KR102229284B1 - Wire rod for high strength steel fiber, high strength steel fiber and manufacturing method thereof - Google Patents

Abstract

The present specification relates to a high-strength steel fiber wire, a high-strength steel fiber, and a manufacturing method thereof, and in detail, a steel fiber wire, a steel fiber, and a manufacturing method thereof capable of securing a high strength of 1500 MPa or more using ultra-low carbon steel are disclosed.
According to an embodiment of the disclosed steel fiber wire rod, the steel fiber wire is in weight %, in weight %, C: greater than 0, 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0%, P: 0.05 to 0.2 %, S: 0.03% or less, containing the remaining Fe and unavoidable impurities, and the microstructure of the cross-section is distributed in an area fraction of 99.5% or more of ferrite having an average grain size of 70 μm or more.

Description

Wire rod for high strength steel fiber, high strength steel fiber, and manufacturing method thereof {WIRE ROD FOR HIGH STRENGTH STEEL FIBER, HIGH STRENGTH STEEL FIBER AND MANUFACTURING METHOD THEREOF}

The present invention relates to a wire rod for high-strength steel fiber, a high-strength steel fiber, and a method for manufacturing the same, and more particularly, to a wire rod for steel fiber, a steel fiber, and a method of manufacturing the same, capable of securing a high strength of 1500 MPa or more using ultra-low carbon steel. .

Typically, steel fibers are used for reinforcing concrete to support the internal earth pressure during tunnel construction. Materials used as steel fibers include low carbon steel, medium/high carbon steel, and generally, low carbon steel of 0.1% by weight or less is required for products requiring low strength of about 1000 MPa, and medium/high carbon steel of 0.3 to 0.7% by weight is weak. It is used for products requiring high strength of 1500 MPa or more.

The first characteristic required for steel fibers is strength, and in recent years, high strength of products is progressing mainly in Europe. This is because the construction of underground and submarine tunnels is underway due to the characteristics of rock masses different from those in Korea, and it is possible to bring effects such as reduction of construction cost and period through high-strength products.

Since steel fiber is a reinforcing material used inside concrete, relatively expensive hard steel wires and piano wires have low price competitiveness, and most of the steel fiber manufacturers do not have facilities capable of heat treatment of piano wires, so their use is also limited.

Methods of increasing the strength in carbon steel include a method of making fine grains according to Hall-Petch Eq. and a method using solid solution strengthening. Increasing C or adding Si or Mn is known as an effective method for enhancing product strength.

However, the addition of Si and Mn increases the cost of the raw material, thereby reducing price competitiveness. In addition, the pearlite structure formed with the increase of the C content is a hard phase, and there is a problem in that it may cause a crack in manufacturing a steel fiber that requires a high processing amount of 98% or more.

0001) Korean Patent Application Publication No. 2008-0054336 (Publication date: July 2, 2003)

In order to solve the above-described problem, the present invention is to provide a wire rod for steel fiber, a steel fiber, and a manufacturing method thereof capable of securing a high strength of 1500 MPa or more by using an ultra-low carbon steel.

As a means for achieving the above object, the wire rod for high-strength steel fiber according to an example of the present invention is in weight%, C: more than 0, 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0%, P: 0.05 To 0.2%, S: 0.03% or less, the remaining Fe and unavoidable impurities are included, and the microstructure of the cross-section is distributed in an area fraction of 99.5% or more of ferrite having an average grain size of 70 μm or more.

In each of the wire rods for high-strength steel fibers of the present invention, it may further include in weight %, Sb: 0.03 to 0.08%.

In each of the high-strength steel fiber wire rods of the present invention, the tensile strength may be 500 MPa or more.

In each of the high-strength steel fiber wire rods of the present invention, the cross-sectional reduction rate may be 60% or more.

In addition, as a means for achieving the above object, the method for manufacturing a wire rod for high strength steel fibers according to an example of the present invention is in weight%, C: more than 0, 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0 %, P: 0.05 to 0.2%, S: 0.03% or less, maintaining the billet containing the remaining Fe and inevitable impurities in a heating furnace at 1000 to 1200°C for 90 to 120 minutes and then rolling, a temperature of 850 to 950°C And cooling at a rate of 10° C./sec or more to 180 to 220° C. at the coiled temperature in the range.

In the method of manufacturing a wire rod for each high strength steel fiber of the present invention, the cooling step is performed at a rate of 10 to 15° C./sec to 280 to 320° C. at the coiled temperature, and then 30° C./sec to 180 to 220° C. It may include cooling at a higher rate.

In the method of manufacturing a wire rod for each high-strength steel fiber of the present invention, the billet may further include a weight percent, Sb: 0.03 to 0.08%.

In the method of manufacturing a wire rod for each high strength steel fiber of the present invention, the rolling may include sequentially performing rough rolling and finishing rolling in a temperature range of 900 to 1100°C.

In addition, as a means for achieving the above object, the high-strength steel fiber according to an example of the present invention is in weight %, C: more than 0, 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0%, P: 0.05 To 0.2%, S: 0.03% or less, the remaining Fe and unavoidable impurities are included, and the number of twists is 40 or more when a load of tensile strength * cross-sectional area * 0.008 is applied.

In each of the high-strength steel fibers of the present invention, in weight percent, Sb: may further include 0.03 to 0.08%.

In each of the high-strength steel fibers of the present invention, the tensile strength may be 1500 MPa or more.

In each of the high-strength steel fibers of the present invention, the cross-sectional reduction rate may be 60% or more.

In each of the high-strength steel fibers of the present invention, the maximum depth of the corrosion pit formed after immersing the steel fiber in a 5% sulfuric acid solution for 1 hour may be 10 μm or less.

According to an embodiment of the present invention, it is possible to provide a high-strength steel fiber of 1500 MPa or more, and more specifically, to secure freshness and strength, a total ferrite structure is formed based on ultra-low carbon steel having a C content of 0.009% by weight or less, and solid solution It is possible to provide a high-strength steel fiber wire, a steel wire, and a method of manufacturing the same, with increased strength and torsion characteristics by refining grains by increasing the strength through P as a reinforcing element and forming oxide grain boundaries through the addition of Sb.

The high-strength steel fiber according to the embodiment of the present invention has the effect of shortening the construction period and reducing the cost.

1A is a cross-sectional microstructure photograph of a wire rod for steel fibers of Inventive Example 1. FIG.
1B is a cross-sectional microstructure photograph of the steel fiber wire rod of Inventive Example 4.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified into various other forms, and the technical idea of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided in order to more completely explain the present invention to those with average knowledge in the art.

The terms used in the present application are only used to describe specific examples. So, for example, a singular expression includes a plural expression unless the context clearly has to be singular. In addition, terms such as "include" or "include" used in the present application are used to clearly refer to the existence of features, steps, functions, components or combinations thereof described in the specification, but other features It should be noted that it is not used to preliminarily exclude the presence of elements, steps, functions, components, or combinations thereof.

Meanwhile, unless otherwise defined, all terms used in the present specification should be viewed as having 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 in the specification, a specific term should not be interpreted as an excessively ideal or formal meaning. For example, in the present specification, expressions in the singular include plural expressions unless the context clearly has exceptions.

In addition, "about", "substantially" and the like in the present specification are used in or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and are accurate to aid understanding of the present invention. Or absolute figures are used to prevent unreasonable use of the stated disclosure by unconscionable infringers.

The wire rod for high-strength steel fibers according to an example of the present invention is in wt%, C: greater than 0, 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0%, P: 0.05 to 0.2%, S: 0.03% or less , The remaining Fe and unavoidable impurities. In addition, according to an example, the wire rod may be further included in a weight %, Sb: 0.03 to 0.08%.

On the other hand, since the high-strength steel fiber wire is made of high-strength steel fibers having the same alloy composition by dry and wet drawing, the explanation of the reason for limiting the alloy composition of the steel fibers is redundant, so it is omitted, but it can be clearly understood by those skilled in the art. It can be interpreted in the same way as the reason for limiting the alloy composition of the high-strength steel fiber wire within the range.

Hereinafter, the reasons for limiting the alloy composition will be described in detail. All of the following component compositions refer to% by weight unless otherwise specified.

Carbon (C): more than 0 and 0.009% by weight or less

C is an element constituting cementite and is an element that effectively improves strength when forming a pearlite structure. However, if the C content is excessive, a pearlite structure is formed between ferrites, which may cause disconnection during wire drawing. In addition, when the C content is excessive, as the grain boundary between the hard phase and the soft phase becomes more clear, there is a problem in that the grain boundary corrosion resistance is deteriorated.

In the present invention, in order to prevent the above-described problems, the upper limit of the C content is controlled to 0.009% by weight.

Silicon (Si): 0.07 to 0.25% by weight

Si is a ferrite-hardening element by increasing the tensile strength by about 15 to 20 MPa when increasing 0.1% by weight, and acts as a deoxidizer to remove oxygen in the molten steel. If the Si content is less than 0.07% by weight, it is difficult to sufficiently perform the role of the deoxidizing agent, and if the Si content exceeds 0.25% by weight, the possibility of disconnection during wet drawing due to ferrite hardening increases, so it is preferable to keep it below that.

Manganese (Mn): 0.5 to 2.0% by weight

Mn is an element used to improve hardenability and control S in steel, and in ferritic steel, when Mn increases by 0.1% by weight, the strength increases by about 5 to 10 MPa. If the Mn content is less than 0.5% by weight, it is difficult to secure the hardenability and the target strength, and if the Mn content exceeds 2.0% by weight, it is preferable to keep the amount below that, because work disconnection due to segregation occurs.

Phosphorus (P): 0.05 to 0.2% by weight

P is a solid solution strengthening element that increases the strength by about 90 MPa when 0.1% by weight is added, but in general, P can induce grain boundary segregation when the C content in the steel is high, and may be formed as FeP at the grain boundary. It is known to cause disconnection.

However, in the present invention, grain boundary segregation is prevented by targeting an ultra-low carbon steel having a C content of 0.009% by weight or less, and the formation of FeP can be suppressed by controlling the cooling conditions. Therefore, in the present invention, it is possible to secure a solid solution strengthening effect by actively adding P to the steel. In addition, accordingly, in the present invention, it is possible to compensate for the decrease in strength according to the C content by actively adding P. In addition, the added P is mostly present in the grain in a solid solution state, so that the intergranular corrosion resistance can be improved.

For the above-described effect, in the present invention, P is added in an amount of 0.05% by weight or more to secure a target strength and improve corrosion resistance. However, if the content exceeds 0.2% by weight, the ferrite hardness increases significantly and may cause disconnection during wire drawing, so it is preferable to control the P content to 0.2% by weight or less.

Sulfur (S): 0.03% by weight or less

When S is contained in a large amount, MnS inclusions are generated at the grain boundaries, which lowers the workability, so it is preferable to control the content to 0.03% by weight or less.

In addition, in addition to the above-described components, the present invention may optionally further include antimony (Sb) in order to improve torsional properties. Hereinafter, the reason for limiting the antimony content will be described.

Antimony (Sb): 0.03 to 0.08% by weight

Sb is an Sb oxide that is segregated at the austenite grain boundary, so that the austenite grain size can be refined during high-temperature rolling, and the ferrite grain size transformed by cooling in the micronized austenite grain is also refined, thereby increasing strength. .

In addition, in the present invention, Sb is added to improve torsional properties. When the crystal plane rotates in the drawing direction [001], the ferrite grains refined by the addition of Sb rotate with relatively low intergranular defects and voids, but the load (stress) is small, so the torsion characteristics of the steel are improved. do.

For the above-described effect, in the present invention, Sb is added in an amount of 0.03% by weight or more, thereby securing torsion characteristics due to refinement of ferrite grains. However, when the Sb content is 0.1% by weight or more, the amount of Sb oxide segregated at the austenite grain boundary increases to form Sb clusters, which may deteriorate ductility and cause brittle fracture, so the content is less than 0.1% by weight. It is desirable to control. According to an example, more preferably, the upper limit of the Sb content is controlled to be 0.08% by weight or less for wire drawing processability.

The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in a typical manufacturing process, this cannot be excluded. Since the impurities are known to anyone of ordinary skill in the manufacturing process, all the contents are not specifically mentioned in the present specification.

In the microstructure of the cross-section of the wire rod for high strength steel fibers according to an example of the present invention having the above alloy composition, ferrite having an average grain size of 70 μm or more may be distributed in an area fraction of 99.5% or more. According to the present invention, the wire rod for high-strength steel fibers uses ultra-low carbon steel having a C content of 0.009% by weight or less to limit the pearlite structure that can cause disconnection during wire drawing, and the main structure of the steel is made of ferrite as described above.

In addition, the high strength steel fiber wire rod according to an example of the present invention may have a tensile strength of 500 MPa or more.

In addition, the wire rod for high-strength steel fibers according to an example of the present invention may have a cross-sectional reduction ratio (RA) of 60% or more.

Hereinafter, a method of manufacturing a high-strength steel fiber wire rod according to the present invention will be first described, and then a detailed description will be given of a method of manufacturing a high-strength steel fiber.

The method of manufacturing a wire rod for high strength steel fibers according to an embodiment of the present invention is in weight%, C: more than 0, 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0%, P: 0.05 to 0.2%, S: Rolling after maintaining the billet containing 0.03% or less, remaining Fe and inevitable impurities in a heating furnace at 1000 to 1200°C for 90 to 120 minutes, winding at a temperature range of 850 to 950°C, and 180 at the coiling temperature And cooling to 220° C. at a rate of 10° C./sec or more. According to an example, the billet may be further included in a weight percent, Sb: 0.03 to 0.08%.

The billet having the above alloy composition is heated in a heating furnace for the above-described temperature range and time to sufficiently dissolve a solid solution strengthening element for securing strength. Then, the heated billet is rolled under normal rolling conditions. According to an example of the present invention, the rolling may include sequentially performing rough rolling and finishing rolling in a temperature range of 900 to 1100°C.

In addition, according to an example of the present invention, the cooling step includes cooling from the coiling temperature to 280 to 320°C at a rate of 10 to 15°C/second, and then cooling to 180 to 220°C at a rate of 30°C/second or more. Can include. In the present invention, by cooling from 280 to 320°C to 180 to 220°C at a high-speed cooling rate of 30°C/sec or more, the amount of solid solution P can be maintained and FeP formation can be suppressed.

The high-strength steel fiber wire rod manufactured according to the above-described steps may have a tensile strength of 500 MPa or more.

In addition, the wire rod for high-strength steel fibers according to an example of the present invention may have a cross-sectional reduction ratio (RA) of 60% or more.

The high-strength steel fiber according to an embodiment of the present invention is obtained by drawing a wire for high-strength steel fiber manufactured according to the above manufacturing process.

A method of manufacturing a high-strength steel fiber according to an embodiment of the present invention may include dry and wet drawing of the above-described high-strength steel fiber wire up to a final reduction of 99%.

The high-strength steel fiber manufactured according to the above-described steps may have a number of twists of 40 or more when a load of tensile strength * cross-sectional area * 0.008 is applied.

In addition, according to an example of the present invention, it is possible to improve the torsion characteristics by adding Sb. Ferrite grains refined by the addition of Sb rotate with relatively low intergranular defects, voids, etc., but the load (stress) is small, so the torsional characteristics of the steel can be improved.

For the above-described effect, according to an example, the high-strength steel fiber of the present invention can control the Sb content to 0.03 to 0.08% by weight. By adding the Sb content in an amount of 0.03% by weight or more, it is possible to secure a torsion characteristic due to refinement of ferrite grains, and while controlling the upper limit of the content to 0.08% by weight or less, sufficient wire drawing workability can be secured. The high-strength steel fiber having the Sb content controlled at 0.03 to 0.08% by weight has improved torsional properties such that the number of twists is 45 or more when a load of tensile strength * cross-sectional area * 0.008 is applied.

In addition, the high-strength steel fiber according to an example of the present invention may have a tensile strength of 1500 MPa or more.

In addition, the high-strength steel fiber according to an example of the present invention may have a cross-sectional reduction ratio (RA) of 60% or more.

In addition, the high-strength steel fiber according to an example of the present invention has excellent corrosion resistance, and the maximum depth of the corrosion pit formed after the steel fiber is immersed in a 5% sulfuric acid solution for 1 hour may be 10 μm or less.

In the present invention, while preventing the problem that the intergranular corrosion resistance is deteriorated according to the C content targeting the ultra-low carbon steel, it is possible to improve the intergranular corrosion resistance because the positively added P is mostly present in the grain in a solid solution state. For this reason, the corrosion resistance of the high-strength steel fiber can be improved.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and matters reasonably inferred therefrom.

{Example}

Steel having the composition shown in Table 1 below was made into steel in a converter, and then cast (1.8m/min) under normal conditions to produce a playing billet (cross section: 160*160mm ² ). Then, it was held at a heating furnace temperature of 1010°C for 90 minutes, rolled, and then wound at a coiling temperature of 880°C and cooled to 300°C at 12°C/sec. Thereafter, in order to suppress the formation of FeP, a wire rod for high strength steel fiber was manufactured by cooling to 200° C. at 30° C./sec. The strength and cross-sectional reduction ratio (RA) of the manufactured wire rod are shown in Table 1.

The prepared high-strength steel fiber wire rod was dry and wet-drawn by the customer to a final reduction of 99%, and was made of high-strength steel fiber with a diameter of 0.55 mm. At this time, the speed of wet drawing is 30m/sec, the reduction amount per pass is 12%, and the die approach angle is 12 degrees. The tensile strength, cross-sectional reduction rate (RA), twist (times), delamination occurrence, and corrosion pit of the prepared high-strength steel fiber are shown in Table 2 below.

In Table 2, the evaluation of the torsional properties of the high-strength steel fibers was performed by applying a load of tensile strength * cross-sectional area * 0.008 to the manufactured steel fibers and measuring the number of twists based on the torsion length 100 * D (D: diameter of the steel fiber). The measured number of twists is shown in Table 2.

In addition, the evaluation of the corrosion resistance of the high-strength steel fibers in Table 2 was performed by measuring the corrosion pits formed in the depth direction from the steel fiber surface after immersing the steel fiber in a 5% sulfuric acid solution for 1 hour. The measured corrosion pit is shown in Table 2.

Ingredient (% by weight) Wire rod C Si Mn Sb P S Seal
burglar
(MPa) RA
(%) Comparative Example 1 0.0084 0.19 0.75 0 0.004 0.0048 502 70.2 Invention Example 1 0.0086 0.18 0.74 0 0.06 0.0047 592 68.5 Inventive Example 2 0.0068 0.20 0.78 0 0.11 0.0048 627 67.8 Invention Example 3 0.0068 0.25 0.82 0 0.17 0.0055 657 67.0 Invention Example 4 0.0072 0.25 0.81 0 0.20 0.0054 697 66.9 Comparative Example 2 0.0066 0.22 0.77 0 0.24 0.0048 732 68.2 Inventive Example 5 0.0068 0.25 0.82 0.03 0.17 0.0055 677 68.0 Invention Example 6 0.0072 0.25 0.81 0.08 0.16 0.0054 702 67.1 Comparative Example 3 0.0068 0.25 0.82 0.1 0.17 0.0055 Brittle
Destruction X Comparative Example 4 0.27 0.21 0.79 0 0.16 0.0064 575 58.0 Comparative Example 5 0.52 0.22 0.82 0 0.19 0.0051 820 49.1

Steel fiber Seal
burglar
(MPa) RA
(%) torsion
(time) Delamination corrosion
feet
(㎛) Comparative Example 1 1320 68.4 38.9 Not occurring 15.7 Invention Example 1 1508 63.6 40.0 Not occurring 9.8 Inventive Example 2 1540 72.1 40.5 Not occurring 9.7 Invention Example 3 1630 73.0 40.1 Not occurring 5.2 Invention Example 4 1692 60.1 40.2 Not occurring 10.0 Comparative Example 2 monorail X X X X Inventive Example 5 1681 62.5 48.5 Not occurring 9.8 Invention Example 6 1765 67.8 49.2 Not occurring 5.3 Comparative Example 3 Brittle
Destruction X X X X Comparative Example 4 monorail X X X X Comparative Example 5 monorail X X X X

Hereinafter, each invention example and a comparative example are evaluated with reference to Tables 1 and 2.

Unlike the ultra-low carbon steel targeted by the present invention, Comparative Examples 4 and 5, which are medium/high carbon steels with C content of 0.27% by weight and 0.52% by weight, respectively, are broken when processing the pearlite structure produced as a result of excessive increase in carbon content. Caused. In addition, in the case of medium/high carbon steels such as Comparative Examples 4 and 5, there is a disadvantage that ancillary processes such as LP (constant temperature) heat treatment must be essentially included in order to improve workability.

In Table 1, except for Comparative Example 4.5, the C content of each Inventive Example and Comparative Examples 1 to 3 corresponds to about 0.008% by weight of ultra-low carbon steel. The alloy compositions of each Inventive Example and Comparative Examples 1 to 3 were similarly composed except for the P and Sb contents.

Inventive Examples 1 to 4 and Comparative Examples 1 and 2 were made of steel fiber wire and steel fiber by varying the P content, and Inventive Examples 3, 5 and 6 and Comparative Example 3 changed the Sb content to change the Sb content to make the steel fiber wire and steel fiber. It was prepared with. Hereinafter, the physical properties of the steel fiber wires and steel fibers of the invention examples and comparative examples according to the P and Sb contents are evaluated.

(1) Evaluation of physical properties of steel fiber wire rod and steel fiber according to P content

Referring to Comparative Examples 1 and 2 and Inventive Examples 1 to 4 of Table 2, it can be seen that as the P content increases, the tensile strength of the steel fiber wire rod and the steel fiber increases due to the effect of solid solution strengthening. In addition, it can be seen that the added P is mostly present in the mouth in a solid solution state, and the corrosion resistance is improved by satisfying all corrosion pits having a maximum depth of 10 μm or less.

However, as in Comparative Example 1, when the P content was 0.004% by weight and the content was less than 0.05% by weight, the target tensile strength value of 1500 MPa was not achieved in the final steel fiber, and the number of twists was also 40 times or less. . In addition, the measured corrosion pits were also 15.7 µm, indicating poor corrosion resistance.

In addition, as in Comparative Example 2, when the P content was 0.24% by weight, and the content exceeded 0.2% by weight, the ferrite hardness was excessively increased, leading to disconnection during the drawing process for producing the final steel fiber.

On the other hand, referring to Inventive Examples 1 to 4 in which the P content is controlled to 0.05 to 0.2% by weight, the target tensile strength of 1500 MPa or more, a cross-sectional reduction rate of 60% or more, and a maximum depth of 10 μm or less are satisfied. It can be seen that it can be made of steel fibers.

Meanwhile, FIGS. 1A and 1B correspond to microstructure photographs in cross-sections of the steel fiber wires of Inventive Examples 1 and 4, respectively. 1A and 1B, it can be seen that the cross-sectional microstructure of the steel fiber wires of Inventive Examples 1 and 4 is composed of the entire ferrite, and the average grain size of the ferrite is 70 μm and the minimum grain size is 30 μm. Able to know. As for the ferrite grain size according to FIGS. 1A and 1B, referring to each drawing, it can be seen that the grain size does not decrease as the P content increases. From this, it can be seen that in the examples of the present invention, P is well dissolved in the mouth.

According to the above, it can be seen that the P content is preferably controlled to be 0.05 to 0.2% by weight as in the present invention.

(2) Evaluation of physical properties of steel fiber wire rod and steel fiber according to Sb content

Inventive Examples 3, 5, 6 and Comparative Example 3 of Table 2 were differently composed of 0% by weight, 0.03% by weight, 0.08% by weight, and 0.1% by weight of the Sb content, and other alloy compositions were similarly composed.

Referring to Table 2, it can be seen that as the Sb content increases, the tensile strength of the steel fiber wire and steel fiber increases. In addition, when comparing Inventive Example 3 with Inventive Examples 5 and 6, when Sb was added, the ferrite grains refined by the addition of Sb had relatively low intergranular defects and voids, and the load (stress) was small to rotate. It can be seen that the number of twisting is more than 5 times than the case where is not added, so that the twisting characteristics are better.

However, in the case of Comparative Example 3 in which the Sb content exceeded 0.08% by weight to 0.1% by weight was excessively added, the Sb cluster segregated at the austenite grain boundary was excessively formed, and thus brittle fracture behavior was shown in the manufacture of the wire rod.

According to the above, it can be seen that the Sb content is preferably controlled to 0.03 to 0.08% by weight in order to improve the torsional properties of the final steel fiber as in the present invention.

As described above, although exemplary embodiments of the present invention have been described, the present invention is not limited thereto, and those of ordinary skill in the art are within the scope of not departing from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.

Claims (13)

In wt%, C: more than 0 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0%, P: 0.05 to 0.2%, S: more than 0 0.03% or less, including the remaining Fe and unavoidable impurities,
The microstructure of the cross section is a wire rod for high strength steel fibers in which ferrite with an average grain size of 70㎛ or more is distributed in an area fraction of 99.5% or more. The method of claim 1,
In weight%, Sb: a wire rod for high-strength steel fibers further comprising 0.03 to 0.08%. The method of claim 1,
A wire rod for high-strength steel fibers with a tensile strength of 500 MPa or more. The method of claim 1,
High-strength steel fiber wire rod with a cross-sectional reduction of more than 60%. By weight %, C: more than 0 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0%, P: 0.05 to 0.2%, S: more than 0 0.03% or less, billet containing the remaining Fe and unavoidable impurities Rolling after maintaining 90 to 120 minutes in a heating furnace of 1000 to 1200 ℃;
Winding in a temperature range of 850 to 950°C; And
Cooling at a rate of 10° C./sec or more from 180 to 220° C. at the wound temperature. The method of claim 5,
The cooling step,
A method for producing a wire rod for high strength steel fiber comprising cooling at a rate of 10 to 15° C./sec to 280 to 320° C. at the coiled temperature and then cooling to 180 to 220° C. at a rate of 30° C./sec or more. The method of claim 5,
The billet,
A method of manufacturing a wire rod for high-strength steel fibers further comprising, in weight%, Sb: 0.03 to 0.08%. The method of claim 5,
The rolling step,
A method of manufacturing a wire rod for high strength steel fiber comprising sequentially performing rough rolling and finishing rolling in a temperature range of 900 to 1100°C. In wt%, C: more than 0 0.009% or less, Si: 0.07 to 0.25%, Mn: 0.5 to 2.0%, P: 0.05 to 0.2%, S: more than 0 0.03% or less, including the remaining Fe and unavoidable impurities,
High-strength steel fiber with a number of twists of 40 or more when a load of tensile strength * cross-sectional area * 0.008 is applied. The method of claim 9,
In weight%, Sb: high-strength steel fibers further comprising 0.03 to 0.08%. The method of claim 9,
High-strength steel fiber with a tensile strength of 1500 MPa or more. The method of claim 9,
High-strength steel fiber with a cross-sectional reduction rate of 60% or more. The method of claim 9,
High-strength steel fiber having a maximum depth of 10 μm or less of a corrosion pit formed after immersing the steel fiber in a 5% sulfuric acid solution for 1 hour.

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