KR102181731B1 - High strength steel wire with improved drawability and the method for manufacturing the same - Google Patents

Abstract

A high-strength steel wire with improved drawability is disclosed. The disclosed steel wire is a weight percent, C: 0.95 to 1%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.3%, Cr: 0.4 to 0.8%, the rest contains Fe and inevitable impurities, and the reduction ratio (reduction ratio) ) Is 40% or more, and the tensile strength is 1,800Mpa or more.

Description

High strength steel wire with improved drawability and its manufacturing method {HIGH STRENGTH STEEL WIRE WITH IMPROVED DRAWABILITY AND THE METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a high-strength steel wire having excellent drawability and a manufacturing method thereof.

In general, several methods can be used to obtain a high-strength steel wire.

First of all, a method of increasing the strength of the material itself can be used. That is, as one of the methods for obtaining a high-strength steel wire, a method of increasing the strength of the material itself by adding a large amount of a reinforcing element that increases the strength of the steel may be used. A representative example of such a strengthening element is carbon. When the carbon content increases, the fraction of hard cementite inside the wire rod increases, and the lamellar spacing of the pearlite structure becomes dense, so that the strength of the material is improved. In addition to carbon, technologies for adding various alloying elements have been proposed.

Alternatively, a method of increasing the work hardening rate can be used. Steel wires and the like are manufactured by drawing and heat treatment of a rolled wire rod. Strength can be significantly improved by increasing the work hardening rate when drawing the wire rod. That is, when the work hardening rate is increased during wire drawing, the lamellar spacing becomes finer, the work hardening coefficient increases, and the degree of integration of dislocations increases, thereby increasing the strength of the steel wire.

As another method, strength can be improved by increasing the wire strain rate of the steel wire. At this time, the wire strain rate of the material is closely related to the ductility of the material, and the strength is improved as the material itself is easily processed without disconnection during wire drawing.

Since all of the above-described methods do not work independently but are interrelated to change the strength of the steel wire, there is a limit to improving the strength of the steel wire by controlling them independently.

Due to the addition of an alloying element during the manufacture of high-strength steel, a disconnection occurs in the subsequent steel wire manufacturing process after the wire rod rolling, and the conductivity of the steel wire decreases. Therefore, there is a need to develop a steel that can increase the strength while securing the drawability by grasping the degree of influence of the alloying element on the strength of the steel wire.

Embodiments of the present invention are intended to provide a high-strength steel wire with improved drawability while securing strength and a method of manufacturing the same.

The high-strength steel wire with improved drawability according to an embodiment of the present invention is weight %, C: 0.95 to 1%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.3%, Cr: 0.4 to 0.8%, and the rest is Fe And inevitable impurities, a reduction ratio of 40% or more, and a tensile strength of 1,800 MPa or more.

In addition, the electrical conductivity of the steel wire may be 8% IACS or more.

In addition, the tensile strength of the steel wire may be 1,800 to 2,300Mpa.

The method of manufacturing a high-strength steel wire with improved drawability according to an embodiment of the present invention is in wt%, C: 0.95 to 1%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.3%, Cr: 0.4 to 0.8%, The rest of the wire rod containing Fe and inevitable impurities are wired to a strain (e) in the range of 1.65 to 1.80 to obtain a steel wire; And heat-treating the steel wire at 280 to 350°C.

In addition, prior to the wire drawing, the step of LP heat treatment; may further include.

In addition, the LP　 heat treatment temperature may be 500 ~ 630 ℃.

According to the present invention, it is possible to provide a steel wire having high strength by suppressing the occurrence of delamination, which acts as an obstacle for increasing strength, and having excellent torsional characteristics as well as increasing freshness.

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 exemplary embodiments presented here, but may be embodied in other forms. In the drawings, in order to clarify the present invention, portions not related to the description may be omitted, and sizes of components may be slightly exaggerated to aid understanding.

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

Singular expressions include plural expressions, unless the context clearly has exceptions.

The high-strength steel wire with improved drawability according to an aspect of the present invention is in wt%, C: 0.95 to 1%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.3%, Cr: 0.4 to 0.8%, and the remainder is Fe and It contains inevitable impurities, has a reduction ratio of 35% or more, and a tensile strength of 1,800Mpa or more.

Hereinafter, the reason for limiting the numerical value of the content of the alloying component in the examples of the present invention will be described. Hereinafter, unless otherwise specified, the unit is% by weight.

The content of C is 0.95 to 1%.

Carbon (C) is an element added to improve the strength of the steel wire, and it is preferable to add 0.95% or more. However, when the content is excessive, strength improvement is obtained, but there is a problem that ductility is lowered, and the upper limit thereof may be limited to 1%.

The content of Mn is 0.3 to 0.8%.

Manganese (Mn) is an element that is effective in increasing the hardenability and can be added by 0.3% or more. However, if the content is excessive, there is a problem of causing central segregation and causing low-temperature tissue, and the upper limit can be limited to 0.8%.

The content of Si is 0.1 to 0.3%.

Silicon (Si) is a solid solution element in a ferrite phase, and may be added 0.1% or more to secure strength. However, when the content is excessive, the ferrite phase is taken out and there is a problem in the wire drawing process, and by forming a stress field during solid solution in ferrite, the movement of free electrons is strongly suppressed, thereby reducing the conductivity of the steel wire. Therefore, the upper limit can be limited to 0.3%.

The content of Cr is 0.4 to 0.8%.

Chromium (Cr) is a component that improves strength and ductility by miniaturizing the layered structure of pearlite, and is preferably added in an amount of 0.4% or more. However, if the content is excessive, the constant temperature transformation rate is reduced to affect productivity, and the upper limit may be limited to 0.8%.

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

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

A method of manufacturing a high-strength steel wire with improved drawability according to another aspect of the present invention, in weight%, C: 0.95 to 1%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.3%, Cr: 0.4 to 0.8% , Obtaining a steel wire by drawing the wire rod containing Fe and inevitable impurities in the range of 1.65 to 1.80% of the rest; And heat-treating the steel wire at 280 to 350°C.

The steel wire of the present invention can be manufactured by manufacturing a wire rod satisfying the above-described alloy composition, and then passing through a process of drawing the wire rod.

First, a billet having the above composition is hot-rolled at 850 to 1,100°C, and then cooled to manufacture a wire rod. In order for the manufactured wire rod to be suitable for wire drawing, it is preferable to heat-treat the wire rod before wire drawing. The LP heat treatment refers to a process of transforming a wire rod heat-treated at a high temperature into a structure suitable for wire drawing by quenching in a lead bath.

According to the disclosed embodiment, it is preferable to form fine pearlite by heat treating the wire rod at 500 ~ 630 °C.

During the LP　 heat treatment, if the temperature is less than 500°C, there is a concern that a low-temperature structure will occur and deteriorate the wire drawing. On the other hand, if the temperature exceeds 630°C, the pearlite layer spacing becomes coarse and thus strength cannot be secured. have.

Thereafter, in order to increase the strength of the wire rod subjected to LP heat treatment, the steel wire is manufactured by wire drawing.

When drawing the wire rod, the wire drawing can be controlled so that the strain (ε) of the wire rod satisfies the range of 1.65 to 1.80%. If the strain rate of the wire rod is less than 1.65%, sufficient strength cannot be secured, and if it exceeds 1.65%, there is a problem that the wire breakage occurs due to excessive work hardening.

The strain (e) is expressed as 2ln(di/df). Here, di means the initial diameter of the steel wire before wire drawing, and df means the diameter of the steel wire after wire drawing.

After wire drawing, heat treatment is performed on the steel wire in a temperature range of 280 to 350°C. When the heat treatment temperature is less than 280° C., aging occurs in the steel wire, making it difficult to move dislocations, and thus wire-drawing processability cannot be secured. On the other hand, when the heat treatment temperature exceeds 350°C, the sheet-like cementite contained in the pearlite structure of the steel wire changes into a spherical shape, and thus tensile strength cannot be secured.

As described above, in the disclosed embodiment, heat treatment is performed after wire drawing, thereby suppressing the occurrence of delamination and improving torsion characteristics. In more detail, the disclosed embodiment may increase the cross-sectional reduction rate of the steel wire to 40% or more by performing heat treatment after wire drawing, prevent the occurrence of delamination of the steel wire during stranded wire processing, and have a tensile strength of 1800 MPa or more and Conductivity of 8% IACS or more can be secured.

Therefore, the steel wire according to the disclosed embodiment can be applied to an ACSR (Aluminum Conductor Steel Reinforced) (ACSR) steel wire for a transmission line in which the above characteristics are required.

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

A wire rod was manufactured by hot rolling an ingot having a component range of Table 1 at 900°C.

division Ingredient (% by weight) C Si Mn Cr Invention Lecture 1 0.92 0.15 0.5 0.6 Invention Lecture 2 0.97 0.2 0.5 0.6 Comparative lecture 1 0.97 2.0 0.5 0.3

Thereafter, wire drawing and heat treatment were performed under the conditions of Table 2 below to manufacture a steel wire.

The mechanical properties (tensile strength, cross-sectional reduction rate, and delamination occurrence) of the prepared Examples and Comparative Examples were measured, and the results are shown in Table 2 below.

Tensile strength was measured by processing a tensile specimen of the hot-rolled wire rod according to ASTM E8 standard, and then performing a tensile test after following the above-described steel wire manufacturing method.

RA means the reduction ratio, and it is a measurement of the change in the cross-sectional area of the tensile specimen broken during the tensile test of the material, and expresses the ductility of the material as a numerical value.

In addition, the number of rotations until the breakage of the steel wire was taken as the number of twists in the torsion test in which the lateral stress was applied, and it was checked whether or not a helical break failure appeared in the broken part of the wire, and the presence or absence of delamination was shown in Table 2 below.

division Wire Manufacture process Mechanical properties Conductivity
(%IACS) Fresh strain (%) Heat treatment temperature The tensile strength
(MPa) RA(%) Whether or not delamination has occurred Example 1 Invention Lecture 1 1.71 330℃ 2040 54 Not occurring 8.45 Example 2 Invention Lecture 2 1.71 330℃ 2164 51 Not occurring 8.42 Comparative Example 1 Invention Lecture 1 1.92 240℃ 2163 56 Occur 8.41 Comparative Example 2 Invention Lecture 2 1.71 240℃ 2199 57 Occur 8.40 Comparative Example 3 Comparative lecture 1 1.71 240℃ 1976 27 Occur 4.79 Comparative Example 4 Comparative lecture 1 1.71 330℃ 2163 28 Occur 4.80

As shown in Table 2, Examples 1 and 2 prepared with components and conditions conforming to the present invention not only secured a tensile strength of 2,200 MPa or more, but also had a RA of 40% or more, and delamination It can be seen that this did not occur. Therefore, it can be seen that according to the disclosed embodiment, the strength can be increased without reducing the ductility.

In addition, Examples 1 and 2 showed a conductivity of 8% IACS or more, and thus can be applied to materials for transmission lines. It is believed that this is due to the alloy design of the present invention in which the content of Si, which is a solid solution strengthening element, is reduced to 0.3% or less to facilitate the movement of free electrons to secure electrical conductivity.

In addition, in the case of Examples 1 and 2, by increasing the heat treatment temperature compared to Comparative Examples 2 and 3 to suppress the aging phenomenon, even if the strain in the suggested range was applied, the occurrence of delamination of the steel wire was suppressed.

On the other hand, in Comparative Example 1, the wire strain rate was 1.92%, out of the range of 1.65 to 1.80%, and delamination occurred during wire drawing due to excessive work hardening.

In Comparative Example 2, the heat treatment temperature was as low as 240° C., and the dislocation was difficult to move, and delamination occurred during wire drawing.

Comparative Examples 3 and 4 showed that the RA value was less than 40%, indicating that the material was not sufficiently softened. This may deteriorate the ductility of the steel wire and deteriorate the wire drawing. In addition, since the conductivity is less than 8% IACS, it is unreasonable to apply to the material for transmission line targets in the present invention.

In conclusion, in wt% according to the disclosed embodiment, C: 0.95 to 1%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.3%, Cr: 0.4 to 0.8%, the rest is a steel wire containing Fe and inevitable impurities By optimizing the wire strain and heat treatment temperature, it is possible to increase the strength while securing the wire drawability and conductivity.

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

Claims (6)

In wt%, C: 0.95 to 1%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.3%, Cr: 0.4 to 0.8%, the remainder contains Fe and inevitable impurities,
The reduction ratio is more than 40%,
The tensile strength is 1,800 to 2,300Mpa,
High-strength steel wire with improved drawability with a conductivity of 8%IACS or higher delete delete In wt%, C: 0.95 to 1%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.3%, Cr: 0.4 to 0.8%, the remainder is LP heat treatment at 500 to 630 °C of a wire including Fe and inevitable impurities The step of doing;
Obtaining a steel wire by wire drawing the LP heat-treated wire rod at a strain rate (e) of 1.65 to 1.80%; And
Heat-treating the steel wire at 280 to 350°C; Method for manufacturing a high-strength steel wire with improved drawability. delete delete