Wire rod, steel wire and method for manufacturing thereof

Abstract

A wire rod according to the present invention comprises, in weight%, 1.00-1.20% of C, 1.00-1.50% of Si, 0.10-0.50% of Mn, 0.30-0.80% of Cr, and 0.50-1.50% of Al, and the remainder being Fe and other inevitable impurities, wherein the microstructure observed in the cross section 1 / 2D to 3 / 2D (D: diameter) includes, as an area fraction, 95% or more of pearlite, and includes 5% or less of massive proeutectoid cementite having, in an area of 100 ㎛{2, an average thickness of 1 ㎛ or more.

Description

Wire rod, steel wire and method of manufacturing the same

[0001] The present invention relates to a high-strength wire rod and steel wire applicable to bridge cables such as suspension bridges and cable-stayed bridges, and steel wires for reinforcing concrete, and a method for manufacturing the same, and relates to a wire rod and steel wire and a method for manufacturing the same, which suppresses the formation of massive pro-eutectoid cementite at grain boundaries by adding aluminum to carbon steel having 1.0% C or more, thereby securing drawability and torsional properties.

[0002] Cables and other materials are used to connect piers and decks in suspension or cable-stayed bridges. These are either twisted strands or bundles of multiple strands connected in parallel. Bridge cables also require high strength, as increasing the strength of the steel wires reduces the amount of material actually used and shortens the construction period.

[0003] The high-strength steel wire is based on an empirical formula proposed by Embury et al. in the 1960s. According to this formula, the most effective methods for improving strength include: 1) increasing the material's strength, 2) improving the work-hardening rate by refining the initial structure, which can impede dislocation movement, and 3) increasing the amount of wire drawing.

[0004] The main use of alloying elements is to increase the strength of the material and improve the work hardening rate by controlling the structure. C has the effect of solid solution strengthening and precipitation strengthening, Cr reduces C diffusion in austenite and increases the nucleation sites, thereby refining the structure and increasing the drawability, and Si plays a role in increasing the initial strength by strengthening the solid solution in ferrite and refining the pearlite structure. Lastly, increasing the draw amount is an efficient way to increase the strength. The strength increases exponentially when the draw amount increases, and this is because the pearlite structure rotates completely in the drawing direction to form a fiber-like structure. As the draw amount increases, the content of carbon existing in cementite that diffuses into ferrite increases, and when this carbon becomes supersaturated in ferrite, it acts like martensite, and the formation of this structure greatly increases the strength.

[0005] The present invention relates to a high-strength wire rod and steel wire applicable to bridge cables such as suspension bridges and cable-stayed bridges, and steel wires for reinforcing concrete, and a method for manufacturing the same, and the purpose of the present invention is to provide a wire rod and steel wire and a method for manufacturing the same, in which bulky proeutectoid cementite formed at grain boundaries is suppressed by adding aluminum to carbon steel having 1.0% C or more, thereby securing drawability and torsional properties.

[0006] According to one embodiment of the present invention, a wire rod includes, in wt%, C: 1.00% to 1.20%, Si: 1.00% to 1.50%, Mn: 0.10% to 0.50%, Cr: 0.30% to 0.80%, and Al: 0.50% to 1.50%, the remainder being Fe and other unavoidable impurities, and a microstructure observed in a cross-section of 1 / 2D to 3 / 2D (D: diameter) includes pearlite at an area fraction of 95% or more, and massive proeutectoid cementite having an average thickness of 1 ㎛ or more is 100 ㎛. 2 Includes less than 5% of the area.

[0007] Additionally, the wire according to one embodiment of the present invention may have an average tensile strength of 1630 MPa or more at room temperature.

[0008] Additionally, the wire according to one embodiment of the present invention may have a cross-sectional reduction ratio of 14% or more.

[0009] Additionally, the wire according to one embodiment of the present invention may have an average scale thickness of 20 μm or less.

[0010] A method for manufacturing a wire rod according to another embodiment of the present invention comprises the steps of: preparing a billet containing, in wt%, C: 1.00% to 1.20%, Si: 1.00% to 1.50%, Mn: 0.10% to 0.50%, Cr: 0.30% to 0.80%, and Al: 0.50% to 1.50%, with the remainder being Fe and other unavoidable impurities; heating and hot-rolling the billet; coiling it at Acm+20°C to Acm+100°C; and stellmore cooling it to 350°C to 400°C at 8°C / s to 12°C / s.

[0011] According to another embodiment of the present invention, a steel wire comprises, in wt%, C: 1.00% to 1.20%, Si: 1.00% to 1.50%, Mn: 0.10% to 0.50%, Cr: 0.30% to 0.80%, and Al: 0.50% to 1.50%, the remainder being Fe and other unavoidable impurities, and after Zn plating, the tensile strength of the plating wire is 2250 MPa or more, the torsion is 13 times or more, and the elongation is 6.5% or more.

[0012] A method for manufacturing a steel wire according to another embodiment of the present invention comprises the steps of: preparing the above-described wire material; performing pickling and constant temperature heat treatment; performing freshening at a freshening amount of 77% to 85%; and performing Zn plating.

[0013] According to the present invention, it is possible to manufacture an ultra-high strength steel wire using a hypereutectoid wire with added aluminum, and by applying this to a bridge cable, it is effective in reducing the amount of cable used and shortening the air shortening.

[0014] Figure 1 is a photograph of the microstructure at the center of the cross-section of the wire of Invention Example 1 taken using a scanning electron microscope (SEM).

[0015] Figure 2 is a photograph of the microstructure at the center of the cross-section of the wire of Comparative Example 1 taken using a scanning electron microscope (SEM).

[0016] Preferred embodiments of the present invention are described below. However, the embodiments of the present invention may be modified in various ways, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0017] The terminology used in this application is solely for the purpose of describing specific examples. Therefore, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Additionally, it should be noted that terms such as "comprise" or "have" used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the presence of other features, steps, functions, components, or combinations thereof.

[0018] Meanwhile, unless otherwise defined, all terms used herein should be considered to have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Therefore, unless explicitly defined herein, specific terms should not be interpreted in an overly idealistic or formal sense.

[0019] In addition, the terms "about", "substantially", etc. in this specification are used in the sense of or close to the numerical value when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly using the disclosure in which exact or absolute numerical values ​​are mentioned to aid understanding of the present invention.

[0020] Unless otherwise specifically stated herein, percentages indicating the content of each element are based on weight.

[0021] First, the wire according to the present invention will be described.

[0022] According to one embodiment of the present invention, a wire includes, in weight %, C: 1.0% to 1.2%, Si: 1.0% to 1.5%, Mn: 0.1% to 0.5%, Cr: 0.3% to 0.8%, and Al: 0.5% to 1.5%, the remainder being Fe and other unavoidable impurities, and a microstructure observed in a cross-section of 1 / 2D to 3 / 2D (D: diameter) includes pearlite at an area fraction of 95% or more, and massive proeutectoid cementite having an average thickness of 1 ㎛ or more is 100 ㎛. 2 Includes less than 5% of the area.

[0023] Hereinafter, the reasons for numerical limitation of the alloy component content in the embodiment of the present invention will be explained.

[0024] C (Carbon): 1.00% to 1.20%

[0025] C is the element that can most effectively increase material strength, and a 0.1% increase in C has a strength increase effect of 100 MPa. If C is added less than 1.00%, it is difficult to achieve the product target strength, and if it exceeds 1.20%, the fraction of massive proeutectoid cementite increases, causing wire breakage during drawing processing. Therefore, it is controlled to be below that. Preferably, it may be 1.02% to 1.20%, and more preferably, it may be 1.05% to 1.20%.

[0026] Si (silicon): 1.00% to 1.50%

[0027] Si is a solid-solution strengthening element that increases the strength to 15 MPa when added at 0.1%, but when used as a bridge steel wire, it plays a role in suppressing the decrease in tensile strength during plating because it segregates at the Si carbide interface and slows the diffusion of carbon. Therefore, when it is less than 1.00%, the tensile strength decreases, and when it exceeds 1.50%, wire breakage occurs during drawing due to center segregation disadvantage and increased decarburization, so it is controlled below that. Preferably, it may be 1.05% to 1.45%, and more preferably, it may be 1.10% to 1.40%.

[0028] Mn (manganese): 0.10% to 0.50%

[0029] Although manganese is a solid-solution strengthening element, it is added in the present invention to secure hardenability. However, since the hardenability is sufficiently secured when a large amount of hardenable elements such as C and Cr are included, and since a center segregation disadvantage is expected due to a high C content, it is necessary that the manganese content does not exceed 0.50%. Preferably, it may be 0.15% to 0.45%, and more preferably, it may be 0.15% to 0.40%.

[0030] Cr (chromium): 0.30% to 0.80%

[0031] When 0.1% Cr is added, it increases the tensile strength to 40 MPa and helps increase the work hardening rate during drawing processing because it reduces the cementite thickness. Therefore, when it is less than 0.30%, the target strength cannot be secured, and when it exceeds 0.80%, coarse chromium carbides are formed, which induces wire breakage during processing and causes delamination when the plating wire is twisted. Therefore, it is controlled to be below that. It may be preferably 0.35% to 0.75%, and more preferably 0.60% to 0.80%.

[0032] Al (aluminum): 0.50% to 1.50%

[0033] Aluminum (Al) is generally used as a deoxidizer because it has a good affinity for oxygen, but it is also known as an element that has a solid solution strengthening effect in ferrite and suppresses the formation of proeutectoid cementite while refining pearlite. In the present invention, by adding Al to carbon steel with 1.0% C or more, the strength and torsional properties can be improved by suppressing the refinement of the structure and the formation of massive proeutectoid cementite. Aluminum is contained in an amount of 0.50% or more, but when it exceeds 1.50%, the formation of composite inclusions such as Al2O3 and Al-Si-O causes nozzle clogging problems, so it is controlled to be less than that. Preferably, it may be 0.65% to 1.45%, and more preferably, it may be 0.60% to 1.40%.

[0034] The remaining component of the present invention is iron (Fe). However, during the typical manufacturing process, unintended impurities from raw materials or the surrounding environment may inevitably be mixed in, and thus cannot be excluded. Since these impurities are readily apparent to anyone skilled in the art of typical manufacturing, their full details are not specifically discussed in this specification.

[0035]

[0036] According to one embodiment of the present invention, the wire has a microstructure observed in a cross section of 1 / 2D to 3 / 2D (D: diameter) that includes pearlite at an area fraction of 95% or more and massive proeutectoid cementite at a thickness of 1 ㎛ or more at a thickness of 100 ㎛. 2 Includes less than 5% of the area.

[0037] As mentioned above, increasing the carbon content is an effective way to increase the strength. However, when the carbon content increases beyond the eutectoid composition, proeutectoid cementite is formed at the grain boundary. Film-like proeutectoid cementite is reused during constant temperature heat treatment, so there is no problem, but massive proeutectoid cementite is problematic because it is not reused, and there is a risk of wire breakage during wire drawing or delamination during torsion test even if the product is formed. Therefore, when massive proeutectoid cementite with an average thickness of 1㎛ or more is formed, it is formed at 100㎛. 2 Controlled to 5% or less in area, preferably 4.5% or less, and more preferably 4.0% or less.

[0038] Through this, the wire according to one embodiment of the present invention can secure high strength even before drawing with an average tensile strength of 1630 MPa or more at room temperature, can have a cross-sectional reduction ratio of 14% or more, and can have excellent scale peelability with an average scale thickness of 20 ㎛ or less.

[0039] Next, a method for manufacturing a wire according to the present invention is described.

[0040] A method for manufacturing a wire rod according to one embodiment of the present invention comprises the steps of: preparing a billet containing, in wt%, C: 1.00% to 1.20%, Si: 1.00% to 1.50%, Mn: 0.10% to 0.50%, Cr: 0.30% to 0.80%, and Al: 0.50% to 1.50%, with the remainder being Fe and other unavoidable impurities; heating and hot-rolling the billet; coiling it at Acm+20°C to Acm+100°C; and stellmore cooling it to 350°C to 400°C at 8°C / s to 12°C / s.

[0041] The reason for the numerical limitation of the component range of each alloy composition is as described above, and each manufacturing step is explained in more detail below.

[0042] The step of preparing the billet may be a normal billet manufacturing process.

[0043] In addition, the step of heating and rolling the billet can be performed by a conventional process. For example, after manufacturing a billet having the above-described alloy composition, the billet can be rolled after maintaining it at a heating furnace temperature of 950°C to 1050°C for 90 to 120 minutes for normalizing and forming austenite. If the temperature is maintained below 950°C, there is a problem that the charging time becomes long, and if the temperature is maintained above 1050°C, there is a heating furnace load. Therefore, it is preferable to control it to 950°C to 1050°C. In addition, if it is maintained below 90 minutes, it may be difficult to form central austenite, and if it is maintained above 120 minutes, coarse grain growth may occur.

[0044] Coiling temperature: Acm+20℃ to Acm+100℃

[0045] The coiling temperature affects the formation of proeutectoid cementite and the thickness of the scale. Even if the formation of massive proeutectoid cementite is suppressed by adding Al, the formation of film-shaped proeutectoid cementite is inevitable at temperatures below the Acm point for carbon steels with a content of 1.0% or more. When the Acm temperature is below +20℃, proeutectoid cementite is actively formed, and when it exceeds +100℃, the high temperature causes the formation of thick scale, making it difficult to peel off, which increases the pickling bath retention time. Therefore, it is desirable to control it below that temperature.

[0046] Step of cooling the stelmore to 350°C to 400°C at 8°C / s to 12°C / s

[0047] Cooling is performed to 400℃, where pearlite transformation is stably completed. At temperatures exceeding this, pearlite growth occurs, resulting in poor processability due to coarsening of the tissue, and the high temperature during coil handling makes the worker's environment unsafe. Therefore, cooling is controlled in the range of 350℃ to 400℃ at 8℃ / s to 12℃ / s.

[0048] Next, a steel wire and a method for manufacturing the same according to the present invention are described.

[0049] According to one embodiment of the present invention, a steel wire contains, in wt%, C: 1.00% to 1.20%, Si: 1.00% to 1.50%, Mn: 0.10% to 0.50%, Cr: 0.30% to 0.80%, and Al: 0.50% to 1.50%, the remainder being Fe and other unavoidable impurities, and after Zn plating, the tensile strength of the plated wire is 2250 MPa or more, the twisting is 13 times or more, and the elongation is 6.5% or more. When the tensile strength of the plated wire is less than 2250 MPa, the cable cutting force is low, which causes a problem in cable stability and does not greatly reduce the amount of cable used, and when the twisting of the plated wire is less than 13 times, many internal defects occur, and when the elongation is less than 6.5%, the processability is poor, which may limit its application as a steel wire for cables.

[0050] A method for manufacturing a steel wire according to one embodiment of the present invention comprises the steps of: preparing the above-described wire material; performing pickling and constant temperature heat treatment; performing fresh processing at a fresh processing amount of 77% to 85%; and performing Zn plating.

[0051] The pickling can be performed under conditions of 3 to 5% hydrochloric acid at a temperature ranging from 70°C to 90°C, and the Zn plating treatment step can be performed by hot-dip zinc plating treatment or electrolytic zinc plating treatment, but is not limited thereto.

[0052] The present invention will be described in more detail through the following examples.

[0053] (Example)

[0054] The rear end of a billet cast by vacuum melting 75 kg of steel having the same composition as in Table 1 was welded, and the billet was maintained at a heating furnace temperature of 950°C to 1050°C for 90 to 120 minutes, and then rolled to produce 11 mm. The manufactured comparative examples and inventive examples were coiled at the coiling temperature in Table 2 and finished by stelmore cooling at 10°C / s.

[0055] In addition, the manufactured wire rod was pickled at 80℃ under 4% hydrochloric acid conditions, and then heat-treated at an isothermal temperature at 580℃ and dry-drawn to produce steel wire with a total area reduction of 77.5% (or total deformation: 1.49).

[0056] The mechanical properties of the wire rod, microstructure, and mechanical properties after drawing and plating were measured and are shown in Tables 1 and 2 below.

[0057] In addition, in the case of measuring the tensile strength of the wire, a 40 cm long piece was cut from the 2 rings (circumference: 3.2 m) at the rear end of the coil and a tensile test was performed. The tensile speed (cross head speed) was 70 m / m and the length of the balanced section was 30 cm. The diameter was measured before the tensile test using a stereo projector, and the diameter of the necked part after the tensile test was used to measure the cross-sectional reduction ratio (= 1-(after tensile test / before certification test)^2)*100).

[0058] In the case of measuring the tensile strength of the steel wire according to the present invention, the tensile test specimen length is 40 cm, the tensile speed (cross head speed) is 100 m / m, and the equilibrium length is 30 cm, which is the same as the wire rod. The elongation is determined as the % of the elongated length compared to the initial length of 30 cm, and in the case of torsion, the back load is load (kg) x 0.008, the length is 100D (D: diameter), and the number of fractures is confirmed while rotating the non-fixed chuck in the same direction while fixing one chuck.

[0059] In addition, the area fraction of massive cementite and pearlite was measured at x3000 magnification using a scanning electron microscope in a part where the massive cementite or pearlite was placed parallel to the electron beam without being tilted, and the average was calculated by setting n to 10.

[0060] The thickness of the pre-existing scale was measured using an optical microscope at x200 magnification in areas where the scale was relatively intact, and the number of n was set to 5 and the average was calculated.

[0061] The scale peelability was evaluated using a tensile tester (test piece length 30 cm) until destruction. If there was little residual scale on the surface when visually inspected, it was evaluated as good, otherwise it was evaluated as bad. The weight was measured before the tensile test and after destruction. If there was less than 0.05 residual scale, it was evaluated as good, and if it exceeded this, it was evaluated as bad.

[0062] Weight %CSiMnCrAlCoiling temperature (℃)Stelmore cooling speed (℃ / s)Average tensile strength of wire (MPa)Reduction of cross-sectional area (%)Comparative example 10.951.300.500.601.00Acm+5010158916Invention example 11.051.300.500.601.00Acm+5010168216Invention example 21.001.300.500.601.00Acm+5010163014Invention example 31.201.300.500.601.00Acm+5010183516Comparative example 2 1.251.300.500.601.00Acm+501018376Comparative Example 31.050.800.500.601.00Acm+5010160411Invention Example 41.051.100.500.601.00Acm+5010165515Invention Example 51.051.400.500.601.00Acm+5010169914Comparative Example 41.051.600.500.601.00Acm+ 501017358Comparative Example 51.051.300.800.601.00Acm+5010174310Comparative Example 61.051.300.500.201.00Acm+5010152916Invention Example 61.051.300.500.801.00Acm+5010176515Comparative Example 71.051.300.501.001.00Acm+501018414Comparative Example 81.051.300.5 00.600.20Acm+5010160015Invention Example 71.051.300.500.600.60Acm+5010164515Invention Example 81.051.300.500.601.40Acm+5010172414Comparative Example 91.051.300.500.601.80Acm+501017604Comparative Example 101.051.300.500.601.00Acm+12010164712

[0063] Thickness 1㎛ or more Massive cementite area fraction (%) Wire scale thickness (㎛) Scale peelability Drawing amount (%) Fresh tensile strength (MPa) Plated tensile strength (MPa) Torsion (100D, times) Elongation (%) Comparative example 1511.8 Good 77 23442269 176.2 Invention example 1412.0 Good 77 24422369 156.5 Invention example 2511.0 Good 77 23522278 146.7 Invention example 3312.0 Good 77 2560 2484 146.8 Comparative example 21613.0 Good 77 In process Breakage in process Breakage in process Breakage in process Breakage in process Single wire Comparison Example 3611.0 Good 7723492187195.7 Invention Example 4510.0 Good 7724032321136.8 Invention Example 5412.0 Good 7724542370136.5 Comparison Example 41511.0 Good 77 In process Single wire In process Single wire In process Single wire In process Single wire In process Single wire Comparison Example 51212.0 Good 77 In process Single wire In process Single wire In process Single wire In process Single wire Comparison Example 6412.0 Good 7722892221186.1 Invention Example 6311.0 Good 7724902415156.7 Comparison Example 71711.0 Good 77 In process Single wire In process Single wire In process Single wire In process Single wire In process Single wire comparison example 81613.0 Good 7723252253 Single wire during delamination processing Invention honor example 7510.0 Good 7723942316156.8 Single wire during delamination processing Invention honor example 8310.0 Good 7724752392136.5 Comparison example 9712.0 Good 7724212351 Single wire during delamination processing Invention honor example 10624.8 Poor 77 Single wire during processing Invention honor example ...

[0064] In the case of invention examples 1 to 3, the wire tensile strength was 1630 MPa or more, the RA (reduction in cross-sectional area) was 14% or more, and no wire breakage occurred during drawing. The final plating wire tensile strength was 2250 MPa or more, which was high strength, and no delamination occurred during a torsion test, and it was confirmed that the wire was good for 14 or more times, and the elongation was also 6.5% or more.

[0065] However, in the case of Comparative Example 1, which had the lowest carbon content of 0.95%, the wire properties and microstructure were within the scope of the present invention, but the final plating wire tensile strength was less than 2250 MPa. On the other hand, in the case of Comparative Example 2, which had a carbon content exceeding 1.20%, the wire tensile strength was high, but wire breakage occurred during processing.

[0066] In the case of Comparative Example 3 with a Si content of 0.80%, the wire drawing process is good, but it can be confirmed that the tensile strength decreases significantly during plating, and accordingly, it is difficult to secure the target properties. In the case of Inventive Examples 4 and 5, the Si content satisfies the range of the present invention, so it can be confirmed that no wire breakage occurs during processing and that the decrease in tensile strength after plating is also reduced. However, in the case of Comparative Example 4 with a Si content of 1.60%, wire breakage occurred during drawing.

[0067] Comparative Example 5, in which the Mn content exceeded 0.50%, showed a short circuit during drawing upon approval, confirming that high Mn addition is not suitable when designing carbon steel with Al addition and 1.0% or more.

[0068] Since Cr increases strength and refines pearlite, which is advantageous for fresh workability, Inventive Examples 1 and 6, which satisfy 0.30% to 0.50%, did not cause wire breakage during processing, and the tensile strength of the plating wire satisfied 2250 MPa or more, enabling high strength, torsional properties, and elongation to be secured. However, Comparative Example 6, which has a Cr content of only 0.20%, had low tensile strengths of the wire rod and plating wire, and Comparative Example 7, which has a Cr content of 1.00%, caused wire breakage during processing due to coarse Cr carbides.

[0069] Inventive Examples 1, 7, and 8, which satisfy the Al content of 0.50% to 1.50%, show an area fraction of massive cementite with a thickness of 1 μm or more of 5% or less, so it is thought that Al has an effect of suppressing massive cementite. However, in the case of Comparative Example 8, where the Al content is only 0.20%, it was confirmed that the area fraction (%) of massive cementite with a thickness of 1 μm or more was as high as 16%. In addition, in the case of Comparative Example 9, where the Al content is 1.80%, no wire breakage occurred during drawing, but delamination occurred during the torsion test of the plating wire, and it was confirmed that the elongation was also low. FIG. 1 and FIG. 2 are microstructures observed at the center of the cross-section of the wire rods of Inventive Example 1 and Comparative Example 8, and it can be confirmed that the formation of massive proeutectoid cementite is suppressed due to the addition of Al.

[0070] Comparative Example 10 is not suitable in terms of processing because the coiling temperature exceeds Acm+100℃ and the scale thickness is 20㎛ or more, which is much larger than that of the invention example, resulting in poor scale exfoliation and requiring long-term immersion in a pickling tank.

[0071] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and spirit of the claims set forth below.

Claims

1. Containing, by weight%, C: 1.00% to 1.20%, Si: 1.00% to 1.50%, Mn: 0.10% to 0.50%, Cr: 0.30% to 0.80% and Al: 0.50% to 1.50%, the remainder being Fe and other inevitable impurities, The microstructure observed in the cross section 1 / 2D~3 / 2D (D: diameter) contains pearlite with an area fraction of 95% or more, 100㎛ of monstrous protolith cementite with an average thickness of 1㎛ or more 2 Pre-existing materials, including less than 5% of the surface area.

2. In claim 1, Wire having an average tensile strength of 1630 MPa or more at room temperature.

3. In claim 1, Wire rod with a cross-sectional reduction rate of 14% or more.

4. In claim 1, Wire with an average scale thickness of 20㎛ or less.

5. A step of preparing a billet containing, by weight%, C: 1.00% to 1.20%, Si: 1.00% to 1.50%, Mn: 0.10% to 0.50%, Cr: 0.30% to 0.80%, and Al: 0.50% to 1.50%, the remainder being Fe and other unavoidable impurities; A step of heating and hot rolling the above billet; Step of winding at Acm+20℃ to Acm+100℃; and A method for manufacturing a wire rod, comprising the step of stelmore cooling to 350°C to 400°C at 8°C / s to 12°C / s.

6. Containing, by weight%, C: 1.00% to 1.20%, Si: 1.00% to 1.50%, Mn: 0.10% to 0.50%, Cr: 0.30% to 0.80% and Al: 0.50% to 1.50%, the remainder being Fe and other inevitable impurities, A steel wire having a tensile strength of 2250 MPa or more, a twist of 13 times or more, and an elongation of 6.5% or more after zinc plating.

7. A step of preparing the precursor of claims 1 to 4; Step of pickling and constant temperature heat treatment; A step of fresh processing with a fresh processing amount of 77% to 85%; and A method for manufacturing a steel wire, comprising a step of performing zinc plating treatment.

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