RU2746613C1 - Steel wire that requires straightness and the method of its making - Google Patents

Abstract

FIELD: steel wires.

SUBSTANCE: proposed is steel wire, which requires straightness, and a method of manufacturing steel wire, where the steel wire is a wire subjected to a drawing operation, a heating operation in a state in which tension is applied, and a cooling operation, where when winding the wire on a winding part having a diameter which is greater than the wire diameter for a given period of time and then measuring the straightness of the 400 mm long wire, the straightness of the wire is less than or equal to 30 mm, and the method includes a wire preparation step, a heating step, a cooling step, and a straightness measurement step.

EFFECT: strain aging of the steel wire is stimulated to improve the straightness characteristics after aging.

5 cl, 11 dwg

Description

Technology area

The present invention relates to a steel wire excellent in straightness and a method for manufacturing the same, and more particularly, to a steel wire excellent in straightness, and a method of manufacturing the same, in which, since the steel wire is heated at a predetermined temperature or higher for a short period of time, it is possible to stimulate strain aging of the steel wire to improve the straightness performance after aging.

State of the art

In general, steel wire is used in various industrial fields and is applied to automobile tires, industrial belt conveyors, and the like. Steel wire used for different purposes, as described above, must have different quality characteristics. In particular, when steel wire is used as a material for reinforcing tires, the straightness of the steel wire is required.

Steel wire used in various fields of industry is not used immediately after its manufacture, but several months after it has been wound on spools with a given inner diameter and stored. However, when the steel wire is used after being wound on spools and stored as above, the straightness of the steel wire is not maintained.

When the straightness of the steel wire is not maintained, it may not be possible to use it in industrial areas where straightness is required. In particular, if the straightness is poor when steel wire is used as a tire reinforcement material, it may affect the manufacturability of the tire and may cause curling and tip-up phenomena, and thus tire manufacturers may experience difficulties in rolling and cutting processes. In addition, when the straightness of the steel wire is not maintained, it may be difficult to use the steel wire in various fields that require the straightness of the steel wire.

The straightness of the steel wire changes for the following reasons. For steel wire, carbon steel is used as the material, and the carbon steel contains embedded C and N atoms of the solid solution, which move over time and are fixed at the nearest dislocations. Therefore, when a steel wire is produced and wound on coils with a predetermined inner diameter, the straightness thereof changes due to diffusion and anchoring of the C and N atoms, and hence deteriorates.

Known steel wires may not provide excellent straightness due to the disadvantages noted above. In other words, although the known steel wires have excellent straightness characteristics immediately after manufacture, after being wound on coils with a given inner diameter and elapsed for a long period of time, their straightness characteristics change due to strain aging under stress in the elastic section, and thus they do not meet the quality characteristics of straightness.

Description of incarnations

There is provided a steel wire excellent in straightness and a method for manufacturing the same in which by heating the steel wire at a predetermined temperature or higher for a short period of time, strain aging of the steel wire is stimulated to improve the straightness after aging.

In accordance with one aspect of the present invention, a steel wire excellent in straightness may be a wire that has undergone a drawing operation, a heating operation in a state in which tension is applied, and a cooling operation, where, when winding the wire onto a winding part having a diameter, which is greater than the diameter of the wire, for a given period of time and the subsequent measurement of the straightness of the wire with a length of 400 mm, the straightness of the wire is less than or equal to 30 mm.

The heating temperature in the heating operation may be from about 80 ° C to about 220 ° C.

The heating temperature and heating time in the wire heating operation may satisfy Equation A below, and the heating temperature in the heating operation may be greater than or equal to 80 ° C, wherein Equation A is: T + 15.67 ln (t) ≥ 300, where T is the heating temperature expressed in terms of the absolute temperature in K, at is the heating time in seconds.

The heating time in the heating operation can be from about 0.02 seconds to about 10 seconds, and the tension applied to the wire during the heating operation can be from about 1% to about 50% of the cutting resistance.

In accordance with another aspect of the present invention, a method for producing a steel wire excellent in straightness may include the step of preparing the wire to be wire; an operation of heating the wire in a state in which tension is applied; a wire cooling operation and a straightness measurement operation in which the wire is wound on a winding part having a diameter greater than the wire diameter for a predetermined period of time, and then the straightness of the wire is measured, and when measuring the straightness of a 400 mm long wire in the measurement operation, the straightness is less than or equal to 30 mm.

The wire may include a plurality of wires, the method further comprising the step of twisting and coiling the plurality of wires together.

The heating temperature in the heating operation may be from about 80 ° C to about 220 ° C.

The heating temperature and heating time in the heating operation may satisfy the following Equation A, and the heating temperature in the heating operation may be greater than or equal to 80 ° C, wherein Equation A is: T + 15.67 ln (t) ≥ 300, where T is the heating temperature expressed in terms of the absolute temperature in K, at is the heating time in seconds.

The heating time in the heating operation can be from 0.02 seconds to 10 seconds, and the tension applied to the wire during the heating operation can be from 1% to 50% of the cutting resistance.

The present invention relates to a steel wire excellent in straightness and a method for manufacturing the same in which since the steel wire is heated at a predetermined temperature or higher for a short period of time, strain aging of the steel wire can be promoted to improve the straightness after aging.

Also, since the steel wire is heated at a predetermined temperature or higher for a short period of time, the microstructure of the steel wire may not change significantly. Thus, strain aging of the steel wire can be promoted without deteriorating the physical properties of the steel wire and with improving the straightness performance after aging.

Brief Description of Drawings

FIG. 1 is a view showing straightness measurement of a steel wire having excellent straightness performance according to an embodiment;

in fig. 2 is a graph showing the performance versus heating time of a steel wire having excellent straightness characteristics according to an embodiment;

in fig. 3 is a table illustrating the straightness in the manufacture of a steel wire by applying a tension of 1% of the cutting resistance and heating the wire by varying the heating time and heating temperature of the wire, according to an embodiment;

in fig. 4 is a table illustrating the straightness in the manufacture of steel wire by applying a tension of 5% of the cutting resistance and heating the wire with varying heating time and heating temperature of the wire, according to an embodiment;

in fig. 5 is a table illustrating the straightness in the manufacture of a steel wire by applying a tension of 15% of the cutting resistance and heating the wire by varying the heating time and heating temperature of the wire, according to an embodiment;

in fig. 6 is a table illustrating the straightness in the manufacture of steel wire by applying a tension of 30% of the cutting resistance and heating of the wire with varying heating time and heating temperature of the wire, according to an embodiment;

in fig. 7 is a table illustrating the straightness in the manufacture of a steel wire by applying a tension of 50% of the cutting resistance and heating the wire by varying the heating time and heating temperature of the wire, according to an embodiment;

in fig. 8 is a table illustrating the straightness in the manufacture of a steel wire by applying a tension of 1% of the cutting resistance and heating the wire with an increase in the heating time of the wire, in accordance with an embodiment;

in fig. 9 is a table showing the values of Equation A as a function of the heating temperature and heating time and the straightness value after 30 days, according to an embodiment;

in fig. 10 is a graph illustrating the change in tensile strength of the wire as a function of the heating temperature, and

in fig. 11 is a flowchart illustrating a method for manufacturing a steel wire excellent in straightness according to an embodiment.

Implementation of the invention

The present invention relates to a steel wire excellent in straightness and a method for manufacturing the same in which the steel wire is heated at a predetermined temperature or higher for a short period of time, which promotes strain aging of the steel wire to improve the straightness performance after aging. In the following, exemplary embodiments are described in detail with reference to the accompanying drawings.

As shown in FIG. 1, a steel wire excellent in straightness according to an embodiment includes a wire 110 which, after a drawing operation, is subjected to a heating operation in a state in which a tension is applied, and subjected to a cooling operation. Although wire 110 has been wound on a winding part for a predetermined period of time or longer, its straightness is less than or equal to 30 mm.

As shown in FIG. 1, the straightness according to the embodiment can be measured as follows. Wire 110 is wound around a winding piece with a diameter greater than that of wire 110 for a predetermined period of time. Thereafter, the end 111 of the coiled wire 110 is secured at 120 and the wire 110 is vertically lowered. Here, the wire 110 is lowered to a length of 400 mm. In other words, the distance between the end 111 of the wire 110 and the other end 112 of the wire 110 is 400 mm.

The straightness of the wire 110 can be determined by the distance between the first axis 121 forming a vertical line from point 120 and the other end 112 of the wire 110. In more detail, when the distance between the first axis 121 and the other end 112 of the wire 110 is small, the steel wire has excellent straightness. and when the distance between the first axis 121 and the other end 112 of the wire 110 is large, the steel wire has poor straightness.

Since the steel wire according to the embodiment is heated at a predetermined temperature or higher for a short period of time in order to promote strain aging of the steel wire, when measuring the straightness after winding the wire 110 on the winding part for a predetermined period of time, the straightness of the wire 110 can be kept less than or equal to 30 mm. (Here, the predetermined period of time that the wire 110 is wound on the winding part may be from six months to one year, but is not limited to this period.)

Wire 110 in accordance with an embodiment can be made of carbon steel, and wire 110 can be made of carbon steel from about 0.5 mass. % to about 1.1 wt. %.

After the drawing operation has been performed, the wire 110 may be heated in a state in which tension is applied, and the drawing operation may indicate that the wire 110 may be subjected to a drawing process. In particular, proprietary processing can be performed to provide high strength and machinability to wire 110. By performing the proprietary treatment of the wire 110, a microstructure of pearlite is achieved, which is an agglomerate of carbon-based cementite and ferrite formed from Fe.

A plurality of wires 110 may be provided and subjected to a drawing process, and may perform an operation of twisting and coiling the plurality of wires 110 together. However, the coiling operation can be omitted if necessary, and thus, when the wire 110 is used as the only steel wire, the coiling operation can be omitted.

The drawing process is a process in which a large deformation occurs in the material, and the pearlite structure of high-carbon steel is deformed, which promotes the decomposition of cementite in the lamellar layer. During the decomposition of cementite by deformation arising in the process of drawing, the fractions of the introduced C and N atoms of the solid solution in the ferrite matrix increase.

In the present invention, strain aging occurs as an embedded solid solution atom, such as C or N, becomes attached to a dislocation over time, and its factors may include not only the atomic density of the solid solution, but also time, temperature, dislocation density, and etc. In addition, through the drawing process, a high dislocation density occurs inside the material, which is accompanied by high plastic deformation, and the aging phenomenon is further enhanced.

In other words, when a fully drawn steel wire is wound on a coil with a predetermined inner diameter, cementite decomposes over time, resulting in strain aging accompanied by a change in straightness, and thus the target straightness may not be achieved.

To prevent this, the wire 110 according to the embodiment is subjected to a heating operation in which it is heated in a state in which tension is applied, and then subjected to a cooling operation, thereby artificially stimulating and completing the diffusion of solid solution atoms. Since the diffusion of the solid solution atoms is artificially stimulated and terminated as described above, even after the wire 110 is wound around the winding piece with a predetermined inner diameter, the aging phenomenon does not occur in the wire 110.

As described above, the steel wire according to the embodiment has improved straightness due to the fact that strain aging of the wire 110 is promoted, but strain aging can be promoted so as not to affect other physical properties of the wire 110.

To this end, the heating time in the heating operation of the wire 110 according to an embodiment can be from about 0.02 seconds to about 10 seconds, and can also be from about 0.02 seconds to about 5 seconds.

When the wire 110 is heated for too long in the heating operation of the wire 110, the strain aging of the wire 110 can be enhanced, but the production rate of the steel wire can be reduced.

As shown in FIG. 2, as the heating time increases in the heating operation of the wire 110, the productivity of the steel wire decreases and the productivity decreases rapidly when the heating time is greater than or equal to 10 seconds. In other words, when the heating time is increased in the heating operation of the wire 110, since the production rate slows down, the productivity may decrease and hence the production cost may increase.

In addition, when the wire 110 is not heated for a sufficient time in the heating operation of the wire 110, strain aging is not promoted. In particular, with a heating time of 0.01 s, i.e. less than 0.02 s, in the operation of heating the wire 110, because the heating time is too short, the carbon atoms formed during the decomposition of cementite at the interface between cementite and ferrite do not have sufficient driving force to move into the ferrite region, and thus accelerate when carbon is fixed on the dislocation, does not occur. Thus, the heating time in the heating operation of the wire 110 can be from about 0.02 seconds to about 10 seconds, and can also be from about 0.02 seconds to about 5 seconds.

At the same time, the heating temperature and heating time in the heating operation of the wire 110 according to the embodiment can satisfy Equation A below, and the heating temperature in the heating operation of the wire 110 can be greater than or equal to 80 ° C. Equation A: T + 15.67 ln (t) ≥300, where T is the heating temperature expressed in terms of the absolute temperature in K, and t is the heating time in seconds.

As shown in FIG. 3-7, when the heating temperature and heating time in the heating operation of the wire 110 do not satisfy Equation A, the strain aging of the wire 110 is insufficient, and therefore, the straightness of the wire 110 is not improved.

FIG. 3 illustrates the heating of wire 110 by applying a tension equal to 1% of the cut resistance thereto; FIG. 4 illustrates the heating of wire 110 when a tension of 5% of the cut resistance is applied thereto; FIG. 5 illustrates the heating of wire 110 when a tension of 15% of the cut resistance is applied thereto; FIG. 6 illustrates the heating of wire 110 when a tension of 30% of the cutting resistance is applied thereto; FIG. 7 illustrates the heating of wire 110 when a tension of 50% of the cutting resistance is applied thereto. The numerical values in FIG. 3-7 are straightness values of wire 110 measured using the straightness measurement method described above.

In the present invention, the heating temperature of the wire 110 may be greater than or equal to 80 ° C. When the heating temperature of the wire 110 is less than 80 ° C, even if the heating temperature and heating time in the heating operation of the wire 110 satisfy Equation A, strain aging of the wire 110 may not be promoted.

More specifically, the embodiments of 60 ° C -1 s and 40 ° C -1 s shown in FIG. 3, 60 ° C - 1 s and 40 ° C - 1 s, shown in FIG. 4, 60 ° C - 1 s and 40 ° C - 1 s, shown in Fig. 5, 60 ° C - 1 s and 40 ° C - 1 s, shown in FIG. 6, as well as 60 ° C - 1 s and 40 ° C - 1 s, shown in FIG. 7 satisfy Equation A, but since the heating temperature is less than 80 ° C, strain aging is not promoted, and thus the straightness deteriorates.

FIG. 8 shows that the heating temperature of the wire 110 is less than 80 ° C and the heating time increases (greater than or equal to 10 seconds). As seen in FIG. 8, although the heating time becomes longer when the heating temperature is less than 80 ° C, strain aging of the wire 110 is not stimulated. As described above, when the heating temperature of the wire 110 is less than 80 ° C, although the heating time of the wire 110 is increased, strain aging is not promoted.

Strain aging occurs as an embedded solid solution atom, such as C or N, becomes attached to a dislocation over time, and its factors may include not only the atomic density of the solid solution, but also time, temperature, dislocation density, etc. ... In other words, a predetermined temperature is necessary to anchor the embedded solid solution atoms such as C or N to dislocations over time, and when the heating temperature of wire 110 is less than 80 ° C, the embedded solid solution atoms such as C or N are not attached to dislocations over time, and thus strain aging is not stimulated.

Therefore, even if the heating temperature and heating time in the heating operation of the wire 110 satisfy Equation A, when the heating temperature in the heating operation is less than 80 ° C, strain aging is not promoted.

Also, even if the heating temperature in the heating operation of the wire 110 is more than 80 ° C, when the heating temperature and the heating time in the heating operation of the wire 110 do not satisfy Equation A, strain aging is not promoted. In more detail, as shown in FIG. 9, in cases of 80 ° C, 0.01 s, 0.02 s, and 0.03 s, since the heating temperature in the heating operation is greater than or equal to 80 ° C, but the condition of Equation A is not met, strain aging is not accelerated, and hence, straightness is not improved.

Also, even if the heating temperature in the heating operation of the wire 110 is greater than or equal to 80 ° C, when the heating time in the heating operation of the wire 110 is less than 0.02 seconds, strain aging is not promoted. In more detail, as shown in FIG. 9, in cases of 100 ° C - 0.01 s, 150 ° C - 0.01 s, and 200 ° C - 0.01 s, since the heating temperature in the heating operation is greater than or equal to 80 ° C and satisfies Equation A, but time heating is insufficient, deformation aging is not accelerated.

This is because the heating time in the heating operation of the wire 110 is too short. Although the heating temperature in the heating operation of the wire 110 is greater than or equal to 80 ° C, when the heating time in the heating operation of the wire 110 is too short, an embedded solid solution atom such as C or N is not fixed to the dislocation over time, and thus the deformation aging is not accelerated.

Thus, the heating temperature and heating time in the heating operation of the wire 110 can satisfy Equation A, and the heating temperature in the heating operation of the wire 110 can be greater than or equal to 80 ° C. In other words, although the heating temperature is greater than or equal to 80 ° C when the heating time is too short, strain aging is not promoted, and thus, the heating time in the heating operation of the wire 110 may be greater than or equal to 0.02 seconds.

According to an embodiment, the tension applied to the wire 110 during the heating operation of the wire 110 may be from about 1% to about 50% of the cutting resistance. The tension applied to the wire 110 during the heating operation of the wire 110 affects the heating temperature and heating time.

As described above, the heating operation promotes strain aging due to the diffusion of the embedded solid solution atoms, and when the tension applied to the wire 110 is increased, the straightness of the wire 110 is improved, and under the same heating conditions, a stronger effect of improving the straightness is exhibited. Therefore, the tension applied to the wire 110 during the heating operation of the wire 110 can be more than 1% of the cutting resistance.

However, when the tension applied to the wire 110 during the heating operation of the wire 110 is too great, the physical properties of the wire 110 may deteriorate due to the tension. Therefore, the tension applied to the wire 110 during the heating operation of the wire 110 may be less than 50% of the cutting resistance. (As used herein, cut resistance is one of the physical properties of the wire and refers to the strength at the point in time that the wire is cut by applying tension from both ends of the wire in the axial direction.)

However, the tension applied to the wire 110 is not limited to about 1% to about 50% of the cutting resistance, and a suitable tension can be applied if necessary.

The heating temperature in the heating operation of the wire 110 according to the embodiment may be from about 80 ° C to about 220 ° C. The reason why the heating temperature may be greater than or equal to 80 ° C is described above, and therefore, explanations are omitted here. As shown in FIG. 10, when the temperature is less than or equal to 220 ° C in the heating operation of the wire 110, the tensile strength can be increased without significantly changing the microstructure.

However, when the heating temperature becomes much higher than 220 ° C, the aspect of the physical properties of the wire 110 becomes unacceptable enough to observe changes in the microstructure, and the tensile strength gradually decreases. In other words, when the heating temperature is more than 220 ° C, strain aging may be promoted, but the tensile strength of the wire 110 may decrease. Thus, the heating temperature in the heating operation of the wire 110 may be from about 80 ° C to about 220 ° C.

A steel wire excellent in straightness according to the above embodiment can be produced by the following method. All the properties of the steel wire having excellent straightness characteristics described above can be applied to the method for manufacturing the steel wire having excellent straightness characteristics according to the embodiment described later.

As shown in FIG. 11, the method according to the embodiment includes a wire preparation step S110, a heating step S130, a cooling step S140, and a straightness measurement step S150.

The wire preparation step S110 is a drawn wire preparation step. When the wire preparation step S110 includes a wire drawing step 110, various types of processes may be included.

The method for manufacturing a steel wire excellent in straightness according to the embodiment may further include a coiling step S120. The coiling operation S120 is an operation in which a plurality of wires 110 are provided and the plurality of wires 110 are twisted and coiled with each other. The stranding step S120 can be included in the production of the steel wire, which is a multi-strand wire, but can be omitted in the production of the single-strand steel wire.

The heating operation S130 is an operation of heating the drawn wire 110 in a state in which tension is applied. In the heating operation S130, the heating temperature may be from about 80 ° C to about 220 ° C.

Also, the heating temperature and heating time in the heating operation S130 may satisfy Equation A: T + 15.67 ln (t) ≥300 (where T is the heating temperature expressed in terms of the absolute temperature in K, at is the heating time in s ), and the heating temperature in the heating operation S130 may be greater than or equal to 80 ° C.

Also, the heating time in the heating step S130 can be from about 0.02 seconds to about 10 seconds, and the tension applied to the wire 110 in the heating step S130 can be from about 1% to about 50% of the cutting resistance. However, the tension applied to the wire 110 is not limited to about 1% to about 50% of the cutting resistance, and therefore a suitable tension can be applied as needed.

The numerical ranges of the heating temperature, heating time, and tension in the heating step S130 are the same as described above for the steel wire having excellent straightness characteristics according to the embodiment, and therefore, detailed descriptions thereof are omitted here.

The cooling operation S140 is a cooling operation of the wire 110 that has been subjected to the heating operation S130. Since the wire 110, which has been subjected to the heating step S130, is exposed to an environment suitable for the diffusion of C and N in the wire 110, if the winding is carried out with insufficient cooling, strain aging may not be completely suppressed. Therefore, the wire 110 that has been subjected to the heating step S130 can be cooled by the cooling step S140.

The cooling temperature in the cooling operation S140 may be less than or equal to 50 ° C, and when the cooling temperature in the cooling operation S140 is low, the effect can be enhanced, and thus, the cooling can be performed at a cooling temperature less than or equal to 50 ° C. In more detail, the cooling operation S140 can be performed at room temperature. However, the cooling temperature in the cooling step S140 is not limited to this and can be changed as needed. The cooling operation S140 can be performed in various ways, and methods such as air cooling, cooling with reducing and inert gas, water cooling and the like can be used.

Straightness measurement step S150 is an operation in which wire 110 is wound around a winding piece having a diameter larger than that of wire 110 for a predetermined period of time, and then the straightness of wire 110 is measured.

As shown in FIG. 1, straightness can be measured in the straightness measurement step S150 as follows. Wire 110 is wound around a winding piece with a diameter greater than that of wire 110 for a predetermined period of time. Thereafter, the end 111 of the wire 110 that has been wound is fixed at 120 and the wire 110 is vertically lowered. Here, the wire 110 is lowered to a length of 400 mm. In other words, the distance between the end 111 of the wire PO and the other end 112 of the wire 110 is 400 mm.

The straightness of the wire 110 measured in the straightness measurement step S150 may be the distance between the first axis 121 forming a vertical line from point 120 and the other end 112 of the wire 110. In more detail, when the distance between the first axis 121 and the other end 112 of the wire 110 is small, the steel wire has excellent straightness, and when the distance between the first axis 121 and the other end 112 of the wire 110 is large, the steel wire has poor straightness.

In the method for manufacturing a steel wire excellent in straightness according to the embodiment, when the wire 110 is wound on a winding part for a predetermined period of time as in the above method, and then the straightness of the 400 mm long wire 110 is measured in the straightness measurement step S150, a steel wire can be obtained which is a wire 110 having a straightness less than or equal to 30 mm.

The steel wire excellent in straightness and the method for producing the same according to the above-described embodiments have the following advantages.

In a steel wire excellent in straightness and its manufacturing method according to the embodiments, since the steel wire is heated at a predetermined temperature for a short period of time, strain aging of the steel wire can be promoted to improve the straightness after aging.

Also, in a steel wire excellent in straightness and its manufacturing method according to the embodiments, since the steel wire is heated at a predetermined temperature for a shorter period of time, the microstructure of the steel wire may not change significantly, and thus strain aging can be promoted. without deteriorating the physical properties of the steel wire to improve the straightness performance after aging.

More specifically, in a steel wire excellent in straightness and a method for making the same according to the embodiments, since the wire is heated for a short period of time (about 0.02 seconds to about 10 seconds, or about 0.02 seconds to about 5 seconds ), the straightness of the wire can be improved without changing the physical properties of the wire.

In the present invention, in order to promote strain aging of the wire when the wire is heated for a short period of time, the heating temperature and heating time in the wire heating operation may satisfy Equation A: T + 15.67 In (t) ≥300 (where T is the heating temperature expressed in terms of the absolute temperature in K, at represents the heating time in s), and the heating temperature in the heating operation may be greater than or equal to 80 ° C.

As shown in FIG. 3-9, when the conditions described above are not met, strain aging is insufficiently stimulated. However, in the case of a steel wire excellent in straightness according to the embodiment, the wire can be heated to satisfy the above conditions, and thus, the straightness of the wire can be improved without changing the physical properties of the wire.

For a steel wire having excellent straightness characteristics and a method of making the same according to the embodiments, Equation A: T + 15.67 In (t) ≥300 (where T is the heating temperatures expressed in terms of the absolute temperature in K, at is the heating time in s) can be modified as follows. Equation A above can be modified as follows: 420> T + 15.67 In (t)> 300 and Equation A may have an upper limit of 420.

As the heating temperature and heating time increase and the value of Equation A increases, strain aging can be promoted. However, when the upper limit of Equation A exceeds 420, the economic and operational aspects may be ineffective. In addition, when the heating temperature and heating time increase above the upper limit 420 in Equation A, the risk of affecting the physical properties of the wire may increase, and thus Equation A above can be expressed as 420≥T + 15.67 ln (t ) ≥300.

Although the invention has been specifically shown and described with reference to exemplary embodiments, the present invention is not limited to these embodiments, and various changes in form and detail can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention is defined in the appended claims.

Claims (10)

1. Steel wire, which requires straightness, which is a wire subjected to a drawing operation, a heating operation in a state in which tension is applied, and a cooling operation, where, when winding the wire on a winding part having a diameter that is larger than the diameter of the wire, for a period time and subsequent measurement of the straightness of the 400 mm long wire, the straightness of the wire is less than or equal to 30 mm, where the heating temperature in the heating operation is 80 ° C to 220 ° C, the heating temperature and the heating time in the heating operation of the wire satisfy Equation A below, and the temperature heating operation in heating operation is greater than or equal to 80 ° C, where Equation A is: T + 15.67 ln (t) ≥ 300, where T is the heating temperature expressed in terms of absolute temperature in K and t is the heating time in s, where the heating time in the heating operation is from 0.02 s to 10 s. 2. The steel wire of claim 1, wherein the tension applied to the wire during the heating operation is 1% to 50% of the cutting resistance. 3. A method of manufacturing steel wire, which requires straightness, including: the operation of preparing the wire, which is subjected to drawing; an operation of heating the wire in a state in which tension is applied; a wire cooling step; and a wire straightness measuring step in which the wire is wound on a winding part having a diameter that is larger than the wire diameter for a period of time, and then the straightness of the wire is measured, wherein when measuring the straightness of a wire with a length of 400 mm at the stage of measuring straightness, the straightness of the wire is less than or equal to 30 mm, where the heating temperature in the heating operation is 80 ° C to 220 ° C, the heating temperature and heating time in the wire heating operation satisfy Equation A below, and the heating temperature in the heating operation is greater than or equal to 80 ° C, where Equation A is: T + 15.67 ln (t) ≥ 300, where T is the heating temperature expressed as absolute temperatures in K and t is the heating time in s, where the heating time in the heating operation is from 0.02 s to 10 s. 4. The method of claim 3, wherein the wire comprises a plurality of wires, and the method further comprises the step of coiling and twisting the plurality of wires together. 5. The method of claim 3, wherein the tension applied to the wire during the heating step is 1% to 50% of the cutting resistance.

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