JP3108231B2 - Steel cord - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord, and more particularly to a steel cord for reinforcing a rubber composite. More specifically, it is manufactured from a wire by cold drawing, and has a diameter of 0.6 to 0.1 mm.
A 15-mm thin steel wire used as a reinforcing wire fiber for rubber, plastic, etc., which is exposed to corrosive and degraded environments under static and dynamic stress-strain over a long period of time, mainly like tires. The present invention relates to a steel cord applied to a rubber composite product used.

[0002]

2. Description of the Related Art Conventionally, radial tires have been used under relatively mild conditions, both mechanically and environmentally due to corrosion deterioration. As a result, they are used under high input stress-strain, and coupled with the improvement of tire durability, the corrosion deterioration environment is becoming more severe and diversified.

Further, from the viewpoint of protection of the global environment, the demand for reduction of fuel consumption and, therefore, the weight of vehicle bodies, especially tires, has been further strengthened, and various improvements in the performance of steel cord reinforcing materials have been demanded.

[0004] Among the requirements, the most important performance is the tire cord break resistance (referred to as CBU resistance) of a steel cord. Tire cord breakage is mainly caused by hydrogen embrittlement and corrosion fatigue resistance, and also caused by the internal pressure of the tire being reduced for some reason, and the tire must be driven a certain distance in a run flat state. Often it is.

[0005] In such a low internal pressure state, the tire of a vehicle loaded with a load is greatly bent and undergoes large bending deformation until double wheel contact occurs. In extreme cases, the ply cord may receive even a large input that causes plastic deformation. Flat tires and low-floor automobiles tend to promote an increase in ply cord large bending input during run flat.

However, conventionally, it has been impossible to sufficiently improve the CBU resistance, that is, the CBU resistance generated at a low internal pressure (low internal pressure CBU resistance), from the viewpoint of the material of a steel cord for a tire. I came. This low internal pressure resistant CBU
Since the gender tends to deteriorate as the code becomes stronger, improvement of this performance has become a very important issue as the code becomes stronger.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to determine what material parameters govern the contradictory properties of high strength and low internal pressure resistance in a thin steel wire manufactured with high surface reduction. An object of the present invention is to provide a steel cord for reinforcing a rubber composite, which achieves both high strength and low internal pressure resistance to CBU.

[0008]

A hypoeutectoid comprising two phases of pearlite / ferrite or ferrite / cementite.
An important physical property parameter of a fine wire having a high surface area reduced eutectoid pearlite steel is hardness, which expresses ductility and brittleness.

The present inventor has conducted extensive studies on the relationship between the basic physical properties and the fracture at the time of large bending input, and as a result, it has been found that the hardness distribution controls the fracture at the time of large bending input. Breakability at the time of large bending input corresponds to this hardness distribution very well.Specifically, if there is a certain relationship between the surface layer and the internal hardness distribution, high strength and breakability at the time of large bending input are obtained. We found that it was possible to resolve the contradiction.

The present invention provides a method of creating a hardness distribution that can achieve both high strength and low internal pressure CBU resistance by finding such new findings.

That is, according to the present invention, the carbon content is 0.60 to 0.60.
0.90% carbon steel, a hypoeutectoid to eutectoid pearlite steel consisting of two phases of pearlite / ferrite or ferrite / cementite, having a tensile strength of 250 to 450 kg / mm ² ,
The Vickers hardness distribution in a thin steel wire having a wire diameter of 0.6 to 0.15 mm satisfies a monotonically increased inverse V-shaped distribution from the surface layer to the inside, or the inside is constant and the surface layer has a lower Vickers hardness. It is a steel cord having a fine wire satisfying the inverted U-shaped distribution.

The diameter of the thin wire of the present invention is 0.6 to 0.15 mm.
Or a thin wire having a wire diameter of 0.4 to 0.15 mm. Tensile strength is 250 ~
Although it is 450 kg / mm ² , the higher the strength of the cord, the greater the importance of improving its low internal pressure resistance to CBU. The steel cord may be composed of one thin wire, or a plurality of thin wires may be aligned in parallel or twisted. Further, a thin wire may be partially provided.

The reinforced thin wire cord drawn and reduced through a die in a normal drawing process has a hard surface portion, and has a V-shaped (or U-shaped) hardness distribution. In the present invention, this hardness distribution is changed to a reverse V-shaped distribution monotonically increased from the surface layer to the inside or a hardness distribution in which the inside is constant and the surface layer has lower hardness. The hardness uses Vickers hardness.

A method of changing the hardness distribution of a V-shaped (or U-shaped) cord from an M-shaped cord to an inverted V-shaped (or inverted U-shaped) cord is to repeatedly apply mechanical plastic deformation. It is possible. As other methods, it is also possible to apply a skin pass at the final drawing step, or to appropriately arrange and optimize a die series of drawing.

In the case of a steel cord thin wire, since the bending input is larger at the surface layer, in the present invention, the distribution of hardness in the thin wire is made to have an inclination. In particular, the bending input as a ply material of a steel radial tire for trucks and buses is used. Below, it is important to lower the hardness of the surface layer and not to lower the hardness of the central part. For example, even in the case of an M-shaped distribution as shown in FIG.
This is probably because a significant concentration of distortion occurs at the top of the M-shape.

FIG. 8 shows the correlation between the filament surface strain in the rubber / cord composite and the fracture life as a cord fracture simulation at low internal pressure and large bending input. It is clear that Example 1 described below is significantly improved as compared with Comparative Example 1 and Conventional Example 1. The smaller the filament surface strain, the greater the number of bendings before breaking, but in Example 1 of the hardness distribution of the present invention, the number of bendings is largest.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples, in comparison with conventional examples and comparative examples, but the present invention is not limited to these examples. In the laboratory, the rupture property at the time of large bending input was evaluated from the rupture life and the morphology of the torsion value test and the rupture life in the belt bending fatigue test.

With respect to the fine wire having a tensile strength of 340 kg / mm ² level, the hardness distribution of the conventional example 1 (FIG. 4) and the hardness distribution of the comparative example (FIG. 5) and the hardness distribution of the steel cord of the present invention in Example 1 (FIG. Table 1 shows the results of the breaking life and the breaking mode of the torsion value test for 6) of Conventional Example 1, Comparative Example, and Example 1. In Example 1, the hardness was distributed by repeatedly applying mechanical plastic deformation.

[Table 1]

FIG. 9 shows the conventional example and the embodiment of the present invention in which the horizontal axis represents the position of the central portion and both surface portions of the fine line and the vertical axis represents the Vickers hardness of the fine line having a tensile strength of 380 kg / mm ² level. 7 shows the results of measuring the hardness of the thin wire of the comparative example.
Hardness distribution of Conventional Example 2 (FIG. 9B), M-shaped hardness distribution of Comparative Example 2 (FIG. 9C), and Example 2 of steel cord of the present invention
Table 2 shows the results of the fracture life and the fracture mode of the torsion value test for the hardness distribution (FIG. 9A). Example 2
Although this hardness distribution was formed by optimizing the die series, it could not be achieved simply by increasing the number of passes, which is the number of passes through the die. Is possible.

[Table 2]

In order to clarify the effects of the present invention, a tire was prototyped using the steel cords of Conventional Example 1, Comparative Example 1, and Example 1, and the evaluation results are shown in Table 3. Example 1
No CBU occurred, but in Conventional Example 1, CBU occurred. In Comparative Example 1, 20 to 50% of the filaments were broken.

[Table 3]

[0021]

According to the present invention, the hardness distribution from the surface layer to the inside of the steel cord is formed into an inverted V-shape or an inverted U-shape. The inconsistency which became large was solved, and the CBU resistance at the time of low internal pressure was improved with the high strength cord, and the breaking life of the steel cord was able to be improved.

[Brief description of the drawings]

FIG. 1 shows an inverted V-shaped hardness distribution from the surface layer to the inside of the steel cord of the present invention.

FIG. 2 shows an inverted U-shaped hardness distribution from the surface layer to the inside of the steel cord of the present invention.

FIG. 3 shows an M-shaped hardness distribution of a steel cord of a comparative example.

FIG. 4 shows a hardness distribution (V-shape) of a steel cord of Conventional Example 1.

FIG. 5 shows measured values of an M-shaped hardness distribution of a steel cord of a comparative example.

FIG. 6 shows measured values of an inverted V-shaped hardness distribution of the steel cord of Example 1 of the present invention.

FIG. 7 is an explanatory view of a general torsional break mode.

FIG. 8 shows a bending test result of the high tension belt. The vertical axis represents the surface strain of the filament, and the horizontal axis represents the number of times of bending until breaking.

FIG. 9 shows the measurement results of the hardness distribution of Example 2 (A), Conventional Example (B), and Comparative Example 2 (C) of a high-tensile steel cord having a tensile strength of 380 kg / mm ² .

FIG. 10 is an explanatory diagram of the definition of the step height of torsional break.

Claims (1)

(57) [Claims] 1. A subeutectoid to eutectoid pearlite steel having a carbon content of 0.60 to 0.90% and comprising two phases of pearlite / ferrite or ferrite / cementite, and having a tensile strength of 250 to 450 kg. / mm ² , wire diameter 0.6 ~
Vickers hardness distribution in 0.15mm fine steel wire,
A steel cord that satisfies a monotonically increased inverse V-shape distribution from the surface layer to the inside, or a fine wire in which the inside is constant and the surface layer satisfies an inverted U-shape distribution having a lower Vickers hardness.