KR101917461B1 - High strength wire rod and heat-treated wire rod having excellent drawability and method for manufacturing thereof - Google Patents

Abstract

Cr: 0.3 to 0.7%, V: 0.05 to 0.1%, Sol.Al: 0.02 to 0.05%, P: 0.1 to 1.2% (R: 0.015% or less) in the direction of the surface of the wire from the center of the wire to the wire, the wire being made up of 0.015% or less of S, 0.015% or less of S, 0.002 to 0.01% of N and 0.01% or less of O and the balance Fe and unavoidable impurities. The length of the longest cemented cementite is 10% or less of the grain boundary length of the austenite grains in which the longest cemented cementite is deposited, and a heat treated wire rod using the same. A process for producing them is disclosed.

Description

TECHNICAL FIELD [0001] The present invention relates to a high-strength wire rod, a heat-treated wire rod, and a method of manufacturing the same,

The present invention relates to a high-strength wire having excellent drawability, a heat-treated wire using the wire, and a method of manufacturing the same. More particularly, the present invention relates to a high strength wire rod excellent in drawability which can be preferably used for a cable for a cable- Wire, a heat-treated wire using the wire, and a method of manufacturing the wire.

The strength of bridges for bridges and anchor ropes for marine structures are mostly determined by the strength of the raw wire. The most effective way to increase the strength of wire is the addition of alloying elements. As a part of this, there are many studies to increase the strength of wire by adding V.

V is the most widely used element in the development of HSLA (High Strength Low Alloy) steel, which has been mainly used for low carbon steel, and which suppresses recrystallization during hot rolling and improves mechanical properties by refining the crystal grains by precipitation. On the other hand, the purpose of utilizing V in high carbon steels is somewhat different, and has been applied mainly to direct drawing wire which omits LP (Lead Patenting) heat treatment. Direct drawing wire rods are basically required to have a fine pearlite structure similar to that of patenting material and to have a strength as high as 10 kg / mm ² as compared with wire rods obtained by forced air cooling. For this purpose, a microalloying method Is most effective and V is known as an element that meets this purpose. V improves the hardenability by delaying the pearlite transformation, and when it is added above a certain amount, it precipitates and strengthens precipitation, so it helps to secure the mechanical properties of LP heat treatment level by continuous cooling in large diameter high carbon drawing material . However, since the V-carbide precipitation depends on the cooling rate in the high carbon steel which normally gives rapid cooling after continuous wire rolling, it is difficult to control the occurrence or degree of precipitation, There is a possibility that a low-temperature structure may be formed in the wire rod cooling step because the speed difference of the pearlite transformation is largely changed.

One of the objects of the present invention is to provide a high-strength wire rod, a steel wire, and a manufacturing method thereof excellent in drawability.

In one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising, by weight, 0.9 to 1.2% of C, 0.8 to 1.4% of Si, 0.2 to 0.6% of Mn, 0.3 to 0.7% of Cr, 0.05 to 0.1% of V, 0.02 to 0.05% of P, 0.015% or less of S, 0.015% or less of S, 0.002 to 0.01% of N and 0.01% or less of O, the balance being Fe and inevitable impurities, , The length of the long-stiff cemented cementite in the region up to 1 / 4r (r: radius of the wire) is 10% or less of the grain boundary length of the austenite grains in which the long- .

Another aspect of the present invention is to provide a method of manufacturing a multilayer ceramic substrate having a composition comprising 0.9 to 1.2% of C, 0.8 to 1.4% of Si, 0.2 to 0.6% of Mn, 0.3 to 0.7% of Cr, 0.05 to 0.1% of V, 0.02 to 0.05% of P, 0.015% or less of P, 0.015% or less of S, 0.002 to 0.01% of N and 0.01% or less of O, the balance Fe and unavoidable impurities to a temperature of 1050 to 1200 캜 , Finishing the reheated slab at a temperature of 950 캜 or more to obtain a wire rod, winding the wire rod at a temperature of 930 캜 or more, and cooling the wound wire rod to 600 캜 at a rate of 10 캜 / sec or more Secondarily cooling the primary-cooled wire rod to a temperature of 500 ° C at a rate of 1.0 to 1.5 ° C / sec, and tertiarily cooling the secondary-cooled wire rod to room temperature at a rate of 10 ° C / sec The present invention also provides a method for producing a wire rod.

Another aspect of the present invention is a ferritic stainless steel comprising, by weight, 0.9 to 1.2% of C, 0.8 to 1.4% of Si, 0.2 to 0.6% of Mn, 0.3 to 0.7% of Cr, 0.05 to 0.1% of V, : 0.02 to 0.05%, P: not more than 0.015%, S: not more than 0.015%, N: not more than 0.002 to 0.01%, O: not more than 0.01%, the balance Fe and unavoidable impurities, 2,000 / mm < ² > or more.

Another aspect of the present invention is a ferritic stainless steel comprising, by weight, 0.9 to 1.2% of C, 0.8 to 1.4% of Si, 0.2 to 0.6% of Mn, 0.3 to 0.7% of Cr, 0.05 to 0.1% of V, : 0.02 to 0.05%, P: not more than 0.015%, S: not more than 0.015%, N: not more than 0.002 to 0.01%, O: not more than 0.01%, and remainder Fe and unavoidable impurities at a temperature of 1050 to 1200 ° C A step of finishing rolling the reheated slab at a temperature of 950 캜 or higher to obtain a wire rod; winding the wire rod at a temperature of 930 캜 or higher; cooling the rolled wire rod to 600 캜 at a rate of 10 캜 / Second cooling the primary wire at a rate of 1.0 to 1.5 ° C / sec up to 500 ° C; tertiary cooling the secondary wire at a rate of 10 ° C / sec to room temperature; A step of subjecting the tertiary-cooled wire rod to an austenizing heat treatment at 950 to 1050 ° C, and a step of subjecting the austenized wire material to a constant-temperature transformation heat treatment at 550 to 650 ° C It provides a method for preparing a heat-treated wire.

As one of various effects of the present invention, the high-strength wire rod according to the present invention is excellent in drawing workability and can be suitably used as a material for a cable for a cable-stayed bridge and a suspension bridge, and an anchor line for a marine structure.

The various and advantageous advantages and effects of the present invention are not limited to the above description, and can be more easily understood in the course of describing a specific embodiment of the present invention.

FIG. 1 is a graph showing a change in tensile strength of a heat-treated wire rod according to an embodiment of the present invention while flowing at 15 to 20% per pass.

High carbon steel wire rods used for cables for officers and suspension bridges, marine structural anchor lines, etc., achieve high strength on the basis of full pearlite structure based on a large amount of work hardening by continuous drawing. In order to achieve high strength, it is essential to increase the pearlitic cementite fraction and narrow the interlamellar spacing. For this purpose, the C content is continuously increased, and the alloy elements such as Si and Cr And the induction hardening of ferrite and the like have been induced. The most important element among the various alloying elements is C, which generally increases the C content, thereby increasing the cementite content in the pearlite and making the lamellar spacing finer. However, the continuous increase in the C content is due to the increase of the cementite content Since the cementite phase is precipitated in the cementitious phase, it can not withstand the deformation during the drawing process, and voids are generated to cause problems in the ductility of the final product. Therefore, the amount of the cementing process is reduced and the ultimate strength increase . Under these circumstances, the inventors of the present invention have conducted in-depth research to provide a method for increasing the amount of drawing while increasing the carbon content. As a result, the Si content is increased and a small amount of V is added thereto. , It is possible to separate and fine-grain the cementite cementite on the network generated in the old austenite grain boundaries even in a relatively high carbon range. In the case where the obtained wire rod is subjected to constant temperature transformation It has been found that when the austenite grain growth is delayed by the fine precipitation of VC, micro pearlite nodule can be obtained after transformation, and strength and ductility can be ensured simultaneously through the transformation. Thus, the present invention has been accomplished.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a high strength wire excellent in drawability, which is one aspect of the present invention, will be described in detail.

First, the alloy component and preferable content range of the high strength wire of the present invention will be described in detail. It is to be noted that the content of each component described below is based on weight unless otherwise specified.

C: 0.9 to 1.2%

C is the most effective element to increase the strength of the material. It is known that when the C is increased by 0.1% in the pearlite steel, the strength can be improved by about 100 MPa. However, as the C content increases, the effect of the increase in strength decreases as the C content of the super-calcite increases. As a result, the thermodynamic stability of austenite becomes unstable and a faster cooling rate This is because a certain level of cooling rate is required for a commercial cooling system, but the effect of increasing the strength is reduced. In order to secure the desired strength in the present invention, it is preferable to add 0.9% or more, more preferably 0.95% or more, and still more preferably 0.98% or more. However, when the content is excessively excessive, it is preferable to add not more than 1.2%, and it is preferable to add not more than 1.18% It is more preferable to add them.

Si: 0.8 to 1.4%

Si is mostly used in ferrite during austenite-> pearlite transformation, and its diffusion rate is slower than that of C without being distributed to cementite, so that when a large amount of Si is employed, the pearlite transformation is generally slowed down. Therefore, it has an effect of refining the spacing of pearlite layers, and is basically an element effective in increasing strength because it exhibits solid solution strengthening effect while being dissolved in ferrite. In addition, Si is mainly present in the ferrite and cementite interface part, and it is preferable to set the Si content high because it helps stability of cementite during drawing and heat treatment. When Si is less than 0.8%, it is difficult to stabilize the cementite. When the Si content exceeds 1.4%, it is difficult to remove the scale because the surface portion Fe ₂ SiO ₄ scale is excessively generated.

Mn: 0.2 to 0.6%

Mn is not added to the full pearlite steels in a strength increasing effect, but is added in order to maintain the granularity at an appropriate level according to the cooling performance of the linear heat treatment and the LP heat treatment. If the Mn content is less than 0.2%, it is difficult to see the ingot effect. If the Mn content exceeds 0.6%, it is high carbon steel. Therefore, the martensite structure can be formed in the segregation part together with the C content.

Cr: 0.3 to 0.7%

Cr is a very useful element for increasing the strength of heat-treated wire rods by increasing the spacing between pearlite layers during constant-temperature transformation, enhancing work hardening during wire drawing, and widening the limits of wire drawing. If it is less than 0.3%, it is difficult to obtain a sufficient interlayer spacing refinement effect, and when it exceeds 0.7%, the cementite formation is not smooth and is present in the form of segmented dolomite.

V: 0.05 to 0.1%

V is precipitated during the LP heat treatment to finer the austenite grain size (AGS), and it is an element that partially precipitates even during the patenting and exhibits precipitation strengthening effect. In addition, it inhibits the generation of cementite cementite in the form of network in the C-rich high-purity quartz. Therefore, it is possible to increase the C content without generating a cementite cementite through the addition of V, thereby making it possible to further increase the strength. If it is less than 0.05%, it is difficult to exhibit the expected effect. If it exceeds 0.1%, it is preferable to add the ferrite ferrite to the austenite grain boundary system.

Sol.Al: 0.02 to 0.05%

Sol.Al, like Si, is an element that inhibits the growth of austenite grains during wire rolling by forming AlN precipitates by bonding with nitrogen (N) in the steel together with ferrite solid solution strengthening. In order to obtain such an effect, it is preferable that the content is 0.02% or more, more preferably 0.025% or more. However, if the content is excessive, Al ₂ O ₃ inclusions, which are high melting point inclusions, may become coarse and deteriorate the drawability. Therefore, the upper limit of the Al content is preferably limited to 0.05%.

P: not more than 0.015%

P is a typical impurity in steel, and it is preferable to actively remove P because it decreases the toughness of steel when it is included in steel. However, in order to control P below a certain level, the cost and effort to be injected increases exponentially, so the upper limit of P content should be limited to 0.015%.

S: not more than 0.015%

S is inevitably contained in the steel and must be removed as much as P. The reason is that S combines with Mn, Fe and the like in the steel to form coarse inclusions such as MnS and FeS in the grain boundary and the center portion. In order to prevent this, it is preferable that the upper limit of the S content is limited to 0.015%.

N: 0.002 to 0.01%

N reacts with Al in the steel and precipitates as a precipitate of AlN, thereby suppressing the austenite growth, making the steel finer and improving the drafting property. In order to obtain such an effect, it is preferable that it is at least 0.002% or more, more preferably 0.003% or more. However, when the content is excessive, N causes aging hardening with an interstitial element, which may cause a decrease in drawability during drawing. To prevent this, the upper limit of the N content is preferably limited to 0.01%, and more preferably limited to 0.009%.

O: not more than 0.01%

O is an impurity inevitably contained in the steel. When the content is excessive, various types of oxidative inclusions are produced and grown, thereby deteriorating the drawability. In order to prevent this, the upper limit of the O content is preferably limited to 0.01%, and more preferably, limited to 0.006%.

The rest of the composition is Fe. However, it is not possible to exclude inevitable impurities that are not intended from the raw material or the surrounding environment in a conventional manufacturing process, since they may be inevitably incorporated. These impurities are not specifically referred to in this specification, as they are known to one of ordinary skill in the art.

BEST MODE FOR CARRYING OUT THE INVENTION The microstructure of a high-strength wire rod excellent in drawability of the present invention will be described in detail below.

The high strength wire of the present invention comprises pearlite as a main structure and preferably a complete pearlite (pearlite of about 99 area% or more), but in addition to pearlite which is a main structure, a second pearlite such as bainite, And does not exclude the inclusion of a phase. However, in the presence of the second phase, deformation may concentrate during drawing processing, which may lead to deterioration of the drawing processability. In order to prevent this, it is preferable to control the sum of the area ratios of the second phases to be 1% or less.

The length of the rootstone cementite having the longest length in the region from the center of the wire to the surface of the wire in the region from 1 / 4r (r: the radius of the wire) is the length of the grain boundary of the austenite grains Of not more than 10%.

In the present invention, the length of the individual cubic cementite is limited because the individual length of the cubic cementite to be deposited has an important influence on the drawing processability of the wire. Therefore, when the length of the individual cubic cementite is longer than a certain length, It is bent or broken during processing to form pores between the base structure and the cornerstone cementite and grow as cracks in the subsequent processing to deteriorate the drawing processability of the wire material. On the other hand, in the present invention, the reason why the length of the individual cornerstone cementite is limited by the relative ratio of the length of the austenite grain to the grain boundary length is that when the primary stone cementite is precipitated in the austenite grain boundary, The rotation of the phase occurs, and at this time, much damage is applied to the cornerstone cementite. Therefore, when the length of the individual cornerstone cementite is equal to or larger than the grain boundary length of the austenite grains, And the growth of cracks and cracks can easily occur.

According to one example, the total length of the cornerstone cementite in the region from the center of the wire to the surface direction of the wire to 1 / 4r (r: radius of the wire) may be less than 1% of the grain boundary total length of the old austenite grains. If the total length of the cornerstone cementite exceeds 1% of the grain boundary total length of the old austenite grains, pore generation and crack growth can easily occur, and the wire drawing workability may be deteriorated.

According to one example, the maximum thickness of the cornerstone cementite may be less than 1 m. If the maximum thickness of the quartz cementite exceeds 1 탆, plastic deformation of the quartz cementite is difficult, so that generation of voids and crack growth can easily occur, and the drawing workability of the wire material may deteriorate.

According to one example, the V-based precipitate having a size of 10 nm or more may be 10 / mm ² or less. When V-based precipitates having a size of 10 nm or more exceed 10 / mm ² , a network type of elementary stone cementite is formed, and the drawing workability of the wire rod may deteriorate.

The high strength wire of the present invention described above can be manufactured by various methods, and the manufacturing method thereof is not particularly limited. However, as a preferable example, it can be produced by the following method.

Hereinafter, a method of manufacturing a high strength wire having excellent drawability, which is another aspect of the present invention, will be described in detail.

First, the slab having the above-mentioned component system is reheated to a temperature of 1050 to 1200 占 폚. In the present invention, V is not induced in the wire material state but V is contained in a solid state. If the V-type precipitate remains on the heating furnace, it can not be removed in the subsequent step. Therefore, it is necessary to completely dissolve the V-type precipitate precipitated in this step, and it is necessary to reheat at a temperature of 1050 캜 or higher. However, if the temperature is excessively high, the occurrence of scale becomes excessive and a large loss occurs. Therefore, it is necessary to reheat at a temperature of 1200 ° C or less.

Next, the reheated slab is finely rolled to a temperature of 950 占 폚 or more to obtain a wire rod, which is then wound at a temperature of 930 占 폚 or more. This is to prevent the temperature of the material from falling below the Acm temperature during rolling of the wire to prevent the formation of a hard stone cementite.

Next, the wound wire rod is subjected to primary cooling at a rate of 10 DEG C / sec or higher to 600 DEG C, primary cooling the wire rod to 500 DEG C at a rate of 1.0 to 1.5 DEG C / sec, The wire is thirdly cooled to room temperature (about 25 ° C) at a rate of 10 ° C / sec.

The object of the cooling rate control of the wire rod is to suppress the generation of V-type precipitates while keeping the non-pearlite structure such as the cornerstone cementite or martensite to be minimized, so that the V remains in the over-solid state. Thus, from the coiling temperature up to 600 占 폚, the quenched cementite is quenched at a rate of 10 占 폚 / sec or more, and in the section from 600 占 폚 to 500 占 폚, it is slowly cooled at a rate of 1.0 to 1.5 占 폚 / And then quenched at a rate of 10 ° C / sec or more to suppress precipitation of V-type precipitates after pearlite transformation.

Hereinafter, a heat treatment wire excellent in drawability, which is another aspect of the present invention, will be described in detail.

The heat-treated wire rod of the present invention is obtained by subjecting the aforementioned high-strength wire rod to constant-temperature transformation, and is characterized by containing V-based precipitates having a size of 10 to 70 nm at 2,000 / mm ² or more. The V-type precipitates are not precipitated in the wire rod state, but the V-grains which have been dissolved are precipitated while being subjected to a constant temperature transformation heat treatment. Such V-type precipitates lead to an increase in the strength of the heat-treated wire rod and miniaturization of AGS (Auestenite grain size). If the V-based precipitate having a size of 10 to 70 nm is contained at less than 2,000 pores / mm ² , it may be difficult to secure the desired strength.

According to one example, the heat treated wire of the present invention comprises pearlite as the main structure, and in this case, the pearlite average nodule size may be 15 탆 or less (excluding 0 탆). If the pearlite average nodule size exceeds 15 탆, it may be difficult to secure the desired strength.

The heat-treated wire rod of the present invention has an advantage that the strength is extremely excellent. According to one example, the heat-treated wire rod of the present invention has a diameter of 13 mm and a tensile strength of 1,600 MPa or more. Here, the wire diameter of the heat-treated wire is limited to 13 mm because it does not necessarily mean that the heat-treated wire must have a wire diameter of 13 mm, and the tensile strength of the heat-treated wire depends largely on the wire diameter. .

The heat-treated wire rod of the present invention has an advantage of excellent drawability, and according to an example, the wire diameter may be 13 mm and the tensile strength at break of 2,400 MPa or higher at a strain of 2.0.

Hereinafter, a method of manufacturing a heat-treated wire rod excellent in drawability, which is another aspect of the present invention, will be described in detail.

First, the above-mentioned high-strength wire rod is prepared, and then subjected to an austenizing heat treatment at 950 to 1050 ° C. This is because V and the dissolved V are not completely reused and some precipitation occurs to inhibit austenite grain growth. If the temperature exceeds 1050 DEG C, V can be completely reused, while when 950 DEG C or less, May not completely dissolve.

According to one example, osteonising can be carried out for 3 to 5 minutes. If it is less than 3 minutes, there is a fear that the austenitization is not sufficiently performed, while if it exceeds 5 minutes, there is a fear that the freshness of the austenitic grain growth is lowered.

Next, the austenized wire rod is heat-treated at a constant temperature of 550 to 650 ° C. If the heat treatment temperature is less than 550 ° C, the upper bainite may be mixed or the pearlite may not grow smoothly, resulting in deterioration of the drawing processability. On the other hand, when the temperature is more than 650 ° C, the pearlite lamella interval is widened, Can be deteriorated.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the description of these embodiments is intended only to illustrate the practice of the present invention, but the present invention is not limited thereto. And the scope of the present invention is determined by the matters described in the claims and the matters reasonably deduced therefrom.

(Example)

The slab having the composition shown in the following Table 1 was reheated at a temperature of 1100 占 폚 and then subjected to finish rolling at a temperature of 980 占 폚 to obtain a wire rod. Thereafter, the mixture was wound at a temperature of 950 캜 and subjected to primary cooling at a rate of 20 캜 / sec to 600 캜, secondary cooling at a rate of 1.0 캜 / sec to 500 캜, and tertiary cooling at a rate of 10 캜 / Respectively. The microstructures of the thirdarily cooled wire rod were observed, and the mechanical properties were measured. The results are shown in Table 2 below. In Table 2, RA means the reduction ratio of area.

Remarks Alloy component (% by weight) C Si Mn Cr V Sol.Al P S N O Inventory 1 0.92 1.3 0.3 0.6 0.07 0.03 0.01 0.01 0.004 0.006 Inventory 2 1.01 1.1 0.4 0.5 0.08 0.03 0.01 0.01 0.003 0.005 Inventory 3 1.15 0.9 0.5 0.4 0.09 0.04 0.01 0.01 0.004 0.006 Comparison 1 0.91 1.3 0.3 0.6 - 0.04 0.01 0.01 0.004 0.006 Comparative material 2 0.96 1.1 0.4 0.5 - 0.03 0.01 0.01 0.004 0.006 Comparative material 3 1.14 0.9 0.5 0.4 - 0.03 0.01 0.01 0.004 0.006

Remarks Microstructure Mechanical properties Perlite fraction (area%) ① ② ③ ④ The tensile strength
(MPa) RA
(%) Inventory 1 > 99% 6% 0.5% 0.8 4 1427 24 Inventory 2 > 99% 5% 0.5% 0.7 6 1501 22 Inventory 3 > 99% 6% 0.6% 0.6 3 1579 21 Comparison 1 > 99% 11% 1.2% 1.2 190 1375 25 Comparative material 2 > 99% 12% 1.3% 1.2 210 1458 24 Comparative material 3 > 99% 11% 1.2% 1.1 200 1559 13 (1) In a region from the center of the wire to the surface of the wire in the region from 1 / 4r (r: the radius of the wire), the longest cemented cementite has the longest length. The austenite grains Percentage of grain boundary length (%)
(%) Of the total length of the cornerstone cementite to the total intergranular grain length of the old austenite grains in the area from the center of the wire material to the surface direction of the wire material to 1 / 4r (r: radius of the wire material)
③: Maximum thickness of the corner stone cementite (μm)
④: Number of V-type precipitates having a size of 10 nm or more per unit area (pieces / mm ² )

Referring to Table 2, it can be seen that the full pearlite structure of 99% or more by area is secured in both the inventive material and the comparative material, but the occurrence of the cornerstone cementite is remarkably reduced in the case of the inventive material. The total amount of basic stone cementite is also reduced to less than half, and the thickness is also reduced. It can be seen that the length of the individual cornerstone cementite is also shortly segmented to within 10%. On the other hand, in the case of the inventive material, the number per unit area of the V-type precipitate having a size of 10 nm or more is also properly controlled.

Next, each wire rod was subjected to osteonizing heat treatment at 980 ° C for 3 minutes, followed by heat treatment at 580 ° C for 3 minutes to obtain a heat treated wire rod. The microstructure of the heat-treated wire rod was observed, and mechanical properties were measured. The results are shown in Table 3 below.

Microstructure Mechanical properties Perlite fraction (area%) Perlite average nodule size (μm) Number of V precipitates per unit area (number / mm ² ) of 10 to 70 nm size The tensile strength
(MPa) RA
(%) Inventory 1 > 99% 12 2078 1527 27 Inventory 2 > 99% 12 2544 1613 26 Inventory 3 > 99% 11 2899 1689 26 Comparison 1 > 99% 17 No 1495 27 Comparative material 2 > 99% 18 No 1558 28 Comparative material 3 > 99% 18 No 1599 22

As shown in Table 3, inventive materials 1 to 3 satisfying both the alloy composition and the manufacturing conditions proposed in the present invention are suitably controlled so that the number of V-type precipitates having a size of 10 to 70 nm is not less than 2,000 / mm ² And the pearlite nodule size is finely controlled to 15 μm or less. As a result, the tensile strength exhibits an improved value of about 100 MPa as compared with the comparative material. The strength difference between the inventive material and the comparative material was maintained at a level similar to that in the wire rod state.

FIG. 1 is a graph showing a change in tensile strength of a heat-treated wire rod according to an embodiment of the present invention while flowing at 15 to 20% per pass. As a whole, in the early stage of the drawing process, the strength difference is maintained by the difference in strength after the LP heat treatment, and the material is decreased in the width of the strength increase from the strain 2.0. This means that the material itself shows the limit of the drawing process, and in the actual torsion test, delamination occurred more frequently. When the final wire diameter was 5mmΦ, all of the inventive materials could secure a strength of 2,400 MPa or more, and it was possible to obtain super high strength and ductility without delamination.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments, but various modifications and changes may be made without departing from the scope of the invention. To those of ordinary skill in the art.

Claims (12)

Cr: 0.3 to 0.7%, V: 0.05 to 0.1%, Sol.Al: 0.02 to 0.05%, P: 0.1 to 1.2% (R: 0.015% or less) in the direction of the surface of the wire from the center of the wire to the wire, the wire being made up of 0.015% or less of S, 0.015% or less of S, 0.002 to 0.01% of N and 0.01% or less of O and the balance Fe and unavoidable impurities. The length of the longest cemented cementite in the region up to the radius of the wire rod is not more than 10% of the grain boundary length of the austenite grains in which the longest cemented cementite is deposited.
The method according to claim 1,
Wherein the total length of the corner stone cementite in the area from the center of the wire to the surface direction of the wire is 1% or less of the total grain boundary length of the old austenite grains in the area from 1 / 4r (r: radius of the wire).
The method according to claim 1,
The maximum thickness of the cornerstone cementite is 1μm or less.
The method according to claim 1,
A wire rod containing pearlite as main structure.
The method according to claim 1,
A V-type precipitate having a size of 10 nm or more is 10 / mm ² or less.
The method according to claim 1,
And the carbon content is 0.98 to 1.2 wt%.
Cr: 0.3 to 0.7%, V: 0.05 to 0.1%, Sol.Al: 0.02 to 0.05%, P: 0.1 to 1.2% 0.015% or less, S: 0.015% or less, N: 0.002 to 0.01%, O: 0.01% or less, the balance Fe and unavoidable impurities to a temperature of 1050 to 1200 캜;
Finishing the reheated slab at a temperature of 950 캜 or higher to obtain a wire rod;
Winding the wire rod at a temperature of 930 캜 or higher;
Cooling the wound wire rod to 600 DEG C at a rate of 10 DEG C / sec or more;
Secondarily cooling the primary-cooled wire rod to a temperature of 500 ° C at a rate of 1.0 to 1.5 ° C / sec; And
Cooling the secondarily cooled wire rod to room temperature at a rate of 10 ° C / sec or more;
Wherein the wire rope is made of a metal.
Cr: 0.3 to 0.7%, V: 0.05 to 0.1%, Sol.Al: 0.02 to 0.05%, P: 0.1 to 1.2% 0.015% or less, S: 0.015% or less, N: 0.002 ~ 0.01%, O: 0.01% or less, balance Fe and unavoidable containing impurities, including V-containing precipitate to 2,000 / mm ² or more with a 10 ~ 70nm size Heat treated wire rod.
9. The method of claim 8,
A heat-treated wire rod including pearlite as a main structure and having a pearlite average nodule size of 15 μm or less (excluding 0 μm).
9. The method of claim 8,
Heat treated wire of 13mm in diameter and having a tensile strength of 1,600MPa or more.
9. The method of claim 8,
Heat treated wire having a wire diameter of 13 mm and a tensile strength of 2,400 MPa or higher at a strain of 2.0.
Cr: 0.3 to 0.7%, V: 0.05 to 0.1%, Sol.Al: 0.02 to 0.05%, P: 0.1 to 1.2% 0.015% or less, S: 0.015% or less, N: 0.002 to 0.01%, O: 0.01% or less, the balance Fe and unavoidable impurities to a temperature of 1050 to 1200 캜;
Finishing the reheated slab at a temperature of 950 캜 or higher to obtain a wire rod;
Winding the wire rod at a temperature of 930 캜 or higher;
Cooling the wound wire rod to 600 DEG C at a rate of 10 DEG C / sec or more;
Secondarily cooling the primary-cooled wire rod to a temperature of 500 ° C at a rate of 1.0 to 1.5 ° C / sec;
Cooling the secondarily cooled wire rod to room temperature at a rate of 10 ° C / sec or more;
Subjecting the thirdarily cooled wire material to an austenizing heat treatment at 950 to 1050 占 폚; And
Subjecting the austenized wire to heat treatment at 550 to 650 ° C;
Wherein the heat treatment is carried out at a temperature of not less than < RTI ID =

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