Wire rod and manufacturing method therefor

Abstract

The present invention relates to a wire rod and a manufacturing method therefor. According to the wire rod of the present invention and the manufacturing method therefor, the wire rod not only has excellent strength and toughness but can also be drawn without disconnecting during wire drawing, thus having excellent workability, drawability, and productivity.

Description

Wire rod and method of manufacturing the same

[0001] The present application relates to a wire and a method for manufacturing the same.

[0002] Tire cord wire is a product manufactured into ultra-fine wire through drawing and patterning heat treatment processes.

[0003] Recently, the transition from internal combustion engine vehicles to electric vehicles has been accelerating, and accordingly, automotive parts manufacturers are demanding the development of materials capable of high strength and performance. In particular, as the weight of electric vehicles increases due to the weight of the battery, high performance is required for suspension and tire components compared to those of conventional internal combustion engine vehicles.

[0004] Furthermore, in the tire cord industry, as thinner wire diameters after drawing are advantageous for increasing the strength of steel wire through work hardening, there is an increasing need for the development of materials with excellent drawing processability to achieve high strength.

[0005] However, drawing ultrafine wires entails high work hardening, which increases sensitivity to defects such as non-metallic inclusions, surface defects, and decarburization, leading to wire breakage. Since wire breakage during drawing not only reduces workability and productivity but also poses safety risks, reducing the frequency of breakage is a problem that must be solved.

[0006] Currently, increasing the carbon content is the most widely used method to increase strength. However, problems arise where ductility decreases due to central segregation within the material caused by the increased carbon content and an excessive increase in the cementite fraction. To overcome this, research is being conducted on improving strength through the addition of alloying elements and refining the lamellar spacing of the pearlite structure; however, excessive addition of alloying elements increases the likelihood of low-temperature structures causing wire breakage during drawing, and also results in the disadvantage of increased manufacturing costs.

[0007] Therefore, in order to compensate for these problems and disadvantages, there is a need for a wire rod that not only has excellent strength and toughness but also excellent fresh processability, and a method for manufacturing the same.

[0008] The objective of the present application is to provide a wire rod having excellent strength and toughness as well as excellent fresh processability, and a method for manufacturing the same.

[0009] To solve the above problem, the wire of the present application comprises, in weight%, C: 0.70% or more and 1.10% or less, Si: 0.15% or more and 0.50% or less, Mn: 0.20% or more and 0.90% or less, Cr: 0.03% or more and 0.40% or less, P: 0.015% or less, S: 0.015% or less, Cu: 0.20% or less, Ni: 0.20% or less, Al: 0.015% or less, and N: 0.005% or less, and the remainder comprises Fe and other unavoidable impurities, satisfying the following general formula 1.

[0010] [General Formula 1]

[0011] AⅩB ≥ 40000

[0012] In the above general formula 1, A is tensile strength (MPa) and B is cross-sectional shrinkage rate (%).

[0013] The above wire rod is a wire rod manufactured by reheating a billet, hot rolling it, coiling it, and then cooling it, and can satisfy the following general formula 2.

[0014] [General Formula 2]

[0015] ILS(D / 4) ≤ 162-3.9(2ⅩCr+Mn / 3)ⅩC R

[0016] In the above General Formula 2, ILS(D / 4) is the lamellar interlayer spacing of the pearlite structure measured at 1 / 4 of the wire rod diameter after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

[0017] In addition, the above wire rod is a wire rod manufactured by reheating a billet, hot rolling it, coiling it, and then cooling it, and can satisfy the following general formula 3.

[0018] [General Formula 3]

[0019] ILS(D / 2) ≤ 188-7.2(2ⅩCr+Mn / 3)ⅩC R

[0020] In the above General Formula 3, ILS(D / 2) is the lamellar interlayer spacing of the pearlite structure measured at half the diameter of the wire rod after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

[0021] In addition, the above wire can satisfy the following general formula 4.

[0022] [General Formula 4]

[0023] 0.20 ≤ 2ⅩCr+Mn / 3

[0024] In the above general formula 4, Cr is the chromium content (weight%) contained in the wire, and Mn is the manganese content (weight%) contained in the wire.

[0025] In addition, the above wire may include pearlite having an area fraction of 90% or more and ferrite having an area fraction of 10% or less inside.

[0026] In addition, the method for manufacturing a wire rod according to the present application comprises, in weight percent, a hot rolling step of reheating and then hot rolling a billet containing C: 0.70% or more and 1.10% or less, Si: 0.15% or more and 0.50% or less, Mn: 0.20% or more and 0.90% or less, Cr: 0.03% or more and 0.40% or less, P: 0.015% or less, S: 0.015% or less, Cu: 0.20% or less, Ni: 0.20% or less, Al: 0.015% or less and N: 0.005% or less, and the remainder being Fe and other unavoidable impurities; and a cooling step of coiling and then cooling the hot-rolled wire rod, wherein the wire rod after cooling satisfies the following general formula 1.

[0027] [General Formula 1]

[0028] AⅩB ≥ 40000

[0029] In the above general formula 1, A is tensile strength (MPa) and B is cross-sectional shrinkage rate (%).

[0030] In addition, the wire rod can satisfy the following general formula 2 after cooling.

[0031] [General Formula 2]

[0032] ILS(D / 4) ≤ 162-3.9(2ⅩCr+Mn / 3)ⅩC R

[0033] In the above General Formula 2, ILS(D / 4) is the lamellar interlayer spacing of the pearlite structure measured at 1 / 4 of the wire rod diameter after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

[0034] In addition, the method for manufacturing the above wire can satisfy the following general formula 3.

[0035] [General Formula 3]

[0036] ILS(D / 2) ≤ 188-7.2(2ⅩCr+Mn / 3)ⅩC R

[0037] In the above General Formula 3, ILS(D / 2) is the lamellar interlayer spacing of the pearlite structure measured at half the diameter of the wire rod, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

[0038] In addition, the above billet can satisfy the following general formula 4.

[0039] [General Formula 4]

[0040] 0.20 ≤ 2ⅩCr+Mn / 3

[0041] In the above general formula 4, Cr is the chromium content (weight%) contained in the billet, and Mn is the manganese content (weight%) contained in the billet.

[0042] In addition, in the above cooling step, the cooling rate of the wire rod up to 350℃ after winding may be 8.5 ℃ / s or more and 20 ℃ / s or less.

[0043] According to the wire rod and the method for manufacturing the same of the present application, not only are the strength and toughness excellent, but the wire breakage during drawing processing is prevented, thereby enabling excellent drawing processability such as workability and productivity.

[0044] The wire of the present application comprises, in weight%, C: 0.70% or more and 1.10% or less, Si: 0.15% or more and 0.50% or less, Mn: 0.20% or more and 0.90% or less, Cr: 0.03% or more and 0.40% or less, P: 0.015% or less, S: 0.015% or less, Cu: 0.20% or less, Ni: 0.20% or less, Al: 0.015% or less, and N: 0.005% or less, and the remainder comprises Fe and other unavoidable impurities, satisfying the following general formula 1.

[0045] [General Formula 1]

[0046] AⅩB ≥ 40000

[0047] In the above general formula 1, tensile strength (MPa) is given, and B is the reduction in area (%).

[0048] The wire of the present application comprises the aforementioned components and satisfies the aforementioned general formula 1, thereby not only having excellent strength and toughness, but also preventing wire breakage during drawing, which can result in excellent drawing processability such as workability and productivity. In this specification, the cross-sectional shrinkage rate refers to the difference between the minimum cross-sectional area after fracture of the specimen during a tensile test and the original cross-sectional area of ​​the specimen before the test, expressed as a percentage.

[0049] Specifically, the value of the wire rod calculated by the above general formula 1 may be 42,000 or more, 44,000 or more, or 46,000 or more. Although the upper limit of the value calculated by the above general formula 1 is not specifically restricted in that the larger the value, the better the strength and toughness, for example, it may be 100,000 or less, 85,000 or less, or 70,000 or less. By satisfying the above general formula 1, the wire rod may have excellent drawing processability.

[0050] The tensile strength of the above wire may be 1,000 MPa or more and 1,300 MPa or less. Specifically, the lower limit of the tensile strength of the above wire may be 1,010 MPa or more or 1,020 MPa or more, and the upper limit may be 1,290 MPa or less. The above wire may have high strength by satisfying the aforementioned range of tensile strength.

[0051] In addition, the cross-sectional shrinkage rate of the wire may be 35% or more. Specifically, the cross-sectional shrinkage rate of the wire may be 36% or more or 37% or more. In addition, the upper limit of the cross-sectional shrinkage rate of the wire may be 60% or less, 55% or less, or 50% or less. By satisfying the aforementioned ranges for cross-sectional shrinkage rate, the wire may possess high toughness, which prevents wire breakage during drawing processing, thereby ensuring excellent drawing processability, such as workability and productivity. The cross-sectional shrinkage rate may be the result measured based on the transverse cross-sectional area after conducting a tensile test on the wire.

[0052] In one example, the wire rod is manufactured by reheating a billet, hot rolling it, coiling it, and then cooling it, and can satisfy the following general formula 2.

[0053] [General Formula 2]

[0054] ILS(D / 4) ≤ 162-3.9(2ⅩCr+Mn / 3)ⅩC R

[0055] In the above General Formula 2, ILS(D / 4) is the lamellar interlayer spacing of the pearlite structure measured at 1 / 4 of the wire rod diameter after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

[0056] The above wire rod is manufactured by the aforementioned manufacturing method and satisfies the above general formula 2, thereby not only having excellent strength and toughness, but also preventing wire breakage during drawing, which can result in excellent drawing processability such as workability and productivity. The above pearlite structure is a structure in which cementite (Fe3C) and ferrite form alternating layers. At this time, the spacing between the cementite layers is called the lamellar spacing of the pearlite structure.

[0057] For example, the lamellar spacing (ILS(D / 4)) of the pearlite structure measured at 1 / 4 of the diameter of the wire rod after cooling may be less than 151 nm, specifically, 149 nm or less or 147 nm or less. Additionally, the lower limit of the lamellar spacing (ILS(D / 4)) of the pearlite structure measured at 1 / 4 of the diameter of the wire rod after cooling is not specifically limited, but may be, for example, 100 nm or more, 110 nm or more, or 120 nm or more. The wire rod may possess high toughness by satisfying the aforementioned ranges for the lamellar spacing (ILS(D / 4)) of the pearlite structure measured at 1 / 4 of the diameter of the wire rod after cooling. A detailed description of the manufacturing method of the wire rod is the same as described below, so it will be omitted. At this time, the lamellar spacing (ILS(D / 4)) of the pearlite structure measured at 1 / 4 of the diameter of the wire after cooling may be the average value calculated by cutting the wire into a cross section after cooling to prepare a specimen, acquiring 10 images at a magnification of 50,000x using a scanning electron microscope (SEM), and measuring 20 lamellar spacings at 1 / 4 of the diameter of the wire after cooling using image analysis software.

[0058] In another example, the above wire rod is a wire rod manufactured by reheating a billet, hot rolling it, coiling it, and then cooling it, and can satisfy the following general formula 3.

[0059] [General Formula 3]

[0060] ILS(D / 2) ≤ 188-7.2(2ⅩCr+Mn / 3)ⅩC R

[0061] In the above General Formula 3, ILS(D / 2) is the lamellar interlayer spacing of the pearlite structure measured at half the diameter of the wire rod after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C RThis is the cooling rate (°C) of the wire rod up to 350°C after winding.

[0062] The above wire is manufactured by the manufacturing method described above and satisfies the above general formula 3, so that not only is the strength and toughness excellent, but the wire breakage during drawing processing is prevented, and thus the drawing processability, such as workability and productivity, can be excellent.

[0063] For example, the above wire may have a lamellar spacing (ILS(D / 2)) of the aforementioned pearlite structure that is less than 164 nm, specifically, 163 nm or less. Additionally, the lower limit of the lamellar spacing (ILS(D / 2)) of the aforementioned pearlite structure is not specifically limited, but may be, for example, 100 nm or more, 110 nm or more, or 120 nm or more. The above wire may possess high toughness by satisfying the aforementioned range for the lamellar spacing (ILS(D / 2)) of the aforementioned pearlite structure. A detailed description of the manufacturing method of the above wire is the same as described below, so it will be omitted. At this time, the lamellar spacing (ILS(D / 2)) of the pearlite structure measured at half the diameter of the wire after cooling may be the average value calculated by cutting the wire into a cross-section after cooling to prepare a specimen, acquiring 10 images at a magnification of 50,000x using a scanning electron microscope (SEM), and measuring 20 lamellar spacings at half the diameter of the wire after cooling using image analysis software.

[0064] The alloy composition of the above wire is explained below.

[0065] C: 0.70 wt% or more, 1.10 wt% or less

[0066] Carbon (C) is an element that forms niobium (Nb) and vanadium (V)-based precipitates and is dissolved in the matrix to increase the strength of the steel. The above carbon is required to have a content of 0.70 wt% or more to ensure sufficient strength of the wire rod, but if the content exceeds 1.10 wt%, it causes center segregation, which lowers toughness, and may reduce drawing workability due to the formation of proeutectoid cementite. Therefore, in order to simultaneously secure excellent strength and toughness, the above carbon may be included in the wire rod in an amount of 0.70 wt% or more and 1.10 wt% or less, and specifically, in an amount of 0.70 wt% or more and 1.05 wt% or less.

[0067] Si: 0.15 wt% or more, 0.50 wt% or less

[0068] Silicon (Si) is an element that is effective for deoxidation and improves strength by being dissolved in ferrite. If the silicon is included in the wire rod in an amount less than the lower limit of the aforementioned range, it may be difficult to achieve deoxidation effects and strength. Furthermore, if the silicon is included in the wire rod in an amount exceeding the upper limit of the aforementioned range, toughness is reduced, ductility is reduced due to improved deformation resistance, it is disadvantageous for removing surface scale during pickling, and it may promote decarburization on the surface of the wire rod. Accordingly, the silicon may be included in the wire rod in an amount of 0.15 wt% or more and 0.50 wt% or less, specifically, in an amount of 0.16 wt% or more and 0.48 wt% or less.

[0069] Mn: 0.20 wt% or more, 0.90 wt% or less

[0070] Manganese (Mn) is an element that is effective for deoxidizing steel and improves strength by being dissolved in ferrite. In addition, as an austenite stabilizing element, the manganese can lower the Al, Al, and Acm transformation temperatures, delay pearlite transformation to refine the interlamellar spacing, and form MnS inclusions to prevent brittleness in steel. If the manganese is included in the wire rod below the lower limit of the aforementioned range, it may be difficult to achieve deoxidation effects and strength. Furthermore, if the manganese is included in the wire rod above the upper limit of the aforementioned range, it may cause center segregation and create a low-temperature structure upon cooling of the wire rod, thereby reducing drawing workability. Accordingly, the manganese may be included in the wire rod in an amount of 0.20 wt% or more and 0.90 wt% or less, specifically, in an amount of 0.22 wt% or more and 0.89 wt% or less.

[0071] Cr: 0.03 wt% or more, 0.40 wt% or less

[0072] Chromium (Cr) is an element that increases the strength of steel and improves its hardenability and corrosion resistance. Additionally, the chromium can delay pearlite transformation, thereby refining the interlamellar spacing and improving strength and ductility. If the chromium is included in the wire rod in an amount less than the lower limit of the aforementioned range, there is no effect of refining the interlamellar spacing, and thus the effect of improving strength and toughness may be insufficient. Furthermore, if the chromium is included in the wire rod in an amount exceeding the upper limit of the aforementioned range, it increases hardenability, causing a low-temperature structure during cooling of the wire rod, which can lead to wire breakage during drawing, and since it is an expensive element, it may increase manufacturing costs. Therefore, the chromium may be included in the wire rod in an amount of 0.03 wt% or more and 0.40 wt% or less, and specifically, in an amount of 0.03 wt% or more and 0.38 wt% or less, 0.03 wt% or more and 0.35 wt% or less, or 0.03 wt% or more and 0.33 wt% or less.

[0073] P: 0.015 wt% or less

[0074] Phosphorus (P) is a residual element that must be removed during steelmaking. If the phosphorus is included in the wire rod in an amount exceeding the upper limit of the aforementioned range, it can cause brittleness due to grain boundary segregation and the formation of Fe3P compounds. Accordingly, the phosphorus may be included in the wire rod in an amount of 0.015 wt% or less, specifically, in an amount greater than 0 wt% and less than or equal to 0.015 wt%, in an amount greater than or equal to 0.004 wt% and less than or equal to 0.015 wt%, or in an amount greater than or equal to 0.008 wt% and less than or equal to 0.014 wt%.

[0075] S: 0.015 wt% or less

[0076] Sulfur (S) is a residual element that must be removed during steelmaking and forms MnS non-metallic inclusions. If the sulfur is included in the wire rod in an amount exceeding the upper limit of the aforementioned range, excessive MnS may be formed, which may reduce toughness. Therefore, the sulfur may be included in the wire rod in an amount of 0.015 weight% or less, and specifically, may be included in an amount greater than 0 weight% and less than or equal to 0.015 weight%.

[0077] Cu: 0.20 wt% or less

[0078] Copper (Cu) is an element that increases the strength and improves the corrosion resistance of steel, and it may be segregated at the interface between the surface layer of the base material and the surface scale (iron oxide). If the copper is included in the wire rod in an amount exceeding the upper limit of the aforementioned range, surface cracks may occur during rolling of the wire rod at high temperatures. Therefore, the copper may be included in the wire rod in an amount of 0.20 weight% or less, and specifically, it may be included in an amount greater than 0 weight% and less than or equal to 0.20 weight% or greater than 0 weight% and less than or equal to 0.19 weight%.

[0079] Ni: 0.20 wt% or less

[0080] Nickel (Ni) is an element that increases the strength and improves the corrosion resistance of steel, and it can be segregated at the interface between the surface layer of the base material and the surface scale (iron oxide). In addition, the nickel can be effective in reducing surface cracks caused by the Cu enrichment layer. If the nickel is included in the wire rod in an amount exceeding the upper limit of the aforementioned range, it can reduce fatigue life due to the excessive formation of residual austenite and increase manufacturing costs as it is an expensive element. Therefore, the nickel may be included in the wire rod in an amount of 0.20 wt% or less, specifically, in an amount greater than 0 wt% and less than or equal to 0.20 wt% or greater than 0 wt% and less than or equal to 0.15 wt%.

[0081] Al: 0.015 wt% or less

[0082] Aluminum (Al) is an element that acts as a strong deoxidizer, improves toughness by refining the grain size of austenite, and forms Al-based hard non-metallic inclusions. If the aluminum is included in the wire rod in an amount exceeding the upper limit of the aforementioned range, coarse Al-based hard inclusions may be excessively formed, which may cause wire breakage during drawing. Therefore, the aluminum may be included in an amount of 0.015 weight% or less, specifically, in an amount greater than 0 weight% and less than or equal to 0.015 weight% or greater than 0 weight% and less than or equal to 0.010 weight%.

[0083] N: 0.005 wt% or less

[0084] Nitrogen (N) combines with elements such as Al, Ti, V, and Nb to form precipitates and is an element effective in refining the grain size of austenite. If the nitrogen is included in the wire rod in an amount exceeding the upper limit of the aforementioned range, it may form excessive precipitates, causing a variation in strength, and may adversely affect the wire drawing performance due to interaction with dislocations during wire drawing. Therefore, the nitrogen may be included in the wire rod in an amount of 0.005 wt% or less, specifically, in an amount greater than 0 wt% and less than or equal to 0.005 wt% or greater than 0 wt% and less than or equal to 0.0047 wt%.

[0085] Remaining Fe and other unavoidable impurities

[0086] The aforementioned unavoidable impurities are impurities unintentionally incorporated from raw materials or the surrounding environment during the ordinary manufacturing process; as this is widely known in the art, a detailed description is omitted. In one embodiment of this application, the addition of elements other than the components of the wire described above is not excluded, and various elements may be included within a scope that does not impair the technical concept of this application. If additional elements are included, they may be included to replace the remainder, iron (Fe).

[0087] In one example, the above wire can satisfy the following general formula 4.

[0088] [General Formula 4]

[0089] 0.20 ≤ 2ⅩCr+Mn / 3

[0090] In the above general formula 4, Cr is the chromium content (weight%) contained in the billet or wire rod, and Mn is the manganese content (weight%) contained in the billet or wire rod.

[0091] Specifically, the value calculated by the above general formula 4 may be 0.21 or higher. Additionally, the upper limit of the value calculated by the above general formula 4 is not specifically limited, but, for example, may be 1.00 or lower, and specifically, may be 0.90 or lower or 0.80 or lower. Since the value calculated by the above general formula 4 satisfies the aforementioned range, the wire rod not only has excellent strength and toughness, but also excellent wire drawing performance, such as workability and productivity, by preventing wire breakage during wire drawing.

[0092] In addition, the wire may contain pearlite having an area fraction of 90% or more and ferrite having an area fraction of 10% or less. If the wire contains more than 10% ferrite, it may be impossible to secure the desired strength and cross-sectional shrinkage rate. Therefore, the microstructure contained within the wire may satisfy the area fraction of the aforementioned range. At this time, the area fraction of the pearlite and ferrite structures contained within the wire may be the average value calculated by preparing a specimen by cutting the wire in a cross-section, acquiring 10 images at 200x magnification using an optical microscope, and measuring the area fraction of the pearlite and ferrite structures using image analysis software.

[0093] This application also relates to a method for manufacturing a wire. The method for manufacturing the wire relates to a method for manufacturing the wire, and since specific details regarding the wire described below can be applied in the same way as those described for the wire, they will be omitted.

[0094] The above method for manufacturing the wire rod includes a hot rolling step and a cooling step, and after cooling, the wire rod satisfies the above general formula 1. According to the method for manufacturing the wire rod of the present application, it is possible to manufacture a wire rod that not only has excellent strength and toughness, but also has excellent wire drawing properties such as workability and productivity by preventing wire breakage during drawing.

[0095] The above hot rolling step is a step of manufacturing a billet into a wire rod having a desired diameter, and is performed by reheating and then hot rolling a billet containing, in weight percent, C: 0.70% or more and 1.10% or less, Si: 0.15% or more and 0.50% or less, Mn: 0.20% or more and 0.90% or less, Cr: 0.03% or more and 0.40% or less, P: 0.015% or less, S: 0.015% or less, Cu: 0.20% or less, Ni: 0.20% or less, Al: 0.015% or less, and N: 0.005% or less, and the remainder being Fe and other unavoidable impurities. Since a specific description of the composition of the above billet is the same as that described in the above wire rod, it will be omitted.

[0096] In one example, the billet may satisfy the above general formula 4.

[0097] Specifically, the value calculated by the above general formula 4 may be 0.21 or higher. Additionally, the upper limit of the value calculated by the above general formula 4 is not specifically limited, but may be, for example, 1.00 or lower, and specifically, 0.90 or lower or 0.80 or lower. By satisfying the aforementioned range for the value calculated by the above general formula 4, the billet can simultaneously improve the strength and toughness of the wire rod being manufactured, and also improve wire drawing performance, such as workability and productivity, by preventing wire breakage during drawing processing.

[0098] The above hot rolling may be performed after reheating the billet at a temperature of 1000°C or higher and 1170°C or lower for at least 90 minutes. Specifically, during the reheating, the temperature may be 1010°C or higher and 1165°C or lower. Additionally, during the reheating, the upper limit of the time may be 400 minutes or less. If the reheating is performed for less than the lower limit of the aforementioned temperature range and / or less than the lower limit of the aforementioned time range, the surface quality of the product may deteriorate due to the temperature drop and the rolling roll may be subjected to a load. Furthermore, if the reheating is performed for more than the upper limit of the aforementioned temperature range and / or more than the upper limit of the aforementioned time range, the decarburization reaction may be maximized, leading to a deterioration in the surface quality of the product after rolling due to surface decarburization. Therefore, the reheating may be performed within the aforementioned temperature range and the aforementioned time range.

[0099] In addition, the hot rolling may be performed at an inlet temperature of a precision rolling mill ranging from 850°C to 1000°C. If the inlet temperature of the precision rolling mill during the hot rolling is below the lower limit of the aforementioned range, the load on the rolling equipment increases, which may result in surface defects such as roll wear and folding. Furthermore, if the inlet temperature of the precision rolling mill during the hot rolling exceeds the upper limit of the aforementioned range, localized grain coarsening or surface decarburization may occur on the product surface, and product surface roughness defects may occur. Therefore, the hot rolling may be performed within the aforementioned inlet temperature range.

[0100] The above cooling step is a step of cooling the wire rod manufactured by hot rolling after winding it.

[0101] For example, the above-mentioned winding may be performed at a temperature of 800°C or higher and 900°C or lower. If the winding temperature is below the lower limit of the aforementioned range during winding, the probability of low-temperature structure formation and the strength of the product increase, which may lead to reduced drawing and processability. Additionally, if the winding temperature exceeds the upper limit of the aforementioned range during winding, the quality of the scale may deteriorate. Specifically, if the winding temperature exceeds the upper limit of the aforementioned range during winding, blister-shaped scale may form due to the thermal expansion coefficient of the scale FeO and the product, the scale may grow thickly at high temperatures, and a scale phase unfavorable for pickling may be formed. Therefore, the above-mentioned winding may be performed within the aforementioned temperature range.

[0102] In addition, in the above cooling step, the cooling rate of the wire rod up to 350℃ after winding (C R ) may be 8.5 ℃ / s or more and 20 ℃ / s or less. Specifically, in the above cooling step, the cooling rate of the wire rod up to 350℃ after winding (C R The cooling rate may be 8.8 ℃ / s or higher and 15 ℃ / s or lower. In the cooling step, by performing cooling at the aforementioned range of cooling rates up to 350℃ after winding, the interlamellar spacing of the pearlite structure can be refined, thereby enabling the production of a wire rod with high strength, high toughness, and excellent wire drawing properties such as workability and productivity by preventing wire breakage during drawing. At this time, cooling may be performed using blowing air. In the cooling step, if cooling is performed using blowing air up to 350℃ after winding, for example, from 400℃ to 500℃, a thick surface oxide scale is formed, making it difficult to remove the scale during pickling, which may cause quality degradation such as wire breakage during drawing.

[0103] In one example, the wire rod after cooling may satisfy the above general formula 2. Since the specific explanation of the above general formula 2 is the same as that described in the above wire rod, it will be omitted. By satisfying the above general formula 2 after cooling, the wire rod not only has excellent strength and toughness, but also prevents wire breakage during drawing, thereby having excellent drawing processability such as workability and productivity.

[0104] In another example, the wire rod after cooling can satisfy the above general formula 3. Since the specific explanation of the above general formula 3 is the same as that described in the above wire rod, it will be omitted. By satisfying the above general formula 3 after cooling, the wire rod can be manufactured to have excellent strength and toughness, as well as excellent wire drawing properties such as workability and productivity by preventing wire breakage during drawing.

[0105]

[0106] The present application will be described in more detail below through embodiments according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the embodiments presented below.

[0107]

[0108] Preparation Examples 1 to 10

[0109] Preparation of the billet

[0110] Billets containing the components shown in Table 1 below, the remainder of Fe, and other unavoidable impurities were each prepared.

[0111] Billet Composition (Weight%) Satisfaction with General Formula 4 CsiMnPSCuNiCrAlN Preparation Example 10.7 10.16 0.39 0.01 0.00 60.14 0.08 0.04 0.01 0.00 440 Preparation Example 20.8 30.2 0.48 0.01 0.00 50.02 0.01 0.03 0.00 20.00 370 Preparation Example 30.8 30.45 0.87 0.00 90.014 0.03 0.10 0.03 0.00 50.00 470 Preparation Example 40.9 30.19 0.28 0.00 80.00 60.02 0.01 0.18 0.00 10.00 320 Preparation Example 50.920.480.890.0120.0140.190.150.140.0070.0042OPreparationYes60.820.220.650.0090.0050.020.010.210.0010.0043OPreparationYes70.820.170.220.0140.0150.100.110.330.0010.0039OPreparationYes81.020.240.350.0090.0060.040.050.220.0010.0041OPreparationYes 90.720.200.440.0090.0040.010.010.020.0010.0034XPrep 101.010.520.370.0110.0080.020.010.030.0020.0041X

[0112] Example 1

[0113] Manufacturing of wire rods

[0114] As shown in Table 2 below, the billet of Preparation Example 1 was reheated at 1011°C for 98 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 866°C, and the hot-rolled wire rod was coiled at 811°C and cooled to 350°C at a cooling rate of 10.1°C / s to produce a wire rod.

[0115]

[0116] Example 2

[0117] Manufacturing of wire rods

[0118] As shown in Table 2 below, the billet of Preparation Example 2 was reheated at 1059°C for 121 minutes, then hot-rolled at an inlet temperature of 921°C of a precision rolling mill, and the hot-rolled wire rod was coiled at 887°C and then cooled to 350°C at a cooling rate of 12.0°C / s to produce a wire rod.

[0119]

[0120] Example 3

[0121] Manufacturing of wire rods

[0122] As shown in Table 2 below, the billet of Preparation Example 3 was reheated at 1158°C for 226 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 936°C, and the hot-rolled wire rod was coiled at 884°C and cooled to 350°C at a cooling rate of 12.7°C / s to produce a wire rod.

[0123]

[0124] Example 4

[0125] Manufacturing of wire rods

[0126] As shown in Table 2 below, the billet of Preparation Example 4 was reheated at 1163°C for 277 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 980°C, and the hot-rolled wire rod was coiled at 868°C and then cooled to 350°C at a cooling rate of 11.2°C / s to produce a wire rod.

[0127]

[0128] Example 5

[0129] Manufacturing of wire rods

[0130] As shown in Table 2 below, the billet of Preparation Example 5 was reheated at 1152°C for 265 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 945°C, and the hot-rolled wire rod was coiled at 895°C and then cooled to 350°C at a cooling rate of 11.7°C / s to produce a wire rod.

[0131]

[0132] Example 6

[0133] Manufacturing of wire rods

[0134] As shown in Table 2 below, the billet of Preparation Example 6 was reheated at 1055°C for 132 minutes, then hot-rolled at an inlet temperature of 922°C of a precision rolling mill, and the hot-rolled wire rod was coiled at 895°C and then cooled to 350°C at a cooling rate of 9.7°C / s to produce a wire rod.

[0135]

[0136] Example 7

[0137] Manufacturing of wire rods

[0138] As shown in Table 2 below, the billet of Preparation Example 7 was reheated at 1160°C for 293 minutes, then hot-rolled at an inlet temperature of 971°C of a precision rolling mill, and the hot-rolled wire rod was coiled at 860°C and then cooled to 350°C at a cooling rate of 8.8°C / s to produce a wire rod.

[0139]

[0140] Example 8

[0141] Manufacturing of wire rods

[0142] As shown in Table 2 below, the billet of Preparation Example 8 was reheated at 1155°C for 165 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 992°C, and the hot-rolled wire rod was coiled at 852°C and then cooled to 350°C at a cooling rate of 10.8°C / s to produce a wire rod.

[0143]

[0144] Comparative Example 1

[0145] Manufacturing of wire rods

[0146] As shown in Table 2 below, the billet of Preparation Example 1 was reheated at 1013°C for 101 minutes, then hot-rolled at an inlet temperature of 868°C of a precision rolling mill, and the hot-rolled wire rod was coiled at 815°C and then cooled to 350°C at a cooling rate of 7.5°C / s to produce a wire rod.

[0147]

[0148] Comparative Example 2

[0149] Manufacturing of wire rods

[0150] As shown in Table 2 below, the billet of Preparation Example 2 was reheated at 1060°C for 122 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 917°C, and the hot-rolled wire rod was coiled at 890°C and cooled to 350°C at a cooling rate of 6.9°C / s to produce a wire rod.

[0151]

[0152] Comparative Example 3

[0153] Manufacturing of wire rods

[0154] As shown in Table 2 below, the billet of Preparation Example 3 was reheated at 1156°C for 226 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 935°C, and the hot-rolled wire rod was coiled at 888°C and cooled to 350°C at a cooling rate of 8.0°C / s to produce a wire rod.

[0155]

[0156] Comparative Example 4

[0157] Manufacturing of wire rods

[0158] As shown in Table 2 below, the billet of Preparation Example 4 was reheated at 1166°C for 278 minutes, then hot-rolled at an inlet temperature of 983°C of a precision rolling mill, and the hot-rolled wire rod was coiled at 870°C and then cooled to 350°C at a cooling rate of 7.8°C / s to produce a wire rod.

[0159]

[0160] Comparative Example 5

[0161] Manufacturing of wire rods

[0162] As shown in Table 2 below, the billet of Preparation Example 5 was reheated at 1152°C for 265 minutes, then hot-rolled at an inlet temperature of 942°C of a precision rolling mill, and the hot-rolled wire rod was coiled at 894°C and then cooled to 350°C at a cooling rate of 6.3°C / s to produce a wire rod.

[0163]

[0164] Comparative Example 6

[0165] Manufacturing of wire rods

[0166] As shown in Table 2 below, the billet of Preparation Example 6 was reheated at 1050°C for 128 minutes, then hot-rolled at an inlet temperature of 919°C of a precision rolling mill, and the hot-rolled wire rod was coiled at 894°C and then cooled to 350°C at a cooling rate of 8.2°C / s to produce a wire rod.

[0167]

[0168] Comparative Example 7

[0169] Manufacturing of wire rods

[0170] As shown in Table 2 below, the billet of Preparation Example 7 was reheated at 1159°C for 292 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 968°C, and the hot-rolled wire rod was coiled at 856°C and then cooled to 350°C at a cooling rate of 5.1°C / s to produce a wire rod.

[0171]

[0172] Comparative Example 8

[0173] Manufacturing of wire rods

[0174] As shown in Table 2 below, the billet of Preparation Example 8 was reheated at 1158°C for 172 minutes, then hot-rolled at an inlet temperature of 991°C of a precision rolling mill, and the hot-rolled wire rod was coiled at 850°C and then cooled to 350°C at a cooling rate of 7.9°C / s to produce a wire rod.

[0175]

[0176] Comparative Example 9

[0177] Manufacturing of wire rods

[0178] As shown in Table 2 below, the billet of Preparation Example 9 was reheated at 1020°C for 105 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 870°C, and the hot-rolled wire rod was coiled at 822°C and then cooled to 350°C at a cooling rate of 9.2°C / s to produce a wire rod.

[0179]

[0180] Comparative Example 10

[0181] Manufacturing of wire rods

[0182] As shown in Table 2 below, the billet of Preparation Example 10 was reheated at 1153°C for 169 minutes, then hot-rolled at the inlet temperature of a precision rolling mill at 1033°C, and the hot-rolled wire rod was coiled at 859°C and then cooled to 350°C at a cooling rate of 8.8°C / s to produce a wire rod.

[0183] Reheating Temperature (°C) Reheating Time (Min) Precision Rolling Mill Inlet Temperature (°C) Coiling Temperature (°C) Cooling Rate to 350°C After Coiling (°C) Example 1 10 119 886 68 11 10.1 Example 2 10 59 12 19 218 87 12.0 Example 3 11 58 22 69 36 88 4 12.7 Example 4 11 63 27 79 80 868 11.2 Example 5 11 52 265 94 58 95 11.7 Example 6 10 55 13 29 22 89 5 9.7 Example 7 11 60 29 39 7 18 60 8.8 Example 8 11 55 165 99 28 52 10.8 Comparative Example 1 10 13 10 186 88 15 7.5 Comparative Example 210601229178906.9 Comparative Example 311562269358888.0 Comparative Example 411662789838707.8 Comparative Example 511522659428946.3 Comparative Example 610501289198948.2 Comparative Example 711592929688565.1 Comparative Example 811581729918507.9 Comparative Example 910201058708229.2 Comparative Example 10115316910338598.8

[0184] Evaluation Example 1. Evaluation of satisfaction of General Formula 1

[0185] For the wires manufactured in the examples and comparative examples, tensile tests were performed according to ASTM-E8 to measure tensile strength and reduction of area, and whether they satisfied the following general formula 1 was evaluated, and the results are shown in Table 3 below. Specifically, the tensile test can be performed by cutting each wire into 50 cm lengths along the longitudinal direction and mounting them on the jig of a tensile testing machine. At this time, the reduction of area (RA; Reduction of Area) is calculated using the following general formula 5, and specifically, it is calculated by expressing the difference between the minimum cross-sectional area after the wire is fractured by stretching each wire in the longitudinal direction and the original cross-sectional area of ​​the wire before the tensile test as a percentage.

[0186] [General Formula 1]

[0187] AⅩB ≥ 40000

[0188] In the above general formula 1, A is tensile strength (MPa) and B is cross-sectional shrinkage rate (%).

[0189] [General Formula 5]

[0190]

[0191] In the above general formula 5, A0 is the original cross-sectional area of ​​the wire before the tensile test, and A1 is the minimum cross-sectional area after the wire is fractured by stretching the wire in the longitudinal direction.

[0192]

[0193] Evaluation Example 2. Evaluation of satisfaction of General Formula 4

[0194] The billets of the manufacturing examples used in the examples and comparative examples were evaluated to satisfy the following general formula 4, and the results are shown in Table 1 above.

[0195] [General Formula 4]

[0196] 0.20 ≤ 2ⅩCr+Mn / 3

[0197] In the above general formula 4, Cr is the chromium content (weight%) contained in the billet, and Mn is the manganese content (weight%) contained in the billet.

[0198]

[0199] Evaluation Example 3. Evaluation of satisfaction of General Formula 2

[0200] For the wires produced in each of the examples and comparative examples, it was evaluated whether they satisfied the following general formula 2, and the results are shown in Table 3 below. At this time, the lamellar spacing (ILS(D / 4)) of the pearlite structure measured at 1 / 4 of the diameter of the wires produced in each of the examples and comparative examples was prepared by cutting each wire into a cross-section to make a specimen, acquiring 10 images at a magnification of 50,000x using a scanning electron microscope (SEM), measuring 20 lamellar spacings at 1 / 4 of the diameter of each wire using image analysis software, and calculating the average value.

[0201] [General Formula 2]

[0202] ILS(D / 4) ≤ 162-3.9(2ⅩCr+Mn / 3)ⅩC R

[0203] In the above General Formula 2, ILS(D / 4) is the lamellar interlayer spacing of the pearlite structure measured at 1 / 4 of the wire rod diameter after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

[0204]

[0205] Evaluation Example 4. Evaluation of satisfaction of General Formula 3

[0206] For the wires produced in each of the examples and comparative examples, it was evaluated whether they satisfied the following general formula 3, and the results are shown in Table 3 below. At this time, the lamellar spacing (ILS(D / 2)) of the pearlite structure measured at half the diameter of the wires produced in each of the examples and comparative examples was prepared by cutting each wire into a cross-section to make a specimen, acquiring 10 images at a magnification of 50,000x using a scanning electron microscope (SEM), measuring 20 lamellar spacings at half the diameter of each wire using image analysis software, and calculating the average value.

[0207] [General Formula 3]

[0208] ILS(D / 2) ≤ 188-7.2(2ⅩCr+Mn / 3)ⅩC R

[0209] In the above General Formula 3, ILS(D / 2) is the lamellar interlayer spacing of the pearlite structure measured at half the diameter of the wire rod after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

[0210]

[0211] Evaluation Example 5. Evaluation of wire breakage frequency during tire cord manufacturing

[0212] The frequency of wire breakage in the drawing and stranding processes for manufacturing tire cord from 1 ton of wire produced in each of the examples and comparative examples was evaluated, and the results are shown in Table 3 below.

[0213] Tensile Strength (MPa) Cross-sectional Shrinkage Rate (%) Satisfaction of General Formula 1 ILS (D / 4) (nm) Satisfaction of General Formula 2 ILS (D / 2) (nm) Satisfaction of General Formula 3 Frequency of breakage during tire cord manufacturing (turns / ton) Example 1 10 2146 O 147 O 168 O 3 Example 2 11 27 42 O 141 O 163 O 2 Example 3 11 76 46 O 121 O 130 O 0 Example 4 12 05 43 O 133 O 137 O 1 Example 5 12 54 48 O 129 O 135 O 2 Example 6 11 48 43 O 125 O 140 O 1 Example 7 11 96 51 O 124 O 129 O 0 Example 8 12 833 7 O 125 O 131 O 4 Comparative Example 196639X193X213X10 Comparative Example 2103533X181X202X12 Comparative Example 3104338X157X172X7 Comparative Example 4110236X164X176X8 Comparative Example 5112035X158X171X7 Comparative Example 6107037X151X173X7 Comparative Example 7107235X153X165X8 Comparative Example 8119631X155X164X15 Comparative Example 997441X184X195X7 Comparative Example 10121132X169X182X11

[0214] As shown in Table 1 above, although the wire rods produced in each of Comparative Examples 1 to 8 satisfied General Formula 4 by using the same billet as the wire rods produced in each of Examples 1 to 8, as shown in Table 2 above, the cooling rate up to 350°C after winding did not satisfy a specific range. Consequently, as shown in Table 3 above, the lamellar interlayer spacing of the pearlite structure was formed coarsely, failing to satisfy General Formulas 2 and 3, and as a result, the tensile strength and cross-sectional shrinkage rate decreased, and it was confirmed that General Formula 1 was also not satisfied. Accordingly, it was confirmed that the wire rods produced in each of Comparative Examples 1 to 8 suffered from reduced drawing processability, with more than 5 single strands per ton occurring during tire cord manufacturing.

[0215] In addition, as shown in Table 1 above, since the wire rods manufactured in Comparative Examples 9 and 10, respectively, used billets that did not satisfy General Formula 4, it was confirmed that, as shown in Table 2 above, although the cooling rate up to 350°C after winding satisfied a specific range, the tensile strength and cross-sectional shrinkage rate were low and did not satisfy General Formula 1, as shown in Table 3 above. Accordingly, it was confirmed that the wire rods manufactured in Comparative Examples 9 and 10, respectively, suffered from reduced drawing processability, with more than 5 single strands per ton occurring during tire cord manufacturing.

[0216] That is, as shown in Table 1 above, the wire rods produced in each of Examples 1 to 8 used a billet satisfying General Formula 4, and as shown in Table 2 above, the cooling rate up to 350°C after winding satisfied a specific range, thereby forming fine lamellar interlayer spacing of the pearlite structure, satisfying General Formulas 2 and 3 as shown in Table 3 above, and consequently, it was confirmed that General Formula 1 was also satisfied as the tensile strength and cross-sectional shrinkage rate were improved. Accordingly, it was confirmed that the wire rods produced in each of Examples 1 to 8 had excellent drawing processability, with the number of wire breakage occurrences during tire cord manufacturing being less than 5 times per ton.

Claims

1. In wt%, comprising C: 0.70% or more and 1.10% or less, Si: 0.15% or more and 0.50% or less, Mn: 0.20% or more and 0.90% or less, Cr: 0.03% or more and 0.40% or less, P: 0.015% or less, S: 0.015% or less, Cu: 0.20% or less, Ni: 0.20% or less, Al: 0.015% or less, and N: 0.005% or less, and the remainder comprising Fe and other unavoidable impurities, Wire satisfying the following general formula 1: [General Formula 1] AⅩB ≥ 40000 In the above general formula 1, A is tensile strength (MPa) and B is cross-sectional shrinkage rate (%).

2. In Paragraph 1, A wire rod manufactured by reheating a billet, hot rolling it, coiling it, and cooling it, Wire satisfying the following general formula 2: [General Formula 2] ILS(D / 4) ≤ 162-3.9(2ⅩCr+Mn / 3)ⅩC R In the above General Formula 2, ILS(D / 4) is the lamellar interlayer spacing of the pearlite structure measured at 1 / 4 of the wire rod diameter after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

3. In Paragraph 1, A wire rod manufactured by reheating a billet, hot rolling it, coiling it, and cooling it, Wire satisfying the following general formula 3: [General Formula 3] ILS(D / 2) ≤ 188-7.2(2ⅩCr+Mn / 3)ⅩC R In the above General Formula 3, ILS(D / 2) is the lamellar interlayer spacing of the pearlite structure measured at half the diameter of the wire rod after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

4. In Paragraph 1, A wire satisfying the following general formula 4. [General Formula 4] 0.20 ≤ 2ⅩCr+Mn / 3 In the above general formula 4, Cr is the chromium content (weight%) contained in the wire, and Mn is the manganese content (weight%) contained in the wire.

5. In Paragraph 1, A wire rod comprising pearlite having an area fraction of 90% or more and ferrite having an area fraction of 10% or less.

6. A hot rolling step of reheating and then hot rolling a billet comprising, in wt%, C: 0.70% or more and 1.10% or less, Si: 0.15% or more and 0.50% or less, Mn: 0.20% or more and 0.90% or less, Cr: 0.03% or more and 0.40% or less, P: 0.015% or less, S: 0.015% or less, Cu: 0.20% or less, Ni: 0.20% or less, Al: 0.015% or less and N: 0.005% or less, and the remainder being Fe and other unavoidable impurities; and A method for manufacturing a wire rod comprising a cooling step of cooling after winding a hot-rolled wire rod, A method for manufacturing a wire rod that satisfies the following general formula 1 after cooling: [General Formula 1] AⅩB ≥ 40000 In the above general formula 1, A is tensile strength (MPa) and B is cross-sectional shrinkage rate (%).

7. In Paragraph 6, A method for manufacturing a wire rod that satisfies the following general formula 2 after cooling: [General Formula 2] ILS(D / 4) ≤ 162-3.9(2ⅩCr+Mn / 3)ⅩC R In the above General Formula 2, ILS(D / 4) is the lamellar interlayer spacing of the pearlite structure measured at 1 / 4 of the wire rod diameter after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

8. In Paragraph 6, A method for manufacturing a wire rod that satisfies the following general formula 3 after cooling: [General Formula 3] ILS(D / 2) ≤ 188-7.2(2ⅩCr+Mn / 3)ⅩC R In the above General Formula 3, ILS(D / 2) is the lamellar interlayer spacing of the pearlite structure measured at half the diameter of the wire rod after cooling, Cr is the chromium content (weight%) contained in the billet, Mn is the manganese content (weight%) contained in the billet, and C R This is the cooling rate (°C / s) of the wire rod up to 350°C after winding.

9. In Paragraph 6, The above billet is a method for manufacturing a wire rod satisfying the following general formula 4: [General Formula 4] 0.20 ≤ 2ⅩCr+Mn / 3 In the above general formula 4, Cr is the chromium content (weight%) contained in the billet, and Mn is the manganese content (weight%) contained in the billet.

10. In Paragraph 6, A method for manufacturing a wire rod in which, in the above cooling step, the cooling rate of the wire rod up to 350℃ after winding is 8.5℃ / s or more and 20℃ / s or less.

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