KR102075219B1 - Manufacturing method for high carbon steel wire rod reduced mechanical property deviation - Google Patents

Abstract

According to an aspect of the present invention, a method of manufacturing a high carbon steel wire rod having reduced material deviation provides an optimum condition for a movement speed of a conveyor in a cooling process of a high carbon steel wire rod and an air flow amount provided for cooling the high carbon steel wire rod. The material deviation of the center and the edge of the high carbon steel wire can be effectively reduced.

Description

Manufacturing method for high carbon steel wire rod reduced mechanical property deviation}

The present invention relates to a method for manufacturing a high carbon steel wire rod having a reduced material deviation, and more particularly, to a method for manufacturing a high carbon steel wire rod which effectively improves a material deviation caused by a cooling deviation.

Recently, in order to improve fuel efficiency, secure safety, and improve the controllability of automobiles, there is a growing demand for lighter weight of automotive tires. In order to reduce the weight of the tire, the amount of rubber used must be reduced, and to increase the strength of the tire cord is essential. When the strength of the tire cord is increased by about 10%, the weight of the rubber required for tire production is reduced by about 10%, so that the tire for automobile can be effectively lightened by improving the strength of the tire cord. In addition, reducing the weight of the tire cord itself also greatly contributes to the weight reduction of the tire for cars, the demand for high strength ultra-fine steel wire is increasing. In addition, the ultrafine steel wire is rapidly increasing the disconnection rate during processing, it is urgent to develop a material deviation reduction technology to improve this.

Republic of Korea Patent Publication No. 10-0711404 (August 30, 2007)

According to one aspect of the invention, there can be provided a method for producing a high carbon steel wire with reduced material deviation.

The subject of this invention is not limited to what was mentioned above. Those skilled in the art will have no difficulty understanding the additional subject matter of the present invention from the general contents of this specification.

High carbon steel wire with reduced material deviation according to an aspect of the present invention, in weight percent, C: 0.9 ~ 0.93%, Mn: 0.25 ~ 0.35%, Si: 0.15 ~ 0.25%, the remaining Fe and other unavoidable impurities In addition, the microstructure is a pearlite structure, has an average tensile strength of 1175 ~ 1275MPa, the tensile strength deviation of the center side and the edge side of the wire coil may be 15MPa or less.

Method for producing a high carbon steel wire with reduced material deviation according to an aspect of the present invention, in weight%, C: 0.9 ~ 0.93%, Mn: 0.25 ~ 0.35%, Si: 0.15 ~ 0.25%, the remaining Fe and other unavoidable Reheating the billet containing impurities; Rolling the billet to provide a wire coil; First cooling the wire coil at a first cooling rate; The primary cooled wire coil may be secondly cooled at a second cooling rate slower than the first cooling rate.

The primary cooling and the secondary cooling may be performed on a conveyor belt for transporting the wire coil in one direction.

The second cooling rate may be gradually decreased along the traveling direction of the wire coil.

The movement speed of the wire rod coil may gradually increase along the movement path of the wire rod coil.

The movement path of the wire rod coil is divided into a first section corresponding to the primary cooling and a second section corresponding to the secondary cooling, and the air blowing amount provided for cooling the wire rod coil in the first section is the wire coil. The blowing amount is equally supplied along the moving direction of and the blowing amount provided for cooling the wire rod coil in the second section may be gradually decreased along the moving direction of the wire rod coil.

At the start point of the second section, the air volume is blown at an air volume corresponding to the air volume of the end point of the first section, and at the end point of the second section, the air volume is 70-90% of the air volume at the start point of the second section. have.

According to an aspect of the present invention, a method of manufacturing high carbon steel with reduced material deviation provides optimal flow rates for a conveyor moving speed and cooling of a high carbon steel wire rod in a cooling process of a high carbon steel wire rod. Material deviation of the center and the edge of the carbon steel wire rod can be effectively reduced.

The present invention relates to a method for manufacturing a high carbon steel wire with reduced material deviation, and will be described below in the preferred embodiments of the present invention. Embodiments of the invention may be modified in various forms, the scope of the invention should not be construed as limited to the embodiments described below. These embodiments are provided to explain in detail the present invention to those skilled in the art.

Hereinafter, the steel composition of the present invention will be described in more detail. Hereinafter, unless otherwise indicated,% indicating the content of each element is based on weight.

High carbon steel wire with reduced material deviation according to an aspect of the present invention, in weight percent, C: 0.9 ~ 0.93%, Mn: 0.25 ~ 0.35%, Si: 0.15 ~ 0.25%, the remaining Fe and other unavoidable impurities can do.

C: 0.9 to 0.93%

C is an element contributing to the strength improvement of the material. For example, when 0.1% is added, the strength may be improved to about 100 MPa. The present invention is to provide a high-strength tire cord wire bar, the C content for securing strength may be 0.9% or more. However, when the content of C is excessively added, it is highly likely that the cornerstone cementite is formed, and increases not only the strength of the material but also the hardness, and the upper limit of the C content of the present invention may be limited to 0.93%.

Mn: 0.25-0.35%

Mn is an austenite stabilizing element and also an element contributing to strength improvement. Therefore, in order to achieve this effect, the present invention may include 0.25% or more of Mn. However, Mn is an element which is easily arranged at the grain boundary, and easily forms a quenched structure such as bainite and martensite in the Mn segregation part, so that the workability may be reduced during the drawing process. You can limit it to

Si: 0.15 ~ 0.25%

Si is an element used as a deoxidizer and is an element which contributes to strength improvement and toughness improvement. Therefore, the present invention can limit the lower limit of the Si content to 0.15% to achieve this effect. On the other hand, when the content of Si is excessive, causing ductility reduction, the present invention can limit the upper limit of the Si content to 0.25%.

Hereinafter, the microstructure and physical properties of the present invention will be described in more detail.

The high carbon steel wire rod having a reduced material deviation according to an aspect of the present invention may include a pearlite structure as a microstructure. The high carbon steel wire rod with reduced material deviation according to an embodiment of the present invention is intended to have a uniform pearlite structure on the surface side and the center side of the wire rod, and to suppress the formation of the quench structure in the wire rod as much as possible. This is because when the quenching structure is mixed, the material deviation of wire rod and the disconnection of wire drawing are likely to occur, and the quality of the final tire cord may be degraded.

The high carbon steel wire rod having a reduced material deviation according to an aspect of the present invention may have an average tensile strength of 1175 to 1275 MPa, and a variation in tensile strength between the center side and the edge side of the wire coil may be 15 MPa or less. That is, the high carbon steel wire with reduced material deviation according to an aspect of the present invention has a tensile strength suitable for high-strength tire cords, in particular, the tensile strength deviation of the center coil and the edge of the wire coil by uniform cooling of the wire coil Can be secured at a level of 15 MPa or less. Therefore, the wire coil according to an aspect of the present invention can sufficiently prevent the lowering of the error rate due to disconnection at the time of drawing, and can effectively prevent the deterioration of the final product.

Hereinafter, the manufacturing method of the present invention will be described in more detail.

According to an aspect of the present invention, there is provided a method of manufacturing a high carbon steel wire with reduced material deviation, the method comprising: reheating a billet provided with the aforementioned composition; Rolling the billet to provide a wire coil; First cooling the wire coil at a first cooling rate; The primary cooled wire coil may be secondly cooled at a second cooling rate slower than the first cooling rate.

The composition content of the billet of the present invention corresponds to the composition content of the above-described steel bar, the description of the reason for limiting the composition content of the billet of the present invention will be replaced by the description of the reason for limiting the composition content of the steel described above.

Billet Reheat

Reheating of the billet may be carried out at a temperature of 900 ° C. or higher to form a uniform austenite structure. However, when the reheating temperature of the billet is excessively high, it may cause furnace damage due to high heat, and economically undesirable, the upper limit of the billet reheating temperature of the present invention may be 1100 ° C.

Rolling

The reheated billet may be rolled to provide a wire coil, and the finish rolling temperature may be performed at 800 to 1050 ° C. In order to prevent excessive rolling load, the finish rolling temperature may be 800 ° C. or higher, and preferably 900 ° C. or higher. If the finish rolling temperature is excessively high, the final pearlite structure may be excessively coarse by inhibiting austenite recovery, recrystallization and grain growth. Therefore, the upper limit of the finishing rolling temperature of this invention may be 1000 degreeC.

Cooling

Cooling of the present invention can be carried out by blowing cooling air to the wire coil transported on the conveyor belt. That is, after the end of rolling, the wire coil is sequentially deposited on the conveyor belt, and moves in one direction along the conveyor belt. On one side of the conveyor belt, a plurality of blowers are arranged at regular intervals along the longitudinal direction of the conveyor belt, and the respective blowers operate to blow cooling air toward the wire coil moving along the conveyor belt to cool the wire. You can. Conveyor belts are divided by sections, and the moving speed can be adjusted independently for each section, and the blowers disposed along the conveyor belt can also individually control the airflow.

In general, the wire rods stacked on the conveyor belt are piled up with the preceding material and the trailing material overlapped with each other, and the loading density at the center side of the wire coil and the edge density side of the wire coil are remarkably different. In general, the loading density on the edge portion of the wire rod coil may be about 10 times the loading density on the central portion. Therefore, even if cooling is performed by the blower, the edge portion side of the wire rod coil is cooled slowly compared with the center side of the wire rod coil, and thus, a material deviation of the wire rod coil may occur. Accordingly, the present invention is to provide an optimum cooling conditions, to provide a method for producing a minimum material deviation of the wire coil.

The movement path of the wire rod moving by the conveyor belt may be divided into a first section and a second section according to the cooling speed of the wire rod coil. That is, the wire rod coil may be cooled at the first cooling rate in the first section, and the wire coil may be cooled at the second cooling rate in the second section.

Specifically, the moving speed of the wire rod coil may be gradually adjusted upward along the movement path of the wire rod coil. In addition, although the blowing amount in the first section may be supplied uniformly along the moving direction of the wire rod coil, the blowing amount in the second section may be supplied to gradually decrease along the moving direction of the wire rod coil. In addition, the blowing amount at the end point of the first section and the blowing amount at the start point of the second section may correspond to each other, and the blowing amount at the end point of the second section may be 70 to 90% of the blowing amount at the start point of the second section. That is, the average blowing amount in each section in the first section is maintained higher than the average blowing amount in each section in the second section, and the average blowing amount in each section in the second section gradually decreases along the moving direction of the wire rod. The blowing amount at the end point of the second section may be maintained at a level of 70 to 90% of the blowing amount at the end point of the first section.

The present invention divides the movement path of the wire rod coil into a first section and a second section. In the first section, a relatively rapid cooling condition may be provided, and in the second section, a relatively slow cooling condition may be provided. Slow cooling conditions can be provided in which the air flow gradually decreases. Therefore, the microstructure of the high carbon steel by the cooling of the present invention can be provided with a uniform pearlite structure. That is, based on the continuous cooling transformation curve (CCT curve), the wire coil of the present invention is cooled between the pearlite transformation start point and the end point, thereby providing a uniform pearlite structure as a microstructure.

Specifically, the primary cooling may be started in the temperature range of 650 ~ 750 ℃ and end in the temperature range of 450 ~ 550 ℃, it can be quenched to the transformation start point of the pearlite tissue in the primary cooling. Therefore, formation of the cornerstone cementite inside a wire rod can be suppressed as much as possible. In addition, the secondary cooling is started in the temperature range of 450 ~ 550 ° C and ends in the temperature range of 150 ~ 250 ° C, the cooling rate of the secondary cooling may be gradually reduced along the direction of movement of the wire coil. Therefore, it is possible to provide an optimum constant temperature transformation condition for pearlite transformation in the secondary cooling, thereby forming a uniform pearlite structure in the central portion and the surface layer portion of the wire rod.

In addition, the feed speed of the wire rod coil may be adjusted to increase gradually along the moving direction of the wire rod coil. That is, the moving speed of the wire rod coil in the first section and the second section gradually increases along the moving direction of the wire rod coil, and the moving speed of the wire rod coil in the second section is higher than the moving speed of the wire rod coil in the first section. It can be faster. Accordingly, the distance between the wire rod coils can be widened along the moving direction of the wire rod coil, thereby effectively eliminating the phenomenon in which heat inside the wire rod coil aggregates at the edge of the wire rod coil.

The present invention will be described in more detail with reference to the following examples.

(Example)

The wire coils were manufactured by hot rolling the billets prepared under the same conditions, and the wire coils were cooled under the conditions described in Tables 1 and 2 below. Table 1 means the speed of the conveyor belt for each section, Table 2 means the blowing amount for each section. In Table 1 and Table 2, # means the number of the conveyor belt, and the air volume 100 of Table 2 means the maximum air volume of the individual blower.

division First section speed
(m / s) 2nd section speed
(m / s) #One #2 # 3 # 4-11 # 12 Comparative example 0.75 0.75 0.75 0.75 0.75 Example 1 0.75 0.80 0.85 0.85 0.95 Example 2 0.80 0.85 0.90 0.90 0.95

division First section air flow rate Second section airflow #One #2 # 3 #4 # 5 # 6 # 7 #8 # 9 # 10 # 11 # 12 Comparative example 50 100 100 100 100 100 100 100 100 100 100 100 Example 1 50 100 100 100 100 90 90 90 90 80 80 70 Example 2 50 100 100 80 80 80 80 80 70 70 70 70

The tensile strengths of the edge and the center were measured for each wire rod under the conditions of Table 1 and Table 2, and the average of the tensile strength and the variation of the tensile strength of the edge and the center are shown in Table 3 below. In addition, each wire rod was processed by the conditions of Table 1 and Table 2, the defect rate during the drawing process is also shown in Table 3 below.

division The tensile strength
(MPa) Tensile Strength Deviation
(MPa) Defective rate
(%) Comparative example 1292 26.3 3.6% Example 1 1245 12.6 0.1% Example 2 1242 12.1 0.08%

As shown in Table 3, in Examples 1 and 2 satisfying the conditions of the present invention, it has a tensile strength in the range of 1175 ~ 1275MPa, it can be confirmed that the deviation of the tensile strength is also good to the level of 15MPa or less. In addition, in the case of Examples 1 and 2, the defect rate at the time of drawing is 0.1% or less, it can be confirmed that the drawing workability is excellent.

On the other hand, in the comparative example, the tensile strength was excessively high due to subcooling, and it was confirmed that the deviation of the tensile steel exceeded 15 MPa because it did not provide cooling conditions for the initial quenching and the late slow cooling. In addition, in the case of the comparative example, the defective rate during the fresh processing exceeds 3%, it can be confirmed that the workability is relatively inferior.

Accordingly, the method of manufacturing a high carbon steel wire rod having a reduced material deviation according to an aspect of the present invention provides an optimum condition for a conveyor moving speed and a cooling amount provided for cooling the high carbon steel wire rod in a cooling process of the high carbon steel wire rod. Bar, material deviation of the center and the edge of the high carbon steel wire can be effectively reduced.

Although the present invention has been described in detail through the embodiments, other forms of embodiments are also possible. Therefore, the spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (6)

delete By weight, reheating the billet comprising C: 0.9-0.93 wt%, Mn: 0.25-0.35%, Si: 0.15-0.25%, remaining Fe and other unavoidable impurities;
Rolling the billet to provide a wire coil;
First cooling the wire coil at a first cooling rate;
The primary cooled wire coil is second cooled at a second cooling rate slower than the first cooling rate,
The movement path of the wire coil is divided into a first section corresponding to the primary cooling and a second section corresponding to the secondary cooling,
The blowing amount provided for cooling the wire rod coil in the first section is equally supplied along the moving direction of the wire rod coil,
The blowing amount provided for cooling the wire rod coil in the second section is supplied to gradually decrease along the moving direction of the wire rod coil, and the second cooling rate is gradually decreased along the traveling direction of the wire rod coil.
At the start point of the second section, the air blowing amount is blown at a blowing amount corresponding to the blowing amount at the end point of the first section,
The method of manufacturing a high carbon steel wire rod with reduced material deviation, which is blown at the end point of the second section at a blowing amount of 70 to 90% of the start point of the second section. The method of claim 2,
The primary cooling and the secondary cooling is carried out on a conveyor belt for conveying the wire coil in one direction, a material deviation reduced high carbon steel wire manufacturing method. delete delete delete