JP3291638B2 - Manufacturing method of high strength ultra-fine steel wire with excellent twist characteristics - 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 steel wire for a steel cord used as a reinforcing material for a tire or the like, in particular, a high-strength ultrafine steel wire having excellent torsion characteristics after drawing.

[0002]

2. Description of the Related Art Conventionally, a steel cord used as a reinforcing material for rubber products such as steel tires for automobiles is produced by twisting a steel wire having a diameter of about 0.2 mm.
In recent years, a demand for weight reduction of tires has led to a tensile strength of 3600.
High-strength steel wires of not less than MPa have been required.

[0003] In general, the final strength of a steel wire largely depends on the processing strain, and the greater the processing strain, the higher the strength. On the other hand, ductility tends to deteriorate when the processing strain increases.
When using a conventional carbon steel wire rod, the tensile strength is 3600MP
In order to obtain a high strength of a or more, it is necessary to further increase the processing strain. However, when a carbon steel wire is used, strength can be obtained by a conventional drawing method,
The torsion value, which is important as a property of the steel wire for steel cord, is low, and it is not possible to suppress cracks generated in the longitudinal direction of the steel wire during the torsion test.
It was about Pa.

On the other hand, for example, Japanese Patent Application Laid-Open No. 5-2004
In Japanese Patent No. 28, in the continuous drawing step of a fixed area reduction rate of 15 to 18%, the reduction rate of the final die is set to about 1 of a fixed area reduction rate.
A technique for producing a high-strength steel wire having high torsion ductility by performing wire drawing at 0 to 90% has been proposed. It is thought that the torsional characteristics are affected by the residual tensile stress of the steel wire surface layer, but there are still many unclear points. Conventionally, skin pass, straightening, shot peening and the like have been proposed as methods for suppressing residual stress. For example, Journal of the Japan Institute of Metals, Vol. 21, 1957, NO. Page 540 of 9
Describes that residual stress in the surface layer of a steel wire can be reduced to the compression side by skin pass drawing with a reduction in area of 1% or less.

[0005]

Problems to be Solved by the Invention
According to the wire drawing method proposed in Japanese Patent Publication No. 8 (1994), when a die having a large friction coefficient is used as the final die, ductility is deteriorated due to heat generation, the die is extremely worn, and the final die has a friction coefficient of low friction. When a small die is used, the work hardening of the steel wire may be reduced, and the practicality is not clear because these points are not mentioned at all.

Further, Journal of the Japan Institute of Metals, Vol. 21, 195.
7 years NO. No. 9, page 540, in order to introduce a compressive residual stress to the surface of a steel wire, the skin pass reduction rate must be 1% or less, in which case the reduction rate is very small. Therefore, the probability of occurrence of the disconnection of the cutie increases. For this reason, it is difficult to use it industrially.

[0007] However, it is clear from the studies of the present inventors that the processing conditions in the final die greatly affect the properties of the steel wire. An object of the present invention is to provide a method of manufacturing a high-strength ultrafine steel wire having excellent twisting characteristics by optimizing a friction coefficient and an approach angle of a final die in a continuous drawing process and performing skin pass drawing. is there.

[0008]

Means for Solving the Problems The present inventors have studied in detail the effect of the final die on the torsion characteristics of an ultrafine steel wire, particularly the relationship between the friction coefficient of the die, the approach angle, and the area reduction. . As a result, it has been found that the twisting characteristics can be greatly improved by optimizing the material and shape of the final die and performing skin pass drawing.

The present invention relates to a method for manufacturing a fine steel wire using a slip type fine wire drawing machine in which a plurality of dies are arranged, wherein the final die has a friction coefficient of 0.03 to 0.15 and an approach angle of 6 to 12. The present invention provides a method for producing a high-strength ultra-fine steel wire having excellent torsion characteristics, characterized in that skin pass wire drawing is performed with an angle of reduction of 2 to 11%.

[0010]

First, in the present invention, the reason why the area reduction rate of the final die is limited as described above is as follows. If the reduction in area of the final die exceeds 11%, the occurrence of vertical cracks during the twist test cannot be suppressed. Therefore, the upper limit of the area reduction rate of the final die is set to 11%. On the other hand, if the area reduction rate of the final die is less than 2%, the effect is saturated and the risk of cuppy breakage increases. Therefore, the lower limit of the area reduction rate of the final die is set to 2%.

FIG. 1 shows that a 0.20 mm ultrafine steel wire drawn under the conditions shown in the drawing was subjected to a torsion test, with the reduction rate of the final die set at 1 to 14%, The effect on the repetition characteristics was examined. In FIG. 1, the mark ○ indicates a torsion value in a state where there is no vertical crack, and the mark ● indicates a torsion value in which a vertical crack has occurred. It is apparent from FIG. 1 that the twisting characteristics are good when the reduction rate of the final die is within the range of the present invention.

Next, the reason why the friction coefficient of the final die is limited as described above is as follows. The coefficient of friction of the final die can vary depending on the material of the die and the lubricant used. If the friction coefficient of the final die exceeds 0.15, the generation of longitudinal cracks during the twist test cannot be suppressed, and the heat generated during drawing is large, and the ductility is deteriorated. Therefore, the upper limit of the friction coefficient of the final die is set to 0.15. On the other hand, even if the friction coefficient of the final die is less than 0.03, the effect is saturated and the work hardening of the steel wire is small. Therefore, the lower limit of the friction coefficient of the final die is set to 0.03.

FIG. 2 shows that the friction coefficient of the final die is 0.02 to 0.02.
Drawing was performed under the conditions described in the figure as 0.20.
A twist test was conducted on a 0 mm ultrafine steel wire to examine the effect of the friction coefficient of the final die on the twist characteristics. FIG.
In the figure, ○ indicates the torsion value without vertical cracks,
The mark indicates the twist value at which the vertical crack occurred. As is clear from FIG. 2, the twisting characteristics are good in the range of the present invention.

The approach angle of the final die is 6 to
The reason why the angle is limited to 12 ° will be described. If the approach angle is less than 6 °, the vertical crack during the twist test is suppressed, but the twist value is reduced and the cut-off is easily generated.
Therefore, the lower limit of the approach angle is set to 6 °. On the other hand, if the approach angle exceeds 12 °, longitudinal cracks during the twist test cannot be suppressed, and the wire diameter becomes larger than the die diameter. Therefore, the upper limit of the approach angle is set to 12 °.

FIG. 3 shows an approach angle of the final die of 5 to 5.
Drawing was performed at 16 ° under the conditions described in the figure.
A twist test was performed on a fine steel wire having a diameter of 1 mm to examine the effect of the approach angle of the final die on the twist characteristics.
In FIG. 3, the mark ○ indicates a torsion value in a state where there is no vertical crack, and the mark ● indicates a torsion value in which a vertical crack has occurred. As is clear from FIG. 3, the twisting characteristics are good within the range of the present invention.

Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

[0017]

EXAMPLE A 5.5 mmφ hot-rolled wire of JIS SWRH82A was drawn to 3 mm, subjected to intermediate patenting, further drawn to 1.48 mm and 1.57 mm, and subjected to final patenting to obtain a wire. did. The tensile strength and the drawing were measured for the above wires.
Further, by continuous drawing, the wire was drawn to 0.20 mm under the drawing conditions described in Tables 1 and 2 (continuation of Table 1), and a tensile test and a twist test were performed. The value and the occurrence of longitudinal cracks during the torsion test were investigated. The torsion test was performed by setting the distance between the chucks to 100 times the wire diameter. When a vertical crack occurred, the number of occurrences of vertical cracks was defined as a torsion value. Good or more was evaluated as good.

No. 5 and No. 5 In No. 19, since the area reduction rate of the final die was as large as 12.5%, vertical cracks occurred during the twist test. No. Nos. 1 to 4 and Nos. Nos. 15 to 18 are examples of the present invention, which have high strength and good torsion characteristics. N
o. 6 and no. In No. 20, since the approach angle of the final die is as small as 5 °, vertical cracks during the twist test can be suppressed, but the twist value is low. No. 10 and no. As for No. 24, since the approach angle of the final die was as large as 14 °, a vertical crack occurred during the torsion test. No. 7 to 9 and No. 7; 21
23 to 23 are examples of the present invention, which have high strength and good torsion characteristics.

No. 14 and No. In No. 28, since the coefficient of friction of the final die was as large as 0.17, a vertical crack occurred during the twist test. No. Nos. 11 to 13 and Nos. 25-27
Is an example of the present invention, and has high strength and good torsion characteristics.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

As described above, the present invention optimizes the friction coefficient and approach angle of the final die in the continuous wire drawing process and draws the skin pass in the final die to obtain a high strength of 3600 MPa or more. It is capable of producing ultrafine steel wire having excellent twisting characteristics, and has a great industrial effect.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a reduction ratio of a final die in a continuous drawing step and a twisting characteristic.

FIG. 2 is a diagram illustrating a relationship between a friction coefficient and a twist characteristic of a final die.

FIG. 3 is a diagram showing an approach angle and a twisting characteristic of a final die.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-317616 (JP, A) JP-A-3-104821 (JP, A) JP-A-4-280944 (JP, A) JP-A-6-1994 158224 (JP, A) JP-A-7-265936 (JP, A) JP-A-54-125366 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21C 1/00-19 / 00

Claims (1)

(57) [Claims] 1. A method for manufacturing a fine steel wire using a slip-type fine wire drawing machine in which a plurality of dies are arranged, wherein the final die has a friction coefficient of 0.03 to 0.15, an approach angle of 6 to 12 °, A method for producing a high-strength ultrafine steel wire having excellent torsion characteristics, wherein skin-pass drawing is performed with a reduction in area of 2 to 11%.