JPS5933173B2 - Continuous heat treatment method for copper-coated steel wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous heat treatment method for copper-coated steel wire, and in particular, an object of the present invention is to improve tensile strength and elongation by subjecting copper-coated steel wire to short-time heat treatment. It is an object of the present invention to provide a heat treatment method that can increase the wire size appropriately and also greatly improve the drawability.

Copper-coated steel wire, which consists of a copper core wire and a copper coating layer, has greater tensile strength than copper wire, and has superior corrosion resistance and moderate conductivity compared to steel wire, so it is mainly used as outdoor wire for communication cables. It has been used as a conductor for grounding cables and lead wires for electronic components such as capacitors.

As the core material of the copper-coated steel wire, a medium-high carbon steel wire containing a carbon content of 0.4% or more is usually used.

Further, the proportion occupied by the copper coating layer in the cross-sectional area of the wire is often about 25 to 40 parts.

Mechanical properties such as tensile strength, yield strength, and elongation are strongly influenced by the properties of the copper core wire.

Furthermore, the mechanical properties of medium-high carbon steel wire change significantly compared to those of copper due to heat treatment and wire drawing.

Therefore, the heat treatment and wire drawing of copper-coated steel wires have been carried out in a manner similar to the heat treatment and wire drawing methods of steel wires.

When cold drawing a steel wire, a heat treatment called patenting treatment is performed in advance to improve cold workability.

Patenting treatment is a heat treatment in which a steel wire is heated to the A3 transformation point or higher and then cooled with molten metal such as lead at an appropriate cooling rate to obtain a strong sorbite structure containing a large amount of fine pearlite. It is.

Patenting is often used for copper-clad steel wires as well, to further draw wires whose cold workability has been reduced through strong cold drawings, or to obtain wires with high tensile strength and elongation. be done.

Conventionally, in the patenting process of copper-coated steel wire, the wire is
A tubular electric furnace was used for continuous heating to temperatures above three transformation points.

Furthermore, if a molten metal bath of metal such as lead is used to obtain an appropriate cooling rate, a large amount of molten metal adheres to the surface of the copper-coated steel wire and contaminates it, since the surface of the copper-coated steel wire is clean copper.

Therefore, the cooling process of copper-coated steel wire is carried out in a gas such as steam.
Alternatively, for example, it has been carried out in a molten salt bath containing 55% potassium nitrate and 45% potassium nitrite at a temperature of 170 to 500°C.

In the method of heating the copper-coated steel wire, which is the first stage of the patenting process, by passing it through a tubular electric furnace, the preferable heating temperature of the copper core of the steel-coated steel wire is usually 850°C or higher, so the temperature of the furnace material is There was a drawback that the wire deteriorated significantly, requiring frequent repairs, and that the wire was heated only in the furnace, and the preheating section was included in the furnace length, resulting in a long furnace length.

In methods in which the cooling process is performed using gas or molten salt, the copper-coated steel wire is always cooled at a constant temperature, so the cooling rate decreases as the wire cools, resulting in a slow processing speed.

In addition, when cooling with molten salt, the temperature at the part exiting the molten salt is such that the copper oxidizes considerably, so in order to obtain a clean surface, after cooling in the molten salt, it is necessary to further cool the copper in a reducing or inert gas atmosphere. It needed to be cooled down.

This method requires long cooling pipes and is impractical, so in practice the material was cooled in the atmosphere and oxides were removed by pickling.

In any of the conventional methods, in order to increase the production speed, it is necessary to significantly increase the length of the equipment, and it is difficult to continuously perform heat treatment and cold wire drawing.

Furthermore, as the use of copper-coated steel wire expands, wires with higher tensile strength and elongation are required, and thinner wires are also required. Processability has become unsatisfactory with conventional heat treatment.

The present invention solves the above-mentioned problems of the conventional method, and can significantly improve the mechanical properties and cold workability of copper-coated steel wire at high speed even with relatively small-scale equipment. The purpose is to provide a continuous heat treatment method that can be easily combined with subsequent steps in tandem.

The present invention involves continuously feeding a copper coated steel wire and then heating the wire at 725° to 1083° in a reducing or inert gas atmosphere.
This is a continuous heat treatment method for a copper-coated steel wire, characterized in that the wire is heat-treated by heating the wire to a temperature of C and then passing through hot water at a boiling point of 90 DEG C. to cool it.

In the present invention, when a heated wire is immersed in hot water, boiling occurs over the entire surface of the heated wire, and the surface is uniformly wrapped in a vapor film, so that heat is conducted through the vapor film. Ru.

Although the cooling rate due to heat conduction through the vapor film is faster than the cooling rate in a molten salt bath, it is approximately 0° C./sec, which is suitable for patenting processing.

When the wire is further cooled to below 200°C, nucleate boiling occurs and the cooling rate increases.

Therefore, if the length of the cooling section is the same, the production speed can be significantly increased compared to the conventional method, and an ideal sorbite structure can be obtained, with high tensile strength, elongation,
Wire drawability can be improved.

Moreover, since the copper-coated steel wire is cooled to a temperature almost equivalent to that of hot water without being exposed to the atmosphere, there is no surface oxidation.

The heat treatment method of the present invention exhibits its characteristics effectively by utilizing Joule heat generated by passing electricity through a copper-coated steel wire, that is, energization heating, as a heat source for heating before the patenting process.

That is, when the wire is heated by electricity, there is little deterioration of the heating furnace (・o) Moreover, since the preheating part can be taken out of the furnace, the length of the furnace can be shortened.

Furthermore, if the inside of the furnace is maintained in a reducing atmosphere, even if the material is oxidized by preheating in the atmosphere, it will be reduced within the furnace, so there is no problem at all.

After heating, the process of immersing in hot water without being exposed to the atmosphere can be easily carried out as described in the detailed description below.

The advantage of combining electrical heating and boiling water cooling is that it can be easily carried out using simple equipment, and the pearlite crystal grains can be made extremely fine by rapid cooling, and the processing speed can be improved even when the equipment is miniaturized. It's about doing.

Further, the heat treatment method of the present invention exhibits its characteristics even more effectively when applied to a method in which heat treatment and wire drawing are performed continuously.

Conventional heat treatment methods require significantly longer equipment to heat-treat and draw copper-coated steel wire while continuously feeding it, and the wire surface becomes oxidized after heat treatment. The subsequent wire drawing may cause oxides to dig into the wire surface,
There was a problem with burn-in.

According to the heat treatment method of the present invention, the wire surface after heat treatment is clean and the above problem does not occur at all.

One of the effects of applying the heat treatment method of the present invention to copper-coated steel wires is that steel wires tend to form scales during hot working or heating processes, and after heating steel wires with scales attached,
Immersion in hot water not only inhibits the formation of a uniform vapor film, but also scale has poor thermal conductivity compared to steel.
Unlike non-uniform scale, which causes non-uniform cooling rates, copper-clad steel wire has no scale and the copper core wire is covered with a copper layer with high thermal conductivity, so the temperature of the copper core wire is uniform. This means that a tissue with high toughness can be obtained.

Another effect is that heat dissipation during the cooling process occurs at the surface, and in the case of steel wires, the cooling rate of the surface layer is too high, producing a large amount of martensite, making the surface layer slightly brittle compared to the inside. In contrast, with copper-coated steel wire, the surface layer that is rapidly cooled is copper, and the copper core wire does not become brittle in any part.

In normal steel wires, when the diameter is 3.5 mmφ or less, the structure tends to become unstable when cooled with boiling water due to the above effect, but with copper-coated steel wires, even with a diameter of 2 mmφ, a good structure can be obtained stably. I can do it.

The copper-coated steel wire to which the heat treatment method is applied in the present invention is
It may be manufactured by any method such as a plating method, a cladding method, a dipping method, or a welding method.

In addition, the raw material steel wire or steel round bar used for manufacturing copper-coated steel wire usually has good cold drawability, and the heat treatment method of the present invention involves coating it with copper and then cold-working it. It is usually applied during or at the final step of the wire drawing process at a point where cold drawability has decreased or to adjust the mechanical properties of the final product.

If processing to significantly reduce the wire diameter is required, the heat treatment of the present invention can be performed two or more times in the processing step.

As the heating method in the heat treatment method of the present invention, heating using a tubular furnace, induction heating, infrared heating, etc. can be applied.
Heating with a tube furnace has the drawbacks mentioned above.

In addition, induction heating and infrared heating require special and complicated equipment, which requires higher equipment costs and is less energy efficient than current heating, which can be heated using only a transformer and power supply roll or power tank. As the heating method in the heat treatment of the present invention, electrical heating is most suitable.

Next, the wire heating is done to prevent oxidation of the copper layer surface.
It must be carried out in a reducing or inert gas atmosphere.

As the reducing gas, for example, hydrogen gas or ammonia decomposition gas (nitrogen dehydrogen) can be used, and as the inert gas atmosphere, nitrogen gas or the like can be used.

In either heating method, the temperature of the wire must be heated to the A3 transformation point or higher.

The preferable heating temperature is the A3 transformation point or higher, the temperature at which all of the pearlite becomes austenite in an equilibrium state, and is 725° C. when the austenite has a eutectoid composition, although it varies depending on the carbon content in the steel and the composition of the alloy.

Normally, the heating temperature should be about 100 to 200°C higher than the A3 transformation point, and 900°C when the carbon content is 0.65%.
The front and back are suitable.

However, the temperature must not exceed the melting point of the copper layer and must be 1083° C. or lower.

In the method of heating the wire by energizing it, the temperature of the copper-coated steel wire is
Wire diameter, wire speed, wire resistance and specific heat, copper cross-sectional area ratio, surface condition, current, time, type of atmospheric gas, flow rate,
Appropriate conditions are selected because the temperature changes depending on the temperature and other factors, and there is also heat generation due to transformation and heat generation due to contact resistance with the power supply roll.

In practice, at the transformation point, the amount of heat lost by radiation is much larger than the amount of heat transferred from the wire to the gas by film heat conduction, so a heat balance method that balances the heat generated by resistance and radiant heat, ■ From 2RT T - = 4.886 (□) 4 πd l 100, give a current value and gradually increase the current while measuring the exit temperature of the wire, increasing the current so that the exit temperature of the wire reaches the desired temperature. Drain and heat.

In order to sufficiently carry out the pearlite transformation of the copper core wire, it is necessary to maintain the wire at a temperature above the transformation point for 10 seconds to 5 minutes.

For example, when the carbon content of the copper core wire is 0.65%, the holding time at 900° C. should be at least 20 seconds, preferably 2 minutes.

The current used for energization may be either direct current or alternating current.

The higher the temperature of the hot water used for cooling in the heat treatment method of the present invention, the thicker the vapor film formed on the surface of the copper-coated steel wire and the longer the duration of the vapor film. is reduced, making it suitable for patenting heat treatment.

Therefore, the upper limit of the temperature is preferably the boiling point of hot water, and if the lower limit is 90° C. or less, the vapor film becomes non-uniform and no practical effect can be obtained.

Adding a surfactant to the hot water further increases the stability of the vapor film.

Such surfactants include polyvinyl alcohol (P
VA) is suitable because it causes less deterioration, turbidity and foaming during use and has excellent wettability, and other alkyl sulfonates and alkylaryl sulfonates [for example, Lion Tarsent 30 (trade name, the same applies hereinafter)] , higher fatty acid alkali salts (e.g. potash soap), alkyl sulfates (e.g. Emar), formalin condensed naphthalene sulfonates (e.g. Solvalai S-80), alkylnaphthalene sulfonates (e.g. Perex NB), and anions such as cationic activators, such as quaternary ammonium salts (e.g. Cathiolite BC-100), fatty acid amine salts, polyoxyethylene alkyl ether M (e.g. Noniolite NL-10), polyoxyethylene alkylphenol ethers (e.g. Nonionic surfactants such as Liponox NAT) and surfactants such as fluorocarbon surfactants (e.g. Florard FC-95) can be used.

The amount of these surfactants added is 0.1 to 11 parts of hot water.
The appropriate amount is 20g, and the particularly preferred addition amount for practical purposes is 2 to 3j! /l.

For example, in hot water to which 0.2 g/l of polyvinyl alcohol has been added, the duration of the vapor film becomes about 30 times longer, the vapor film becomes thicker, and the cooling rate of the wire becomes slower.

Adding various electrolytes for the purpose of raising the boiling point of hot water, reducing the cooling rate of the wire appropriately, or increasing the electrical conductivity of hot water when heating the wire by electrolyzing the hot water while electrolyzing the hot water. I can do it.

Such electrolytes include salts such as sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium nitrate, potassium nitrate, sodium carbonate, potassium carbonate, etc.
Inorganic compounds such as alkalis such as sodium hydroxide and acids such as sulfuric acid and phosphoric acid can be used.

These compounds can also be used to increase the boiling point of hot water, moderately reduce the cooling rate of the wire, and reduce the amount of evaporation of the hot water. It can also be added by a method of supplying power to the

The higher the amount of these compounds added, the better for the purpose of raising the boiling point of hot water or increasing the electrical conductivity, but if it is too large, they will precipitate and adhere to the wire surface, impairing the uniformity of the vapor film, so For example, when sodium sulfate is added alone, a concentration of 50 to 100 g/l is suitable.

By adding these inorganic compounds and surfactants, it is possible to easily obtain hot water with a boiling point of over 100°C that provides an appropriate cooling rate to the wire.

When heating a copper-coated steel wire, there are two methods of heating the wire by energizing it: a method of directly supplying power from a power supply roll, and a method of supplying power from an electrode via an electrolytic solution.

In the method of directly feeding power to the wire from the power supply roll, a large current flows through the contact area between the wire and the power supply roll, which tends to cause overheating. Spray water or immerse part or all of the roll in a water bath to prevent abnormal temperature rise at the contact area.

The power supply roll may be made of any metal or alloy such as copper, brass, or stainless steel, or a conductive material such as a nonmetallic material such as graphite.

If a method of immersing part or all of the roll in cooling water to cool the contact area is adopted at the outlet side of the heating device, the hot water used for cooling the wires must also be used as the power supply roll cooling water. You can also do it.

Further, a power supply roll may be placed between the heating device and the cooling hot water tank, or a power supply roll may be used after the cooling hot water tank.

FIG. 1 is a top view illustrating an example of the electrical heating method in the method of the present invention.

The figure shows power supply tanks 4 and 4 when electrically heating copper-coated steel wire 3 while supplying power from electrodes 1 and 1' through electrolytes 2 and 2'.
' and a view from above of the heating device 5.

In the figure, direct current is used to heat the wire 3, and the current forms a circuit in which the current flows from the ■ side of the power supply 6 through the power supply tank 4, the wire 3, and the power supply tank 4' to the ○ side of the power supply 6. do.

If the polarity of the power source 6 is reversed, the current flows in the opposite direction, and in alternating current, these currents flow alternately.

Since electrode reactions occur on the surfaces of the electrodes and wires, care must be taken to prevent the electrodes and wires from being corroded by electrolysis and interfering with the heat treatment method of the present invention.

For example, sodium sulfate, which is less corrosive and generates less toxic gas, is used as the electrolyte, and lead, which is less corrosive in both the anode and the cathode in the sulfate aqueous solution, is used, and before entering the heating tank 5. By making the wire 3 an anode in the power supply tank 4 and a cathode in the power supply tank 4' on the exit side, there is no problem of corrosion of the electrodes, and the copper-coated steel wire that has gone through these steps can be used once during power supply before heating. Although the surface is oxidized, it is reduced again by power supply after heating, so ultimately the surface remains clean and does not cause any problems.

When the wire is used as a cathode and the following electrode reaction 2H+2e-+H2 is caused, hydrogen embrittlement may occur with a simple steel wire, but with a copper-coated steel wire, the copper core is covered with copper that has a low hydrogen diffusion rate. Because of this, hydrogen embrittlement does not occur.

The power supply tank 4' may also be used as a cooling hot water tank, and power may be supplied between heating and cooling or after cooling.

Although it is necessary to feed power at at least two places, it is optional to use a combination of two or more types of power feeding methods or to feed power at three or more places.

However, the great advantage of using electrical heating in the present invention is that at least one power supply device is installed in the rear half of the cooling water tank or after the cooling water tank, and the copper coating is immersed in the cooling water tank. While the steel wire is being cooled by hot water, a current for electrical heating is passed through part or all of the wire to heat the wire, and the cooling rate in the hot water tank is appropriately slowed down. can get.

With copper-coated steel wire, even if it is simply cooled with hot water, the cooling rate of the steel material is relatively slow due to the copper coating layer compared to a simple steel wire, and it can be reduced to a relatively thin wire, for example, 2.0 mm.
It can be applied up to φ.

However, even with copper-coated steel wires, if the diameter is less than 1.6 mm, the cooling rate is too high when cooling with hot water, and there is a tendency for the martensitic structure to increase and become brittle.

If the cooling rate is slowed down by heating with electricity while cooling with hot water, the heat treatment method of the present invention can be applied to even thinner wires of about 1.2 mmφ.

In the heat treatment method of the present invention, another method for reducing the cooling rate for heat treating a thin wire is achieved by exposing it to air during cooling with hot water.

However, in the latter case, the cooling time using hot water needs to be extremely short, for example, 3 seconds or less, making it difficult to control the time, so the former method is more advantageous.

In addition, it is possible to divide part of the current applied for heating to a copper-coated steel wire immersed in cooling hot water to supply power between the heating tank and the cooling hot water, or at least to one side of the front half of the cooling hot water tank. This can be carried out by providing a power supply device in the rear half of the cooling hot water tank or at least one of the outlets of the cooling hot water tank.

In the area where the copper-coated steel wire moves from the heating device to the cooling hot water tank, the temperature of the wire is high and the surface is susceptible to oxidation, so exposure to the atmosphere must be avoided.

This can be accomplished with a simple device, such as the one shown in FIG.

FIG. 2 is a longitudinal sectional view illustrating an example of the method of heating and hot water cooling in the method of the present invention.

In the device shown in the figure, hot water 8 filled in a hot water tank 7 passes through a hot water outlet 10 that also serves as an inlet to the hot water tank 7 on a line 3, and is connected to a closed box with a circulation pipe 12 attached to a hot water storage tank 11 at the bottom. 13, and the liquid is collected in the hot water storage tank 11.

Between the heating device 14 and the sealed box 13 are partition walls 15, 15.
' is provided to prevent the cooling hot water 8 from entering the high-temperature heating device 14 and causing the heating device 14 to be rapidly cooled and destroyed.

Hot water 8 is heated by a heater 16 and pumped by a pump 17.
The water then flows into the hot water tank 7 again.

The water level of the hot water 8 is adjusted by a separately provided outlet 9.

The atmospheric gas of the heating device 14 is distributed between two partition walls 15 and 15.
The gas enters through the gas inlet 18 provided between ' and flows out from the heating device 14 to the gas outlet 19.

Since the heat treatment method for copper-coated steel wire of the present invention mainly uses hot water for cooling, cooling is relatively fast, and therefore, high-speed heat treatment is possible with relatively small equipment, and the temperature at the exit of the heat treatment device is low. A wire drawing machine is installed near the exit, and the wire drawing process is performed using a wire drawing die, and a great effect is achieved when heat treatment and wire drawing are performed continuously.

In particular, if electrical heating is used, the heating tank can be shortened, so even if heat treatment and wire drawing are performed continuously, the equipment is relatively short.

For example, if a copper-coated steel wire with a diameter of 2 mm is heat treated and then drawn to a diameter of 0.6 mrn using 10 dies, and the winding speed is 100 m/min, the length of the heat treatment equipment is approximately 20 m. It can be used for practical purposes only.

Next, embodiments of the present invention will be described.

Example 1: A diameter of 4,8 m with a copper core containing 0.65% carbon and 0.4% manganese, and a copper cross-sectional area ratio of 30.
After drawing a copper-plated steel wire of 2.3 mm to a diameter of 2.3 mm,
900 in a forming gas atmosphere at a linear speed of 5 m/min.
By continuously passing through a 7 m tubular electric furnace heated to ℃ and a 1.5 m hot water tank filled with 97 °C hot water containing 0.05 weight percent polyvinyl alcohol,
Heat treatment was performed.

The surface of the copper-coated steel wire after heat treatment is clean, its tensile strength is 82.5 kg/ma, the elongation is 11 factors, and the reduction ratio is 631.
It showed good mechanical properties.

When approximately 2000 m of this wire was drawn to a diameter of 1.02 mm, it was not broken even once, and good wire drawability was observed.

Example 2: A copper clad steel wire with a diameter of 6.0 cages having a copper core containing carbon of 0.8 ratio and a copper cross-sectional area ratio of 20 ratio was drawn into a 3.5 cage. Heat treatment was performed continuously at a speed of 5 m.

Heating was performed by passing a current of 200 A through this wire using a 5 m heating device in a forming gas atmosphere, and hot water cooling was performed under the same conditions as in Example 1.

The tensile strength of the copper clad steel wire after heat treatment is 101 kg/
vttA.

The elongation was 7.3, and the wire could be drawn to a diameter of L8mm without any problems.

Example 3: The copper-coated steel wire drawn to 1.02 mm after the heat treatment in Example 1 was continuously heat treated at a wire speed of Ion.

At this time, a total of three power supply rolls immersed in the liquid were installed, one each at the entrance of the heating device, 10 m from the bulkhead of the hot water tank, and 30 crrL from the outlet of the hot water tank, and the wires were powered twice each. A current of 150 A was passed through the wire from the roll at the entrance of the heating device to the roll at the front of the hot water tank, and 90 A from the roll at the front of the hot water tank to the roll at the rear.

The atmosphere in the heating layer is a nitrogen gas atmosphere, and the hot water tank is
．． 90°C hot water containing 0.6% polyvinyl alcohol was used.

The inlet of the heating device was 5 m, and the length of the hot water tank was 2 m.

When the wire heat-treated in this way was drawn, the result was 0.5
Even the basket was a hindrance (I was able to draw the wire).

As described above, the continuous heat treatment method of the present invention is capable of treating copper-coated steel wire at 725° to 1°C in a reducing or inert gas atmosphere.
The heat treatment is performed by heating the wire to a temperature of 0.83°C and then passing it through hot water at a boiling point of 90°C to cool it, resulting in an appropriate cooling rate and a uniform fine sorbite structure, which improves wire drawability. In addition to improving tensile strength and elongation, the cooling time to low temperatures is short, so high-speed heat treatment is possible with relatively small-scale equipment, and there is no oxidation discoloration during the process, so subsequent It has the advantage of being easy to tandem with wire drawing.

Further, the present invention utilizes electrical heating to heat the wire, thereby increasing the efficiency of heating, shortening the length of the furnace, and reducing the deterioration of the furnace.

In addition, if the cooling rate is controlled by applying current to part or all of the wire being cooled with hot water, it becomes possible to patent even a thin wire without causing brittleness.

[Brief explanation of the drawing]

FIG. 1 is a top view illustrating an example of the electrical heating method in the method of the present invention. FIG. 2 is a longitudinal sectional view illustrating an example of the method of heating and hot water cooling in the method of the present invention. 1.1'...Power supply electrode, 2,2', 8...
...Hot water, 3...Copper coated steel wire, 4, 4', 7
......Cooling hot water tank, 5.14...Heating device, 6...Power source for energizing heating, 9...Overflow port, 10...・Hot water outlet, 11・
...Hot water storage tank, 12...Hot water circulation pipe, 13...Sealed box, 15,15'...
Partition wall, 16... Heater, 17... Pump, 18... Gas inlet, 19...
Gas outlet.

Claims (1)

[Claims] 1. While continuously feeding the copper-coated steel wire, the wire is heated to a temperature of 725° to 1083°C in a reducing or inert gas atmosphere, and then immersed in hot water with a boiling point of 90°C. A continuous heat treatment method for a copper-coated steel wire, characterized in that the wire is heat-treated by passing through and cooling the wire. 2. The continuous heat treatment method for a copper-coated steel wire according to claim 1, wherein the heating of the wire is performed by heating the wire by applying an electric current to the wire. 3. The method for continuous heat treatment of a copper-coated steel wire according to claim 2, wherein the conduction of electricity to the wire is performed by supplying electricity from an electrode through an electrolyte while causing an electrode reaction on the surface of the wire. 4. In the process of cooling the wire by passing it through hot water,
The continuous heat treatment method for copper-coated steel wire according to claim 1, 2, or 3, wherein the cooling rate is adjusted by energizing part or all of the wire. 5. Claims 1, 2, 3, or 4, in which after cooling with hot water, the wire is subsequently drawn using a wire drawing die.
Continuous heat treatment method for copper-coated steel wire as described in .