JP4318235B2 - Steel wire manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a steel wire excellent in strength and drawability.
[0002]
[Prior art]
Steel cords are manufactured by repeatedly drawing and heat-treating high carbon steel wires. Such heat treatment is performed in order to soften the steel wire that has been work-hardened by wire drawing, and to perform wire drawing in the next wire drawing step. That is, the work-hardened steel wire is heated to a point A1 (temperature above the temperature in the phase diagram of the carbon steel is a solution state and becomes a crystal structure below the temperature) in a heating furnace to become austenite, followed by Then, it is cooled and held at 500 ° C. to 600 ° C. in a lead bath or the like to obtain a pearlite structure excellent in workability, and then subjected to the next wire drawing step.
[0003]
In the heat treatment of a high carbon steel wire containing about 0.70 to 0.90 mass% of carbon, surface decarburization is likely to occur, and the atmosphere in the furnace is adjusted to suppress decarburization. Since the decarburization of the surface of the steel wire in the heat treatment is a factor for reducing the strength of the steel wire and the subsequent wire drawing, it is required to suppress the decarburization as much as possible in the heat treatment.
[0004]
[Problems to be solved by the invention]
However, since the decarburization cannot be sufficiently suppressed only by adjusting the atmosphere in the furnace and the decarburization occurs in trouble, a method for stably suppressing the decarburization has been still demanded.
[0005]
Accordingly, an object of the present invention is to provide a method for producing a steel wire that suppresses decarburization as much as possible and is excellent in strength and drawability when heat-treated to a drawn high carbon steel wire.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor has found that there is a relationship between the properties of the steel wire surface scale generated in the heating furnace and the decarburization phenomenon. It has been found that the object can be achieved by controlling the scale thickness in the furnace within a specific range, and the present invention has been completed.
[0007]
That is, the steel wire manufacturing method of the present invention is a steel wire for manufacturing a steel wire by subjecting a high carbon steel wire containing 0.70 to 0.90 mass% of carbon to wire drawing and heat treatment in a heating furnace. In the manufacturing method of
A heat treatment in the heating furnace in advance borax on the surface of the high carbon steel wire rod to ^1mg / ^{m 2 ~25mg} / m 2 adhesion coating,
The scale thickness in the heating furnace is controlled within a range of 0.7 μm to 1.4 μm.
[0008]
In the present invention, by performing the heat treatment in the heating furnace in advance borax on the surface of the high carbon steel wire rod to 1mg / m ² ~25mg / m ² adhesion coating, the scale thickness in said heating furnace It becomes possible to control to a desired range.
[0009]
In the present invention, after the coating treatment with borax, the steel wire is drawn using a lubricant mainly composed of calcium stearate, and before the heat treatment, the heat-treated steel wire is heat-treated in a heating furnace. It is preferable that the steel wire is washed with a multi-stage countercurrent washing bath so that the borax concentration of the solution in the final washing bath is from 1 g / l to 12 g / l. As a result, it is preferable to perform water washing while controlling the electrical conductivity of the solution at 1.0 to 4.5 mS / cm. Thereby, the coating amount of borax can be easily controlled within the above range.
[0010]
Further, the multi-stage counter-current type water washing bath replenishes the water in the final water washing bath, sends the increased amount of the solution in the final water washing bath to the previous water washing bath, sequentially sends the increased amount toward the river, This is a water-washing method that treats the increased amount of solution in the eye wash bath, and controls the borax concentration of the solution in the final wash bath, and finally determines the amount of waste liquid in the first wash bath and the amount of water supplied in the final wash bath. It is preferable to carry out by controlling based on the electric conductivity of the solution in the washing bath.
[0011]
The process leading to the completion of the present invention will be described in detail below.
The drawn steel wire has a lubricant such as borax and calcium stearate remaining on the surface thereof, and when heated as it is, the oxide film generated in the heating furnace becomes thick, and cracks are easily formed when the scale is bent. As a result, during the heat treatment performed through the furnace, the oxide film peels off when the steel wire comes into contact with the guide, etc., and the metal surface of the steel wire is directly exposed to the atmosphere, and the protective function of the oxide film is lost. It was first elucidated that decarburization occurred.
[0012]
On the other hand, if the lubricant or the like remains on the surface of the steel wire, a desired oxide film is not generated. Therefore, decarburization can be reduced by removing the lubricant before the heat treatment. Even if all the borax is removed, the decarburization phenomenon still occurs. In this regard, as a result of further intensive investigations, the present inventors have found that when a predetermined amount of borax remains on the surface of the steel wire rod, a target oxide film is generated and decarburization can be reduced as much as possible. It was. Based on these findings, the present invention has been completed, the mechanical properties of the scale have been improved, and it has become possible to suppress decarburization.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described.
In the steel wire manufacturing method of the present invention, the scale thickness in the heating furnace is controlled within the range of 0.7 μm to 1.4 μm. As is apparent from the graph of FIG. 1 showing the result of examining the relationship between scale thickness and decarburization after heat treatment of a steel wire having a wire diameter of 1.3 mm and a carbon content of 0.8% by weight, the scale thickness Decarburization can be satisfactorily suppressed when is in the range of 0.7 μm to 1.4 μm. That is, when the scale thickness is less than 0.7 μm, the oxide film is not generated to the extent that it covers the entire surface of the steel wire, whereas when it exceeds 1.4 μm, the scale thickness becomes too thick and cracks are likely to occur. is there. In FIG. 1, the vertical axis indicates the decarburization depth (mm) measured by observing the cross section of the steel wire.
[0014]
The scale thickness of the heating furnace as a preferred means to within the above range, Heading that the borax to advance the steel wire material surface before the heat treatment it is sufficient to 1mg / m ² ~25mg / m ² adhesion coating It was done. That is, it was found that the borax concentration in the scale is a factor that determines the scale thickness in the control to the desired scale thickness range. FIG. 2 is a graph showing the relationship between the borax concentration in the scale and the scale thickness when the heat treatment conditions are made constant, and the scale thickness increases in an exponential manner proportional to the borax concentration in the scale. As a result, it was found that it is possible to obtain the scale thickness of the object of borax adhesion amount in a heating furnace by setting a 1mg / m ² ~25mg / m ² of the steel wire material surface before the heat treatment.
[0015]
A predetermined amount of borax can be coated on a steel wire by immersing the washed steel wire in a borax aqueous solution having a predetermined concentration. However, the steel wire is subjected to a borax film treatment by wire drawing, and further steered. Since the lubricant mainly composed of calcium phosphate remains, a desired borax adhesion amount can be obtained by washing the drawn steel wire with water. That is, when the steel wire is washed with water, the lubricant is first dissolved and removed, and then the borax is dissolved and removed, but by adjusting the degree of washing, that is, washing with a multistage countercurrent washing bath, the final washing bath By adjusting the degree of the degree of water washing, a predetermined amount of borax can be adhered to the surface of the steel wire after washing.
[0016]
Furthermore, since the borax is ionized and the lubricant is not ionized in the washing bath solution, the borax concentration in the solution can be easily analyzed by measuring the electric conductivity. FIG. 3 shows the relationship between the amount of borax adhesion and the electrical conductivity of the solution. It can be seen that the correlation is very high.
[0017]
The control of the borax concentration of the solution in the final water bath is performed by controlling the amount of waste liquid in the first water bath and the amount of water replenished in the final water bath in the multi-stage countercurrent water bath. FIG. 4 schematically shows a suitable example of such a multi-stage countercurrent water washing bath. In this multi-stage counter-current water washing bath, the steel wire is washed with water and a predetermined amount of borax is adhered. In the example shown in the figure, there are three-stage washing baths 2 to 4, and each bath is an overflow type washing bath, and the solution in the storage tanks 5 to 7 provided under these baths is circulated by a pump P. Then, the steel wire 1 passing through each washing bath is washed with water.
[0018]
The final rinsing bath 4 is provided with an electrical conductivity meter 9 for measuring electrical conductivity, which is a substitute characteristic for concentration analysis of Borax, and the electrical conductivity is measured. If the borax concentration in the final water washing bath 4 becomes higher than a predetermined level, the solution in the first water washing bath 2 is extracted, and the final water washing bath is returned to the original liquid level by the liquid level detector 8 provided in the first water washing bath 2. Water is supplied from the water supply pipe 10 to the liquid storage tank 7 in 4 to adjust the concentration. Liquid storage holes 11 and 12 are provided in the storage tanks 5 to 7 of the multistage counter-current type washing bath, and the solution increased by replenishing the water by adjusting the concentration of the liquid in the final washing bath 4 is used as the previous water. It returns to the washing bath 3 and is added to the washing solution of the washing bath 3, and then it is returned to the river in order to withdraw the liquid from the storage tank 5 in the first washing bath 2 and replenish the reduced liquid. By providing the liquid return holes 11 and 12, the liquid level in the liquid storage tanks 5 to 7 can be kept constant.
[0019]
In order to stably maintain the borax concentration of the solution in the final washing bath 4 within a predetermined range, the electrical conductivity is measured and the solution is replenished continuously, and is extracted once in the first washing bath. By reducing the amount of liquid and increasing the number of times of measurement of electrical conductivity, it can be well maintained within the target borax concentration range.
[0020]
In addition, as another method of making the solution concentration of the final water bath constant, an overflow type liquid return hole is provided in the first water bath in the final water bath, and the electric conductivity of the solution is measured in the final water bath, On the basis of this, water can be replenished to the final washing bath, the increased water can be returned to the river through the liquid return hole, and the overflowed water in the first washing bath can be treated as a waste liquid.
[0021]
【Example】
The present invention will be described based on examples. The following treatment was performed on the drawn steel wire having a carbon content of 0.8% by mass and a wire diameter of 1.3 mm using the multistage countercurrent washing bath shown in FIG. First, a cleaning treatment was performed in advance, and then the steel wire was heated at 900 ° C. for 3 seconds in an inert gas atmosphere such as argon or nitrogen gas, then rapidly cooled to 560 ° C. and held for 3 seconds to obtain a pearlite structure.
[0022]
In the present embodiment, the liquid of the first rinsing bath 2 is extracted and the water is replenished to the final rinsing bath 4 so that the electric conductivity of the final rinsing bath 4 is in the range of 1.0 to 4.5 ms / cm. Went. In the actual treatment, the electric conductivity of the liquid in the final washing bath 4 was controlled within a range of 3.0 ± 0.5 ms / cm. The amount of borax adhered to the steel wire by this treatment was 12 to 18 mg / m ² , the scale thickness was in the range of 0.9 to 1.2 μm, and the decarburization depth was 2 μm or less.
[0023]
On the other hand, when the electrical conductivity of the final rinsing bath 4 was not controlled as in the above-described embodiment and the water was excessively washed, the decarburization depth was 5 to 25 μm. On the other hand, 5-15 μm decarburization was observed when the water washing was insufficient.
Here, the depth of decarburization was measured by etching a cross section of the heat treated steel wire and observing it with an optical microscope.
[0024]
【The invention's effect】
As described above, in the method for manufacturing a steel wire according to the present invention, by controlling the scale thickness in the heating furnace within a specific range, decarburization is suppressed well, and the strength and the wire drawing property are excellent. A steel wire is obtained. In the present invention, the scale thickness can be controlled within a desired range by preliminarily depositing and coating a predetermined amount of borax on the surface of the steel wire and performing heat treatment in a heating furnace. Further, before the heat treatment, the steel wire is washed with a multi-stage countercurrent washing bath, and when controlling the borax concentration of the solution in the final washing bath, the electrical conductivity of the solution falls within a specific range as a substitute characteristic of the borax concentration. By adjusting to, the coating amount of borax can be easily controlled within a desired range.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between scale thickness and decarburization.
FIG. 2 is a graph showing the relationship between the borax concentration in the scale and the scale thickness when the heat treatment conditions are made constant.
FIG. 3 is a graph showing the relationship between the amount of borax adhesion and the electrical conductivity of a solution.
FIG. 4 is a schematic view showing a suitable example of a multi-stage countercurrent water washing bath.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steel wire material 2 Initial water-washing bath 3 Intermediate water-washing bath 4 Final water-washing bath 5 Initial liquid storage tank 6 Intermediate liquid storage tank 7 Final liquid storage tank 8 Liquid level detector 9 Electrical conductivity meter 10 Water supply pipe 11,12 Liquid return hole

Claims (4)

In the method of manufacturing a steel wire, the steel wire is manufactured by subjecting a high carbon steel wire containing 0.70 to 0.90 mass% of carbon to wire drawing and heat treatment in a heating furnace .
A heat treatment in the heating furnace in advance borax on the surface of the high carbon steel wire rod to ^1mg / ^{m 2 ~25mg} / m 2 adhesion coating,
A method of manufacturing a steel wire, wherein the scale thickness in the heating furnace is controlled within a range of 0.7 μm to 1.4 μm. After the film forming process by borax, multistage Upon wire drawing using a lubricant mainly composed of calcium stearate, heat treating the drawn steel wire in a heating furnace, prior to the heat treatment, the steel wires Washing with a counter-current washing bath, the borax concentration of the solution in the final washing bath is 1 g / l to 12 g / l, and the borax adheres to the surface of the high carbon steel wire rod after being removed from the final washing bath the process according to claim 1 steel wire wherein the amount is ^{1mg / m 2 ~25mg / m 2} .   The method for producing a steel wire according to claim 2, wherein the washing is carried out by controlling the electrical conductivity of the solution to 1.0 to 4.5 mS / cm as a substitute characteristic of the borax concentration of the solution in the final washing bath.   The multi-stage counter-current flush bath replenishes the water in the final flush bath, sends the increment of the solution in the final flush bath to the previous flush bath, sequentially sends the increment toward the river, and the first first stage This is a water-washing system that treats the increased amount of water in the water-washing bath, and controls the borax concentration of the solution in the final water-washing bath. The manufacturing method of the steel wire of Claim 3 performed by controlling based on the electrical conductivity of the solution of this.

Images