Method for manufacturing molten steel, wire rod, and method for manufacturing wire rod

Abstract

A wire rod according to an embodiment of the present invention comprises 0.70-1.10 wt% of carbon (C), 0.15-0.50 wt% of silicon (Si), 0.20-0.90 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P), 0.015 wt% or less of sulfur (S), 0.2 wt% (excluding 0) of copper (Cu), 0.20 wt% or less (excluding 0) of nickel (Ni), 0.03-0.40 wt% of chromium (Cr), 0.010 wt% or less (excluding 0) of aluminum (Al), 0.005 wt% or less (excluding 0) of nitrogen (N), and the remainder of iron (Fe) and other inevitable impurities. According to an embodiment of the present invention, with respect to a cut surface of the wire rod cut in a direction perpendicular to the longitudinal direction of the wire rod, the maximum size of non-metallic inclusions is 40 μm or less, and the value of [formula 1] measured in any one of a plurality of regions is 40 or less. [Formula 1] (1×n1)+(5×n2)+(20×n3) In formula 1, n1 represents the number of inclusions having a maximum diameter of 5 μm or more but less than 10 μm, n2 represents the number of inclusions having a maximum diameter of 10 μm or more but less than 20 μm, and n3 represents the number of inclusions having a maximum diameter of 20 μm or more.

Description

Method for manufacturing molten steel, wire rod and method for manufacturing wire rod

[0001] The present invention relates to a method for manufacturing molten steel, a wire rod, and a method for manufacturing a wire rod. More specifically, it relates to a method for manufacturing electric furnace molten steel for producing a wire rod having excellent drawing workability, a wire rod produced by the electric furnace molten steel, and a method for manufacturing a wire rod.

[0002] Tire cord is a reinforcing material embedded within rubber to enhance the stability, drivability, and durability of tires mounted on driving mechanisms such as automobiles.

[0003] Tire cord materials can be broadly classified into steel and polymer synthetic fibers (polyester, nylon, etc.).

[0004] Steel tire cords are widely used recently because they have high strength and excellent heat resistance compared to polymer synthetic fiber tire cords.

[0005] Steel tire cord is manufactured into an ultra-fine wire state by undergoing wire drawing and patterning heat treatment processes.

[0006] When ultrafine wire undergoes drawing processing, high work hardening occurs, which can lead to wire breakage due to non-metallic inclusions, surface defects, decarburization layers, and residual scale that is not removed after pickling.

[0007] In particular, if coarse non-metallic inclusions are present within the wire, voids occur at the interface between the non-metallic inclusions and the matrix of the wire, and these voids can cause wire breakage during the wire drawing and stranding processes.

[0008] Reducing the frequency of wire breakage during tire cord manufacturing is a problem that must be solved, as wire breakage not only lowers workability and productivity but can also lead to worker safety accidents.

[0009] Meanwhile, wire rods for tire cords are generally produced in blast furnace-converter operations. This is because the blast furnace-converter process produces molten iron using iron ore as a raw material and utilizes it to manufacture products, allowing for the production of higher-quality products compared to the electric furnace process, where scrap is the primary raw material.

[0010] However, as the realization of carbon neutrality is increasingly demanded internationally across all industrial sectors, active research is underway in the steel industry on electric furnace process technologies to replace the blast furnace-converter process, which emits a large amount of carbon dioxide, with an electric furnace process that can secure quality equivalent to or superior to that of blast furnace-converter products.

[0011] However, since the electric furnace process uses scrap and reduction iron as primary raw materials, the carbon content in the molten steel is low, which presents a problem in that nitrogen removal through the decarburization reaction is not easily achieved.

[0012] In the case of wire rods, if the nitrogen content exceeds a preset range, it not only adversely affects cold workability during drawing but can also become a factor in quality deterioration.

[0013] The inventors of the present invention propose a method for manufacturing wire rods with excellent drawing processability, while having quality equivalent to or superior to that of wire rods produced in a blast furnace-converter process, through an electric furnace process.

[0014] The purpose of the present invention is to provide electric furnace molten steel for manufacturing a wire rod having excellent physical properties and excellent drawing processability, a wire rod manufactured using the same, and a method for manufacturing the wire rod.

[0015] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0016] A wire rod according to one embodiment of the present invention comprises 0.70 to 1.10 wt% carbon (C), 0.15 to 0.50 wt% silicon (Si), 0.20 to 0.90 wt% manganese (Mn), 0.015 wt% or less phosphorus (P), 0.015 wt% or less sulfur (S), 0.2 wt% copper (Cu) (excluding 0), 0.20 wt% or less nickel (Ni) (excluding 0), 0.03 to 0.40 wt% chromium (Cr), 0.010 wt% or less aluminum (Al) (excluding 0), 0.005 wt% or less nitrogen (N) (excluding 0), and the remainder being iron (Fe) and other unavoidable impurities.

[0017] According to one embodiment of the present invention, in the cross-section of a wire cut in a direction perpendicular to the longitudinal direction of the wire, the maximum size of non-metallic inclusions is 40 μm or less, and the value of [Equation 1] measured in any one of the plurality of regions is 40 or less.

[0018] [Equation 1]

[0019] (1×n1)+(5×n2)+(20×n3)

[0020] In Equation 1, n1 is the number of inclusions with a maximum diameter of 5 μm or more and less than 10 μm, n2 is the number of inclusions with a maximum diameter of 10 μm or more and less than 20 μm, and n3 is the number of inclusions with a maximum diameter of 20 μm or more.

[0021] According to one embodiment of the present invention, the arithmetic mean value of [Equation 1] measured in the plurality of regions may be 5 or less.

[0022] According to one embodiment of the present invention, the final microstructure may comprise 90 vol.% or more of pearlite and the remainder being ferrite.

[0023] According to one embodiment of the present invention, the cross-sectional shrinkage rate may be 30% or more.

[0024] According to one embodiment of the present invention, the total amount of non-metallic inclusions in the cut surface may be 0.05% or less of the total area.

[0025] The tensile strength of the wire according to one embodiment of the present invention is 1000 MPa or more.

[0026] A method for manufacturing a wire rod according to one embodiment of the present invention comprises (a) a molten steel manufacturing step of melting raw materials to produce molten steel, (b) a continuous casting step of producing a semi-finished product, and (c) a wire rod rolling step of hot rolling the semi-finished product.

[0027] The wire rod that has undergone the above (c) wire rod rolling step contains 0.70 to 1.10 wt% carbon (C), 0.15 to 0.50 wt% silicon (Si), 0.20 to 0.90 wt% manganese (Mn), 0.015 wt% or less phosphorus (P), 0.015 wt% or less sulfur (S), 0.2 wt% copper (Cu) (excluding 0), 0.20 wt% or less nickel (Ni) (excluding 0), 0.03 to 0.40 wt% chromium (Cr), 0.010 wt% or less aluminum (Al) (excluding 0), 0.005 wt% or less nitrogen (N) (excluding 0), and the remainder is iron (Fe) and other unavoidable impurities.

[0028] According to one embodiment of the present invention, in the cross-section of a wire cut in a direction perpendicular to the longitudinal direction of the wire, the maximum size of non-metallic inclusions is 40 μm or less, and the value of [Equation 1] measured in any one of the plurality of regions is 40 or less.

[0029] [Equation 1]

[0030] (1×n1)+(5×n2)+(20×n3)

[0031] In Equation 1, n1 is the number of non-metallic inclusions with a maximum size of 5 μm or more and less than 10 μm, n2 is the number of non-metallic inclusions with a maximum size of 10 μm or more and less than 20 μm, and n3 is the number of non-metallic inclusions with a maximum size of 20 μm or more.

[0032] According to one embodiment of the present invention, in the (a) molten steel manufacturing step, the raw material may include at least one of reduced iron, molten iron, and iron scrap.

[0033] According to one embodiment of the present invention, the (a) molten steel manufacturing step may include a (a-1) raw material charging step of supplying the raw material to a melting furnace, a (a-2) melting step of melting the raw material to produce molten steel, a (a-3) tapping step of tapping the molten steel to the outside of the melting furnace, and an (a-4) adding step of adding a slag-forming agent to the molten steel.

[0034] According to one embodiment of the present invention, the melting furnace may be an electric furnace.

[0035] According to one embodiment of the present invention, the basicity of the slag material may be 1.0 or less.

[0036] According to one embodiment of the present invention, the slag material may comprise 35 to 50 weight percent of calcium oxide (CaO) and the remainder being silicon oxide (SiO2).

[0037] According to one embodiment of the present invention, the slag material may further include 3 weight% or less of aluminum oxide (Al2O3) and 3 weight% or less of magnesium oxide (MgO) to replace the silicon oxide (SiO2).

[0038] According to one embodiment of the present invention, the (a) molten steel manufacturing step further includes a (a-5) first refining step for refining the molten steel, and the (a-5) first refining step may be RH (Rhodium-Hartmann).

[0039] According to one embodiment of the present invention, the (a) molten steel manufacturing step further includes a (a-6) second refining step for refining the molten steel, and the (a-6) second refining step may be a LTS (Laddle Treatment System).

[0040] A method for manufacturing molten steel according to one embodiment of the present invention comprises a raw material charging step of supplying the raw material to a melting furnace, a melting step of melting the raw material to produce molten steel, a tapping step of tapping the molten steel to the outside of the melting furnace, and an addition step of adding a slag-forming agent to the molten steel.

[0041] The above slag material comprises 35 to 50 weight% calcium oxide (CaO), 3 weight% or less aluminum oxide (Al2O3) and 3 weight% or less magnesium oxide (MgO) and the remainder silicon oxide (SiO2).

[0042] According to one embodiment of the present invention, the basicity of the slag material may be 1.0 or less.

[0043] According to one embodiment of the present invention, the raw material may include at least one of reduced iron, molten iron, and iron scrap.

[0044] According to one embodiment of the present invention, the melting furnace may be an electric furnace.

[0045] A slag flux according to one embodiment of the present invention is added to molten steel produced in a melting furnace. The slag flux comprises 35 to 50 weight% calcium oxide (CaO), 3 weight% or less aluminum oxide (Al2O3) and 3 weight% or less magnesium oxide (MgO) and the remainder silicon oxide (SiO2).

[0046] According to one embodiment of the present invention, the basicity of the slag material may be 1.0 or less.

[0047] According to one embodiment of the present invention, by controlling the average cleanliness index of the wire rod, the total amount of non-metallic inclusions, and the maximum size of non-metallic inclusions within a preset range through the alloy composition system and manufacturing process described above, it is possible to manufacture a wire rod having excellent drawing processability and uniform physical properties.

[0048] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims.

[0049] FIG. 1 is an exemplary drawing for explaining a method for calculating the average cleanliness index of a wire according to one embodiment of the present invention.

[0050] FIG. 2 is a flowchart illustrating a method for manufacturing a wire rod according to one embodiment of the present invention.

[0051] Figure 3 is a detailed flowchart of the molten steel manufacturing steps of Figure 2.

[0052] Figure 4 is a flowchart showing the detailed steps of the wire rod rolling step of Figure 2.

[0053] Hereinafter, preferred embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited or restricted by the following embodiments.

[0054] Additionally, when it is stated that a component (or area, layer, part, etc.) is "on," "connected," or "combined" with another component, it means that it may be directly placed / connected / combined with the other component, or that a third component may be placed between them.

[0055] Terms such as "include" or "have" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0056] In order to clearly explain the present invention, detailed descriptions of related prior art that are irrelevant to the explanation or that may unnecessarily obscure the essence of the invention have been omitted. Furthermore, when assigning reference numerals to the components of each drawing in this specification, identical or similar reference numerals are assigned to identical or similar components throughout the entire specification.

[0057] Furthermore, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0058] Unless otherwise specified, the notation 'A ~ B' for numerical values ​​A and B shall mean 'A or greater, B or less'. In such notation, if a unit is attached only to numerical value B, that unit shall also apply to numerical value A.

[0059] Hereinafter, embodiments of the present invention will be described in detail.

[0060]

[0061] Seonjae

[0062] A wire rod according to one embodiment of the present invention comprises 0.70 to 1.1 wt% carbon (C), 0.15 to 0.5 wt% silicon (Si), 0.20 to 0.9 wt% manganese (Mn), 0.015 wt% or less phosphorus (P) (excluding 0), 0.015 wt% or less sulfur (S) (excluding 0), 0.2 wt% or less copper (Cu) (excluding 0), 0.2 wt% or less nickel (Ni) (excluding 0), 0.03 to 0.40 wt% chromium (Cr), 0.010 wt% or less aluminum (Al) (excluding 0), 0.005 wt% or less nitrogen (N), and the remainder being iron (Fe) and other unavoidable impurities.

[0063] Hereinafter, the role and content of each alloy element included in the wire rod according to one embodiment of the present invention will be described in detail.

[0064]

[0065] Carbon (C)

[0066] Carbon (C) is an effective element for increasing strength, but as the carbon content increases, strength improves but toughness decreases.

[0067] If carbon (C) is added below a preset range, the strength of the final product, the tire cord, cannot be secured.

[0068] Conversely, if carbon (C) is added in excess of a preset range, the cross-sectional shrinkage rate decreases along with a decrease in toughness, and a decrease in fresh workability may result from the formation of proeutectoid cementite.

[0069] Accordingly, in the wire rod according to one embodiment of the present invention, the carbon (C) content can be controlled to 0.70 to 1.1 weight%, preferably 0.72 to 1.02 weight%.

[0070]

[0071] Silicon (Si)

[0072] Silicon (Si) is an element that is effective in increasing strength and deoxidation, and increases carbon activity.

[0073] If silicon (Si) is added below a preset range, it is difficult to achieve deoxidation effects and secure strength.

[0074] Conversely, if silicon (Si) is added in excess of a preset range, it reduces toughness, increases deformation resistance, and may make it difficult to remove surface scale during the pickling process.

[0075] In addition, if silicon (Si) is added in excess of a preset range, it can excessively promote decarburization, which may reduce fresh processability as the thickness of the decarburized layer increases.

[0076] Accordingly, in a wire rod according to one embodiment of the present invention, the silicon (Si) content can be controlled to 0.15 to 0.5 weight%, preferably 0.16 to 0.48 weight%.

[0077]

[0078] Manganese (Mn)

[0079] Manganese (Mn) is an element that increases the strength of wire rods while being effective for deoxidation, and it prevents red-hot brittleness by forming MnS inclusions. Additionally, manganese (Mn) is an element that reduces carbon activity.

[0080] If manganese (Mn) is added below a preset range, the deoxidation effect is reduced, it is difficult to secure strength, and there are problems such as inducing red-hot brittleness.

[0081] In addition, if manganese (Mn) is added below a preset range, the effect of inhibiting decarburization is insufficient, which may reduce fresh processing performance as the thickness of the decarburized layer increases.

[0082] If manganese (Mn) is added in excess of a preset range, segregation may occur in the center of the wire, and the formation of a low-temperature structure may occur upon cooling. Specifically, martensite may form upon cooling.

[0083] Accordingly, in the wire rod according to one embodiment of the present invention, the content of manganese (Mn) can be controlled to 0.2 to 0.9 weight%, preferably 0.22 to 0.89 weight%.

[0084]

[0085] Ph(P)

[0086] Phosphorus (P) is a residual element that must be removed during the steelmaking process. If the phosphorus content exceeds 0.015 weight%, it can cause brittleness due to grain boundary segregation and the formation of Fe3P compounds.

[0087] Accordingly, in a wire rod according to one embodiment of the present invention, the phosphorus (P) content can be controlled to 0.015 weight% or less, preferably 0.014 weight% or less.

[0088]

[0089] Yellow (S)

[0090] Sulfur (S) is a residual element that must be removed during the steelmaking process and forms MnS nonmetallic inclusions.

[0091] If the sulfur content exceeds 0.015 weight%, the toughness is reduced due to the excessive formation of sulfides such as MnS.

[0092] Accordingly, in the wire according to one embodiment of the present invention, sulfur (S) can be controlled to 0.015 weight% or less.

[0093]

[0094] Copper (Cu)

[0095] Copper (Cu) is an element that contributes to increasing the strength and improving the corrosion resistance of wire rods. However, if copper (Cu) is added in excess of a preset range, it may cause cracks on the surface during high-temperature rolling of the wire rod.

[0096] Accordingly, in a wire rod according to one embodiment of the present invention, the copper (Cu) content can be controlled to 0.2 weight% or less (excluding 0), preferably 0.04 to 0.19 weight%.

[0097] According to one embodiment of the present invention, copper (Cu) may originate from iron scrap, which is a raw material.

[0098] According to one embodiment of the present invention, the physical properties of a wire rod can be improved by utilizing the positive function of copper (Cu), a tramp element contained in iron scrap.

[0099] However, the source of copper (Cu) is not limited to iron scrap, and it may be added separately as needed.

[0100]

[0101] Nickel (Ni)

[0102] Nickel (Ni) is an element that contributes to increasing the strength and improving the corrosion resistance of wire rods. In addition, nickel (Ni) is an element that effectively reduces surface cracks caused by the copper (Cu) enrichment layer during hot rolling, and it is also an element that reduces carbon diffusivity.

[0103] However, if nickel (Ni) is added in excess of a preset range, the fatigue life of the product may be reduced due to the excessive formation of residual austenite structure.

[0104] Accordingly, in a wire rod according to one embodiment of the present invention, the nickel (Ni) content can be controlled to 0.20 weight% or less (excluding 0), preferably 0.05 to 0.17 weight%.

[0105] According to one embodiment of the present invention, nickel (Ni) may originate from iron scrap, which is a raw material.

[0106] According to one embodiment of the present invention, the physical properties of a wire rod can be improved by using nickel (Ni) contained in iron scrap.

[0107] Accordingly, the manufacturing cost of wire rods can be lowered by recycling nickel (Ni), a high-grade element, from iron scrap.

[0108] However, the source of nickel (Ni) is not limited to iron scrap, and it may be added separately as needed.

[0109]

[0110] Chrome (Cr)

[0111] Chromium (Cr) is an element that contributes to the increase in strength and hardenability of wire rods. In addition, chromium is an element that improves the corrosion resistance of wire rods. Furthermore, chromium is an element that effectively reduces carbon activity.

[0112] If chromium (Cr) is added below a preset range, it is difficult to secure the required strength, and the effect of suppressing decarburization is insufficient, which may reduce fresh processability as the thickness of the decarburized layer increases.

[0113] If chromium (Cr) is added in excess of a preset range, the occurrence of low-temperature tissue can cause breakage during the subsequent freshing process. In addition, excessive addition of chromium (Cr) can lead to an increase in manufacturing costs.

[0114] Accordingly, in a wire rod according to one embodiment of the present invention, the chromium (Cr) content can be controlled to 0.03 to 0.40 weight%, preferably 0.04 to 0.33 weight%.

[0115]

[0116] Aluminum (Al)

[0117] Aluminum (Al) is an element that acts as a powerful deoxidizer, improves toughness by refining the austenite grain size, and forms non-metallic inclusions.

[0118] However, if aluminum (Al) is added in excess of a preset range, it may excessively form coarse aluminum-based non-ductile inclusions, which can cause wire breakage during drawing.

[0119] Accordingly, in a wire rod according to one embodiment of the present invention, the aluminum (Al) content can be controlled to 0.01 weight% or less (excluding 0), preferably 0.001 to 0.007 weight%.

[0120]

[0121] Nitrogen (N)

[0122] Nitrogen (N) is an element that combines with elements such as aluminum (Al), titanium (Ti), vanadium (V), and niobium (Nb) to form precipitates and is effective in refining the grain size of austenite.

[0123] However, if nitrogen (N) is added in excess of a preset range, excessive formation of precipitates may cause variations in strength and adversely affect cold workability during fresh processing.

[0124] Accordingly, in a wire rod with excellent fresh processing properties according to one embodiment of the present invention, the nitrogen (N) content can be controlled to 0.005 weight% or less (excluding 0), preferably 0.0039 to 0.0046 weight%.

[0125] In addition to the components of the lecture described above, the remainder may contain Fe and unavoidable impurities. Unavoidable impurities are those introduced during the manufacturing process, and since this is widely known in the field, a detailed explanation is omitted.

[0126] In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. If additional elements are included, they may be included to replace the remainder of Fe.

[0127]

[0128] According to one embodiment of the present invention, electric furnace molten steel is produced by the aforementioned alloy composition system and the manufacturing process described below, and by using this to extremely precisely control the size, total amount, and cleanliness of non-metallic inclusions included in the microstructure of the wire rod, a wire rod having excellent physical properties and drawing processability can be produced.

[0129] In the cross-section of a wire according to one embodiment of the present invention, the maximum size of non-metallic inclusions is 40 μm or less, and the total amount of non-metallic inclusions is 0.05 vol.% or less based on the area of ​​the cross-section.

[0130] If the maximum size of non-metallic inclusions exceeds 40 μm, the drawing processability of the wire may be significantly reduced. Here, the maximum size of non-metallic inclusions refers to the size of the largest non-metallic inclusion consisting of a single spherical or angular particle with an aspect ratio of 5 or less, observed by observing the sample with an optical microscope or an electron microscope among the various non-metallic inclusions present in the sample.

[0131] In the present invention, the "size of the non-metallic inclusion" is defined based on the diameter of the corresponding figure. The diameter of the figure refers to the distance between the two farthest points within the figure, and this applies to all two-dimensional figures including circles, ellipses, and polygons. Specifically, in the case of an ellipse, the length of the major axis becomes the diameter.

[0132] In polygons, it is measured as the distance between the two farthest vertices, while in the case of concave polygons, it can be measured as the maximum distance between two vertices or between a vertex and an edge. In this invention, when comparing the sizes of shapes, this diameter length is used as the standard.

[0133] For example, a shape with diameter D is considered to be twice the size of a shape with diameter D / 2. This definition enables consistent size comparisons regardless of the shape or type of the shape and is used to clearly describe the relative sizes of various shape elements in embodiments of the present invention.

[0134] In the present invention, the size of a non-metallic inclusion can be defined as the size of a single wire by cutting a plurality of predetermined regions of the wire, calculating the average of the area sizes of at least one non-metallic inclusion observed at each cut surface, and calculating the average value again for the average values ​​calculated at each cut surface.

[0135] In this specification, the cross-section of the wire refers to the cross-section obtained when the wire is cut in a direction perpendicular to the longitudinal direction of the wire.

[0136] According to one embodiment of the present invention, in the cross-section of a wire, the cleanliness index measured in any area may be 40 or less. Any area may be arbitrarily designated in the cross-section of the wire.

[0137] For example, when multiple regions are defined at a specific cross-section of a wire and the cleanliness index in each region is measured, the cleanliness index in all regions may be 40 or less.

[0138] The cleanliness index can be defined by the following [Equation 1].

[0139]

[0140] [Equation 1]

[0141] (1×n1)+(5×n2)+(20×n3)

[0142]

[0143] In Equation 1, n1 represents the number of non-metallic inclusions with a size of 5 μm or more and less than 10 μm, n2 represents the number of non-metallic inclusions with a size of 10 μm or more and less than 20 μm, and n3 represents the number of non-metallic inclusions with a size of 20 μm or more.

[0144] According to Equation 1, the cleanliness can be calculated by applying weights based on the size of non-metallic inclusions that affect fresh processing performance.

[0145] According to one embodiment of the present invention, not only is the maximum size or total amount of non-metallic inclusions included in the microstructure of the wire rod controlled, but the cleanliness of the wire rod is also controlled by controlling the number of non-metallic inclusions having a size of 5 μm or more and less than 40 μm that affect the wire rod's

[0146]

[0147] According to one embodiment of the present invention, the average cleanliness index of the wire can be determined by the cleanliness index measured in each area.

[0148] Specifically, the average cleanliness index can be determined by the arithmetic mean of the cleanliness index values ​​measured in each of the multiple regions observed at the cross-section of the wire.

[0149] For example, in one embodiment of the present invention, a cleanliness index can be measured in five or more areas, and an average cleanliness index can be calculated through the arithmetic mean value thereof.

[0150] The number of multiple regions is not limited to what has been described above, but the sum of the areas of the multiple regions may be greater than half the area of ​​the cross-section.

[0151] FIG. 1 is a drawing for explaining the average cleanliness index of a wire rod according to one embodiment of the present invention.

[0152] The regions (#1 to #5) defined on the cross-section of the wire shown in FIG. 1 and the number of non-metallic inclusions observed in regions (#1 to #5) are examples for the sake of understanding, and the present invention is not limited thereto.

[0153] Below, we will explain in detail the method for calculating the cleanliness index and the average cleanliness index.

[0154] Referring to FIG. 1, first to fifth regions (#1 to #5) may be defined on the cross-section of the wire. The area of ​​each region may be 5.5 mm × 11 mm.

[0155] Each region is observed at a magnification of 200x using a microscope. An optical microscope or a scanning electron microscope may be used. The aspect ratio is 5 or less.

[0156] In the first region (#1), four non-metallic inclusions with a maximum size of 5 μm or more and less than 10 μm were observed. Accordingly, the cleanliness index of the first region (#1) calculated by Equation 1 is 4.

[0157] In the second region (#2), one non-metallic inclusion with a maximum size of 10 μm or more and less than 20 μm was observed. Accordingly, the cleanliness index of the second region (#2) calculated by Equation 1 is 5.

[0158] In the third region (#3), two non-metallic inclusions with a maximum size of 5 μm or more and less than 10 μm were observed. Accordingly, the cleanliness index of the third region (#3) calculated by Equation 1 is 2.

[0159] In the fourth region (#4), one non-metallic inclusion with a maximum size of 5 μm or more and less than 10 μm was observed. Accordingly, the cleanliness index of the fourth region (#4) calculated by Equation 1 is 1.

[0160] In the fifth region (#5), two non-metallic inclusions with a maximum size of 5 μm or more and less than 10 μm were observed, and one non-metallic inclusion with a maximum size of 10 μm or more and less than 20 μm was observed. Accordingly, the cleanliness index of the fifth region (#5) calculated by Equation 1 is 7.

[0161] In conclusion, the arithmetic mean of the cleanliness index in the first area (#1) to the fifth area (#5) is 3.8.

[0162] According to one embodiment of the present invention, the average cleanliness index of the wire may be 5 or less.

[0163] According to one embodiment of the present invention, when the average cleanliness index exceeds 5, even if there are no large non-metallic inclusions of a maximum size of 40 μm or more in the microstructure of the wire rod, the wire rod may have inferior wire rod drawing performance due to a large number of non-metallic inclusions of a size that affects wire drawing performance.

[0164]

[0165] The tensile strength (TS) of the wire according to one embodiment of the present invention may be 1000 MPa or more.

[0166] The cross-sectional shrinkage rate of the wire according to one embodiment of the present invention may be 30% or more.

[0167] Here, the cross-sectional shrinkage rate is a value expressed as a percentage of the reduction in cross-sectional area when the wire breaks due to tension in the longitudinal direction.

[0168] For example, the cross-sectional shrinkage rate can be defined as follows.

[0169] [Sectional Shrinkage Rate]

[0170] (A0 - A1) / A0 × 100 (%)

[0171] In the above formula, A0 represents the cross-sectional area of ​​the wire before tension, and A1 represents the cross-sectional area of ​​the wire after tension.

[0172] The final microstructure of the wire rod according to one embodiment of the present invention may include 90 vol.% or more of pearlite and ferrite.

[0173] However, the final microstructure of the wire is not limited to what has been described above and may include other structures replacing ferrite.

[0174] Hereinafter, a method for manufacturing a wire rod according to one embodiment of the present invention will be described in detail.

[0175]

[0176] Method for manufacturing wire

[0177] Hereinafter, a method for manufacturing a wire according to one embodiment of the present invention will be described.

[0178] FIG. 2 is a flowchart illustrating a method for manufacturing a wire rod according to one embodiment of the present invention.

[0179] A method for manufacturing a wire rod according to one embodiment of the present invention comprises (a) a molten steel manufacturing step of melting raw materials, (b) a continuous casting step of manufacturing a semi-finished product, and (c) a wire rod rolling step of hot rolling the semi-finished product.

[0180] According to one embodiment of the present invention, (a) the molten steel manufacturing step is a step of manufacturing molten steel by melting raw materials.

[0181] Figure 3 is a detailed flowchart of the molten steel manufacturing steps of Figure 2.

[0182] Referring to FIG. 3, (a) the molten steel manufacturing step may include (a-1) a raw material charging step, (a-2) a melting step, (a-3) a tapping step, and (a-4) an addition step.

[0183] (a-1) In the first charging step, raw materials are charged into a melting furnace. The raw materials may include at least one of blast furnace molten iron, iron scrap, and reduced iron.

[0184] Reduced iron may include DRI (Direct Reduced Iron), HBI (Hot Briquettied Iron), LRI (Low Reduced Iron), etc.

[0185] (a-2) The melting step is a step of melting the raw materials. (a-2) The melting step can be performed by an electric furnace.

[0186] Specifically, electric furnace operation involves charging raw materials into the furnace and then melting them using electrical energy. For example, the furnace may be an Electric Arc Furnace (EAF). An EAF can melt raw materials through arc heat generated between electrodes. While an EAF may operate on alternating current (AC), it is not limited to this, and a direct current (DC) method is also applicable.

[0187] However, the types of electric furnaces are not limited to those described above. For example, other types of electric furnaces, such as ESF (Electric Smelting Furnace) and EIF (Electric Induction Furnace), may also be used.

[0188] (a-3) The tapping step discharges the molten steel produced in step (a-2) out of the electric furnace. For example, the molten steel may be transferred from the electric furnace to a ladle. The ladle containing the molten steel may be moved by a means of transport to a location where a subsequent process is carried out.

[0189] (a-4) The addition step is the step of adding a slag modifier to the molten steel. The slag modifier can improve the quality of the molten steel by controlling the chemical composition of the slag that is tapped together with the molten steel.

[0190] According to one embodiment of the present invention, the slag-forming material can control the basicity of the slag.

[0191] Specifically, the slag flux may contain 35 to 50 weight percent calcium oxide (CaO), 3 weight percent or less aluminum oxide (Al2O3) (excluding 0), 3 weight percent or less magnesium oxide (MgO) (excluding 0), and the remainder silicon oxide (SiO2).

[0192] In the case of a slag flue, if the calcium oxide (CaO) content is less than 35 weight%, the viscosity of the slag increases, making it difficult to remove inclusions. If the CaO content exceeds 50 weight%, high-melting point oxides such as CaO, 2CaO·SiO2 are formed, raising the melting point of the slag and reducing the ability to remove non-metallic inclusions.

[0193] In the case of a slag-based material, if the content of aluminum oxide (Al2O3) exceeds 3 weight%, the formation of aluminum oxide-based inclusions may be promoted as the amount of aluminum (Al) picked up into the molten steel increases due to the reaction between the slag and the molten steel.

[0194] Therefore, in the present invention, the formation of inclusions can be suppressed by controlling the content of aluminum oxide (Al2O3) contained in the slag material to within the above range.

[0195] In the case of a slag material, if the magnesium oxide (MgO) content exceeds 3 weight%, polygonal coarse non-metallic inclusions may be formed.

[0196] According to one embodiment of the present invention, the basicity of the slag flue may be 1.0 or less. The basicity is of the slag am.

[0197] If the basicity of the slag flue exceeds 1.0, high-melting point oxides such as calcium oxide (CaO) and 2CaOSiO2 are produced, which raises the melting point of the slag and reduces the ability to remove non-metallic inclusions, and also increases the content of aluminum oxide (Al2O3), which increases the wire breakage rate during drawing.

[0198] According to one embodiment of the present invention, (a) the molten steel manufacturing step may further include (a-5) a first refining step and (a-6) a second refining step.

[0199] (a-5) The first refining step may be RH (Rhodium-Hartmann). (a-5) The first refining step may remove non-metallic inclusions and nitrogen from the molten steel.

[0200] To this end, (a-5) the first refining step can process the molten steel using an inert gas under a preset vacuum. Argon (Ar) can be used as the inert gas. The inert gas can cause non-metallic inclusions in the molten steel to float to the surface and be absorbed into the slag.

[0201] Specifically, (a-5) in the first refining step, the reflux flow rate of argon (Ar) can be controlled to 900 to 1100 L / min, the vacuum treatment time to 20 minutes or more, and the vacuum level to 2 mbar or less.

[0202] If the reflux flow rate of argon (Ar) deviates from the preset range or the vacuum treatment time is less than 20 minutes, the average cleanliness index of the wire may exceed the preset value, non-metallic inclusions with a size of 40 μm or more (hereinafter referred to as large non-metallic inclusions) may be formed, and the effect of removing nitrogen may also be insufficient.

[0203] According to one embodiment of the present invention, (a-5) a wire rod having high purity can be manufactured by controlling the reflux flow rate of the inert gas and the vacuum treatment time in the first refining step with extreme precision.

[0204] (a-6) The second refining step may be a Ladder Treatment System (LTS). (a-6) The second refining step can remove impurities from the molten steel to mix the molten steel uniformly and improve the cleanliness of the molten steel.

[0205] (a-6) In the second refining step, a wire may be added to the molten steel. The wire may contain calcium (Ca). For example, calcium (Ca) can remove impurities, including sulfur (S), from the molten steel.

[0206] (a-6) In the second refining stage, bubbles can be generated using an inert gas. As the bubbles move to the upper layer of the molten steel, they combine with non-metallic inclusions or nitrogen, thereby removing them. Argon (Ar) can be used as the inert gas.

[0207] Specifically, (a-6) in the second refining step, the process can be carried out by controlling the argon (Ar) flow rate to 100 L / min or less and the bubbling time to 7 minutes or more.

[0208] If the argon (Ar) flow rate exceeds 100 L / min, the formation of large non-metallic inclusions can be suppressed, but the cleanliness of the wire rod may decrease as re-oxidation occurs while the non-metallic inclusions mix with the slag.

[0209] In addition, if the bubbling time is less than 7 minutes, the removal effect of non-metallic inclusions may be insufficient.

[0210] According to one embodiment of the present invention, (a-6) a second refining step is additionally performed after (a-5) a first refining step, and the flow rate of the inert gas and the bubbling time in (a-6) the second refining step are precisely controlled to further improve the cleanliness of the wire rod.

[0211] According to one embodiment of the present invention, in the (b) continuous casting step, the molten steel produced in the (a) molten steel manufacturing step can be used to produce a semi-finished product.

[0212] In this embodiment, the semi-finished product may be a billet. However, it is not limited thereto, and it is also possible to manufacture it in the form of a slab or a bloom.

[0213] Figure 4 is a flowchart showing the detailed steps of the wire rod rolling step of Figure 2.

[0214] Referring to FIG. 4, (c) the wire rod rolling step may include (c-1) a reheating step, (c-2) a precision rolling step, and (c-3) a coiling step.

[0215] (c-1) In the reheating step, the semi-finished product can be reheated. (c-1) The reheating step can be performed under conditions of a reheating temperature of 1000 to 1170°C and a reheating time of 90 minutes or more.

[0216] If the reheat temperature exceeds a preset range, an excessive decarburization layer may form on the surface. Conversely, if the reheat temperature is below a preset range, the equipment load during precision rolling increases, and defects such as cobble may occur during rolling.

[0217] (c-2) In the precision rolling stage, wire rods can be manufactured by rolling semi-finished products. (c-2) In the precision rolling stage, the rolling process can be performed multiple times. (c-2) The precision rolling stage can be performed under conditions of an inlet temperature of 850 to 1000℃.

[0218] If the precision rolling inlet temperature exceeds a preset range, an excessive decarburization layer may form. Conversely, if the precision rolling inlet temperature is below a preset range, the load on the rolling equipment increases, and surface defects such as rolling folds may occur.

[0219] (c-3) In the winding step, the precision-rolled wire rod can be wound. (c-3) The winding step can be performed under conditions of a winding temperature of 800 to 900°C, preferably 800 to 870°C.

[0220] If the winding temperature exceeds a preset range, the thickness of the decarburization layer may be excessively formed, and the thickness of the surface scale may be thick, which may cause wire breakage during drawing and stranding. Conversely, if the winding temperature is below a preset range, a large difference from the rolling temperature may occur, resulting in defects in the winding shape.

[0221] According to one embodiment of the present invention, through the alloy composition system and manufacturing process described above, the average cleanliness index of the wire rod, the total amount of non-metallic inclusions, the number of non-metallic inclusions within a set standard size, the maximum size of non-metallic inclusions, the thickness of the decarburization layer, and the thickness of the scale layer are controlled within a preset range, thereby producing a wire rod with excellent drawing processability and uniform physical properties.

[0222] Below, a method for manufacturing a tire cord using a wire rod produced through the aforementioned alloy composition system and process, and the tire cord itself, will be described.

[0223]

[0224] Tire cord manufacturing method and tire cord

[0225] A method for manufacturing a tire cord according to one embodiment of the present invention may include (d) a pickling step, (e) a first drawing step, (f) a heat treatment step, (g) a plating step, (h) a second drawing step, and (i) a stranding step.

[0226] (d) The pickling step can clean the surface of the wire by exposing it to a pickling solution. (d) The pickling step can remove surface scale from the wire and form an iron oxide layer on the surface of the wire. Accordingly, the surface characteristics of the wire can be improved and corrosion resistance can be enhanced. The pickling solution contains an acidic substance, for example, the pickling solution may contain sulfuric acid, hydrochloric acid, etc.

[0227] (e) The first drawing step may be a dry drawing process. For example, in (e) the first drawing step, the wire rod after rolling can be processed into a wire rod having a diameter of 1 to 2 mm using a dry extension wire device.

[0228] (f) The heat treatment step may be a patterning heat treatment. For example, the (f) heat treatment step may heat treat the wire rod at a temperature range of 800 to 900°C.

[0229] (g) The plating step may be a step of forming a plating layer on the surface of the wire. For example, in the (g) plating step, a brass plating layer may be formed on the surface of the wire. Specifically, in the (g) plating step, copper and zinc plating may be performed on the surface of the wire, respectively, and a brass plating layer may be formed through diffusion treatment.

[0230] (h) The second drawing step may be a wet drawing process. For example, in (h) the second drawing step, a drawing with a diameter of 1 to 2 mm can be processed into a wire with a diameter of 0.15 to 0.40 mm through wet drawing using a wet lubricant.

[0231] (i) The stranding stage can manufacture a tire cord by twisting multiple wires that have undergone (h) the second drawing stage at a preset pitch.

[0232] According to one embodiment of the present invention, a method for manufacturing a tire cord can significantly improve the production efficiency of the tire cord by minimizing the frequency of wire breakage occurring during wire drawing by manufacturing the tire cord using a wire rod with excellent wire drawing properties.

[0233] A tire cord according to one embodiment of the present invention is placed in the belt area of ​​a vehicle tire to improve the durability of the tire and improve the stability of vehicle driving.

[0234] The tensile strength of a tire cord according to one embodiment of the present invention may be 3.2 GPa or more.

[0235]

[0236] Experimental Example

[0237] In the following, preferred experimental examples will be examined to aid in understanding the present invention. The following experimental examples are intended only to aid in understanding the present invention, and the present invention is not limited by the following examples.

[0238] Table 1 shows the alloy composition systems of Examples 1 to 4 and Comparative Examples 1 to 6.

[0239] Table 2 shows the composition of the slag-forming material, the basicity of the slag-forming material, the process conditions of the first refining step, and the process conditions of the second refining step introduced during the manufacturing process of Examples 1 to 4 and Comparative Examples 1 to 6.

[0240] Table 3 shows the total amount of non-metallic inclusions, the maximum size of non-metallic inclusions, the average cleanliness index, and the frequency of wire breakage during tire cord manufacturing observed in the wires of Examples 1 to 4 and Comparative Examples 1 to 6.

[0241] The total amount of non-metallic inclusions, the maximum size of non-metallic inclusions, and the average cleanliness index in Table 3 were measured by cutting the wire according to each experimental example in a direction perpendicular to the length direction of the wire, and then magnifying the cut surface of the wire to 200x using an optical microscope.

[0242] The average cleanliness index was calculated by calculating the cleanliness index for each of the five areas.

[0243] In addition, the total amount of non-metallic inclusions and the maximum size of non-metallic inclusions were measured in the five areas mentioned above.

[0244] The wire breakage frequency in Table 3 was measured as the wire breakage frequency that occurred when a tire cord was manufactured using the wire according to each experimental example. More specifically, it is the average wire breakage frequency that occurred when a tire cord was manufactured using three sets of coils wound with the wire according to each experimental example.

[0245] Classification CsiMnPSCuNiCrAlN Example 1 0.7 20.16 0.4 10.00 90.00 70.15 0.17 0.04 0.00 30.00 44 Example 2 0.8 20.17 0.22 0.01 40.01 50.10 0.11 0.33 0.00 10.00 39 Example 3 0.9 20.4 80.890.0120.0140.190.150.140.0070.0042 Example 41.020.240.350.0090.0060.040.050.220.0010.0041 Comparative Example 10.730.180.420.0090.0080.010.020.030. 0090.0045 Comparative Example 20.8 20.2 20.6 50.0090.005 0.02 0.01 0.2 10.001 0.0043 Comparative Example 30.8 60.1 60.2 50.01 00.006 0.08 0.07 0.3 20.002 0.0046 Comparative Example 40.9 20.2 00.4 10.00 80.0080.020.010.030.0070.0045 Comparative Example 50.930.450.850.0080.0120.100.080.160.0050.0041 Comparative Example 61.010.420.390.0100.0090.150.070.150.0080.0060

[0246] Classification Slag Fragmentation Material 1st Refining Stage 2nd Refining Stage Weight % Basicity Argon (Ar) Reflux Flow Rate (l / min) Vacuum Treatment Time (min) Argon (Ar) Flow Rate (l / min) Bubbling Time (min) CaOSiO2Al2O3MgO Example 1 43.05 2.90.7 1.70.8 19132 1.132 8.2 Example 2 36.76 1.50.50.70.60 1.01 125.54 07.1 Example 3 45.147.92.22.50.94 1.09 723.39 41 1.2 Example 4 38.35 7.50.60.50.67 1.06 527.6 627.5 Comparative Example 1 43.05 2.90.71.70.8 1875 25.03 37.1 Comparative Example 2 36.76 1.50.50.70.60 1,122 21.5 32 10.1 Comparative Example 3 38.35 7.50.60.50.67 1,050 19.18 8 2.3 Comparative Example 4 50.95.5 41.30.8 9.25 99 8 20.75 48.8 Comparative Example 5 43.146.15.73.60.93 95 32 2.5 12 17.5 Comparative Example 6 55.15.93 5.71.5 9.3 41,072 15.33 57.7

[0247] Classification Non-metallic Experimental Example Total amount of inclusions (%, JIS G0555) Maximum inclusion size (㎛) Average cleanliness index Frequency of wire breakage during tire cord manufacturing (times / coil) Example 1 0.0 3 2 1 7.5 3.6 1 Example 2 0.0 2 0 1 4.6 1.8 None Example 3 0.0 2 5 2 2.2 4.2 2 Example 4 0.0 3 8 3 5.7 2.6 None Comparative Example 1 0.0 5 5 4 3.7 6.8 4 Comparative Example 2 0.0 6 1 5 2.3 7.4 5 Comparative Example 3 0.0 5 8 4 5.9 6.2 5 Comparative Example 4 0.0 6 0 5 1.0 8.2 8 Comparative Example 5 0.0 5 2 3 8.6 6.4 4 Comparative Example 6 0.0 6 3 5 5.1 1 0.2 1 1

[0248] Referring to Tables 1 to 3, in the case of Comparative Examples 1 and 2, the argon reflux flow rate in the first refining step fell outside the preset range. Specifically, in Comparative Example 1, the argon reflux flow rate was 875 L / min, which is less than the minimum value of 900 L / min. In Comparative Example 2, the argon reflux flow rate was 1,122 L / min, which is greater than the maximum value of 1,100 L / min. Accordingly, in the case of Comparative Examples 1 and 2, the total amount, maximum size, and cleanliness of non-metallic inclusions fell outside the preset range.

[0249] Specifically, in Comparative Examples 1 and 2, the total amount of non-metallic inclusions was 0.055 vol% and 0.061 vol%, the maximum size of non-metallic inclusions was 43.7 μm and 52.3 μm, and the average cleanliness index was 6.8 and 7.4.

[0250] In the case of Comparative Example 3, the vacuum treatment time in the first refining step was insufficient, and the bubbling time in the second refining step was insufficient.

[0251] Specifically, in Comparative Example 3, the vacuum treatment time in the first refining step was 19.1 minutes, and the bubbling time in the second refining step was 2.3 minutes.

[0252] Accordingly, in Comparative Example 3, the removal effect of non-metallic inclusions was insufficient, so the total amount of non-metallic inclusions was 0.058 vol%, the maximum size of non-metallic inclusions was 45.9 μm, and the average cleanliness index was 6.2.

[0253] In the case of Comparative Example 4, the content ratio of the slag-forming material was not satisfied. Specifically, the content of calcium oxide (CaO) was 50.9 wt%, the content of silicon oxide (SiO2) was 5.5 wt%, and the content of aluminum oxide (Al2O3) was 41.3 wt%.

[0254] Accordingly, in Comparative Example 4, the basicity of the slag was 9.25, and consequently, the total amount of non-metallic inclusions was 0.060, the maximum size of non-metallic inclusions was 45.9, and the average cleanliness index was 8.2.

[0255] In the case of Comparative Example 5, the content ratio of the slag fluxing agent was not satisfied. The content of aluminum oxide (Al2O3) was 5.7 wt%, and the content of magnesium oxide (MgO) was 3.6 wt%. That is, in Comparative Example 5, the slag fluxing agent did not satisfy the preset content ratio, so the basicity of the slag was 9.25.

[0256] In addition, in the case of Comparative Example 5, the argon flow rate in the second refining step exceeded the preset range and was 121 L / min.

[0257] Therefore, in Comparative Example 5, the removal effect of non-metallic inclusions was insufficient, so the total amount of non-metallic inclusions was 0.052 vol% and the average cleanliness index was 6.4.

[0258] In the case of Comparative Example 6, the content ratio of the slag fluxing material was not satisfied. Specifically, the content of calcium oxide (CaO) was 55.1 wt%, the content of silicon oxide (SiO2) was 5.9 wt%, and the content of aluminum oxide (Al2O3) was 35.7 wt%. That is, in Comparative Example 6, the slag fluxing material did not satisfy the preset content ratio, so the basicity of the slag was 9.34.

[0259] In addition, in the case of Comparative Example 6, the vacuum treatment time in the first refining step was 15.3 minutes, which did not satisfy the minimum vacuum treatment time.

[0260] Accordingly, in Comparative Example 6, the removal effect of non-metallic inclusions was insufficient, so the total amount of non-metallic inclusions was 0.063, the maximum size of non-metallic inclusions was 55.1, and the average cleanliness index was 10.2. In addition, in Comparative Example 6, due to the insufficient vacuum treatment time, the nitrogen content was also 0.0060 wt%.

[0261] As a result, Comparative Examples 1 to 6 fail to satisfy at least one of the conditions regarding the slag content, the process conditions of the first refining step, and the process conditions of the second refining step, so the fresh processing capability exceeds 2 times, and it can be confirmed that the frequency of wire breakage is more than 2 times when compared to the Examples.

[0262] As described above, preferred embodiments according to the present invention have been examined. It is obvious to those skilled in the art that, in addition to the comparative examples and embodiments described above, the present invention may be embodied in other specific forms without departing from the spirit or scope thereof. Therefore, the embodiments described above should be regarded as illustrative rather than restrictive, and accordingly, the present invention is not limited to the description above but may be modified within the scope of the appended claims and their equivalents.

Claims

1. In a wire rod comprising 0.70 to 1.10 wt% carbon (C), 0.15 to 0.50 wt% silicon (Si), 0.20 to 0.90 wt% manganese (Mn), 0.015 wt% or less phosphorus (P), 0.015 wt% or less sulfur (S), 0.2 wt% copper (Cu) (excluding 0), 0.20 wt% or less nickel (Ni) (excluding 0), 0.03 to 0.40 wt% chromium (Cr), 0.010 wt% or less aluminum (Al) (excluding 0), 0.005 wt% or less nitrogen (N) (excluding 0), and the remainder being iron (Fe) and other unavoidable impurities, In the cross-section of a wire cut in a direction perpendicular to the longitudinal direction of the wire, The maximum size of non-metallic inclusions is 40 μm or less, and Wire, for which the value of [Equation 1] measured in any one of the multiple regions is 40 or less: [Equation 1] (1×n1)+(5×n2)+(20×n3) (In Equation 1, n1 represents the number of non-metallic inclusions with a maximum size of 5 μm or more and less than 10 μm, n2 represents the number of non-metallic inclusions with a maximum size of 10 μm or more and less than 20 μm, and n3 represents the number of non-metallic inclusions with a maximum size of 20 μm or more.) 2. In Paragraph 1, The arithmetic mean value of [Equation 1] measured in the above plurality of regions is 5 or less, Seonjae.

3. In Paragraph 1, The final microstructure comprises at least 90 vol.% pearlite and the remainder being ferrite, Seonjae.

4. In Paragraph 1, with a cross-sectional shrinkage rate of 30% or more, Seonjae.

5. In Paragraph 1, At the above cut surface, The total amount of non-metallic inclusions is 0.05% or less of the total area, Seonjae.

6. In Paragraph 1, tensile strength of 1000 MPa or higher, Seonjae.

7. (a) molten steel manufacturing step of melting raw materials to produce molten steel; (b) a continuous casting step for manufacturing semi-finished products; and (c) wire rod rolling step for hot rolling semi-finished products; Includes, The wire rod that has undergone the above (c) wire rod rolling step is, It contains 0.70 to 1.10 wt% carbon (C), 0.15 to 0.50 wt% silicon (Si), 0.20 to 0.90 wt% manganese (Mn), 0.015 wt% or less phosphorus (P), 0.015 wt% or less sulfur (S), 0.2 wt% copper (Cu) (excluding 0), 0.20 wt% or less nickel (Ni) (excluding 0), 0.03 to 0.40 wt% chromium (Cr), 0.010 wt% or less aluminum (Al) (excluding 0), 0.005 wt% or less nitrogen (N) (excluding 0), and the remainder being iron (Fe) and other unavoidable impurities, In the cross-section of a wire cut in a direction perpendicular to the longitudinal direction of the wire, The maximum size of non-metallic inclusions is 40 μm or less, and A method for manufacturing a wire, wherein the value of [Equation 1] measured in any one of a plurality of regions is 40 or less: [Equation 1] (1×n1)+(5×n2)+(20×n3) (In Equation 1, n1 represents the number of non-metallic inclusions with a maximum size of 5 μm or more and less than 10 μm, n2 represents the number of non-metallic inclusions with a maximum size of 10 μm or more and less than 20 μm, and n3 represents the number of non-metallic inclusions with a maximum size of 20 μm or more.) 8. In Paragraph 7, In the above (a) molten steel manufacturing step, The above raw material comprises at least one of reduced iron, molten iron, and iron scrap, Method for manufacturing wire.

9. In Paragraph 7, The above (a) molten steel manufacturing step (a-1) A raw material charging step for supplying the above raw material to a melting furnace; (a-2) melting step for producing molten steel by melting the above raw materials; and (a-3) tapping step of tapping the molten steel to the outside of the melting furnace; (a-4) Addition step of adding a slag-forming agent to the molten steel above; including, Method for manufacturing wire.

10. In Paragraph 9, The above melting furnace is an electric furnace, Method for manufacturing wire.

11. In Paragraph 9, The basicity of the above slag flue is 1.0 or less, Method for manufacturing wire.

12. In Paragraph 11, The above slag material is, Comprising 35 to 50 weight percent calcium oxide (CaO) and the remainder silicon oxide (SiO2), Method for manufacturing wire.

13. In Paragraph 7, The above (a) molten steel manufacturing step is, (a-5) further comprising a first refining step for refining the above molten steel, The above (a-5) first refining step is RH (Rhodium-Hartmann), Method for manufacturing wire.

14. In Paragraph 13, The above (a) molten steel manufacturing step is, The above molten steel is further refined in a second refining step (a-6), and further includes a second refining step. The above (a-6) second refining step is an LTS (Laddle Treatment System), Method for manufacturing wire.

15. Raw material charging step for supplying raw materials to the melting furnace; A melting step for producing molten steel by melting the above raw materials; A tapping step of tapping the molten steel to the outside of the melting furnace; and Addition step of adding a slag-forming agent to the molten steel; Includes, The above slag material is, Comprising 35 to 50 wt% calcium oxide (CaO), 3 wt% or less aluminum oxide (Al2O3) and 3 wt% or less magnesium oxide (MgO) and the remainder silicon oxide (SiO2), Method for manufacturing molten steel.

16. In Paragraph 15, The basicity of the above slag flue is 1.0 or less, Method for manufacturing molten steel.

17. In Paragraph 15, The above raw material comprises at least one of reduced iron, molten iron, and iron scrap, Method for manufacturing molten steel.

18. In Paragraph 15, The above melting furnace is an electric furnace, Method for manufacturing molten steel.

19. A slag-forming agent added to molten steel produced in a melting furnace, The above slag flux comprises 35 to 50 weight% calcium oxide (CaO), 3 weight% or less aluminum oxide (Al2O3) and 3 weight% or less magnesium oxide (MgO) and the remainder silicon oxide (SiO2). Slag slag.

20. In Paragraph 19, The basicity of the above slag flue is 1.0 or less, Slag slag.

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