Wire rod, manufacturing method therefor, and tirecord manufactured using same

Abstract

A wire rod with excellent drawing workability according to an embodiment of the present invention comprises: 0.70 to 1.10 wt% of carbon (C), 0.15 to 0.50 wt% of silicon (Si), 0.20 to 0.90 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P), 0.015 wt% or less of sulfur (S), 0.02 to 0.35 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 balance being iron (Fe) and other inevitable impurities. According to an embodiment of the present invention, in the cross-section cut in the direction perpendicular to the longitudinal direction of the wire rod, the maximum thickness of a decarburized layer, observed along the circumferential direction of the cross-section, is 0.08 mm or less.

Description

Wire and its manufacturing method and tire cord manufactured using the same

[0001] The present invention relates to a wire rod, a method for manufacturing the same, and a tire cord manufactured using the same, and more specifically, to a wire rod having improved wire drawing processability and uniform quality by controlling the thickness of a decarburized layer, a method for manufacturing the same, and a tire cord manufactured using the same.

[0002] Tire cord is a reinforcing material embedded inside rubber to improve the stability, drivability, and durability of tires installed in vehicles such as automobiles.

[0003] Tire cord materials can be broadly categorized into steel and high-molecular synthetic fibers (polyester, nylon, etc.).

[0004] Steel tire cords have been widely used recently because they have higher strength and superior heat resistance compared to high-molecular synthetic fiber tire cords.

[0005] Steel tire cord is manufactured into ultra-fine wires through a drawing processing and patterning heat treatment process.

[0006] When a fine wire is processed through fresh processing, it entails high work hardening, so short circuits may occur due to non-metallic inclusions, surface defects, decarburization layers, and residual scale that is not removed after pickling.

[0007] When a wire breaks during the manufacturing of tire cord, not only does it reduce workability and productivity, but it can also cause safety accidents for workers, so reducing the number of wire breaks is an issue that must be resolved.

[0008] In particular, if the decarburization layer on the surface of the wire is thick, it may not only cause wire breakage during drawing processing, but also cause the internal quality of the tire cord to be uneven, thereby reducing the fatigue resistance properties of the tire cord.

[0009] Meanwhile, wire for tire cords is typically produced in blast furnace-converter operations. This is because blast furnace-converter operations produce molten iron from iron ore, which is then used to manufacture products. This allows for higher-quality products compared to electric furnace operations, which primarily use scrap as a raw material.

[0010] However, in light of the international trend of accelerating carbon neutrality across most industries, the steel industry urgently needs to develop a technology that can replace blast furnace-converter furnace operations, which emit significant amounts of carbon dioxide, while ensuring quality equivalent to or superior to blast furnace-converter furnace products.

[0011] The present invention has been devised to solve the above problems, and its purpose is to provide a wire having excellent fresh processability and uniform internal quality, a method for manufacturing the same, and a tire cord manufactured using the same.

[0012] The tasks of the present invention are not limited to the tasks mentioned above, and other tasks not mentioned will be clearly understood by those skilled in the art from the description below.

[0013] According to one embodiment of the present invention, a wire rod having excellent processability comprises carbon (C) 0.70 to 1.10 wt%, silicon (Si) 0.15 to 0.50 wt%, manganese (Mn) 0.20 to 0.90 wt%, phosphorus (P) 0.015 wt% or less, sulfur (S) 0.015 wt% or less, chromium (Cr) 0.02 to 0.35 wt%, aluminum (Al) 0.010 wt% or less (excluding 0), nitrogen (N) 0.005 wt% or less (excluding 0), the remainder iron (Fe) and other unavoidable impurities.

[0014] According to one embodiment of the present invention, in a cross-section cut in a direction perpendicular to the longitudinal direction of the wire, the maximum thickness of the decarburized layer observed along the circumferential direction of the cross-section is 0.08 mm or less.

[0015] According to one embodiment of the present invention, the wire satisfies the following equation 1.

[0016] [Formula 1]

[0017] 0.1 ≤ (2ⅹCr) / Si

[0018] (In Equation 1, Cr represents the content of chromium, Si represents the content of silicon, and the unit is weight%.)

[0019] According to one embodiment of the present invention, a wire rod having excellent processability may further include 0.2 wt% (excluding 0) of copper (Cu) and 0.15 wt% or less (excluding 0) of nickel (Ni).

[0020] The final microstructure of a wire rod having excellent processability according to one embodiment of the present invention may include pearlite of 90 vol.% or more and the remainder ferrite.

[0021] A wire rod having excellent fresh processability according to one embodiment of the present invention may have a cross-sectional shrinkage ratio of 30% or more.

[0022] According to one embodiment of the present invention, the thickness of the decarburized layer may be 0.05 mm or less.

[0023] According to one embodiment of the present invention, the content of carbon (C) may be 0.7 to 0.95 wt%.

[0024] According to one embodiment of the present invention, the tensile strength is 1000 MPa or more,

[0025] A method for manufacturing a wire rod having excellent fresh processability according to one embodiment of the present invention includes (a) a melting step of melting a raw material, (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.

[0026] The wire rod that has gone through the above (c) wire rod rolling step contains carbon (C) 0.70 to 1.10 wt%, silicon (Si) 0.15 to 0.50 wt%, manganese (Mn) 0.20 to 0.90 wt%, phosphorus (P) 0.015 wt% or less, sulfur (S) 0.015 wt% or less, chromium (Cr) 0.02 to 0.35 wt%, aluminum (Al) 0.010 wt% or less (excluding 0), nitrogen (N) 0.005 wt% or less (excluding 0), the remainder iron (Fe) and other unavoidable impurities.

[0027] According to one embodiment of the present invention, in a cross-section cut in a direction perpendicular to the longitudinal direction of the wire, the maximum thickness of the decarburized layer observed along the circumferential direction of the cross-section is 0.08 mm or less.

[0028] According to one embodiment of the present invention, the wire satisfies the following equation 1.

[0029] [Formula 1]

[0030] 0.1 ≤ (2ⅹCr) / Si

[0031] (In Equation 1, Cr represents the content of chromium, Si represents the content of silicon, and the unit is weight%.)

[0032] According to one embodiment of the present invention, in the (a) melting 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, (a) the melting step may be performed in at least one of a blast furnace and an electric furnace.

[0034] According to one embodiment of the present invention, the wire rod that has gone through the (c) wire rod rolling step may further include 0.2 wt% or less of copper (Cu) and 0.15 wt% or less of nickel (Ni).

[0035] According to one embodiment of the present invention, the (c) pre-rolling step may include a (c-1) reheating step of reheating the semi-finished product at 1000 to 1170°C for 90 minutes or more, a (c-1) precision rolling step of hot-rolling the reheated semi-finished product at an inlet temperature of 850 to 1000°C, and a (c-3) coiling step of coiling the hot-rolled product at 800 to 900°C.

[0036] According to one embodiment of the present invention, the cross-sectional shrinkage rate of the wire rod that has gone through the above (c) wire rod rolling step may be 30% or more.

[0037] According to one embodiment of the present invention, the final microstructure of the wire rod that has gone through the above (c) wire rod rolling step may include pearlite of 90 vol.% or more and the remainder ferrite.

[0038] A tire cord according to one embodiment of the present invention comprises a plurality of wires. Here, the maximum thickness of the decarburized layer observed in the cross-section of the wires is 0.08 mm or less.

[0039] The above-mentioned pre-existing condition satisfies the following equation 1.

[0040] [Formula 1]

[0041] 0.1≤ (2ⅹCr) / Si

[0042] (In Equation 1, Cr represents the content of chromium, Si represents the content of silicon, and the unit is weight%.)

[0043] According to one embodiment of the present invention, the wire may contain carbon (C) 0.70 to 1.10 wt%, silicon (Si) 0.15 to 0.50 wt%, manganese (Mn) 0.20 to 0.90 wt%, phosphorus (P) 0.015 wt% or less, sulfur (S) 0.015 wt% or less, chromium (Cr) 0.02 to 0.35 wt%, aluminum (Al) 0.010 wt% or less (excluding 0), nitrogen (N) 0.005 wt% or less (excluding 0), the remainder iron (Fe) and other unavoidable impurities.

[0044] According to one embodiment of the present invention, the wire may further include 0.2 wt% (excluding 0) of copper (Cu) and 0.15 wt% or less (excluding 0) of nickel (Ni).

[0045] According to one embodiment of the present invention, the maximum thickness of the decarburized layer may be 0.05 mm or less.

[0046] According to one embodiment of the present invention, the tensile strength may be 3.2 GPa or more.

[0047] According to one embodiment of the present invention, a wire rod having excellent fresh processability can have excellent fresh processability and uniform physical properties by controlling the thickness of the decarburized layer on the surface of the wire rod.

[0048] In addition, the tire cord according to one embodiment of the present invention can be manufactured using a wire having excellent fresh processability and thus have an excellent tensile strength of 3.2 GPa or more.

[0049] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0050] Figure 1 is a flowchart showing a method for manufacturing a wire rod having excellent fresh processing properties according to one embodiment of the present invention.

[0051] Figure 2 is a flowchart showing detailed steps of the wire rolling step shown in Figure 1.

[0052] Figure 3 is a flowchart showing a method for manufacturing a tire cord according to one embodiment of the present invention.

[0053] Figure 4 is an enlarged photograph showing the decarburization layer of a specimen according to a test example.

[0054] Hereinafter, with reference to the attached drawings, preferred embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited or restricted by the following examples.

[0055] Additionally, when a component (or region, layer, portion, etc.) is referred to as being "on," "connected to," or "coupled to" another component, it means that it can be directly placed / connected / coupled to the other component, or that a third component may be placed between them.

[0056] Terms such as "include" or "have" should be understood to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0057] In order to clearly explain the present invention, a detailed description of a part that is irrelevant to the description or a related known technology that may unnecessarily obscure the gist of the present invention has been omitted, and when adding reference signs to components of each drawing in this specification, the same or similar reference signs are attached to the same or similar components throughout the specification.

[0058] In addition, terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0059] Unless otherwise specified, the notation 'A to B' for numerical values ​​A and B means 'A or more and B or less'. In such notation, if a unit is attached only to numerical value B, the unit shall be applied to numerical value A as well.

[0060] Hereinafter, embodiments of the present invention will be described in detail.

[0061] Wire rod with excellent freshness and processability

[0062] A wire rod with excellent fresh processability according to one embodiment of the present invention

[0063] It contains 0.70 to 1.1 wt% of carbon (C), 0.15 to 0.5 wt% of silicon (Si), 0.20 to 0.9 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P) (excluding 0), 0.015 wt% or less of sulfur (S) (excluding 0), 0.02 to 0.35 wt% of chromium (Cr), 0.010 wt% or less of aluminum (Al) (excluding 0), 0.005 wt% or less of nitrogen (N), and the remainder of iron (Fe) and other unavoidable impurities.

[0064] Hereinafter, the role and content of each alloy element included in a wire rod with excellent fresh processability according to one embodiment of the present invention will be described in detail.

[0065] carbon (C)

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

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

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

[0069] Accordingly, in the wire rod having excellent fresh processability according to one embodiment of the present invention, the content of carbon (C) can be controlled to 0.70 to 1.1 wt%, preferably 0.7 to 0.95 wt%.

[0070] Silicon (Si)

[0071] Silicon (Si) is an element that is effective in increasing strength and deoxidation, and increases carbon activity.

[0072] If silicon (Si) is added below the preset range, it is difficult to secure the deoxidation effect and strength.

[0073] Conversely, if silicon (Si) is added in excess of the preset range, it may reduce toughness, increase deformation resistance, and make it difficult to remove surface scale during the acid pickling process.

[0074] Additionally, if silicon (Si) is added in excess of the preset range, it may excessively promote decarburization, thereby reducing fresh workability as the thickness of the decarburization layer increases.

[0075] Accordingly, in a wire having excellent fresh processability according to one embodiment of the present invention, the content of silicon (Si) can be controlled to 0.15 to 0.5 wt%, preferably 0.16 to 0.48 wt%.

[0076] manganese (Mn)

[0077] Manganese (Mn) is an element that increases the strength of wire rods while being effective in deoxidation. It also forms MnS inclusions, preventing red-hot embrittlement. Manganese (Mn) also reduces carbon activity.

[0078] When manganese (Mn) is added below the preset range, the deoxidation effect is reduced, it is difficult to secure strength, and there is a problem of causing red-hot embrittlement.

[0079] In addition, when manganese (Mn) is added below a preset range, the effect of inhibiting decarburization is insufficient, which may reduce fresh workability as the thickness of the decarburization layer increases.

[0080] When manganese (Mn) is added in excess of the preset range, segregation may occur in the center of the wire, and low-temperature structure formation may occur during cooling. Specifically, martensite may be formed during cooling.

[0081] Accordingly, in the wire rod having excellent fresh processability according to one embodiment of the present invention, the content of manganese (Mn) can be controlled to 0.2 to 0.9 wt%, preferably 0.22 to 0.89 wt%.

[0082] Person (P)

[0083] Phosphorus (P) is a residual element that must be removed during the steelmaking process. If the phosphorus content exceeds 0.015 wt%, it can cause embrittlement due to grain boundary segregation and the formation of Fe3P compounds.

[0084] Accordingly, in a wire having excellent fresh processability according to one embodiment of the present invention, the content of phosphorus (P) can be controlled to 0.015 wt% or less.

[0085] Yellow (S)

[0086] Sulfur (S) is a residual element that must be removed during the steelmaking process and forms MnS non-metallic inclusions.

[0087] When the sulfur content exceeds 0.015 wt%, the toughness is reduced due to excessive generation of sulfides such as MnS.

[0088] Accordingly, in a wire having excellent fresh processability according to one embodiment of the present invention, sulfur (S) can be controlled to 0.015 wt% or less.

[0089] copper (Cu)

[0090] Copper (Cu) is an element that contributes to increased strength and improved corrosion resistance in wire rods. However, if copper (Cu) is added beyond the preset range, it can cause surface cracks during high-temperature wire rolling.

[0091] Accordingly, in a wire having excellent fresh processability according to one embodiment of the present invention, the content of copper (Cu) can be controlled to 0.2 wt% or less (excluding 0), preferably 0.02 to 0.19 wt%.

[0092] According to one embodiment of the present invention, copper (Cu) may be derived from iron scrap. However, this is not limited to the source, and may be added separately as needed.

[0093] Nickel (Ni)

[0094] Nickel (Ni) is an element that contributes to increased strength and improved corrosion resistance in wire rods. Furthermore, nickel (Ni) effectively reduces surface cracking during hot rolling caused by copper (Cu)-enriched layers, and also reduces carbon diffusion.

[0095] However, if nickel (Ni) is added beyond the preset range, the fatigue life of the product may be reduced due to excessive formation of retained austenite. Furthermore, excessive nickel (Ni) addition can lead to increased manufacturing costs.

[0096] Accordingly, in a wire having excellent fresh processability according to one embodiment of the present invention, the content of nickel (Ni) can be controlled to 0.15 wt% or less (excluding 0), preferably 0.01 to 0.15 wt%.

[0097] chromium (Cr)

[0098] Chromium (Cr) is an element that contributes to the strength and hardenability of wire rods. It also enhances the corrosion resistance of wire rods. Furthermore, chromium (Cr) effectively reduces carbon activity.

[0099] If chromium (Cr) is added below the preset range, it is difficult to secure the required strength, and the effect of suppressing decarburization is insufficient, which may reduce the fresh workability as the thickness of the decarburization layer increases.

[0100] If chromium (Cr) is added in excess of the preset range, it can cause short circuits during subsequent drawing processes due to low-temperature tissue formation. Furthermore, excessive addition of chromium (Cr) can lead to increased manufacturing costs.

[0101] Accordingly, in a wire rod having excellent fresh processability according to one embodiment of the present invention, the content of chromium (Cr) can be controlled to 0.02 to 0.35 wt%, preferably 0.03 to 0.33 wt%.

[0102] Aluminum (Al)

[0103] Aluminum (Al) is an element that acts as a strong deoxidizer, improves toughness by refining the austenite grain size, and forms non-metallic inclusions.

[0104] However, if aluminum (Al) is added in excess of the preset range, excessive formation of coarse aluminum-based non-combustible inclusions may cause short circuits during drawing.

[0105] Accordingly, in a wire having excellent fresh processability according to one embodiment of the present invention, the content of aluminum (Al) can be controlled to 0.01 wt% or less (excluding 0), preferably 0.001 to 0.01 wt%.

[0106] Nitrogen (N)

[0107] Nitrogen (N) combines with elements such as aluminum (Al), titanium (Ti), vanadium (V), and niobium (Nb) to form precipitates and is an effective element for refining the grain size of austenite.

[0108] However, if nitrogen (N) is added in excess of the preset range, a deviation in strength may occur due to excessive formation of precipitates, and this may adversely affect cold workability during fresh processing.

[0109] Accordingly, in a wire having excellent fresh processability according to one embodiment of the present invention, the nitrogen (N) content can be controlled to 0.005 wt% or less (excluding 0), preferably 0.0032 to 0.0044 wt%.

[0110] In addition to the aforementioned components, the remainder may contain iron and unavoidable impurities. Unavoidable impurities are impurities introduced during the manufacturing process, and as these are widely known in the field, a detailed description will be omitted.

[0111] 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 range that does not impair the technical spirit of the present invention. When additional elements are included, they may be included to replace the remaining Fe.

[0112] In a wire rod having excellent fresh processability according to one embodiment of the present invention, the thickness of the decarburized layer may be 0.08 mm or less, preferably 0.05 mm or less.

[0113] A decarburized layer is a layer of carbon lost from the surface of a metal material. Decarburized layers can form when carbon is lost from the surface of a metal material exposed to high temperatures.

[0114] In particular, decarburization can have a detrimental effect on the process of manufacturing tire cord using wire.

[0115] Specifically, as the decarburization layer increases in thickness, it can reduce the hardness of the wire surface and cause strength loss. This can make the wire more susceptible to deformation during dry or wet drawing processes, increasing the risk of wire breakage.

[0116] Additionally, as the decarburization layer increases in thickness, it brings the wire surface into more intensive contact with oxygen, potentially causing corrosion. This can lead to wire being more susceptible to water corrosion during wet drawing.

[0117] Additionally, as the decarburization layer thickness increases, the amount of impurities present on the surface of the wire may increase. This may cause microscopic defects in the wire during subsequent processes.

[0118] As mentioned above, minimizing the thickness of the decarburized layer may be a very important technology for manufacturing wire rods with excellent fresh processability.

[0119] Accordingly, the inventor of the present invention devised a method for minimizing the thickness of the decarburized layer by precisely controlling the content ratio between elements affecting carbon activity.

[0120] In a wire having excellent fresh processability according to one embodiment of the present invention, silicon (Si) and chromium (Cr) can satisfy the following equation 1.

[0121] 0.1 ≤ (2×Cr) / Si

[0122] (In Equation 1, Cr represents the content of chromium, Si represents the content of silicon, and the unit is weight%.)

[0123] According to Equation 1, the thickness of the decarburization layer can be controlled by adjusting the ratio of chromium (Cr), which reduces the activity of carbon, and silicon (Si), which increases the activity of carbon.

[0124] Specifically, Equation 1 can control the thickness of the decarburized layer by designing the weighted value of the chromium (Cr) content (i.e., 2xCr in Equation 1) and the ratio of silicon (Si) to be greater than 0.1, while minimizing the thickness of the decarburized layer and taking into account other required properties of the wire (e.g., tensile strength, etc.).

[0125] According to one embodiment of the present invention, the thickness of the decarburized layer of the wire satisfying Equation 1 may be 0.08 mm or less.

[0126] According to one embodiment of the present invention, in order to further control the thickness of the decarbonization layer, Equation 2 or Equation 3 may be satisfied.

[0127] In a wire having excellent processability according to one embodiment of the present invention, silicon (Si), chromium (Cr), and manganese (Mn) can satisfy the following equation 2.

[0128] [Formula 2]

[0129] 1 ≤ (6×Cr + Mn) / (3×Si)

[0130] (In Equation 2, Cr represents the content of chromium, Si represents the content of silicon, and Mn represents the content of manganese, and the unit is weight%.)

[0131] According to Equation 2, the thickness of the decarburization layer can be controlled by adjusting the ratio of chromium (Cr) and manganese (Mn), which reduce the activity of carbon, and silicon (Si), which increases the activity of carbon.

[0132] Specifically, Equation 2 can control the thickness of the decarburized layer by designing the ratio of the sum of the weighted value of the chromium (Cr) content and the manganese (Mn) content (i.e., [6xCr+Mn] in Equation 2) to the weighted value of the silicon (Si) content (i.e., 3xSi in Equation 2) to be 1 or more, while minimizing the thickness of the decarburized layer and taking into account other required properties of the wire (e.g., tensile strength, etc.).

[0133] According to one embodiment of the present invention, the thickness of the decarburized layer of the wire satisfying Equation 2 may be 0.05 mm or less.

[0134] In a wire having excellent processability according to an embodiment of the present invention, silicon (Si), chromium (Cr), manganese (Mn), and nickel (Ni) can satisfy the following equation 3.

[0135] [Formula 3]

[0136] 1 ≤ (12×Cr + 2×Mn + 3×Ni) / (6×Si)

[0137] (In Equation 3, Cr represents the content of chromium, Si represents the content of silicon, Mn represents the content of manganese, and Ni represents the content of nickel, and the unit is weight%.)

[0138] According to Equation 3, the thickness of the decarburization layer can be controlled by adjusting the ratio of chromium (Cr), manganese (Mn), and nickel (Ni), which reduce the activity of carbon, and silicon (Si), which increases the activity of carbon.

[0139] Specifically, Equation 3 can control the thickness of the decarburized layer by designing the ratio of the sum of values ​​that give different weights to each of chromium (Cr), manganese (Mn), and nickel (Ni) (i.e., [12ⅹCr+2ⅹMn+3ⅹNi] in Equation 2) to the value that gives weight to the content of silicon (Si) (i.e., 3ⅹSi in Equation 2) to be 1 or more, while minimizing the thickness of the decarburized layer and taking into account other required physical properties of the wire (e.g., tensile strength, etc.).

[0140] According to one embodiment of the present invention, the thickness of the decarburized layer of the wire satisfying Equation 3 may be 0.05 mm or less.

[0141] In conclusion, a wire rod having excellent workability according to one embodiment of the present invention can be manufactured using the alloy composition system described above and the manufacturing process described below.

[0142] In particular, the wire rod having excellent fresh processability according to one embodiment of the present invention can minimize the thickness of the decarburized layer by precisely controlling the content ratio between elements affecting carbon activity through the above-described formula.

[0143] In a wire having excellent fresh processability according to one embodiment of the present invention, the total amount of non-metallic inclusions may be 0.05 vol.% or less, and the maximum size of the non-metallic inclusions may be 40 ㎛ or less on average.

[0144] Preferably, the total amount of non-metallic inclusions is 0.021 to 0.025 vol.%, and the maximum size of the non-metallic inclusions can be 17.1 to 17.3 ㎛.

[0145] According to one embodiment of the present invention, the average thickness of the surface scale of the wire may be 8 ㎛ or less, preferably 7.2 ㎛ or less.

[0146] Accordingly, the surface scale layer of the wire can be completely removed through the pickling process. This reduces the frequency of wire breakage during the drawing process.

[0147] As a result, according to one embodiment of the present invention, by controlling the thickness of the decarburized layer, the total amount of non-metallic inclusions, the maximum size of the non-metallic inclusions, and the thickness of the scale layer within preset ranges, the frequency of wire breakage occurring during tire cord manufacturing can be significantly reduced.

[0148] The tensile strength (TS) of the wire rod having excellent fresh processability according to one embodiment of the present invention may be 1000 MPa or more, preferably 1050 to 1250 MPa.

[0149] According to one embodiment of the present invention, the cross-sectional shrinkage of a wire rod with excellent processability may be 30% or more. Here, the cross-sectional shrinkage is a value expressed as a percentage of the decrease in cross-sectional area when the wire rod is stretched longitudinally and breaks. For example, the cross-sectional shrinkage may be defined as follows:

[0150] [Cross-sectional shrinkage]

[0151] [(A0-A1) / A0]×100(%)

[0152] In the above formula, A0 means the cross-sectional area of ​​the wire before tension, and A1 means the cross-sectional area of ​​the wire after tension.

[0153] The final microstructure of a wire having excellent fresh processability according to one embodiment of the present invention may include pearlite and ferrite of 90 vol.% or more.

[0154] However, the final microstructure of the wire is not limited to that described above, and may include other structures replacing ferrite.

[0155] Hereinafter, a method for manufacturing a wire rod having excellent fresh processability according to one embodiment of the present invention will be described in detail.

[0156] Method for manufacturing wire rod with excellent freshness and processability

[0157] Hereinafter, a method for manufacturing a wire rod having excellent fresh processing properties according to one embodiment of the present invention will be described.

[0158] Figure 1 is a flowchart showing a method for manufacturing a wire rod having excellent fresh processing properties according to one embodiment of the present invention.

[0159] A method for manufacturing a wire rod having excellent fresh processing properties according to one embodiment of the present invention includes (a) a melting step of melting a raw material, (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.

[0160] According to one embodiment of the present invention, (a) the melting step is a step of melting a raw material to produce molten metal. (a) The melting step can be performed by at least one of a blast furnace and an electric furnace.

[0161] When using a blast furnace, raw materials may include iron ore and coke. Specifically, the blast furnace process involves loading the raw materials into the furnace and then simultaneously melting and reducing them using hot air.

[0162] The molten iron produced in the blast furnace can be turned into molten steel with the alloy composition controlled within a preset range and impurities removed through a subsequent steelmaking process.

[0163] When using an electric furnace, the raw material may include at least one of iron scrap and reduced iron. For example, the raw material may include 0 to 100 wt% direct reduced iron and the remainder iron scrap. The reduced iron may include direct reduced iron (DRI), hot briquettized iron (HBI), low reduced iron (LRI), etc.

[0164] Specifically, the electric furnace process can melt raw materials by loading them into an electric furnace and then using electrical energy. For example, the electric furnace can be an Electric Arc Furnace (EAF). An EAF melts raw materials through the heat generated by the arc between electrodes. While an EAF can be an alternating current (AC) system, it is not limited to this; a direct current (DC) system can also be used.

[0165] 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.

[0166] The method of using a blast furnace and an electric furnace together is a manufacturing method in which a portion of the molten iron produced in the blast furnace is charged into the electric furnace to ultimately produce molten metal within the electric furnace.

[0167] Here, the raw material may include blast furnace molten iron, iron scrap, and reduced iron. For example, the raw material may include 15 to 30 wt% blast furnace molten iron, 15 to 30 wt% reduced iron, and the remainder iron scrap.

[0168] If the amount of molten iron charged into the electric furnace falls below the preset range, complete melting of reduced iron and scrap iron may be difficult. Conversely, if the amount of molten iron exceeds the preset range, molten iron production increases, potentially resulting in excessive carbon dioxide emissions from blast furnace operations.

[0169] If the amount of reduced iron charged into the electric furnace falls below the preset range, the proportion of iron scrap in the raw material increases, which may degrade the physical properties of the wire rod due to tramp elements contained in the iron scrap. Conversely, if the amount of reduced iron charged into the electric furnace exceeds the preset range, the increased amount of reduced iron, which is more difficult to melt than the iron scrap, may make complete melting of the raw material difficult.

[0170] In the case of using the electric furnace described above or using a blast furnace and an electric furnace together, a process of processing the molten metal produced in the electric furnace can be carried out.

[0171] For example, molten metal produced in an electric furnace can undergo a vacuum degassing process. Specifically, the vacuum degassing process can treat the molten metal using an inert gas under a preset vacuum level. The inert gas can be argon (Ar).

[0172] Specifically, the vacuum degassing process can be performed by controlling the argon (Ar) reflux flow rate to 900 to 1100 ℓ / min, the vacuum treatment time to 20 minutes or more, and the vacuum level to 2 mbar or less. This allows for the control of the maximum size of non-metallic inclusions and the nitrogen content that affect the fresh processability.

[0173] According to one embodiment of the present invention, in the (b) continuous casting step, the molten metal produced in the (a) melting step can be produced in the form of a semi-finished product.

[0174] In this embodiment, the semi-finished product may be a billet. However, this is not limited to this, and it is also possible to manufacture it in the form of a slab or bloom.

[0175] Figure 2 is a flowchart showing detailed steps of the wire rolling step shown in Figure 1.

[0176] Referring to FIG. 2, the (c) pre-rolling step may include a (c-1) reheating step, a (c-2) precision rolling step, and a (c-3) coiling step.

[0177] (c-1) In the reheating step, the semi-finished product can be reheated. (c-1) The reheating step can be performed under the conditions of a reheating temperature of 1000 to 1170°C and a reheating time of 90 minutes or more.

[0178] If the reheating temperature exceeds the preset range, excessive decarburization may occur on the surface. Conversely, if the reheating temperature falls below the preset range, equipment load during precision rolling increases, potentially resulting in defects such as cobbles during rolling.

[0179] (c-2) In the precision rolling stage, semi-finished products can be rolled to manufacture wire rods. (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°C.

[0180] If the precision rolling inlet temperature exceeds the preset range, excessive decarburization may occur. Conversely, if the precision rolling inlet temperature falls below the preset range, the load on the rolling equipment increases, potentially causing surface defects such as rolling folds.

[0181] (c-2) The diameter of the wire that has gone through the precision rolling step may be 4 mm to 7 mm, preferably 4.5 to 6 mm.

[0182] However, the diameter of the wire rod is not limited to the above-mentioned, and the diameter of the wire rod may vary depending on the rolling conditions.

[0183] (c-3) In the winding stage, the precision rolled wire can be wound. (c-3) In the winding stage, the winding temperature

[0184] Semi-finished products can be rolled to manufacture wire rods. (c-2) The precision rolling step can be performed under conditions of a coiling temperature of 800 to 900°C.

[0185] If the coiling temperature exceeds the preset range, the decarburization layer may become excessively thick and the surface scale may become thick, potentially causing wire breakage during drawing and twisting. Conversely, if the coiling temperature falls below the preset range, the difference from the rolling temperature may be significant, resulting in coil shape defects.

[0186] According to one embodiment of the present invention, by controlling the thickness of the decarburized layer, the total amount of non-metallic inclusions, the maximum size of the non-metallic inclusions, and the thickness of the scale layer within preset ranges through the above-described alloy composition and manufacturing process, a wire rod having excellent fresh workability and uniform physical properties can be manufactured.

[0187] Below, a tire cord manufacturing method and tire cord using wire manufactured through the aforementioned alloy composition and process will be described.

[0188] Tire cord manufacturing method and tire cord

[0189] Figure 3 is a flowchart showing a method for manufacturing a tire cord according to one embodiment of the present invention.

[0190] Referring to FIG. 3, a method for manufacturing a tire cord according to an 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 twisting step.

[0191] (d) The pickling treatment step can clean the surface of the wire by exposing it to a pickling solution. (d) The pickling treatment step can remove surface scale from the wire and form an iron oxide layer on the wire surface. Accordingly, the surface properties of the wire can be improved and its corrosion resistance can be enhanced. The pickling solution contains an acidic substance, such as sulfuric acid or hydrochloric acid.

[0192] (e) The first drawing step may be a dry drawing process. For example, in (e) the first drawing step, the wire after wire rolling may be processed into a wire having a diameter of 1 to 2 mm using a dry extension device.

[0193] (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.

[0194] (g) The plating step may be a step for forming a plating layer on the surface of the wire. For example, the (g) plating step may form a brass plating layer on the surface of the wire. Specifically, the (g) plating step may be performed by plating copper and zinc on the surface of the wire, respectively, and forming a brass plating layer through diffusion treatment.

[0195] (h) The second drawing step may be a wet drawing process. For example, in the (h) second drawing step, a wire having a diameter of 1 to 2 mm may be processed into a wire having a diameter of 0.15 to 0.40 mm through wet drawing using a wet lubricant.

[0196] (i) The wire-stretching step can manufacture a tire cord by twisting a plurality of wires that have gone through the (h) second freshening step at a preset pitch.

[0197] A method for manufacturing a tire cord according to one embodiment of the present invention can greatly improve the production efficiency of tire cord by manufacturing the tire cord using a wire having excellent fresh processing properties, thereby minimizing the frequency of wire breakage occurring during fresh processing.

[0198] A tire cord according to one embodiment of the present invention can be arranged in a belt area of ​​a vehicle tire to improve the durability of the tire and thereby enhance the stability of vehicle driving.

[0199] The tensile strength of the tire cord according to one embodiment of the present invention may be 3.2 GPa or more.

[0200] Exam example

[0201] Below, we will examine preferred test examples to aid understanding of the present invention. The following test examples are provided solely to aid understanding of the present invention, and the present invention is not limited to the following examples.

[0202] Tables 1 and 2 show the alloy compositions and formulae 1 to 3 values ​​of Test Examples 1 to 9. Table 3 shows the manufacturing process conditions of Test Examples 1 to 9. Table 4 shows the maximum thickness of the decarburized layer of Test Examples 1 to 9. The diameter of the wire specimens according to Test Examples 1 to 9 is 5.5 mm.

[0203] The maximum thickness of the decarburized layer shown in Table 4 was measured by cutting the wires according to Test Examples 1 to 9 in a direction perpendicular to the longitudinal direction of the wires, observing the decarburized layer along the circumferential direction of the cut surface using an optical microscope, and measuring the thickness of the thickest decarburized layer.

[0204] The wire breakage frequency in Table 4 was measured by measuring the wire breakage frequency that occurred when tire cords were manufactured using the wires according to Test Examples 1 to 9. More specifically, it is the average wire breakage frequency that occurred when tire cords were manufactured using three sets of coils wound with the wires according to each Test Example.

[0205]

[0206]

[0207]

[0208]

[0209] Fig. 4 is an enlarged photograph showing the decarburization layer of a specimen according to a test example. Specifically, Fig. 4(a) shows the shape and maximum thickness of the decarburization layer observed in the specimens according to Test Example 1, Fig. 4(b) shows Test Example 3, Fig. 4(c) shows Test Example 5, and Fig. 4(d) shows Test Example 8, respectively.

[0210] Referring to Tables 1 to 4, Test Examples 1 to 9 satisfied both the content range of each element and the manufacturing process conditions described above.

[0211] The values ​​of [Formula 1] in each of Test Examples 1 to 9 were all 0.1 or greater. Accordingly, the maximum thickness of the decarburized layer observed in the specimens according to Test Examples 1 to 9 was all 0.08 mm or less. The frequency of disconnection in the specimens according to Test Examples 1 to 9 was 4 or less.

[0212] Referring to Fig. 4, it was observed that the maximum thickness of the decarburized layer of the specimens according to Test Examples 1, 3, 5 and 8 in Fig. 4 was all 0.08 mm or less.

[0213] Referring to Tables 1 to 4 and Fig. 4, the value of [Formula 2] in each of Test Examples 1 to 5 was 1 or greater, and the value of [Formula 2] in each of Test Examples 6 to 9 was less than 1. The maximum thickness of the decarburized layer observed in the specimens according to Test Examples 1 to 5 was 0.05 mm or less, and the maximum thickness of the decarburized layer observed in the specimens according to Test Examples 6 to 9 all exceeded 0.05 mm.

[0214] As a result, it can be confirmed that the frequency of disconnection of the specimens according to Test Examples 1 to 5, in which the value of [Formula 2] is 1 or more, is 1 or less, and the frequency of disconnection is significantly reduced compared to the specimens according to Test Examples 6 to 9.

[0215] Referring to Tables 1 to 4 and Fig. 4, the value of [Formula 3] in each of Test Examples 1 to 5 was 1 or greater, and the value of [Formula 3] in each of Test Examples 6 to 9 was less than 1. The maximum thickness of the decarburized layer observed in the specimens according to Test Examples 1 to 5 was 0.05 mm or less, and the maximum thickness of the decarburized layer observed in the specimens according to Test Examples 6 to 9 all exceeded 0.05 mm.

[0216] As a result, it can be confirmed that the frequency of disconnection of the specimens according to Test Examples 1 to 5, in which the value of [Formula 3] is 1 or more, is 1 or less, and the frequency of disconnection is significantly reduced compared to the specimens according to Test Examples 6 to 9.

[0217] According to one embodiment of the present invention, the thickness of the decarburized layer can be controlled to 0.05 mm by extremely precisely controlling the content ratio between elements that increase carbon activity (silicon (Si)) and elements that decrease carbon activity (manganese (Mn), chromium (Cr), nickel (Ni)).

[0218] Accordingly, the loss of hardness and strength of the wire surface caused by excessive formation of a decarburized layer can be prevented, and the average frequency of wire breakage in the subsequent drawing process can be significantly reduced to 1 or less by minimizing the amount of impurities.

[0219] As described above, preferred embodiments of the present invention have been described. It will be apparent to those skilled in the art that the present invention can be embodied in other specific forms, in addition to the comparative examples and examples described above, without departing from the spirit or scope thereof. Therefore, the above-described embodiments should be considered illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description, but may be modified within the scope of the appended claims and their equivalents.

Claims

1. In a wire rod containing carbon (C) 0.70 to 1.10 wt%, silicon (Si) 0.15 to 0.50 wt%, manganese (Mn) 0.20 to 0.90 wt%, phosphorus (P) 0.015 wt% or less, sulfur (S) 0.015 wt% or less, chromium (Cr) 0.02 to 0.35 wt%, aluminum (Al) 0.010 wt% or less (excluding 0), nitrogen (N) 0.005 wt% or less (excluding 0), the remainder iron (Fe) and other unavoidable impurities, In the cross section cut in a direction perpendicular to the longitudinal direction of the above wire, The maximum thickness of the decarburized layer located along the circumferential direction of the above cross-section is 0.08 mm or less, A wire rod with excellent fresh processability satisfying the following equation 1: [Formula 1] 0.1 ≤ (2ⅹCr) / Si (In Equation 1, Cr represents the content of chromium, Si represents the content of silicon, and the unit is weight%.) 2. In paragraph 1, Further containing 0.2 wt% of copper (Cu) (excluding 0) and 0.15 wt% or less of nickel (Ni) (excluding 0). Wire rod with excellent freshness and processability.

3. In paragraph 1, The final microstructure contains more than 90 vol.% pearlite and the remainder ferrite. Wire rod with excellent freshness and processability.

4. In paragraph 1, With a cross-sectional shrinkage rate of 30% or more, Wire rod with excellent freshness and processability.

5. In paragraph 1, The thickness of the above decarbonization layer is 0.05 mm or less. Wire rod with excellent freshness and processability.

6. In paragraph 1, The content of carbon (C) is 0.7 to 0.95 wt%, Wire rod with excellent freshness and processability.

7. In paragraph 1, Tensile strength is 1000 MPa or more, Wire rod with excellent freshness and processability.

8. (a) Dissolution step of dissolving raw materials; (b) a continuous casting step for manufacturing a semi-finished product; and (c) hot-rolling step of a semi-finished product; Including, The wire rod that has gone through the above (c) wire rolling step is, Contains carbon (C) 0.70 to 1.10 wt%, silicon (Si) 0.15 to 0.50 wt%, manganese (Mn) 0.20 to 0.90 wt%, phosphorus (P) 0.015 wt% or less, sulfur (S) 0.015 wt% or less, chromium (Cr) 0.02 to 0.35 wt%, aluminum (Al) 0.010 wt% or less (excluding 0), nitrogen (N) 0.005 wt% or less (excluding 0), the remainder iron (Fe) and other unavoidable impurities. In the cross section cut in a direction perpendicular to the longitudinal direction of the above wire, The maximum thickness of the decarburized layer located along the circumferential direction of the above cross-section is 0.08 mm or less, A method for manufacturing a wire rod having excellent fresh processability satisfying the following formula 1: [Formula 1] 0.1≤ (2ⅹCr) / Si (In Equation 1, Cr represents the content of chromium, Si represents the content of silicon, and the unit is weight%.) 9. In paragraph 8, (a) In the dissolution stage, The above raw material comprises at least one of reduced iron, molten iron and iron scrap. A method for manufacturing wire rods with excellent freshness and processability.

10. In paragraph 8, (a) In the dissolution stage, carried out in at least one of the furnaces and electric furnaces, A method for manufacturing wire rods with excellent freshness and processability.

11. In paragraph 8, The wire rod that has gone through the above (c) wire rolling step is, Further comprising 0.2 wt% or less of copper (Cu) and 0.15 wt% or less of nickel (Ni), A method for manufacturing wire rods with excellent freshness and processability.

12. In paragraph 8, The above (c) pre-rolling step is: (c-1) Reheating step of reheating the above semi-finished product at 1000 to 1170 ℃ for 90 minutes or less; (c-1) Precision rolling step of hot rolling the reheated semi-finished product at an inlet temperature of 850 to 1000 ℃; and Including a coiling step (c-3) of coiling the hot-rolled product at 800 to 900 ℃. A method for manufacturing wire rods with excellent freshness and processability.

13. In paragraph 8, The wire rod that has gone through the above (c) wire rolling step is, With a cross-sectional shrinkage rate of 30% or more, A method for manufacturing wire rods with excellent freshness and processability.

14. Contains multiple pre-existing elements, The maximum thickness of the decarburized layer located on the cross section of the above-mentioned wire is 0.08 mm or less, Tire code satisfying the following equation 1: [Formula 1] 0.1 ≤ (2ⅹCr) / Si (In Equation 1, Cr represents the content of chromium, Si represents the content of silicon, and the unit is weight%.) 15. In paragraph 14, The above-mentioned wire is a tire cord containing carbon (C) 0.70 to 1.10 wt%, silicon (Si) 0.15 to 0.50 wt%, manganese (Mn) 0.20 to 0.90 wt%, phosphorus (P) 0.015 wt% or less, sulfur (S) 0.015 wt% or less, chromium (Cr) 0.02 to 0.35 wt%, aluminum (Al) 0.010 wt% or less (excluding 0), nitrogen (N) 0.005 wt% or less (excluding 0), the remainder iron (Fe) and other unavoidable impurities.

16. In paragraph 15, The above-mentioned wire further contains 0.2 wt% of copper (Cu) (excluding 0) and 0.15 wt% or less of nickel (Ni) (excluding 0). Tire code.

17. In paragraph 14, The maximum thickness of the above decarbonization layer is 0.05 mm or less, Tire code.

18. In paragraph 14, Tensile strength of 3.2 GPa or more, Tire code.

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