Steel wire rod, steel wire and method for manufacturing the same

Abstract

A steel wire according to one embodiment of the present application contains, by weight%, 0.1 to 0.5% of carbon (C), 0.01 to 0.6% of silicon (Si), 0.6 to 1.6% of manganese (Mn), 0.01 to 1.4% of chromium (Cr), more than 0% and not more than 0.02% of nitrogen (N); at least one selected from 0.01 to 0.06% of aluminum (Al), 0.005 to 0.03% of niobium (Nb), 0.001 to 0.03% of titanium (Ti), or 0.01 to 0.3% of vanadium (V); and the remainder of iron (Fe) and inevitable impurities. The microstructure of the steel wire contains ferrite and pearlite, and the ferrite has an average grain size of 3 µm or less, a uniform elongation of 3.5% or more, and a yield ratio of 90% or more.

Description

Technical Field

[0001] This disclosure relates to wire rods and steel wires that can simultaneously omit spheroidizing softening annealing and QT (Quenching and Tempering) strengthening heat treatment, and more particularly, to wire rods and steel wires that can omit heat treatment by controlling the microstructure through optimized rolling and subsequent process variables. Background Technology

[0002] Cold heading wire is classified into heat-treated products manufactured through softening annealing and strengthening heat treatments such as QT, and non-heat-treated products manufactured without separate heat treatment. Heat-treated products are effective in improving die life during cold forging, but they suffer from low productivity due to the long annealing time and additional straightening costs due to warping during the final QT heat treatment. Non-heat-treated steels, however, offer high economic efficiency by omitting the spheroidizing and QT heat treatment processes and have numerous advantages in terms of productivity and efficiency because straightening is not required.

[0003] Non-heat-treatable steel (microalloyed steel) allows for the omission of QT heat treatment by ensuring the tensile properties of the final product solely through subsequent wire drawing and by controlling the wire's microstructure. Furthermore, it offers the advantage of ensuring products with a wide range of strengths by controlling the wire drawing reduction rate.

[0004] However, regarding the microstructure of wire composed of ferrite and pearlite, drawing beyond the critical processing rate can lead to herringbone internal cracks, thus limiting the drawing reduction rate. Furthermore, compared to QT heat-treated materials with a martensitic structure, it is impossible to ensure a yield strength ratio (YR ratio) of 90% or greater (the ratio of yield strength (YS) to tensile strength (TS)). Moreover, the difficulty in ensuring a uniform elongation representing ductility from yield strength (YS) to tensile strength (TS) imposes limitations on applications such as fastening bolts in the plastic zone, thus restricting the complete replacement of QT heat-treated materials.

[0005] Therefore, there is a need to develop product manufacturing methods that can ensure comparable physical properties even when existing QT heat treatment is omitted. Summary of the Invention

[0006] Technical issues

[0007] This disclosure aims to provide wires and steel wires that can ensure tensile properties comparable to those of QT heat-treated materials by overcoming the shortcomings of existing non-heat-treated steels without changing their chemical composition, as well as methods for manufacturing them.

[0008] The problems to be addressed by this disclosure are not limited to those described above, and other issues not mentioned will be clearly understood by those skilled in the art from the following description.

[0009] Technical solution

[0010] As a means of achieving the above objectives, the steel wire according to one example of this disclosure may contain, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and at least one selected from 0.01% to 0.06% aluminum (Al), 0.005% to 0.03% niobium (Nb), 0.001% to 0.03% titanium (Ti), and 0.01% to 0.3% vanadium (V), with the balance being iron (Fe) and unavoidable impurities, wherein the microstructure comprises ferrite and pearlite, the ferrite having an average grain size of 3 μm or less, a uniform elongation of 3.5% or more, and a yield strength ratio of 90% or more.

[0011] Furthermore, the tensile strength of the steel wire according to one example of this disclosure can be from 800 MPa to 1300 MPa.

[0012] Furthermore, according to one example of this disclosure, the steel wire may be free of cracks when the L-section is at an angle of ±45° relative to the drawing direction.

[0013] Furthermore, the wire according to one example of this disclosure may contain, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and at least one selected from 0.01% to 0.06% aluminum (Al), 0.005% to 0.03% niobium (Nb), 0.001% to 0.03% titanium (Ti), and 0.01% to 0.3% vanadium (V), with the balance being iron (Fe) and unavoidable impurities, wherein the microstructure comprises proeutectoid ferrite, residual pearlite, and 10% or less bainite and martensite by area fraction, and the average grain size of the proeutectoid ferrite microstructure is 5 μm or less.

[0014] Furthermore, the tensile strength of the wire according to one example of this disclosure can be from 650 MPa to 850 MPa.

[0015] Furthermore, in one example of the wire according to this disclosure, cracks may not exist inside the L-section of the wire obtained by drawing and extruding the wire at a processing rate of 30% to 70% when the angle relative to the drawing direction is ±45°.

[0016] (Where, section L refers to the section parallel to the rolling direction.)

[0017] Furthermore, a method for manufacturing steel wire according to one example of this disclosure may include: preparing a steel billet containing, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and containing, by weight percentage (wt%), aluminum (Al) selected from 0.01% to 0.06% and 0.005% to 0.06% aluminum (C), more than 0.01% to 0.02% nitrogen (N), and more than 0.01% to 0.02% nitrogen (C). The steel billet contains at least one of 0.03% niobium (Nb), 0.001% to 0.03% titanium (Ti), and 0.01% to 0.3% vanadium (V), with the balance being iron (Fe) and unavoidable impurities; the billet is heated to 950°C to 1200°C; the billet is hot-rolled at 700°C to 900°C to produce wire rod; the hot-rolled wire rod is cooled at a cooling rate of 3°C / second to 15°C / second; and the cooled wire rod is drawn and extruded at a processing rate of 30% to 70%.

[0018] Furthermore, a method for manufacturing steel wire according to one example of this disclosure may also include dehydrogenating the drawn and extruded wire at a temperature of 200°C to 600°C for 30 to 60 minutes.

[0019] Furthermore, in a method for manufacturing steel wire according to one example of this disclosure, the steel billet can be hot-rolled at a temperature of 700°C to 800°C to manufacture wire rod.

[0020] Furthermore, in a method for manufacturing steel wire according to one example of this disclosure, the hot-rolled wire can be cooled at a cooling rate of 4°C / second to 5°C / second.

[0021] Furthermore, a method for manufacturing steel wire according to one example of this disclosure may also include dehydrogenating the drawn and extruded wire at a temperature of 300°C to 450°C for 30 to 60 minutes.

[0022] Beneficial effects

[0023] According to one embodiment of this disclosure, steel wire can be manufactured that can ensure tensile properties comparable to those of QT heat-treated materials by overcoming the shortcomings of existing non-heat-treated steel.

[0024] Furthermore, according to one embodiment of this disclosure, the yield strength ratio (YR ratio), which is the ratio of yield strength (YS) to tensile strength (TS), can be ensured to be 90% or greater, and the uniform elongation representing ductility from yield strength (YS) to tensile strength (TS) can be ensured to be 3.5% or greater, so that steel wires for fastening bolts in plastic regions can be manufactured by replacing QT heat-treated materials. Detailed Implementation

[0025] Preferred embodiments of this disclosure will be described below. However, embodiments of this disclosure can be modified in various other forms, and the technical spirit of this disclosure is not limited to the embodiments described below. Furthermore, embodiments of this disclosure are provided to illustrate this disclosure more completely to those skilled in the art.

[0026] The terminology used in this application is for the purpose of describing specific instances only. Therefore, for example, singular expressions include plural expressions unless the context clearly indicates otherwise. Furthermore, it should be noted that terms such as “comprising / including” or “having” as used in this application are used to explicitly indicate the presence of the features, steps, functions, components, or combinations thereof described in the specification, and are not intended to presuppose the presence of other features, steps, functions, components, or combinations thereof.

[0027] Furthermore, unless otherwise defined, all terms used herein should be assumed to have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Therefore, unless explicitly defined in this specification, certain terms should not be interpreted in an overly idealized or formalistic sense. For example, unless the context clearly indicates an exception, singular expressions in this specification include plural expressions.

[0028] Furthermore, the terms “about,” “substantially,” etc., used in this specification are used in a numerical or near-numerical sense when they represent unique manufacturing and material tolerances in their stated meaning, and are intended to prevent unethical infringers from unfairly using the precise or absolute numerical values ​​mentioned herein to aid in the understanding of this disclosure.

[0029] Sometimes wire is subjected to spheroidizing annealing to ensure machinability. Spheroidizing annealing for other processes requires significant heat treatment costs and time, thereby reducing productivity and increasing the manufacturing cost of the material.

[0030] In addition, spheroidizing materials are cold-formed and subjected to QT heat treatment to ensure the physical properties of the final product. Since QT heat treatment is carried out at high temperatures of 800°C or higher, it has been identified as one of the main causes of environmental pollution due to large amounts of CO2 emissions. For this reason, many inventors are making efforts to omit spheroidizing and QT heat treatment.

[0031] Therefore, in the manufacture of cold-forged products such as bolts, as a result of in-depth research on measures to omit spheroidizing and QT heat treatment, it was determined that by optimizing alloy composition and manufacturing conditions to control the grain size of the final product, physical properties comparable to those of spheroidizing and QT heat treatment can be ensured even when spheroidizing and QT heat treatment are omitted, thus leading to the completion of this disclosure.

[0032] The steel wire will be described in detail below.

[0033] According to one example of this disclosure, the steel wire contains, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), and more than 0% and less than 0.02% nitrogen (N), and

[0034] It contains at least one of aluminum (Al) selected from 0.01% to 0.06%, niobium (Nb) selected from 0.005% to 0.03%, titanium (Ti) selected from 0.001% to 0.03%, and vanadium (V) selected from 0.01% to 0.3%, and may contain the balance iron (Fe) and unavoidable impurities.

[0035] The function and content of the components contained in the steel wire according to this disclosure will be described below. The percentages (%) for the following components refer to weight (%).

[0036] The C content can be from 0.1% to 0.5%.

[0037] Carbon is an element added to ensure a certain level of strength. The reason for limiting the carbon content to 0.1% or more is to ensure sufficient initial tensile strength before wire drawing and to ensure the work hardening rate of wire drawing by ensuring an appropriate pearlite fraction. Furthermore, while a content exceeding 0.5% promotes ensuring initial strength, it also promotes the formation of internal cracks during wire drawing due to the coarsening of the pearlite structure. Therefore, 0.1% to 0.5% is preferred, and more preferably, the carbon content is limited to the range of 0.2% to 0.48%.

[0038] The Si content can be from 0.01% to 0.6%.

[0039] Si is a representative substitution element and is added to ensure a certain level of strength. Si content below 0.01% makes it difficult to ensure the strength of the steel, while content exceeding 0.6% significantly increases the yield strength, thereby deteriorating cold forgeability, for example, causing damage to forming tools during cold forging. Therefore, 0.01% to 0.6% is preferred, and more preferably, the silicon content is limited to the range of 0.05% to 0.4%.

[0040] The Mn content can be from 0.6% to 1.6%.

[0041] Mn is an element that forms substitutional solid solutions in the matrix for solid solution strengthening, and it is an element that can ensure the target strength without degrading ductility. It is also a representative austenite forging. Adding Mn in amounts less than 0.6% fails to guarantee strength due to solid solution strengthening, and makes it difficult to achieve the desired improvement in toughness. Furthermore, Mn content exceeding 1.6% makes it difficult to suppress center segregation, which may promote the formation of internal cracks during wire drawing. Therefore, it is preferable to limit the Mn content to 0.6% to 1.6%.

[0042] The Cr content can range from 0.01% to 1.4%.

[0043] Cr is added to ensure the hardenability of the steel, similar to Mn. Adding Cr in amounts less than 0.01% may make it difficult to ensure sufficient hardenability. Furthermore, compared to this amount, Cr content exceeding 1.4% provides no significant improvement in hardenability and may promote the formation of coarse iron carbides, resulting in poor impact energy absorption. Therefore, it is preferable to limit the Cr content to between 0.01% and 1.4%.

[0044] The nitrogen content can be greater than 0% and 0.02% or less.

[0045] In this disclosure, the nitrogen (N) content is preferably controlled to 0.02% or less. Contents exceeding 0.02% may lead to a deterioration in the toughness / ductility of the material due to dissolved nitrogen not bound as precipitates.

[0046] The Al content can be from 0.01% to 0.06%.

[0047] It is preferable to limit the Al content to 0.01% to 0.06%. An aluminum content below 0.01% makes it difficult to ensure sufficient deoxidation capacity, while an aluminum content above 0.05% may increase hard inclusions such as Al2O3, and in particular, may cause nozzle blockage due to inclusions during continuous casting.

[0048] The Nb content can be from 0.005% to 0.03%.

[0049] Nb precipitates during heating or rolling to refine the austenite grains, making it easier to ensure the target proeutectoid ferrite fraction and suppressing the deterioration of the material's ductility / toughness. Simultaneously, it ensures the target tensile strength through sufficient work hardening during wire drawing. Contents less than 0.005% make it difficult to ensure the desired grain refinement effect due to insufficient precipitation, while additions exceeding 0.03% may adversely affect grain refinement due to coarsening of the precipitates.

[0050] The Ti content can be from 0.001% to 0.03%.

[0051] Ti precipitates during heating or rolling to refine the austenite grains, making it easier to ensure the target proeutectoid ferrite fraction and suppressing the deterioration of the material's ductility / toughness. Simultaneously, it ensures the target tensile strength through sufficient work hardening during wire drawing. Contents less than 0.001% make it difficult to ensure the desired grain refinement effect due to insufficient precipitation, while additions exceeding 0.03% may instead reduce ductility / toughness due to coarsening of the precipitates, or act as a factor leading to internal cracking during wire drawing.

[0052] The vitamin (V) content can range from 0.01% to 0.3%.

[0053] V precipitates during the cooling process of the wire to improve the work hardening rate during drawing, thus ensuring the target tensile strength can be consistently achieved. However, additions of less than 0.01% result in insufficient precipitation, making it difficult to achieve the desired effect, while additions of more than 0.3% may lead to internal cracks or adversely affect ductility / toughness.

[0054] The remaining component of this disclosure is iron (Fe). However, in the ordinary manufacturing process, unintended impurities may inevitably be introduced from the raw materials or the surrounding environment, and therefore cannot be eliminated. Since impurities are known to any person skilled in the art in the ordinary manufacturing process, not all details are specifically mentioned in this specification.

[0055] The following will describe in detail one embodiment of a steel wire having the above-described alloy composition according to the present disclosure.

[0056] According to one example of this disclosure, the steel wire comprises, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and contains at least one selected from 0.01% to 0.06% aluminum (Al), 0.005% to 0.03% niobium (Nb), 0.001% to 0.03% titanium (Ti), and 0.01% to 0.3% vanadium (V), with the balance being iron (Fe) and unavoidable impurities. The microstructure of the steel wire may comprise ferrite and pearlite, wherein the average grain size of the ferrite may be 3 μm or less, preferably 1.5 μm or less, and most preferably 1.3 μm. The wire has a diameter of 3 μm or less, a uniform elongation of 3.5% or more, preferably 4.0% or more, and a yield strength ratio of 90% or more, preferably 94% or more, and most preferably 94.9% or more. With the steel wire manufactured according to the composition and process of this disclosure, a fine microstructure of 3 μm or less can be ensured, enabling an excellent yield strength ratio of 90% or more without QT heat treatment, and ensuring a uniform elongation of 3.5% or more.

[0057] In this disclosure, grain size refers to the diameter of a circle that is assumed to have an area equal to the grain area. Furthermore, the average grain size can be calculated as (measured area / number of grains). 0.5 The grain size can be calculated based on a plane parallel to the cross-section perpendicular to the rolling direction (TD plane). In this case, it is assumed that several hexagons are connected, and the grain size is evaluated using an image analyzer with a built-in analysis program (the grain measurement method of ASTM E112).

[0058] Furthermore, the tensile strength of the steel wire according to one example of this disclosure can be from 800 MPa to 1300 MPa, preferably from 1000 MPa to 1300 MPa, and most preferably from 1053 MPa to 1190 MPa.

[0059] Furthermore, according to one example of this disclosure, the steel wire may be free of cracks when the L-section is at an angle of ±45° relative to the drawing direction.

[0060] (Where, section L refers to the section parallel to the rolling direction.)

[0061] Furthermore, the wire according to one example of this disclosure contains, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and contains at least one selected from 0.01% to 0.06% aluminum (Al), 0.005% to 0.03% niobium (Nb), 0.001% to 0.03% titanium (Ti), and 0.01% to 0.3% vanadium (V), with the balance being iron (Fe) and unavoidable impurities, wherein the microstructure comprises proeutectoid ferrite, residual pearlite, and 10% or less bainite and martensite by area fraction, and the average grain size of the proeutectoid ferrite microstructure may be 5 μm or less.

[0062] Furthermore, the tensile strength of the wire according to one example of this disclosure can be from 650 MPa to 850 MPa, preferably from 700 MPa to 850 MPa, and most preferably from 756 MPa to 830 MPa.

[0063] Furthermore, in one example of the wire according to this disclosure, as a result of a crack initiation test conducted after drawing and extruding the wire at a processing rate of 30% to 70%, no cracks were found within the L-section of the wire at an angle of ±45° relative to the drawing direction. As described above, preventing the occurrence of herringbone cracks at an angle of ±45° makes it possible to prevent wire breakage during drawing or premature breakage during the use of the final product, thereby reducing process costs and improving the service life of the final product.

[0064] (Where, section L refers to the section parallel to the rolling direction.)

[0065] Furthermore, a method for manufacturing steel wire according to one example of this disclosure may include: preparing a steel billet containing, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and containing, selected from 0.01% to 0.06% aluminum (Al), 0.005% to 0.03% niobium (Nb), 0 The steel billet contains at least one of titanium (Ti) and vanadium (V) from 0.001% to 0.03%, and the balance of iron (Fe) and unavoidable impurities; the billet is heated to 950°C to 1200°C; the billet is hot-rolled at 700°C to 900°C, preferably 700°C to 800°C, to produce wire rod; the hot-rolled wire rod is cooled at a cooling rate of 3°C / second to 15°C / second, preferably 4°C / second to 5°C / second; and the cooled wire rod is drawn and extruded at a processing rate of 30% to 70%.

[0066] Furthermore, a method for manufacturing steel wire according to one example of this disclosure may also include dehydrogenating the drawn and extruded wire at a temperature of 200°C to 600°C, preferably 300°C to 450°C, for 30 to 60 minutes.

[0067] For the rolling conditions of the wire rod disclosed herein, it is preferable to perform finish rolling on steel billets heated to 950°C to 1200°C within a temperature range of 700°C to 800°C. Temperatures below 700°C lead to difficulties in roll breakage and coiling due to high rolling loads, which may result in uneven cooling of the material due to poor coiling shape. On the other hand, temperatures above 800°C make it difficult to stably ensure precipitates, and may lead to problems in controlling the target microstructure due to grain coarsening.

[0068] Subsequently, in this disclosure, the final wire can be manufactured by cooling the hot-rolled wire at a cooling rate of 3°C / s to 15°C / s. Cooling rates below 3°C / s make it difficult to achieve the target grain refinement due to grain coarsening after rolling, which may lead to difficulties in ultimately ensuring the desired physical properties. On the other hand, during rapid cooling exceeding 15°C / s, the untransformed austenite phase transforms into a low-temperature hard structure, which may cause material damage or breakage during wire drawing, and there is a concern about a significant increase in the pearlite fraction, leading to internal cracking.

[0069] The wire of this disclosure manufactured by the manufacturing process described above may contain 30% to 90% by area proeutectoid ferrite, residual pearlite, and 10% or less bainite and martensite as microstructure, may have a proeutectoid ferrite microstructure with an average grain size of 5 μm or less, and may have a tensile strength of 650 MPa to 850 MPa.

[0070] Subsequently, the tensile strength of the final product is ensured through the wire drawing process. At this point, by limiting the appropriate wire drawing and extrusion rate to 30% to 70%, a target tensile strength of 800 MPa to 1300 MPa can be ensured based on this rate. A rate of 30% or less cannot ensure the target stable tensile properties, while a rate exceeding 70% results in herringbone cracks at an angle of ±45° relative to the drawing direction within the material, leading to wire breakage during drawing or premature breakage during the final product's use. Therefore, the range of wire drawing rates can be limited to the above limits.

[0071] To ensure the final product's shape, cold forming is performed, followed by dehydrogenation and stress relief treatment at approximately 200°C to 600°C for 30 to 60 minutes. This improves the ductility and toughness reduced by wire drawing, ensures the yield strength ratio, and ensures uniform elongation. As a result, steel wires with an average grain size of 3 μm or less ferrite structure, a tensile strength of 800 MPa to 1300 MPa in the final product, and a uniform elongation of 3.5% or greater can be manufactured.

[0072] The present disclosure will be described in detail below through examples.

[0073] (Example)

[0074] Under the manufacturing conditions shown in Table 1, wire rods were manufactured using steel billets with the composition shown in Table 1 below, and the area fractions of bainite and martensite formed in the wire rods manufactured under these manufacturing conditions, the average grain size of the proeutectoid ferrite structure, and the tensile strength of the wire rods are shown in Table 1. In Table 1, Experimental Examples 1 to 5 satisfy the composition range and manufacturing conditions of this disclosure, while Comparative Examples 1 to 5 show cases outside the composition range or manufacturing conditions of this disclosure.

[0075] In addition, for each of the wires manufactured as described above, the presence or absence of cracks was measured at an angle of ±45° relative to the drawing direction inside the L section of the wire after drawing and extrusion according to the manufacturing conditions in Table 2, and for the wires that were additionally subjected to dehydrogenation treatment after drawing and extrusion, the tensile strength, uniform elongation, average grain size of the ferrite structure and yield strength ratio of the wire were measured and are shown in Table 2 below.

[0076] In Tables 1 and 2 below, the average grain size of the proeutectoid ferrite microstructure and the average grain size of the ferrite microstructure of the steel wire were evaluated using the ASTM E112 method and measured using a high-resolution SEM electron microscope during the evaluation.

[0077] Furthermore, the presence of internal cracks was examined by observing the steel wire under an optical microscope. In terms of tensile strength and yield strength, specimens were prepared according to the manufacturing conditions in Tables 1 and 2, based on ASTM E8 standards. Measurements were performed using a tensile testing machine, and the yield-to-tensile ratio was derived from these measurements. With uniform elongation, the elongation values ​​from yield strength to tensile strength were obtained from the tensile curves and are shown in Tables 1 and 2 below.

[0078] [Table 1]

[0079]

[0080] [Table 2]

[0081]

[0082] As can be seen from Tables 1 and 2, in Comparative Examples 1 to 5, which do not meet the component content or manufacturing conditions of this disclosure, Comparative Examples 1, 2, and 4 determined the difference in tensile strength between the wire and steel wire products. Furthermore, in Comparative Examples 3 to 4, where the average size of the proeutectoid ferrite structure and the grain size of the steel wire microstructure were coarsened, internal cracks appeared during wire drawing, and specifically, in Comparative Example 3, a difference in uniform elongation of 2.4% was determined as a result. On the other hand, in Experimental Examples 1 to 3, the average grain size of the proeutectoid ferrite before wire drawing was precisely ensured to be 4.4 μm, and therefore, despite the high drawing amount, no herringbone cracks were observed inside the steel wire product. It was determined that despite high tensile strength, a high uniform elongation of 4.0% or greater and an excellent yield strength ratio of 94.9% or greater could be ensured.

[0083] Furthermore, although exemplary embodiments of the present disclosure have been described above, the present disclosure is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and spirit of the appended claims without departing from the spirit and spirit of the appended claims.

Claims

1. A steel wire comprising, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and comprising at least one selected from 0.01% to 0.06% aluminum (Al), 0.005% to 0.03% niobium (Nb), 0.001% to 0.03% titanium (Ti), and 0.01% to 0.3% vanadium (V), with the balance being iron (Fe) and unavoidable impurities. The microstructure consists of ferrite and pearlite. The ferrite described therein has an average grain size of 3 μm or less. Where the uniform elongation is 3.5% or greater, and The yield strength ratio is 90% or greater.

2. The steel wire according to claim 1, The tensile strength ranges from 800 MPa to 1300 MPa.

3. The steel wire according to claim 1, The steel wire is free of cracks when it is at an angle of ±45° relative to the drawing direction inside the L-section (where the L-section refers to the section parallel to the rolling direction).

4. A wire comprising, by weight percentage (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and comprising at least one selected from 0.01% to 0.06% aluminum (Al), 0.005% to 0.03% niobium (Nb), 0.001% to 0.03% titanium (Ti), and 0.01% to 0.3% vanadium (V), with the balance being iron (Fe) and unavoidable impurities. The microstructure comprises proeutectoid ferrite, retained pearlite, and bainite and martensite comprising 10% or less by area fraction, and The average grain size of the proeutectoid ferrite structure is 5 μm or smaller.

5. The wire according to claim 4, The tensile strength ranges from 650 MPa to 850 MPa.

6. The wire according to claim 4, The wire obtained by drawing and extruding the wire at a processing rate of 30% to 70% has no cracks in its L-section at an angle of ±45° relative to the drawing direction (wherein the L-section refers to the section parallel to the rolling direction).

7. A method for manufacturing steel wire, the method comprising: Prepare a steel billet comprising, by weight percent (wt%), 0.1% to 0.5% carbon (C), 0.01% to 0.6% silicon (Si), 0.6% to 1.6% manganese (Mn), 0.01% to 1.4% chromium (Cr), more than 0% and less than 0.02% nitrogen (N), and at least one selected from 0.01% to 0.06% aluminum (Al), 0.005% to 0.03% niobium (Nb), 0.001% to 0.03% titanium (Ti), and 0.01% to 0.3% vanadium (V), with the balance being iron (Fe) and unavoidable impurities; The steel billet is heated to 950°C to 1200°C; The steel billet is hot-rolled at 700°C to 900°C to produce wire rod; The hot-rolled wire is cooled at a rate of 3°C / second to 15°C / second. as well as The cooled wire is drawn and extruded at a processing rate of 30% to 70%.

8. The method for manufacturing steel wire according to claim 7, It also includes dehydrogenation treatment of drawn and extruded wires at temperatures ranging from 200°C to 600°C for 30 to 60 minutes.

9. The method for manufacturing steel wire according to claim 7, The steel billet is subjected to fine hot rolling at a temperature of 700°C to 800°C to produce wire rod.

10. The method for manufacturing steel wire according to claim 7, The cooling is performed on the hot-rolled wire at a cooling rate of 4°C / second to 5°C / second.

11. The method for manufacturing steel wire according to claim 7, It also includes dehydrogenation treatment of drawn and extruded wires at temperatures of 300°C to 450°C for 30 to 60 minutes.

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