stellite carbon iron in the center portion, and Fig. 2B shows that the inclination is not 15°. The following example of the Borne iron tissue image.

<The range of the {110} plane of the ferrite-grained iron in the longitudinal direction is in the range of 2.0 to 8.0. The degree of accumulation of the {110} plane of the ferrite-grained iron with respect to the longitudinal direction of the steel wire is in the range of 2.0 to 8.0. When the accumulation degree of the {110} plane of the ferrite iron is less than 2.0 or more than 8.0, the electrical conductivity of the steel wire is lowered, which is not preferable. Further, from the viewpoint of electrical conductivity and tensile strength, the accumulation degree of the {110} plane of the ferrite iron is preferably 2.2 to 5.5, and preferably 3.0 to 4.5.

The accumulation of ferrite iron is measured by the following method. In other words, in the radial direction of the cross section of the longitudinal direction (wire drawing direction) of the steel wire shown in FIG. 3B, the center portion to the D/4 (D-line steel wire diameter) region is formed by the X-ray diffraction method. 110} Pole map, the maximum value of the polar density (ratio of random orientation) of the point observed in the RD direction (the length direction of the steel wire) is taken as the cumulative degree of the {110} plane of the ferrite iron. Here, the accumulation degree of the {110} plane of the ferrite iron obtained by X-ray diffraction refers to the ferrite grain iron phase contained in the Borne iron structure, and the ferrite grain iron structure other than the Borne iron structure. The degree of accumulation calculated by the information obtained by the person. Further, the measurement conditions of the X-ray diffraction of the present embodiment are as follows. X-ray diffraction device: manufactured by Rigaku Co., Ltd. Product name: RINT2200 (tube) (RINT2000/PC series) X-ray source: MoKα Divergence slit: 1/4° (0.43mm)

<Wire diameter (diameter): 1.4 mm or more> The steel wire of the present embodiment has a wire diameter of 1.4 mm or more. As long as the wire diameter is 1.4 mm or more, it is easy to manufacture the coated steel wire from the wire drawing of the wire and the metal coating layer such as aluminum or zinc around the steel wire. Therefore, the steel wire of the present embodiment is excellent not only in terms of electrical conductivity and tensile strength but also in terms of ease of processing and production cost. The steel wire diameter of the present embodiment is preferably 1.5 mm or more, and more preferably 1.6 mm or more. However, when the diameter of the steel wire is too large, the length of the layered stellite carbon iron is not easily shortened. Therefore, the steel wire diameter of the present embodiment is preferably 4.2 mm or less, and preferably 4.0 mm or less.

<Resistivity and Tensile Strength> The steel wire of the present embodiment is excellent in both conductivity and tensile strength. The electrical resistivity as the conductivity index in the steel wire of the present embodiment is preferably less than 19.0 μΩ × cm, preferably less than 18.0 μΩ × cm, and more preferably less than 17.0 μΩ × cm. Further, the tensile strength of the steel wire of the present embodiment is preferably 1,500 MPa or more, more preferably 1600 MPa or more, and still more preferably 2,000 MPa or more. As a part of the examples described later, it was found that a steel wire having a resistivity of less than 18.0 μΩ × cm and a tensile strength of 2000 MPa or more, or even a specific resistance of less than 17.0 μΩ × cm and a tensile strength of 2000 MPa or more can be realized.

The coated steel wire according to the present embodiment has the steel wire of the above-described embodiment and the metal coating layer covering the steel wire. In other words, the coated steel wire-based metal of the present embodiment is coated with a steel wire. The metal coating layer contains, for example, at least one of zinc, a zinc alloy, aluminum, an aluminum alloy, copper, a copper alloy, nickel, or a nickel alloy. The metal coating layer may be a plating layer or a coating layer. The plating layer may be a plating layer or a molten plating layer. The metal coating layer formed by the melt plating has a case where an alloy layer is formed at the interface between the steel wire and the metal coating layer. The alloy layer may be exemplified by a ZnFe alloy layer, an AlFe alloy layer, a NiFe alloy layer, and a CuFe alloy layer. By having a metal coating layer, the electrical conductivity of the entire coated steel wire can be improved.

Next, a preferred method for producing the steel wire of the present embodiment and the coated steel wire of the present embodiment will be described. The production method described below is merely an example, and the steel wire of the present embodiment and the method for producing the coated steel wire of the present embodiment are not limited to the following, as long as the steel wire or the coated steel wire satisfying the scope of the present invention can be obtained. Manufacturing conditions.

<Fusing Step, Casting Step, and Hot Rolling Step> After the steel having the above-described composition is melted, a steel sheet (small steel blank) is produced by continuous casting or the like, and hot rolling is performed. Block rolling can also be carried out after casting. In the case of hot rolling of the steel sheet, it is preferred to heat the steel sheet to a temperature of 1000 to 1100 ° C and to obtain a wire having a temperature of 900 to 1000 ° C as a finishing temperature.

<Cooling Step> The wire after the hot rolling step is subjected to water cooling, air cooling, furnace cooling, and/or cooling by immersion in a molten bath. At this time, it is preferable to set the cooling pattern in accordance with the C content. When the C content is 0.40 to 0.70%, the final rolling is cooled to a temperature range of 800 to 920 ° C (first cooling) at an average cooling rate of 20 ° C / s or more, followed by cooling at an average cooling rate of 5 to 20 ° C / s. It is cooled to 600 to 500 ° C (third cooling) at an average cooling rate of 5 ° C / s or lower to 800 to 600 ° C (second cooling). When the cooling rate of the first cooling is less than 20 ° C / s, the initial precipitation iron is likely to be formed, and the fraction of the Borne iron structure is lowered. Further, when the stop temperature of the first cooling is less than 800 ° C, the particle size of the Worthite iron is not refined and sufficient hardenability is not obtained. On the other hand, when the stop temperature of the first cooling is more than 920 ° C, the initial precipitation iron is likely to be formed in the subsequent cooling process, and the fraction of the Borne iron structure is lowered.

Further, when the cooling rate of the second cooling is less than 5 ° C / s, the formation of the ferrite is likely to decrease due to the formation of the initial precipitated iron. On the other hand, when the cooling rate of the second cooling is more than 20 ° C / s, the distribution of the ferrite in the second to third cooling and the distribution of the alloy elements are insufficient. Further, when the cooling rate of the third cooling is more than 5 ° C / s, the distribution of the alloying elements is less likely to occur, so that the electrical conductivity is lowered.

However, in the cooling, when the residence time of 600 to 500 ° C is longer than 33 seconds (about 3.0 ° C / s or less in terms of average cooling rate), the alloy element is sufficiently distributed, so the average is 800 to 600 ° C. The cooling rate can also be 20 ° C / s or more. Further, for example, a lead bath, a salt bath, or a fluidized bed furnace may be used to terminate the metamorphosis, and then heated to a temperature range of 600 to 400 °C.

Further, when the C content is more than 0.70 and not more than 1.10%, the final rolling is carried out by cooling to 800 to 920 ° C at an average cooling rate of 20 ° C / s or more, and immersing in a molten salt of 500 to 600 ° C for 30 seconds or more. Make the Borne iron metamorphosis.

In the present embodiment, the completion temperature of the rolling is the surface temperature of the wire immediately after the final rolling, and the average cooling rate in the cooling step after the final rolling refers to the cooling rate of the center portion of the wire.

The wire obtained by the above-mentioned manufacturing step is, for example, 80% or more of the metal structure in the cross section is a ferrite structure, and the average lamellar spacing of the Borne iron structure is 50 to 170 nm, and the layered snow in the Borne iron structure The average length of the carbon iron is 1.5 μm or less. Further, from the viewpoint of obtaining the steel wire of the present embodiment by the following wire drawing step, the wire diameter of the wire produced in the above-described production step is preferably 3.0 to 14.0 mm.

<Wire Pulling Step> Next, the wire material is subjected to wire drawing processing to obtain a steel wire. The wire drawing process is preferably performed by applying a wire having a true strain of 1.5 to 2.4 to the wire. The true strain is preferably 1.7~2.1. When the wire is pulled under the above conditions, the wire resistivity after the wire is pulled is reduced by about 1.0 to 1.5 μΩ × cm (that is, the conductivity is improved) with respect to the wire before the wire is pulled. Further, even if the steel strain (for example, the steel species K used in the examples described later) is different, and the true strain is less than 1.5 or more than 2.4, a steel wire having a low electrical resistivity and a high tensile strength can be obtained. However, even for such a steel grade, a steel wire having a high tensile strength and a lower electrical resistivity can be easily obtained by imparting a true strain of 1.5 to 2.4. As the wire drawing speed of the wire is increased, the strain increases, the average layered interval becomes smaller, the average length of the layered stellite carbon iron becomes larger, and the inclination of the layered stellite carbon iron becomes smaller. The proportion of the Borne iron structure of the stellite carbon iron with an angular difference of 15° or more increases, and the accumulation degree of the {110} plane of the ferrite iron becomes higher. When the wire drawing is performed under the condition that the true strain is less than 1.5, the proportion of the stellite carbon iron having an angular difference of 15 or less is insufficient, and the electrical conductivity is lowered. On the other hand, when the wire drawing is performed under the condition that the true strain is more than 2.4, the amount of solid solution C in the ferrite is increased, and the conductivity is lowered.

According to the manufacturing method including the above steps, the steel wire of the present embodiment can be produced.

<Covering Step> Next, a metal coating layer was formed on the obtained steel wire. The method of forming the metal coating layer may be any one of a plating method, a melt plating method, and a coating method. The thickness of the metal coating layer at this time is preferably from about 0.7% to about 20% with respect to the diameter of the wire or the steel wire. Thereby, the coated steel wire of this embodiment is manufactured. The coating step can also be performed between the cooling step and the wire drawing step. In other words, after the metal coating layer is formed on the wire material, the coated steel wire of the present embodiment can be obtained even if the wire drawing process is performed. Example

Next, an embodiment of the present invention will be described. The conditions in the examples are a conditional example used to confirm the applicability and effects of the present invention, and the present invention is not limited by the conditional example. The present invention can be obtained using various conditions without departing from the gist of the present invention.

The molten steel melted according to the chemical composition shown in Table 1 (however, the remainder is Fe and impurities) was cast into an ingot in a 50 kg vacuum melting furnace. Each of the ingots was heated at 1,250 ° C for 1 hour, and then hot-forged into a rod wire having a diameter of 15 mm at a completion temperature of 950 ° C or higher, and then naturally cooled to room temperature. The hot forged material was cut to a diameter of 10 mm by cutting, and cut into a length of 1500 mm by cutting. The cut material was heated at 1050 ° C for 15 minutes in a nitrogen atmosphere, and then hot rolled to a completion temperature of 900 ° C or higher to obtain a rolled steel having a diameter of 7 mm.

After that, a part of the rolled and rolled material is finally cooled in the atmosphere by an electric fan to 900 ° C, and then sealed in a low-temperature heating furnace in 10 seconds to have an average cooling rate of 6 ° C / s in the furnace. The mixture was cooled to 600 ° C, and cooled to 400 ° C in an oven at an average cooling rate of 1 ° C / s. After cooling to 400 ° C, it was taken out and naturally cooled to room temperature to obtain a steel wire (condition No. 5 of the cooling step of Table 2). . Moreover, after the final rolling, the other rolled material is air-cooled to 850 ° C or 900 ° C in the atmosphere by an electric fan, and then immersed in the lead bath in accordance with the condition number 2 to 4 of the cooling step shown in Table 2 within 10 seconds. It was taken out and naturally cooled to room temperature to obtain a steel wire. The average cooling rate in each temperature domain is shown in Table 2. In addition, other rolled webs were hot rolled to a diameter of 7 mm and then cooled in an air by an electric fan to room temperature (condition 2 of the cooling step of Table 2). The average cooling rate in each temperature domain is shown in Table 2. Even after a part of the rolled material was immersed in a lead bath at 640 ° C after the final rolling, it was immediately cooled at 100 ° C / s to be 400 ° C or less (condition No. 1 of the cooling step of Table 2). The average cooling rate in each temperature domain is shown in Table 2.

Among the obtained wires, a metal coating layer was formed by performing a hot-dip galvanizing method or an aluminum-clad method on Test Nos. 1 to 31.

Thereafter, the steel portion included in the wire rod was subjected to a normal strain as shown in Table 3, and a steel wire or a coated steel wire having a steel portion having a diameter of 2.0 mm to 3.5 mm was obtained.

Thereafter, a steel coating layer made of zinc was formed by subjecting a steel wire of Test No. 32 in which the coating layer was not formed before the wire drawing to a hot-dip galvanizing method.

The metal coating layer was removed from the coated steel wire obtained by the above-mentioned method using hydrochloric acid or sodium hydroxide, and the steel wire was taken out, and the tensile strength and electrical conductivity of the steel wire were evaluated. <Tensile Strength> Three tensile test pieces in the form of strands of 350 mm in length were taken from the steel wire. The tensile test piece was subjected to a tensile test at a normal temperature at a tensile speed of 200 mm and 10 mm/min between the chucks, and the tensile strength (TS) was measured, and the average value was taken as the tensile strength of the test material.

<Electrical conductivity> A test piece for conductivity measurement having a length of 60 mm was cut out from a steel wire, and the specific resistance was measured by a 4-terminal method at a temperature of 20 °C.

Further, the obtained steel wire was measured for each tissue fraction, the average layered interval of the layered stellite carbon, the average length of the layered stellite carbon iron, and the inclination (angle difference) with respect to the longitudinal direction of the steel wire was 15°. The area ratio of the Borne iron structure of the layered Xueming carbon iron and the accumulation degree of the {110} plane of the ferrite iron. <Average laminar spacing> The L-section is embedded in a resin and polished into a mirror surface for each steel wire, and then etched with a bitter etchant, and then 5 or more shots are taken at 5,000 to 10,000 times by FE-SEM. Digital image of any area of the Bora block. The average layered interval in each photograph was measured using an image analysis device. <Area ratio of each tissue> A photograph of a metal structure was taken at a magnification of 2000 times for the observation of the average layered interval of the cross-section of each steel wire, and each tissue region was divided, and the average value of the area ratio of each tissue was calculated by image analysis. Further, although Table 3 shows the area ratios of the Borne iron structure and the ferrite iron structure, in the steel wires of the total non-100% of the tissues, the tough iron structure and/or other microstructures were observed. Ma Tian scattered iron organization.

<Average length of layered stellite carbon iron> The average length of layered stellite carbon in the ferritic structure is measured by FE-SEM using a sample for measuring the average layered interval, and analyzing the structure The result is obtained. As shown in Fig. 1, in the L section of the steel wire, the axial center position (D/2) to the D/4 position (D-steel wire diameter) of the steel wire is set. The set area is a rectangular area with a length of D/2 on each side. Further, the rectangular region is divided into nine equal-divided meshes, and the vertices of the divided meshes are taken as observation positions. The imaging area was set at a magnification of 10000 times at each observation position, and the drawing direction was horizontally aligned with the image, and the surface of the cross section was taken by FE-SEM. After image analysis of the image of the shooting area, the binarized carbon-carbon portion and other parts (fertilizer iron portion) are binarized to determine the length of the long-side snow-capped carbon iron. Further, after the average length of the obtained simon carbon, the average length of the ferritic carbon iron was calculated.

<area ratio of the ferritic structure of the layered ferritic carbon iron which is inclined within 15 degrees with respect to the longitudinal direction of the steel wire> Next, each image captured when measuring the average length of the layered stellite carbon is used for the image In the center of the layered ferritic carbon iron in the center of the ferritic carbon-iron structure, the two ends of a layer of stellite carbon iron are connected by a line segment to measure the angular difference from the horizontal direction to confirm whether it is below 15°. Within the scope. When the total area of the iron structure with respect to the wave number of the total number of shots is 40 area% or more based on the total of the wave iron structure within 15 degrees of the inclination of the layered stellite in the longitudinal direction of the steel wire, The bronze structure having the layered stellite carbon iron which is inclined within 15° with respect to the longitudinal direction of the steel wire is 40% or more in terms of area ratio.

<Accumulation degree of the {110} plane of the ferrite iron> Next, the accumulation degree of the {110} plane of the ferrite iron is as shown in Figs. 3A to 3B, and the cross section with respect to the direction of the wire (RD direction) of the steel wire In the region from the center to the D/4 (D-line steel wire diameter) in the radial direction, the {110} pole map is created by the X-ray diffraction method, and the polar density of the point observed in the RD direction (with random The maximum value of the azimuth ratio is the cumulative degree of the {110} plane of the ferrite iron. The measurement conditions of the X-ray diffraction are as described above.

The results are shown in Tables 1 to 3.

[Table 1]

[Table 2]

[table 3]

As is clear from Table 3, in the case of Test Nos. 19 to 22 and 28 to 30 which are outside the conditions specified in the present invention, at least one of the above characteristics did not reach the target value (tensile strength: 1500 MPa or more, and specific resistance: less than 19.0 μΩ). ×cm, diameter: 1.4mm or more). On the other hand, all of the above-mentioned characteristics of Test Nos. 3 to 18, 23, 26, 27, 31, and 32 which fully satisfy the conditions specified in the present invention reached the target value. Further, in the test numbers 11 to 14, 26, 27, and 32, the steel type K was used, but in the test numbers 11 to 14, 32 in which the true strain was 1.5 to 2.4 in the wire drawing process, the specific resistance was particularly lowered. Industrial availability

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

D‧‧‧ steel wire diameter

RD‧‧‧ steel wire length direction

TD‧‧ direction

Fig. 1 is a view showing a section (L section) parallel to the longitudinal direction of the steel wire, and is a schematic view showing a method of measuring the average length of the layered stellite in the ferritic carbon-iron structure. Fig. 2A is a view for explaining a method of measuring the area ratio of the ferritic structure of the layered ferritic carbon iron having an inclination (angle difference) of 15 or less with respect to the longitudinal direction of the steel wire, showing a layered snow inclined within 15°; A photo of an example of a carbon iron. Fig. 2B is a view for explaining a method of measuring the area ratio of the ferritic structure of the layered ferritic carbon iron having an inclination (angle difference) of 15 or less with respect to the longitudinal direction of the steel wire, showing a layer shape not inclined within 15°; A photo of a case of Xueming Carbon. Fig. 3A is a view showing a L section of a steel wire, showing a pattern of the TD direction and the RD direction. Fig. 3B is a view showing a L-section of a steel wire, and is a schematic view for explaining a method of measuring the accumulation degree of the ferrite iron.

Claims (4)

A steel wire characterized by having a chemical composition in mass %, comprising: 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: 0~0.050%, V: 0~0.10%, Nb: 0~0.050%, Mo: 0~0.20%, B: 0~0.0030%, the remaining part is composed of Fe and impurities; The metal structure comprises 80% by area or more of a ferritic carbon-iron-containing iron-iron structure; the layered stellites are spaced apart from each other, that is, an average layered interval of 28 to 80 nm; the layered stellite carbon-iron The average length is 22.0 mm or less; the Borne iron structure has a layer of stellite carbon iron which is inclined within 15° with respect to the longitudinal direction of the steel wire, and has an iron structure of 40% by area or more; The degree of accumulation of the {110} plane of the ferrite iron with respect to the longitudinal direction obtained by the diffraction method is in the range of 2.0 to 8.0; and has a diameter of 1.4 mm or more. The steel wire of the claim 1 has a chemical composition containing at least one or more selected from the group consisting of: Cr: 0.01 to 0.70%, Al: 0.001 to 0.070%, Ti : 0.002~0.050%, V: 0.002~0.10%, Nb: 0.002~0.050%, Mo: 0.02~0.20%, B: 0.0003~0.0030%. A coated steel wire characterized by comprising: a steel wire according to claim 1 or 2; and a metal coating layer covering the steel wire. The coated steel wire according to claim 3, wherein the metal coating layer comprises at least one of zinc, a zinc alloy, aluminum, an aluminum alloy, copper, a copper alloy, nickel or a nickel alloy.