JPH08325964A - Steel wire and steel cord for rubber reinforcement - Google Patents

Abstract

PURPOSE: To obtain a rubber-reinforcing steel cord having high fatigue resistance by heat-treating and plating a specific carbon steel wire, drawing the wire to obtain a steel wire having a tensile strength higher than a specific level and twisting a plurality of the steel wires. CONSTITUTION: A carbon steel wire having a carbon content of 0.60-0.65wt.% is subjected to quenching heat-treatment in a gas furnace, etc., quenched with water immediately after pearlite transformation, subjected to pretreatment such as electrolytic pickling, plated with copper and zinc to form a double-plated layer and drawn to obtain a steel wire having a diameter (d) of 0.10-0.40mm and a tensile strength (YN/mm<2> ) satisfying the formula, y>=-1960d+3290. A steel cord is produced by twisting a plurality of the steel wires by a Buncher wire twister.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Solid wires and cords for reinforcing rubber products, typically tires and high-pressure hoses, are brass-plated steel wires with a diameter of 0.10 to 0.40 mm for vulcanizing and adhering to rubber, and the like. It has a structure in which multiple strands are twisted together. These steel wires and cords for rubber reinforcement are required to have toughness and high durability. In practice, for example, the wire diameter is 0.25 mm and 2800 N / mm.
It has a diameter of ² or more, a diameter of 0.35 mm and a diameter of 2600 N / mm ² or more. Since such a steel wire requires high strength, it can be used as a raw material steel wire rod at 0.7%.
It was made by using a high carbon steel wire rod containing 0 to 0.75% by weight of carbon and subjecting it to wire drawing with a total area reduction rate of about 95.0 to 96.0%. Furthermore, using a high carbon steel wire rod having a carbon content of 0.80 to 0.85%,
It is becoming more common to manufacture by wire drawing with a total area reduction rate of about 6.0 to 97.0%.

As described above, conventionally, a high carbon steel wire having a carbon content of 0.70% by weight or more has been used as a raw material for a rubber-reinforcing steel wire. The reason is that the carbon content is lower than this. And because of lack of strength. In addition, increasing the strength of the wire like the latter is to use steel wire with a higher carbon content to increase the strength before final drawing as much as possible and to reduce the total area reduction ratio (total working ratio) in final drawing. This is to increase the strength by working hardening by increasing the degree. However, since the cost of the steel wire rod increases as the carbon content increases, it is not economical. Therefore, it is preferable to use a steel wire rod having a low carbon content to be a tough wire. However, in order to produce a high strength steel wire with a steel wire material having a carbon content of less than 0.70% by weight, the total reduction in area in the final wire drawing must be very high. The obtained steel wire exceeds the so-called processing limit, and the toughness deteriorates significantly. Further, as the carbon content of the steel wire used decreases, the working limit generally decreases, and it becomes difficult to obtain higher strength. As a result, a wire break occurs in the wire drawing process, making it impossible to perform the prescribed processing, or even if a steel wire of the desired strength is obtained, the wire will frequently break during the subsequent twisting process and can be made into a cord. Even if it disappears or becomes a cord product, its durability becomes extremely poor. For example, when such a steel wire is used to reinforce a high-pressure hose, problems such as a spiral scoring process in the forming process and a disconnection during braiding of a blade, which causes a great trouble, occur.

[0004]

DISCLOSURE OF THE INVENTION The present invention was made by research in order to solve the above problems, and the object is to make 0.60 to 0.65 C% carbon steel. An object of the present invention is to provide a steel wire and a steel cord for reinforcing a rubber product which is tough and can be used as a reinforcing material for a rubber product while using a wire and which is inexpensive.

[0005]

To achieve the above object, the present invention uses a carbon steel wire rod containing carbon in an amount of 0.60 to 0.65% by weight, which is subjected to heat treatment and plating.
A steel wire having a diameter of 0.10 to 0.40 mm obtained by wire drawing, the steel wire having a tensile strength satisfying the following formula, and further having a one-way twist and a reverse twist. The torque reduction rate in the torque-torque test is 7% or less. Y ≧ -1960d + 3290 [Y: Tensile strength (N / mm ² ),
d: diameter (mm)]

The steel wire as described above can be obtained, for example, by performing final wet drawing under the following conditions. As a drawing die, the approach angle 2α is 8 to 1
0 °, the bearing length 0.25~0.35d ₁ (d ₁ =
Use a die hole diameter). For finish drawing, a double die in which two drawing dies are arranged in series is used, and skin pass wire drawing is performed with a surface reduction rate of 1.2 to 3.9% in the die on the exit side. Sintered diamond nibs are used for the double die and at least several drawing dies upstream of this. The temperature of the steel wire immediately after passing the final die is 150 ° C.
Control is performed as follows.

[0007]

The present invention uses a carbon steel wire rod having a low carbon content which is not used at present, and therefore the cost is low in this respect. Moreover, the present invention adopts a twist test by one-way twist-reverse twist as a means for determining the toughness limit that determines the quality of workability and fatigue resistance in the wire drawing process, twisting process and hose forming process. A steel wire whose torque reduction rate in the test is in the range of 0 to 7% is used. Therefore, the steel wire is an ultra-high-strength steel wire for rubber reinforcement that has both high strength and toughness, good twisting efficiency, and good fatigue resistance despite the low carbon content of the raw steel wire. Steel cords made by twisting multiple strands are excellent in high strength, high toughness and fatigue resistance,
By using it as a reinforcing material for rubber products, cost reduction and weight reduction can be realized.

More specifically, simply twist in one direction and twist-
When the torque curve is measured, there are two types, one is a normal curve in which the torque continuously rises to the right and reaches the break, and the other is that the torque is extremely unstable between the break and the torque is reduced. Appears. It is considered that such a decrease in torque is caused by the formation of fine cracks inside the steel wire during twisting, which also means that the wire has been drawn beyond the working limit. In the case where the toughness of the steel wire is particularly poor, a torque reduction already occurs in this test. However, even if we actually used a steel wire that did not show a torque drop (torque unstable part) in this test and twisted it to make a steel cord, a wire breakage occurred and durability was insufficient. Many things appeared. Therefore, the judgment of the toughness is insufficient and inaccurate in the torque reduction judgment by this test.

In view of the above, according to the present invention, light tension is applied in the direction of the axis of the steel wire as a predetermined gripping interval, and while maintaining a straight line, the wire is twisted at a constant speed in a constant direction (for example, clockwise direction) a predetermined number of times, and then twisted once. A harsh twist-torque test is performed in which the steel wire is stopped and subsequently twisted in the opposite direction (eg, counterclockwise) until the steel wire breaks. In the unidirectional-reverse twisting method, not only the unidirectional twisting-torque as shown in FIG. 2A, but also the backward unidirectional twisting after the unidirectional twisting as shown in FIG. 2B. Even during torque, only the steel wire having a torque reduction rate of 7% or less has good toughness. The steel wire itself has high strength and good fatigue resistance. Further, the strength of the steel cord made by twisting a plurality of steel wires is naturally lower than the collective strength of the steel wires, but the strength of the wires can be efficiently used and the durability is also good. On the other hand, when the torque reduction did not occur in the unidirectional twisting stage, but the torque reduction rate was 8% or more in the reverse twisting stage, the toughness was substantially poor, and the strength was relatively poor, and the resistance was low. Fatigue is also relatively poor.

In order to quantitatively obtain the above-mentioned torque decrease, the present inventors conducted a twist-torque test by a unidirectional-reverse-direction twisting method on many steel wires having different diameters and materials, and Time-The reduction rate of torque was measured. As a result, the torque reduction rate is 8 in any case.
If it is more than 0.1%, the above-mentioned good characteristics cannot be obtained. That is, in the twist-torque curve of FIG. 2B, the torsional elastic limit in the first unidirectional twist, that is, the torque value at the upper limit of the straight line rising to the right in the figure is T, and the lowering part torque in the reverse twist. When the minimum value is t, the torque decrease rate ΔT is represented by the following equation. However, when there is no torque decrease, t = T. ΔT = [(T− | t |) / T] × 100 (%) If the torque decrease rate ΔT is 8% or more, the above-described problem occurs, and therefore, in the present invention, the torque decrease rate ΔT is within 7%. The parameter that makes the toughness good is adopted only for the steel wire that exhibits the above characteristics. Such parameters of the present invention can well simulate a situation in which a steel cord having a 1 × n structure, and further, a steel cord having an n + m structure represented by 2 + 2 are twisted in a certain direction and then untwisted. Therefore, the obtained steel cord is also appropriate.

Regarding the method for producing a steel wire according to the present invention, first, the content of C is 0.60 to 0.60.
A carbon steel wire with 0.65% by weight is used. Specifically, this is a hard steel wire (SW) specified in JIS G 3506.
(RH) or a piano wire (SWRS) equivalent to JIS G 3502 is preferably used. However, Cr or Ni may be added as a required amount as an alloy element. This carbon steel wire rod is formed into a wire having an intermediate diameter according to a conventional method, and thereafter,
Heat treatment and plating are performed to finally finish the steel wire with a target diameter by wet wire drawing. In the wet wire drawing step, the present invention adopts specific conditions. That is, in the final heat treatment (patenting), the heat treatment is performed by selecting appropriate conditions so as to obtain a uniform fine pearlite structure. As a result, the tensile strength of the wire is 1039 ~
It is about 1137N / mm ² . Next, in the final wet drawing with liquid lubricant, the approach angle (2
α) is set to 8 to 10 °, and the bearing length I is set to 0.25 to 0.35d ₁ with respect to the hole diameter d ₁ .

Conventionally, an approach angle of about 12 ° has been adopted as the lowest draw-out force in wire drawing, but in the present invention, it is set to a lower angle. This is because the wire work hardening degree in each drawing is increased to increase the strength, the work on the surface and inside of the wire is made more uniform, and the surface residual stress generated in the wire is reduced. The reason for increasing the work hardening degree is that the total workability (total area reduction rate) must be extremely high in order to obtain the same strength as a wire using a low carbon content steel wire rod with a wire using a higher carbon content. This is because this exceeds the working limit, frequent disconnection occurs, and the toughness of the wire is greatly deteriorated, which is not practical. Therefore, the present invention is 8 to 10 °
The low working angle die is used to keep the total working ratio relatively low. However, if the angle is smaller than 8 °, the drawing resistance becomes too large, which is not preferable. Further, the bearing length 1 of the die is 0.5d about ₁ with respect to pore diameter d ₁ in the conventional is employed, the heat generation becomes remarkably due to pulling resistance increases. Therefore, in order to reduce the contact area with the steel wire and suppress the heat generation of the steel wire, the bearing length was shortened, and by reducing the drawing resistance while increasing the wire drawing limit by balancing this with the approach angle. You can

Further, in the present invention, in the final drawing, the surface reduction is divided by using a double die in which two dies are stacked, and the skin pass is performed by the rear (up) side die.
The surface reduction rate of this skin pass is preferably 1.2 to 3.9%. The skin pass area reduction rate exceeds 4.0%,
If it is less than 1.1%, the effect of relaxing the residual stress is reduced. Further, by adopting the skin pass area reduction rate, the wire temperature immediately after passing through the final die can be reduced by about 25 to 40 ° C. as compared with a normal single pass. Furthermore, the present invention is applicable to at least a few sheets (double die 2).
A sintered diamond nib die (hereinafter abbreviated as diamond die) is used for about 4 sheets or more including the sheet. The reason for this is that there is a problem that the die life is shortened due to the increase in the work hardening degree per die as compared with the conventional high C material processing. That is, the surface of a conventional tungsten carbide sintered alloy nib die (hereinafter abbreviated as alloy die) is relatively rough,
Large pullout resistance. For this reason, the surface of the steel wire that has been pulled out also becomes rough, which adversely affects fatigue resistance. On the other hand, the surface of sintered diamond nibs is smoother than that of sintered alloy nibs, so the drawing resistance can be reduced by wire drawing, and the surface of steel wires can also be smoothed. it can. In addition, although diamond dies themselves are quite expensive, they do not thicken the hole diameter due to pulling out, have a very long life, and save time and time for replacement and production stop time, so it is generally cheap. Become. Therefore, all drawing dies may use diamond dies, but in some cases only a few diamond dies may be used from the final die, and a conventional alloy die may be used upstream thereof.

The temperature of the steel wire immediately after passing through the final die is preferably kept at 150 ° C. or lower. This makes it possible to suppress embrittlement due to aging. This temperature may be maintained only by the above-mentioned skin pass, but it may be further carried out by using a cooler to keep the temperature of the lubricating liquid low. By adopting the above-mentioned wet wire drawing conditions, while using a steel wire rod having a carbon content of 0.60 to 0.65% by weight, a conventional steel wire rod having a carbon content of 0.70 to 0.75% by weight is used for production. It has strength and toughness equivalent to or better than that of steel wires and cords, and has excellent fatigue resistance.

The present invention includes a steel cord in which a plurality of the steel wires are twisted, the structure of the steel cord is a 1 × n structure, and further, a plurality of steel wires are arranged on the outer periphery of the steel cord and twisted. Matched items, 2 + 2,
Includes all 3 + 3 and other n + m structures. Since this steel cord also uses a steel wire that clears the specified torque reduction rate in the above-mentioned special toughness limit determination method, it has good strength and toughness, and exhibits excellent fatigue resistance.

The present invention will be described below with reference to the accompanying drawings.
FIG. 3 shows a flow chart of a process of manufacturing a steel wire according to the present invention, and as a raw material, JIS G 3506
Alternatively, it is carbon steel equivalent to a hard steel wire rod or a piano wire rod specified in JIS G 3502, and its C content is 0.60.
~ 0.65 wt% wire is used. The lower limit of the C content is set to 0.60%, because when the carbon content is less than this, the tensile strength T ≧ −19 even if the above-mentioned final wire drawing conditions are adopted.
This is because 60d + 3290 N / mm ² cannot be obtained. The upper limit is set to 0.65% because if the carbon content exceeds the upper limit, the effect of the conventional steel wire rod and the cost will be reduced.
The raw material wire having a diameter of about 4.0 to 5.5 mm is used. This raw material wire rod is dry-drawn to a predetermined intermediate diameter using a powder lubricant, and heat treated and plated.
Then, the plated intermediate diameter steel wire is wet drawn to obtain a desired steel wire.

In the dry wire drawing step, the raw material wire is pickled and coated, and the surface is reduced to an intermediate diameter by continuous dry wire drawing to obtain an intermediate diameter steel wire. Next, the heat treatment, plating, and plating diffusion steps are performed. This heat treatment
For example, the heating is performed using a gas direct-fired heating furnace, in which the intermediate diameter steel wire is heated to about 900 to 960 ° C. for a predetermined time to be austenitized. Next, the intermediate diameter steel wire is quenched in a heated fluidized sand or molten lead cooling furnace at about 500 to 560 ° C. to undergo pearlite transformation. In this heat treatment (patenting treatment),
A uniform fine pearlite structure that does not include different structures such as bainite structure.

Next, this intermediate diameter steel wire is electrolytically pickled in the pretreatment tank to remove the oxide film on the surface. Then, it is passed through an electroplating bath, and a predetermined amount of copper plating and zinc plating are sequentially applied to form a two-layer plating. The steel wire is then passed through a diffusion furnace using heated fluidized sand, or the steel wire is directly energized and heated to cause the plated copper and zinc to diffuse into each other into brass. Then, it cools and becomes a final raw material steel wire. In this diffusion treatment, heating is performed at a temperature of about 600 ° C. for a predetermined time, but if there is a large amount of β brass, the subsequent wire drawing workability deteriorates. Therefore, as much α α brass as possible does not decrease 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 produced in this manner is drawn to a target diameter by a continuous wet drawing machine using a liquid lubricant. In this wet drawing process, the present invention adopts the following conditions. (1) The temperature of the lubricating liquid is kept below a certain value by using a cooler, and the final drawing die is double die for skin pass wire drawing, and the temperature of the steel wire immediately after the wire drawing is maintained at 150 ° C or lower. (2) The wire drawing die approach angle is 8 to 10 °, and the bearing length is 0.25 when the hole diameter (drawing diameter) is d _1.
and d ₁ ~0.35d _1. (3) The skin pass reduction ratio of the final double die is 1.2.
~ 3.9%. (4) Sintered diamond nibs are used for several or more pieces including the final double die from the end.

FIG. 4 schematically shows the wet drawing process. Reference numeral 10 denotes a lubricating liquid tank, which contains a lubricating liquid 11 in which a normal steel wire lubricant is dissolved in water at a concentration of 10 to 30%. A payoff reel 13 is installed upstream of the lubricating liquid tank 10, and a steel wire take-up reel 14 as a final product is installed downstream of the lubricating liquid tank 10 via a traverser 140. The lubricating liquid tank 10
Inside, a pair of capstans 12 and 12 'are rotatably provided horizontally so as to be immersed in the lubricating liquid 11, and the downstream capstan 12' is driven by a variable speed motor (not shown). It is like this. A plurality of drawing dies D are arranged between the pair of capstans 12 and 12 'so that the steel wires hooked in the grooves of the capstans 12 and 12' are sequentially drawn out by passing through the drawing dies. It has become. A circulating pump 15 and a cooler 16 are provided outside the lubricating liquid tank 10 to forcibly drain the lubricating liquid from the tank, cool the cooling liquid, and return it to the tank to form a circulation system. The temperature is controlled to a predetermined temperature.

FIG. 5 shows the drawing die D, 1 is a die body, 2 is a nib built in the die body 1, and the nib 2 has an angle 2α of the approach portion 20 of 8
The angle is -10 °, and the length l of the bearing 21 is 0.25 to 0.35d ₁ . FIG. 6 shows a finishing or final drawing die D ', in which the normal dies 5a and the skin pass dies 5b are arranged in close proximity to each other in the casings 4 and 4 so as to obtain a predetermined surface reduction rate by dividing into two. It consists of a double die. The normal die 5a and the skin-passing die 5b have nibs 2a and 2b made of sintered diamond, respectively. The nibs 2a and 2b have an angle (2α) of the approach portion 20 of 8 to 1 respectively.
0 °, the size of the bearing portion 21 is 0.25 to 0.35d
_{It is 1} .

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 97.8% by the above-mentioned die group. The reason is that the total reduction rate is 96.5.
If it is less than 0.1%, the tensile strength of the steel wire will be insufficient, and if it is 97.8% or more, the workability will be too high and the toughness of the steel wire will be deteriorated. The number of times of drawing is generally selected from 20 to 25 times. It is preferable that the reduction rate of each time by the drawing die is lower in the latter stage, and the double die is used as the finish as described above to release the residual stress of pulling on the surface of the steel wire. It is almost zero. The skin bath surface reduction rate by the skin pass die 5b at the finish surface reduction rate is 4.0% or more, which is too large to reduce residual stress, and conversely, 1.1% or less, which is too small. However, the amount of processing is too small and the effect of relaxing residual stress is small. In the present invention, the tensile strength of the wire is Y = -19
It is possible to manufacture up to about 60d + 3577 (N / mm ² ).

[0023]

EXAMPLES Specific examples of the present invention will be described below. (Specific Example 1) 1) As a raw material wire rod, a piano wire rod defined by JIS G 3502: diameter 5.5 mm was used. The components are% by weight, C: 0.62%, Si: 0.20%, Mn: 0.
51% is the balance Fe and unavoidable impurities. The raw material wire rod was subjected to pickling and coating pretreatment, and was then dry drawn to obtain two kinds of intermediate diameter wires having diameters of 1.95 mm and 2.14 mm. 2) This intermediate wire is first used for about 95
After heating to 0 ° C., quenching was performed in a fluidized bed furnace at about 520 ° C., and immediately after completion of pearlite transformation, water cooling was performed. The tensile strength of the wire at this time is 1.95 mm in diameter.
078 N / mm ² , diameter 2.14 mm is 1058
It was N / mm ² . Then, after pretreatment (electrolytic pickling), the copper and zinc are passed through an electrolytic copper plating bath and an electrolytic zinc plating bath.
Layer plating was applied. Subsequently, the wire was heated to about 500 ° C. in a fluidized bed diffusion furnace to perform a plating diffusion treatment, and then gradually cooled to obtain an intermediate raw material wire. 3) Then, wire drawing with a wet continuous wire drawing machine, finishing diameter 0.3
A 5 mm steel wire was obtained. As the lubricating liquid at this time, a normal wet lubricating liquid having a concentration of about 10% was used, and the liquid temperature was kept low through a cooler by circulating it to maintain the wire temperature at 150 ° C. or lower immediately after passing through the upward die.

[Regarding Examples 1 to 3, Comparative Examples 1 to 3 and Conventional Example 1] Wires were manufactured by changing the conditions for the above-mentioned wet wire drawing, and set as Examples and Comparative Examples, respectively. In addition, Examples 1 and 2 and Comparative Examples 1 and 2 used an intermediate diameter wire having a diameter of 1.95 mm, and Example 3 used an intermediate diameter wire having a diameter of 2.14 mm. For comparison, nominal C: 0.72% by weight
A wire manufactured by using the steel wire rod of No. 1 was set as Conventional Example 1.
Table 1 shows the above wire drawing conditions and the steel wire properties obtained thereby.

(Specific example 2) Using the same wire as in specific example 1, the diameter is 1.26 mm (tensile strength = 1117 N / m).
m ² ) intermediate raw material wire was obtained. Next, in the same manner as in Example 1, the wire was drawn by a wet continuous wire drawing machine to obtain a steel wire having a finished diameter of 0.20 mm. [Examples 4 to 6, Comparative Examples 3 and 4 and Conventional Example 2] Wires were manufactured by changing the wet drawing conditions in Concrete Example 1, and were set as Examples and Comparative Examples, respectively. A wire manufactured from a nominal 0.72 C% by weight steel wire rod was used as Conventional Example 2. Table 2 shows the above wire drawing conditions and the properties of the wires obtained thereby.

(Specific Example 3) Using the wire having a diameter of 0.20 mm and the wire having a diameter of 0.35 mm obtained in Specific Examples 1 and 2, a steel cord was manufactured by twisting together with a buncher type twisting machine. In this steel cord, three 0.20 mm wires are twisted at once in the Z direction to produce a 1 × 3 core strand, and a diameter of 0.3 mm is formed around the core strand.
It is a steel cord (pitch of core strands: 9.5 mm, side pitch: 17.5 mm) having a structure of 1 × 3 + 6 obtained by helically twisting 6 side wires of 5 mm in the S direction. [Examples 1a to 3a, Comparative Examples 1a to 2a and Conventional Example 3
Regarding] The steel cord manufactured by combining the wires of Examples 1 and 4 is referred to as Example 1a, and the steel cord combining the wires of Example 2 and Example 5 is referred to as Example 2a.
and a steel cord in which the wires of Example 3 and Example 6 are combined is referred to as Example 3a. In addition, a steel cord in which the wires of Comparative Example 1 and Comparative Example 3 are combined is referred to as Comparative Example 1a, and a steel cord in which the wires of Comparative Example 2 and Comparative Example 4 are combined is referred to as Comparative Example 2a. Further, a steel cord in which the wires of Conventional Example 1 and Conventional Example 2 are combined is referred to as Conventional Example 1a. These characteristics are shown in Table 3.

As shown in FIG. 7, the twisting test in Tables 1 and 2 was carried out by setting the gripping distance L between the fixed-side gripping tool 6 and the movable-side gripping tool 7 to 300d (d is a steel wire diameter). While lightly applying axial tension to the steel wire extending from the grip 6, the movable grip 7 is twisted by the variable speed motor 9 at a twist speed of 30 rpm in only one direction until the wire breaks. In each case, after twisting 10 times in one direction, twisting was performed at the above-mentioned twisting speed until the steel wire was broken in the opposite direction, and a twist-torque curve was taken for each determination. In Tables 1 and 2, “one-way twist test result” and “one-way-reverse twist test result”
Indicates a torque reduction rate ΔT of 0 to 7% (good),
X indicates that the torque decrease rate ΔT is 8% or more (defective). In Tables 1 and 2, "fatigue limit" refers to the bending stress when the wire does not break even after 10 ⁷ rotations in the Hunter type bending fatigue test. Moreover, in Table 3, “◯” of “strandability” indicates no problem, Δ indicates disconnection, and × indicates many disconnections. “Fatigue resistance” means that a strip-shaped sample obtained by vulcanizing a steel cord in rubber is stretched over three rolls having a predetermined diameter in a staggered arrangement under a load of 10% of the cord breaking load. This is the result of measuring the number of repetitions until the cord was broken by repeatedly moving the roll to the left and right and repeatedly bending the cord.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

As is clear from Table 1 and Table 2, Example 1
Nos. 6 to 6 have a tensile strength equal to or higher than that of the conventional example having a C content of 0.70 to 0.75% by weight and a good toughness in spite of using a wire having a smaller C content. It also has good fatigue resistance. As is clear from Examples 1a to 3a in Table 3, the steel cord also has good stranded wire properties, breaking load and fatigue resistance. On the other hand, in Comparative Examples 1 and 2, since the skin pass area reduction rate is inappropriate, the toughness is poor and the fatigue limit is inferior. In Comparative Example 4, the bearing length of the die and the skin pass area reduction rate are inadequate, so that the residual stress is large and the fatigue limit is inferior.
Since Comparative Example 3 does not use a skin pass, the residual stress is high, the toughness is insufficient, and the fatigue limit is remarkably inferior. Because of these, the steel cord is also inferior to the conventional example in the twisting property, the breaking load, and the fatigue resistance.

[0032]

According to the first aspect of the present invention described above, a wire having a carbon content of 0.60 to 0.65% by weight, which has been said to be unusable as a rubber reinforcing wire, has a carbon content of 0. The steel wire for rubber reinforcement, which has strength equal to or higher than that of a wire made of 70 to 0.75% by weight, good toughness, and excellent fatigue resistance, can be provided at a low cost. can get. Further, according to claim 2, since the steel wire having the above characteristics is used, an excellent effect that a steel cord having a high reinforcing effect on a rubber product and being inexpensive can be provided can be obtained.

[Brief description of drawings]

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

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

FIG. 4 schematically shows a wet drawing process in the present invention, (a) is a plan view and (b) is a 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 in torsional elastic limit t Minimum value of torque value in lowered part D'Final drawing die 2 Nib 20 Approach part 21 Bearing part 5a Normal die 5b Skin pass die

Claims (2)

[Claims] 1. A carbon steel wire rod containing carbon in an amount of 0.60 to 0.65% by weight, which is heat treated and plated, and then drawn to have a diameter of 0.10 to 0.40 mm. Steel wire having a tensile strength satisfying the following formula, and after being twisted in one direction,
A high-strength steel wire for reinforcing a rubber product, which has a characteristic of a torque reduction rate of 7% or less in a twist-torque test in which a reverse twist is performed. Y ≧ -1960d + 3290 [Y: Tensile strength (N / mm ² ),
d: diameter (mm)] 2. A steel cord for reinforcing rubber products, comprising a plurality of the steel wires according to claim 1 twisted together.