KR20080073842A - Producing a steel filament for super high tenacity steel cord - Google Patents

Abstract

A method for manufacturing a steel wire for a super high tenacity steel cord is provided to limit delamination, and to reduce the dice use and dice reduction by optimizing an approach angle of a dice which is installed in a wet wire draw bench, a dice tip material, and the dice reduction per a unit. A steel cord is manufactured by a hot rolled steel in which carbon content is 0.90 to 0.97 wt%, chrome content is 0.10 to 0.40 wt%, and a diameter is 5.5mm. A super high tenacity steel cord has a diameter of 0.1 to 0.4 mm and tensile strength of 360 to 420kg/mm^2. The super high tenacity steel cord is drawn by passing the steel cord through a dice which is installed in a wet wire draw bench. An approach angle of a dice tip installed in the wet wire draw bench is 7 to 9°. A dice reduction per an initial deformation section unit is 8 to 13%, a dice reduction per a middle deformation section unit is 14 to 17%, and a dice reduction per an end deformation section unit is 13 to 14% by using the dice in which cobalt content of the dice tip is 2 to 4 weight%.

Description

Producing a steel filament for super high tenacity steel cord}

1 is a cross-sectional view showing the shape of the die tip for steel cord production

2 is a graph showing the relationship between tensile strength and reduction rate

The present invention relates to a method for manufacturing steel wire for ultra high strength steel cord, and more particularly, by controlling the final drawing processing conditions appropriately, even if high speed drawing, the diameter without occurrence of the lamination phenomenon is 0.1 ~ 0.4 mm and the tensile strength It relates to a method for producing a steel wire for ultra high strength steel cord of 360 ~ 420 kg / mm2.

Steel cords used for reinforcing rubber products such as tires are manufactured through processes such as steelmaking, hot rolled wire, drawing, heat treatment (patenting), drawing, heat treatment, coating (plating), and drawing. This will be described in detail as follows.

First, using a hot rolled wire of a constant diameter (mostly 5.5 mm) made of carbon steel with a carbon content of 0.6 to 0.97% by weight, one time of heat-treatment and one to two drawing processes were performed to obtain a diameter of 0.8. A steel wire that is from 2.0 mm is manufactured.

Then, once again the pattening heat treatment was performed to recover the processed metal internal structure, and then copper plating with a thickness of 0.5 to 1.5 μm was applied thereon, and within 0.3

After the galvanizing of 1.0 μm in sequence, the thermal diffusion process of various methods to obtain a brass plating layer, and then the steel wire for steel reinforcement for the reinforcement into a rubber product is produced by drawing a diameter of 0.1 to 0.6 mm.

Wire rods manufactured in this way are used by twisting into various structures (1x3, 1x4, 2 + 2, 2 + 7, 3 + 6, 3 + 9 + 15, etc.) according to the use. Strength, modulus, heat resistance, fatigue resistance Compared with other inorganic and organic fibers, it is useful for reinforcing rubber products such as tires and conveyor belts.

In the case of tire steel cord steel wire, the tensile strength of the wire should have a strength characteristic of at least 280 kg / mm2 and generally, the wire tensile strength of 280 to 300 kg / mm2 is normal tensile steel cord and the wire tensile strength of 320 High Tensile steel cords with a tensile strength of 360 to 380 kg / mm2, Super Tensile and Ultra Tensile steels with 400 to 420 kg / mm2 It is classified by code.

If the steel cord steel wire has high strength, it can satisfy the sufficient stiffness in a small amount compared to the existing steel cord, thereby not only improving the tire weight and rolling resistance, but also reducing the cost and fuel economy of the vehicle. Can improve.

However, it is also important to secure the tensile strength of the above-described super-strength steel wire, but above all, the characteristic required for the steel cord steel wire is that there should be no disconnection phenomenon during drawing and high-speed stranded wire work.

In particular, in the case of the steel wire of the ultra-high strength steel cord, since the tensile strength must satisfy the strength characteristic of 380kg / mm2 or more, the carbon content of 0.90 wt% or more is added to about 0.20 wt% of chromium, which is a work hardening and work hardenability strengthening element. It is common to do

However, in this case, since a large amount of chromium is added, the excessive reduction ratio (%) of high carbon steel (usually 96% or more) causes torsional stress in the twisted pair process, causing the delamination phenomenon, which is a splitting of the wire. Therefore, there has been a difficulty in producing high strength steel cords.

Hereinafter, the delamination phenomenon related to the reduction ratio will be described in detail.

Delamination is a helical C-shaped fracture of a wire break at instantaneous propagation of surface cracks in the longitudinal direction when the residual stress of wires subjected to work deformation by wires remains and receives lateral stress (twist) of the wires. It is a phenomenon that shows a defect, and occurs mainly when the deformation and high surface temperature of the high-carbon, high-alloy steel processing.

In order to solve this problem, conventionally, the total reduction ratio (area ratio between the initial wire diameter area and the final wire diameter) is made as small as possible to reduce the amount of deformation, thereby reducing the surface residual stress.

In this technique, the decrease in strength due to the reduction of the total reduction rate was reduced by the addition of alloying elements, and the surface stress concentration was dispersed by proper die approach angle.

In addition, by using a suitable lubricant, it was intended to reduce the surface roughness and reduce the lamination phenomenon by minimizing die roughness by minimizing the die surface roughness.

However, the above conventional method has the following problems.

First, the method of reducing the total reduction rate and adding the alloy is the cost of adding the alloy.

Delamination still occurs because the total reduction rate must exceed 96% for the rise and production of fine wires below 0.30mm.

Also, in recent years, this method is difficult to apply due to the trend of ultra fine wire for improving tire performance of steel cords.

Second, although the surface stress concentration is dispersed to some extent by reducing the die approach angle, as the angle decreases, the die life is significantly reduced, and it is difficult to completely remove the surface stress.

Third, the method of optimizing the lubricant and reducing the surface roughness has a slight effect, but does not solve the fundamental problem of the delamination phenomenon.

The present invention has been made in order to solve the above-mentioned problems in the prior art, the diameter is 0.1 ~ 0.4 mm without the occurrence of the delamination phenomenon even if high-speed drawing by controlling the final drawing processing conditions appropriately, the tensile strength 360 ~ 420 kg An object of the present invention is to provide a method for producing a steel wire for ultra high strength steel cord of / mm2.

Referring to the manufacturing method of the steel wire for ultra-high strength steel cord of the present invention for achieving the above object in detail.

The present invention, using a hot-rolled wire having a carbon content of 0.90 to 0.97 wt%, a chromium content of 0.10 to 0.40 wt% and a diameter of 5.5 mm to install a brass plated wire that has undergone the drawing process and heat treatment inside the wet drawing machine. In the drawing method of a brass plated wire rod which is drawn in a length direction at the same time as it is drawn to a wire rod of a desired diameter by passing through multiple dies so that the wire is drawn stepwise with a certain range of reduction rate, it is installed inside the wet drawing machine. Regarding the manufacturing method of steel wire for super-strength steel cord having a diameter of 0.1 to 0.4 mm and a tensile strength of 360 to 420 kg / mm2 by adjusting the die angle approach angle, tip material change, and die reduction rate per unit pass in the optimum range. will be.

In the drawing process performed to obtain a desired diameter in the steel cord manufacturing process, the steel wire is drawn through the die as shown in FIG.

The die consists of a tip through which the actual steel wire passes and a case surrounding the tip. The die tip is divided into four parts as shown in FIG. 1 to facilitate the introduction of lubricant. To reduce the cross-sectional area and friction to the actual steel wire, the bearing to determine the actual wire diameter, the bearing to determine the actual wire diameter, and to prevent the die's strength due to the tensile force at the time of drawing and the defect of the fresh steel wire. It consists of a back relief.

The shape of the dice is determined and used in the most suitable form depending on the material and the wire diameter of the wire to be drawn.

In addition, die tips of various materials are used depending on the application, but in general, an alloy die tip obtained by sintering tungsten carbide (WC) powder at a high temperature is used in a steel cord manufacturing process.

In general, the conventional alloy die tip has an approach angle of 10 to 12 degrees, and the material of the tip is 94 to 95% of tungsten carbide, 5 to 7% of cobalt (Co), and a small amount of tantalum carbide (Tac) and niobium carbide ( NbC) and the like.

In the present invention, it is preferable that the angle of the approach of the die tip is 7 to 9 degrees, and if the angle of approach is less than 7 degrees, as the angle becomes too small, the die life is significantly reduced and the tensile stress at the center of the steel wire is excessively increased. This is because there is a high probability of breakage due to concentration, and when the approach angle exceeds 9 degrees, the angle is too large to reduce the effect of dispersing the surface stress of the wire.

In addition, the cobalt content of the die tip is preferably set to 2 to 4% by weight, and if the cobalt content is less than 2% by weight, cobalt is not uniformly distributed as the cobalt content that acts as a binder becomes too small. Tungsten carbide easily falls off, causing die breakage. If the cobalt content exceeds 4% by weight, the hardness of the die tip itself decreases due to the high cobalt content with low hardness. This will occur.

In addition, the die reduction rate per unit pass is changed for each total fresh reduction rate of wet drawing. That is, in the section where the initial reduction rate is 30% or less, the die reduction rate per unit pass is 8 to 13%, and the intermediate reduction rate is 30 to 96%. It is preferable to adjust the die reduction rate per unit pass to 14 to 17%, and to adjust the die reduction rate per unit pass to 13 to 14% in a section where the terminal reduction rate is 96% or more.

The reason is that in the stress distribution according to the total reduction ratio of the wire rod composed of 0.90 wt% carbon and 0.20 wt% chromium, as shown in FIG. In the present invention, the application of the die reduction rate per unit pass in such a different stress distribution section is likely to cause over-accumulation in the early and late deformation periods, thereby causing disconnection and delamination. The reduction rate per pass was optimized as described above.

The following examples are for illustrative purposes only and are not intended to limit the claims of the present invention.

Example  One

As shown in Table 1, when the copper plated diameter 1.50mm wire rod manufactured using a hot rolled wire having a diameter of 0.9mm having a carbon content of 0.90 wt% and a chromium content of 0.20 wt% was drawn to 0.25 mm, the approach angle was 8 degrees. Using dies with a cobalt content of 3% by weight, the die reduction rate per unit pass of the initial strain section was 9%, the die reduction rate was 15% per unit pass, and the die reduction rate was 13% per unit pass. The final drawing was carried out by adjusting to make the steel wire for ultra-high strength steel cord according to the present invention, and the results of evaluating the physical properties are shown in Table 1.

Example  2

Brass-plated diameter 1.50mm wire rod made from hot rolled wire with diameter of 5.5mm with carbon content of 0.90 wt% and chrome content of 0.20 wt% is 0.25mm, so that the approach angle is 8 degrees, cobalt content of die tip Using this 3% by weight die, adjust the die reduction rate per unit pass in the initial strain section to 10%, die reduction rate per unit pass in the middle strain section to 16%, and die reduction rate per unit pass in the final strain section to 14%. Table 1 shows the results of preparing the steel wire for ultra high strength steel cord according to the present invention and evaluating the physical properties thereof.

Comparative example  One

Brass-plated diameter 1.50mm wire rod made from hot rolled wire with diameter of 5.5mm with carbon content of 0.90 wt% and chromium content of 0.20 wt% is 0.25mm. Approach angle is 4 degrees, cobalt content of die tip Using this 3% by weight die, adjust the die reduction rate per unit pass of the initial strain section to 9%, die reduction rate per unit pass of the middle strain section to 15%, and die reduction rate per unit pass of the final strain section to 13%. Table 1 shows the results of preparing the steel wire for ultra high strength steel cord according to the present invention and evaluating the physical properties thereof.

Comparative example  2

Brass-plated diameter 1.50mm wire rod made from hot rolled wire with diameter of 5.5mm with carbon content of 0.90 wt% and chrome content of 0.20 wt% is 0.25mm. Approach angle 12 degrees, cobalt content of die tip Using this 3% by weight die, adjust the die reduction rate per unit pass of the initial strain section to 9%, die reduction rate per unit pass of the middle strain section to 15%, and die reduction rate per unit pass of the final strain section to 13%. Table 1 shows the results of preparing the steel wire for ultra high strength steel cord according to the present invention and evaluating the physical properties thereof.

Comparative example  3

Brass-plated diameter 1.50mm wire rod made from hot rolled wire with diameter of 5.5mm with carbon content of 0.90 wt% and chrome content of 0.20 wt% is 0.25mm, so that the approach angle is 8 degrees, cobalt content of die tip Using this 1% by weight die, adjust the die reduction rate per unit pass in the initial strain section to 9%, die reduction rate per unit pass in the middle strain section to 15%, and die reduction rate per unit pass in the final strain section to 13%. Table 1 shows the results of manufacturing the steel wire for ultra high strength steel cord of the present invention and evaluating the physical properties thereof.

Comparative example  4

Brass-plated diameter 1.50mm wire rod made from hot rolled wire with diameter of 5.5mm with carbon content of 0.90 wt% and chrome content of 0.20 wt% is 0.25mm, so that the approach angle is 8 degrees, cobalt content of die tip Using this 6% by weight die, adjust the die reduction rate per unit pass in the initial strain section to 9%, die reduction rate per unit pass in the middle strain section to 15%, and die reduction rate per unit pass in the final strain section to 13%. Table 1 shows the results of preparing the steel wire for ultra high strength steel cord according to the present invention and evaluating the physical properties thereof.

Comparative example  5

Brass-plated diameter 1.50mm wire rod made from hot-rolled wire with diameter of 5.5mm with carbon content of 0.90 wt% and chromium content 0.20 wt% to 0.25mm, with approach angle of 8 degrees and cobalt content of die tip Using this 3% by weight die, adjust the die reduction rate per unit pass in the initial strain section to 15%, die reduction rate per unit pass in the middle strain section to 15%, and die reduction rate per unit pass in the final strain section to 15%. Table 1 shows the results of preparing the steel wire for ultra high strength steel cord according to the present invention and evaluating the physical properties thereof.

Physical property measurement method used in the present invention is as follows.

1) Tensile Strength (Kg / ㎡)

         It was measured using an Instron tensile tester (1 Ton).

2) Dice Usage (Kg / ea)

  The amount of wire produced per die was evaluated in the final drawing process.

3) Disconnection rate (times / ton)

  Final drawing process The number of times the wire was cut during production of 1 ton was evaluated.

TABLE 1

As shown in the above examples and comparative examples, in the embodiment of the present invention, a steel wire for ultra-high strength steel cords having good die usage and disconnection rate without delamination occurs.

The present invention is a method for drawing a brass plated wire, 0.1 ~ 0.4 mm in diameter without generating a delamination phenomenon by optimizing the approach angle, tip material and die reduction per unit pass of the die installed inside the wet drawing machine Ultra high strength steel wire with a tensile strength of 360 ~ 420 kg / ㎜ can be produced, and furthermore, there is an effect that can reduce the die usage and disconnection rate.

Claims (1)

Brass-plated wires manufactured using hot rolled wires containing carbon content from 0.90 to 0.97 wt% and chromium content from 0.10 to 0.40 wt% and 5.5 mm in diameter were passed through multiple dies installed inside the wet drawing machine. Is 0.1 ~ 0.4mm and the tensile strength is 360 ~ 420kg / mm2 for the super-strength steel wire, the approach angle of the die tip installed inside the wet drawing machine is 7 ~ 9 degree, and the cobalt content of the die tip is 2 ~ 4 weight. Using dies of%, the die reduction rate per unit pass of the initial strain section is 8-13%, the die reduction rate is 14-17% per unit pass, and the die reduction rate is 13-14% per unit pass. Method for producing a steel wire for ultra high strength steel cord, characterized in that for drawing

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