KR102147701B1 - Manufacturing method of high carbon steel wire having excellent torsional characteristics and strength - Google Patents

Abstract

The present specification relates to a method for manufacturing a high-strength steel wire applicable to a tire cord, and the like, and discloses a method for manufacturing a high-carbon steel wire having excellent torsional properties and strength.
According to an embodiment of the disclosed high carbon steel steel manufacturing method, in weight %, C: 0.97 to 1.12%, Si: 0.1% or less, Mn: 0.2 to 0.5%, Cr: 0.1 to 0.5%, B: 0.001 to 0.005% , Ti: 0.01~0.02%, N: 0.006% or less, P and S: 0.02% or less, manufacturing a wire rod containing the remaining Fe and other impurities, first drawing the wire rod, brazing heat treatment of the drawn wire rod And the step of secondary drawing the heat-treated wire rod, and the step of heat-treating the solder bath includes heating at a heating rate of 50 to 100°C/s to a target temperature of 1000 to 1050°C, and then maintaining the heat treatment for 20 seconds or less. Characterized in that.

Description

Manufacturing method of high carbon steel wire having excellent torsional characteristics and strength}

The present invention relates to a method of manufacturing a high-carbon steel wire, and more particularly, to a high-carbon steel wire having excellent torsional properties and strength, and a method of manufacturing the same.

Typically, steel wires used for tire cords, such as reinforcement materials for tire carcasses and belts, are manufactured using the following method. Molten steel with a carbon strength in the eutectoid-overeutectoid range is cast into bloom. The cast bloom is rolled to form a billet, and the billet is homogenized in a heating furnace to homogenize the structure into a single phase of austenite. After that, the wire rod is downsized to 5.0 to 6.0 mm through rolling of the wire rod, and the wire rod is cooled at an appropriate speed at which no cornerstone ferrite or cornerstone cementite is formed on a stellmor cooling table, thereby manufacturing a wire rod having a pearlite structure. After that, it becomes fresh according to its use and use by the customer. In general, the heat treatment that imparts ductility to the material is included once, usually twice, in some cases, and a final steel wire is obtained through dry and wet wire drawing, and a twisted wire work is additionally included after twisting the same steel wires.

Steel wires used in tire cords are required to have excellent strength and torsional properties. This is because, as the tire cord becomes high-strength, the cord structure becomes simple, and this makes it possible to reduce the weight of the tire itself in addition to the weight of the reinforcement. As another required characteristic, there is an excellent twisting characteristic, because delamination does not occur during the twisting process of twisting wires for the manufacture of the final product, and disconnection does not occur when the number of twisting is high.

In order to increase the strength of the steel wire, 1) the strength of the wire or heat treatment material is increased and the amount of wire drawn is fixed, 2) the amount of alloy is fixed and the amount of wire drawn is increased, 3) the amount of alloy is increased and Methods such as increasing the amount of wire drawn are used. Up to now, the high strength has been mainly performed through 1) increasing alloying elements such as C and Cr.

Among the alloying elements for strengthening the steel wire, C is an element that can greatly improve the strength even if a small amount is added compared to other elements, and it is known that the tensile strength increases by 100 MPa when 0.1% by weight is added.

However, in the case of a hypereutectic steel having a C content of more than 0.97% by weight, grain boundaries such as cornerstone cementite are formed, the cementite thickness increases, and the fineness of the pearlite interlayer spacing does not proceed well. In this way, since the cementite fraction and thickness that does not deform in hypereutectoid steel increases, the increase rate of the tensile strength of the steel wire decreases, and there is a problem that a void occurs at the interface between ferrite and cementite during wire drawing.

Korean Patent Registration Publication No. 10-1767821 (Notification date: August 14, 2017)

In order to solve the above-described problem, the present invention is to provide a high-carbon steel wire having excellent torsional properties and strength by suppressing cracks formed at the interface between ferrite and cementite during wire drawing, and a manufacturing method thereof.

The manufacturing method of the high carbon steel wire according to an embodiment of the present invention is in weight %, C: 0.97 to 1.12%, Si: 0.1% or less, Mn: 0.2 to 0.5%, Cr: 0.1 to 0.5%, B: 0.001 to 0.005%, Ti: 0.01 ~ 0.02%, N: 0.006% or less, P and S: 0.02% or less, preparing a wire rod containing the remaining Fe and other impurities, the first drawing of the wire rod, the drawn Including the step of soldering the wire rod and secondary drawing the heat-treated wire rod, and the step of performing the soldering bath heat treatment is performed at a heating rate of 50 to 100°C/s to a target temperature of 1000 to 1050°C, followed by 20 seconds. Heat treatment by holding for the following.

In addition, the first drawing may be dry fresh up to 65-75% of the total reduction rate.

In addition, the secondary drawing may be wet fresh up to 97-98% of the total reduction rate.

The high carbon steel wire according to another embodiment of the present invention is by weight %, C: 0.97 to 1.12%, Si: 0.1% or less, Mn: 0.2 to 0.5%, Cr: 0.1 to 0.5%, B: 0.001 to 0.005% , Ti: 0.01~0.02%, N: 0.006% or less, P and S: 0.02% or less, contains Fe and other impurities, and the number of twists is more than 60 times when a load of tensile strength * cross-sectional area * 0.008 is applied.

In addition, the tensile strength may be 4300 MPa or more.

In addition, the number of cracks after twisting according to the load may be 5 or less per 100 μm ² .

According to an embodiment of the present invention, the size of the pearlite nodule can be reduced by improving the heating rate of the high-temperature heating furnace and reducing the holding time during the solder bath heat treatment, thereby suppressing cracks occurring during wire drawing. As a result, it is possible to provide a high-carbon steel wire having excellent torsional properties and strength.

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 this 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, specific terms should not be interpreted in an excessively ideal or formal sense. 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 at 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 unfair use of the stated disclosure by unconscionable infringers.

Steel wires used in tire cords and the like are required to have excellent torsional properties and strength. In order to improve the strength, 1) increase the strength of wire rod or heat treatment material and fix the wire cutting amount by adding C, Cr, Si or increasing the amount of alloy, 2) fixing the amount of alloy and increasing the amount of wire drawing, 3) increasing the amount of alloy and wire drawing There were various methods such as increasing the amount. In the case of adding 1) C and Cr, which are mainly used, grain boundaries such as cornerstone cementite are formed as the carbon content increases, the cementite thickness increases, and the fineness of the pearlite interlayer spacing does not proceed well. During processing, there is a problem that a void occurs at the interface between ferrite and cementite.

In the present invention, the size of the pearlite nodule can be reduced by improving the heating rate of the high-temperature heating furnace during the soldering process and reducing the holding time, thereby suppressing cracks that occur during drawing, thus providing a high-carbon steel wire having excellent torsional properties and strength. can do.

The steel wire having excellent torsional properties and strength according to an embodiment of the present invention is weight %, C: 0.97 to 1.12%, Si: 0.1% or less, Mn: 0.2 to 0.5%, Cr: 0.1 to 0.5%, B: 0.001 ~0.005%, Ti: 0.01~0.02%, N: 0.006% or less, P and S: 0.02% or less, and the remaining Fe and other impurities are included.

Hereinafter, the reason for the numerical limitation of the content of the alloy component element in the examples of the present invention will be described. Unless otherwise stated, units can be interpreted as weight percent.

Carbon (C): 0.97 to 1.12% by weight

C is the main element for securing strength, and C, which is a substitutional element, mainly exists as cementite. When the C content is increased, the cementite fraction increases and the strength is known to increase. When the C content is increased, the strength of 100 MPa increases. When C is less than 0.97%, it is difficult to achieve the target strength of the present invention, and when C content is more than 1.12%, brittle fracture occurs due to problems such as deterioration of freshness due to the formation of central segregation or grain boundary formation of cornerstone cementite. I can. Therefore, the content of C is preferably set to 0.97 to 1.12%.

Silicon (Si): 0.1% by weight or less

Si is a solid solution strengthening element of ferrite and is dissolved in ferrite, and in pearlite, it is an element segregating in ferrite and at the interface between cementite and ferrite. When the Si content is increased by 0.1%, the tensile strength is increased by 14 to 16 MPa, but it is unsuitable for steel wires in which a large amount of wire drawing is given due to deterioration of the drawability due to hardening of ferrite. Therefore, when the Si content is more than 0.1%, it is preferable to control it to 0.1% or less because wire drawing is difficult.

Chrome (Cr): 0.1 to 0.5% by weight

Cr is a ferrite stabilizing element and greatly increases its strength. In addition, since it is a substitutional element that can be easily located at a general site in cementite, it is easily substituted with Fe, thereby minimizing the thickness of cementite and improving the work hardening rate. For the above effect, the content of Cr is preferably 0.1% or more. However, when it exceeds 0.5%, the transformation nose is delayed, and coarse chromium carbide is formed to lower productivity, so it is preferable to be less than that. Therefore, it is preferable to control the Cr content to 0.1 to 0.5%.

Manganese (Mn): 0.2 to 0.5% by weight

Mn is an austenite stabilizing element, and is mainly added to secure hardenability or increase strength during heat treatment. If less than 0.2% is added, it is difficult to secure hardenability, and if it is more than 0.5%, disconnection during processing due to central segregation is likely to occur, so it is preferable to add less than that. Therefore, it is preferable to control the Mn content to 0.2 to 0.5%.

Boron (B): 0.001 to 0.005% by weight

C diffusion to the outside occurs naturally in order to maintain concentration parallelism.If intergranular ferrite is formed along the austenite interface, it causes disconnection during the final wet drawing, or cracks propagate in the longitudinal direction when torsional stress is applied. Lamination can occur.

In the present invention, B exists at the austenite interface and serves to suppress the formation of intergranular ferrite that occurs during heat treatment. If the addition amount is less than 0.001%, the effect of the addition cannot be expected, and when the addition amount exceeds 0.005%, the grain boundary strength may be lowered due to precipitation of boron-based nitride at the grain boundary, thereby reducing hot workability. Therefore, it is preferable to control the B content to 0.001 to 0.005%.

Titanium (Ti): 0.01~0.02% by weight

Ti is an element having good bonding strength with N and suppresses the formation of boron-based nitride, so that by adding Ti, B can exist in a soluble state, thereby improving the hardenability. If the amount is less than 0.01%, the effect of the addition is insufficient, and if it exceeds 0.02%, a coarse nitride may be formed and mechanical properties may be hindered. Therefore, it is preferable to control the Ti content to 0.01 to 0.02%.

Nitrogen (N): 0.006% by weight or less

N is an element that causes age hardening by being fixed to the dislocations formed in the ferrite matrix during wire drawing, and when excessively contained, BN is formed in the mouth in the B-added steel to suppress the effect of B. Therefore, it is preferable to control the N content to 0.006% or less.

Phosphorus (P) and sulfur (S): 0.02% by weight or less

P and S are impurities, and the lower the content is, the better, but if the content is too limited, the cost for removing impurities in the steelmaking process increases. In addition, when the content of P and S increases, the ductility of the material decreases, and the wire drawability decreases. Therefore, it is important to manage the upper limit of the content of P and S in general. In the present invention, it is preferable to control the upper limit of P and S to 0.02%.

The steel wire of the present invention manufactured with the above alloy composition may have a tensile strength of 4300 MPa or more.

In addition, in the case of applying a load of tensile strength * cross-sectional area * 0.008 based on 200D (D: product diameter) after maintaining the steel wire at 150° C. for 1 hour, the number of twists may be 60 or more, and at this time, delamination does not occur. May not.

In addition, the number of cracks after twisting according to the applied load may be 5 or less per 100 μm ² of the steel wire of the present invention.

Hereinafter, a method of manufacturing a high-carbon steel wire having excellent torsional properties and strength of the present invention will be described in detail.

The manufacturing method of the steel wire according to an embodiment of the present invention is in weight %, C: 0.97 to 1.12%, Si: 0.1% or less, Mn: 0.2 to 0.5%, Cr: 0.1 to 0.5%, B: 0.001 to 0.005% , Ti: 0.01 to 0.02%, N: 0.006% or less, P and S: 0.02% or less, preparing a wire rod containing the remaining Fe and other impurities (hereinafter referred to as'component system'), the wire rod 1 The step of primary drawing, the step of soldering the drawn wire rod, and the step of secondary drawing the heat-treated wire rod, and the step of performing the soldering bath heat treatment is a temperature increase of 50 to 100°C/s to a target temperature of 1000 to 1050°C. After heating at a speed, it is characterized in that heat treatment is performed by holding for 20 seconds or less. Hereinafter, each manufacturing step will be described.

Steps of manufacturing wire rod

The molten steel that satisfies the above component system can be cast into a bloom, and then rolled to produce a billet. The billet is then heated to 1000-1100℃. By heating in the above temperature range, it is possible to maintain a single phase of austenite, prevent coarsening of austenite grains, and effectively dissolve remaining segregation, carbides and inclusions. When the heating temperature is less than 1000°C, it is difficult to obtain the above-described effect by heating. On the other hand, when it exceeds 1100°C, there is a problem that the surface quality is inferior due to severe scale generation and decarburization.

A wire rod is manufactured by hot rolling the heated billet as described above. When the hot rolling is performed at less than 950°C, there is a concern that the rolling load is increased and the rolling roll may be damaged. In addition, when the temperature of hot rolling exceeds 1050°C, there is a problem that the austenite grains are coarse, making it difficult to secure the target strength. Therefore, it is preferable that the hot rolling is controlled to be performed at 950 to 1050°C. After the wire rod rolling, it is preferable to cool to a temperature range for a subsequent winding process through a conventional water cooling method.

It is preferable to manufacture a wire rod having target physical properties through a winding and cooling process for the wire rod manufactured as described above. In the present invention, the winding process may be performed in a temperature range of 890 to 910°C. Here, the winding temperature is based on the temperature of the wire surface.

After completing the winding process, a cooling process may be performed. At this time, it is preferable to cool down to A _e1 temperature (about 730°C) at a temperature of 890 to 910°C on the surface of the wound wire. The cooling process may be performed in a stell to ensure a homogeneous structure, and is preferably performed at a cooling rate of 20 to 25°C/sec. When the cooling rate is less than 20° C./sec, there is a problem that cornerstone cementite and pearlite are formed, and when it exceeds 25° C./sec, it is impossible on the stell.

The wire rod obtained by the above-described manufacturing process may have a tensile strength of 1350 MPa or more and a cross-sectional shrinkage of 28% or more.

The step of first drawing the wire rod

As described above, the billet is heated, hot-rolled, wound, and cooled to produce a wire rod, followed by descaling treatment such as pickling, and then first drawing. The primary drawing is dry drawing and can be performed up to a total reduction rate of 65 to 75% using a drawing machine.

Leading heat treatment of the drawn wire rod

The primary wire rod can be heat treated by soldering. The soldering bath heat treatment can be performed by high-temperature heating to a target temperature of 1000 to 1050°C at a heating rate of 50 to 100°C/s, then holding for a short time of 20 seconds or less, and immersing in a soldering bath at 560 to 600°C for 20 seconds. have.

The size of the pearlite nodule, which is the microstructure of the wire rod heat-treated by the solder bath heat treatment step, may be controlled to be 15 μm or less. As a result of controlling the size of the pearlite nodule to 15㎛ or less, the propagation of cracks formed at the interface between ferrite and cementite during wet drawing is suppressed by finer particle size. It has excellent characteristics of twisting, delamination occurrence, and number of cracks after twisting.

On the other hand, it is preferable that the heating rate is 50 to 100°C/s. If the heating rate is less than 50°C/s, the size of the pearlite nodule of the heat treatment line cannot be controlled sufficiently small, and high-temperature heating to exceed 100°C/s is restricted due to equipment.

The holding time at the target temperature of 1000 to 1050°C is preferably set to a short time of 20 seconds or less. If it exceeds 20 seconds, the size of the pearlite nodule cannot be controlled sufficiently small.

The heat treatment wire obtained by brazing heat treatment of the wire described above includes a pearlite matrix structure as a microstructure, and the size of the pearlite nodule in the present invention is preferably controlled to 15 μm or less. In addition, the heat treatment line may have a cross-sectional shrinkage of 45% or more.

Secondary drawing of the heat-treated wire rod

The wire rod subjected to brazing heat treatment is secondarily drawn to obtain the final product, high carbon steel wire. Secondary drawing is wet drawing and can be performed up to 97-98% of total reduction rate using a drawing machine. The final drawing process may further include a heat treatment process maintained at 150° C. for 1 hour in order to remove internal stress formed therein by the second fresh drawing.

The high carbon steel wire, which is the final product obtained by secondary wire drawing, may have a tensile strength of 4300 MPa or more.

In addition, when a load of tensile strength * cross-sectional area * 0.008 is applied based on 200D (D: product diameter) after maintaining at 150℃ for 1 hour, the number of twists may be more than 60 times, and delamination may not occur at this time. .

In addition, the number of cracks after twisting with the applied load may be 5 or less per 100 μm ² of the steel wire of the present invention.

The present invention will be described in more detail through the following examples. However, the following examples are intended to illustrate the present invention in more detail, and the technical idea of the present invention is not limited to the following examples.

{Example}

The steel wires of each of the following invention examples and comparative examples were sequentially manufactured as a step of manufacturing a wire rod, a step of first drawing the wire rod, a step of brazing heat treatment of the drawn wire rod, and a step of secondary drawing the heat-treated wire rod.

In the manufacturing process of the steel wires of each of the invention examples and comparative examples, as shown in Table 2 below, in the solder bath heat treatment, the temperature increase rate and the holding time conditions are different in the high-temperature heating furnace. All other manufacturing processes were performed under the same conditions.

The molten steel having the component composition shown in Table 1 below was manufactured as a wire rod through the following manufacturing process. Specifically, after casting molten steel having the alloy composition of Table 1 to obtain a billet, the billet was maintained at a temperature of 1000°C or higher for 90 minutes to austenize, hot-rolled at 900°C or higher, and after passing through a water cooling zone, a winder ( Laying head, L/H) after winding at 900°C, cooling at 24°C/s to A _e1 temperature (about 730°C), each wire was manufactured. After forced aging at room temperature for 7 days, the tensile strength (TS) and section reduction rate (RA) of each wire were measured and described in Table 1.

division Weight (wt.%) Wire C Si Cr Mn B Ti N P S TS
(MPa) RA
(%) Comparative Example 1 1.12 0.09 0.22 0.32 0.002 0.018 0.006 0.015 0.013 1450 27 Comparative Example 2 1.02 0.08 0.21 0.33 0.002 0.02 0.005 0.012 0.011 1412 28 Comparative Example 3 0.97 0.10 0.23 0.31 0.002 0.01 0.005 0.009 0.014 1380 31 Invention Example 1 1.12 0.09 0.22 0.32 0.002 0.018 0.006 0.015 0.013 1448 28 Inventive Example 2 1.02 0.08 0.21 0.33 0.002 0.02 0.005 0.012 0.011 1421 29 Invention Example 3 0.97 0.10 0.23 0.31 0.002 0.01 0.005 0.009 0.014 1388 30

In Table 1, the composition of the wire rods of each of the invention examples and comparative examples was almost the same in the amount of alloys such as silicon (Si) and chromium (Cr) excluding carbon (C), and the carbon (C) was increased to 0.97 to 1.12%. . It can be seen from Table 1 that the tensile strength (TS) of the wire rod of each of the invention examples and comparative examples increases to 1380 MPa or more (maximum 1450 MPa) as the carbon content increases, and that the cross-sectional shrinkage ratio (RA) is 28% or more.

Each wire rod in Table 1 was descaled and first drawn (dry drawing), and then solder bath heat treatment was performed. In Table 2 below, a wire wire means a wire rod that has been drawn first, and a heat treatment wire means a wire rod obtained by brazing heat treatment of the wire rod. Table 2 below shows the results of the solder bath heat treatment conditions, tensile strength (TS), and cross-sectional shrinkage (RA) of the wires and wires.

The size of the pearlite nodule measured in Table 2 below is defined as a nodule boundary when the crystal orientation of the ferrite structure is measured using an EBSD (Electron Backscatter Diffraction) equipment, and the difference between adjacent ferrite crystal orientations is 15°. And, it is the measured value of the size of the border drawn at this time.

division Fresh line Lead bath heat treatment Heat treatment wire High temperature heating furnace LP TS
(MPa) RA
(%) Elevated temperature
speed
(C/s) goal
Temperature
(C) maintain
time
(sec.) goal
Temperature
(C) maintain
time
(sec.) TS
(MPa) RA
(%) Nodule size
(㎛) Comparative Example 1 2550 26 20 1020 42 600 20 1510 34 22 Comparative Example 2 2512 27 20 1022 41 600 20 1502 32 24 Comparative Example 3 2480 24 20 1020 42 600 20 1438 36 25 Invention Example 1 2545 28 50 1021 20 600 20 1527 47 12 Inventive Example 2 2528 27 80 1019 18 600 20 1500 45 11 Invention Example 3 2471 27 100 1020 15 600 20 1478 48 10

The wires of Table 2 were prepared by dry-drawing each wire of Table 1 to 75% of the reduction rate. Referring to Table 2, each dry-drawn wire had a value in which the tensile strength increased by 1000 MPa or more compared to the wire rod, and the cross-sectional shrinkage ratio (RA) decreased to about 27% compared to the wire rod.

The solder bath heat treatment in Table 2 is performed under different conditions in Comparative Examples 1 to 3 and Inventive Examples 1 to 3. The soldering bath heat treatment of Inventive Examples 1 to 3 is performed by heating in a high-temperature heating furnace to a target temperature of 1020°C at a heating rate of 50 to 100°C/s, holding for 20 seconds or less, and immersing in a soldering bath of 600°C. On the other hand, Comparative Examples 1 to 3 are different from Inventive Examples 1 to 3 in that heating at a heating rate of 20°C/s to a target temperature of 1020°C in a high-temperature heating furnace and then maintaining for about 40 seconds.

As a result of the solder bath heat treatment under different conditions, the heat treatment wires of Inventive Examples 1 to 3 had a cross-sectional shrinkage (RA) of 45% or more, and the cross-sectional shrinkage (RA) was increased by about 10% compared to the heat treatment wires of Comparative Examples 1 to 3. From the above results, it can be seen that the heat treatment wires of Inventive Examples 1 to 3 are superior to the heat treatment wires of Comparative Examples 1 to 3 in ductility and wire drawing processability.

This is because the size of the pearlite nodules of the heat treatment wires of Inventive Examples 1 to 3 is 15 μm or less, and the size of the pearlite nodules of the heat treatment wires of Comparative Examples 1 to 3 is about 10% or more smaller. This is because it is advantageous in improving the wire drawing processability due to the effect of suppressing crack propagation by miniaturization.

The heat treatment wires of each comparative example and invention example according to Table 2 were wet-fresh at a reduction rate of 97.5% and then maintained at 150°C for 1 hour to determine the tensile strength (TS) of the steel wire, whether or not twisting, delamination occurred, and the number of cracks after twisting. The measurement results for are shown in Table 3 below.

In Table 3, the torsion characteristics were measured by applying a load of tensile strength (TS) * cross-sectional area * 0.008 (hereinafter'load') based on 200D (D: product diameter) to the steel wires of each of the comparative examples and invention examples. The measured torsional characteristics are the occurrence of delamination (%), the number of twists, and the number of cracks (n/100㎛ ² ). In the following, the measurement results were reviewed based on the measured torsion characteristics.

division Steel wire (final fresh wire) TS
(MPa) torsion
(time) Delamination
Occurs or not Number of cracks
(n/100㎛ ² ) Comparative Example 1 4100 42 50% occurrence 18 Comparative Example 2 4080 45 48% occur 14 Comparative Example 3 4010 48 45% occur 10 Invention Example 1 4490 60 0% occurrence 4 Inventive Example 2 4410 62 0% occurrence 2 Invention Example 3 4320 65 0% occurrence One

Referring to Table 3, since the minimum tensile strength (TS) value of the steel wires of Inventive Examples 1 to 3 is 4320 MPa or more, which is higher than the maximum tensile strength (TS) value of the steel wires of Comparative Examples 1 to 3, 4100 MPa. It can be seen that the steel wire of 3 has better tensile strength (TS) than the steel wires of Comparative Examples 1 to 3.

Referring to Table 3, the steel wires of Inventive Examples 1 to 3 have a maximum number of twists of 60 or more without delamination when a load is applied, whereas the steel wires of Comparative Examples 1 to 3 have a maximum delamination of 50% and the number of twists is about 40 to 50 times. It was only. From this, it can be seen that the steel wires of Inventive Examples 1 to 3 have better torsion characteristics than the steel wires of Comparative Examples 1 to 3.

The number of cracks (n/100 μm ² ) refers to the number of cracks observed in the center (-1/2D to +1/2D) region of the cross-section of each steel wire after twisting by the applied load. Referring to Table 3, it can be seen that the number of cracks of the steel wires of Comparative Examples 1 to 3 is about 10 to 20 per 100 μm ² , whereas the number of cracks of the steel wires of Inventive Examples 1 to 3 is 4 or less per 100 μm ² It can be seen that it is significantly less than the number of cracks of the steel wires of Comparative Examples 1 to 3.

The reason that the steel wires of Inventive Examples 1 to 3 are superior to the steel wires of Comparative Examples 1 to 3 in terms of the above-described tensile strength (TS), torsion, delamination, and the number of cracks after torsion is superior to Inventive Examples 1 to 3 before wet drawing. This is because the size of the pearlite nodule, which is the microstructure of the heat treatment wire, is controlled to be 15 μm or less, and as a result, the propagation of cracks formed at the interface between ferrite and cementite during wet drawing is suppressed by finer particle size.

In the present invention, in order to obtain the above-described effect, pearlite, which is the microstructure of the heat treatment wire before wet drawing, is heated to a target temperature of 1020° C. at a heating rate of 50 to 100° C./s, and then maintained for a short time of 20 seconds or less. The size of the nodule is controlled to 15㎛ or less.

In the foregoing, 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 not departing from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.

Claims (8)

By weight %, C: 0.97~1.12%, Si: 0.1% or less, Mn: 0.2~0.5%, Cr: 0.1~0.5%, B: 0.001~0.005%, Ti: 0.01~0.02%, N: 0.006% or less , P and S: preparing a wire rod containing 0.02% or less, remaining Fe and other impurities;
First drawing the wire rod;
Leading heat treatment of the drawn wire rod; And
Including the step of secondary drawing the heat-treated wire rod,
The step of heat-treating the lead bath comprises heating at a temperature increase rate of 50 to 100°C/s to a target temperature of 1000 to 1050°C, and then heat treatment by holding for 20 seconds or less. The method of claim 1,
The first drawing is a method of manufacturing a high-carbon steel wire, characterized in that dry drawing is performed up to a total reduction rate of 65 to 75%. The method of claim 1,
The second drawing is a method of manufacturing a high-carbon steel steel wire, characterized in that wet-drawing to a total reduction rate of 97 to 98%. The method of claim 1,
The size of the pearlite nodule of the heat-treated wire rod is a method of manufacturing a high carbon steel wire of 15㎛. The method of claim 1,
A method of manufacturing a high-carbon steel wire having a cross-sectional shrinkage of 45% or more of the heat-treated wire rod. By weight %, C: 0.97~1.12%, Si: 0.1% or less, Mn: 0.2~0.5%, Cr: 0.1~0.5%, B: 0.001~0.005%, Ti: 0.01~0.02%, N: 0.006% or less , P and S: 0.02% or less, containing the remaining Fe and other impurities,
When a load of tensile strength * cross-sectional area * 0.008 is applied, the number of twists is more than 60,
High carbon steel wire, characterized in that manufactured by the manufacturing method according to claim 1. The method of claim 6,
High carbon steel steel wire, characterized in that the tensile strength is 4300 MPa or more. The method of claim 6,
High carbon steel wire, characterized in that the number of cracks after twisting according to the load is 5 or less per 100㎛ ² .