TWI604068B - Steel wire rod and method for manufacturing the same - Google Patents

Description

Steel wire and steel wire manufacturing method

FIELD OF THE INVENTION The present invention relates to a steel wire used as a material for overhead transmission lines, various ropes, and the like, and a method of manufacturing the same.

BACKGROUND OF THE INVENTION Aluminum Conductor Steel-Reinforced cable (hereinafter referred to as "ACSR") has a galvanized steel wire disposed at the center, and the hard aluminum wire is concentric and the layers are oppositely opposed to each other. The wires that make up. The ACSR steel wire has so far mainly served as a tensile material for aluminum wire. The steel wire for ACSR is a steel wire obtained by drawing a ferritic steel wire and galvanizing, and a steel wire obtained by forming a steel wire with an aluminum layer as a surface layer for improving corrosion resistance. Aluminum-Clad Steel Wire, etc.

From the viewpoint of improving the power transmission efficiency, in order to reduce the specific gravity of the entire electric wire and increase the aluminum area, there is a demand for higher strength and smaller diameter of the steel core portion of the ACSR steel wire.

For example, as a means of improving the power transmission efficiency of the ACSR, the ACSR is lightweight, the aluminum cross-sectional area is increased, and the resistance of the steel wire is reduced. For example, from the viewpoint of weight reduction of the ACSR, Patent Document 1 discloses a method of reducing the specific gravity of the ACSR by making the core of the ACSR a carbon fiber. Further, from the viewpoint of reducing the electric resistance of the steel wire, Patent Document 2 discloses a method of limiting the electrical conductivity of the steel wire by limiting the C, Si, and Mn contents of the steel wire to a small amount.

In addition, in the IEC61232 developed by the International Electrotechnical Commission, the torsional characteristics required for the aluminum facing steel wire are limited to 20 or more. Therefore, in addition to high strength and fine diameter, the aluminum facing steel wire also has a demand for high ductility. From the viewpoint of improving the torsional characteristics, it is disclosed in Patent Document 3 that a small amount of Ni is added to the steel wire, thereby minimizing the size of the wave-like iron block and the layer-like interval of the steel wire, and increasing the shrinkage ratio and strength of the steel wire. The method.

However, according to the ACSR obtained by the technique disclosed in the aforementioned Patent Document 1, since the core wire is made of a high-priced carbon fiber, the unit price is higher than that of the ACSR using the steel wire as the core wire. Further, since the technique disclosed in Patent Document 2 lowers the alloying element content of the steel wire, it is difficult to secure the strength of the tensile material of the steel core portion as the steel wire. Furthermore, in the technique disclosed in Patent Document 3, since Ni is added and Ni is dissolved in the layered ferrite iron to increase the electric resistance of the steel wire, it is not preferable from the viewpoint of reducing the electric resistance.

Further, in general, there is a tendency that there is a proportional relationship between the tensile strength of the steel wire and the electrical resistivity of the steel wire, and it is difficult to manufacture a steel wire having both high tensile strength and high electrical conductivity. Recently, in order to reduce the specific gravity of the electric wire, a steel wire rod having a tensile strength of 1050 MPa or more, more preferably 1100 MPa or more, has been sought. However, according to the technology up to the present, it is difficult to impart sufficient electrical conductivity to a steel wire having such a tensile strength as the above-mentioned use. Prior technical literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-176333. Patent Document 2: JP-A-2003-226938 Patent Document 3: International Patent Publication No. WO2012/124679

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the invention is to provide a steel wire rod having high tensile strength and relatively low tensile strength and electrical resistivity, and further providing a twistable structure. Steel wire rod with excellent steel wire and its manufacturing method. In particular, in the present invention, a steel wire having a relatively high electrical conductivity (i.e., low electrical resistivity) for high tensile strength and a method for producing the same are provided.

As described above, in general, there is a tendency that there is a proportional relationship between the tensile strength of the steel wire and the electrical resistivity of the steel wire. The present inventors have investigated the relationship between the tensile strength TS (MPa) and the specific resistance ρ (μΩ ‧ cm) in the steel wire rods up to the present time, and as a result, it has been found that the electrical resistivity of the steel wire for ACSR to date is substantially below Within the scope. When the Si content is 0.100% by mass or more, when ρ>0.0155×TS+1.25 Si content is less than 0.100% by mass, ρ>0.0155×TS-0.95, therefore, the tensile strength TS and the specific resistance ρ of the steel wire are at the Si content. When the content is 0.100% by mass or more, when the following formula (1) is satisfied, and when the Si content is less than 0.100% by mass, the following formula (2) is satisfied, and the electrical resistivity of the steel wire is improved as compared with the current level. . ρ≦0.0155×TS+1.25 (1) ρ≦0.0155×TS-0.95 (2) Further, the right side of the formula (1) or (2) may be substituted into the tensile strength. The value is called the resistivity limit value. The "steel wire having high electrical conductivity" in the present invention means a steel wire having a specific resistance lower than a resistivity limit value obtained by the tensile strength and the above formula (1) or (2).

Means for Solving the Problems The gist of the present invention is as follows.

(1) A steel wire according to one aspect of the present invention has a chemical composition of C: 0.60 to 1.10%, Si: 0.005 to 0.350%, Mn: 0.10 to 0.90%, and Cr: 0.010 to 0.300%, per unit mass%. N: 0.0100% or less, P: 0.030% or less, S: 0.030% or less, Al: 0 to 0.070%, Ti: 0 to 0.030%, V: 0 to 0.100%, Nb: 0 to 0.050%, Mo: 0~ 0.20% and B: 0 to 0.0030%, and the remainder is composed of Fe and impurities; when the distance from the circumferential surface to the central axis is r in units of mm, the region from the central axis to r × 0.5 The tissue in the center portion contains 80 to 100% by area of Boron iron, and a total of 0% by area or more and less than 20% by area of the initial precipitation iron, the preliminary precipitation of ferritic carbon, the granulated iron and the toughened iron; The average layered interval of the above-mentioned bristo iron in the center portion is 50 to 100 nm, the average length of the layered stellite in the center portion is 1.9 μm or less, and the average wave size of the center portion is 15.0 to 30.0. Mm; the structure in the surface layer portion of the region from the circumferential surface to r × 0.1 includes 70 to 100% by area of the above-mentioned bundi iron, and the average wave-like iron block size of the surface layer portion is the aforementioned flat portion of the center portion 0.40 times the size of the waves to iron, 0.87 times or less. (2) The steel wire according to the above (1), wherein the chemical composition is Si: 0.100 to 0.350% by mass%, and the average wave size of the surface layer is 17.0 μm or less, and the steel wire is The relationship between the tensile strength TS [MPa] and the specific resistance ρ [μΩ ‧ cm] can also satisfy the following formula (i). ≦ ≦ 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 155 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢 钢The average wave iron block size is 0.80 times or less of the average wave iron block size of the center portion, and further, the relationship between the tensile strength TS [MPa] and the specific resistance ρ [μΩ ‧ cm] of the steel wire rod may be The following formula (ii) is satisfied. (b) The steel wire rod according to any one of the above (1) to (3), wherein the chemical component may be selected from the group consisting of Al: 0.001 by mass%. ~0.070%, Ti: 0.002 to 0.030%, V: more than 0 and 0.100% or less, Nb: more than 0 and 0.050% or less, Mo: more than 0 and 0.20% or less, and B: 0.0003 to 0.0030%. At least one or two or more of the ethnic groups. (5) A method of producing a steel wire according to another aspect of the present invention includes the step of casting a cast piece, wherein the chemical composition of the cast piece contains C: 0.60 to 1.10%, Si: 0.005 to 0.350%, and Mn per unit mass%; : 0.10 to 0.90%, Cr: 0.010 to 0.300%, N: 0.0100% or less, P: 0.030% or less, S: 0.030% or less, Al: 0 to 0.070%, Ti: 0 to 0.030%, V: 0 to 0.100 %, Nb: 0~0.050%, Mo: 0~0.20%, and B: 0~0.0030%, and the remainder is composed of Fe and impurities; heating the cast piece to a temperature range of 1150 ° C or more and 1250 ° C or less a step of heating the temperature; maintaining the temperature of the slab at the heating temperature for 600 to 7200 seconds; and subjecting the slab after the holding to hot rolling to a finishing temperature of 950 ° C to 1050 ° C or less a step of hot-rolling steel; a step of water-cooling the hot-rolled steel to a temperature range of 780° C. or more and 840° C. or less; and a step of winding the hot-rolled steel after the water-cooling in a temperature range of 780° C. or higher and 840° C. or lower; The hot-rolled steel after the coiling is in the range of 4.5 to 25 seconds after the coiling, at 450 ° C or higher and by the following formula (i Ii) a step of toughening by immersing the molten salt at a temperature lower than T1 ° C for 20 to 200 seconds; and heating the toughened hot-rolled steel to a temperature range of 540 to 600 ° C The temperature of the fire is maintained at the tempering temperature for 30 to 600 seconds, and then tempered by cooling to room temperature to obtain a steel wire. T1 [°C] = -r' [mm] × 16 + 580... The formula (iii) r' is a distance from the circumferential surface of the hot-rolled steel to the central axis in units of mm. (6) The method for producing a steel wire according to the above (5), wherein the chemical component may be selected from the group consisting of Al: 0.001 to 0.070%, Ti: 0.002 to 0.030%, and V: more than 0. 0.10% or less, Nb: more than 0 and 0.050% or less, Mo: more than 0 and 0.20% or less, and B: 0.0003 to 0.0030%, at least one or two or more of the groups.

Advantageous Effects of Invention According to the present invention, a steel wire rod having high tensile strength and relatively low tensile strength and low electrical resistivity is provided, and a steel wire material capable of producing a steel wire excellent in torsion property and a method for producing the same are provided.

MODE FOR CARRYING OUT THE INVENTION Hereinafter, a steel wire according to an embodiment of the present invention and a method for producing the same will be described.

The steel wire 1 of the present embodiment shown in Fig. 1 has a predetermined chemical composition, and the structure of the center portion 11 in the region from the central axis of the steel wire 1 to r × 0.5, and from the circumferential surface of the steel wire to The structure of the surface layer portion 12 of the region up to r × 0.1 is controlled to a predetermined shape. The r is the distance from the circumferential surface of the steel wire 1 to the central axis of the steel wire 1. First, the chemical composition of the steel wire rod according to the present embodiment will be described. The unit of chemical composition is mass%.

(C: 0.60 to 1.10%) C increases the fraction of stellite carbon in the ferritic structure of the steel, and at the same time refines the layered interval of the ferritic structure and enhances the strength of the steel wire. When the C content is less than 0.60%, it is difficult to obtain a wave amount of iron which is limited in the embodiment, and the strength of the steel wire rod is lowered. In order to make the amount of the Borne iron structure within the limits, the C content should be above 0.60%. The C content is preferably 0.65% or more, preferably 0.70% or more. On the other hand, when the C content exceeds 1.10%, the electrical conductivity of the steel wire is lowered, and at the same time, the precipitation of the ferritic carbon iron is formed and the ductility of the steel wire is lowered. Therefore, the upper limit of the C content is 1.10%. In order to improve the ductility of the steel wire, it is effective to reduce the amount of the precipitated ferritic carbon, so the C content is preferably 1.05% or less, preferably 1.00% or less, more preferably 0.95% or less.

(Si: 0.005 to 0.350%) Si is an element which improves the hardenability of the steel wire, and is an effective element for suppressing the formation of the precipitated carbon-carbon in the case of toughening, and is solid solution strengthening of the steel wire and Deoxidation is also an effective element. However, when the Si content is less than 0.005%, it becomes difficult to control the Borne iron structure to a predetermined configuration, and it is difficult to suppress the formation of the prostaglanded carbon-carbon in the case of suppressing the C content. Therefore, the lower limit of the Si content is 0.005%. On the other hand, Si segregates in the ferrite iron of the Borne iron structure, so that the electrical resistivity of the steel wire increases. If Si is contained in excess of 0.350%, the electrical resistivity of the steel wire material is significantly increased. Therefore, the Si content is limited to 0.005 to 0.350%.

The more the Si content, the greater the tensile strength of the steel wire and the lower the electrical conductivity of the steel wire. In the case of seeking a steel wire having a higher strength, the Si content of the steel wire may be 0.100 to 0.350%. At this time, as will be described later, the tensile strength TS (MPa) and the specific resistance ρ (μΩ·cm) of the steel wire rod desirably satisfy the following formula (1). ρ≦0.0155×TS+1.25......(1)

On the other hand, when a steel wire having a higher conductivity is sought, the Si content of the steel wire may be 0.005% or more and less than 0.100%. At this time, as will be described later, the tensile strength TS (MPa) and the specific resistance ρ (μΩ·cm) of the steel wire rod preferably satisfy the following formula (2). ρ≦0.0155×TS-0.95...(2)

Further, by increasing the Si content, the structure is controlled to a predetermined constitution, and the yield is improved, so that the Si content is preferably 0.010% or more, preferably 0.030% or more. Further, in order to obtain a steel wire and a steel wire having a lower electrical resistivity, the Si content is preferably 0.250% or less, preferably 0.200% or less, more preferably 0.150% or less.

(Mn: 0.10% to 0.90%) Mn is a deoxidizing element and has an action of fixing S in steel to MnS to suppress hot brittleness, and suppressing a decrease in electrical conductivity due to solid solution S. Further, Mn can improve the hardenability at the time of toughening of the steel wire rod, and lower the area ratio of the initial precipitated iron structure of the steel wire rod, and the effect of reinforcing the strength of the steel wire rod. However, when the Mn content is less than 0.10%, the effect of the aforementioned action will not be sufficiently obtained. Therefore, the lower limit of the Mn content is 0.10%. On the other hand, Mn lowers the electrical conductivity of steel. Therefore, the upper limit of the Mn content is 0.90%. Further, in order to sufficiently ensure the hardenability of the steel while ensuring the electrical conductivity, the upper limit of the Mn content is preferably 0.80% or less, more preferably 0.60% or less.

(Cr: 0.010% to 0.300% or less) Cr is an element which improves the hardenability, and is an element which reduces the layered interval of the ferrite and thereby increases the tensile strength of the steel wire. In order to obtain this effect, it is necessary to make the Cr content be 0.010% or more. The Cr content is preferably 0.020% or more. On the other hand, when a steel wire rod is produced in a toughening condition in which Cr distribution hardly occurs, there is a case where Cr may lower the electrical conductivity. In order to prevent a decrease in electrical conductivity, the upper limit of the Cr content is 0.300%. The Cr content is more preferably 0.250% or less.

In the steel wire rod of the present embodiment, the N, P, and S contents are further limited as described below. Since N, P, and S are not essential to the steel wire of the present embodiment, the lower limit of the N, P, and S contents is 0%.

(N: 0.0100% or less) N will reduce the ductility of steel by strain aging during cold working. In particular, when the N content exceeds 0.0100%, the ductility of the steel wire is lowered, and the electrical conductivity is also lowered. Therefore, the N content is limited 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) Although P helps to strengthen the solid solution of ferrite, it greatly reduces the ductility of the steel wire. In particular, when the P content exceeds 0.030%, the wire drawability when the steel wire is drawn into a steel wire is remarkably lowered. Therefore, the P content is limited to 0.030% or less. And the P content is preferably below 0.012%.

(S: 0.030% or less) S is an element which causes red hot brittleness and lowers ductility of steel. When the S content exceeds 0.030%, the ductility of the steel wire rod is remarkably lowered, so the S content is limited to 0.030% or less. And the S content is preferably below 0.010%.

In addition to the above-described elements, the steel wire of the present embodiment may contain one or two or more elements selected from the group consisting of Al, Ti, V, Nb, Mo, and B. However, since the steel wire of the present embodiment exhibits excellent characteristics without containing Al, Ti, V, Nb, Mo, and B, the lower limit of the contents of Al, Ti, V, Nb, Mo, and B is 0%.

(Al: 0 to 0.070%) Al is a deoxidizing element and is an element which fixes N by the formation of a nitride and refines the particle size of the Worthite iron. In order to obtain this effect, the Al content may be made 0.001% or more. Further, if Al is not fixed by nitride, but is present as free Al in the layered ferrite, the electrical conductivity of the steel wire is lowered. Therefore, the upper limit of the Al content is set to 0.070%. The Al content is preferably 0.060% or less, more preferably 0.050% or less.

(Ti: 0 to 0.030%) Ti is a deoxidizing element and is an element capable of refining the particle size of the Worthite iron by forming a carbonitride. In order to obtain this effect, the Ti content may be made 0.002% or more. On the other hand, when the Ti content exceeds 0.030%, there is a case where coarse nitride is mixed in the steel making stage, and there is a possibility that carbides are precipitated in the toughening treatment of the hot rolled steel, and the ductility of the steel wire is lowered. The situation. Therefore, the upper limit of the Ti content is made 0.030%. And the Ti content is preferably less than 0.025%.

(V: 0 to 0.100%) V is an element which improves hardenability, and the tensile strength of steel is raised by depositing a carbonitride. In order to obtain this effect, the V content may be made more than 0% or more. On the other hand, when the V content is excessive, the end of metamorphosis at the time of toughening becomes long, and coarse carbonitrides are precipitated, which further reduces the ductility and toughness of the steel wire. Therefore, the upper limit of the V content is 0.100%. And the V content is preferably 0.080% or less.

(Nb: 0 to 0.050%) Nb is an element which improves hardenability, and is an element which can refine the particle size of the Worthite iron by precipitation of a carbide. In order to obtain this effect, the Nb content may be made more than 0% or more. On the other hand, when the Nb content exceeds 0.050%, the metamorphic end time at the time of toughening becomes long. Therefore, the Nb content is made 0.050% or less. And the Nb content is preferably from 0.002 to 0.020%.

(Mo: 0 to 0.20%) Mo is an element which improves the hardenability and reduces the amount of iron in the initial precipitation. In order to obtain this effect, the Mo content may be made more than 0% or 0.02% or more. However, when the Mo content is excessive, the end time of metamorphosis at the time of toughening of the steel wire becomes long. Therefore, the upper limit of the Mo content is 0.20%. And the Mo content is preferably 0.10% or less.

(B: 0 to 0.0030%) B is an element which improves the hardenability, and is an element which suppresses the formation of the initial precipitated iron and increases the amount of iron. In order to obtain this effect, the B content may be made 0.0003% or more. On the other hand, when the B content exceeds 0.0030%, when the steel wire is toughened, M ₂₃ (C, B) ₆ is precipitated on the Worstian iron grain boundary in the supercooled state, and the ductility of the metal wire is impaired. Therefore, the B content should be 0.0003~0.0030%. The B content is preferably 0.0020% or less.

The remainder of the chemical composition of the steel wire of the present embodiment contains iron and impurities. The impurity means an element which is mixed from the raw material or the steel production step, and is allowed in a range which does not adversely affect the steel wire of the present embodiment.

Next, the structure of the steel wire rod of the present embodiment will be described. The target value of the tensile strength of the steel wire rod of the present embodiment is preferably 1050 MPa or more, preferably 1100 MPa or more. In order to obtain a steel wire having such tensile strength and having high electrical conductivity and ductility, the center portion 11 and the surface layer portion 12 of the steel wire 1 of the present embodiment must have a structure as described below. As long as the configurations of the center portion 11 and the surface layer portion 12 are appropriately controlled, it is not necessary to separately control the configuration of the transition region between the center portion 11 and the surface layer portion 12. Therefore, the configuration of the transition region of the steel wire rod of the present embodiment is not particularly limited. Further, the tensile strength of the steel wire rod of the present embodiment is not limited to the above-described target value, and can be set depending on the application.

(The organization of the center: contains 80 to 100% of the amount of Boron, and a total of 0% by area or less and less than 20% by area of the initial precipitation iron, toughened iron, smelting ferritic carbon and 麻田散铁Etc.) The center of the tissue contains 80 to 100% of the Borne iron structure, and a total of 0% by area or less and less than 20% by area of the initial precipitation iron, toughened iron structure, primary precipitation of ferritic carbon and Ma Tian Organizations other than the Borne iron such as iron. When the amount of the Bronze structure in the center portion is less than 80% by area, and the amount of the structure other than the Borne iron is 20% by area or more, sufficient tensile strength cannot be obtained. In order to further increase the tensile strength, the lower limit of the amount of ferrite in the center portion of the steel wire rod of the present embodiment may be 82 area%, 85 area%, 87 area%, 90 area%, or 92 area%. The upper limit of the amount of the structure other than the Borne iron may be 18 area%, 15 area%, 13 area%, 10 area%, or 8 area%. Since the center portion of the steel wire rod according to the present embodiment does not require a structure other than the iron, the upper limit of the amount of the ferrite in the center portion of the steel wire according to the present embodiment is 100% by area, and other than the Bora iron. The lower limit of the amount of tissue is 0 area%. However, in order to increase the yield, the upper limit of the amount of ferrite in the center portion of the steel wire rod of the present embodiment may be 99 area%, 98 area%, or 97 area%, and other than the Bora iron. The lower limit of the amount of the tissue may be 1 area%, 2 area%, or 3 area%.

(Surface structure: containing 70 to 100% by area of Borne iron) The surface layer structure contains 70 to 100% by area of Boron. In the surface layer portion and the center portion of the steel wire rod, the respective processing and heat history are different in the manufacturing stage and the heat treatment stage of the steel wire rod, and the actual metamorphic temperature is lower with respect to the center portion and the surface layer portion. Therefore, the amount of iron in the surface portion of the steel wire generally becomes less than the amount of iron in the center portion of the steel wire. However, when the amount of iron in the surface layer portion of the steel wire rod becomes less than 70%, the torsional properties of the steel wire rod deteriorate due to insufficient ductility of the surface portion of the steel wire rod. Therefore, the amount of iron in the surface layer portion of the steel wire rod of the present embodiment is set to 70 area% or more. The lower limit of the amount of ferrite in the surface portion of the steel wire may be 72 area%, 75 area%, or 80 area%. The structure of the surface layer portion of the steel wire according to the present embodiment is not necessary for the structure other than the pulverized iron. Therefore, the upper limit of the amount of ferrite in the surface layer portion of the steel wire according to the present embodiment is 100% by area, other than the Bora iron. The lower limit of the amount of tissue is 0 area%. However, in order to increase the yield, the upper limit of the amount of ferrite in the surface layer portion of the steel wire rod of the present embodiment may be 99 area%, 98 area%, or 97 area%, and the amount of tissue other than the ferrite. The lower limit may be 1 area%, 2 area%, or 3 area%. The structure other than the Borne iron contained in the surface layer portion of the steel wire rod is the same as the center portion of the steel wire rod, and is exemplified by the initial precipitation iron, the toughened iron structure, the preliminary precipitation of the ferritic carbon iron, and the Ma Tian iron. Description. However, since the surface layer portion of the steel wire rod is subjected to large processing deformation, there is a case where the surface layer portion of the steel wire rod is excessively deformed and the structure of the type cannot be determined. The amount of ferrite in the surface portion of the steel wire is a value that does not contain such an unrecognizable type of tissue.

Further, the Bora iron has a layered structure in which the ferrite iron and the swarf carbon iron are laminated in layers. In the present embodiment, the layered ferrite iron (the ferrite iron constituting the boehmite) and the layered smoky carbon iron (the swarf carbon iron constituting the boehmite) are the same as the above-mentioned preliminary precipitation ferrite and the initial Analysis of Xueming carbon iron is different.

(Average laminar spacing of the Wolla iron in the center portion: 50 to 100 nm) The average lamellar spacing of the Wolla iron structure in the center portion of the steel wire rod of the present embodiment is in the range of 50 to 100 nm. In the case where the distribution of the alloy elements toward the layered ferrite is equal, the smaller the layer spacing, the higher the conductivity. Therefore, the average lamellar spacing of the Wolla iron structure in the center portion of the steel wire rod is 100 nm or less. The upper limit of the average lamellar spacing of the ferrite structure at the central portion of the steel wire is preferably 98 nm, 95 nm, 93 nm, or 90 nm. On the other hand, in the case where the average lamellar spacing of the Bronze structure in the center portion is lower than 50 nm, the heat treatment condition is high, and since the amount of the alloying elements is high and the alloying elements are hard to be distributed, 50 nm is set as the lower limit.

(The average length of the layered stellite carbon in the center portion: 1.9 μm or less) The inventors of the present invention found the average length of the layered stellite in the center of the steel wire of the present embodiment and the steel wire. The conductivity is related, and the average length of the layered stellite carbon iron becomes shorter as the layered stellite carbon iron is broken, and the electrical conductivity of the steel wire becomes higher. When the average length of the layered stellite in the central portion of the steel wire exceeds 1.9 μm, the electrical conductivity of the steel wire is not sufficiently increased. Therefore, the average length of the layered stellite in the center of the steel wire of the present embodiment is set to 1.9 μm or less. The average length of the layered stellite in the center portion of the spun iron is preferably 1.8 μm or less, 1.6 μm or less, 1.5 μm or less, 1.4 μm or less, or 1.3 μm or less. In order to cut the layered stellite carbon in the center of the steel wire and to have an average length of 1.9 μm or less, as described later, the average wave size of the center portion of the steel wire must be set to 15 μm or more. And the method of manufacturing the steel wire must include tempering.

(The average wave size of the center portion is 15.0 to 30.0 μm.) As described above, the average length of the layered stellite in the center of the steel wire of the present embodiment is 1.9 μm or less. of. In order to obtain a steel wire having such a layered stellite carbon, as will be described later, it is necessary to temper the hot-rolled steel of the intermediate material of the steel wire under predetermined conditions after the toughening step of generating the ferritic iron. And disconnect the layered Xueming carbon iron. The inventors of the present invention found that the smaller the average wave size of the center portion, the more difficult it is to break the layered Xueming carbon iron during tempering.

In the portion grasped by the inventors of the present invention, when the average wave size of the center portion is less than 15.0 μm, the average length of the layered stellite in the center portion of the ferritic iron is 1.9 μm or less. It has become extremely difficult. Therefore, it is necessary to set the average wave block size of the center portion of the steel wire rod of the present embodiment to 15.0 μm or more. The average wave iron size of the center portion of the steel wire may be limited to 17.0 μm or more, 18.0 μm or more, or 20.0 μm or more.

On the other hand, the larger the average wave size of the center portion, the smaller the ductility of the steel wire becomes. By merely making the average wave size of the surface layer portion of the steel wire member small as described later, the ductility of the steel wire can be ensured without interfering with the breaking of the layered stellite carbon of the steel wire. However, if the average wave size of the center portion exceeds 30.0 μm, the ductility of the steel wire cannot be satisfactorily maintained even if this feature is utilized. Therefore, it is necessary to set the average wave size of the center portion to 30.0 μm or less. The average wave size of the center portion may be limited to 27.0 μm or less, 25.0 μm or less, or 20.0 μm or less.

(Average wave size of the surface layer: 0.40 times or more and 0.87 times or less of the average wave size of the center portion) Metal wire (steel wire) obtained by wire drawing of steel wire, surface layer of steel wire The organization will greatly affect the ductility to torsional deformation. By refining the size of the wave iron in the surface layer portion of the steel wire rod, the unevenness of the structure can be suppressed, and the ductility of the metal wire obtained by the wire drawing process of the steel wire can be improved. However, as described above, if the size of the entire iron wire of the steel wire rod is made fine, the breakage of the layered stellite carbon iron is hindered. Therefore, it is necessary to refine the waved iron in the surface layer portion so that the ratio of the average wave to the iron block size in the center portion of the iron block size with respect to the average wave of the surface layer portion (hereinafter sometimes referred to as "PBS ratio" ") becomes 0.87 or less. Thereby, the ductility of the steel wire (and the ductility of the wire produced by the wire drawing process of the steel wire) can be ensured without hindering the breaking of the layered stellite. The PBS ratio is more preferably set to 0.85 or less. Further, the lower limit of the PBS ratio is not particularly limited. However, since it is difficult to make the PBS ratio lower than 0.40 in view of equipment capability, the lower limit value of the PBS ratio can be set to 0.40, 0.50, or 0.60. .

Further, in the steel wire rod (hereinafter abbreviated as "low Si steel wire rod") having a Si content of 0.005% or more and less than 0.100%, the PBS ratio is preferably 0.80 or less. Fig. 3 is a graph showing the relationship between the PBS ratio of the low Si steel wire and the twist value of the metal wire obtained from the low Si steel wire. The inventors of the present invention manufactured various low-Si steel wires and measured the relationship between the PBS ratio of these low-Si steel wires and the twist value of the metal wires obtained from such low-Si steel wires. As a result, as shown in FIG. 3, it is understood that the smaller the PBS ratio of the low Si steel wire, the larger the twist value of the metal wire, and particularly when the PBS ratio is 0.80 or less, the twist value of the metal wire is remarkably improved. When the Si content is less than 0.10%, the growth rate of the bucks iron block becomes faster and the size of the iron nuggets becomes easier to coarsen. Therefore, when compared with the center portion, the PBS is compared with the absolute value of the PBS. The comparison is suitable as an indicator of the ductility of the surface organization. Further, the metal wire obtained from the low Si steel wire having a PBS ratio of more than 0.87 was subjected to layer peeling in the test.

Furthermore, in the case of a steel wire having a Si content of 0.100 to 0.350% (hereinafter referred to as "high-Si steel wire"), it is preferable to set the average wave size of the surface layer of the steel wire (surface PBS). It is more preferably 17.0 μm or less and 16.0 μm or less. Fig. 4 is a graph showing the relationship between the surface layer PBS of the high Si steel wire and the twist value of the metal wire obtained by the steel wire. The inventors of the present invention manufactured various high-Si steel wires, and measured the torsion values of the surface PBS of the high-si steel wire and the wire obtained by the high-si steel wire. As a result, as shown in FIG. 4, it is understood that the smaller the surface layer PBS of the high-Si steel wire rod is, the larger the twist value of the metal wire is. In particular, when the surface layer PBS is 17.0 μm or less, the twist value of the metal wire is remarkably improved.

In the steel wire rod of the present embodiment, from the viewpoint of improving both the strength and the electrical conductivity of the steel wire of the ACSR, the tensile strength TS of the steel wire of the formula (1) should be used in the high Si steel wire ( The relationship between MPa) and resistivity ρ (μΩ•cm) should be governed by the formula (2) in low-Si steel wires. ρ≦0.0155×TS+1.25...(1) ρ≦0.0155×TS-0.95...(2)

High Si steel wire is used for articles that are not critical to electrical conductivity but require high tensile strength. Low-Si steel wire is used for products where the limitation on tensile strength is not critical, but high conductivity is required. In view of the difference in such applications, in high-Si steel wire and low-Si steel wire, different formulas should be used to regulate the relationship between tensile strength and electrical resistivity. Since the steel wire of the present embodiment has the above-described various characteristics, it has tensile strength and electrical resistivity satisfying the formula (1) or (2).

Next, a method of specifying the structure of the steel wire of the present embodiment will be described. Hereinafter, a cross section parallel to the longitudinal direction of the steel wire and including the central axis of the steel wire is referred to as an L cross section, and a cross section perpendicular to the longitudinal direction of the steel wire is referred to as a C cross section.

The average lamellar spacing of the Wolla iron in the center portion 11 is obtained by mirror-grinding the L-section of the steel wire, etching through a picral, and using FE-SEM (field emission scanning). Electron microscopy) The tissue observation was performed and the results of the tissue observation were analyzed. The tissue observation was performed at the nine observation positions 13 shown in FIG. The observation position 13 in the L section of the steel wire 1 is disposed at the apex, the center, and the midpoint of the four sides of the rectangular area, the rectangular area being the length of the four sides equal to the radius r of the steel wire 1, and the two sides being parallel to the steel wire 1 The length direction is centered on the central axis 14 of the steel wire 1. At each of the observation positions 13, a region in which 30% or more of the aspect ratio of the stellite-shaped carbon-iron was 30% or more was avoided, and the cross-sectional surface was photographed by FE-SEM at a magnification of 10,000 times. Image analysis of the electronic image of the shooting area and binarization of the layered stellite carbon iron portion, eliminating and linearizing the thickness, further drawing a vertical line or a horizontal line on each pixel of the electronic image to be stellite carbon 1/2 of the average of the divided line segments is taken as the average layered interval. In addition, the average layered interval is based on the principle described in "Measurement Morphology" (Murashima, etc., issued on July 30, 2014, Uchida, Otsuka) p115~p117. The average value of the average layered intervals in the nine FE-SEM images of the nine observation positions 13 can be regarded as the average layer interval of the center portion of the steel wire.

Further, the average length of the layered stellite in the Borne structure of the center portion 11 is obtained by the following procedure. In the FE-SEM image captured as described above, the layered stellite carbon iron portion was binarized in the same manner as described above, and the layered stellite carbon contained in the FE-SEM image was calculated by image analysis. The average length of iron. Then, the average of the average layered stellite carbon lengths in the nine FE-SEM images of the nine observation positions 13 can be regarded as the average length of the layered stellite carbon in the center portion.

Further, the rate of the Borne iron structure in the center portion is obtained by the following procedure. For the nine observation positions 13 of the average layer interval of the cross section of the steel wire described above, a photograph of the metal structure was taken at a magnification of 2000 times. In each of the photographs, the tissue portion other than the Borne iron was lined up, and the area ratio was measured by image analysis. The difference in the area ratio of the tissue portion other than the entire wave of iron is the area ratio of the wave iron in each photograph. The average value of the area ratio of the Borne iron in each of the photographs can be regarded as the rate of the Borne iron structure at the center portion.

The rate of the Borne iron structure of the surface layer portion from the circumferential surface of the steel wire rod to the region of r × 0.1 was obtained by the following procedure. In the C section of the steel wire (the section perpendicular to the rolling surface), a photograph of the metal structure centered on the circumferential surface of the steel wire to a depth of r × 0.05 was taken at a magnification of 2,000 times at at least four positions. The photographing position is preferably equally arranged along the outer circumference of the C section. For example, when the photographing position is four positions, it is preferable to arrange it every 90 degrees along the outer circumference of the C section. The area ratio of the ferritic iron in the photograph of the metal structure can be obtained by the same method as the method of measuring the composition of the ferritic structure in the center. The average value of the area ratio of the Bronze in each photograph can be regarded as the wave-to-iron structure ratio of the surface layer portion.

The average wave block size of the center portion and the surface portion of the steel wire rod is obtained by EBSD (Electron Backscatter Diffraction Image Method). The average wave iron size of the center portion is obtained by using the following observation points: for the nine observation positions 13 shown in FIG. 2 of the L section of the steel wire, the field of view size is 250 μm×250 μm, and the EBSD method is used to measure each field of view. The average wave size of the iron is calculated, and then the average of the average wave size of each field of view is calculated. Further, in the measurement, a region surrounded by a boundary having a difference in orientation of 9 or more was regarded as one wave of iron nuggets, and analyzed by a measurement method of Johnson-Saltykov. The average wave-shaped iron block size of the surface layer portion is obtained by measuring at least four observation positions of the C-section of the steel wire material which are equally arranged along the outer circumference of the C-section, and measuring the same as the center portion. The center of the measurement field of view was set to be from the circumferential surface of the steel wire to a depth of r × 0.05.

The electrical resistance of the steel wire is measured by the following procedure. After removing the scale of the steel wire surface layer and correcting it into a straight rod, the electric resistance was measured by a 4-terminal method. The length and current value to be measured are selected within the range where the temperature of the steel wire does not change due to energization, and the effective number is measured to the third position.

Next, a method of manufacturing the steel wire rod of the present embodiment will be described. The method for producing a steel wire according to the present embodiment includes a step S1 of casting a cast piece, a step S2 of heating the cast piece, and a step S3 of maintaining the temperature of the heated cast piece as shown in Fig. 5; Step S4 of preparing the hot-rolled steel by hot rolling, and step S5 of performing the water-cooling of the hot-rolled steel; and step S6 of winding the hot-rolled steel after the water cooling; and the heat after the coiling Step S7 of rolling the steel toughening; and step S8 of tempering the toughened hot-rolled steel to obtain a steel wire. The manufacturing conditions are explained in detail below.

(Casting S1) In the method for producing a steel wire according to the present embodiment, first, after the steel is melted, a cast piece having the chemical composition of the steel wire of the present embodiment is produced by continuous casting or the like. Before the hot rolling to be described later, the cast piece may be subjected to block rolling to obtain a steel sheet.

(heating S2: heating temperature 1150 ° C or more and 1250 ° C or less) (holding S3: holding time at the above heating temperature for 600 seconds or more and 7200 seconds or less) The slab is heated to fall before the hot rolling is performed. The heating temperature in the range of 1150 to 1250 ° C is then maintained at this heating temperature for 600 seconds or more. Further, the maximum temperature of the slab in the heating S2 is referred to as a heating temperature. When the heating and holding under the conditions are not performed, the solid solution of the carbonitride contained in the cast piece becomes insufficient, and the average wave block size at the center portion becomes outside the above-mentioned limit range. Further, if the average wave size of the central portion is not within the predetermined range as described above, the splitting of the layered stellite will not proceed, so when the heating and holding under this condition is not performed, the center portion The average stellite carbon iron of the layered stellite carbon iron is also outside the above range, and the electrical conductivity of the steel wire is impaired. Further, from the viewpoint of suppressing decarburization, the holding time is preferably 7200 seconds or less.

(Hot Rolling S4: Finishing Temperature: 950° C. or more and 1050° C. or less) The steel sheet which is cooled once after the cast piece is rolled and held again by heating is subjected to hot rolling to become hot rolled steel. The finishing temperature must be set to 950 ° C to 1050 ° C in the hot rolling. When the finishing temperature is not suitable, the average wave size of the center will become outside the limits. The reason for this is that when the finishing temperature exceeds 1050 ° C, the Worthfield iron particles after the hot rolling is coarsened, so that the ferrite is not sufficiently formed in the subsequent cooling, and thus the surface layer portion cannot be obtained. For the case of ductility, when the finishing temperature is lower than 950 ° C, it is difficult to reduce the size ratio of the surface portion to the center portion of the wave iron block within the limit.

(Water-cooling S5: Cooling stop temperature: 780°C or more and 840°C or less) (Winding S6: Winding temperature: 780°C or more and 840°C or less) (Toughening S7: Within 9 to 25 seconds from the end of winding to the start of immersion, The molten salt temperature is 450 ° C or more and T1 ° C or less, and the immersion time is 20 to 200 seconds. Next, the hot rolled steel after completion rolling is water-cooled and wound up. The water cooling stop temperature and the coiling temperature are set in the range of 780 to 840 °C. Next, the coiled hot-rolled steel is toughened by immersing in a molten salt having a temperature of 450 ° C or more and T 1 ° C or less for 20 seconds or more within 9 to 25 seconds after coiling. T1 is a value defined by the following formula (3). The symbol "r'" included in the formula (3) represents the radius of the hot rolled steel (that is, the radius of the hot rolled steel) in units of mm. In order to control the composition of the iron and iron of the steel wire, water cooling, coiling and toughening are the most important. Further, from the viewpoint of productivity, the immersion time for the molten salt is preferably 200 seconds or less. T1[°C]=-r’[mm]x16+580...(3)

When the water cooling stop temperature and the coiling temperature, and the time from the end of the winding to the start of the immersion are outside the above range, the average wave size of the surface portion of the steel wire does not become the average wave of the center portion. The size is less than 0.87 times. The reason for this is because the particle size of the Worthite iron in the surface layer is coarsened, and the size of the Brest iron block is also coarsened. Further, the water cooling starts immediately after the end of the hot rolling. Therefore, the water cooling start temperature becomes substantially the same as the above-described finishing temperature. When the water cooling start temperature is lower than 950 ° C, it is also estimated that the composition of the wave iron is not moderately controlled.

When the molten salt temperature is outside the above range, the amount of ferrite in the center portion of the steel wire becomes less than 80 area%, or the average layered interval of the waved iron in the center portion of the steel wire becomes more than 100 nm. The reason for this is because when the temperature of the molten salt is lower than 450 ° C, the formation of the toughened iron structure becomes dominant, so the rate of the iron-to-iron structure is reduced, and when the temperature of the molten salt is above the temperature of T1, the layered interval is changed. It is thick and becomes more than 100 nm. Further, when the immersion time is outside the above range, since the subsequent step is performed in a state where the ferromagnetic metamorphosis is not completed, it becomes impossible to control the wave fraction or the layer interval.

(tempering S8: tempering temperature 540 ° C ~ 600 ° C, tempering time 30 ~ 600 seconds) The toughened hot rolled steel is tempered by: heating to a temperature range above 540 ° C The tempering temperature is maintained at this tempering temperature for 30 seconds or more and then cooled to room temperature. Also, from the viewpoint of productivity, the tempering time should be 600 seconds or less. Further, if the tempering temperature is too high, the strength of the steel wire rod is insufficient due to excessive tempering, so the tempering temperature is set to 600 ° C or lower. Further, the tempering temperature is the highest heating temperature in the tempering S8, and the tempering time is the time during which the temperature of the hot-rolled steel is maintained at the tempering temperature.

By the tempering under the above conditions, the layered stellite carbon in the center portion was cut, and the steel wire having an average stellite carbon iron having a length of 1.9 μm or less in the center portion of the stellite carbon-iron was obtained. Since the layered stellite carbon iron is not sufficiently cut when at least one of the tempering temperature and the tempering time is insufficient, the average stellite carbon of the layered stellite carbon in the center of the steel wire becomes more than 1.9 μm, the electrical conductivity of the steel wire was damaged. When the tempering temperature is too high, the strength will decrease.

Since the steel wire rod of the present embodiment has the following characteristics, it has high tensile strength and electrical conductivity: the center portion contains 80 to 100% by area of the pulverized iron, and the average layered interval of the pulverized iron at the center portion is 50 Å. The average snow-capped carbon iron length of the layered stellite carbon iron at 100 nm is 1.9 μm or less. Since the high tensile strength and electrical conductivity due to these characteristics are maintained after the wire drawing process of the steel wire rod, the steel wire obtained by drawing the steel wire of the present embodiment has high tensile strength. And conductivity. Furthermore, since the steel wire of the present embodiment has a feature that the average wave size of the surface layer portion is 0.87 times or less the average wave size of the center portion, the ductility of the surface layer portion is good. Therefore, the steel wire obtained by drawing the steel wire of the present embodiment is excellent in torsional properties. In other words, according to the steel wire rod of the present embodiment, a steel wire excellent in tensile strength, electrical conductivity, and torsion property can be obtained.

EXAMPLES Next, examples of the invention will be described. The conditions in the examples are examples of conditions used to confirm the workability and effects of the present invention, and the present invention is not limited to such a condition. The present invention can be formed by various conditions as long as the object of the present invention can be achieved without departing from the gist of the present invention.

The steel of the chemical composition shown in Tables 1 and 2 was cast to obtain a cast piece of 300 mm × 500 mm. In Tables 1 and 2, the values below the level generally regarded as impurities are indicated by the symbol "-". These cast pieces were formed into steel sheets of a 122 mm square section by block rolling. The steel sheets were heated to the heating temperatures shown in Tables 3 and 4 and held at this heating temperature for a certain period of time. The holding time at the heating temperature is between 900 and 1200 seconds. After heating and temperature maintenance, the steel sheets were hot rolled at the finishing temperatures shown in Tables 3 and 4, and hot rolled steel having a wire diameter (diameter) shown in Tables 3 and 4 was formed. The hot rolled steel was water-cooled to the coiling temperatures shown in Tables 3 and 4 and coiled. Thereafter, the hot-rolled steel was immersed in a salt bath having the salt temperatures shown in Tables 3 and 4 to be toughened within 9 seconds to 25 seconds from the coiling, and the ferrite was metamorphosed. The immersion time of the hot rolled steel in the salt bath was set to 30 seconds. Thereafter, after the temperature is maintained by the tempering temperatures shown in Tables 3 and 4, and the tempering time shown in Tables 3 and 4 is maintained, the hot-rolled steel is cooled to room temperature and tempered to obtain a steel. Wire.

The steel wires produced are shown in Tables 5 and 6.

The amount of ferrite contained in the center portion of the steel wire rod (the wave-to-iron structure ratio at the center portion) was obtained by taking the FE section of the steel wire rod and photographing the nine shown in Fig. 2 using FE-SEM. The photograph of the tissue at the observation position specifies the non-Bourne region included in the photographs of each organization, and the area ratio of the non-Bope region of each organization photograph is obtained by image analysis, and each area is calculated based on the area ratio of the non-wave iron region. Organize the photo-rate of the area of the Bronze, and then average the rate of the area of the waves of the organizations. The amount of ferrite contained in the surface layer portion of the steel wire rod (the wave-to-iron structure ratio in the surface layer portion) was obtained by photographing the structure of four observation positions using FE-SEM in the C section of the steel wire rod. The four observation positions are uniformly arranged along the outer circumference of the C section, and the depth from the circumferential surface of the steel wire rod is r × 0.05, and the non-wave iron region included in each tissue photograph is determined. Through the image analysis, the area ratio of the non-Bourne region of each organization's photograph is obtained, and the area ratio of the wave iron of each organization's photograph is calculated based on the area ratio of the non-wave iron region, and the average area ratio of the wave-like iron of each organization photograph is averaged. .

The average wave iron block size (center PBS) at the center of the steel wire rod was obtained by using the following observation points: for the nine observation positions 13 shown in Fig. 2 of the L section of the steel wire rod, the field of view size was 250 μm × 250 μm, and EBSD was used. The method measures the average wave size of the iron in each field of view, and then calculates the average of the average wave size of each field of view. In the measurement, a region surrounded by a boundary having a difference in orientation of 9 or more was regarded as one wave of iron nuggets, and analyzed by a measurement method of Johnson-Saltykov. The average wave iron block size (surface layer PBS) of the steel wire surface layer portion is obtained by at least four observation positions and the center portion of the C-section of the steel wire material which are equally arranged along the outer circumference of the C-section. The measurement was carried out in the same manner. The center of the measurement field of view was set to be from the circumferential surface of the steel wire to a depth of r × 0.05. The ratio of the average wave block size of the surface portion of the steel wire to the average wave block size of the center portion of the steel wire (surface layer/center PBS ratio) is obtained by dividing the center PBS by the surface layer PBS. Further, in the steel wire rod in which the amount of ferrite is deviated from the limit of 5% or more of the present invention, the measurement of the average wave size of the iron block is omitted. Therefore, the surface PBS and/or the center PBS and the PBS ratio of the steel wire having the amount of the Bored iron outside the limits of the present invention are indicated by oblique lines.

The average lamellar spacing (average lamellar spacing) of the Wolla iron at the center of the steel wire is obtained by taking the FE observation at the nine observation positions shown in Fig. 2 in the L section of the steel wire. The photographs were collected, and the average layered interval of the Borne iron contained in the photographs of each organization was obtained by the above image analysis, and the average layered intervals in the photographs of the respective tissues were further averaged.

The average length of the layered stellite carbon in the center of the steel wire (average stellite carbon length) is obtained by: in the L section of the steel wire, the FE shown in Fig. 2 is taken by FE-SEM. Observe the photo of the tissue at the position, and obtain the average length of the layered ferritic carbon iron contained in the photo of each organization by the above image analysis, and then average the average length of the layered stellite in the photos of each organization. .

Tables 7 and 8 show the mechanical properties and electrical characteristics of the obtained steel wire and the wire obtained by dry-drawing the steel wire with a true strain ε = 2.2.

The tensile strength TS of the steel wire rod was determined by a tensile test. For each steel wire rod, the tensile test piece was made up of three pieces each having a length of 350 mm, and each tensile test piece was subjected to a tensile test at a tensile speed of 10 mm/min at normal temperature, and three tensile test pieces were pulled. The average of the tensile strength is set to the tensile strength of the steel wire. In the present embodiment, it is judged that the steel wire having a tensile strength of 1050 MPa or more has sufficient tensile strength.

The electrical resistivity ρ of the steel wire rod was determined by taking a test piece having a length of 60 mm from the steel wire and measuring the specific resistance of the test piece by a four-terminal method at normal temperature. The steel wire having a specific resistance equal to or lower than the specific resistance limit value regulated by the above formula (1) or (2) is judged to have a relatively low electrical resistivity with respect to tensile strength and a sufficient electrical conductivity. Moreover, the formula (1) is applied to the high Si steel wire, and the formula (2) is applied to the low Si steel wire. For reference, the numerical formula (the limit value calculation formula) to which each steel wire is applied is also shown in Tables 7 and 8 in the equations (1) and (2).

Furthermore, the steel wire was subjected to a dry wire drawing of a true strain ε = 2.2 as described above to form a metal wire, and the wire was evaluated. The wire drawing condition is to set the average shrinkage ratio of each pass to 17%. The obtained metal wire was subjected to a torsion test in which the puncture distance was 100 times the wire diameter and the torsion speed was 20 rpm, and the average value (torsion value) of the number of breakage breaks and the presence or absence of longitudinal cracking (layer peeling) were confirmed. ). Again, the number of times is calculated in 0.5 units. A steel wire material having a twisting value of 24.5 or more and a metal wire material which is not peeled off in the torsion test is judged to be a steel wire which can obtain a metal wire having excellent torsional characteristics.

[Table 1]

[Table 2]

[table 3]

[Table 4]

[table 5]

[Table 6]

[Table 7]

[Table 8]

In Tables 1 to 6, the bottom line is added to the values outside the scope of the present invention. In the case of the test numbers 41 to 61 in which the conditions are limited by the present invention, the at least one characteristic does not reach the target value. With respect to this, the test numbers 1 to 40 satisfying all the conditions restricted in the present invention are values in which all of the above characteristics are set as the target.

1‧‧‧Steel wire
11‧‧‧ Central Department
12‧‧‧ Surface Department
13‧‧‧ observation position
14‧‧‧ center axis
R‧‧‧ Radius

Fig. 1 is a cross-sectional view along the line C of the steel wire rod of the embodiment. Fig. 2 is a view showing a measurement position of an L-section of the steel wire rod of the present embodiment and an average length of the layered stellite carbon in the ferrite structure. Fig. 3 is a graph showing the ratio of the average wave-to-iron particle diameter of the surface layer portion of the steel wire material having a Si amount of less than 0.100% to the average wave-to-iron particle diameter of the center portion (PBS ratio), and is made of steel wire A graph of the relationship between the torsion values of the resulting metal wires. 4 is a graph showing the relationship between the average wave iron block size (surface layer PBS) and the twist value of the metal wire in the surface layer portion of the steel wire rod having a Si amount of 0.100 to 0.350%. Fig. 5 is a flow chart showing a method of manufacturing the steel wire rod of the embodiment.

Claims (6)

A steel wire characterized by having a chemical composition of C: 0.60 to 1.10%, Si: 0.005 to 0.350%, Mn: 0.10 to 0.90%, Cr: 0.010 to 0.300%, and N: 0.0100% or less per unit mass%; P: 0.030% or less, S: 0.030% or less, Al: 0 to 0.070%, Ti: 0 to 0.030%, V: 0 to 0.100%, Nb: 0 to 0.050%, Mo: 0 to 0.20%, and B: 0 to 0.0030%, and the remainder is composed of Fe and impurities. When the distance from the circumferential surface to the central axis is r in units of mm, the tissue in the center portion of the region from the central axis to r × 0.5 Containing 80 to 100% by area of Boron, and a total of 0% by area or less and less than 20% by area of the initial precipitation iron, the primary precipitation of ferritic carbon, the granulated iron and the toughened iron; The average layered spacing of the ferrite is 50 to 100 nm; the average length of the layered stellite in the center portion is 1.9 μm or less; and the average wave size of the center portion is 15.0 to 30.0 μm; The structure in the surface layer portion of the region from the circumferential surface to the range of r × 0.1 includes 70 to 100% by area of the above-mentioned wave iron; and the average wave iron block size of the surface layer portion is the center portion The average size of said iron waves of 0.40 times, 0.87 times or less. The steel wire according to claim 1, wherein the chemical composition is Si: 0.100 to 0.350% by mass%; the average wave size of the surface layer is 17.0 μm or less; and the steel wire is stretched. The relationship between the strength TS [MPa] and the specific resistance ρ [μΩ‧cm] satisfies the following formula (1): ρ ≦ 0.0155 × TS + 1.25 (1). The steel wire of claim 1, wherein the chemical composition is Si: 0.005% or more and less than 0.100% by mass%; and the average wave size of the surface layer is the average wave of the center portion Further, the relationship between the tensile strength TS [MPa] of the steel wire and the specific resistance ρ [μΩ‧cm] satisfies the following formula (2): ρ≦0.0155×TS-0.95... (2). The steel wire according to any one of claims 1 to 3, wherein the chemical component is selected from the group consisting of Al: 0.001 to 0.070%, Ti: 0.002 to 0.030%, V: more than 0, and 0.100%. Hereinafter, at least one or two or more of Nb: more than 0 and 0.050% or less, Mo: more than 0 and 0.20% or less, and B: 0.0003 to 0.0030%. A method for producing a steel wire characterized by comprising the step of casting a cast piece, wherein the chemical composition of the cast piece contains C: 0.60 to 1.10%, Si: 0.005 to 0.350%, and Mn: 0.10 to 0.90% by mass%. Cr: 0.010 to 0.300%, N: 0.0100% or less, P: 0.030% or less, S: 0.030% or less, Al: 0 to 0.070%, Ti: 0 to 0.030%, V: 0 to 0.100%, Nb: 0 ~0.050%, Mo: 0~0.20%, and B: 0~0.0030%, and the remainder is composed of Fe and impurities; heating the cast piece to a heating temperature in a temperature range of 1150 ° C or more and 1250 ° C or less a step of maintaining the temperature of the slab at the heating temperature for 600 to 7200 seconds; and the step of preparing the hot-rolled steel by subjecting the slab after the holding to hot rolling to a finishing temperature of 950 ° C to 1050 ° C or less a step of water-cooling the hot-rolled steel to a temperature range of 780° C. or more and 840° C. or less; and winding the hot-rolled steel after the water-cooling in a temperature range of 780° C. or higher and 840° C. or lower; The above-mentioned hot-rolled steel is in the range of 450 ° C or more within 9 to 25 seconds after the above-mentioned winding, and is as follows (3) a step of toughening by immersing the molten salt at a temperature lower than T1 ° C for 20 to 200 seconds; and heating the toughened hot-rolled steel to a temperature range of 540 to 600 ° C The tempering temperature is maintained at the tempering temperature for 30 to 600 seconds, and then tempered by cooling to room temperature to obtain a steel wire. T1[°C]=-r'[mm]×16+580... (3) r' is the distance from the circumferential surface of the hot-rolled steel to the central axis in mm. The method for producing a steel wire according to claim 5, wherein the chemical component is selected from the group consisting of Al: 0.001 to 0.070%, Ti: 0.002 to 0.030%, V: more than 0, and 0.100% or less, Nb. : at least one or two or more of the group consisting of more than 0 and 0.050% or less, Mo: more than 0 and 0.20% or less, and B: 0.0003 to 0.0030%.