Steel wire for reinforcing concrete, steel fiber and method for manufacturing the same

Abstract

The present specification relates to a concrete reinforcing steel fiber wire, a steel fiber, and a manufacturing method thereof, and particularly, a reinforced concrete reinforcing steel fiber wire for a tunnel and a floor, a steel fiber, and a manufacturing method thereof are disclosed. According to one disclosed concrete reinforcing steel fiber wire embodiment, the wire comprises, by weight: C: 0.01% to 0.04%, Si: 0.07% to 0.3%, Mn: 1.0% to 2.0%, P: 0.1% to 0.3%, and the balance of Fe and other inevitable impurities, wherein, when the radius of the wire is r, the area fraction of ferrite is 90% or more within a region from the center of the cross section perpendicular to the longitudinal direction to 0.95*r, and the remaining portion comprises pearlite, wherein the average grain size of the ferrite can be 30 µm or less and the colony size of the pearlite can be 10 µm or less.

Description

Technical Field

[0001] This disclosure relates to steel fiber reinforced concrete wires, steel fibers, and methods for manufacturing the same, and more particularly to steel fiber reinforced concrete wires, steel fibers, and methods for manufacturing the same for reinforcing channels and base plates. Background Technology

[0002] Steel fibers are used to reinforce concrete to support the soil pressure inside during tunnel construction. Domestically, low-strength steel fibers are primarily used, with 0.1% by weight or less of low-carbon steel being incorporated. However, a high-strength steel fiber market has recently emerged in Europe and the Middle East, where bedrock is weak. This is due to the increasing use of tunnel boring machines (TBMs) for tunnel construction, replacing explosive methods. Furthermore, the high-strength steel fiber market is expected to continue its growth due to the use of high-strength steel fibers in slab-on-pile (SOP) construction in weak soil conditions.

[0003] Steel fibers are prepared by using spare slabs or wires in a dry-wet drawing process at a processing company to produce steel wires with a final diameter of 0.4 mm to 1.0 mm, cutting them into uniform workpieces with a length of 40 mm to 100 mm, and shaping them. For use as steel fibers, they require bending properties in the final forming process, but strength is the primary requirement.

[0004] Methods to improve the strength of carbon steel include reducing grain size according to the Hall-Petch equation and ensuring strength by applying processing allowances. In particular, wire drawing is the most economical and effective method for increasing strength. During wire drawing, if the steel's microstructure is pearlite, the strength increases exponentially during processing. This is because the cementite inside the pearlite undergoes plastic deformation, while carbon and dislocations combine due to cementite decomposition. When pearlite and ferrite are mixed, fracture problems may occur during wire drawing because pearlite is a relatively harder phase compared to ferrite.

[0005] Meanwhile, the lead-patenting (LP) heat treatment prior to wire drawing, which imparts ductility to the steel to prevent such fracture problems, is expensive and time-consuming, leading to increased manufacturing costs. Therefore, steel fiber manufacturers tend to skip LP heat treatment to reduce manufacturing costs. Since pearlite, which causes fracture, forms during wire drawing of high-carbon steel, it is unsuitable for composition systems that omit LP heat treatment; therefore, new composition systems are needed. Summary of the Invention

[0006] Technical issues

[0007] To address the aforementioned issues, this disclosure provides wire for concrete reinforcement with steel fibers, steel fibers, and methods for manufacturing them, which can omit lead quenching (LP) heat treatment to ensure high strength and save costs.

[0008] Technical solution

[0009] According to one embodiment of this disclosure, the steel fiber wire for concrete reinforcement comprises, by weight percentage (wt%): 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder Fe and other unavoidable impurities, and 90% or more of ferrite area fraction and the remainder pearlite in a region from the center of the cross-section perpendicular to the longitudinal direction to 0.95*r, where r is the radius of the wire, wherein the average ferrite grain size is 30 μm or less, and the pearlite cluster size is 10 μm or less.

[0010] The steel fiber reinforced wire for concrete can satisfy the following formula (1):

[0011] (1)TS WR -8(120[C]+14[Si]+20[Mn]+100[P])≥0

[0012] In equation (1), [C], [Si], [Mn], and [P] each refer to the weight percentage (wt%) of the element, and TS WR This refers to the tensile strength of the wire.

[0013] The average ferrite grain size of the steel fiber reinforced concrete wire can be 15 μm or smaller, and the pearlite cluster size can be 5 μm or smaller.

[0014] Concrete-reinforced steel fiber wires can form an oxide scale layer with a thickness of 10 μm to 15 μm on the surface, with a total oxide scale content of 0.4% to 0.6% by weight, and a residual oxide scale content of 0.05% by weight or less after mechanical stripping.

[0015] The tensile strength of steel fiber reinforced concrete wire can be 450 MPa or greater.

[0016] The cross-sectional shrinkage rate of steel fiber reinforced concrete wire can be 80% or greater.

[0017] According to one embodiment of this disclosure, a method for manufacturing wire rod for concrete reinforcement steel fibers includes: heating a steel billet, the steel billet comprising, by weight %: 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder being Fe and other unavoidable impurities; preparing the wire rod by hot rolling the steel billet at 1000°C to 1150°C or by finish rolling the steel billet at A3-70°C to A3°C; winding the prepared wire rod; and cooling the wound wire rod to A1°C at 1°C / second to 5°C / second, and then cooling it from A1°C to 200°C at 15°C / second to 20°C / second.

[0018] The method can satisfy the following equation (2):

[0019] (2) TE-TL / H≤100℃

[0020] In equation (2), TE is the surface temperature of the wire before entering the finishing mill, and TL / H is the temperature of the winding machine.

[0021] In the method, the wire prepared by hot rolling at 1000°C to 1150°C has an average ferrite grain size of 30 μm or less and a pearlite cluster size of 10 μm or less.

[0022] In the method, the wire prepared by precision rolling at A3-70°C to A3°C has an average ferrite grain size of 15 μm or less and a pearlite cluster size of 5 μm or less.

[0023] According to one embodiment of this disclosure, the concrete reinforcing steel fiber contains, by weight %: 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder Fe and other unavoidable impurities, and satisfies the following formula (3).

[0024] (3)TS F -TS WR -[15 / (1.5*FGS 0.1 )]*e 4.61 ≥0

[0025] In equation (3), TS F This refers to the tensile strength of steel fibers, TS WR This refers to the tensile strength of the wire, and FGS refers to the average ferrite grain size.

[0026] The tensile strength of concrete-reinforced steel fibers can be 1600 MPa or greater.

[0027] According to one embodiment of this disclosure, a method for manufacturing concrete-reinforcing steel fibers includes: manufacturing wire rods comprising, by weight percent: 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder being Fe and other unavoidable impurities, and 90% or more of ferrite area fraction and the remainder being pearlite in a region from the center of a section perpendicular to the longitudinal direction to 0.95*r, where r is the radius of the wire rod, by dry drawing and wet drawing with a total shrinkage rate of 99% or more, the wire rod having an average ferrite grain size of 30 μm or less and a pearlite cluster size of 10 μm or less, wherein the breakage rate during drawing may be 0.5 times / ton.

[0028] Beneficial effects

[0029] This disclosure provides high-strength concrete-reinforced steel fiber wire, steel fibers, and methods for manufacturing the same for reinforcing channels and base plates. According to this disclosure, high strength is ensured by applying phosphorus (P) to low-carbon steel, and excellent wire drawing processability is ensured by precision rolling in a two-phase (ferrite and pearlite) range from A3-70°C to A3°C. Therefore, dry and wet drawing can be performed without intermediate lead hardening (LP) heat treatment, and the drawing process can have a significantly reduced breakage rate. Detailed Implementation

[0030] According to one embodiment of this disclosure, the steel fiber wire for concrete reinforcement comprises, by weight percentage (wt%): 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder Fe and other unavoidable impurities, and 90% or more of ferrite area fraction and the remainder pearlite in a region from the center of the cross-section perpendicular to the longitudinal direction to 0.95*r, where r is the radius of the wire, wherein the average ferrite grain size may be 30 μm or less, and the pearlite cluster size may be 10 μm or less.

[0031] Invention Embodiments

[0032] Embodiments of this disclosure will now be described. However, embodiments of this disclosure can be modified in many different forms and should not be construed as limited to the embodiments set forth herein. Embodiments of this disclosure are provided to fully convey the concepts provided herein to those skilled in the art.

[0033] The terminology used herein is for illustrative purposes only. For example, singular expressions include plural expressions unless the context clearly indicates otherwise. It will also be understood that, when used in this specification, the terms “comprising” and / or “including” specify the presence of the said feature, integer, step, operation, element, and / or component, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0034] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Furthermore, unless explicitly defined otherwise, particular terms should not be construed as having an overly ideal or formal meaning. It should be understood that, unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0035] Throughout the instruction manual, words such as “about” and “basically” are used to indicate that the numerical value used with the word falls within a range around that value, in order to prevent unethical infringers from improperly using descriptions that mention absolute values.

[0036] Throughout this specification, the terms “(crystal) grain size” or “cluster size” may refer to the equivalent circle diameter (ECD) of a grain or cluster.

[0037] In one embodiment of this disclosure, the concrete-reinforced steel fiber wire may contain, by weight percentage (wt%): 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder Fe and other unavoidable impurities.

[0038] The reasons for limiting the composition of the steel fiber reinforcing wire for concrete will now be described in detail. The reasons for limiting the alloy composition of the steel fiber for concrete according to this disclosure are the same as those for limiting the alloy composition of the wire, and therefore, for convenience, the description is omitted.

[0039] The content of C is from 0.01% to 0.04% by weight.

[0040] Carbon (C) is an element that constitutes cementite and effectively enhances strength during the formation of pearlite. To ensure the target strength, the C content is added in this disclosure at 0.01 wt% or more. However, if the C content is excessive, pearlite will form between ferrite particles, and the increased pearlite fraction may lead to fracture during wire drawing, and intergranular corrosion resistance will deteriorate as the grain boundaries between the hard and soft phases become more defined. With this in mind, the upper limit of the C content in this disclosure can be limited to 0.04 wt%.

[0041] The Si content is from 0.07% to 0.3% by weight.

[0042] Si is a ferrite hardening element that increases tensile strength by about 15 MPa to 20 MPa per 0.1 wt% addition and is used as a deoxidizer to remove oxygen from molten steel. With this in mind, 0.07 wt% or more of Si is added in this disclosure. However, if the Si content is too high, a large amount of Fe2SiO4 with excellent adhesion to the substrate may form, potentially leading to poor oxide scale peeling; therefore, the upper limit of the Si content is limited to 0.3 wt% in this disclosure.

[0043] The Mn content is 1.0% to 2.0% by weight.

[0044] To improve the strength of the wire, Mn is added at 1.0 wt% or more. However, if the Mn content is too high, processing breakage may occur due to segregation; therefore, the upper limit of the Mn content is limited to 2.0 wt%.

[0045] The content of P is 0.1% to 0.3% by weight.

[0046] P is the most effective element for improving strength after C and N. To ensure the target strength, P is added at 0.1% by weight or more. However, if the P content is too high, it may lead to fracture due to surface crack formation during continuous casting; therefore, the upper limit of the P content is limited to 0.3% by weight in this disclosure.

[0047] In this disclosure, the remaining component is iron (Fe). During normal manufacturing processes, unintended impurities may inevitably be introduced from raw materials or the surrounding environment, which cannot be excluded. These impurities are known to those skilled in the art in ordinary manufacturing processes, and therefore not all impurities are specifically mentioned in this specification.

[0048] In one embodiment of this disclosure, the steel fiber reinforced concrete wire can satisfy the aforementioned alloy composition and the following formula (1):

[0049] (1)TS WR -8(120[C]+14[Si]+20[Mn]+100[P])≥0

[0050] In equation (1), [C], [Si], [Mn], and [P] each refer to the weight percentage (wt%) of the element, and TS WR This refers to the tensile strength of the wire.

[0051] Equation (1) illustrates the correlation between the tensile strength of the wire and the content of the alloy components, which affects the strength of the final steel fiber product. This correlation is obtained by considering solid solution strengthening and grain size-based strengthening by adding alloy components. In this disclosure, from the perspective of strengthening the strength of steel fibers, it is desirable to satisfy Equation (1).

[0052] In one embodiment of this disclosure, the concrete-reinforced steel fiber wire may contain 90% or more of ferrite area fraction and the remainder pearlite in a region from the center of the cross-section perpendicular to the longitudinal direction to 0.95*r, where r is the radius of the wire. In this disclosure, the target strength is ensured by limiting the pearlite microstructure formed at grain boundaries by 0.04 wt% or less of low-carbon steel with a low C content, which could lead to fracture during wire drawing, so that the main microstructure of the steel is formed by ferrite as described above, followed by the use of solid solution strengthening elements. If the ferrite area fraction is less than 90% or the pearlite area fraction exceeds 10%, fracture may occur during wire drawing.

[0053] In one embodiment of this disclosure, the average ferrite grain size may be 30 μm or less, and the pearlite cluster size may be 10 μm or less. A smaller average ferrite grain size is more advantageous for strength, and a smaller pearlite cluster size is more advantageous for wire drawing properties, because pearlite clusters may act as crack initiation sites during wire drawing. Therefore, in one embodiment of this disclosure, the average ferrite grain size may be 15 μm or less, and the pearlite cluster size may be 5 μm or less. According to one embodiment of this disclosure, grain refinement can be achieved through finishing rolling performed in a two-phase section.

[0054] The concrete-reinforced wire according to this disclosure has excellent oxide scale removal characteristics. For example, the oxide scale layer formed on the surface can have a thickness of 10 μm to 15 μm, the total oxide scale amount can be 0.4% to 0.6% by weight, and the residual oxide scale amount after mechanical peeling can be 0.05% by weight or less.

[0055] The tensile strength of steel fiber reinforced concrete wire can be 450 MPa or greater.

[0056] The cross-sectional shrinkage rate of steel fiber reinforced concrete wire can be 80% or greater.

[0057] The method for manufacturing concrete-reinforcing steel fiber filaments according to this disclosure will now be described in detail. As described above, the concrete-reinforcing steel fiber filaments can be manufactured by various methods, and it should be noted that there are no specific limitations on the manufacturing method.

[0058] In one embodiment of this disclosure, a method for manufacturing wire rod for concrete reinforcement steel fibers may include heating a steel billet comprising the aforementioned alloy composition; preparing the wire rod by hot rolling the steel billet at 1000°C to 1150°C or by fine rolling the steel billet at A3-70°C to A3°C; winding the prepared wire rod; and cooling the wound wire rod.

[0059] The steel billet can be heated at 1000℃ to 1200℃.

[0060] Heated steel billets can be hot-rolled at 1000°C to 1150°C, or finish-rolled at A3-70°C to A3°C to produce wire rods. Finish rolling in the two-phase (ferrite and pearlite) range at A3-70°C to A3°C refines the average ferrite grain size and pearlite cluster size, thereby further increasing strength and reducing the number of voids at grain boundaries, thus preventing processing fracture. Generally, as the carbon content increases, pearlite forms better, and the pearlite cluster size becomes coarser, leading to fracture during wire drawing. Therefore, even at relatively high carbon contents ranging from 0.02 wt% to 0.04 wt%, finish rolling can prevent fracture during wire drawing by refining the pearlite cluster size.

[0061] In one embodiment, the average ferrite grain size of the wire prepared by hot rolling at 1000°C to 1150°C may be 30 μm or less, and the pearlite cluster size may be 10 μm or less.

[0062] In another embodiment, the average ferrite grain size of the wire prepared by precision rolling at A3-70°C to A3°C can be 15 μm or less, and the pearlite cluster size can be 5 μm or less.

[0063] The prepared wire is wound and cooled to A1°C at a rate of 1°C / second to 5°C / second, and then cooled from A1°C to 200°C at a rate of 15°C / second to 20°C / second. In the oxide scale of the wire, FeO (argumentite) is relatively easier to remove than Fe3O4 (magnetite). Since FeO grows rapidly at A1°C or higher, a sufficiently thick FeO layer can be formed by slowly cooling it down to A1°C at a rate of 1°C / second to 5°C / second. To suppress the transformation of FeO to Fe3O4 from A1°C to 200°C, the FeO fraction in the oxide scale layer can be maintained by rapidly cooling it down to room temperature at a rate of 15°C / second to 20°C / second. The concrete-reinforced steel fiber wire manufactured as described above has improved oxide scale peeling characteristics. A1°C varies depending on the alloy composition and is approximately 720°C in this disclosure.

[0064] A method for manufacturing concrete-reinforced steel fiber wire according to one embodiment of this disclosure can satisfy the following formula (2):

[0065] (2) TE-TL / H≤100℃

[0066] In equation (2), TE is the surface temperature of the wire before entering the finishing mill, and TL / H is the temperature of the winding mill. In equation (2), by reducing the difference between the temperature of the winding mill and the surface temperature of the wire before entering the finishing mill, the material deviation of the product can be reduced and the formation of low-temperature transformation structure can be suppressed. Regarding methods to reduce the temperature difference, water spraying can be reduced or a short period of cooling can be performed after hot rolling.

[0067] Wire rod is manufactured into steel fibers through dry and wet drawing, cutting, and forming. Wire rod can be manufactured by including dry and wet drawing steps with a total shrinkage rate of 99% or greater, and the breakage rate during drawing can be 0.5 times / ton or less. Furthermore, the LP heat treatment used to impart ductility to the steel between dry and wet drawing can be omitted.

[0068] In one embodiment of this disclosure, the concrete reinforcing steel fiber may have the aforementioned alloy composition and satisfy the following formula (3):

[0069] (3)TS F -TS WR -[15 / (1.5*FGS 0.1 )]*e 4.61 ≥0

[0070] In equation (3), TS F This refers to the tensile strength of steel fibers, TS WR This refers to the tensile strength of the wire, and FGS refers to the average ferrite grain size. The tensile strength of steel wire and steel fiber is mainly determined by the strength of the wire and the grain size of the steel after the wire is drawn, and in particular by the increase in strength through the applied processing amount rather than by the increase in strength through solid solution strengthening. According to this disclosure, micron-sized ferrite is rotated in the longitudinal direction and then becomes a long fibrous structure of tens of nanometers, and thus the strength is significantly improved. Equation (3) derives the correlation between the tensile strength of steel fiber, the tensile strength of wire, and the average ferrite grain size by reflecting the aforementioned factors. In this disclosure, it is desirable to satisfy Equation (3) from the perspective of strengthening the strength of steel fiber.

[0071] In one embodiment of this disclosure, the tensile strength of the concrete-reinforced steel fibers can be 1600 MPa or greater.

[0072] The present disclosure will now be described in more detail with reference to the following embodiments. However, the following embodiments are illustrative examples to describe the present disclosure in more detail and should not be construed as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims and their equivalents.

[0073] {Implementation Plan}

[0074] Steel with the alloy composition shown in Table 1 below is manufactured in an electric furnace and then cast to produce 160×160mm steel. 2 Billet. The billet was heated in a furnace at 1090°C for 90 minutes and then finished rolled at the finishing rolling temperatures in Table 1 to produce wire rod. The produced wire rod was wound at 910°C and cooled from the winding temperature to A1°C at the cooling rate in Table 1, and then cooled from A1°C to 200°C at 18°C / second.

[0075] [Table 1]

[0076]

[0077] The average ferrite grain size (FGS), pearlite cluster size, wire tensile strength, section reduction rate, residual oxide scale, total oxide scale, and the left side of equation (1) of the produced wire are shown in Table 2 below.

[0078] [Table 2]

[0079]

[0080] The oxide scale was removed from the cooled wire using a mechanical stripping method, followed by shrinkage at a total shrinkage rate of 99% through dry drawing (87% shrinkage) and wet drawing (92% shrinkage) without intermediate LP heat treatment. The wire was then cut and formed into steel fibers. Table 3 shows the tensile strength, surface crack initiation, and breakage rate during wire drawing of the manufactured steel fibers. In Table 3, "-" indicates no measurement results due to breakage.

[0081] [Table 3]

[0082]

[0083] Referring to Tables 1 to 3, the examples and comparative examples are compared for evaluation. The role of C: Comparative Examples 1 and 2

[0084] In the embodiments, the C content is in the range of 0.01% to 0.04% by weight to improve wire strength, and the breakage rate during wire drawing is 0.5 times / ton or less, thus the wire drawing processability is excellent. On the other hand, Comparative Example 1 obtained a strength of 1430 MPa but could not guarantee the target strength, and in Comparative Example 2, the C content was too high, resulting in breakage.

[0085] The role of Si: Comparative Example 3

[0086] In Comparative Example 3, the Si content exceeded 0.3% by weight and had a residual oxide scale content of 0.06% by weight, which was worse than other embodiments. Furthermore, in Comparative Example 3, the wire breakage rate during wire drawing was 8 times / ton, resulting in poor wire drawing processability.

[0087] The role of Mn: Comparative Example 4

[0088] In Comparative Example 4, the Mn content exceeded 2.0% by weight, resulting in segregation and low-temperature structure, which in turn led to breakage during wire drawing.

[0089] The role of P: Comparative Example 5

[0090] In Comparative Example 5, the excessive P content led to numerous breakages during wire drawing.

[0091] The role of finishing rolling temperature: Comparative Example 6

[0092] In Comparative Example 6, a relatively large amount of C was contained, and the finishing rolling was carried out outside the two-phase range of A3-70°C to A3°C. Therefore, pearlite clusters were coarsely formed and broke off during wire drawing.

[0093] The effect of cooling rate from winding temperature to A1 temperature: Comparative Example 7

[0094] In Comparative Example 7, rapid cooling from the winding temperature to the A1 temperature resulted in a relatively small FeO fraction, which was easily removed, thus leading to poor oxide scale removal characteristics. Consequently, a large amount of residual oxide scale was formed compared to the examples.

[0095] The function of equation (1): Compare Example 1

[0096] Comparative Example 1 does not satisfy Equation (1) and cannot ensure the target strength.

[0097] Schemes of the present disclosure have been described to date, but the present disclosure is not limited thereto, and it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the scope of the appended claims.

[0098] [Industrial Applicability]

[0099] According to one embodiment of this disclosure, concrete-reinforced steel fiber wire, steel fiber, and a method for manufacturing the same can be provided to omit lead quenching (LP) heat treatment to ensure high strength while reducing costs.

Claims

1. A steel fiber reinforced concrete wire, comprising, by weight percentage (wt%): 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder Fe and other unavoidable impurities, and The wire contains 90% or more of the ferrite area fraction and the remaining pearlite within a region extending from the center of the cross-section perpendicular to the longitudinal direction to 0.95*r, where r is the radius of the wire. The ferrite described herein has an average grain size of 30 μm or less, and The pearlite cluster size is 10 μm or smaller.

2. The wire according to claim 1 satisfies the following formula (1): In equation (1), [C], [Si], [Mn] and [P] each refer to the weight percentage of the element, and TS WR This refers to the tensile strength of the wire.

3. The wire according to claim 1, wherein the average grain size of the ferrite is 15 μm or less, and The pearlite cluster size is 5 μm or smaller.

4. The wire according to claim 1, wherein the thickness of the oxide layer formed on the surface of the wire is 10 μm to 15 μm, the total oxide layer content is 0.4% to 0.6% by weight, and the residual oxide layer content after mechanical stripping is 0.05% by weight or less.

5. The wire according to claim 1, wherein the tensile strength of the wire is 450 MPa or greater.

6. The wire according to claim 1, wherein the cross-sectional shrinkage rate of the wire is 80% or greater.

7. A method for manufacturing steel fiber reinforced concrete wire, the method comprising: Heated steel billet, the steel billet comprising, by weight percentage (wt%): 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder Fe and other unavoidable impurities; as well as Wire rods are prepared by hot rolling the steel billet at 1000°C to 1150°C or by finish rolling the steel billet at A3-70°C to A3. The prepared wire is wound up; as well as The wound wire is cooled to A1 at a rate of 1°C / second to 5°C / second, and then cooled from A1 to 200°C at a rate of 15°C / second to 20°C / second.

8. The method according to claim 7, satisfying the following formula (2): In equation (2), TE is the surface temperature of the wire before entering the finishing mill, and TL / H is the temperature of the winding machine.

9. The method of claim 7, wherein the wire prepared by hot rolling at 1000°C to 1150°C has an average grain size of ferrite of 30 μm or less and a cluster size of pearlite of 10 μm or less.

10. The method of claim 7, wherein the wire prepared by precision rolling at A3-70°C to A3 has an average grain size of ferrite of 15 μm or less and a cluster size of pearlite of 5 μm or less.

11. A concrete reinforcing steel fiber, comprising, by weight percentage (wt%): 0.01% to 0.04% C, 0.07% to 0.3% Si, 1.0% to 2.0% Mn, 0.1% to 0.3% P, the remainder Fe and other unavoidable impurities, The concrete-reinforced steel fibers satisfy the following formula (3): In equation (3), TS F This refers to the tensile strength of steel fibers, TS WR This refers to the tensile strength of the wire, and FGS refers to the average grain size of ferrite.

12. The concrete reinforcing steel fiber according to claim 11, wherein the tensile strength is 1600 MPa or greater.

13. A method for manufacturing steel fibers to reinforce concrete, characterized in that, The steel fibers are manufactured by dry and wet drawing of the wire according to claim 1 with a total shrinkage rate of 99% or greater, wherein the breakage rate during drawing is 0.5 times / ton or less.

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