KR20160082622A - Wire rod and steel wire having high strength and manufacturing method for the same - Google Patents

Abstract

The present invention relates to a high-strength wire material which has an enhanced processing hardening rate through using vanadium carbides precipitated from a martensite structure, a steel wire, and a manufacturing method thereof. According to an embodiment of the present invention, the high-strength wire material with the enhanced processing hardening rate includes: 0.1 to 0.4 wt% of C; 0.4 to 1.7 wt% of V; 0.001 to 0.2 wt% of Si; 0.1 to 0.2 wt% of Mn; 0.025 or less wt% of P; 0.026 or less wt% of S; 0.001 to 0.03 wt% of Ti; 0.001 to 0.003 wt% of B; residual P; and other unavoidable impurities. The V and C satisfies the relational formula 1. The V and C represent the content of each element in wt%.

Description

TECHNICAL FIELD [0001] The present invention relates to a high strength wire, a heat-treated wire,

TECHNICAL FIELD The present invention relates to a high-strength wire rod, a heat-treated wire rod, a steel wire, and a method of manufacturing the same, which are excellent in work hardening rate.

Daekyung Steel Wire is used for PC steel wire, cable for bridge, anchor rope, etc. used for reinforcing concrete, and it is required to secure high strength. By securing such characteristics, it becomes possible to simplify the twisted structure, so that the weight of the steel wire is reduced and the span distance between the bridges is increased.

Examples of the method of increasing the strength of the steel wire include a method of external drawing a wire having a high carbon pearlite structure and a method of increasing the strength by grain refinement.

The steel wire or the like is drawn and annealed to produce a pearlite microstructure. By increasing the work hardening rate during drawing of the wire rod, the strength can be greatly improved. That is, when the work hardening rate is increased in the drawing process, the lamellar spacing becomes finer, the work hardening coefficient increases, and the integration degree of dislocation increases, so that the strength of the steel wire increases.

Although the above method effectively increases the strength of the steel wire, there is a problem that the ductility of the high carbon steel itself is low, and the fresh wire maker can not give a fresh machining amount as desired.

On the other hand, there are various methods such as increasing the solid solution strengthening elements such as C, Si, and Mn, or increasing the work hardening rate by adding Cr. However, there are limitations in increasing the strength of the large diameter steel wire .

In order to solve this problem, the inventors of the prior art tried to utilize a composite structure steel made of ferrite, bainite, martensite, etc. instead of pearlite structure steel as a drawing wire. In order to avoid plate-shaped martensite, the wire having a composite structure has a carbon concentration of 0.5 wt% or less, so that the work hardening rate through drawing is lower than that of the pearlite structure steel.

Therefore, there is a demand for development of high-strength wire materials, steel wires and methods for manufacturing them, which have excellent work hardening rates.

It is an object of the present invention to provide a high-strength wire rod and a heat-treated wire rod excellent in work hardening ratio by appropriately controlling the contents of V and C and microstructure, and a method of manufacturing them.

One aspect of the present invention is

0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities, V and C satisfy the following relational expression 1,

Wherein the microstructure is a ferrite single phase and comprises vanadium carbide.

[Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

The number of the vanadium carbides may be 1.2 x ^{10 8} / mm ² or more, and the size may be 20 to 500 nm.

The tensile strength of the wire may be 730 MPa or more.

Another aspect of the present invention is

0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities, V and C satisfy the following relational expression 1,

The microstructure is a rut-martensite single phase, and includes a vanadium carbide.

[Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

The tensile strength of the heat-treated wire rod may be 1230 MPa or more.

Another aspect of the present invention is

0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , 0.001 to 0.003% of B, and the balance of Fe and other unavoidable impurities, wherein V and C satisfy the following relational expression 1, the microstructure is a rath-martensite single phase, and the ruthenes of the martensite are arranged in the drawing direction And a high strength steel wire including vanadium carbide.

 [Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

The tensile strength of the steel wire may be 1960 MPa or more and the section reduction ratio may be 30% or more.

Another aspect of the present invention is

0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities,

Heating the slab having V and C satisfying the following relational expression 1 at 1000 to 1150 캜;

Hot-rolling the heated billet to obtain a wire rod; And

And cooling the wire rod at a cooling rate of 1 to 10 ° C / second.

[Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

The hot rolling may be performed at a temperature of 950 to 1100 캜.

Another aspect of the present invention is

Wherein the high-strength wire rod is heated to 1000 to 1150 ° C and quenched at a cooling rate of 20 ° C / sec or more to produce a heat-treated wire rod.

Another aspect of the present invention is

And a method for manufacturing a high strength steel wire by manufacturing the steel wire by drawing the high-strength heat-treated wire rod.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof can be understood in more detail with reference to the following specific embodiments.

According to the present invention, it is possible to provide a high strength steel wire for large diameter by improving the work hardening rate through the vanadium carbide precipitated in the martensite structure, thereby simplifying the twisted wire structure, reducing the weight of the steel wire and increasing the span distance between the bridges There is an effect that can be made.

According to the present invention, it is possible to provide a high strength steel wire which can be effectively applied to PC steel wires, cables for bridges, and anchor ropes used for reinforcing concrete.

Fig. 1 is a (Fe_1.49V_0.02Ti_0.002B) -C equilibrium state diagram calculated by Thermocalc.
Fig. 2 is a micrograph of a scanning electron microscope of Inventive Example 3, wherein (a) is a microstructure photograph of a wire, (b) is a microstructure photograph of a heat-treated wire before heat treatment, This is a microstructure photograph of the post-steel wire.
FIG. 3 shows the results of thermal desorption spectrometry to compare resistance to hydrogen peroxide breakdown.

The inventors of the present invention have recognized that it is difficult to increase the strength of the steel wire for large diameter because the work hardening rate is small during drawing of pearlitic structure steel, and the resistance is poor. In order to solve these problems, the inventors of the present invention have found that a vanadium precipitation hardened steel having a matrix of martensite structure is subjected to a drawing process to obtain an excellent initial hardness as well as an excellent work hardening ratio. Further, the vanadium carbide is used as a non- It is possible to increase the fracture resistance. Thus, the present invention has been completed.

Hereinafter, the high strength wire according to one aspect of the present invention will be described in detail.

According to one aspect of the present invention, there is provided a high strength wire according to one aspect of the present invention, which comprises 0.1 to 0.4% of C, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, : 0.025% or less, Ti: 0.001 to 0.03%, B: 0.001 to 0.003%, balance Fe and other unavoidable impurities, V and C satisfy the following relational expression 1 and include vanadium carbide, It is a ferrite single phase.

[Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

Hereinafter, the reason why the alloy composition of the steel is controlled will be described.

Carbon (C): 0.1 to 0.4 wt%

C is the most effective element for strengthening the river. Most of the steel C exists in the form of carbides. Carbides not only act as sites of dislocation generation during deformation through the precipitation strengthening effect, but also act as obstacles to dislocation movement, thereby increasing work hardening and increasing strength. Increasing the carbon content increases the amount of precipitate, which is effective in increasing the strength, but it causes generation of coarse carbides and the like, resulting in lower productivity and drawability. When the carbon content exceeds 0.4%, the coarse carbide can be precipitated, so that the upper limit of the carbon content is preferably 0.4%. The upper limit of the more preferable carbon content is 0.35%. When the carbon content is less than 0.1%, it is difficult to secure the intended strength of the present invention, so that the lower limit of the carbon content is preferably 0.1%. A more preferable lower limit is 0.15%, and a still more preferable lower limit is 0.2%.

Vanadium (V): 0.4 to 1.7 wt%

V is an element that bonds with carbon to form carbide of VC form. Stoichiometrically V = C = 4.24: 1. If V is added in a ratio of 4 to 4.5 times the weight of C, V is stoichiometrically bonded to C to form VC, so that VC precipitates are formed in the ferrite matrix, which does not form carbides such as cementite The existing steel can be obtained. Vanadium carbide is a mild carbide whose elastic modulus is known to be 380 GPa and is effective in dislocation dislocation. When the vanadium content exceeds 1.7%, it is not bonded to carbon and is supersaturated and economically unnecessary, so that the upper limit of the vanadium content is preferably 1.7%. A more preferred upper limit is 1.6%, and a still more preferable upper limit is 1.5%. When the content of vanadium is less than 0.4%, it is difficult to secure the intended strength of the present invention, so that the lower limit of the vanadium content is preferably 0.4%. More preferably 0.5%, and still more preferably 0.6%.

Silicon (Si): 0.001 to 0.2 wt%

Si increases the strength by the solid solution strengthening effect and lowers the drawing workability in the VC precipitation strengthened steel. Also, the diffusion rate of carbon may be increased to cause decarburization during the austenizing heat treatment. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the Si content is preferably limited to 0.2%. It is preferable to control Si as low as possible, but since it is inevitably contained inevitably in a manufacturing process, the lower limit of the Si content is preferably limited to 0.001%.

Manganese (Mn): 0.1 to 0.2 wt%

The manganese is excellent in the fineness after? Austenizing heat treatment and is effective for the transformation to the martensite base, and the strength is increased by the solid solution strengthening effect. When the amount is less than 0.1%, the above effect is insufficient and the effect of precipitating S into MnS is insufficient, which may cause high-temperature brittleness due to S. Therefore, the lower limit of the Mn content is preferably 0.1%. However, when added in an amount exceeding 0.2%, segregation, inclusion or the like is formed to increase the brittle fracture sensitivity of the high strength steel wire of the present invention, so that the upper limit of the Mn content is preferably 0.2%.

Boron (B): 0.001 to 0.003 wt%

Boron is effective in transforming to martensite base by making excellent fineness in? Finishing after osteining heat treatment. Therefore, it is effective to add 0.001% or more, but when it is added in excess of 0.003%, the brittle fracture sensitivity due to segregation increases. Therefore, boron is preferably contained in an amount of 0.001 to 0.003% by weight.

Titanium (Ti): 0.001 to 0.03 wt%

Titanium first binds to the nitrogen introduced as impurities in the steel, inhibiting vanadium and boron from forming nitrides. Vanadium and boron are made free from nitride formation, and serve as vanadium and boron. It is preferable to add 0.001% or more for the formation of titanium nitride. However, when it is added in an amount exceeding 0.03%, a carbide element may be formed to hinder the formation of vanadium carbide. Therefore, titanium is preferably contained in an amount of 0.001 to 0.03% by weight.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

However, since phosphorus and sulfur are generally referred to as impurities, a brief description thereof is as follows.

Phosphorus (P): 0.025% by weight or less

The phosphorus is inevitably contained as an impurity and is preferably controlled as low as possible. Theoretically, it is preferable to limit the phosphorus content to 0%, but it is inevitably contained inevitably in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the phosphorus content is preferably limited to 0.025 wt%. If the content of P is less than 0.001% by weight, the production cost of the refining process is greatly increased. Therefore, it is more preferable to control the P content to 0.001% to 0.025%.

Sulfur (S): 0.025% by weight or less

The sulfur is inevitably contained and is preferably controlled as low as possible. Theoretically, it is advantageous to limit the content of sulfur to 0%, but it is inevitably contained inevitably in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the sulfur content is preferably limited to 0.025 wt%. If the content of S is less than 0.001% by weight, the production cost of the refining process is greatly increased. Therefore, the content of S is more preferably controlled to 0.001% to 0.02%.

Further, in addition to the above-mentioned conditions, the alloy composition of the steel wire preferably satisfies the following relational expression (1).

[Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

When the V / C ratio is less than 4.0, the amount of C is high and the base martensite becomes stronger than necessary at the time of the heat treatment of martensite, thereby deteriorating the freshness. When the V / C ratio exceeds 4.5, vanadium is added to the martensite base It is supersaturated to deteriorate the drawability. Therefore, it is preferable that V and C satisfy 4.0? V / C? 4.5.

The microstructure of the wire is substantially ferrite single phase.

It is needless to say that the microstructure of the wire rod is substantially ferrite single phase and does not exclude that other phases are included within the scope of attaining the object of the present invention.

If more than 5% of carbide in the form of pearlite in the microstructure is formed, the added carbon may be exhausted and the work hardening rate may be insufficient due to insufficient formation of vanadium carbide.

The wire includes a vanadium carbide in a ferrite base.

The number of the vanadium carbides may be 1.2 x ^{10 8} / mm ^{2 or} more, and the size may be 20 to 500 nm.

When the number of the vanadium carbides is less than 1.2 x ^{10 8} / mm ² , the number of the vanadium carbides is preferably 1.2 x ^{10 8} / mm ² or more since a coarse carbide is formed and the strength is lowered and the drawing workability is lowered.

In addition, since vanadium carbide of less than 20 nm precipitates at the matching interface and acts as a diffusible hydrogen trap, it is less effective in improving resistance to delayed fracture. On the other hand, vanadium carbide exceeding 500 nm can form pores by interrupting the rotation of the martensite rath during the drawing process.

The tensile strength of the wire may be 730 MPa or more.

When the strength of the wire rod is less than 730 MPa, there is a possibility that the desired strength can not be secured after the wire is drawn.

Hereinafter, a high-strength heat-treated wire according to another aspect of the present invention will be described in detail.

Here, the heat-treated wire rod refers to a wire rod obtained by heat-treating a wire rod before it is manufactured into a steel wire. That is, it is a wire material after heat treatment.

The high-strength heat-treated wire according to another aspect of the present invention comprises

0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities, V and C satisfy the following relational expression 1,

The microstructure contains more than 95% of rut martensite, and includes vanadium carbide.

[Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

The high-strength heat-treated wire rod satisfies the above-mentioned component system, and the microstructure is substantially a rut-martensite single phase.

It is needless to say that it does not exclude that other phases are included in the scope of the present invention.

When plate-shaped martensite is formed not in the form of a rath, there is a problem that rotation of the martensite is not easy during drawing, resulting in poor drawability.

The heat-treated wire rod contains vanadium carbide in a rath-martensite base.

The number of the vanadium carbides may be 1.2 x ^{10 8} / mm ^{2 or} more, and the size may be 20 to 500 nm.

When the number of the vanadium carbides is less than 1.2 x ^{10 8} / mm ² , the number of the vanadium carbides is preferably 1.2 x ^{10 8} / mm ² or more since a coarse carbide is formed and the strength is lowered and the drawing workability is lowered.

In addition, since vanadium carbide of less than 20 nm precipitates at the matching interface and acts as a diffusible hydrogen trap, it is less effective in improving resistance to delayed fracture. On the other hand, vanadium carbide exceeding 500 nm can form pores by interrupting the rotation of the martensite rath during the drawing process.

The tensile strength of the heat-treated wire rod may be 1230 MPa or more.

When the tensile strength of the heat-treated wire rod is less than 1230 MPa, there is a possibility that the strength after the wire drawing is not secured.

Hereinafter, a high strength steel wire according to another aspect of the present invention will be described in detail.

The high strength steel wire according to another aspect of the present invention

0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , 0.001 to 0.003% of B, and the balance of Fe and other unavoidable impurities, wherein V and C satisfy the following relational expression 1 and include vanadium carbide, the microstructure is a rath-martensite single phase, Are arranged in the drawing direction.

 [Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

It is preferable that the high strength steel wire has martensite raths arranged in the drawing direction and vanadium carbide precipitates in the raths

The number of the vanadium carbides may be 1.2 x ^{10 8} / mm ^{2 or} more, and the size may be 20 to 500 nm.

When the number of the vanadium carbides is less than 1.2 x ^{10 8} / mm ² , the number of the vanadium carbides is preferably 1.2 x ^{10 8} / mm ² or more since a coarse carbide is formed and the strength is lowered and the drawing workability is lowered.

In addition, since vanadium carbide of less than 20 nm precipitates at the matching interface and acts as a diffusible hydrogen trap, it is less effective in improving resistance to delayed fracture. On the other hand, vanadium carbide exceeding 500 nm can form pores by interrupting the rotation of the martensite rath during the drawing process.

The steel wire may have a tensile strength of 1960 MPa or more and a section reduction ratio of 30% or more.

When the cross-sectional reduction ratio (RA) of the steel wire is less than 30% per pass, the cross-sectional reduction rate excessively increases the number of passes required to achieve the total reduction ratio, and the strain is accumulated relatively more on the wire surface than on the inside, The distribution tends to become non-uniform, which may adversely affect the mechanical properties of the final product.

When the tensile strength and the sectional reduction ratio are satisfied, the structure used as the rope is simplified while maintaining a high strength, thereby reducing the overall weight of the steel wire or the rope.

Therefore, the steel wire can be preferably applied to a large diameter steel wire having a diameter of 2 mm or more.

Hereinafter, a method of manufacturing a high strength wire according to another aspect of the present invention will be described in detail.

According to another aspect of the present invention, there is provided a method of manufacturing a high-

0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities,

Heating the slab having V and C satisfying the following relational expression 1 at 1000 to 1150 캜;

Hot-rolling the heated billet to obtain a wire rod; And

And cooling the wire rod at a cooling rate of 1 to 10 ° C / second.

[Relation 1]

4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),

Heating step

And the billet satisfying the above-mentioned component system is heated to 1000 to 1150 캜. By heating the steel strip in the temperature range described above, coarsening of the austenite grains can be prevented, and residual segregation, carbides and inclusions can be effectively dissolved.

When the heating temperature of the steel strip exceeds 1150 DEG C, the austenite grains become very coarse and it is difficult to obtain a high strength and high-strength wire rod. On the other hand, if it is less than 1000 ° C, the above-mentioned effect due to heating may not be sufficient. Here, the term "steel" refers to all semifinished products such as blooms and billets, which can be produced from wire rods.

Hot-rolled Wire rod  Steps to Obtain

The heated steel strip is hot-rolled to obtain a wire rod. At this time, the rolling is preferably performed at a temperature of 950 to 1100 캜. When the rolling temperature is lower than 950 DEG C, it is difficult to obtain the intended microstructure of the present invention, and there is a possibility that soft ferrite is secured. On the other hand, when the rolling temperature exceeds 1100 ° C, the size of the austenite grains increases and the strength and ductility may be lowered. Therefore, the hot rolling is preferably performed at 950 to 1100 占 폚.

Cooling step

The wire rod thus produced is cooled. At this time, the cooling is preferably performed at a rate of 1 to 10 DEG C / second. When the cooling rate is less than 1 캜 / second, the vanadium carbide is coarsened and it is difficult to obtain the microstructure to which the present invention is intended. On the other hand, if the cooling rate exceeds 10 DEG C / second, a hard texture may be formed, which may make it difficult to secure the drawing processability before the post-heat treatment process. Therefore, it is preferable that the cooling rate is in the range of 1 to 10 DEG C / sec. After the cooling step, the step of winding may be further included to facilitate the storage and movement of the cooled wire rod.

Hereinafter, a method for manufacturing a high-strength heat-treated wire, which is another aspect of the present invention, will be described in detail.

According to another aspect of the present invention, there is provided a method of manufacturing a high-strength heat-

The high-strength wire is heated to 1000 to 1150 캜 and quenched at a cooling rate of 20 캜 / sec or more to produce a heat-treated wire rod.

Preferably, the heat treatment is quenched at a cooling rate of 20 ° C / sec or more by subjecting to austenizing heat treatment at 1000 to 1150 ° C.

When the heating temperature is lower than 1000 ° C, the ferrite is not completely converted into austenite, and thus the desired strength can not be obtained. When the heating temperature is higher than 1150 ° C, vanadium carbide is completely dissolved in the austenite, Resulting in deterioration of the drawing processability.

After the heating, the wire rods are quenched at a cooling rate of 20 ° C / sec or more to have a martensite base and a microstructure in which non-used vanadium carbide is present.

The wire roughening material, that is, the heat-treated wire rod may have a tensile strength of 1230 MPa or more. When the tensile strength of the heat-treated wire rod is less than 1230 MPa, there is a possibility that the strength after the wire drawing is not secured.

Hereinafter, a method of manufacturing a high strength steel wire according to another aspect of the present invention will be described in detail.

According to another aspect of the present invention, there is provided a method of manufacturing a high strength steel wire, wherein the high strength heat treated wire is drawn to produce a steel wire.

The steel wire thus obtained may have martensite raths arranged in the drawing direction and vanadium carbide of 20 nm or more and 500 nm or less, for example, may be precipitated in the rut.

The steel wire thus produced may have, for example, a tensile strength of 1960 MPa or more and a section reduction ratio of 30% or more.

In the present invention, a conventional drawing method can be applied to the drawing, and is not particularly limited.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

Steels of the component system described in Table 1 below were cast. Thereafter, it was heated at 1100 DEG C by a conventional method, and the 13 mm wire rod hot-rolled at a temperature of 1000 DEG C was cooled at a rate of 8 DEG C / sec. Then, the tensile strength of the wire rod was measured and shown in Table 2 below.

Examples 1 to 3 and Comparative Example 1 of the wire rod produced under the above conditions were subjected to an austenizing heat treatment at 1050 占 폚 and then quenched into 60 占 폚 oil to prepare heat treated wire rods (wire rods).

Here, the heat treatment conditions refer to the Fe-C state diagram of FIG. 1, and the state diagram of FIG. 1 is the Fe-C state diagram to which the alloy element of Inventive Example 3 is added. In the case of Inventive Example 3, the austenite (γ) and vanadium carbide (VC) two-phase region is about 900 to 1200 ° C. In the present invention, since the base structure is martensite and the purpose of making maximum use of the non-solid vanadium carbide, the austenizing heat treatment is performed in the two-phase region.

Of the heat-treated wire rods which were heat-treated under the above-mentioned conditions, Comparative Examples 2 to 3 were softened by heat treatment at 560 ° C (Lead Patenting, LP).

The microstructures and tensile strengths of the heat-treated wires prepared under the above conditions were measured and are shown in Table 2 below.

The heat-treated wire rod was drawn at room temperature to a reduction rate of 76.7%, and then the tensile strength, cross-sectional reduction rate, and torsional characteristics of a wire having a diameter of 100 times were measured.

division C
(weight%) V
(weight%) Si
(weight%) Mn
(weight%) Ti
(weight%) B
(weight%) V / C Carbide count Inventory 1 0.15 0.65 0.05 0.10 0.02 0.002 4.33 1.8 Inventory 2 0.26 1.06 0.05 0.11 0.02 0.002 4.08 3.0 Inventory 3 0.35 1.49 0.05 0.11 0.02 0.002 4.26 4.2 Comparative Example 1 0.35 - 0.23 0.72 - - - Comparative Example 2 0.82 - 0.2 0.74 - - - Comparative Example 3 0.92 - 0.21 0.75 - - - Comparative Example 4 0.35 1.38 0.05 0.11 0.02 0.002 3.94 3.9 Comparative Example 5 0.10 0.39 0.05 0.10 0.02 0.002 3.90 1.1 Comparative Example 6 0.09 0.37 0.05 0.11 0.02 0.002 4.11 1.0 Comparative Example 7 0.41 1.65 0.05 0.10 0.02 0.002 4.02 4.9

However, the unit of the number of carbides in Table 1 is 10 ⁸ / mm ² .

division Tensile Strength (MPa) Steel wire
RA (%) torsion
Character rating
(time) Heat-treated wire (wire for fresh wire)
Microstructure Wire rod Heat treated wire rod (
Fresh wire)  Steel wire Inventory 1 736 1344 1966 34 18 Martensite Inventory 2 787 1391 2234 34 16 Martensite Inventory 3 833 1435 2317 31 16 Martensite Comparative Example 1 490 1655 1922 17 Dil lamination Martensite Comparative Example 2 1035 1105 1751 36 18 Pearlite Comparative Example 3 1120 1188 1828 33 15 Pearlite Comparative Example 4 815 1422 2255 29 Dil lamination Martensite Comparative Example 5 705 1201 1931 33 18 Martensite Comparative Example 6 711 1208 1944 35 19 Martensite Comparative Example 7 881 1511 2288 27 Dil lamination Martensite

As shown in Table 2, in Examples 1 to 3, the strength increased as the weight of C and V increased, and the reduction rate of the section of the steel wire after drawing was 30% or more.

As a result of evaluating the torsional characteristics, delamination (spiral fracture) did not occur and good characteristics were exhibited.

As shown in Tables 1 and 2, Comparative Example 1 is carbon steel to which vanadium is not added. The strength of the heat-treated wire rod was higher than those of Inventive Examples 1 to 3, but it was difficult to generate and fix dislocations by vanadium carbide. Is lower than that in Inventive Examples 1 to 3.

In Comparative Example 1, it is expected that the strength of the martensite base is high and the drafting workability will be insufficient as 0.35% by weight of carbon is all solubilized to form martensite. In Comparative Example 1, the cross-sectional reduction rate of the drawn steel wire was inferior to that of Example 3 which is a similar carbon component, and it was found that the cross-sectional reduction rate of the wire rod of the present invention was not satisfied. In the case of Inventive Example 3, unlike Comparative Example 1, the martensitic matrix structure had a carbon content lower than that of Comparative Example 1, and thus the drawing processability was excellent. That is, Example 3 is superior to Comparative Example 1 in terms of the work hardening rate through the use of vanadium carbide which is not solidified, and thus the tensile strength of the steel wire after the drawing is excellent.

Comparative Examples 2 and 3 are perlite structural steels used as conventional large diameter steel wires. The pearlitic structure steel has lower tensile strength than the martensitic structure steel, and thus the tensile strength of the post-drawing steel wire can not secure the tensile strength of the wire material intended by the present invention.

In Comparative Example 4, the V / C ratio is less than 4.0, and as the vanadium is added, the freshworkability is shown to be due to the supersaturated carbon content.

In Comparative Example 5, the V / C ratio was less than 4.0, indicating that the vanadium content was insufficient due to the addition of vanadium, thereby failing to secure the tensile strength of the wire and steel wire intended by the present invention.

In Comparative Example 6, it can be seen that the tensile strength of the wire and the steel wire intended by the present invention can not be ensured due to the low carbon content.

In Comparative Example 7, it can be seen that delamination occurred in the steel wire due to a high carbon content.

2 is a photograph showing the microstructure of hot-rolled wire, heat-treated wire, and drawn wire of Inventive Example 3 to facilitate understanding of the present invention.

As shown in FIG. 2, the hot-rolled wire rod is composed of ferrite and vanadium carbide (FIG. 2-a). As a result of the analysis of FIG. 2-a, the vanadium carbide was about 4.2 × 10 ⁸ / mm ² . And its size was about 20 to 100 nm.

Further, it can be seen that the heat-treated wire material subjected to heat treatment under the above-mentioned heat treatment conditions is composed of rut martensite and non-solidified vanadium carbide (Fig. 2-b).

Further, it can be seen that the martensite raths are arranged in a line in the drawing direction after the deformation by the drawing conditions (Fig. 2-c). From the fact that the martensite raths are arranged in a line, it can be deduced that the drawing workability is excellent due to the deformation through rotation of the martensite rath.

FIG. 3 is a graph showing the results of thermal desorption spectrometry analysis of the hydrogen release rate according to the temperatures of Examples 3 and 3 in order to compare the hydrogen embrittlement resistance of the steel wire after drawing.

When hydrogen was injected electrochemically randomly, Example 3 and Comparative Example 3 showed two peaks at which hydrogen was emitted. The diffusive hydrogen peak appearing at the low temperature of Inventive Example 3 is emitted from the hydrogen trapped at the potential and the non-diffusible hydrogen peak emitted at the high temperature of 500 ° C or higher is released from the hydrogen trapped at the vanadium carbide interface.

On the other hand, the diffusive hydrogen peak appearing at the low temperature of Comparative Example 3 is emitted from the hydrogen trapped at the potential, and the non-diffusible hydrogen peak emitted at around 300 ° C is released from the hydrogen trapped in the pearlite. Generally, hydrogen is trapped in a high temperature region. It is known that the trapped hydrogen is not easily diffused. Therefore, the hydrogen-delay fracture resistance of the inventive Example 3 having a hydrogen trapping portion released at a high temperature of 500 ° C or more is excellent.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (12)

0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities, V and C satisfy the following relational expression 1,
Wherein the microstructure is a ferrite single phase, and comprises vanadium carbide.
[Relation 1]
4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),
The method according to claim 1,
Wherein the number of the vanadium carbides is 1.2 x ^{10 8} / mm ² or more and the size is 20 to 500 nm.
The method according to claim 1,
Wherein the wire has a tensile strength of 730 MPa or more.
0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities, V and C satisfy the following relational expression 1,
Wherein the microstructure is a rut-martensite single phase, and comprises vanadium carbide.
[Relation 1]
4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),
5. The method of claim 4,
Wherein the number of the vanadium carbides is 1.2 x ^{10 8} / mm ² or more and the size is 20 to 500 nm.
5. The method of claim 4,
Wherein the wire has a tensile strength of 1230 MPa or more.
0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities, V and C satisfy the following relational expression 1,
Wherein the microstructure is a rath-martensite single phase, the rut of the martensite is arranged in the drawing direction, and the high strength steel wire comprising vanadium carbide.
[Relation 1]
4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),
8. The method of claim 7,
Wherein the steel wire has a tensile strength of 1960 MPa or more and a section reduction ratio of 30% or more.
0.1 to 0.4% of V, 0.4 to 1.7% of V, 0.001 to 0.2% of Si, 0.1 to 0.2% of Mn, 0.025% or less of P, 0.025% or less of S and 0.001 to 0.03% of Ti, , B: 0.001 to 0.003%, balance Fe and other unavoidable impurities,
Heating the slab having V and C satisfying the following relational expression 1 at 1000 to 1150 캜;
Hot-rolling the heated billet to obtain a wire rod; And
And cooling the wire rod at a cooling rate of 1 to 10 占 폚 / sec.
[Relation 1]
4.0? V / C? 4.5 (where V and C represent the respective contents (% by weight)),
10. The method of claim 9,
Wherein the hot rolling is performed at a temperature of 950 to 1100 占 폚.
A method for manufacturing a high-strength heat-treated wire rod in which the wire according to any one of claims 1 to 3 is heated to 1000 to 1150 ° C and quenched at a cooling rate of 20 ° C /
A method for manufacturing a high strength steel wire by manufacturing the steel wire by drawing the high strength heat treated wire according to any one of claims 4 to 6.

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