JP2996786B2 - Manufacturing method of carcass cord for passenger car tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-strength, high-ductility ultrafine wire used for reinforcing rubber tires of trucks, buses, passenger cars and the like.
The present invention relates to a method for producing a high-strength, high-ductility carcass cord for a passenger car tire having a diameter of 0.05 mm or more and 0.09 mm or less and a tensile strength of 4500 MPa or more by drawing.

[0002]

2. Description of the Related Art Rubber tires for trucks, buses, passenger cars and the like are reinforced with steel cords made by twisting wires having a diameter of 0.15 to 0.35 mm as necessary, and organic fibers such as nylon and polyester. Used for embedding. Reinforcing wires used for these rubber tires are roughly divided into three types according to the place where they are used, as shown in “Wire Product Readers” edited by the Wire Products Association and the Japan Wire Products Exporters Association. The carcass part and breaker part , Used in the bead section. As a reinforcing wire used for the carcass part, a steel cord is used for trucks and buses, and organic fibers such as nylon and polyester are used for passenger cars.

[0003] Steel cords have the advantages of, for example, (1) a high heat radiation effect and little heat generation, and (2) the carcass portion can be made thin so that the weight of the tire can be reduced. Uses a steel cord. However, in the case of a tire for a passenger car, if a conventional steel cord is used, the weight of the tire increases, so that organic fibers such as nylon and polyester are used. As a conventionally developed ultrafine wire for a steel cord, for example, Japanese Patent Application Laid-Open No. 60-204865 discloses a method of controlling the Mn content to less than 0.3% to suppress the generation of a supercooled structure after lead patenting. By regulating the amounts of elements such as C, Si, Mn, etc., ultra-fine wires and high-carbon steel wire rods for steel cords with little breakage during twisting and high strength and high ductility have been disclosed. 1988
Japanese Patent No. 24046 discloses a wire for high toughness and high ductility ultrafine wire in which the tensile strength of a lead patenting material is increased by setting the Si content to 1.00% or more to reduce the wire drawing rate. I have.

[0004]

Conventionally, carcass cords used for passenger cars are made of organic fibers such as nylon and polyester, and the appearance of reinforcing lines having higher strength is expected to reduce the weight of tires. Specifically, carcass cords are required to be made steel even for passenger cars in accordance with the reduction in weight and performance of tires, and the appearance of wires for carcass cords having a diameter of 0.09 mm or less and a tensile strength of 4500 MPa or more has been increasing. Requested.

An object of the present invention is to provide a method of manufacturing a carcass cord satisfying such a demand.

[0006]

The present invention has the following features to attain the above object. Ie weight%
C: 0.90% to 1.10%, Si: 0.4
%, Mn: 0.5% or less, Cr: 0.10% or more and 0.30% or less, with the balance being iron and unavoidable impurities,
In addition, using a hot-rolled wire having an unavoidable Al content of 0.003% or less, a wire diameter of 0.50 to 0.50 is drawn by inserting an intermediate patenting process at least once.
After that, in the final patenting process, a gamma treatment was performed in a temperature range of 900 to 1000 ° C, and immediately a constant temperature transformation process was performed in a temperature range of 560 to 590 ° C to obtain a wire having a tensile strength of 1400 to 1600 MPa. After that, after further brass plating having a thickness of 1 to 3 μm, final wet drawing is performed to reduce the wire diameter to 50 to 90 μm.
Wherein the wire has a tensile strength of 4500 MPa or more. In the present invention, the approach angle of the die used for drawing may be 8 to 12 °, and two or more carcass cord wires obtained by such a method may be used by twisting.

[0007]

The present invention will be described below in detail. First, the reasons for limiting the steel composition of the present invention are as follows. In normal patenting treatment, proeutectoid ferrite precipitates along with the prior austenite grain boundaries even in the eutectoid component having a C content of about 0.8%, and this proeutectoid ferrite causes a decrease in ductility after drawing. The present inventors have found that Although C is an economical and effective strengthening element, it is also an effective element for reducing the amount of precipitated cementite.
Therefore, in order to increase the ductility by forming an ultrafine wire having a tensile strength of 360 kgf / mm ² or more, it is necessary to add C in an amount of 0.90% or more. If it is too high, the ductility is reduced and the wire drawability is deteriorated. Therefore, the upper limit is set to 1.10%.

[0008] Si is an element necessary for the deoxidation of steel, so when its content is too small, the deoxidizing effect becomes insufficient. Also, Si forms a solid solution with the ferrite phase in the pearlite formed after the heat treatment and increases the strength after patenting, but on the other hand, it reduces the ductility of the ferrite and decreases the ductility of the ultrafine wire after drawing, so that the content is 0.4% or less. And

Mn is desirably added in a small amount to ensure the hardenability of steel. However, the addition of a large amount of Mn causes segregation and bainite during patenting,
Since the supercooled structure called martensite is generated and the subsequent drawability is impaired, the content is set to 0.5% or less.

In the case of the hypereutectoid steel as in the present invention, a cementite network is easily generated in the structure after patenting, and a cementite having a large thickness is likely to precipitate. In order to achieve high strength and high ductility in this steel, it is necessary to make pearlite fine and eliminate the cementite network and thick cementite as described above. Cr has the effect of suppressing the appearance of such abnormal portions of cementite and further reducing pearlite. However, the addition of a large amount increases the dislocation density in the ferrite after the heat treatment, and significantly impairs the ductility of the ultrafine wire after the drawing. Therefore, the amount of Cr added is set to 0.10% or more where the effect can be expected, and 0.40% or less which does not increase the dislocation density in ferrite and does not impair ductility. The content of S is set to 0.020% or less in order to secure the ductility as in the case of the conventional ultrafine steel wire, and the content of P is set to 0.020% or less because P impairs the ductility of the wire similarly to S. desirable.

As a cause of reducing the ductility of ultrafine wires, Al
The ₂ O _3, Al ₂ O _3, such as MgO-Al ₂ O ₃ is present in the non-ductile inclusions mainly. Therefore, in the present invention, in order to avoid a decrease in ductility due to non-ductile inclusions, Al
The content is set to 0.003% or less.

As described above, in the ultrafine wire according to the present invention, the amount of C is increased due to the increase in strength after the patenting treatment, and the appearance of proeutectoid cementite and the deterioration of the pearlite lamellar shape due to this are added with Cr. To achieve an increase in strength due to finer pearlite. In addition, the ductility of the cementite layer became comparable to that of conventional steel due to the refinement of pearlite. Further, Cr, Si, Mn
By keeping the amount of addition low, the ductility of the ferrite phase was maintained at the same level as that of the conventional steel, and the ductility of the material was increased. By the component design that realizes an increase in strength after patenting treatment only by such microstructural refinement, the strength and ductility after patenting have been successfully improved over conventional steel. Therefore, although the strength after patenting is increased, the ductility deterioration of the ultrafine wire manufactured by increasing the drawing rate remains at the same level as that of conventional steel, and high strength and high ductility have become possible.

Next, the reasons for limiting the production method of the present invention are as follows. When the wire diameter during the final patenting process is less than 0.5 mmφ, a wire having a strength of 4500 MPa or more cannot be obtained for a wire having a diameter of 0.05 to 0.09 mmφ. Also, 0.90mm
When the diameter exceeds φ, the strength of a wire of 50 to 80 μm becomes too high, the ductility of the wire is reduced, and delamination (longitudinal cracking of the wire) is likely to occur.
90 mmφ or less.

The diameter is 0.09 mm or less and the tensile strength is 45
In order to obtain a strength of 00 MPa or more, the heating temperature at the time of the final patenting treatment is set so that the re-dissolution of the carbide proceeds sufficiently.
100 ° C or higher, and the growth of γ grains does not proceed too much 100
It must be performed at 0 ° C. or lower.

The isothermal transformation temperature is set to 560 ° C. or more at which the amount of bainite does not precipitate and 590 ° C. or less at which the strength does not decrease unnecessarily.

[0016] The tensile strength of the patented material patented as described above should be at least 1400MPa.
It is necessary to adjust to more than a, and even if the strength is most likely to occur, unless it is not more than 1600 MPa, an abnormal part such as bainite appears and the ductility is reduced.

When the plating process performed after the final patenting process is less than 1 μm, the wire drawing reduction rate is high.
The plating thickness is set to 1 μm or more because sufficient plating does not remain on the drawn wire and the adhesion when embedded in the tire is significantly impaired. When the plating thickness exceeds 3 μm, the plated portion is easily peeled off during wire drawing, so that the thickness is 3 μm or less.

In the case of a carcass cord for a passenger car, if the wire diameter is less than 0.05 mmφ, the stranded wire processing becomes extremely difficult. If the wire diameter exceeds 0.09 mm, it is difficult to obtain a strength of 4500 MPa or more.

In the case of the method of the present invention, the workability in the initial stage of wire drawing is reduced because the amount of C added is higher than that of the conventional steel cord. Therefore, it is desirable to use a drawing die having an approach angle of 8 ° to 12 ° based on a 10 ° approach angle, instead of a conventionally used die based on an approach angle of 14 °. This is because when using a die with a low angle of approach angle, the compressive stress component acting on the central part during wire drawing increases, resulting in more uniform processing,
This is because it is possible to suppress microcracks that are likely to occur in the early stage of wire drawing.

[0020]

EXAMPLES As shown in Table 1 (chemical components) and Table 2 (processing conditions and characteristics), 1 to 1 based on the method of the present invention were used.
Carcass cords were manufactured using the manufacturing method of No. 0 and the manufacturing methods 11 to 17 for comparison. The manufacturing process is as shown in FIG. 1, and the wire diameter of the 5.5 mmφ wire manufactured by hot rolling is set to a wire diameter for performing a final patenting process by wire drawing and LP processing. After the final patenting process was performed on this wire, brass plating was performed, and final wet drawing was performed to obtain a final wire. Thereafter, stranded wire processing was performed to obtain a carcass cord. Sample 2 for stranded wire workability
When 0 kg was twisted, the number of disconnections within 1 was indicated by で, and when the number of disconnections was 2 or more, × was indicated.

[0021]

[Table 1]

[0022]

[Table 2]

Nos. 1 to 10 are manufactured according to the method of the present invention as shown in Tables 1 and 2. In the wire drawing, the dies having the approach angles shown in Table 2 are used. Done. These inventive steels have tensile strength,
Both drawability and stranded wire workability show excellent characteristics.

Comparative method 11 is a case where steel having a different chemical composition from the method of the present invention is used. 4500MP due to different steel composition
The strength higher than a is not obtained. Comparative method 12 is a case where the wire diameter at the time of final patenting is different from the method of the present invention.
Since the initial wire diameter is small, a strength of 4500 MPa or more is not obtained. Comparative method 13 is a case where the gamma temperature is different from the method of the present invention. Since the gamma temperature is low, strength after final patenting cannot be obtained at 1400MPa or more, and 4500MPa after drawing.
The above strength is not obtained. In addition, the stranded wire processing characteristics are also poor. Comparative method 14 is a case where the isothermal transformation temperature at the time of final patenting is different from that of the present invention. A strength of 1600 MPa or more was obtained after the final patenting treatment, and a high strength of 5130 MPa was obtained after wire drawing, but the stranded wire workability was reduced. Comparative method 15 is the case where the plating thickness after the final patenting treatment is different from the method of the present invention. Since the plating thickness is small, the heat generated during the drawing process is high, and the material is brittle. For this reason, the stranded wire workability is also poor. Comparative method 16 is the case where the finished wire diameter after the final wet drawing is different from the method of the present invention. Since the finished wire diameter is small, the wire after drawing is embrittled, the drawing is reduced, and the workability of the stranded wire is deteriorated. Comparative method 1
7 is a case where the die approach angle used in the method of the present invention and the wire drawing is different. Although the wire strength after wire drawing is satisfactory, the approach angle at the time of wire drawing is large, so that microcracks are inherent and the stranded wire processing characteristics are poor.

[0025]

According to the manufacturing method of the present invention, the diameter is 0.05
A carcass wire having a tensile strength of 5,000 MPa or more and a tensile strength of 5000 MPa or more and a carcass cord manufactured by twisting the wire can be obtained.

[Brief description of the drawings]

FIG. 1 shows a manufacturing process of a sample of an example.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C21D 8/06 C21D 9/52

Claims (3)

(57) [Claims] C: 0.90% to 1.10%, Si: 0.4% or less, Mn: 0.5% or less, Cr: 0.10% to 0.30% by weight%, Using a hot-rolled wire consisting of the balance of iron and inevitable impurities and having an inevitable Al content of 0.003% or less, the wire diameter is reduced to 0 by a drawing process in which intermediate patenting is inserted at least once. .50 ~ 0.90mmφ,
Then, 900 to 10 in the final patenting process
Perform gamma treatment in a temperature range of 00 ° C, and immediately
A constant-temperature transformation treatment in the temperature range of 590 ° C. is performed to obtain a tensile strength of 1
400 to 1600 MPa wire, and then 1 to 1
A method for producing a carcass cord for a passenger car tire, wherein a wire having a diameter of 50 to 90 μm and a wire having a tensile strength of 4500 MPa or more are formed after performing a 3 μm thick brass plating and then performing a final wet drawing. 2. The method according to claim 1, wherein the angle of approach is 8 to
The method for producing a carcass cord for a passenger car tire according to claim 1, wherein a drawing die of 12 ° is used. 3. Manufactured according to claim 1 or 2,
A method for producing a carcass cord for a passenger car tire, wherein two or more carcass cord wires are twisted.