Heat treatment-free concrete reinforcing steel fiber wire rod, steel fiber, and their manufacturing method

Abstract

The present invention provides wire rods and steel fibers for concrete reinforcement that have a tensile strength of 1700 MPa or more and do not break when repeatedly subjected to 90-degree bending 10 times or more, using dry wire drawing and wet wire drawing processes without LP heat treatment, and steel fibers and methods for manufacturing these. [Solution] The wire rod for concrete-reinforcing steel fibers according to one embodiment of the present invention is composed, by weight, of C: 0.005-0.035%, Si: 0.07-0.3%, Mn: 0.07-0.2%, Cr: 1.0-2.2%, P: 0.05% or less, S: 0.05% or less, with the remainder being Fe and other unavoidable impurities, and satisfies the following relational expression 1. [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0 (Here, [C], [Mn], and [Cr] each represent weight percent.)

Description

[Technical Field]

[0001] The present invention relates to wire rods for concrete-reinforcing steel fibers used as concrete reinforcing materials for tunnels, floors, etc., steel fibers, and methods for producing the same. [Background technology]

[0002] Steel fibers vary in diameter and length depending on their intended use, such as tunnels or flooring. Since tunnels are used as shorts, they are thin in diameter and short in length, while flooring materials are relatively thick in diameter and long in length. Steel fibers are made by wiredrawing (dry or wet) using wire rods with diameters of 5.0-7.0 mm. Because of their thin diameter, they require a structure that can withstand high amounts of drawing. Ultra-low carbon steels with a maximum carbon content of 0.03% or 0.035% are used. This is because ferrite has the best wiredrawability. Pearlite can form at grain boundaries, but increasing the fraction creates defects in the hard pearlite, leading to wire breakage.

[0003] While low-strength steel fibers (1000 MPa or less) have traditionally been used, contractors sometimes request high-strength steel fibers (1500 MPa or higher) to reduce construction time and manufacturing costs. Various approaches have been attempted to increase the strength of steel fibers, with one approach being to increase strength by increasing the carbon content. Unlike other elements, carbon is a low-valent element that effectively increases strength during wiredrawing. This is because carbon forms hard cementite, which makes up pearlite. A 0.1% increase in carbon content can increase tensile strength by approximately 100 MPa. However, as mentioned above, the formation of pearlite can cause wire breakage during drawing. To address this issue, isothermal heat treatment (lead patenting, hereafter referred to as LP) is being introduced, which restores ductility and refines grain size during wiredrawing. However, the problem is that isothermal heat treatment is made using lead, which is environmentally unsuitable, and the additional heat treatment process increases manufacturing costs.

[0004] In addition, due to strengthening global environmental standards, scale is removed using mechanical descaling instead of harmful pickling. However, it is important to minimize silicon because it forms fayalite (Fe2SiO4) at the interface between the scale and the base material, which reduces descaling properties. Summary of the Invention [Problem to be solved by the invention]

[0005] In order to solve the above-mentioned problems, the present invention aims to provide a wire rod for concrete-reinforcing steel fiber, a steel fiber, and a method for manufacturing the same, which have a tensile strength of 1700 MPa or more and do not break when repeatedly subjected to 90-degree bending 10 times or more using dry wire drawing and wet wire drawing without LP heat treatment, by controlling Relational Formula 1 and microstructure through alloy composition and manufacturing method.

[0006] The problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0007] The wire rod for concrete-reinforcing steel fibers according to one embodiment of the present invention contains, by weight, C: 0.005 to 0.035%, Si: 0.07 to 0.3%, Mn: 0.07 to 0.2%, Cr: 1.0 to 2.2%, P: 0.05% or less, S: 0.05% or less, with the remainder being Fe and other unavoidable impurities, and satisfies the following relational expression 1:

[0008] [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0

[0009] (Here, [C], [Mn], and [Cr] each represent weight percent.)

[0010] In addition, the microstructure of the wire rod for steel fiber reinforcement of concrete according to one embodiment of the present invention may include quasi polygonal ferrite in an area fraction of more than 98% to less than 100% and cementite in an area fraction of more than 0% to less than 2%.

[0011] In addition, the wire for concrete reinforcing steel fiber according to an embodiment of the present invention may have an average crystal grain size of the quasi-polygonal ferrite in a ¼D range based on the cross section, which is greater than 0 and less than 35 μm (where D represents the diameter of the wire).

[0012] The wire rod for concrete-reinforcing steel fibers according to one embodiment of the present invention may have a tensile strength of 850 MPa or more.

[0013] A method for manufacturing a wire rod for use as a steel fiber for concrete reinforcement according to one embodiment of the present invention includes the steps of: maintaining a billet, which is composed of, by weight, 0.005-0.035% C, 0.07-0.3% Si, 0.07-0.2% Mn, 1.0-2.2% Cr, 0.05% or less P, 0.05% or less S, and the remainder being Fe and other unavoidable impurities, at a temperature in the range of 1,000-1,250°C for 90-120 minutes and rolling the billet to manufacture a wire rod; coiling the manufactured wire rod at a temperature in the range of 880-950°C; and cooling the wire rod after coiling, which includes a first cooling step of cooling the wire rod to 800°C at a rate of 1°C / s or less and a second cooling step of cooling the wire rod to 300°C at a rate of 20°C / s or more.

[0014] In addition, in the method for manufacturing a wire rod for use as a steel fiber for concrete reinforcement according to one embodiment of the present invention, the wire rod satisfies the following relational expression 1.

[0015] [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0

[0016] (Here, [C], [Mn], and [Cr] each represent weight percent.)

[0017] A concrete-reinforcing steel fiber according to one embodiment of the present invention is composed of, by weight, C: 0.005-0.035%, Si: 0.07-0.3%, Mn: 0.07-0.2%, Cr: 1.0-2.2%, P: 0.05% or less, S: 0.05% or less, with the remainder being Fe and other unavoidable impurities, and satisfies the following relational expression 1, and can have a tensile strength of 1700 MPa or more.

[0018] [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0

[0019] (Here, [C], [Mn], and [Cr] each represent weight percent.)

[0020] Furthermore, the concrete-reinforcing steel fiber according to an embodiment of the present invention can be subjected to 90-degree bending repeatedly 10 times or more without breaking.

[0021] A method for manufacturing concrete-reinforcing steel fibers according to one embodiment of the present invention includes dry wiredrawing and wet wiredrawing a wire rod consisting of, by weight %, C: 0.005-0.03%, Si: 0.07-0.3%, Mn: 0.07-0.2%, Cr: 1.0-2.0%, P: 0.05% or less, S: 0.05% or less, and the remainder being Fe and other unavoidable impurities, and satisfying the following Relational Expression 1, wherein LP heat treatment after the dry wiredrawing and before the wet wiredrawing can be omitted, and the tensile strength can be 1700 MPa or more.

[0022] [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0

[0023] (Here, [C], [Mn], and [Cr] each represent weight percent.) [Effects of the Invention]

[0024] According to one embodiment of the present invention, a wire rod for concrete-reinforcing steel fiber, a steel fiber, and a manufacturing method thereof increase initial material strength and work hardening rate by adding a high content of Cr (1.0% or more), which has an excellent solid solution strengthening effect. Meanwhile, the Si and Mn contents, which have poor solid solution strengthening effect or deteriorate scale peeling properties, are minimized, thereby reducing manufacturing costs. This eliminates the need for LP heat treatment and allows processing by wire drawing alone, thereby reducing manufacturing costs and shortening construction time by eliminating the need for rebar in concrete. Furthermore, because scale is removed using mechanical peeling instead of pickling, the product's environmentally friendly image is strengthened, making it competitive in the global market.

[0025] Furthermore, the wire rod for concrete-reinforcing steel fiber, steel fiber, and manufacturing method thereof according to one embodiment of the present invention can omit LP heat treatment during processing, and can achieve a tensile strength of 1700 MPa or more through dry and wet wire drawing, and can withstand 90-degree bending 10 or more times without breakage. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a photograph showing the microstructure of Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The following describes preferred embodiments of the present invention. However, the embodiments of the present invention can be modified into various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

[0028] The terms used in this application are merely used to describe specific examples. Thus, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Note that the terms "comprise" or "include" used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not intended to preclude the presence of other features, steps, functions, components, or combinations thereof.

[0029] On the other hand, unless otherwise defined, all terms used herein should be considered to have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Therefore, unless clearly defined herein, specific terms should not be interpreted in an overly ideal or formal sense. For example, singular expressions in this specification include plural expressions unless there is a clear exception in the context.

[0030] Furthermore, in this specification, the terms "about," "substantially," and the like are used to mean from or near a numerical value when manufacturing and material tolerances inherent in the stated meaning are given, and are used to prevent unscrupulous infringers from unfairly taking advantage of disclosures in which precise or absolute numerical values ​​are stated to aid in the understanding of the present invention.

[0031] The wire rod for concrete-reinforcing steel fibers according to one embodiment of the present invention may consist of, in weight percent, C: 0.005 to 0.035%, Si: 0.07 to 0.3%, Mn: 0.07 to 0.2%, Cr: 1.0 to 2.2%, P: 0.05% or less, S: 0.05% or less, and the remainder being Fe and other unavoidable impurities.

[0032] The reasons for limiting the range of each alloying element are as follows.

[0033] The C content may be 0.005 to 0.035% by weight.

[0034] C is an element that significantly improves strength when pearlite or cementite is formed, but an increase in C content can lead to the problem of the formation of pearlite, which can cause wire breakage during wet drawing. Therefore, if the C content is less than 0.005%, it is difficult to achieve the target strength, and if it exceeds 0.035%, wire breakage occurs during wire drawing due to the formation of grain boundaries of cementite with an area fraction of 2% or more, so it is preferable to control it to below that level.

[0035] The Si content may be 0.07 to 0.3 wt %.

[0036] Si is a ferrite hardening element and has the advantage of improving strength, but it is disadvantageous in terms of scale removal because it forms Fe2SiO4, which has excellent bonding strength with the base material. Therefore, if the Si content exceeds 0.3%, scale removal becomes poor, and it is preferable to control the Si content to 0.07% or more, as this is the limit for preventing the inflow of extraneous slag.

[0037] The Mn content may be 0.07 to 0.2 wt %.

[0038] Mn is an element that strengthens solid solution and improves hardenability, and can combine with S present in steel to form MnS. Therefore, Mn may be contained in an amount of 0.07% or more. However, since the effect of increasing strength is small and the cost may increase, the maximum content is preferably 0.2%.

[0039] The Cr content may be 1.0 to 2.2 wt %.

[0040] In the present invention, Cr is a major solid-solution strengthening element present in ferrite that increases material strength. Adding 0.1% Cr can increase tensile strength by approximately 40 MPa. Furthermore, adding Cr can increase the work hardening rate during wire drawing by more than 300, thereby increasing the strength of the final product. If the Cr content is less than 1.0%, it is difficult to achieve the target strength. If it exceeds 2.2%, when the bloom is charged into a high-temperature heating furnace at a low temperature after continuous casting, cracks may occur due to the difference in stress between the surface and the center caused by the formation of martensite in the center. Therefore, it is preferable to control the Cr content below this level.

[0041] The P and S contents may be 0.05% by weight or less.

[0042] P and S are harmful elements, and if they exceed 0.05%, they will cause breakage during wire drawing due to center segregation, so it is preferable to control them to below that level.

[0043] The remaining component of the present invention is iron (Fe). However, in a normal manufacturing process, unintentional impurities may inevitably be mixed in from raw materials or the surrounding environment, and this cannot be excluded. Since these impurities are known to anyone skilled in normal manufacturing processes, not all of the contents of these impurities will be specifically mentioned in this specification.

[0044] Hereinafter, a wire rod for concrete-reinforcing steel fibers according to one embodiment of the present invention having the above-mentioned alloy composition will be described.

[0045] The wire rod for steel fibers for concrete reinforcement according to one embodiment of the present invention can satisfy Relational Formula 1.

[0046] [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0

[0047] (Here, [C], [Mn], and [Cr] each represent weight percent.)

[0048] In the above relational expression 1, C, Mn, and Cr are elements related to the strength of the material. In particular, the addition of a high Cr content of 1.0% or more, which has an excellent effect on solid solution strengthening, can increase the initial material strength and work hardening rate. However, if such a Cr content is added excessively, internal cracks may occur when the billet is cooled and charged into the heating furnace, causing breakage in the heating furnace, or cobbling may occur during rolling. Therefore, the above relational expression 1 is a relational expression related to the appropriate C, Mn, and Cr contents. If the above relational expression 1 is greater than 0, cracks may occur in the billet, causing cobbling during wire rod rolling, so it is preferable to control the contents below that value.

[0049] Furthermore, by controlling the above Relational Formula 1 to have an appropriate Cr content, internal cracks and cobble formation can be prevented and productivity can be increased, thereby achieving reduction in wire manufacturing costs.

[0050] The microstructure of the wire rod for steel fiber reinforcement of concrete according to one embodiment of the present invention may include, in terms of area fraction, more than 98% to less than 100% quasi polygonal ferrite and more than 0% to less than 2% cementite.

[0051] By forming the main structure of steel from quasi-polygonal ferrite, a low-temperature transformation structure due to a large Cr content, it is possible to prevent wire breakage even if LP heat treatment is omitted, and since strength reduction can be suppressed without the inhibition of elongation compared to when the main structure is formed from polygonal ferrite, higher tensile strength can be obtained. In addition, the addition of Cr results in the formation of carbides such as CrC, which results in less cementite formation compared to when Cr is not added, reducing the probability of wire breakage during drawing.

[0052] Furthermore, if the microstructure of the wire contains cementite at an area fraction of 2% or more, wire breakage may occur during wire drawing due to the formation of cementite grain boundaries, so it is preferable to control the area fraction of cementite to more than 0 and less than 2%.

[0053] In addition, in the wire for concrete-reinforcing steel fiber according to an embodiment of the present invention, the average crystal grain size of the quasi-polygonal ferrite may be greater than 0 and less than or equal to 35 μm within a ¼D range based on the cross section, where D means the diameter of the wire.

[0054] When the average crystal grain size of the quasi-polygonal ferrite is more than 0 to 35 μm, wire breakage during wire drawing can be prevented, and the 90-degree bending property of the final steel fiber can be significantly improved to 10 times or more.

[0055] The wire rod for concrete-reinforcing steel fibers according to one embodiment of the present invention may have a tensile strength of 850 MPa or more.

[0056] A method for producing a wire rod for use as a steel fiber for concrete reinforcement according to one embodiment of the present invention having the above-mentioned alloy composition will be described below.

[0057] The wire rod for steel fiber reinforcement of concrete according to one embodiment of the present invention can be manufactured by preparing a billet having the above-described alloy composition, and then subjecting the billet to reheating, wire rolling, winding, and cooling processes.

[0058] According to one embodiment of the present invention, a method for manufacturing a wire rod for use as a steel fiber for concrete reinforcement includes the steps of: maintaining a billet, which is composed of, by weight, 0.005-0.035% C, 0.07-0.3% Si, 0.07-0.2% Mn, 1.0-2.2% Cr, 0.05% or less P, 0.05% or less S, and the remainder being Fe and other unavoidable impurities, at a temperature in the range of 1,000-1,250°C for 90-120 minutes and rolling the billet to manufacture a wire rod; coiling the manufactured wire rod at a temperature in the range of 880-950°C; and cooling the wire rod after coiling, which includes a first cooling step of cooling the wire rod to 800°C at a rate of 1°C / s or less and a second cooling step of cooling the wire rod to 300°C at a rate of 20°C / s or more.

[0059] After producing a billet having the above-described alloy composition, it is maintained at a furnace temperature of 1,000 to 1,250°C for 90 to 120 minutes for normalizing and austenite formation, and then rolled. Maintaining the temperature below 1,000°C results in a problem of a long charging time, while maintaining the temperature above 1,250°C places a burden on the furnace. Therefore, it is preferable to control the temperature to 1,000 to 1,250°C. Furthermore, maintaining the temperature for less than 90 minutes makes it difficult to form central austenite, and maintaining the temperature for more than 120 minutes can cause coarse grain growth. Therefore, maintaining the temperature for 90 to 120 minutes is preferable.

[0060] The heated billet is rolled under normal rolling conditions, i.e., hot rolling consisting of rough rolling, intermediate rough rolling / finish rolling, and finish rolling in sequence is performed on the heated billet to produce a wire rod.

[0061] For mechanical peeling, a scale of an appropriate thickness (8 to 20 μm) must be formed. For this purpose, the coiling temperature is controlled to 880 to 950°C using a water-cooled table. Below 880°C, the minimum thickness of 8 μm is not met, and above 950°C, although the 20 μm thickness is met, poor coiling shape (requiring capital investment) occurs, so it is preferable to control the temperature below that level.

[0062] In the first cooling stage after coiling, the steel sheet is cooled to 800°C at a rate of 1°C / s or less to increase the scale thickness, in order to remove the scale by mechanical peeling. If the cooling rate in the first cooling stage exceeds 1°C / s, the desired scale thickness for mechanical peeling cannot be achieved.

[0063] After the first cooling stage, in the second cooling stage, it is necessary to suppress the scale transformation from FeO to Fe2O4 to prevent the occurrence of spalling. Therefore, the tensile strength can be increased by suppressing this by cooling to 300°C using a reforming tube on a Stelmor cooling table at a rate of 20°C / s or more. Preferably, the cooling rate in the second cooling stage is 30°C / s or less. If the cooling rate exceeds 30°C / s, the tensile strength desired in the present invention cannot be achieved.

[0064] Moreover, the wire can satisfy the following relational expression 1.

[0065] [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0

[0066] (Here, [C], [Mn], and [Cr] each represent weight percent.)

[0067] A concrete-reinforcing steel fiber according to one embodiment of the present invention having the above-mentioned alloy composition will be described below.

[0068] The concrete-reinforcing steel fiber of the present invention contains, by weight, C: 0.005-0.035%, Si: 0.07-0.3%, Mn: 0.07-0.2%, Cr: 1.0-2.2%, P: 0.05% or less, S: 0.05% or less, with the remainder being Fe and other unavoidable impurities, and satisfies the following relational expression 1, and can have a tensile strength of 1700 MPa or more.

[0069] [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0

[0070] (Here, [C], [Mn], and [Cr] each represent weight percent.)

[0071] Furthermore, the concrete-reinforcing steel fiber of the present invention does not break when subjected to 90-degree bending repeatedly 10 times or more.

[0072] The concrete-reinforcing steel fiber of the present invention can be produced by wiredrawing the wire rod for concrete-reinforcing steel fiber produced as above.

[0073] A method for manufacturing concrete-reinforcing steel fibers having the above-mentioned alloy composition according to one embodiment of the present invention will now be described.

[0074] The method for producing concrete-reinforcing steel fibers of the present invention includes the steps of dry drawing and wet drawing a wire rod consisting of, by weight, 0.005-0.03% C, 0.07-0.3% Si, 0.07-0.2% Mn, 1.0-2.0% Cr, 0.05% or less P, 0.05% or less S, with the remainder being Fe and other unavoidable impurities, and satisfying the following relational expression 1, and wherein LP heat treatment is omitted after the dry drawing and before the wet drawing, and a tensile strength of 1700 MPa or more can be ensured.

[0075] [Relationship 1][C]+0.17*[Mn]+0.25*[Cr]-0.62≦0

[0076] (Here, [C], [Mn], and [Cr] each represent weight percent.)

[0077] The wire is mechanically descaled and then dry-drawn to reduce its size, eliminating the intermediate LP heat treatment and allowing it to be finished by dry-drawing followed by wet-drawing.

[0078] The present invention will be described in more detail below through examples. However, the description of these examples is intended to illustrate the practice of the present invention, and the present invention is not limited by the description of these examples. The scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.

[0079] {Example}

[0080] Steel having the alloy composition shown in Table 1 below is produced in a converter, and then cast under normal conditions into 160x160mm steel. 2 The continuous cast billet was produced. The furnace temperature was then maintained at 1,080°C for 98 minutes, after which it was rolled under normal conditions. After finish rolling, the coiling temperature was controlled to 905°C by cooling on a water cooling stand. The wire rod was produced by primary cooling to 800°C at 0.08°C / s on a Stelmor cooling stand, and secondary cooling was performed at 22°C / s until it was cooled to a reforming tube.

[0081] Tables 1 and 2 show the microstructure and mechanical properties of the test components and wires observed under an optical microscope in a 1 / 4D region based on the cross section, where D is the diameter of the wire. The average grain size of quasi-polygonal ferrite was determined by measuring the area of ​​all grains measured at 100x magnification, converting it to grain size assuming it was circular, and dividing it by the number of grains to define the average grain size.

[0082] FIG. 1 shows that, as a result of observation with an optical microscope, the wire rod of Example 4, which satisfies the alloy composition of the present invention, has a microstructure consisting of quasi-polygonal ferrite and cementite.

[0083] [Table 1]

[0084] [Table 2]

[0085] Here, "no material" means that there was no material to test using a cobblestone. Table 3 below shows the properties of steel fibers manufactured by removing the surface scale from the manufactured wire rod using a mechanical peeling method, followed by dry drawing and wet drawing without LP heat treatment. The tensile test was performed in accordance with ISO 6892-1 at a crosshead speed of 50 m / min. Test pieces were 300 mm long and cut into 20 pieces. The tensile strength of each piece was measured, and the average and deviation were determined. In addition, a 300 mm long steel fiber was used as the test material. A pin with a radius of 2.5 mm (where R is the diameter of the steel fiber: 0.55 mm) was fixed at the center of the length, and the fiber was repeatedly bent 90 degrees in one direction. The number of repeated 90-degree bending cycles until breakage occurred is shown in Table 3 below.

[0086] [Table 3]

[0087] From Tables 1 and 2 above, it can be seen that in Examples 1 to 9, which satisfy the alloy composition, Relational Formula 1, and microstructure of the present invention, the tensile strength of the wire rod for steel fiber is 850 MPa or more. Also, from Table 3, it can be seen that the steel fibers in Examples 1 to 9 have a tensile strength of 1700 MPa or more, and do not break even when subjected to 90-degree bending repeatedly 10 times or more. In the case of Comparative Example 1, the C content was 0.04 wt%, which was excessive and did not satisfy Relational Formula 1, so cobbling occurred during the rolling of the wire rod.

[0088] In the case of Comparative Example 2, the Si content was 0.5 wt %, which was excessive, and therefore Fe2SiO4, which deteriorated the scale spalling property, was formed, and break lines were generated in the processing.

[0089] In the case of Comparative Example 3, the Mn content was 0.5 wt%, which was excessive and did not satisfy Relational Formula 1. As a result, after continuous casting and cooling at room temperature, cracks were generated due to the difference in stress between the inside and outside when the wire was charged into a wire heating furnace, and cobblestones were generated during wire rolling.

[0090] In Comparative Example 4, the Cr content was 0.5 wt %, which was sufficient for wire drawing, but the tensile strength of the steel fiber was 1430 MPa due to the insufficient Cr content, which was inferior to the inventive examples of the present invention.

[0091] In the case of Comparative Example 5, the Cr content was 2.5 wt %, and the added Cr content was excessive, so that the relational expression 1 was not satisfied, and cobble formation occurred during the rolling of the wire rod.

Claims

1. A wire rod for steel fiber reinforcement of concrete, characterized in that it contains, by weight, 0.005 to 0.035% C, 0.07 to 0.3% Si, 0.07 to 0.2% Mn, 1.0 to 2.2% Cr, 0.05% or less P, 0.05% or less S, and the remainder being Fe and other unavoidable impurities, and satisfies the following relational expression 1: [Relationship 1] [C] + 0.17 * [Mn] + 0.25 * [Cr] - 0.62 ≤ 0 (Here, [C], [Mn], and [Cr] each represent weight percent.)

2. 2. The wire rod for steel fibers for concrete reinforcement according to claim 1, wherein the microstructure contains, by area fraction, more than 98% to less than 100% quasi polygonal ferrite and more than 0% to less than 2% cementite.

3. 3. The wire for concrete reinforcing steel fibers according to claim 2, wherein the average crystal grain size of the quasipolygonal ferrite is greater than 0 and less than 35 μm within a 1 / 4D range based on the cross section. (Here, D means the diameter of the wire.)

4. 2. The wire rod for use as a steel fiber for concrete reinforcement according to claim 1, having a tensile strength of 850 MPa or more.

5. a step of producing a wire rod by maintaining a billet containing, in weight percent, C: 0.005 to 0.035%, Si: 0.07 to 0.3%, Mn: 0.07 to 0.2%, Cr: 1.0 to 2.2%, P: 0.05% or less, S: 0.05% or less, and the remainder being Fe and other unavoidable impurities at a temperature range of 1,000 to 1,250°C for 90 to 120 minutes and then rolling the billet; coiling the manufactured wire at a temperature in the range of 880 to 950°C; The cooling step after winding includes a first cooling step of cooling the wire to 800°C at a rate of 1°C / s or less and a second cooling step of cooling the wire to 300°C at a rate of 20°C / s or more.

6. 6. The method for manufacturing wire rods for concrete-reinforcing steel fibers according to claim 5, wherein the wire rods satisfy the following relational expression 1: [Relationship 1] [C] + 0.17 * [Mn] + 0.25 * [Cr] - 0.62 ≤ 0 (Here, [C], [Mn], and [Cr] each represent weight percent.)

7. A concrete-reinforcing steel fiber characterized by comprising, by weight, 0.005 to 0.035% C, 0.07 to 0.3% Si, 0.07 to 0.2% Mn, 1.0 to 2.2% Cr, 0.05% or less P, 0.05% or less S, with the remainder being Fe and other unavoidable impurities, satisfying the following relational expression 1, and having a tensile strength of 1700 MPa or more. [Relationship 1] [C] + 0.17 * [Mn] + 0.25 * [Cr] - 0.62 ≤ 0 (Here, [C], [Mn], and [Cr] each represent weight percent.)

8. 8. The concrete-reinforcing steel fiber according to claim 7, which does not break when repeatedly subjected to 90-degree bending ten or more times.

9. dry drawing a wire rod containing, in weight percent, C: 0.005 to 0.03%, Si: 0.07 to 0.3%, Mn: 0.07 to 0.2%, Cr: 1.0 to 2.0%, P: 0.05% or less, S: 0.05% or less, the remainder being Fe and other unavoidable impurities, and satisfying the following relational expression 1; wet drawing the wire; A method for producing concrete-reinforcing steel fibers, characterized in that the LP heat treatment is omitted after the dry wire drawing and before the wet wire drawing, and the tensile strength is 1700 MPa or more. [Relationship 1] [C] + 0.17 * [Mn] + 0.25 * [Cr] - 0.62 ≤ 0 (Here, [C], [Mn], and [Cr] each represent weight percent.)

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