Steel wire rod for tirecord having excellent drawability, preparation method therefor, and tirecord prepared by using same

Abstract

The present invention relates to a steel wire rod for a tirecord, having excellent drawability, a preparation method therefor, and a tirecord prepared by using same, and implements a steel wire rod for a tirecord, having excellent drawability and 0.005 wt% or less of nitrogen (N), a preparation method therefor, and a tirecord prepared by using same, the steel wire rod comprising 0.70-0.95 wt% of carbon (C), 0.15-0.50 wt% of silicon (Si), 0.30-0.90 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P), 0.015 wt% or less of sulfur (S), 0.10 wt% or less of copper (Cu), 0.05 wt % or less of nickel (Ni), 0.010 wt% or less of aluminum (Al), and the remainder of iron (Fe) and other inevitable impurities.

Description

Wire for tire cord with excellent fresh processability, manufacturing method thereof, and tire cord manufactured using the same

[0001] The present invention relates to a wire for tire cord having excellent fresh processability, 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 mounted on 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 from wire through a drawing process and a patterning heat treatment process, transforming it into an ultra-fine wire. Drawing into ultra-fine wire entails high work hardening, increasing sensitivity to surface defects, nitrogen content, and non-metallic inclusions.

[0006] Therefore, if there are coarse non-metallic inclusions inside the wire, a gap is created at the interface between the inclusions and the base during drawing, which in turn causes wire breakage during the drawing and twisting processes.

[0007] When short circuits occur during the manufacturing of tire cords, not only does workability and productivity decline, but they also pose a safety risk, so reducing the number of short circuits is an issue that must be addressed.

[0008] In addition, since a high nitrogen content not only adversely affects cold workability during fresh processing but also causes quality deterioration, it is strictly controlled to less than 0.005 wt%.

[0009] Meanwhile, electric arc furnace steelmaking uses scrap as the primary raw material and electricity as the primary energy source to produce molten steel. Blast furnace-converter furnace steelmaking involves reducing iron ore in a blast furnace to produce molten iron, which is then transported to a steelmaking plant for pretreatment and a converter process to produce molten steel.

[0010] At this time, since the molten iron produced in the blast furnace has a high carbon content, oxygen is injected in the converter process, and the carbon in the molten steel is removed through a decarburization reaction when oxygen is injected.

[0011] The decarburization reaction generates a large amount of fine CO gas in the molten steel. The difference in partial pressure between the CO gas and the molten steel causes nitrogen to be absorbed and float to the CO gas, which is then removed together. The nitrogen content of the molten steel can be easily controlled during the decarburization reaction, enabling the production of high-purity wire.

[0012] However, since electric furnaces use scrap as their main raw material, the carbon content in the molten steel is low, and this makes the nitrogen removal effect through decarburization reaction unfavorable compared to blast furnace-converter furnace operation.

[0013] In other words, due to the nature of the manufacturing process, electric furnaces have the disadvantage of making it difficult to control nitrogen content below 0.005 wt%. Due to this issue, tire cord wire is typically produced using a high-purity blast furnace-converter process, which facilitates nitrogen content control.

[0014] Moreover, if the surface scale of the wire is thick, there is a problem that it may cause wire breakage during drawing and twisting due to residual scale that is not removed during the pickling process.

[0015] The present invention has been devised to solve the above problems, and its technical purpose is to provide a wire for tire cord having excellent wire drawing processability and a method for manufacturing the same, which can minimize the content of coarse non-metallic inclusions and nitrogen and the thickness of surface scale through an electric furnace process, and reduce the frequency of wire breakage accordingly.

[0016] In addition, the present invention has a technical purpose of providing a tire cord that is manufactured using a wire material for tire cord having excellent fresh processability, while minimizing the frequency of wire breakage and satisfying a tensile strength of 3.2 GPa or more.

[0017] 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.

[0018] According to one embodiment of the present invention, a wire for a tire cord having excellent fresh processability contains carbon (C) 0.70 to 0.95 wt%, silicon (Si) 0.15 to 0.50 wt%, manganese (Mn) 0.30 to 0.90 wt%, phosphorus (P) 0.015 wt% or less, sulfur (S) 0.015 wt% or less, copper (Cu) 0.10 wt% or less, nickel (Ni) 0.05 wt% or less, aluminum (Al) 0.010 wt% or less, the remainder iron (Fe) and other unavoidable impurities, and nitrogen (N) 0.005 wt% or less. Preferably, nitrogen (N) may contain 0.0033 to 0.0037 wt%.

[0019] According to one embodiment of the present invention, the thickness of the surface scale before acid treatment may be 8 ㎛ or less.

[0020] According to one embodiment of the present invention, the thickness of the decarbonization layer may be 0.05 mm or less.

[0021] According to one embodiment of the present invention, the cross-sectional shrinkage ratio may be 30% or more.

[0022] According to one embodiment of the present invention, the non-metallic inclusions may have a total inclusion amount of 0.05 vol.% or less and an inclusion size of 40 ㎛ or less.

[0023] According to one embodiment of the present invention, the tensile strength (TS) may be 1050 to 1250 MPa. If the tensile strength is less than 1050 MPa, the tensile strength of the tire cord manufactured from the wire may be inferior. Conversely, if the tensile strength of the wire exceeds 1250 MPa, the load on the rolling equipment may increase, which may increase the frequency of wire breakage.

[0024] According to one embodiment of the present invention, the final microstructure may include ferrite and 90 vol.% or more of pearlite.

[0025] A method for manufacturing a wire for tire cord having excellent fresh processability according to one embodiment of the present invention comprises: (a) a melting step for melting a raw material, (b) a vacuum degassing step for treating the molten metal, (c) a continuous casting step for manufacturing a semi-finished product, and (d) a hot rolling step for hot rolling the semi-finished product. In the (b) vacuum degassing step, the reflux flow rate of argon (Ar) is 900 to 1100 ℓ / min, and the vacuum treatment time is 20 minutes or more.

[0026] According to one embodiment of the present invention, in the vacuum degassing step (b), the vacuum level may be 2 mbar or less.

[0027] According to one embodiment of the present invention, the wire rod subjected to the hot rolling step (d) may have a final microstructure including ferrite and pearlite of 90 vol.% or more.

[0028] According to one embodiment of the present invention, the wire rod subjected to the hot rolling step (d) may have a surface scale thickness of 8 ㎛ or less.

[0029] According to one embodiment of the present invention, the wire rod subjected to the hot rolling step (d) may have a decarburized layer thickness of 0.05 mm or less.

[0030] According to one embodiment of the present invention, the wire rod subjected to the hot rolling step (d) may have a tensile strength (TS) of 1050 to 1250 MPa.

[0031] According to one embodiment of the present invention, the wire rod subjected to the hot rolling step (d) may have a total amount of non-metallic inclusions of 0.05 vol.% or less.

[0032] According to one embodiment of the present invention, the wire rod subjected to the hot rolling step (d) may have a maximum size of non-metallic inclusions of 40 ㎛ or less on average.

[0033] According to one embodiment of the present invention, the wire rod subjected to the hot rolling step (d) may contain 0.70 to 0.95 wt% of carbon (C), 0.15 to 0.50 wt% of silicon (Si), 0.30 to 0.90 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P), 0.015 wt% or less of sulfur (S), 0.10 wt% or less of copper (Cu), 0.05 wt% or less of nickel (Ni), 0.010 wt% or less of aluminum (Al), the remainder being iron (Fe) and other unavoidable impurities, and 0.005 wt% or less of nitrogen (N).

[0034] According to one embodiment of the present invention, the step of (d) hot rolling may further include the step of (e) pickling.

[0035] A tire code according to one embodiment of the present invention can be manufactured using a wire that has undergone the acid treatment step (e).

[0036] A wire for tire cord with excellent fresh processability according to one embodiment of the present invention and a method for manufacturing the same can minimize the single wire rate that affects the fresh processability of tire cord by controlling the size of non-metallic inclusions while limiting the nitrogen content through a degassing (RH) process.

[0037] In addition, the wire for tire cord with excellent fresh processability and the method for manufacturing the same according to one embodiment of the present invention can minimize the thickness of surface scales by controlling the winding temperature, thereby shortening the surface pickling treatment time during the manufacture of tire cords and minimizing residual scales after the pickling treatment.

[0038] In addition, a tire cord according to one embodiment of the present invention can be manufactured using a wire material for tire cord having excellent fresh processability, and can achieve a tensile strength of 3.2 GPa or more.

[0039] 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.

[0040] Figure 1 is a flowchart showing a method for manufacturing a wire for tire cord with excellent fresh processing according to one embodiment of the present invention.

[0041] Figure 2 is an enlarged photograph illustrating the state of the surface scale and residual scale after acid washing of wire rods according to Examples 5 and 6 and wire rods according to Comparative Examples 6 and 7.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0048]

[0049] Wire for tire cord with excellent fresh processability

[0050] According to one embodiment of the present invention, a wire for tire cord having excellent fresh processability is provided.

[0051] It contains 0.70 to 0.95 wt% of carbon (C), 0.15 to 0.50 wt% of silicon (Si), 0.30 to 0.90 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P), 0.015 wt% or less of sulfur (S), 0.10 wt% or less of copper (Cu), 0.05 wt% or less of nickel (Ni), 0.010 wt% or less of aluminum (Al), the remainder being iron (Fe) and other unavoidable impurities, and may contain 0.005 wt% or less of nitrogen (N).

[0052] Hereinafter, the role and content of each alloy element included in a wire for tire cord having excellent fresh processability according to one embodiment of the present invention will be described in detail.

[0053]

[0054] Carbon (C)

[0055] Carbon (C) is an effective element for increasing strength. However, as the carbon content increases, strength improves but toughness decreases. Therefore, a lower carbon content is preferable. Accordingly, the wire for tire cord with excellent fresh processability according to one embodiment of the present invention has the problem of not being able to secure the strength of the final tire cord if the carbon content is less than 0.70 wt%.

[0056] In addition, when the carbon content exceeds 0.95 wt% of the total weight, a decrease in cross-sectional shrinkage rate may occur along with a decrease in toughness, and a decrease in freshness may occur due to the formation of proeutectoid cementite.

[0057]

[0058] Silicon (Si)

[0059] Silicon (Si) is effective in increasing strength and deoxidation, but if added in excessive amounts, there is a problem of deterioration in toughness, increased deformation resistance, and deterioration in freshness.

[0060] When the silicon content is less than 0.15 wt%, deoxidation and strength are difficult to secure. When the silicon content exceeds 0.50 wt%, toughness decreases, deformation resistance increases, and freshness deteriorates. Surface scale removal during pickling is difficult, and decarburization is accelerated.

[0061] Therefore, the wire for tire cord having excellent fresh processability according to one embodiment of the present invention may contain 0.15 to 0.50 wt% of silicon.

[0062]

[0063] manganese (Mn)

[0064] Manganese (Mn) is an element that is effective in deoxidation while increasing the strength of the wire rod, and is an element that prevents red-hot embrittlement by forming MnS inclusions.

[0065] If the manganese content is less than 0.3 wt%, the deoxidation effect is reduced, it is difficult to secure strength, and there is a problem of causing red-hot embrittlement.

[0066] Conversely, if the manganese content exceeds 0.9 wt%, segregation may occur at the center of the wire, and martensite may be formed upon cooling.

[0067] Therefore, the wire for tire cord having excellent fresh processability according to one embodiment of the present invention may contain 0.3 to 0.9 wt% of manganese.

[0068]

[0069] Person (P)

[0070] 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.

[0071] Therefore, the wire for tire cord having excellent fresh processability according to one embodiment of the present invention may contain phosphorus at 0.015 wt% or less.

[0072]

[0073] Yellow (S)

[0074] Sulfur (S) is a residual element that must be removed during the steelmaking process and forms MnS non-metallic inclusions.

[0075] When the sulfur content exceeds 0.015 wt%, the toughness is reduced due to excessive formation of sulfides such as MnS.

[0076] Therefore, the wire for tire cord having excellent fresh processability according to one embodiment of the present invention may contain sulfur in an amount of 0.015 wt% or less.

[0077]

[0078] copper (Cu)

[0079] Copper (Cu) is an element that contributes to increasing the strength and improving corrosion resistance of wire rods.

[0080] If the copper content exceeds 0.10 wt%, cracks may occur on the surface during wire rolling at high temperatures.

[0081] Therefore, the wire for tire cord having excellent fresh processability according to one embodiment of the present invention may contain copper in an amount of 0.10 wt% or less.

[0082]

[0083] Nickel (Ni)

[0084] Nickel (Ni) is an element that contributes to increasing the strength and improving corrosion resistance of wire rods.

[0085] When the nickel content exceeds 0.05 wt%, excessive formation of retained austenite may result in reduced fatigue life and increased manufacturing cost.

[0086] Therefore, the wire for tire cord having excellent fresh processability according to one embodiment of the present invention may contain nickel in an amount of 0.05 wt% or less.

[0087]

[0088] Aluminum (Al)

[0089] Aluminum (Al) is an element that acts as a strong deoxidizer, improves toughness by refining the austenite grain size, and forms non-metallic inclusions.

[0090] When the content of aluminum exceeds 0.01 wt%, it forms excessive coarse aluminum-based non-combustible inclusions, which causes short circuits during drawing.

[0091] Therefore, the wire for tire cord having excellent fresh processability according to one embodiment of the present invention may contain aluminum in an amount of 0.01 wt% or less.

[0092]

[0093] Nitrogen (N)

[0094] 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.

[0095] If the nitrogen content exceeds 0.005 wt%, excessive formation of precipitates may cause a deviation in strength and adversely affect cold workability during fresh processing.

[0096] Therefore, the wire for tire cord having excellent fresh processability according to one embodiment of the present invention may contain nitrogen in an amount of 0.005 wt% or less. More preferably, it may contain nitrogen in an amount of 0.0033 to 0.0037 wt%.

[0097]

[0098] In addition to the aforementioned steel components, the remainder may contain iron and unavoidable impurities. Unavoidable impurities are impurities introduced during the steelmaking process and the electrical steel sheet manufacturing process. Since these impurities are widely known in the field, a detailed description will be omitted.

[0099] 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.

[0100] In a wire for tire cord 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.

[0101] Preferably, the total amount of non-metallic inclusions may be 0.021 to 0.025 vol.%, and the maximum size of the non-metallic inclusions may be 17.1 to 17.3 ㎛.

[0102] Consequently, according to one embodiment of the present invention, by controlling the total amount of non-metallic inclusions, the maximum size of the non-metallic inclusions, and the nitrogen content within preset ranges, the frequency of wire breakage occurring during tire cord manufacturing can be significantly reduced.

[0103] In addition, according to one embodiment of the present invention, the average thickness of the surface scale of the wire before the acid treatment described below may be 8 ㎛ or less, preferably 7.2 ㎛ or less.

[0104] Accordingly, the residual scale on the surface of the wire after acid treatment can be completely removed, which can further reduce the frequency of wire breakage.

[0105] According to one embodiment of the present invention, the thickness of the decarbonization layer can be controlled to 0.05 mm or less.

[0106] And, according to one embodiment of the present invention, as a result of a tensile strength test evaluation, the cross-sectional shrinkage rate of the wire may be 30% or more.

[0107] According to one embodiment of the present invention, a wire for tire cord having excellent fresh processability may have a tensile strength (TS) of 1050 to 1250 MPa.

[0108] In addition, the wire for tire cord with excellent fresh processability according to one embodiment of the present invention may include a final microstructure of pearlite and ferrite of 90 vol.% or more. However, the final microstructure of the wire is not limited to the above-described structure, and may include other structures replacing ferrite.

[0109] Hereinafter, a method for manufacturing a wire for tire cord having excellent fresh processability according to one embodiment of the present invention will be described in detail.

[0110]

[0111] Method for manufacturing wire for tire cord with excellent fresh processability

[0112] Hereinafter, a method for manufacturing a wire for tire cord with excellent fresh processing according to one embodiment of the present invention will be described.

[0113] Figure 1 is a flowchart showing a method for manufacturing a wire for tire cord with excellent fresh processing according to one embodiment of the present invention.

[0114] A method for manufacturing a wire for tire cord having excellent fresh processing properties according to one embodiment of the present invention comprises: (a) a melting step for melting a raw material, (b) a vacuum degassing step for treating the molten metal, (c) a continuous casting step for manufacturing a semi-finished product, (d) a hot rolling step for hot rolling the semi-finished product, and (e) a pickling step for treating the surface of the hot-rolled product.

[0115] According to one embodiment of the present invention, (a) the melting step involves charging raw materials into a melting furnace to produce molten metal. In this embodiment, the melting furnace may be an electric furnace.

[0116] In general, steelmaking in an electric furnace is a method of manufacturing molten steel using scrap as the main raw material and electricity as the main energy source.

[0117] On the other hand, the blast furnace-converter steelmaking operation is a method of producing molten iron by reducing iron ore in a blast furnace, transporting this molten iron to a steel mill, and manufacturing molten steel through the molten iron pretreatment and converter process.

[0118] Because molten iron contains a high carbon content, oxygen is injected during the converter process, and the carbon within the molten steel can be removed through a decarburization reaction. This decarburization reaction generates a large amount of fine CO gas in the molten steel. Due to the difference in partial pressure between the CO gas and the molten steel, nitrogen is absorbed and floats to the CO gas, and is removed together.

[0119] However, since electric furnaces use scrap as the main raw material, the carbon content in the molten steel is low, and as a result, nitrogen removal through decarburization is disadvantageous compared to blast furnace-converter furnace operation.

[0120] To solve these problems, in a method for manufacturing a wire for tire cord with excellent fresh processing according to one embodiment of the present invention, the optimal conditions of the (b) vacuum degassing step for reducing the maximum size of non-metallic inclusions and the content of nitrogen, which affect quality deterioration factors during the manufacturing of tire cord through electric furnace operation, were derived.

[0121] According to one embodiment of the present invention, (b) the vacuum degassing step processes molten steel produced in an electric furnace. Specifically, in (b) the vacuum degassing step, the reflux flow rate of argon (Ar) may be 900 to 1100 ℓ / min, and the vacuum treatment time may be 20 minutes or more. At this time, the vacuum level of (b) the vacuum degassing step may be controlled to 2 mbar or less.

[0122] Preferably, (b) in the vacuum degassing step, the reflux flow rate of argon (Ar) may be 1008 to 1056 ℓ / min, and the vacuum treatment time in the vacuum degassing process may be 25 to 26 minutes.

[0123] When manufacturing tire cords using wires manufactured under the above process conditions, it was confirmed that the frequency of wire breakage was significantly reduced compared to the existing one.

[0124] According to one embodiment of the present invention, in the (c) continuous casting step, the molten metal that has undergone the (b) vacuum degassing step can be manufactured into a semi-finished product. 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 into a slab or bloom shape.

[0125] According to one embodiment of the present invention, the (d) hot rolling step may include a step of reheating the semi-finished product, a step of hot rolling the semi-finished product, and a step of including the semi-finished product. Specifically, the billet is reheated at a temperature of 1000 to 1150°C for 90 minutes or more. The reheated billet may be precision rolled at a precision rolling inlet temperature of 850 to 1000°C, and then coiled at a coiling temperature of 800 to 870°C.

[0126] A method for manufacturing a wire for tire cord having excellent fresh processability according to one embodiment of the present invention can reheat a billet for 90 minutes or more in a rolling process.

[0127] And, through this hot rolling process, the thickness of the decarburized layer can be controlled to 0.05 mm or less.

[0128] If the billet reheat temperature exceeds 1150℃, excessive decarburization can occur on the surface, potentially degrading the quality of tire cord products. Conversely, if the reheat temperature falls below 1000℃, the load on the rolling equipment increases, potentially causing defects such as cobbles during rolling, and thus reducing rolling productivity.

[0129] If the precision rolling entry temperature exceeds 1000℃, it may be difficult to satisfy the coiling process conditions for reducing the thickness of the surface scale. Conversely, if the precision rolling entry temperature is below 850℃, the load on the rolling equipment increases and surface defects such as rolling folds may occur. Therefore, it is preferable to manufacture the precision rolling at an entry temperature of 850 to 1000℃.

[0130] If the coiling temperature exceeds 870°C, the surface scale will thicken, and even if the manufactured wire is pickled, the scale may remain locally, causing wire breakage during drawing and twisting. Conversely, if the coiling temperature is below 800°C, the difference from the rolling temperature will be significant, which may result in a defective coil shape.

[0131] For example, when the coiling temperature reaches 881 to 933°C, the thickness of the surface scale is approximately 9 to 12 μm, and the surface scale remains even after pickling, making it unsuitable as a tire cord for pickling treatment.

[0132] According to one embodiment of the present invention, the (e) pickling treatment step can remove surface scale by spraying a pickling solution on the product after the hot rolling step.

[0133] The wire for tire cord manufactured by the above-described manufacturing steps may contain nitrogen in an amount of 0.005 wt% or less. More preferably, it may contain nitrogen in an amount of 0.0033 to 0.0037 wt%.

[0134] In addition, in the wire for tire cord, 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 µm or less on average. Preferably, the total amount of non-metallic inclusions may be 0.021 to 0.025 vol.%, and the maximum size of the non-metallic inclusions may be 17.1 to 17.3 µm.

[0135] Accordingly, according to one embodiment of the present invention, the total amount of non-metallic inclusions, the maximum size of non-metallic inclusions, and the nitrogen content can be controlled within preset ranges, thereby significantly reducing the frequency of wire breakage occurring during tire cord manufacturing.

[0136] A method for manufacturing a wire for tire cord having excellent fresh processability according to one embodiment of the present invention can provide a wire for tire cord in which a surface scale having a thickness of 8 ㎛ or less is formed and can be completely removed after pickling, thereby shortening the pickling work time.

[0137] According to one embodiment of the present invention, the thickness of the decarbonization layer can be controlled to 0.05 mm or less.

[0138] And, the wire according to the above manufacturing method may have a cross-sectional shrinkage rate of 30% or more.

[0139] The wire according to the above manufacturing method may have a tensile strength (TS) of 1050 to 1250 MPa.

[0140] The wire according to the above manufacturing method may have a final microstructure of ferrite and pearlite of 90 vol.% or more.

[0141]

[0142] tire code

[0143] A tire cord according to one embodiment of the present invention is manufactured through a series of manufacturing processes including a surface pickling process, a dry drawing process for processing to a diameter of 1 to 2 mm, a patterning heat treatment process, a brass plating process, a wet drawing process for processing to a diameter of 0.15 to 0.40 mm, and a twisting process using the wire material.

[0144] A tire cord according to one embodiment of the present invention minimizes the frequency of wire breakage by using a wire having excellent fresh processability, thereby satisfying a tensile strength of 3.2 GPa or higher.

[0145]

[0146] Comparative examples and examples

[0147] Below, preferred comparative examples and examples are presented to aid in understanding the present invention. However, the following comparative examples and examples are provided solely to aid in understanding the present invention, and the present invention is not limited to the examples below.

[0148] Comparative examples and examples were manufactured in the form of billets through a continuous casting process under the same conditions by melting raw materials of the same quality in an electric furnace, and only the specific process conditions (vacuum degassing step, hot rolling step) were different.

[0149] Table 1 shows the degassing process conditions for manufacturing the specimens of the present example and comparative example, Table 2 shows the measurement results of each specimen implemented according to the degassing process conditions of Table 1, Table 3 shows the rolling process conditions for manufacturing the specimens of the present example and comparative example, and Table 4 shows the measurement results of each specimen implemented according to the rolling process conditions of Table 3.

[0150] Meanwhile, the total amount of non-metallic inclusions in Table 2 was measured according to the JIS G0555 standard test method. Specifically, the wire of each specimen was cut in the longitudinal direction, and the ratio of non-metallic inclusions intersecting with the grid and occupying the wire was expressed as a percentage (%) using a microscope.

[0151] In Table 4, the maximum thickness of the surface scale was measured by observing the cross-section of each specimen under a microscope and measuring the thickness of iron oxide in the circumferential direction with the matrix structure including ferrite and pearlite as the boundary.

[0152] Conditions of vacuum degassing process Argon (Ar) reflux flow rate (ℓ / min) Vacuum treatment time (min) Example 191021 Example 2100825 Example 3105626 Example 4109327 Comparative example 185017 Comparative example 288021 Comparative example 3112519 Comparative example 4119123

[0153] Total amount of non-metallic inclusions (vol.%, JIS G0555) Maximum size of non-metallic inclusions (㎛) Nitrogen content (wt%) Frequency of wire breakage during tire cord manufacturing (times / coil) Example 10.03 321.6 0.00451 Example 20.02 117.10.0037 Non-occurring Example 30.02 517.30.0033 Non-occurring Example 40.02 933.20.00282 Comparative Example 10.06 252.8 0.00646 Comparative Example 20.05 153.6 0.00517 Comparative Example 30.05 445.7 0.00496 Comparative Example 40.05 949.10.00355

[0154] According to Tables 1 and 2 above, in the degassing processes of Examples 1 to 4, the reflux flow rate of argon (Ar) was controlled to 910 ℓ / min, 1008 ℓ / min, 1056 ℓ / min, and 1093 ℓ / min, and the vacuum treatment time was controlled to 21 minutes, 25 minutes, 26 minutes, and 27 minutes.

[0155] On the other hand, the degassing process conditions of Comparative Examples 1 to 4 were such that the reflux flow rate of argon (Ar) in the vacuum degassing process was controlled to 850 ℓ / min, 880 ℓ / min, 1125 ℓ / min, and 1191 ℓ / min, and the vacuum treatment time in the vacuum degassing process was controlled to 17 minutes, 21 minutes, 19 minutes, and 23 minutes.

[0156] As a result, the total amounts of non-metallic inclusions of Examples 1 to 4 were 0.033 vol.%, 0.021 vol.%, 0.025 vol.%, and 0.029 vol.%, respectively. In contrast, the total amounts of non-metallic inclusions of Comparative Examples 1 to 4 were 0.062 vol.%, 0.051 vol.%, 0.054 vol.%, and 0.059 vol.%, respectively, confirming a significant increase compared to Examples 1 to 4.

[0157] In addition, the maximum sizes of the non-metallic inclusions of Examples 1 to 4 were 21.6 µm, 17.1 µm, 17.3 µm, and 33.2 µm, respectively. On the other hand, the maximum sizes of the non-metallic inclusions of Comparative Examples 1 to 4 were measured to be 52.8 µm, 53.6 µm, 45.7 µm, and 49.1 µm, respectively, confirming that they were significantly larger than those of Examples 1 to 4.

[0158] And, the nitrogen contents of Examples 1 to 4 are 0.0045 wt%, 0.0037 wt%, 0.0033 wt%, and 0.0028 wt%, respectively. In contrast, the nitrogen contents of Comparative Examples 1 to 4 were measured to be 0.0064 wt%, 0.0051 wt%, and 0.0035 wt%, confirming that they were significantly larger than those of Examples 1 to 4.

[0159] When manufacturing a tire cord using the wires for tire cords of Examples 1 to 4 and the wires for tire cords of Comparative Examples 1 to 4, the frequency of wire breakage, which represents the number of times per coil, was measured.

[0160] As a result of the measurement, when manufacturing tire cords using the wires for tire cords of Examples 1 to 4, they were measured as 1 time / coil, 0 times / coil (no occurrence), 0 times / coil (no occurrence), and 2 times / coil, respectively.

[0161] On the other hand, when manufacturing tire cords using the wires for tire cords of Comparative Examples 1 to 4, the numbers were measured as 6 times / coil, 7 times / coil, 6 times / coil, and 5 times / coil, respectively.

[0162] Referring to Table 1 and Table 2, it can be confirmed that in the vacuum degassing step, if at least one of the argon exchange flow rate and the vacuum treatment time is outside the preset range, the total amount of non-metallic inclusions increases, the maximum size of non-metallic inclusions increases, or the nitrogen content increases, thereby increasing the frequency of wire breakage during tire cord manufacturing.

[0163] Classification Reheating temperature (℃) Precision rolling entry temperature (℃) Coiling temperature (℃) Example 11010866811 Example 21059921827 Example 31081943853 Example 41137980868 Comparative example 11022873881 Comparative example 21088925920 Comparative example 31121998933 Comparative example 41051922940

[0164] Surface scale maximum thickness (㎛) Presence of residual scale after acid treatment Example 16.1 None Example 26.3 None Example 36.8 None Example 47.2 None Comparative Example 19.3 Yes Comparative Example 210.2 Yes Comparative Example 311.8 Yes Comparative Example 412.2 Yes

[0165] According to Tables 3 and 4 above, in Examples 1 to 4, the reheating temperature of the rolling was controlled to 1010°C, 1059°C, 1081°C, and 1137°C, respectively, and the precision rolling entry temperature was controlled to 866°C, 921°C, 943°C, and 980°C, respectively. In addition, the coiling temperature was controlled to 811°C, 827°C, 853°C, and 868°C, respectively.

[0166] On the other hand, in Comparative Examples 1 to 4, the reheating temperature of the rolling was controlled to 1022 ℃, 1088 ℃, 1121 ℃, and 1051 ℃, respectively, the precision rolling inlet temperature was controlled to 873 ℃, 925 ℃, 998 ℃, and 922 ℃, and the coiling temperature was controlled to 881 ℃, 920 ℃, 933 ℃, and 940 ℃, respectively.

[0167] As can be seen, in Examples 1 to 4, the maximum thickness of the surface scale was measured to be 6.1 ㎛, 6.3 ㎛, 6.8 ㎛, and 7.2 ㎛, respectively.

[0168] On the other hand, in comparative examples 1 to 4, the values ​​were measured as 9.3 μm, 10.2 μm, 11.8 μm, and 12.2 μm, respectively.

[0169] At this time, when checking whether there was residual scale in the wire rods according to Examples 1 to 4 and the wire rods according to Comparative Examples 1 to 4 after each acid treatment, it was confirmed that no residual scale was found in the wire rods according to Examples 1 to 4, but that a considerable thickness of residual scale remained in the wire rods according to Comparative Examples 1 to 4.

[0170] Figure 2 is an enlarged photograph showing the surface scale of wires according to Examples 1 and 2 and wires according to Comparative Examples 2 and 3, and the residual scale after acid washing.

[0171] Referring to Fig. 2, it can be seen that the wires according to Examples 1 and 2 have a maximum thickness (D1) of surface scale of 6.1 ㎛ and 6.3 ㎛, respectively, but the surface scale is completely removed after acid washing, so that no residual scale can be found.

[0172] However, the wire rods according to comparative examples 1 and 2 have a maximum thickness (D1) of the surface scale of 10.22 ㎛ and 11.75 ㎛, respectively, and it can be confirmed that the surface scale is not completely removed even after acid washing and residual scale exists.

[0173] Looking at Table 3, Table 4 and Figure 2 above, in Examples 1 to 4 where the coiling temperature is 870°C or lower, the surface scale is formed thinly and the surface scale is completely removed after pickling, but in Comparative Examples 1 to 4 where the coiling temperature is higher than 870°C, the surface scale is formed thickly and it can be confirmed that residual scale exists even after pickling.

[0174] 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. Containing 0.70 to 0.95 wt% of carbon (C), 0.15 to 0.50 wt% of silicon (Si), 0.30 to 0.90 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P), 0.015 wt% or less of sulfur (S), 0.10 wt% or less of copper (Cu), 0.05 wt% or less of nickel (Ni), 0.010 wt% or less of aluminum (Al), the remainder iron (Fe) and other unavoidable impurities, and 0.005 wt% or less of nitrogen (N). Wire for tire cord with excellent fresh processability.

2. In paragraph 1, Containing 0.0033 to 0.0037 wt% of nitrogen (N), Wire for tire cord with excellent fresh processability.

3. In paragraph 1, The thickness of the surface scale before acid treatment is 8 ㎛ or less, Wire for tire cord with excellent fresh processability.

4. In paragraph 1, The thickness of the decarbonized layer is less than 0.05 mm, Wire for tire cord with excellent fresh processability.

5. In paragraph 1, With a cross-sectional shrinkage rate of 30% or more, Wire for tire cord with excellent fresh processability.

6. In paragraph 1, Non-metallic inclusions have a total inclusion amount of 0.05 vol.% or less and an inclusion size of 40 ㎛ or less. Wire for tire cord with excellent fresh processability.

7. In paragraph 1, Tensile strength (TS) is 1050 to 1250 MPa Wire for tire cord with excellent fresh processability.

8. In paragraph 1, The final microstructure contains ferrite and pearlite of more than 90 vol.%. Wire for tire cord with excellent fresh processability.

9. (a) Dissolving step of dissolving raw materials; (b) Vacuum degassing step for treating the molten metal; (c) a continuous casting step for manufacturing semi-finished products; and (d) a hot rolling step for hot rolling a semi-finished product, In the above (b) vacuum degassing step, the reflux flow rate of argon (Ar) is 900 to 1100 ℓ / min, and the vacuum treatment time is 20 minutes or more. A method for manufacturing wire for tire cord with excellent fresh processability.

10. In paragraph 9, In the above (b) vacuum degassing step, the vacuum level is 2 mbar or less. A method for manufacturing wire for tire cord with excellent fresh processability.

11. In paragraph 9, The wire rod that has undergone the above (d) hot rolling step is, The final microstructure contains ferrite and pearlite of more than 90 vol.%. A method for manufacturing wire for tire cord with excellent fresh processability.

12. In paragraph 9, The wire rod that has undergone the above (d) hot rolling step is, The thickness of the surface scale is 8 ㎛ or less, A method for manufacturing wire for tire cord with excellent fresh processability.

13. In paragraph 9, The wire rod that has undergone the above (d) hot rolling step is, The thickness of the decarbonized layer is less than 0.05 mm, A method for manufacturing wire for tire cord with excellent fresh processability.

14. In paragraph 9, The wire rod that has undergone the above (d) hot rolling step is, Tensile strength (TS) is 1050 to 1250 MPa, A method for manufacturing wire for tire cord with excellent fresh processability.

15. In paragraph 9, The wire rod that has undergone the above (d) hot rolling step is, The total amount of non-metallic inclusions is 0.05 vol.% or less, A method for manufacturing wire for tire cord with excellent fresh processability.

16. In paragraph 9, The wire rod that has undergone the above (d) hot rolling step is, The maximum size of non-metallic inclusions is less than 40 ㎛ on average. A method for manufacturing wire for tire cord with excellent fresh processability.

17. In paragraph 9, The wire rod that has undergone the above (d) hot rolling step is, Containing 0.70 to 0.95 wt% of carbon (C), 0.15 to 0.50 wt% of silicon (Si), 0.30 to 0.90 wt% of manganese (Mn), 0.015 wt% or less of phosphorus (P), 0.015 wt% or less of sulfur (S), 0.10 wt% or less of copper (Cu), 0.05 wt% or less of nickel (Ni), 0.010 wt% or less of aluminum (Al), the remainder iron (Fe) and other unavoidable impurities, and 0.005 wt% or less of nitrogen (N). A method for manufacturing wire for tire cord with excellent fresh processability.

18. In paragraph 9, Further comprising a (e) pickling step after the above (d) hot rolling step, A method for manufacturing wire for tire cord with excellent fresh processability.

19. In paragraph 18, Manufactured using a wire that has undergone the above (e) acid treatment step, Tire code.

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