JP5467789B2 - Al-plated steel wire having good wire drawing workability and manufacturing method thereof - Google Patents

Description

  The present invention is an Al-plated steel wire having an Al-plated coating layer on the surface of a steel core wire, which has good wire drawing workability and is suitable for a conductive member (element wire) such as an automobile wire harness. The present invention relates to a wire and a manufacturing method thereof.

  An automobile wire harness is composed of a large number of conductors, and each conductor is made by bundling several to several tens of “elements”. In recent years, there has been an increasing need for weight reduction and compactness, and there is an increasing demand for thinning wire harnesses. In addition, in order to eliminate the need for separate collection work at the time of car disassembly, a wire harness for a wire harness having a highly recyclable structure has been strongly desired.

  Each wire constituting the wire harness is often fastened to the terminal by “caulking”, and each element wire is required to have a certain strength so that it is not easily broken at the caulking portion. The drawing strength at the caulking fastening portion is required. It is necessary to secure a wire diameter of about 0.2 mm or more in the case of the Cu wire and 1 mm or more in the case of the Al wire for the current wire for the signal wire harness conductor.

  From the viewpoint of recyclability, Al, which can be dissolved together with iron scrap, is superior to Cu, which is an inhibitory element for iron recycling. In terms of electrical conductivity, Al has a larger volume resistivity than Cu, but in the case of a signal wire harness that allows a weak current to flow, there is no problem with Al strands. However, the Al wire has to employ a thick wire diameter in order to solve the shortage of strength as described above, and cannot fully meet the needs for compactness.

  On the other hand, in applications requiring high strength and high corrosion resistance, Al-plated steel wires having steel wires as core wires are known (Patent Documents 1 and 2). Patent Document 1 describes an Al-plated steel wire used for wires for fishing net ropes, power line reinforcement, submarine optical fiber cable reinforcement, and the like. The steel wire disclosed in the example of Patent Document 1 is as thick as 2 to 13 mm in wire diameter, and the purpose of Al plating is to improve corrosion resistance. The Al-plated wire of Patent Document 2 is for high-strength bolts, and FIG. A low-resistance and small-diameter Al-plated steel wire that can be used as a wire of a wire harness has not been put into practical use yet. One of the factors is that the low resistance hot-dip Al-plated steel wire in which Al is adhered around the small-diameter steel core wire is likely to crack inside the Al-plated steel wire during wire drawing.

Japanese Patent Laid-Open No. 3-219005 JP 2004-360022 A

  When manufacturing the strand for conducting wires, a wire drawing step is indispensable in order to obtain a predetermined wire diameter. However, when the steel core wire is subjected to hot-dip Al plating, a brittle Fe—Al alloy reaction layer is formed between the Al plating layer and the steel substrate, and therefore it is not always easy to perform wire drawing. Depending on the hot dipping conditions, severe cracks may occur in the Fe-Al alloy reaction layer even if the wire drawing rate (section reduction rate) is about several percent. According to the study by the inventors, sufficient peeling resistance (especially peeling resistance when subjected to bending back) of the Al plating layer in the process from drawing to wire harness processing and mounting on automobiles. In order to ensure, it is desired that the bonding between the Al plating layer and the steel substrate is maintained in a portion of a total of ½ or more of the entire circumference of the steel substrate derived from the steel core wire. Moreover, when manufacturing the strand for wire harnesses, the performance which can be drawn with a wire drawing rate (cross-sectional reduction rate) of at least 10% or more is required.

  In view of such a current situation, the present invention, when the drawing rate of the hot-dip Al-plated steel wire is, for example, 10% or more, is a total of 1/2 or more of the total circumference of the steel substrate derived from the steel core wire. It is intended to provide a hot-dip Al-plated steel wire having good wire drawing workability so that the bonding between the Al-plated layer / steel substrate is maintained in a part (that is, the crack occurrence rate described later is less than 50%). It is.

  As a result of detailed studies, the inventors have found that when the average thickness of the Fe-Al alloy reaction layer formed between the Al plating layer / steel substrate of the molten Al-plated steel wire is 6 μm or less, cracks during wire drawing It has been found that the resistance to generation is rapidly improved. The present invention has been completed based on such findings.

That is, in the present invention, an Al-plated steel wire having a molten Al plating layer around the steel core wire and not yet subjected to wire drawing after the molten Al plating, in a cross section perpendicular to the longitudinal direction, An Al-plated steel wire with good wire drawing workability in which the average thickness of the Fe—Al-based alloy reaction layer interposed between the Al-plated layer and the Al-plated layer is reduced to 6 μm or less is provided. In the cross section perpendicular to the longitudinal direction, the equivalent circle diameter of the steel substrate portion is, for example, 0.1 to 1 mm, and the area ratio of the Al plating layer (excluding the reaction layer) in the cross section is, for example, 10% or more. Here, when the cross-sectional area of the base steel present in the cross section perpendicular to the longitudinal direction of the Al-plated steel wire S (mm ^2), the circular constant [pi, determined by ^{S = πD 2/4 D (} mm ) Is called the equivalent circle diameter of the steel substrate.

  The present invention also provides an Al-plated steel wire obtained by wire-drawing the above-described Al-plated steel wire (those not yet subjected to wire drawing after hot-dip Al plating).

As a manufacturing method of the above Al-plated steel wire (those not yet subjected to wire drawing after hot-dip Al plating)
(1) The material steel wire is immersed in a molten Al plating bath, and the immersion time is set to a certain time during which the average thickness of the Fe—Al-based alloy reaction layer interposed between the steel substrate and the Al plating layer becomes 6 μm or less after solidification. Manufacturing method to control and lift from the molten Al plating bath, or
(2) A material steel wire having a Ni plating layer with an average thickness of 0.2 to 2 μm on the surface is immersed in a molten Al plating bath, and the immersion time is sufficient for the Ni plating layer to completely disappear after solidification, and the steel. A production method in which the average thickness of the Fe—Al alloy reaction layer interposed between the substrate and the Al plating layer is controlled to a fixed time of 6 μm or less after solidification and pulled up from the molten Al plating bath;
Is provided. In that case, after activating the said raw material steel wire in 300-800 degreeC reducing atmosphere, you may immerse in a molten Al plating bath. As the molten Al plating bath, one having a Si content of 0 to 12% by mass can be used.

  Conventionally, since a brittle Fe-Al alloy reaction layer is generated in a hot-dip Al-plated steel wire, when the wire drawing is performed, cracks are likely to occur in the reaction layer, and therefore the wire drawing rate must be kept low. As a result, according to the present invention, for example, a hot-dip Al-plated steel wire is provided in which the problem of strength reduction caused by cracks in the reaction layer does not become apparent even when the drawing rate (cross-sectional reduction rate) is 10% or more. . This makes it possible to mass-produce molten Al-plated steel wires with a predetermined wire diameter, and replace the conventional copper strands with molten Al-plated steel wires to create a highly recyclable wire harness. Can be realized.

A cross-sectional SEM photograph when a normal hot-dip Al-plated steel wire is drawn at a drawing rate of 30%. The cross-sectional SEM photograph at the time of drawing the hot-dip Al plating steel wire of this invention with a drawing rate of 42%.

Hereinafter, the term “cross section” means a cross section perpendicular to the longitudinal direction of the steel wire unless otherwise specified. The “drawing rate” is expressed by a cross-sectional reduction rate and is calculated by the following formula.
[Drawing rate (%)] = ([Cross sectional area before wire drawing] − [Cross sectional area after wire drawing]) / [Cross sectional area before wire drawing] × 100

The “crack generation rate” between the Al plating layer and the steel substrate means the ratio of the total angle of the arcs of the cracked portions in the entire circumference (360 °) of the steel substrate, and can be determined as follows. In the cross section of the hot-dip Al-plated steel wire after wire drawing, the center point O is the midpoint of the longest diameter of the steel base derived from the steel core wire. Assuming a half-line with the center point O as one end, and rotating the inside of the cross section 360 ° around the center point O as an axis, the rotation angle when the line passes over the crack (becomes on the crack) is Accumulate and set this as θ _TOTAL (°). The crack generation rate is calculated by the following equation.
[Crack occurrence rate (%)] = θ _TOTAL (°) / 360 ° × 100

The average thickness h (μm) of the reaction layer interposed between the Al plated layer / steel substrate is derived from the steel core wire in the observation image of the cross section of the Al plated steel wire that has not been subjected to wire drawing after the molten Al plating. The equivalent circle diameter of the steel substrate is D (μm), and the reaction layer in contact with the steel substrate among the reaction layers existing in the cross section (that is, the reaction layer that is separated into islands in the Al plating layer is not included) Where S ₁ (μm ² ) is the total area, and π is the circumference, it can be determined by the following equation.
[Average thickness h of reaction layer] = S ₁ / (πD)
Here, πD of the denominator corresponds to the circumferential length of the steel substrate. Since the reaction layer conceptually exists outside the circumference, the average thickness h of the reaction layer is slightly smaller than the value determined by the above equation from mathematical accuracy. However, since h is sufficiently smaller than πD, the value of h approximated by the above formula can be adopted as the average thickness of the reaction layer in the present application. The above D and S ₁ can be obtained by image processing, for example, the cross section of the observation image (e.g. SEM image).

  Fig. 1 and Fig. 2 show the generation of cracks in the reaction layer part between the Al plating layer and the steel substrate in the SEM photograph of the cross section perpendicular to the longitudinal direction of the hot-dip Al-plated steel wire subjected to wire drawing. Illustrate the situation. FIG. 1 shows an example in which a normal hot-dip Al-plated steel wire that has not taken countermeasures for suppressing cracks in the reaction layer is drawn at a drawing rate of about 30%. Vigorous cracks are generated in the reaction layer, and the crack generation rate greatly exceeds 50%. Such an Al-plated steel wire cannot fully utilize the tension of the steel base portion derived from the steel core wire as strength, and is inferior in strength level. FIG. 2 corresponds to Example 1 described later of the present invention, and is an example of wire drawing at a wire drawing rate of 42%. Even in this case, the crack generation rate is 45%, and the wire drawing workability is improved.

  The hot-dip Al-plated steel wire of the present invention (not yet drawn after hot-Al plating) has an average thickness of 6 μm or less for the Fe—Al alloy reaction layer interposed between the Al plating layer / steel substrate. It is characterized by being reduced. According to the inventors' detailed examination, when the average thickness of the Fe-Al alloy reaction layer exceeds 6 μm in the cross section of the hot-dip Al-plated steel wire, the reaction is performed even if the drawing rate is several percent. In some cases, severe cracks may occur in the layer portion. When wire drawing of 10% or more is performed, in most cases, the crack generation rate exceeds 50%, which is difficult to put into practical use. However, when hot-dip Al plating is performed so that the average thickness of the Fe—Al-based alloy reaction layer is 6 μm or less, the wire drawing workability is drastically improved. The average thickness of the Fe—Al-based alloy reaction layer is more preferably 5 μm or less, and even more preferably 4 μm or less. However, it is almost impossible to manufacture a product having no reaction layer, and the average thickness is 0.5 μm or more in the tests so far.

  The composition of the Fe—Al-based alloy reaction layer varies depending on the location in the cross section, but usually the Al concentration varies in the range of 25 to 75 mass%, and the balance is Fe and inevitable impurities.

  In consideration of the use of the wire used for conducting wires such as a wire harness, the equivalent circle diameter of the steel substrate portion derived from the steel core wire is 0.1 to 1 mm in the cross section before the wire drawing after the molten Al plating. It is desirable to be. When the steel core wire becomes thin, it becomes difficult to perform hot-dip Al plating. Therefore, it is not easy to stably manufacture hot-dip aluminum-plated steel wire having a circle-equivalent diameter of the steel base portion of less than 0.1 mm. On the other hand, when the equivalent circle diameter of the steel substrate exceeds 1 mm, the load of wire drawing tends to be excessive. Further, the area ratio of the Al plating layer (excluding the reaction layer) in the cross section is desirably 30% or more. If the Al adhesion amount is smaller than that, it tends to be disadvantageous in terms of conductivity. The upper limit of the area ratio of the Al plating layer is restricted by the controllable condition range on the apparatus, and thus does not need to be particularly determined, but may be 95% or less, for example, from the viewpoint of strength as a strand.

  As for the steel wire to be the core wire, for example, a mild steel wire specified in JIS G3505, an iron wire specified in G3532, a hard steel wire specified in G3506, and the like are applicable, but not limited thereto.

  The hot-dip Al-plated steel wire of the present invention in which the generation thickness of the Fe—Al-based alloy reaction layer as described above is reduced is either (1) a technique for shortening the immersion time in the hot-Al plating bath, or (2) steel. It turned out that it can manufacture by the method of immersing the raw material steel plate which gave the thin Ni plating to the surface of the core wire in the hot Al plating bath.

  The technique (1) for shortening the immersion time in the molten Al plating bath can be carried out mainly by increasing the line speed. Depending on the diameter of the raw steel wire (core wire) and the target Al plating adhesion amount, for example, the average thickness of the Fe—Al based alloy layer in the range of 0.05 to 1.5 seconds immersed in a molten Al plating bath A condition that can reduce the thickness to 6 μm or less can be found. The conditions can be grasped in advance by a preliminary experiment, and based on the data, the immersion time may be controlled to a certain time during which the average thickness of the Fe—Al-based alloy layer becomes 6 μm or less after solidification. If the wire diameter of the material steel wire is reduced, it becomes difficult to improve the line speed, but it can be realized by improving the wire feeding accuracy of the apparatus. Depending on the specifications of the apparatus, the immersion time may be managed in the range of 0.1 second or more, or 0.3 second or more.

  The method (2) of immersing the raw steel wire subjected to thin Ni plating in a molten Al plating bath is effective in relaxing the line speed condition. According to the study by the inventors, it has been found that the Ni plating layer present on the surface of the raw steel wire has an action of suppressing the growth of the reaction layer interposed between the Al plating layer / steel substrate. Although the thin Ni plating layer is lost in the molten Al plating bath, the Fe—Al alloy reaction layer is shortened by reducing the time for direct contact between Fe in the steel substrate and Al in the plating bath to react. It is thought that the growth of If the thickness of the Ni plating layer becomes too thick, the Ni plating layer remains even after solidification, and the interface structure between the Al plating layer / steel substrate becomes complicated. In the present invention, the average thickness of the Ni plating layer present on the surface of the material steel wire to be subjected to hot-dip Al plating is set to 0.2 to 2 μm. The thickness is more preferably 0.2 to 1.5 μm, and still more preferably 0.2 to 1.0 μm. If the Ni plating layer is too thin, the effect of suppressing the growth of the reaction layer is not exhibited so much. If it is too thick, the Ni plating layer tends to remain after solidification, and in this case, a complicated interface structure is formed.

  The thin Ni plating layer can be formed by a known electroplating method using, for example, a nickel sulfate bath or a nickel chloride bath. The average thickness of the Ni plating layer can be calculated from the current density and the energization time in electric Ni plating. When wire drawing is performed after Ni plating and before hot-dip Al plating, the processing rate (cross-sectional reduction rate) is calculated. In consideration of this, the average thickness of the Ni plating layer can be controlled.

  When using Ni-plated material steel wire, the immersion time in molten Al plating is sufficient for the Ni plating layer to disappear completely after solidification, and the average thickness of the Fe-Al alloy layer is 6 μm or less after solidification. It may be controlled at a certain time. Specifically, for example, the conditions under which the average thickness of the Fe—Al-based alloy layer can be reduced to 6 μm or less can be found when the immersion time in the molten Al plating bath is 0.05 to 3 seconds. ), The line speed can be reduced.

Activation in a reducing atmosphere immediately before immersion in a molten Al plating bath is effective in improving plating adhesion. Examples of the reducing atmosphere include a gas such as 10% H ₂ —N ₂ , and the temperature is preferably in the range of 300 to 800 ° C.

  The molten Al plating bath can have a Si content of 0 to 12 masses. By adding Si, the growth of the reaction layer can be suppressed, which is effective in improving the wire drawing workability. Further, since the melting point is lowered by the addition of Si, the manufacture becomes easy. However, when the Si content increases, the workability of the Al plating layer decreases. It also leads to a decrease in conductivity. Therefore, when Si is contained in the Al plating bath, the content is preferably 12% by mass or less, and when high workability is required, it is effective to restrict the content to 9% by mass or 6% by mass. When an Al plating bath containing Si is used, Si is also detected in the Fe—Al alloy reaction layer, but there is no particular adverse effect as long as the plating bath composition is in the above range.

Example 1
As the material steel wire, a steel wire having a wire diameter of 0.2 mm (JIS G3505 mild steel wire equivalent material) was prepared. After activating the surface by exposing the material steel wire to an atmosphere of 10% H ₂ -N ₂ gas and 600 ° C. using a plating bath comprising Al and inevitable impurities as a molten Al plating bath, It was immersed in a molten Al plating bath and subjected to molten Al plating by a method of pulling up vertically. At that time, the line speed was set to 70 m / min, and the immersion time in the plating bath was set to 0.8 seconds. The plating adhesion amount was adjusted by nitrogen gas wiping.

  As a result of observing the cross section of the obtained Al-plated steel wire and measuring the average thickness h of the reaction layer interposed between the Al plating layer / steel substrate by the above-mentioned method, the average thickness of the reaction layer was 5. It was 1 μm. As a result of analyzing the reaction layer by SEM-EDX, this reaction layer was an Fe-Al alloy reaction layer, the Al concentration fluctuated in the range of 25 to 75% by mass, and the balance was Fe and inevitable impurities. . The area ratio of the Al plating layer (excluding the reaction layer) in the cross section was 77%.

The above hot-dip Al-plated steel wire was subjected to wire drawing by drawing, and the crack generation rate in the cross section of the obtained Al-plated steel wire was measured by the method described above, and the following results were obtained.
When the drawing rate is 30%, the crack generation rate is 38%.
When the wire drawing rate is 42%, the crack occurrence rate is 45%.
At a wire drawing rate of about 40%, the crack occurrence rate was suppressed to less than 50%, and it was confirmed that the wire has a good wire drawing workability.

<< Comparative Example 1 >>
In Example 1, the same experiment as in Example 1 was performed, except that the line speed of the molten Al plating was 45 m / min and the immersion time in the plating bath was 1.1 seconds. The results were as follows.

  The average thickness of the reaction layer was 8.2 μm. It was confirmed that this reaction layer fluctuated in an Al concentration range of 25 to 75% by mass, and the balance was an Fe—Al alloy reaction layer composed of Fe and inevitable impurities. The area ratio of the Al plating layer (excluding the reaction layer) in the cross section was 79%. When this hot-dip Al plated steel wire was drawn at a drawing rate of 13%, the crack generation rate was 87%, which was inferior to the drawing property.

<< Comparative Example 2 >>
In Example 1, the same experiment as in Example 1 was performed except that the line speed of the molten Al plating was set to 30 m / min and the immersion time in the plating bath was set to 1.6 seconds. The results were as follows.

  The average thickness of the reaction layer was 11.5 μm. It was confirmed that this reaction layer fluctuated in an Al concentration range of 25 to 75% by mass, and the balance was an Fe—Al alloy reaction layer composed of Fe and inevitable impurities. The area ratio of the Al plating layer (excluding the reaction layer) in the cross section was 76%. When this molten Al-plated steel wire was drawn at a drawing rate of 9%, the crack generation rate was 90%, which was inferior to the drawing property.

Example 2
In Example 1, the material steel wire was an electric Ni-plated steel wire having a Ni-plated layer with an average thickness of 0.5 μm, the activation treatment before hot-dip plating was omitted, and the line speed of hot-dip Al plating was The same experiment as in Example 1 was performed except that the immersion time in the plating bath was set to 35 seconds at 1.4 m / min. The results were as follows.

  The average thickness of the reaction layer was 4.8 μm. It was confirmed that this reaction layer fluctuated in an Al concentration range of 25 to 75% by mass, and the balance was an Fe—Al alloy reaction layer composed of Fe and inevitable impurities. The Ni plating layer was completely lost. By using a Ni-plated steel wire as the material steel wire, it was possible to make the reaction layer as thin as or less than in Example 1 even if the line speed was slow. That is, the formation suppression effect of the reaction layer by the Ni plating layer was recognized. The area ratio of the Al plating layer (excluding the reaction layer) in the cross section was 81%.

The crack occurrence rates when the hot-dip Al plated steel wire was drawn were as follows.
When the wire drawing rate is 29%, the crack occurrence rate is 35%.
When the wire drawing rate is 42%, the crack occurrence rate is 44%.
As in Example 1, it was confirmed that the film had good wire drawing workability.

Example 3
In Example 1, the same experiment as in Example 1 was performed except that the molten Al plating bath was a plating bath containing 4% by mass of Si, the remaining Al and inevitable impurities. The reaction layer was an Fe—Al-based alloy reaction layer, and the average thickness, Al concentration, and area ratio of the Al plating layer were the same as in Example 1.

The crack occurrence rates when the hot-dip Al plated steel wire was drawn were as follows.
When the drawing rate is 29%, the crack occurrence rate is 36%.
When the wire drawing rate is 42%, the crack occurrence rate is 44%.
As in Example 1, it was confirmed that the film had good wire drawing workability.

Example 4
In Example 1, the condition of nitrogen gas wiping was adjusted to reduce the amount of plating adhesion, and an Al-plated steel wire having an Al plating layer area ratio smaller than that in Example 1 was produced.

From the manufactured Al-plated steel wire, those having an Al plating layer area ratio of 18% and 39% in the cross section were extracted. The average thickness and composition of these reaction layers had the same tendency as in Example 1. And the crack incidence when the area ratio of this Al plating layer was drawn at a drawing rate of 42% on a molten Al plated steel wire with 18% and 39% was as follows.
Al plating layer area ratio of 18%, crack generation rate 48%
Al plating layer with an area ratio of 39%, crack generation rate 46%
As in Example 1, it was confirmed that the film had good wire drawing workability.

<< Comparative Example 2 >>
In Example 4, the condition of nitrogen gas wiping was adjusted to further reduce the plating adhesion amount, and an Al plated steel wire having a smaller area ratio of the Al plated layer in the cross section was manufactured.

  From the manufactured Al-plated steel wire, one having an area ratio of the Al plating layer in the cross section of 8% was extracted. The average thickness and composition of these reaction layers had the same tendency as in Example 4. When a hot-dip aluminum plated steel wire with an area ratio of 8% was drawn at a drawing rate of 42%, the crack generation rate was 55%, which was inferior to the drawing property. It was.

Claims (5)

An Al-plated steel wire that has a molten Al plating layer around the steel core wire and has not yet undergone wire drawing after the molten Al plating, and corresponds to the circle of the steel substrate in a cross section perpendicular to the longitudinal direction. The diameter is 0.1 to 1 mm, the average thickness of the Fe—Al alloy reaction layer interposed between the steel substrate and the Al plating layer is 0.5 to 6 μm , and the Al plating layer (reaction Al-plated steel wire with good wire drawing workability with an area ratio of 30% or more (excluding the layer) . An Al-plated steel wire obtained by drawing the Al-plated steel wire according to claim 1, wherein the wire-drawing rate defined by the following formula (1) is 10% or more and is defined by the following (A): Al-plated steel wire with a crack generation rate of less than 50% .
[Drawing rate (%)] = ([Cross sectional area before wire drawing] − [Cross sectional area after wire drawing]) / [Cross sectional area before wire drawing] × 100 (1)
(A) In the cross section of the hot-dip Al-plated steel wire after wire drawing, assuming the center point O as the midpoint of the longest diameter of the steel substrate (major axis), a half line with the center point O as one end, When the half line is rotated 360 ° in the cross section around the center point O, the rotation angle when the straight line passes over the crack is integrated, and this is defined as θ _TOTAL (°) by the following formula (2) The crack occurrence rate is calculated.
[Crack occurrence rate (%)] = θ _TOTAL (°) / 360 ° × 100 (2)   A material steel wire having a Ni plating layer with an average thickness of 0.2 to 2 μm on the surface is immersed in a molten Al plating bath, and the immersion time is sufficient for the Ni plating layer to completely disappear after solidification, and the steel substrate and Al An Al-plated steel wire excellent in wire drawing workability that is pulled up from a molten Al plating bath by controlling the average thickness of the Fe-Al alloy reaction layer interposed between the plating layers to a fixed time of 6 μm or less after solidification. Production method. The method for producing an Al-plated steel wire according to claim 3 , wherein the material steel wire is activated in a reducing atmosphere of 300 to 800 ° C and then immersed in a molten Al plating bath. The method for producing an Al plated steel wire according to any one of claims 3 and 4, wherein the Si content in the molten Al plating bath is 0 to 12% by mass.