JP2906025B2 - High strength steel wire and steel cord for reinforcing rubber products and method for producing high strength steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength steel wire used as a reinforcing material for various rubber products such as vehicle tires and hydraulic high-pressure hoses, a method for producing the same, and a high-strength steel cord using the steel wire.

[0002]

2. Description of the Related Art A cord for reinforcing a rubber product such as a tire or a high-pressure hose or a solid wire generally has a diameter of 0.10 brass-plated for vulcanization bonding with rubber.
A steel wire of up to 0.40 mm is used, and with a main purpose of reducing the weight of the product, the diameter is 0.25 mm, 3090 N / mm ² or more, and the diameter is 0.3
High-strength steel wire of 2890 N / mm ² or more at 5 mm is used. Such high strength steel wire is
Conventionally, a high-carbon steel wire containing 0.80% by weight or more of carbon is generally used as a raw steel wire, and is made by wire drawing. That is, for example, when manufacturing the high-strength steel wire with nominally 0.82C% carbon steel, the reduction in area (working rate) is 96.0 to 97.0%.
It was manufactured by moderate wire drawing.

[0003] The reason for using such a high carbon steel material is as follows. If a carbon steel with a lower carbon content is used, the strength itself of the material before processing is low, so that the strength after the final heat treatment is naturally lower than that with a high C content, and thus a high carbon steel material In order to obtain a steel wire having the same strength as that of, a particularly high area reduction (working degree) must be taken in the subsequent wire drawing. However, when such a high degree of work is taken, the steel wire strength increases due to work hardening, but on the other hand, defects occur inside the steel wire to deteriorate toughness, and conversely, tensile strength may decrease. . As a result, the wire breaks during the wire drawing process, making it impossible to perform the specified processing. Because they are gone. Furthermore, if such a steel wire is used to reinforce the high-pressure hose, there will be problems such as a spiral knotting process in the forming process and breakage during knitting to the blade, causing serious troubles. is there. If the degradation of the toughness of the steel wire exceeds a certain limit, the above-mentioned processing defects will occur, and the fatigue resistance will rapidly decrease, which is a serious problem in practice. Therefore, conventionally, the toughness of a manufactured steel wire is generally evaluated based on a torsion value until a fracture is reached. However, in practice, even when the torsion values are almost the same, there is a possibility that both good and bad are obtained in processing such as twisting the cord, and it is difficult to determine the toughness limit. Alternatively, it was difficult to determine the toughness by evaluating other characteristics, such as elongation at break and drawing value. Therefore, the nominal 0.72
With the C% material, a practical high-strength steel wire obtained from a material of 0.82C% or more as shown in FIG. 1 could not be produced. Therefore, conventionally, a high-strength steel wire using a high-carbon steel wire containing 0.80% by weight or more of carbon has been used as a constant cost increase.

[0004]

SUMMARY OF THE INVENTION The present invention has been made by research to solve the above-mentioned problems, and the first object of the present invention is to provide a high carbon steel of 0.80% by weight or more. While using 0.70 to 0.75C% carbon steel wire rod, which has a lower material cost, it has high strength, rich in toughness and fatigue resistance, and aims to appropriately reduce the weight and improve the fatigue resistance of rubber products. It is an object of the present invention to provide a steel wire and a steel cord for reinforcing a rubber product. A second object of the present invention is to provide a method for easily and stably producing a high-strength steel wire having the above characteristics.

[0005] To achieve the first object, the present invention provides:
A steel wire having a diameter of 0.10 to 0.40 mm obtained by using a carbon steel wire rod containing 0.70 to 0.75% by weight of carbon, applying heat treatment and plating, and then drawing. The steel wire has a tensile strength that satisfies the following equation, and has a characteristic of a torque reduction rate of 7% or less in a twist-torque test in which one-way twisting and then reverse twisting are performed. It is what it was. Y ≧ −1960d + 3580 [Y: tensile strength (N / mm ² )
d: diameter (mm)]

[0006] In order to achieve the second object of the present invention,
The present invention uses a carbon steel wire rod containing 0.70 to 0.75% by weight of carbon, and after performing heat treatment and plating,
The wet drawing is performed under the following conditions. Approach angle 2α is 8 to 1 as a drawing die
0 °, the bearing length 0.25~0.35d ₁ (d ₁ =
Finish pulling uses a double die in which two drawing dies are arranged in series, and draws a skin pass with a surface reduction rate of 1.2 to 3.9% at the exit side die. Do. A sintered diamond nib is used for the double die and several drawing dies upstream of this. Immediately after passing the final die, the steel wire temperature is 150 ℃
Control is performed as follows.

[0007]

According to the present invention, a carbon steel wire having a carbon content of 0.70 to 0.75% by weight, which is generally used at present, is used.
In this aspect, the cost is low. The tensile strength is Y ≧
Since it has a high strength of −1960d + 3580 N / mm ² , a good reinforcing effect can be realized with a small number. Note that the upper limit of the strength level of the steel wire is −1960d + 3920N from the relation of the carbon content.
/ Mm ² . Moreover, the present invention employs a one-way torsion-torsion test by reverse torsion as means for determining the toughness limit which determines the quality of workability and fatigue resistance in the hose forming process, such as wire drawing and twisting,
A steel wire manufactured by the above method having a torque reduction rate of 0 to 7% in this test is used. For this reason, the steel wire has both high strength and toughness, and is an ultra-high-strength steel wire for rubber reinforcement with good twisting efficiency and good fatigue resistance, and a steel cord made by twisting a plurality of these wires has high strength and high toughness. It is also excellent in fatigue resistance, and can be used to reduce the cost and weight by using it as a reinforcing material for rubber products.

[0008] In detail, simply twist in one direction and twist
When a torque curve is measured, there are two types: a normal curve in which the torque continuously rises to the right, leading to breakage, and a torque curve, in which the torque becomes extremely unstable and torque decreases during the breakage. Appear. It is considered that such a decrease in torque is caused by minute cracks inside the steel wire during twisting, and this also means that the wire is drawn beyond the working limit. In cases where the toughness of the steel wire is particularly degraded, this test already results in a reduction in torque. However, even if a steel cord which does not show a torque reduction (torque unstable part) in this test is actually used and twisted to form a steel cord, disconnection occurs and fatigue characteristics are insufficient. Many things appeared. Therefore, in the torque reduction judgment by this test, the judgment of the toughness is insufficient and inaccurate.

Accordingly, the present invention provides a method of twisting the steel wire in a predetermined direction (for example, clockwise) at a constant speed and a predetermined number of times while maintaining a linear shape by applying a slight tension in the axial direction of the steel wire as a predetermined grip interval, and then temporarily stopping the twisting. Then reverse until steel wire breaks (eg counterclockwise)
A severe torsion-torque test is performed. And in such a one-way-reverse twist method,
As shown in FIG. 2 (a), the torque reduction rate is not more than 7% not only in the one-way torsion-torque but also in the following reverse-direction torsion-torque after one-way torsion as shown in (b). Only the steel wire having good toughness is provided, and such a steel wire itself has high strength and good fatigue resistance. In addition, the strength of a steel cord made by twisting multiple steel wires is naturally lower than the collective strength of the steel wire, but the tough steel wire with good toughness has a small drop in strength and uses the strength of the steel wire efficiently. And good fatigue resistance. On the other hand, when the torque decrease did not occur in the one-direction torsion stage, but the torque decrease rate was 8% or more in the reverse torsion stage, the toughness was substantially poor, the strength was relatively poor, and the Fatigue is also relatively poor.

The above-mentioned torque reduction rate is obtained by conducting a twist-torque test using a one-way-reverse twist method on a number of steel wires having different diameters and materials, and measuring the rate of the twist-torque reduction. This is because the above-described good characteristics were not obtained when the torque reduction rate was 8% or more in any case. In the torsion-torque curve of FIG. 2 (b), the torque reduction rate is defined as T where the torque value at the first torsion elastic limit in one-way torsion, that is, the torque value at the upper limit of the linear portion rising to the right in the drawing, is T. Assuming that the minimum value of the torque value of the lowering portion is t, the torque reduction rate ΔT is represented by the following equation. However, when there is no decrease in torque, t = T. ΔT = [(T− | t |) / T] × 100 (%) When the torque reduction rate ΔT is 8% or more, the above-described problem occurs. Therefore, the present invention provides a torque reduction rate ΔT of 7% or less. Therefore, a parameter for improving the toughness of only the steel wire exhibiting the above characteristic was adopted. In addition, the parameters of the present invention are 1 × n steel cord, and 2+
Since the situation in which the steel cord is twisted in a certain direction and then untwisted, as represented by the manufacture of a steel cord having an n + m structure represented by 2, can be well simulated, the obtained steel cord is also appropriate.

Next, the present invention provides a method for producing the above steel wire, wherein the content of C is 0.70 to 0.75% by weight.
Use a carbon steel wire having This is, specifically, JI
Hard steel wire (SWRH) or JI indicated by SG 3506
It is preferable to use an equivalent of a piano wire (SWRS) represented by SG3502, but Cr or Ni is used as an alloy element.
May be added in a required amount. Such a carbon steel wire is formed into an intermediate-diameter steel wire according to a conventional method, and after heat treatment and plating, the steel wire is finished to a target diameter by wet drawing.In this wet drawing process, the present invention employs specific conditions. Things. First, the final drawing is performed in a lubricating liquid (wet method), and the temperature of the steel wire immediately after the completion of the drawing is kept at 150 ° C. or lower. Thereby, embrittlement due to aging can be suppressed. For this purpose, the temperature of the lubricating liquid is suppressed, and a skin pass is performed using a double die in which two final drawing dies are stacked. In addition, the skin pass reduction ratio at this time is set to 1.2 to 3.9%, and if the skin pass reduction ratio exceeds 4.0%, the effect of relaxing the residual stress is reduced, which is impossible. Even if the area reduction rate is as small as 1.1% or less, the effect of relaxing the residual stress is reduced, so that it is impossible. Due to the skin pass reduction, the steel wire temperature can be reduced by 25 to 40 ° C. as compared with a normal pass.

Next, a drawing die is set at an approach angle of 8 to 10 °. Conventionally, drawing force in wire drawing is 12 °
Although this is adopted because it is the lowest, the present invention makes the approach angle smaller than this. This is to increase the degree of work hardening, raise the limit of wire drawing, and improve the fatigue resistance by lowering the surface residual stress. The reason for increasing the degree of work hardening is that in order to achieve high strength with a low C% material, the degree of work must be extremely high,
This is because the machining limit is exceeded if it is used as it is. Therefore, the drawing limit is raised by using a low approach angle die of 8 to 10 °, and the work hardening degree for each pass is increased to relatively increase the total workability. Is to be kept low. However, if the angle is less than 8 °, the pull-out resistance of the steel wire is too high, which is not appropriate. In addition, bearing length 1 of the dice for the pore diameter d ₁ 0.25~0.
It is set to 35d _1. The reason is that 0.5
When the bearing length is about d _1, heat is remarkably generated because the pullout resistance increases. Therefore, in order to reduce the contact area with the steel wire and reduce the heat generation of the steel wire, the bearing length was shortened, and the balance between this and the approach angle raised the drawing limit and reduced the drawing resistance. Can be.

Further, the present invention uses sintered diamond nib dies (hereinafter, abbreviated as diamond dies) for at least several pieces (about four or more including two double dies) from the top. The reason for this is that there is a problem that the die life is shortened due to an increase in the degree of work hardening per one die as compared with the processing of a high C material. That is, in a conventional die of a sintered alloy nib of tungsten carbide (hereinafter abbreviated as an alloy die), the surface is rough and the drawing resistance is large, and the surface of the steel wire is also rough,
It also has an adverse effect on fatigue resistance. On the other hand, since the surface of the sintered diamond nib is smoother than the surface of the sintered alloy nib, when the wire is drawn, the drawing resistance is low and the surface of the steel wire can be smoothed. In addition, diamond dies are very expensive in themselves, but the diameter of the hole is hardly increased by pulling out, the life is very long, and the labor and time for replacement and production stop time can be reduced, so it is inexpensive overall. Become. Thus, all dies may be diamond dies, but in some cases only a few diamond dies may be used from the final die and prior to that a conventional alloy die may be used.

The final pass is a skin pass drawing by a double die as described above. As a result, the heat generation of the steel wire can be suppressed to a low level as described above, the surface residual stress of the drawn steel wire can be reduced, and the toughness can be recovered. By adopting the above wet drawing conditions, the degree of work hardening per pass can be increased, and the total degree of drawing can be increased.
Alternatively, a wire rod having a C of about 0.72% by weight corresponding to JIS G3502 and a conventional 0.82% by weight C
It has strength and toughness equivalent to or higher than high-strength steel wires and cords made of wire, and rather, it is superior to conventional products in the fatigue resistance of cords.

The present invention includes a steel cord obtained by twisting a plurality of the steel wires, and the steel cord has a 1 × n structure and a plurality of steel wires arranged around the outer periphery of the 1 × n structure. Stuff, 2 + 2,3
Any of n + m structures such as +3 is optional. This steel cord can also exhibit characteristics of high strength and excellent fatigue resistance because it employs a steel wire that clears the specified torque reduction rate in the special toughness limit determination method described above.

Hereinafter, the present invention will be described with reference to the accompanying drawings.
FIG. 3 shows a flow chart of a process for manufacturing a high-strength steel wire according to the present invention, in which JIS G 3 is used as a raw material.
506 or a carbon steel corresponding to a hard steel wire or a piano wire specified in JIS G 3502 and having a C content of 0.70 to 0.75% by weight. The reason why the lower limit of the C content is set to 0.70% is that if the carbon amount is less than this, the tensile strength T ≧ −1960 d + 3580 N / mm ² cannot be obtained even when the final drawing conditions specified in the present invention are adopted. Because. The reason why the upper limit is set to 0.75% is that if the amount of carbon exceeds this, there is a problem that the cost is substantially the same as that of the conventional steel wire having C of 0.80% or more. As the raw material wire, a wire having a diameter of about 4.0 to 5.5 mm is used. This raw material wire is dry drawn (raw material drawing) to a predetermined intermediate diameter, and heat treatment and plating are performed. Then, the plated steel wire having an intermediate diameter is wet drawn to obtain a target steel wire.

In the material drawing step, the material wire is pickled,
Coating is performed, and the surface is reduced to an intermediate diameter by dry drawing (using a powder lubricant) to obtain an intermediate-diameter steel wire. Next, the process proceeds to a heat treatment, plating, and plating diffusion steps. This heat treatment is performed using, for example, a gas-fired heating furnace or the like. Here, the intermediate-diameter steel wire is heated to about 900 to 960 ° C. for a predetermined time to be austenitized. The intermediate steel wire is then fed into a patenting furnace cooled with heated fluidized sand or molten lead, where it is heated to 500-560 ° C.
Quenched to a degree and transformed into pearlite. In the final heat treatment (patenting treatment), a uniform fine pearlite structure containing no different structures such as a bainite structure is obtained. The strength of the wire at this time is 1100 to 1200 N / mm ^2.
It is preferable to set the degree.

Next, the intermediate-diameter steel wire is subjected to electrolytic pickling in a plating pretreatment tank to remove an oxide film on the surface of the steel wire. Then, it is passed through an electroplating tank, and a predetermined amount of copper plating and zinc plating are sequentially applied to form two-layer plating. The steel wire is then passed through a diffusion furnace using heated fluidized sand, or the steel wire is heated by direct energization, causing the copper and zinc in the plating to diffuse into each other to form brass. Then, it is cooled and becomes a final raw steel wire. In this diffusion treatment, heating is performed at about 600 ° C. for a predetermined time. However, if there is a large amount of β brass, then the wire drawing workability deteriorates, so that α brass is increased as much as possible without reducing the strength of the steel wire. It is preferable to set conditions such as heating time and temperature.

The final raw steel wire with plating thus manufactured is drawn to a target diameter by a wet drawing machine using a liquid lubricant. In the wet drawing process, the present invention employs the following conditions. (1) The temperature of the lubricating fluid is suppressed to a certain value or less by using a cooler, and the final drawing die is made into a double die, and the skin pass is drawn, and the steel wire temperature immediately after drawing is kept at 150 ° C. or less. (2) The drawing die approach angle is 8 to 10 °, and the length of the bearing is 0.25 when the hole diameter (drawing diameter) is d _1.
d to 0.35d. (3) The skin pass reduction ratio of the final double die is 1.2
To 3.9%. (4) A sintered diamond nib is used for several or more pieces including the final double die from the rise.

More specifically, FIG. 4 schematically shows a wet drawing process. Reference numeral 10 denotes a lubricating liquid tank, which is a lubricating liquid 11 obtained by dissolving a normal steel cord lubricant in water at a concentration of 10 to 30%. Is housed. A payoff reel 13 is provided upstream of the lubricant tank 10, and a take-up reel 14 of a steel wire as a final product is provided via a traverser 140 downstream of the lubricant tank 10.
A pair of capstans 12, 12 ′ are rotatably suspended in parallel in the lubricating liquid tank 10 so as to be immersed in the lubricating liquid 11, respectively. It is designed to be driven by a motor. A plurality of drawing dies D are arranged between the pair of capstans 12 and 12 '.
The steel wires hung in the grooves 2 and 12 'are sequentially drawn through a drawing die. A circulating pump 15 and a cooler 16 are provided outside the lubricating liquid tank 11a, and a lubricating liquid is forcibly extracted from the tank and cooled to return to the tank. The temperature is controlled to 30 ° C or lower, preferably about 30 to 35 ° C. And the drawing speed in wet drawing is 50
The temperature is set to 0 m / min or more, but the temperature of the raised steel wire can be set to 150 ° C. or lower by the lubricating liquid temperature control and the effect of the drawn up skin pass.

FIG. 5 shows the drawing die D. Reference numeral 1 denotes a die main body, reference numeral 2 denotes a nib incorporated in the die main body 1, and the nib 2 has an angle 2α of the approach portion 20 of 8.
The bearing ₁ has a length 1 of 0.25 to 0.35 d ₁ . The reason why the approach angle is limited is that the pull-out resistance is higher at less than 8 ° and the toughness of the steel wire is deteriorated at 10 ° or more, as described above. This is because the contact area with the wire increases and the heat generation of the steel wire increases.
FIG. 6 shows a finished or final drawing die D ', in which a normal die 5a and a skin pass die 5b are arranged in close proximity to the casings 4 and 4 so that a predetermined area reduction ratio is obtained by dividing it into two. It consists of a double die. The normal die 5a and the skin pass die 5b incorporate nibs 2a and 2b made of sintered diamond, respectively, and each nib 2a and 2b has an angle (2) of the approach portion 20.
α) is 8 to 10 ° and the size of the bearing part 21 is 0.25
０．３0.35 d ₁ .

The use of a diamond die as described above in the present invention is effective in reducing the pulling force, smoothing the surface of the steel wire, and improving fatigue resistance.
This is because a change in the diameter of the die due to wear and a change in the reduction in area due to the wear can be suppressed. For this reason, at least two of the above-mentioned double dies and two of the above-mentioned double dies have a total of about four diamond dies. Is used. Others may be alloy dies.

In the present invention, wet drawing is performed by setting the number of draws so that the total area reduction rate is about 96.5 to 98.2% by the above-mentioned die group. The reason is that the total area reduction rate is 96.5.
If it is less than 10%, the tensile strength of the steel wire is insufficient, and if it is 98.2% or more, the workability becomes too large, and the toughness of the steel wire deteriorates. The number of times of drawing is generally selected from 20 to 25 times. It is preferable that the area reduction rate every time by the drawing die is set to be a low area reduction rate at a later stage, and the double die is used as a finish,
The residual stress of the tensile force on the surface of the steel wire is released to almost zero, and the skin bath reduction rate by the skin pass die 5b at the finish reduction rate is 4.
If it is too large (0% or more), the effect of relaxing the residual stress is small, and if it is too small (1.1% or less), the working amount is too small and the effect of relaxing the residual stress is small.

[0024]

Next, specific examples of the present invention will be described. (Specific Example 1) 1) As a raw material wire, a piano wire specified in JIS G 3502 was used. Its component is C: 0.72 by weight
%, Si: 0.21%, Mn: 0.52%, the balance being Fe and unavoidable impurities. The raw material wire is pickled, pre-treated for coating, and then dry-drawn to a diameter of 1.65.
mm intermediate steel wire. 2) Approximately 950 ° C of this intermediate diameter wire in a direct fire gas heating furnace
, Followed by quenching in a fluidized bed type patenting furnace at about 520 ° C, and immediately after completion of the pearlite transformation, water cooling. At this time, the tensile strength of the steel wire was 1160 N
/ Mm ² . Next, after electrolytic pickling, two-layer plating of copper and zinc was performed through an electrolytic copper plating bath and an electrogalvanizing bath. Subsequently, the steel wire was heated to about 500 ° C. in a fluidized bed diffusion furnace to perform plating diffusion treatment, and then gradually cooled to obtain an intermediate raw material wire. 3) Next, wire drawing is performed with a wet continuous wire drawing machine, and the finished diameter is 0.2
A 5 mm steel wire was obtained. The lubricating liquid used at this time was an ordinary wet lubricating liquid having a concentration of about 10%. The lubricating liquid was circulated and kept at a low liquid temperature through a cooler to maintain the wire temperature immediately after passing the ascending die at 150 ° C. or lower.

[Examples 1 to 3, Comparative Examples 1 to 3 and Conventional Example 1] Wires were manufactured by changing the conditions of the wet drawing described above, and were used as examples and comparative examples, respectively. A conventional high-strength wire having a nominal C: 0.82 was used as a conventional example.

Table 1 shows the above wire drawing conditions and the properties of the steel wire obtained thereby. In Table 3, Table 5 and Table 6, which will be further described later in Table 1, the twisting test is performed as shown in FIG. 7 in which the gripping distance L between the fixed-side gripper 6 and the movable-side gripper 7 is determined.
Is set to 300d (d is a steel wire diameter), and the movable gripper 7 is twisted by the variable speed motor 9 at a twisting speed of 30 rpm while slightly applying tension in the axial direction of the steel wire extending from the fixed gripper 6, Twisting is performed only in one direction until the wire breaks, and after twisting 10 times in one direction, twisting is performed in the opposite direction at the above-mentioned twisting speed until the steel wire breaks, and a torsion-torque curve is obtained. Was determined. In Table 1 and Tables 5 and 6, which will be described later, "O" in "one-way torsion test result" and "one-way-reverse torsion test result" indicate that torque reduction rate ΔT is 0 to 0.
7% (good), × indicates torque reduction rate ΔT is 8
% Or more (defective).

[0027]

[Table 1]

From Table 1, it can be seen that Examples 1, 2 and 3 have high strength and good toughness. On the other hand, in Comparative Example 1, the residual stress was large due to the large die approach angle, and the toughness was poor due to this effect, the fatigue limit was inferior, and the tensile strength of the wire was low. . In Comparative Example 2, the residual stress was large because the skin pass reduction ratio was too large, and the fatigue limit was inferior. In Comparative Example 3, since no skin pass was used, the residual stress was high, the ascending temperature was also high, the toughness was insufficient, and the fatigue limit was extremely poor.

[Examples 1b, 2b, and 3b] Using the steel wires of Examples 1, 2, and 3, a buncher type twisting machine was used to produce a 2 + 2 tire steel cord. [Comparative Examples 2b and 3b and Conventional Example 1b] Using the steel wires of Comparative Examples 2 and 3 and Conventional Example 1, a steel cord having a 2 + 2 structure was similarly manufactured using a buncher-type stranded wire machine. Table 2 shows the results of examining the stranded wire properties (whether or not there is a trouble such as disconnection), strength, and fatigue resistance when producing the cords. Table 2 and Tables 4 and 7 described later
In the "fatigue resistance", three rotatable rolls having a predetermined diameter are arranged in a staggered manner, and a cord is stretched along the roll under a load of 10% of its breaking load, The roll is repeatedly moved left and right to repeatedly bend the cord, and the number of times until the cord breaks is measured. Numerical values in the table are based on 100 of the conventional example. In the “strandability”, ○ indicates no problem, Δ indicates disconnection, and X indicates many disconnections.

[0030]

[Table 2]

From Table 2, it can be seen that each of the examples has strength and toughness equivalent to or higher than that of a conventional steel cord made of 0.82% by weight C wire, and is not inferior to conventional products in fatigue resistance. On the other hand, in the comparative example, the strength is significantly reduced by the stranded wire, and the fatigue resistance is also poor.

(Example 2) [Examples 4 to 6] Using the same wire rod as in Example 1, a diameter of 1.80 mm (tensile strength = 1150 N / m)
m ² ) of the intermediate raw material wire was obtained. Subsequently, it was drawn by a wet continuous wire drawing machine to produce a steel wire having a diameter of 0.30 mm.
The lubricating liquid concentration was the same as in Example 1, the die approach angle was 10 °, and four diamond dies were used from the top. The skin pass reduction rate was 2.5% in Example 4, 3.5% in Example 5, and 3.0% in Example 6. [Comparative Example 4] A steel wire was manufactured under the same conditions as in Examples 4 to 6, except that the skin pass area reduction rate was 4.5%. [Comparative Example 5] A steel wire was manufactured under the same conditions as in Examples 4 to 6 except that the skin pass was not performed. [Embodiment 7] An intermediate material having a diameter of 1.88 mm (tensile strength = 1140 N / mm ² ) was obtained using the same wire rod as in Embodiment 1. The die and other conditions were drawn according to Example 6, and a steel wire having a diameter of 0.30 mm was produced. [Embodiment 8] An intermediate raw material having a diameter of 1.98 mm (tensile strength = 1120 N / mm ² ) was obtained using the same wire rod as in Embodiment 1. The die and other conditions were drawn according to Example 6, and a steel wire having a diameter of 0.30 mm was produced. [Regarding Conventional Example 2] A conventional high-strength steel wire made of a nominally 0.82% by weight C wire is shown. Table 3 shows the wire drawing conditions and steel wire characteristics for the above.

[0033]

[Table 3]

As is clear from Table 3, Examples 4 to
8 has good tensile strength and toughness. On the other hand, Comparative Examples 4 and 5 have good strength but substantially poor toughness and poor fatigue limit.

[Examples 6b and 8b] The steel wires of Examples 6 and 8 were twisted with a buncher-type twisting machine to produce a 1 × 2 steel cord. [Comparative Examples 4b and 5b and Conventional Example 2b] Using the steel wires of Comparative Examples 4 and 5 and Conventional Example 2, steel cords for tires having a 1 × 2 structure were similarly manufactured. Table 4 shows the characteristics and the like of the above steel cords.

[0036]

[Table 4]

From Table 4, it can be seen that Examples 6b and 8b have 0.82
It is understood that the steel cord of the conventional example 2b made of a weight% C wire has strength and toughness equal to or higher than those of the steel cord of the conventional example 2b, and the fatigue resistance is not inferior to the conventional product. Both tensile strength and toughness are good.
On the other hand, in Comparative Example 4b and Comparative Example 5b, disconnection occurred or occurred frequently in the twisting process due to insufficient toughness. Further, the strength is poor and the fatigue resistance is poor.

(Specific Example 3) [Example 9 and Conventional Example 3] Using the same wire rod as in Example 1, a diameter of 1.40 mm (tensile strength = 1180 N)
/ Mm ² ). Subsequently, it was drawn by a wet wire drawing machine to produce a steel wire having a diameter of 0.20 mm.
As the lubricating liquid, an ordinary wet lubricant having a concentration of about 10% was used. Others were drawn according to Example 3 to produce a steel wire having a diameter of 0.20 mm. Table 5 shows the nominal 0.82% by weight C
Along with a high-strength steel wire made of a wire (conventional example 3), the characteristics are shown. [Embodiment 10] A steel wire having a diameter of 0.35 mm was manufactured according to the conditions of Embodiment 3 using the same intermediate raw material wire as in Embodiment 8. [Comparative Examples 6 and 7] In Comparative Example 6, the conditions of the bearing length and skin pass reduction were changed, and in Comparative Example 7, the wire was drawn under the same conditions as in Example 10 except that no skin pass was performed, and the diameter was also 0.35 mm. Steel wire was manufactured. Table 6 shows the wire drawing conditions and steel wire characteristics as described above together with Conventional Example 4. Conventional example 4 has a nominal value of 0.8.
It is a high-strength steel wire made of 2% by weight C wire.

[0039]

[Table 5]

[0040]

[Table 6]

From Table 6, it can be seen that the effects of the lubricating fluid temperature and the finished steel wire temperature are also significant, and that Comparative Examples 6 and 7 have good strength but poor toughness, and their fatigue limit is also significantly inferior to the conventional example. I understand.

[Embodiment 11] The steel wire of Embodiment 9 was used for the core strand (1 × 3), and the steel wire of Embodiment 9 was used.
0 steel wire for side strand (+6),
A steel cord for tires having a 1 × 3 + 6 structure was manufactured by twisting with a buncher type twisting machine. [Comparative Example 6b and Comparative Example 7b] Using the steel wire of Example 9 for the core strand (1 × 3) and the steel wires of Comparative Example 6 and Comparative Example 7 for the side strand (+6), respectively, using a buncher type A steel cord for a tire having a 1 × 3 + 6 structure was manufactured by twisting with a stranded wire machine. Table 7 shows the characteristics and the like of these steel cords. A high-strength steel cord made of a nominally 0.82% by weight C wire is shown as Conventional Example 5.

[0043]

[Table 7]

From Table 7, according to the present invention, 0.72
Despite using a weight% C class wire rod, 0.8%
It can be seen that a cord having a strength and toughness equal to or higher than that of a conventional cord made of a 2 wt% C wire and having excellent fatigue resistance is obtained.

[0045]

According to the first aspect of the present invention described above, the carbon content is nominally 0. 0 to 0.70% by weight despite the fact that a wire having a carbon content of 0.70 to 0.75% by weight is used.
An excellent effect of providing an ideal rubber reinforcing steel wire having high strength equal to or higher than that of 82% by weight of high strength steel wire and having good toughness and excellent fatigue resistance can be obtained. Further, according to the second aspect, since the steel wire having the above characteristics is used, an excellent effect is obtained that a reinforcing effect for comb products is high and an inexpensive steel cord can be provided. According to claim 3,
In the wire drawing, the degree of work hardening per pass is higher than before, and the total degree of wire drawing can be increased, and a steel wire having the characteristics of claim 1 can be stably manufactured without variation. Excellent effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a used wire and the strength of a practical steel wire.

FIG. 2 is a diagram showing a torsion-torque curve in a torsion-torque test of a steel wire, where (a) is a one-way torsion-torque test, and (b) is a one-way-torque used in the present invention. The case of the reverse twist-torque test is shown.

FIG. 3 is a flowchart showing a manufacturing process of a high-strength steel wire according to the present invention.

4A and 4B schematically show a wet drawing process in the present invention, wherein FIG. 4A is a plan view and FIG. 4B is a cross-sectional view.

FIG. 5 is a sectional view of a drawing die used in the present invention.

FIG. 6 is a sectional view of a final drawing die used in the present invention.

FIG. 7 is an explanatory diagram showing an outline of a torsion-torque test of a steel wire.

[Explanation of symbols]

 Y Tensile strength T Torque value at the limit of torsional elasticity t Minimum value of torque value at reduced part D 'Final drawing die 2 Nib 20 Approach part 21 Bearing part 5a Normal die 5b Dice for skin pass

Claims (3)

(57) [Claims] 1. A carbon steel wire containing 0.70 to 0.75% by weight of carbon, which is subjected to heat treatment and plating, and then drawn to have a diameter of 0.10 to 0.40 mm. Wherein the steel wire has a tensile strength that satisfies the following equation, and has a torque reduction rate of 7% or less in a torsion-torque test in which one-way twisting and then reverse twisting are performed. A high-strength steel wire for reinforcing rubber products, characterized by having: Y ≧ −1960d + 3580 [Y: tensile strength (N / mm ² )
d: diameter (mm)] 2. A high-strength steel cord for reinforcing rubber products, wherein a plurality of the steel wires according to claim 1 are twisted. 3. A carbon steel wire containing 0.70 to 0.75% by weight of carbon, which is subjected to heat treatment and plating, and then to wet drawing under the following conditions. A method for manufacturing high-strength steel wires for reinforcing rubber products. Approach angle 2α is 8 to 1 as a drawing die
0 °, the bearing length 0.25~0.35d ₁ (d ₁ =
Finish pulling uses a double die in which two drawing dies are arranged in series, and draws a skin pass with a surface reduction rate of 1.2 to 3.9% at the exit side die. Do. A sintered diamond nib is used for the double die and several drawing dies upstream of this. Immediately after passing the final die, the steel wire temperature is 150 ℃
Control is performed as follows.