KR20150121081A - High-strength steel wire material exhibiting excellent cold-drawing properties, and high-strength steel wire - Google Patents

Abstract

A high strength steel wire having good drawability and exhibiting a predetermined high strength, and a high strength steel wire and a high strength galvanized steel wire obtained from such a wire material for high strength steel wire. The high strength steel wire rod according to the present invention is characterized in that it comprises 0.80 to 1.3% of C, 0.1 to 1.5% of Si, 0.1 to 1.5% of Mn, more than 0% Of Al, 0.01 to 0.10% of Al, and 0.001 to 0.006% of N, respectively, the balance being iron and inevitable impurities, and satisfying the relationship of the following formula (1).
0.05% ≥ [Ti *] ≥ (0.0023 × [C]) ... (One)
[Ti *] = (total amount of Ti - amount of compound Ti of 0.1 占 퐉 or larger in size), and [C] indicates content of C (% by mass).

Description

HIGH-STRENGTH STEEL WIRE MATERIAL EXHIBITING EXCELLENT COLD-DRAWING PROPERTIES AND HIGH-STRENGTH STEEL WIRE [0002]

The present invention relates to a high strength steel wire useful as a material of a galvanized steel wire used for ropes for bridges and the like, and a high strength steel wire for obtaining such a high strength steel wire. More particularly, the present invention relates to a high strength steel wire for high strength steel wire Wire rod and the like.

Steel ropes or stranded wires subjected to hot-dip galvanizing are used for ropes used for bridges and the like in order to increase corrosion resistance. As a material of such a steel wire, for example, a steel wire having a wire diameter of 5 mm and a tensile strength TS of 1500 to 1700 MPa is shown in JIS G 3548, and carbon steels mainly described in JIS G 3506 are used as the material steel thereof.

In addition to reducing the manufacturing cost, the steel wire as the material of the hot-dip galvanized steel wire has advantages such as reduction of the amount of steel material due to high strength and improvement of freedom of bridge design. In other words, development of a high- Is required.

In producing a galvanized steel wire, the following method is generally employed. First, the wire rods (steel wire rods) produced by hot rolling are placed on a cooling conveyor in a ring shape, and after the pearlite transformation is performed, the wire rods are wound in a coil shape to obtain a wire rod coil. Next, the patterning process is performed to improve the strength and uniformity of the texture. This patterning treatment is a kind of heat treatment. In general, the wire is austenitized by heating it to about 950 ° C by using a continuous furnace, and then dipped in a coolant such as an inlay bath maintained at about 500 ° C to obtain a fine and uniform pearlite structure .

Thereafter, cold drawing is performed, and a steel wire having a predetermined strength is obtained by utilizing the work hardening action of pearlite steel. Thereafter, the substrate is immersed in a molten zinc bath maintained at about 450 캜 and subjected to a plating treatment to form a galvanized steel wire. After the galvanizing treatment, further finishing drawing may be carried out. As the cable for bridges, a parallel wire strand (PWS) or a twisted galvanized steel wire strand bundled with them is used.

In such a series of manufacturing processes, the patterning process is one of the factors that increase the manufacturing cost. Although the patterning treatment is effective for increasing the strength of the wire and uniformizing the quality thereof, there is a problem in terms of environment such as emission of CO ₂ and use of environmental load materials in addition to raising the manufacturing cost. The advantage is great if it is possible to produce the wire after rolling and to make it into a product (that is, to make a steel wire) without heat treatment. It is called "raw drawing" that drawing wire after rolling is processed without heat treatment.

In order to achieve high strength in the raw drawing, it is necessary to use a hyper-eutectoid steel having a high C content in order to compensate for a decrease in strength when the patterning process is omitted. However, with the increase of the C content, there arises a problem that the brilliant stone cementite precipitates on the grain boundaries and the drawing processability is lowered. In view of this, even when the C content is increased to increase the strength, it is desired to realize a wire rod excellent in characteristics capable of raw drawing while suppressing the influence of the cornerstone cementite (referred to as "raw drawability") .

Various techniques have been proposed so far for improving the drafting workability. For example, Patent Document 1 proposes a technique of improving drawing workability by performing cooling after hot rolling in a molten salt bath. This technique is called direct patterning processing. However, in the direct patterning treatment in the molten salt bath, there is a problem that the manufacturing cost is higher and the maintenance property of the equipment is lower than that in the case of air-blowing. Moreover, the drawing performance of the obtained steel material is as low as about 80% at the reduction ratio, and the strength level of the wire (steel wire) is about 180 to 190 kgf / mm ² (1764 to 1862 MPa).

On the other hand, Patent Document 2 discloses a technique for improving the strength of the wire rod by controlling the cooling condition after hot rolling and omitting the patterning process. However, the drawing workability of the steel obtained by this technique is as low as about 50% at the reduction rate, and the strength level of the wire is also about 1350 to 1500 MPa.

Japanese Patent Laid-Open No. 04-289128 Japanese Patent Application Laid-Open No. 05-287451

It is an object of the present invention to provide a wire rod for a high-strength steel wire which is capable of achieving a good drawability and a predetermined high strength, a high-strength steel wire obtained from such a high- .

The wire rod for high strength steel wire according to the present invention which can achieve the above object means a steel wire having a composition of C: 0.80 to 1.3% (meaning the mass%, the same shall apply hereinafter), Si: 0.1 to 1.5%, Mn: P: more than 0% to 0.03% or less, S: more than 0% to 0.03% or less, Ti: 0.02 to 0.2%, Al: 0.01 to 0.10%, and N: 0.001 to 0.006% And satisfies the following expression (1).

0.05% ≥ [Ti *] ≥ (0.0023 × [C]) ... (One)

[Ti *] = (total amount of Ti - amount of compound Ti of 0.1 占 퐉 or larger in size), and [C] indicates content of C (% by mass).

On the other hand, the above-mentioned compound Ti content of 0.1 mu m or more means the amount of compound Ti in the residue filtered through a mesh having an eye size of 0.1 mu m.

In the wire rod for high strength steel wire according to the present invention, it is preferable that the metal structure has a pearlite phase of 90% or more in area ratio and a maximum length of cornerstone cementite of 15 탆 or less. The amount of solid solution N in the wire is preferably more than 0% and not more than 0.0005%.

(A) B: more than 0% and not more than 0.010%, (b) Cr: not less than 0% and not more than 0.5%, (c) V: more than 0% and not more than 0.2% (D) Ni: more than 0% to 0.5%, Cu: more than 0% to 0.5%, Mo: more than 0% to 0.5%, Co: more than 0% to 1.0% And the like, and the properties of the wire rod are further improved depending on the kind of the component to be contained.

The present invention also includes a high-strength steel wire obtained by drawing (for example, drawing) a wire rod for high-strength steel wire as described above. In the high-strength galvanized steel wire produced by hot-dip galvanizing the high-strength steel wire, the tensile strength TS is preferably not less than the tensile strength TS * specified by the following formula (2).

TS * = -87.3D + 2234 (MPa) ... (2)

Where D represents the diameter (mm) of the high strength galvanized steel wire.

According to the present invention, it is possible to obtain a wire rod for high strength steel wire which has excellent drawability and achieves high strength, by strictly specifying the chemical composition of the TiC while taking into account the fine TiC precipitating state. The steel wire obtained from such a high-strength steel wire rod is extremely useful as a material of a hot-dip galvanized steel wire or a stranded wire to be used as a rope material used for bridges and the like.

In order to solve the above problems, the inventors of the present invention have studied the relationship between wire structure and drawing processability. Particularly, the precipitation mechanism of cobalt cementite in the overglaze is also studied. As a result, it has been found that deposition of fine-grain cementite can be suppressed by precipitating fine TiC near the grain boundary. The most effective one is the fine TiC having a size of 0.1 탆 or less, and it is necessary to sufficiently secure the deposition amount of the fine TiC. The higher the C content of the steel, the more cementite is likely to precipitate, thus requiring more fine TiC. Since this effect is difficult to achieve in coarse TiC, it is necessary to precipitate as much fine TiC as possible. It becomes extremely important to appropriately control the deposition amount and the size distribution of TiC.

By precipitating the fine TiC having a size of 0.1 m or less in the vicinity of the austenite grain boundary as described above, grain boundary energy can be reduced and precipitation of the cornerstone cementite can be suppressed. Direct evaluation of fine TiC requires a lot of labor and cost, but can be evaluated simply by using electrolytic extraction residue measurement. That is, at room temperature, the total amount of Ti in the steel is a compound such as TiC or TiN, and the size of TiN is about 5 to 10 mu m. Therefore, when the amount of the compound-form Ti having a size of 0.1 mu m or more, more specifically, the amount of the compound-form Ti in the residue filtered through a mesh having an eye size of 0.1 mu m is measured and a value obtained by subtracting the total amount of Ti from the steel is regarded as [Ti *] , Where [Ti *] represents the amount of fine TiC exiting the mesh. On the other hand, the above-mentioned compound type Ti means Ti present as a compound.

The larger the C content in the steel, the more precipitated cobalt cementite is formed, and a large amount of fine TiC is required. From this relationship, the above-mentioned [Ti *] is 0.0023 x [C] or higher, preferably 0.0023 x [C] + 0.001% or higher, more preferably 0.0023 x [C] + 0.005% or more is required. On the other hand, when a large amount of fine TiC is precipitated, the grain boundary is brittle and the toughness of the wire is lowered, causing vertical cracks at the time of drawing. From this viewpoint, the upper limit of the above-mentioned [Ti *] is 0.05% or less, preferably 0.03% or less, more preferably 0.01% or less.

In the steel wire rope of the present invention, it is necessary to appropriately adjust the chemical composition of the steel wire rope in order to satisfy the basic components as the wire rods and properly control the precipitation state of TiC. From this point of view, the reason for setting the range of the chemical composition of the wire rod is as follows.

(C: 0.80 to 1.3%)

C is an element effective for increasing the strength, and as the C content increases, the strength of the steel wire after cold working is improved. In order to achieve the intended strength level of the present invention, the C content needs to be 0.80% or more. However, if the C content is excessive, corner stone cementite precipitates at the grain boundaries, which hinders drafting workability. From this viewpoint, the C content needs to be 1.3% or less. The lower limit of the C content is preferably 0.84% or more, more preferably 0.90% or more, and the upper limit is preferably 1.2% or less, more preferably 1.1% or less.

(Si: 0.1 to 1.5%)

Si is an effective deoxidizing agent and exhibits an effect of reducing oxide inclusions in the steel. In addition to increasing the strength of the wire rod, there is also an effect of suppressing the cementite granulation accompanied by the thermal history at the time of hot dip galvanizing and suppressing the decrease in strength. In order to exhibit such an effect effectively, Si must be contained in an amount of 0.1% or more. However, if the Si content is excessive, the toughness of the wire rod is deteriorated. Therefore, the Si content should be 1.5% or less. The lower limit of the Si content is preferably 0.15% or more, more preferably 0.20% or more, and the preferable upper limit is 1.4% or less, more preferably 1.3% or less.

(Mn: 0.1 to 1.5%)

Mn has the effect of increasing the strength of the pearlite structure by lowering the transformation temperature at the time of air-blast cooling to greatly enhance the hardenability of the steel material. In order to effectively exhibit these effects, the Mn content needs to be 0.1% or more. However, Mn is an element which is easily segregated, and if it is contained in excess, the hardenability of the Mn segregation portion excessively increases, and there is a risk of generating a supercooled structure such as martensite. Taking these effects into consideration, the upper limit of the Mn content was set to 1.5% or less. The lower limit of the Mn content is preferably 0.2% or more, more preferably 0.3% or more, and the upper limit is preferably 1.4% or less, more preferably 1.3% or less.

(P: more than 0% to 0.03% or less, S: more than 0% to less than 0.03%)

P and S are segregated at the old austenite grain boundaries to embrittle the grain boundaries to lower the fatigue characteristics. Therefore, the lower limit of P and S is preferably as low as possible, but the upper limit thereof is 0.03% or less in industrial production. The content of these is preferably 0.02% or less, more preferably 0.01% or less. On the other hand, P and S are impurities inevitably included in the steel material, and it is difficult to make the amount thereof 0% in view of industrial production.

(Ti: 0.02 to 0.2%)

Ti is an extremely important element in the wire of the present invention, and is finely precipitated in the form of TiC in the vicinity of the grain boundary, thereby exhibiting an effect of suppressing the precipitation of cornerstone cementite. This is due to the function of locally lowering the C content by fixing C in the vicinity of the grain boundary in the form of TiC and the function of mitigating the grain boundary energy by fine TiC of 0.1 μm or less to prevent the nucleation of the cementite. Ti, like Al, also has an effect of grain refinement and toughness improvement due to the formation of nitride. In order to exhibit such an effect, Ti should be contained in an amount of 0.02% or more. However, if the content of Ti becomes excessive, TiC precipitates excessively to brittle the grain boundaries, and toughness is lowered. From this viewpoint, the Ti content should be 0.2% or less. The lower limit of the Ti content is preferably 0.03% or more, more preferably 0.04% or more, and the upper limit is preferably 0.18% or less, more preferably 0.16% or less.

(Al: 0.01 to 0.10%)

Al has a strong deoxidizing effect and has the effect of reducing oxide inclusions in the steel. It is also expected that the grain fine effect by the pinning action of the nitride and the effect of reducing the solid solution N can be expected. In order to exhibit such an effect, it is necessary to contain 0.01% or more of Al. However, when the Al content is excessive, Al-based inclusions such as Al ₂ O ₃ are increased, which causes problems such as an increase in the monofilament ratio during drawing processing. In order to prevent this, the Al content needs to be 0.10% or less. The lower limit of the Al content is preferably 0.02% or more, more preferably 0.03% or more, and the upper limit is preferably 0.08% or less, more preferably 0.06% or less.

(N: 0.001 to 0.006%)

N is an interstitial element which, when solidified in steel, leads to embrittlement due to strain aging, which degrades the toughness of the wire. Therefore, the upper limit of the N content (total N) in the steel is 0.006% or less. However, it is the solid solution N which is solved in the steel which brings about such a bad effect, and the compound N precipitated as the nitride does not adversely affect the toughness. Therefore, it is preferable to control the amount of solute N dissolved in the steel, separately from the total amount of N in the steel, and the solute N amount is preferably 0.0005% or less, and more preferably 0.0003% or less. On the other hand, in industrial production, it is difficult to reduce N in the steel to less than 0.001%, so the lower limit of the N content in the steel is 0.001% or more. On the other hand, the preferred upper limit of the N content in the steel is 0.004% or less, more preferably 0.003% or less.

The contained elements specified in the present invention are as described above, and the remainder is iron and unavoidable impurities. As the unavoidable impurities, the incorporation of the elements introduced by the conditions of the raw material, the material, and the manufacturing facilities can be allowed. (B) Cr: more than 0% to 0.5%; (c) V: more than 0% to not more than 0.2%; (d) Ni: 0 At least one selected from the group consisting of Cu: at least 0.5%, Cu: at least 0.5%, Mo: at least 0.5%, Co: at least 1.0% May be contained individually or appropriately in combination, and the characteristics of the wire may be further improved depending on the kind of the component to be contained. The reason for setting the range when these elements are contained is as follows.

(B: more than 0% to less than 0.010%)

B has an effect of inhibiting the production of pro-eutectoid ferrite and cobalt cementite and making it easy to control the structure to a uniform pearlite structure. Further, by fixing N in the steel in the form of BN, strain aging is suppressed and toughness of the wire is improved. In order to exert their action effectively, B is preferably contained in an amount of 0.0003% or more. More preferably 0.0005% or more, and still more preferably 0.0008% or more. However, when the content of B is excessive, a compound (B-constituent) with iron precipitates and causes cracking during hot rolling. Therefore, the upper limit of B is preferably 0.010% or less. On the other hand, a more preferable upper limit of the content of B is 0.008% or less, and more preferably 0.006% or less.

(Cr: more than 0% to 0.5% or less)

Cr has an effect of increasing the strength and toughness of the wire rod by refining the lamellar spacing of the pearlite. In addition, like Si, there is an effect of suppressing the strength reduction of the wire at the time of zinc plating. However, even if the Cr content is excessive, its effect is saturated and is economically useless, so it is preferable that the Cr content is 0.5% or less as an appropriate content. On the other hand, in order to effectively exhibit the effect of Cr, the content of Cr is preferably 0.001% or more, more preferably 0.05% or more. A more preferable upper limit of the Cr content is 0.4% or less, and more preferably 0.3% or less.

(V: more than 0% to 0.2% or less)

Since V produces minute carbon and nitride (meaning carbides, nitrides and carbonitrides), it has an effect of increasing the strength and making the crystal grains finer. In addition, by suppressing the aging hardening by fixing the solid solution N, In order to effectively exhibit the effect of V, V is preferably contained in an amount of 0.001% or more, more preferably 0.05% or more. However, even when the V content is excessive, its effect is saturated and is not economically usable. Therefore, it is preferable that the content is 0.2% or less as an appropriate content. The V content is more preferably 0.18% or less, and further preferably 0.15% or less.

(Ni: more than 0% to 0.5%, Cu: more than 0% to 0.5%, Mo: more than 0% to 0.5%, Co: more than 0% to 1.0%, and Nb: more than 0% to 0.5% Or more)

Ni is an effective element for increasing the toughness of the steel wire after drawing. In order to effectively exhibit the effect of Ni, it is preferable to contain Ni in an amount of 0.05% or more, more preferably 0.1% or more. However, even when the Ni content is excessive, its effect is saturated and is not economically usable. Therefore, an appropriate Ni content is preferably 0.5% or less, more preferably 0.4% or less, and still more preferably 0.3% or less.

Cu and Mo are effective elements for increasing the corrosion resistance of the steel wire. In order to effectively exhibit such effects, it is preferable that the content is 0.01% or more, more preferably 0.05% or more. However, when the content of Cu is excessively large, Cu reacts with S to segregate CuS in the grain boundary portion, causing flaws in the course of manufacturing the wire rod. Therefore, the upper limit of the Cu content is preferably 0.5% or less, 0.4% or less, and more preferably 0.3% or less.

On the other hand, Mo, like Cu, is an effective element for improving the corrosion resistance of the steel wire. However, if the Mo content is excessive, overcooled structure tends to occur during hot rolling, and the ductility also deteriorates. In view of this, the upper limit of the content of Mo is preferably 0.5% or less, more preferably 0.4% or less, and still more preferably 0.3% or less.

Co has the effect of reducing the corner stone cementite and making it easy to control the texture to a uniform pearlite structure. However, even if Co is contained excessively, its effect is saturated and is not economically useful. Therefore, the upper limit of the Co content is preferably 1.0% or less, more preferably 0.8% or less, and further preferably 0.5% or less. On the other hand, in order to effectively exhibit the effect of Co, the content is preferably 0.05% or more, more preferably 0.1% or more, and still more preferably 0.2% or more.

Like Nb, Nb contributes to grain refinement by forming a nitride, and it is also expected to suppress aging hardening by fixing solid solution N. However, even if Nb is excessively contained, the effect thereof becomes saturated, which is economically useless. Therefore, the upper limit of the Nb content is preferably 0.5% or less, more preferably 0.4% or less, and further preferably 0.3% or less. On the other hand, in order to effectively exhibit the effect of Nb, the content is preferably 0.05% or more, more preferably 0.1% or more, and still more preferably 0.2% or more.

In the wire rod for high strength steel wire of the present invention, it is preferable that the metal structure is made of a pearlite phase as a main body (for example, 90% or more in area ratio), but other phases (for example, It is permissible.

In the present invention, it is preferable that the length of the cornerstone cementite is further controlled. This is because the base stone cementite precipitated on the center side of the wire material D / 4 (D: the diameter of the wire material) causes a crack during the drawing process and causes a cuppy disconnection. The cementite (lamellar cementite) forming the lamellar structure of pearlite has a property of being rotated in the drawing process and oriented in the longitudinal direction of the wire rod. However, the corner stone cementite can not rotate in synchronization with the surrounding tissues, and cracks are generated from the interface thereof. The factor that governs this rotation is the length of the cornerstone cementite. If the length (maximum length) of the cornerstone cementite is larger than 15 탆, it becomes difficult to rotate and becomes a source of cracks, but a short one is easy to rotate and does not hinder the drawability. From this point of view, the length (maximum length) of the cornerstone cementite is preferably 15 占 퐉 or less, more preferably 13 占 퐉 or less, and further preferably 10 占 퐉 or less. On the other hand, the lower limit of the length of the corner stone cementite is not particularly limited, and may be, for example, about 0.1 탆.

The wire rod for high strength steel wire according to the present invention has excellent drawability and can achieve high strength. The tensile strength of the wire of the present invention can be, for example, 1100 MPa or more, and preferably, 1200 MPa or more. The upper limit of the tensile strength is not particularly limited, but is usually about 1500 MPa.

In producing the wire rod for high-strength steel wire according to the present invention, it is possible to produce the steel wire according to the usual production conditions by using a steel piece whose chemical composition is adjusted as described above. However, preferable manufacturing conditions for appropriately adjusting the structure of the wire rod and the like are as follows.

In the process of manufacturing a high carbon steel wire rod, generally, a steel strip adjusted to a predetermined chemical composition is heated and austenitized, a wire rod having a predetermined wire diameter is obtained by hot rolling, and then cooled in a cooling conveyor, . At this time, fine austenite structure accompanied by dynamic recrystallization is obtained during hot rolling, but TiC can be finely dispersed in the vicinity of the grain boundary by precipitating TiC simultaneously with this recrystallization. Here, when the reduction in the reduction in the final rolling 4 passes (4 passes from the final pass to the 4th pass) in which the influence to the crystal grain size is greatest is ε, the reduction ratio ε is 0.4 or more, To finely disperse TiC. Here, the reduction strain ε is represented by ε = ln (S ₁ / S ₂ ) (S ₁ : cross-sectional area of the wire at the inlet side of the rolling roll, and S ₂ : cross-sectional area of the wire at the outlet side). The preferable lower limit of the reduction strain epsilon is 0.42 or more, more preferably 0.45 or more, and the preferable upper limit of the reduction strain epsilon is 0.8 or less, more preferably 0.6 or less.

Further, in the cooling process after rolling, the coarsening of the fine precipitated TiC proceeds. An important requirement at this time is the wicking temperature of the wire rod. It is preferable to control the deposition temperature to 850 to 950 占 폚 to obtain a desired TiC deposition state. If the deposition temperature exceeds 950 占 폚, TiC coarsens, and if it is lower than 850 占 폚, TiC becomes excessively fine and remains. The upper limit of the setting temperature is more preferably 940 占 폚 or lower, and still more preferably 930 占 폚 or lower. The lower limit of the setting temperature is more preferably 870 DEG C or higher, and still more preferably 880 DEG C or higher.

If the cooling rate (average cooling rate) at this time becomes too fast, bainite or the like is likely to be incorporated, and the structure of the main body of the pearlite phase can not be obtained. From this viewpoint, the average cooling rate within the range of the setting temperature is preferably 20 DEG C / second or less, more preferably 18 DEG C / second or less, and further preferably 14 DEG C / second or less. On the other hand, the lower limit of the average cooling rate at this time is preferably 3 deg. C / sec or higher, more preferably 4 deg. C / sec or higher, further preferably 5 deg. C / sec or higher from the viewpoint of less precipitation of crude stone cementite, Seconds.

The high carbon steel wire rod (wire rod for high strength steel wire) of the present invention has a good drawability, and when subjected to drawing, a high strength steel wire exhibiting desired characteristics such as strength and twist value can be obtained. Such a high strength steel wire is generally used as a high strength galvanized steel wire by performing hot dip galvanizing on its surface. The reduction ratio of the drawing is not particularly limited, but the wire of the present invention is good in drawability, and even if the reduction ratio is, for example, more than 80%, or more than 83%, the wire can be fresh without being broken. The upper limit of the reduction ratio is not particularly limited, but is, for example, 95% or less. The hot-dip galvanizing may be performed by immersing the hot-dip galvanizing bath at 350 ° C or higher (preferably 400 ° C or higher) and 550 ° C or lower (preferably 500 ° C or lower) for about 15 seconds to 1 minute. In the steel wire subjected to the drawing process such as the drawing process, the smaller the diameter of the wire, the higher the strength. The tensile strength TS of the high-strength galvanized steel wire is preferably TS * + 50 (MPa) or more, more preferably TS * + 100 (MPa) or more, MPa) or more. On the other hand, the relationship of the following formula (2) is obtained by an experiment.

TS * = -87.3D + 2234 (MPa) ... (2)

Where D represents the diameter (mm) of the high strength galvanized steel wire.

This application claims the benefit of priority based on Japanese Patent Application No. 2013-67465 filed on March 27, The entire contents of the specification of Japanese Patent Application No. 2013-67465 filed on March 27, 2013 are incorporated herein by reference.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is of course not limited by the following Examples, and it is needless to say that the present invention is not limited to the Examples All of which are included in the technical scope of the present invention.

Example

Hot-rolled steel sheets were processed into predetermined wire diameters by using a steel piece (sectional shape: 155 mm x 155 mm) of the chemical composition shown in Table 1 (steel types A to S) shown in Table 1 below, placed on a cooling conveyor in a ring shape, Pearlite transformation was carried out by controlled cooling by means of a cooling method, and then coiled into a coil shape to obtain various rolled material coils. On the other hand, in Table 1, "-" means no addition.

The unadjusted portion of the terminal (that is, the end portion of the rolled material) was cut off and the terminals of the good article were taken out of the obtained rolled material to evaluate the rolled material (rolled material wire diameter, [Ti *], solid N amount, , Texture, tensile strength TS) were evaluated by the following methods. On the other hand, the "heating temperature" in Table 2 is the heating furnace temperature before the hot rolling, and the reduced strain ε is the total reduction reduction in the final rolling four passes (four passes in total from the final pass to the fourth pass). The " average cooling rate " is obtained by averaging the cooling rates from the wick to 800 deg. However, For 5, the average cooling rate from wick temperature to 750 ° C was adopted.

(Distribution state of TiC, evaluation of the amount of solid solution N)

[Ti *] and the amount of dissolved N were evaluated by electrolytic extraction residue measurement. In this measurement, extraction was carried out using a 10% acetylacetone solution, and a mesh of 0.1 mu m was used. The amount of compound Ti in the residue was measured by ICP (Inductively Coupled Plasma) emission spectrometry, the compound type N amount, the compound type B amount by absorbance spectrophotometry, and the amount of AlN by the bromine ester method. The amount of the sample used in the bromine ester method was 3 g, and the amount of the sample used in the emission spectrophotometry was 0.5 g. On the other hand, the precipitation state of TiC does not change unless subjected to a heat treatment of at least 1000 캜 or more, and therefore may be measured after drawing or after hot dip galvanizing. [Ti *] = total amount of Ti - measuring the amount of [Ti *] based on the amount of compound type Ti having a size of 0.1 占 퐉 or larger in size, .

(Tensile strength TS of rolled material, evaluation of tissue)

A tensile test was conducted on the terminal sample of the rolled material to measure the tensile strength TS of the rolled material. At this time, an average value of 3 times (n = 3) was obtained. The state of corner stone cementite was also evaluated by embedding a terminal sample in a resin in the same manner and observing it with a scanning electron microscope (SEM). (Cross section) perpendicular to the longitudinal direction of the wire rod was observed, and the maximum length of the plate-like cornerstone cementite observed on the center side of D / 4 (D: diameter of the wire rod) in the cross section was measured. On the other hand, when the tip of the cornerstone cementite is divided into a plurality of branches, a total of the lengths of the branches is employed.

Production conditions and evaluation results at this time are shown in Table 2 below. On the other hand, in Table 2, the value of 0.0023 x [C] of the rolled material (C is the C content of the rolled material) is also shown.

Each rolled material obtained above was processed to a predetermined diameter by cold drawing and immersed in a molten zinc bath at 440 to 460 캜 for about 30 seconds to obtain a hot-dip galvanized steel wire. The tensile strength TS of the wire (hot-dip galvanized steel wire) was also evaluated by a tensile test. At this time, the average value of three times (n = 3) was measured. Further, the salting-out value was measured by the salting test and the presence of the longitudinal crack was judged from the observation of the wave-front shape. The salting-out value was normalized to the distance between the chucks of 100 mm, which was required before the rupture, and an average value of three times (n = 3) was calculated. In the case of three vertical scoring tests, it was judged that there was vertical scoring even if one vertical scoring was observed.

Table 3 shows the evaluation results of the hot-dip galvanized steel wire (reduction of wire diameter, reduction ratio at cold drawing, tensile strength TS, tensile strength TS * obtained by the above formula (2), and presence or absence of longitudinal cracks).

From these results, it can be considered as follows. That is, 1 to 3 and 8 to 19 satisfied all the requirements stipulated in the present invention, and the whole of the structure had a pearlite phase of not less than 90% by area. No abnormality such as disconnection was observed during the drawing process, and the wire strength and the sintering characteristics after the hot dip galvanizing treatment were good. Of these, 16 and 19, the amount of dissolved N was slightly increased, and the bittern value was slightly lowered.

On the other hand, 4 to 7, and 20 to 23 are examples that do not satisfy any of the requirements specified in the present invention (or do not satisfy the more preferable requirements), and they show an abnormality such as disconnection during drawing processing, It can be seen that either the wire strength after the treatment or the thinning property is inferior.

Of these, 4 can sufficiently suppress the cornerstone cementite because the placement temperature is as high as 1000 ° C and the amount of [Ti *] is reduced (that is, because the TiC is coarsened and the maximum length of the corner stone cementite exceeds 15 μm) I could not, I was disconnected in the middle of freshness. Test No. 5 exhibited vertical cracking due to brittle grain boundary due to excessively large amount of [Ti *] due to low setting temperature of 800 ° C (that is, due to excessively fine TiC).

Test No. 6 shows that the reduction in the final four-pass stress is small, the crystal grains are not sufficiently refined and the amount of [Ti *] is reduced (i.e., TiC is not refined and the maximum length of cornerstone cementite exceeds 15 占 퐉 ), The cementitious stone cementite could not be sufficiently suppressed, and it was broken during the freshness. Test No. 7, the cooling rate became faster and the rolled material structure became a blended structure of pearlite and bainite (area ratio of bainite: 40%).

Test No. 20 is an example using a steel material (grade P) having a low C content, and the strength of the steel wire was lowered. Test No. 21 is an example using an excessive C content (steel grade Q), and it can not suppress cornerstone cementite and is broken.

Test No. 22 is an example using a steel material having a low Ti content (steel type R), and it can not suppress crushed cementite and is broken. No. 23 is an example using an excessive Ti content (steel type S), and the amount of [Ti *] was excessive, and vertical cracks occurred.

Since the wire of the present invention is excellent in raw drawing ability and can attain a high strength, it is suitable for a material of a hot-dip galvanized steel wire or a strand which becomes a rope material used for bridges and the like, and is industrially extremely useful.

Claims (9)

C: 0.80 to 1.3% (the meaning of mass%, the same applies hereinafter for composition)
Si: 0.1 to 1.5%
Mn: 0.1 to 1.5%
P: more than 0% and not more than 0.03%
S: more than 0% and not more than 0.03%
Ti: 0.02 to 0.2%
Al: 0.01 to 0.10%, and
N: 0.001 to 0.006%
Respectively, the balance being iron and inevitable impurities,
A wire for a high-strength steel wire excellent in drawability, characterized by satisfying the following expression (1).
0.05% ≥ [Ti *] ≥ (0.0023 × [C]) ... (One)
[Ti *] = (total amount of Ti - amount of compound Ti of 0.1 占 퐉 or larger in size), and [C] indicates content of C (% by mass). The method according to claim 1,
A wire rod for a high-strength steel wire having a metal structure having a pearlite area of 90% or more in area ratio and a maximum length of cornerstone cementite of 15 μm or less. The method according to claim 1,
A wire rod for a high strength steel wire having an employment amount of N exceeding 0% and not more than 0.0005%. 3. The method of claim 2,
A wire rod for a high strength steel wire having an employment amount of N exceeding 0% and not more than 0.0005%. 5. The method according to any one of claims 1 to 4,
And more preferably more than 0% but not more than 0.5%, Cu: not more than 0% and not more than 0.5%, Mo: not more than 0.010%, Cr: not less than 0% Not less than 0% and not more than 0.5%, Co: not less than 0% and not more than 1.0%, and Nb: not less than 0% and not more than 0.5%. A high strength steel wire obtained by drawing the wire rod for high strength steel wire according to any one of claims 1 to 4. A high strength steel wire obtained by drawing the wire rod for high strength steel wire according to claim 5. A high-strength galvanized steel wire produced by hot-dip galvanizing the high-strength steel wire according to claim 6, wherein the high-strength galvanized steel wire has a tensile strength TS of not less than a tensile strength TS * specified by the following formula (2).
TS * = -87.3D + 2234 (MPa) ... (2)
Where D represents the diameter (mm) of the high strength galvanized steel wire. A high-strength galvanized steel wire produced by hot-dip galvanizing the high-strength steel wire according to claim 7, wherein the high-strength galvanized steel wire has a tensile strength TS of not less than a tensile strength TS * specified by the following formula (2).
TS * = -87.3D + 2234 (MPa) ... (2)
Where D represents the diameter (mm) of the high strength galvanized steel wire.