KR20210080044A - Wire rod with uniform variation in strength and reduction area and manufacturing method thereof - Google Patents

Abstract

The present invention provides a high-strength wire rod capable of suppressing deviation in strength and a cross-section reduction rate caused by a difference in overlap density, and a method for manufacturing the same. According to one embodiment of the present invention, a billet comprises: 0.6 to 0.9 wt% of C; 0.1 to 0.5 wt% of Si; 0.2 to 0.9 wt% of Mn; 0.05 wt% or less (excluding 0 wt%) of Al; and the remaining Fe and unavoidable impurities. The manufacturing method of the wire rod with uniform deviation of strength and a cross-section reduction rate comprises: a step of manufacturing the wire rod by rolling the billet in a form of the wire rod; a step of winding the wire rod in a coil shape; a step of transferring the wound wire rod to a cooling tank; a step of immersing the transferred wire rod in the cooling tank having a shape in which a ring edge portion is deeper than a ring center portion; and a step of blowing and cooling the wire rod extracted from the cooling tank.

Description

Wire rod with uniform strength and area reduction rate deviation and manufacturing method therefor {WIRE ROD WITH UNIFORM VARIATION IN STRENGTH AND REDUCTION AREA AND MANUFACTURING METHOD THEREOF}

The present invention relates to a wire rod having uniform strength and cross-sectional reduction ratio variation, and a method for manufacturing the same, and more particularly, when applying immersion cooling, it is possible to suppress material variation by uniformly cooling the ring edge part and the center part. It relates to a wire rod and a method for manufacturing the same.

After the wire rod is rolled, it is a key technical element for obtaining a high-strength wire rod to secure a fast cooling rate and thus a pearlite structure having a fine lamellar spacing. The reason for controlling the microstructure of the wire rod as described above is that the finer the lamellar spacing, the greater the strength and ductility, which is advantageous in subsequent wire drawing.

On the other hand, the lamellar spacing of pearlite is related to the temperature at which pearlite transformation occurs upon cooling. Specifically, when the cooling rate is relatively fast, the pearlite transformation temperature is low and a fine structure with lamellar spacing is obtained, whereas when the cooling rate is slow, the pearlite transformation temperature is high and a coarse structure with lamellar spacing is obtained. Therefore, it is undesirable that the deviation of the pearlite layer spacing occurs within the wire rod in consideration of the subsequent processing process.

On the other hand, in the case of straightening the hot-rolled wire rod, there is a spatial limitation of the bar equipment in which the length becomes excessive as the wire diameter becomes smaller. Therefore, when cooling the hot-rolled wire rod, it is usually through a laying head. A method of cooling in a state of being wound in the form of a non-concentric circular ring is used. At this time, when the wire moving in a ring shape is viewed from above, there are a ring edge portion having a relatively high material density and a center portion having a relatively low density. This difference in material density acts as a major cause of material material deviation due to non-uniform cooling during subsequent cooling.

Accordingly, the cooling technology of the wire rod has been developed in a direction to secure a high-strength, high-ductility structure by implementing uniform cooling of the ring edge portion and the center portion in order to reduce the material variation of the material while increasing the overall cooling rate.

For example, a technique of immersing a material in a cooling medium such as a salt bath, hot water, or polymer aqueous solution has been proposed instead of the conventional blow cooling (Stelmor method). The immersion cooling method controls the temperature of the cooling medium to obtain a higher cooling efficiency compared to the blowing method, and when the wire rod is immersed in a bath containing the refrigerant, the refrigerant is evenly penetrated into the ring edge with high material density. There is an advantage that relatively uniform cooling can be implemented compared to blow cooling.

However, since the coolant temperature around the edge portion having a high material density is relatively higher than that of the center portion, the edge portion is cooled under a relatively high coolant temperature condition, thereby causing a cooling deviation from the center portion. If the structure of the wire rod cannot be homogenized due to the cooling temperature deviation, the deviation in tensile strength intensifies during subsequent processing, resulting in disconnection, and there is a problem in product reliability.

Accordingly, it is required to develop a wire rod capable of suppressing material deviation between the edge portion and the center portion and a manufacturing method thereof.

An object of the present invention is to provide a wire rod and a method for manufacturing the same, which can suppress material deviation between an edge portion and a center portion while ensuring strength and toughness.

A method of manufacturing a wire rod having uniform strength and cross-sectional reduction ratio deviation according to an embodiment of the present invention, in weight %, C: 0.6 to 0.9%, Si: 0.1 to 0.5%, Mn: 0.2 to 0.9%, Al: 0.05 % or less (excluding 0), manufacturing a wire rod by wire-rolling a billet containing the remaining Fe and unavoidable impurities; winding the wire rod in a coil shape; transferring the wound wire rod to a cooling tank; immersing the transferred wire rod in a cooling bath having a shape in which the depth of the ring edge portion is greater than the depth of the ring center portion; and blowing cooling the wire rod extracted from the cooling tank.

Further, according to an embodiment of the present invention, in the wire rod immersed in the cooling tank, the depth of the edge portion may be 3 times or more and 5 times or less than the depth of the center portion.

In addition, according to an embodiment of the present invention, in the blowing cooling step, it is possible to control the temperature rise of the ring edge portion within 5 seconds after extraction to 50 ℃ or less.

In addition, according to an embodiment of the present invention, the wound wire rod can be transferred to the cooling tank within 3 to 6 seconds.

In addition, according to an embodiment of the present invention, when the ring-shaped wire rod is divided into 8 equal parts, the difference between the maximum value and the minimum value of the tensile strength is less than 3% of the average tensile strength, and the difference between the maximum value and the minimum value of the reduction in area is It may be less than 5% of the average cross-sectional reduction.

The wire rod having uniform strength and cross-sectional reduction rate deviation according to another embodiment of the present invention is, by weight, C: 0.6 to 0.9%, Si: 0.1 to 0.5%, Mn: 0.2 to 0.9%, Al: 0.05% or less ( 0), remaining Fe and unavoidable impurities, and when the ring is divided into 8 equal parts, the difference between the maximum and minimum values of tensile strength is less than 3% of the average tensile strength, and the difference between the maximum and minimum values of the reduction in area is It is less than 5% of the average section reduction.

The wire rod according to the embodiment of the present invention can suppress the material deviation between the edge portion and the center portion while securing strength and toughness, and thus can be applied to various industrial fields.

1 is a diagram schematically illustrating a method of transferring a ring-shaped wire rod.
2 is a view schematically showing a cooling tank of a wire rod according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented in order to sufficiently convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains. The present invention is not limited to the embodiments presented herein and may be embodied in other forms. The drawings may omit the illustration of parts irrelevant to the description in order to clarify the present invention, and may slightly exaggerate the size of the components to help understanding.

Throughout the specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

The singular expression includes the plural expression unless the context clearly dictates otherwise.

1 is a diagram schematically illustrating a method of transporting a ring-shaped wire rod. Referring to FIG. 1, the wire rod is transformed from a straight line to a non-concentric circular coil shape by a laying head. Among the wire rods, the upper and lower edge portions having a high overlap density and a center portion having a relatively low overlap density are formed. exist Hereinafter, the edge portion and the center portion are referred to.

The ring-shaped wire rod goes through a cooling process while being conveyed in an overlapping state by the conveying roller. At this time, due to the difference in the overlap density of the wire coil, there is a difference in the cooling temperature for each part of the wire rod. The deviation of the cooling temperature of the wire rod is proportional to the difference in overlap density, and in the case of high carbon steel with a high carbon content, the deviation of the cooling temperature becomes larger. If the structure of the wire rod cannot be homogenized due to the cooling temperature deviation, the deviation in tensile strength intensifies during subsequent processing, resulting in disconnection, and there is a problem in product reliability.

When a wire rod that has undergone a hot rolling process is drawn without reheating heat treatment, it is the most important issue to minimize the material deviation for each part of the wire rod before drawing.

When the tensile strength and reduction area (RA) were measured by dividing the ring-shaped wire rod into 8 equal parts, the present inventors found that the difference between the maximum and minimum values of tensile strength was less than 5% of the average tensile strength, and the maximum reduction in area was found to be less than 5% of the average tensile strength. When the difference between the value and the minimum value is derived to be less than 5% of the average reduction in section, it was confirmed that there is no problem of material deviation in the final steel wire even if the wire drawing is performed without additional heat treatment, and the present invention was completed.

Hereinafter, a method for manufacturing a wire rod having uniform strength and cross-sectional reduction ratio, which is an aspect of the present invention, will be described in detail.

The wire rod may be manufactured through various wire rod manufacturing techniques commonly known in the art, but preferably may be manufactured through a series of processes to be described later.

The wire rod having uniform strength and cross-sectional reduction ratio according to the disclosed embodiment includes the steps of heating a billet satisfying an alloy composition to be described later, wire rolling the billet, winding the wire into a coil shape, and controlling the wire rod It can be manufactured through a series of processes including the step of immersion cooling under conditions.

Specifically, according to an aspect of the present invention, there is provided a method for manufacturing a wire rod having uniform strength and cross-sectional reduction ratio,

By weight%, C: 0.6 to 0.9%, Si: 0.1 to 0.5%, Mn: 0.2 to 0.9%, Al: 0.05% or less (excluding 0), the remaining Fe and unavoidable impurities, the billet containing Fe and unavoidable impurities preparing a; winding the wire rod in a coil shape; transferring the wound wire rod to a cooling tank; immersing the transferred wire rod in a cooling bath having a shape in which the depth of the ring edge portion is greater than the depth of the ring center portion; and blowing cooling the wire rod extracted from the cooling tank.

Hereinafter, the role and content of each component included in the wire rod according to the present invention will be described. % for the following components means % by weight.

The content of C is 0.6 to 0.9%.

Carbon (C) is an element that forms cementite in a steel wire, and cementite forms pearlite of a layered structure together with ferrite. Since cementite has a higher strength than ferrite, the higher the fraction of cementite, the higher the strength of the material. In addition, as the spacing of the layered structure is uniform and fine, the strength of the material can be further improved.

C is an element that improves the cementite fraction and refines the spacing of the lamellar layered structure, and may be added by 0.6% or more to secure the strength of the wire rod. However, if the content is excessive, the cementite becomes thick and the difference in ductility compared to the adjacent ferrite becomes large and there is a problem that the stress concentration becomes weak, and the upper limit can be limited to 0.9%.

The content of Si is 0.1 to 0.5%.

Si (silicon) is an element that is dissolved in ferrite, which is a matrix, to strengthen steel. can However, when the content is excessive, when the immersion cooling method is applied by greatly increasing the hardenability, there is a problem of overcooling to generate martensite, and the upper limit thereof may be limited to 0.5%.

The content of Mn is 0.2 to 0.9%.

Mn (manganese) is an element that delays pearlite transformation, and may be added in an amount of 0.2% or more in order to easily generate fine pearlite even at a rather slow cooling rate. However, when the content is excessive, when the immersion cooling method is applied by greatly increasing the hardenability, there is a problem of overcooling to generate martensite, and the upper limit thereof may be limited to 0.9%.

The content of Al is 0.05% or less (excluding 0).

Aluminum (Al) is an element that easily reacts with oxygen and is a representative element used for deoxidation in steelmaking. However, when Al exists in steel, there is a risk of generating inclusions, so it is preferable to control so as not to remain in the steel as much as possible.

In addition, Al is involved in the diffusion behavior of carbon at high temperature, and during austenizing heating and maintaining high temperature, it can suppress the reaction of C dissolving from cementite to ferrite, thereby leaving undissolved cementite, the upper limit of which is 0.05 % can be limited.

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 the normal manufacturing process, this cannot be excluded. Since these impurities are known to anyone skilled in the art of manufacturing processes, all details thereof are not specifically mentioned in the present specification.

First, after preparing a billet having the above-described compositional components, a heating step of homogenizing the austenite single phase is performed.

At this time, the range of the heating temperature may be limited to 950 to 1,100 ℃. In the present invention, the heating temperature of the billet was set to 950° C. or higher in order to secure the temperature range for subsequent wire rolling and secure the microstructure of the billet as an austenite single phase. On the other hand, when the heating temperature is excessive, the upper limit of the heating temperature may be limited to 1,100° C. because a problem of poor surface quality occurs due to scale generation and decarburization phenomenon.

Then, the heated billet is wire-rolled and then cooled. At this time, in the wire rod rolling step, it is preferable to perform the finish rolling in a temperature range of 900 to 1,000 ℃.

미만이면, 압연 부하에 의해 압연롤이 파손될 우려가 있으며, 반면 마무리 압연 온도가 1,000℃를 초과하게 되면, 오스테나이트 결정립 크기(Austenite Grain Size, AGS)가 조대해짐에 따라, 추후 냉각단계에서 생성되는 펄라이트 층상간격 및 노듈 크기도 커지게 되어 재질이 열위해지는 문제가 발생한다. Finish rolling temperature is 900

If it is less than, there is a risk that the rolling roll may be damaged by the rolling load. On the other hand, if the finish rolling temperature exceeds 1,000℃, as the austenite grain size (AGS) becomes coarse, the As the spacing between the layers of pearlite and the size of the nodule also increases, there is a problem in that the material is inferior.

Then, it may include a process of cooling to a temperature range for the subsequent winding step through conventional water cooling.

The rolled wire is preferably wound in a ring shape. In the present invention, the winding step may be performed in a temperature range of 750 to 950 °C. Here, the coiling temperature is based on the surface temperature of the wire rod.

Next, a step of transferring the wound wire rod to a cooling tank is performed. After winding, in order to form a scale that acts as a film to protect the material, it is necessary to control the time it takes to move to the cooling tank before immersion. In general, scale is formed on the surface of the hot-rolled wire rod in the process of moving it to the cooling tank in a state exposed to the air. The scale formed on the surface of the wire rod serves as a protective film for the wire rod, so it is important to form it with an appropriate thickness.

At this time, the final scale thickness of the wire rod to which the immersion cooling method is applied depends on the time taken to transfer the wound wire rod to the cooling tank. That is, as the time for transferring the wound wire rod to the cooling tank increases, the thickness of the scale becomes thicker.

In the present invention, by controlling the time from winding to immersion to 3 seconds or more, it was attempted to sufficiently secure the formation of scale serving as a protective film. Considering the problem that scale is formed too thickly and peels off due to thermal shock when immersing in a cooling tank The time from winding up to immersion was limited to 6 seconds or less.

Thereafter, the transferred wire rod is immersed in a cooling bath and cooled.

Specifically, by immersing the ring edge portion in a cooling bath having a shape greater than the depth of the ring center portion, it was attempted to uniformly control the temperature rise of the cooling medium at the edge portion and the center portion.

When the wire rod is immersed in the cooling tank, the temperature of the cooling medium around the wire rod increases little by little as the wire rod is cooled. At this time, the increase in the temperature of the cooling medium is proportional to the amount of heat emitted from the material. Specifically, the higher the mass of the wire rod, the smaller the amount of the cooling medium involved in cooling, the larger the temperature rise of the cooling medium.

If the amount of effective cooling medium involved in cooling is the same at the edge of the wire and the center, the coolant temperature around the edge with high material density is relatively higher than that of the center, so As it cools, a cooling deviation with the center part occurs.

Accordingly, in the present invention, attention is paid to increasing the effective refrigerant amount directly involved in the cooling of the edge portion compared to the center portion, and after a long study, the depth from the edge portion and the center portion to the bottom of the cooling tank has a close effect on the effective coolant amount. found that there is

That is, when the depth from the material to the bottom of the cooling tank is deep, the effective amount of refrigerant increases and the temperature rise of the refrigerant decreases. Conversely, when the depth is shallow, the effective amount of refrigerant decreases and the temperature rise of the refrigerant increases.

Therefore, by immersing in a cooling bath having a shape deeper than the depth of the ring center portion at the ring edge portion, it was attempted to offset the temperature rise of the cooling medium in the ring edge portion having a relatively high material density.

2 is a view schematically showing a cooling tank of a wire rod according to an embodiment of the present invention. In FIG. 2 , the size of the arrow indicates the degree of heat dissipation according to the effective amount of refrigerant. Referring to FIG. 2 , when immersed in a conventional cooling tank, the degree of heat dissipation is similar as the depth of the edge portion and the center portion is the same, and accordingly, a cooling deviation between the edge portion and the center portion occurs. On the other hand, when the depth at the edge of the ring is immersed in a cooling bath having a shape greater than that of the center of the ring, the cooling deviation between the edge and the center can be reduced as the degree of heat dissipation from the edge is greater than that of the center.

Preferably, in consideration of the fact that the density of the edge portion is three or more times that of the center portion, in the wire rod immersed in the cooling tank, the depth of the edge portion may be limited to 3 times or more and 5 times or less of the depth of the center portion.

In addition, the refrigerant in the cooling tank may include at least one selected from the group consisting of high-temperature salt, hot water, and an aqueous polymer solution.

On the other hand, even through the immersion step described above, there are cases in which the pearlite phase transformation is not completed depending on the component system and wire diameter. If the phase transformation in the air is accompanied in this state, there is a problem in that the transformation heat is not suppressed and pearlite having a coarse lamellar interval is formed. This problem is more severe in the edge part with high material density.

Transformation heat is a phenomenon in which a material is locally heated due to a difference in chemical state energy during phase transformation from austenite to pearlite. Transformation heat interferes with heat transfer from the core of the material, which further slows down the cooling rate of the core.

In the present invention, in consideration of this phenomenon, after the wire rod is extracted from the cooling tank, a blow cooling step of controlling the temperature rise of the edge portion to 50° C. or less in a section within 5 seconds was introduced.

If the time after extraction exceeds 5 seconds, it is meaningless to suppress the edge heat generation as the phase transformation in the air is completed. Microstructures with different lamellar spacings of the generated pearlite are derived, and finally, a wire rod with a uniform internal material cannot be secured.

In the case of a wire rod having uniform strength and variation in section reduction rate manufactured according to the above-described manufacturing method, when the ring is divided into 8 equal parts, the difference between the maximum and minimum tensile strength is less than 3% of the average tensile strength, and the maximum value of the reduction in area The difference between and the minimum value is less than 5% of the average cross-sectional reduction rate.

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

Example

After casting an ingot (70Kg) that satisfies the alloy composition shown in Table 1, it is heated in a heating furnace at 1100°C for about 2 hours, and then extracted from the heating furnace and rolled at a temperature of 900°C or higher with wire diameters of 5.5, 8, and 13mm. carried out. Thereafter, the rolled wire rod was cooled by water, and wound at 850° C. to prepare a coil shape.

(weight%) C Si Mn Nb diameter
(mm) Example 1 0.60 0.30 0.90 0.05 5.5 Example 2 0.60 0.10 0.50 0.03 8.0 Example 3 0.60 0.30 0.90 0.05 13.0 Example 4 0.60 0.10 0.50 0.03 5.5 Example 5 0.60 0.50 0.50 0.05 8.0 Example 6 0.70 0.50 0.70 0.01 13.0 Example 7 0.70 0.10 0.20 0.03 5.5 Example 8 0.70 0.30 0.70 0.05 8.0 Example 9 0.70 0.50 0.70 0.01 13.0 Example 10 0.70 0.10 0.20 0.03 5.5 Example 11 0.70 0.30 0.70 0.05 8.0 Example 12 0.80 0.10 0.20 0.01 13.0 Example 13 0.80 0.10 0.20 0.01 5.5 Example 14 0.80 0.50 0.20 0.03 8.0 Example 15 0.80 0.30 0.90 0.01 13.0 Example 16 0.90 0.30 0.90 0.01 5.5 Example 17 0.90 0.50 0.70 0.05 8.0 Example 18 0.90 0.10 0.50 0.03 13.0 Comparative Example 1 0.70 0.10 0.20 0.03 5.5 Comparative Example 2 0.80 0.50 0.20 0.03 8.0 Comparative Example 3 0.90 0.10 0.50 0.03 13.0 Comparative Example 4 0.9 0.1 0.5 0.03 13

Next, according to the conditions described in Table 2, immersion and blowing cooling conditions were changed to cool.

Thereafter, the tensile strength and the reduction in area (RA) were measured by dividing into 8 equal parts for 1 ring of the wire rods of Examples and Comparative Examples, and the average value, the maximum value and the minimum value difference of the average value compared to the average value and the percentage ratio were measured and shown in Table 2 It was. Specifically, the intensity deviation (%) was derived through (maximum intensity-minimum intensity)/average intensity X 100, and RA deviation (%) was derived through (maximum RA-minimum RA)/average RA X 100.

(weight%) Required time from winding to immersion Ratio of edge depth/center depth Maximum exothermic temperature within 5 seconds after extraction Average tensile strength (MPa) strength deviation
(%) Mean RA (%) RA deviation (%) Example 1 3 4 50 1120 2.90 54 5 Example 2 5 4 20 1037 2.50 58.5 4.90 Example 3 6 3.2 50 1050 2.60 61.9 4.70 Example 4 4 3 10 1052 2.30 58.8 4.20 Example 5 6 3.5 40 1081 2.80 55.4 4.50 Example 6 6 3.5 20 1149 2.70 55.0 4.70 Example 7 4 4.2 40 1126 2.90 53.6 4.80 Example 8 3 4.2 20 1180 2.50 48.5 4.60 Example 9 6 4 30 1153 2.30 54.7 4.30 Example 10 6 3 50 1127 2.60 53.5 4.10 Example 11 3 4.2 30 1176 2.80 48.8 3.50 Example 12 4 3.5 30 1164 2.80 54.0 4.20 Example 13 6 4.2 10 1230 2.20 46.3 4.30 Example 14 5 3.2 30 1249 1.50 43.7 3.80 Example 15 5 3 10 1248 2.60 48.1 4.60 Example 16 4 4 20 1420 2.70 33.0 4.70 Example 17 5 3.2 40 1400 2.80 33.1 4.10 Example 18 3 3.5 10 1293 2.50 44.9 4.50 Comparative Example 1 2.9 4.2 40 1130 2.30 53.3 4.30 Comparative Example 2 5 2.9 30 1249 3.02 43.7 5.01 Comparative Example 3 3 3.5 51 1293 3.20 44.9 5.10 Comparative Example 4 3 One 45 1291 3.7 44.8 6.5

Examples and Comparative Examples Tensile strength and section reduction ratio (RA) of each specimen divided into 8 for one ring of wire rod are shown in Table 3 below.

Psalm number One 2 3 4 5 6 7 8 Example 1 TS [MPa] 1,133 1,126 1,101 1,113 1,121 1,124 1,125 1,117 RA [%] 55.0 54.5 52.4 53.4 54.1 54.4 54.5 53.7 Example 2 TS [MPa] 1,021 1,030 1,038 1,041 1,042 1,034 1,047 1,043 RA [%] 56.8 57.9 58.6 58.9 59.0 58.2 59.6 59.0 Example 3 TS [MPa] 1,055 1,047 1,061 1,056 1,033 1,043 1,051 1,054 RA [%] 62.4 61.6 63.1 62.4 60.2 61.3 62.0 62.3 Example 4 TS [MPa] 1,058 1,037 1,045 1,053 1,056 1,057 1,049 1,061 RA [%] 59.3 57.2 58.2 58.9 59.2 59.3 58.5 59.7 Example 5 TS [MPa] 1,078 1,093 1,087 1,063 1,074 1,082 1,085 1,086 RA [%] 55.1 56.4 55.9 53.9 54.8 55.5 55.8 55.9 Example 6 TS [MPa] 1,130 1,142 1,150 1,153 1,154 1,146 1,162 1,155 RA [%] 53.4 54.4 55.1 55.4 55.5 54.7 56.0 55.5 Example 7 TS [MPa] 1,107 1,119 1,127 1,130 1,131 1,123 1,139 1,132 RA [%] 52.0 53.0 53.7 54.0 54.1 53.3 54.6 54.1 Example 8 TS [MPa] 1,192 1,186 1,162 1,173 1,181 1,184 1,185 1,177 RA [%] 49.3 49.0 47.1 47.9 48.6 48.9 49.0 48.2 Example 9 TS [MPa] 1,159 1,137 1,146 1,154 1,157 1,158 1,150 1,163 RA [%] 55.2 53.2 54.1 54.8 55.1 55.2 54.4 55.6 Example 10 TS [MPa] 1131 1132 1124 1139 1133 1109 1120 1128 RA [%] 53.9 54.0 53.2 54.3 54.0 52.1 52.9 53.6 Example 11 TS [MPa] 1,157 1,169 1,177 1,180 1,181 1,173 1,189 1,182 RA [%] 47.6 48.2 48.9 49.2 49.3 48.5 49.3 49.3 Example 12 TS [MPa] 1,177 1,170 1,145 1,157 1,165 1,168 1,169 1,161 RA [%] 54.8 54.5 52.5 53.4 54.1 54.4 54.5 53.7 Example 13 TS [MPa] 1213 1223 1231 1234 1235 1227 1241 1236 RA [%] 45.0 45.7 46.4 46.7 46.8 46.0 47.0 46.8 Example 14 TS [MPa] 1,255 1,255 1,237 1,242 1,250 1,253 1,254 1,246 RA [%] 44.2 44.2 42.5 43.1 43.8 44.1 44.2 43.4 Example 15 TS [MPa] 1,254 1,229 1,241 1,249 1,252 1,253 1,245 1,261 RA [%] 48.6 46.7 47.5 48.2 48.5 48.6 47.8 48.9 Example 16 TS [MPa] 1,436 1,426 1,398 1,413 1,421 1,424 1,425 1,417 RA [%] 33.5 33.5 31.9 32.4 33.1 33.4 33.5 32.7 Example 17 TS [MPa] 1,417 1,406 1,377 1,393 1,401 1,404 1,405 1,397 RA [%] 33.7 33.6 32.3 32.5 33.0 33.5 33.4 32.8 Example 18 TS [MPa] 1,290 1,306 1,299 1,274 1,286 1,294 1,297 1,298 RA [%] 44.6 45.6 45.4 43.6 44.3 45.0 45.3 45.4 Comparative Example 1 TS [MPa] 1,136 1,114 1,123 1,131 1,134 1,135 1,127 1,140 RA [%] 53.8 51.9 52.7 53.4 53.7 53.8 53.0 54.1 Comparative Example 2 TS [MPa] 1,265 1,255 1,227 1,242 1,250 1,253 1,254 1,246 RA [%] 44.5 44.2 42.3 43.1 43.8 44.1 44.2 43.4 Comparative Example 3 TS [MPa] 1,299 1,269 1,286 1,294 1,297 1,298 1,290 1,311 RA [%] 45.4 43.5 44.3 45.0 45.3 45.4 44.6 45.8 Comparative Example 4 TS [MPa] 1,299 1,291 1,308 1,298 1,260 1,287 1,285 1,296 RA [%] 45.3 44.3 46 45.3 43.1 44.2 44.9 45.2

Referring to Table 2, in the wire rods of Examples 1 to 18 satisfying the alloy composition and manufacturing method according to the present invention, the time from winding to immersion is controlled to 3 seconds or more and 6 seconds or less, and the depth of the ring edge portion is By immersing in a cooling tank with a shape deeper than 3 times the depth of the center portion, the temperature rise of the cooling medium in the edge portion and the center portion is uniformly controlled, and the temperature rises in the edge portion within 5 seconds after the wire rod is extracted from the cooling tank. It is possible to satisfy the blowing cooling condition of controlling the temperature to 50° C. or less, thereby securing strength and toughness, as well as suppressing material deviation between the edge portion and the center portion of the wire rod. Accordingly, when the ring-shaped wire rod is divided into 8 equal parts, the difference between the maximum and minimum tensile strength is less than 3% of the average tensile strength, and the difference between the maximum and minimum reduction in area is less than 5% of the average reduction in area. As a result, it was confirmed that the material of the wire rod edge portion and the center portion was uniform.

The alloy compositions of Comparative Examples 1 to 3 satisfy the suggestions of the present invention, but are indicated as Comparative Examples because the manufacturing process conditions are out of the present invention.

Comparative Example 1 is a case in which the strength deviation is less than 3% and the RA deviation is less than 5%, but the time from winding to immersion is less than 3 seconds, so the scale serving as a protective film is not sufficiently formed. When the thickness of the scale is measured in the surface layer part of the cross-section of the material, the protective film is not sufficiently formed means that the area with a thickness of 3 µm or less is 50% or more of the total.

In Comparative Example 2, when the wire rod is immersed and cooled, the depth of the ring edge portion cannot be secured to more than three times the depth of the ring center portion, so the temperature rise of the cooling medium in the ring edge portion having a relatively high material density can be offset. There was no, and the strength deviation was 3.02%, confirming that the material of the wire rod edge part and the center part was not uniform.

In Comparative Example 3, after the wire rod was extracted from the cooling tank, the temperature rise of the edge part could not be suppressed to 50 ° C. or less within 5 seconds, and as a microstructure with different lamellar spacing of pearlite was derived, the strength deviation was 3.20%, The RA deviation was 5.10%, confirming that the material of the edge portion and the center portion of the wire rod was not uniform.

Comparative Example 4 is a case in which the ring edge portion and the center portion are immersed in a conventional cooling bath having a depth ratio of 1. As a cooling deviation occurs between an edge portion having a high material density and a center portion having a relatively low material density, the strength deviation is The deviation of 3.7% and RA was 6.5%, confirming that the material deviation in the edge portion and the center portion of the wire rod was further increased compared to Comparative Examples 1 to 3.

As described above, according to the embodiment of the present invention, when immersion cooling is applied, the ring edge portion and the center portion are cooled uniformly to derive a wire rod having a uniform material of the edge portion and the center portion. Accordingly, it was possible to solve the material deviation problem in the final steel wire even if the wire drawing was directly applied without an additional heat treatment process on the wire rod.

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

Claims (6)

By weight%, C: 0.6 to 0.9%, Si: 0.1 to 0.5%, Mn: 0.2 to 0.9%, Al: 0.05% or less (excluding 0), the remaining Fe and unavoidable impurities, the billet containing Fe and unavoidable impurities preparing a;
winding the wire rod in a coil shape;
transferring the wound wire rod to a cooling tank;
immersing the transferred wire rod in a cooling bath having a shape in which the depth of the ring edge portion is greater than the depth of the ring center portion; and
A method of manufacturing a wire rod having uniform strength and cross-sectional reduction ratio, comprising the step of cooling the wire rod extracted from the cooling tank by blowing. According to claim 1,
In a wire rod immersed in a cooling tank, the edge portion depth is 3 to 5 times the depth of the center portion, and a method of manufacturing a wire rod with uniform strength and cross-sectional reduction rate deviation. According to claim 1,
In the blowing cooling step, the method of manufacturing a wire rod having uniform strength and cross-sectional reduction rate deviation in which the temperature rise of the ring edge portion is controlled to 50° C. or less within 5 seconds after extraction. According to claim 1,
A method of manufacturing a wire rod having uniform strength and cross-sectional reduction rate deviation, in which the wound wire rod is transferred to a cooling tank within 3 to 6 seconds. According to claim 1,
When the ring-shaped wire rod is divided into 8 equal parts, the difference between the maximum and minimum tensile strength is less than 3% of the average tensile strength,
A method of manufacturing a wire rod with uniform strength and variation in the reduction in area in which the difference between the maximum and minimum values of the reduction in area is less than 5% of the average reduction in area. By weight%, C: 0.6 to 0.9%, Si: 0.1 to 0.5%, Mn: 0.2 to 0.9%, Al: 0.05% or less (excluding 0), the remainder including Fe and unavoidable impurities,
When the ring is divided into eight equal parts, the difference between the maximum and minimum values of tensile strength is less than 3% of the average tensile strength, and the difference between the maximum and minimum values of the reduction in area is less than 5% of the average reduction in area. .

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