JP2001123279A - Al-Mg-Si BASE ALLOY COATED STEEL WIRE EXCELLENT IN CORROSION RESISTANCE AND PRODUCING METHOD THEREFOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an Al-Mg-Si base alloy coated steel wire having excellent corrosion resistance in a salt water environment and a fresh water environment and to provide a method for producing the same. SOLUTION: As to this Al-Mg-Si base alloy coated steel wire excellent in corrosion resistance, in an Al-Mg-Si base alloy coated steel wire having a coating layer containing, by mass, 3 to 9% Mg and 2 to 10% Si, and the balance Al with inevitable impurities, the coating layer contains planar particles of an Mg2Si phase. It is preferable that the average value of the maximum size of the planar particles of an Mg2Si phase is controlled to <=20 μm, and the surface of the Al-Mg-Si base alloy coating layer is provided with an organic synthetic resin coating layer composed of a baked type composition, and in which the hardening degree of the coating film after baking is controlled to >=80%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion-resistant aluminum alloy-coated steel wire. In particular, the present invention relates to a corrosion-resistant Al alloy coated steel wire used in various corrosive environments ranging from a high chlorine concentration environment such as a coastal region such as a harbor to a low chlorine concentration environment such as an inland region.

[0002]

2. Description of the Related Art Conventionally, in order to improve the corrosion resistance of a steel wire, a corrosion-resistant steel wire having a layer of Al or Zn formed on the surface of the steel wire has been used. Among them, the Zn-plated steel wire is used as a wire of a suspension bridge cable or the like as a corrosion-resistant steel wire. The corrosion behavior is due to the so-called self-sacrifice of Zn, which acts as an anode for the steel wire, so that the plating is selectively consumed and acts as a cathodic protection, preventing the internal steel wire itself from corrosion. To play. Therefore, Zn
The corrosion of galvanized steel wire is general corrosion, and its behavior does not change even in highly corrosive environments such as coastal areas. However, since the Zn-plated steel wire is literally manufactured by a plating method, the plating thickness is 50 at most.
μ, which limits the improvement of corrosion resistance. As a method for forming a corrosion-resistant Zn layer other than the plating method, a cladding method or an extrusion method can be considered, but it is difficult to carry out the method due to the plastic deformation characteristics unique to Zn.

On the other hand, Al-plated steel wires have excellent corrosion resistance, and it is well known that the corrosion resistance behavior of the Al ₂ O ₃ film formed on the surface plays a large role. However, the effect of Al ₂ O _{3 as} a protective film is in a normal corrosive environment, and a sufficient effect is not necessarily obtained in a highly corrosive environment such as a coastal area.
That is, since the protective film of Al ₂ O ₃ is naturally formed by surface oxidation, there is a portion where coating is partially insufficient due to unevenness of formation, which is a cause of forming deep local corrosion called so-called pitting corrosion. Had become. In the above general corrosion, the progress of the corrosion is slow with time, whereas the pitting corrosion causes fatal damage to the steel wire in a relatively short time.

The present inventors have already made Al and Mg and Si
Al-Mg-Si alloy to which a certain amount of Al is added gives excellent corrosion resistance to steel wires in a high chlorine concentration environment or a low chlorine concentration ring, and also finds that the problem of pitting corrosion is also solved. An Al-Mg-Si alloy plated steel wire was provided. However, this requires a plating temperature of 600 ° C. or higher, and there is a high possibility that the mechanical properties of the steel wire itself are reduced in the plating step. Therefore, it is not suitable for applications requiring high mechanical strength, such as suspension bridge cable wires.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made from the above-mentioned viewpoints, and has an excellent corrosion resistance from a high chlorine concentration environment to a low chlorine concentration environment without deterioration of mechanical properties. An object of the present invention is to provide a Si-based alloy-coated steel wire and a method for producing the same.

[0006]

The inventors of the present invention have focused on Al-Mg-Si-based alloys which impart the above-described high corrosion resistance to steel wires, and as a result, have found that Al-Mg-Si-based It has been found that the presence of plate-like particles of the Mg ₂ Si phase in the alloy layer is indispensable. Based on this finding, Al
Limit the shape and size of the composition and Mg ₂ Si in -mg-Si-based alloy, there is have completed the present invention, has as its gist, (1) mass%, Mg: 3 to 9 %, Si: balance containing 2-10% is in the Al-Mg-Si alloy-coated steel wire having a coating layer made of Al and unavoidable impurities, the coating layer containing tabular grains of Mg ₂ Si phase An Al-Mg-Si alloy coated steel wire having excellent corrosion resistance.

(2) The Al—Mg—Si alloy coated steel wire having excellent corrosion resistance as described in (1) above, wherein the average value of the maximum diameter of the plate-like particles of the Mg ₂ Si phase is 20 μm or less. . (3) On the Al-Mg-Si-based alloy coating layer, there is provided an organic synthetic resin coating layer made of a baking type composition and having a cured degree of 80% or more after baking. Al-Mg excellent in corrosion resistance according to the above (1) or (2)
-Si alloy coated steel wire.

(4) The corrosion resistance described in (1) to (3), wherein the surface of the steel wire is coated with an Al—Mg—Si alloy coating layer simultaneously with the drawing by extrusion. An excellent method for producing an Al-Mg-Si alloy coated steel wire. (5) The method according to (4), wherein all the steps are performed at a temperature of 500 ° C. or less, wherein the Al—Mg—S having excellent corrosion resistance according to (1) to (3).
This is a method for producing an i-based alloy-coated steel wire.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the Al-Mg-Si-based alloy layer of the Al-Mg-Si-based alloy-coated steel wire of the present invention, Mg: 3 to 9% and Si: 2 to 10% by mass%. Al-Mg-Si with the balance being Al and unavoidable impurities
A system alloy coating is used. If the content of Mg is less than 3% by mass, not only does the extrudability and the strength of the coating decrease, but also the corrosion resistance decreases. On the other hand, if the content exceeds 9% by mass, the effect of improving the corrosion resistance is saturated, and the cost is increased by the addition of Mg. Therefore, the content of Mg is 3
To 9% by mass.

When the content of Si is less than 2% by mass,
Since the viscosity of the Al-Mg-Si alloy increases, the extrusion pressure
The force rises and reduces workability. Furthermore, in the coating layer
Mg _TwoSi phase becomes amorphous particles and has polygonal cross section
Since it does not have a plate-like shape, the corrosion resistance also decreases. on the other hand,
If the Si content exceeds 10% by mass, Mg_TwoSi phase
Because plate-like particles are enlarged, corrosion resistance is reduced,
It is not preferable because the die of the extrusion device is damaged. Only
It is difficult to obtain good adhesion with the coating film provided on the coating
Cause such problems. Therefore, the content of Si
Is 2 to 10% by mass.

Since Mg ₂ Si particles have a hard property, the die may be damaged during extrusion. To avoid this, the Mg ₂ Si phase must be in a plate-like precipitation form. On this, it is preferable that the average particle size of the plate-like particles of the Mg ₂ Si phase be 20 μm or less,
More preferably, it is 4 μm or less. Note that Mg ₂ Si
The method for measuring the plate-like particle size of the phase is not particularly specified, but the inventors measured it as follows.

First, a cut piece (about 10 × 10 mm) of an Al—Mg—Si alloy is polished and observed at a magnification of 500 times or more using an optical microscope or an electron microscope (SEM). Next, a field of view in which as many plate-like particles of the Mg ₂ Si phase as possible were selected,
Measure the maximum diameter of each piece. Then, this operation is repeated for three different cut pieces to obtain an average value of a total of 15 plate-like particles, and this is set as an average value of the maximum diameter.
The maximum diameter of each plate-like particle may be determined by visual observation.

Next, a coating method will be described. Since the main component of the coating of the Al-Mg-Si alloy coated steel wire of the present invention is Al, for example, a method based on a known extrusion coating method such as the method disclosed in JP-A-7-155873. Can be used. That is, a steel wire heated to about 250 to 400 ° C.
The steel wire is coated with an Al-Mg-Si alloy extruded at 00 ° C while applying a forward tension to the steel wire.

Here, the extrusion temperature of the Al-Mg-Si alloy is
The degree is not particularly specified, but is preferably 400 to 500 ° C.
And By processing at 400 ° C or higher, M
g_TwoSi particles are easily refined, further improving corrosion resistance
Can be expected. On the other hand, if the temperature exceeds 500 ° C., Mg_TwoSi
It becomes easy to coarsen. That is, the M dissolved in the extrusion process
g_TwoWhen Si precipitates during the cooling process after coating,
Mg that could not be dissolved _TwoWith Si, this becomes the core
Promotes precipitation. As a result, Mg_TwoSi becomes coarse
It will be cool. Mg_TwoWhen Si becomes coarse, corrosion resistance decreases.
For this reason, the extrusion temperature is preferably 500 ° C. or less.

Further, Al-Mg-Si to be subjected to extrusion processing
The system alloy may be used in a state suitable for an extruder, such as a wire or a billet. However, regardless of the state used, those containing plate-like particles of the Mg ₂ Si phase are preferably used, and the average of the maximum diameter is preferably 20 μm.
m or less. Of these, the shape of the Mg ₂ Si phase is substantially determined by the amount of Si added, so the amount of Si added may be controlled, but the size of the Mg ₂ Si phase can be controlled to some extent during the extrusion process. , Its effect is limited, Mg ₂
It is not always possible to completely prevent the die from being damaged by Si particles. Al-Mg with controlled size of Mg ₂ Si
The -Si alloy can be obtained, for example, by the method disclosed in Japanese Patent Application Laid-Open No. 3-27749. By using the above-described coating method, the temperature condition can be suppressed to at most 500 ° C. in the entire process, so that the strength of the steel wire can be maintained and the grain growth of Mg ₂ Si can be suppressed.

Next, it is preferable to apply an organic synthetic resin paint on the Al-Mg-Si alloy coating. Commercially available paints such as acrylic, chlorinated rubber, vinyl chloride, and polyurethane may be used, but epoxy paints are preferred because of their high adhesion and excellent mechanical strength. It is preferably used. Although the composition of the epoxy-based paint may be appropriately adjusted, a series of steps from coating to film formation must be completed within a limited time in a continuous production coating line. Preferably, a bake hardening type is used.

The epoxy resin used for the coating material preferably has an average molecular weight of 300 to 4,000 and an epoxy equivalent of 70 to 5,000, and the number of oxirane rings at the molecular terminals is two or more per epoxy molecule. Further, those obtained by appropriately modifying these epoxy resins may be used. The curing agent is appropriately selected from diamine derivatives (including dicyandiamide and imidazole derivatives), acid anhydrides, phenol derivatives, amine salts, and various modifications thereof.

An appropriate mixing ratio of the epoxy resin and the curing agent is as follows:
Since it depends on the combination of compounds used, it cannot be specified unconditionally. For example, when a primary amine compound is used as the curing agent, the active hydrogen of the curing agent is about 8 parts per 10 parts of the oxirane ring of the epoxy resin. It is good to do so. Further, an inorganic additive such as silica may be added to impart strength and flexibility to the coating film, and the coating may be diluted with an organic solvent to facilitate the coating operation.
However, an organic solvent that does not cause a chemical reaction with an epoxy resin or a curing agent to be used is used.

The coating is performed by dipping the steel wire in the coating or by a spraying method using a suitable coating machine, but other methods may be used. After coating, it is preferable to lighten and rub with a rubber spatula or the like as necessary in order to make the coating film thickness uniform. Baking is performed by an appropriate method such as a hot air drying method, an electric induction heating method, or an infrared heating method. However, regardless of the method of baking, the degree of cure of the film after baking must be 80% or more. Below this, a strong coating cannot be obtained. The degree of cure of the coating film is
It can be estimated by the method disclosed in Japanese Patent Application Publication No. 95-4431.

It is important that the required coating film thickness be individually determined in consideration of the corrosive environment of the basket mat and the like. Therefore, the thickness is not particularly limited here, but is preferably at least 5 μm or more in order to have anticorrosion properties. Also, if it is too thick, it will be easily broken by the impact of stone at the time of construction as described above,
It is preferable that the thickness be up to about 200 μm. A chemical conversion coating such as chromate, phosphate, organic zirconium salt, organic titanium salt, or zirconium salt may be interposed between the alloy coating layer and the organic synthetic resin coating film. When performing the chemical conversion treatment, it is preferable to perform the degreasing after the coated surface is sufficiently degreased. As the chemical solution used for degreasing, a volatile organic solvent or a commercially available product for exclusive use can be used, and the chemical conversion treatment is preferably performed by a dipping method, a spraying method, or another appropriate method.

[0021]

Next, the contents of the present invention will be described in detail based on embodiments. First, an Al—Mg—Si alloy (70 mm × 70 mm billet) containing Mg and Si, the remainder being Al and unavoidable impurities, was extruded onto a steel wire having a diameter of about 6 mm heated to 380 ° C. by electric heating. 48
It was extruded at 0 ° C. and an extrusion ratio of 500 and coated to a thickness of about 200 μ. Then, apply tension in the direction of the steel wire,
The wire was drawn until the wire diameter became 5 mm. Further, as comparative materials, Mg: 6% by mass and Si: 6% by mass are contained, and the balance is Al.
In addition, an Al-Mg-Si alloy coated steel wire composed of unavoidable impurities was produced. The temperature of the plating bath was set at 640 ° C., and the immersion time was 30 seconds. The amount of plating is about 5
It was set to 0 μm.

Approximately 10c from the steel wire thus produced
m was cut out and subjected to a corrosion test. The test piece was prepared by adding a linear cut flaw (5 cm in length) reaching the steel surface at only one location parallel to the longitudinal direction of the steel wire.
The cut surfaces at both ends were sealed with a silicon-based sealant. In the corrosion test, a salt spray test (2000 hours) and a hot water immersion test (5000 hours) were performed, and the presence or absence of red rust was visually evaluated. The hot water immersion test was performed using pure water at a hot water temperature of 40 ° C. while blowing air.
Further, a tensile test was also performed to examine whether or not the strength of the steel wire was reduced by the coating of the Al-Mg-Si alloy. Table 1
Is the result. In this table, the cross-sectional shape of the Mg ₂ Si phase measured from the SEM image (× 1000) of the cross section of the Al—Mg—Si alloy coating layer and the maximum value of the long side of the cross section are described.

From Table 1, it can be seen that the composition of the coating layer is Mg and Si.
3 to 9% by mass and 2 to 10% by mass, respectively,
_When the cross-sectional shape of the 2Si phase was a plate-like particle having a polygonal cross section and the long side of the cross section was 20 μm or less, no red rust was observed in both the salt spray test and the warm water immersion test. However, when the composition of the coating layer is out of the above range, and when the long side in the cross-sectional direction of the Mg ₂ Si phase exceeds 20 μ even if the composition of the coating layer is within the above range, in addition to the generation of red rust, In addition, defects such as poor appearance and scratches on the dies due to deterioration in workability during coating occurred. In addition, of all the steel wires prototyped this time, the strength of only the plated material was reduced, but the strength of the coated material was good without any decrease in strength.

As described above, in the Al—Mg—Si alloy coating, the set of coating layers is Mg: 3 to 9% by mass, and Si:
In the range of 3 to 9% by mass, Mg ₂ Si
And when the Mg ₂ Si phase is plate-like particles having a maximum diameter of 20 μm or less, has excellent corrosion resistance in both high and low chlorine concentration environments, and has reduced mechanical strength. Al-Mg-Si-based alloy coated steel wire free of slag is obtained.

[0025]

[Table 1]

(Example 2) A containing 6% by mass of Mg and Si, respectively, with the balance being Al and unavoidable impurities
The l-Mg-Si alloy was coated in the same manner as in Example 1 and drawn to obtain an Al-Mg-Si alloy coated steel wire having a wire diameter of 5 mm. On the other hand, the organic synthetic resin paint was prepared as follows. First, 5% by mass of fumed silica as an extender was mixed with a bifunctional epoxy resin having an average molecular weight of 380 and an epoxy equivalent of 190, and diluted to 50% with toluene. Thereto, bis-aminopropyl-tetraoxa-spiro-undecane was added as a curing agent so that the weight ratio with the epoxy resin became 2.8 to 3.0: 1.

In the organic synthetic resin paint, the above-mentioned Al-
After immersing the Mg-Si alloy coated steel wire, the steel wire is
Excess paint was removed by passing through a circular hole having a diameter of about 5 mm cut through a rubber plate. The coated steel wire thus coated was kept in a drying oven at 230 ° C. for an arbitrary time. The thickness of the coating was about 10 μm. A sample having a length of 100 mm was cut out from the coated steel wire thus produced, and a flaw having a length of 50 mm reaching the steel surface was artificially provided using a cutter knife. The cut surfaces at both ends of this sample were sealed with a silicone sealant. Using this sample, a salt spray test and a hot water immersion test at 40 ° C. were performed for 2000 times.
After a period of time, the maximum peeling width of the coating film from the flaw was measured.

As a result, when the degree of cure of the coating film was 80% or more, it was 1 mm or less in the salt spray test, and almost no peeling was observed and no red rust was observed in the hot water immersion test. On the other hand, if the degree of cure of the coating film is less than 80%,
In the salt spray test, peeling occurred almost all over, and spot-like red rust was slightly observed. Peeling width is 1 even in hot water immersion test
mm. From these, Al-Mg-S
In the case where a thermosetting organic synthetic coating film is provided on the i-based alloy coating layer, good anticorrosion performance is exhibited when the degree of curing of the coating film is 80% or more.

[0029]

By using the Al--Mg--Si alloy coated steel wire of the present invention, a wire having excellent corrosion resistance can be obtained. In particular, it has excellent corrosion resistance not only in saltwater environments but also in freshwater environments and has no decrease in mechanical strength, so it can be used for structures such as suspension bridge cable wires, and long-term durability can be expected .

Continuing from the front page (72) Inventor Shinichi Yamaguchi 1-1 Niwahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Yawata Works (72) Inventor Keita Suzumura 2-6 Otemachi, Chiyoda-ku, Tokyo 3 Nippon Steel Corporation F-term (reference) 4K044 AA02 AB04 BA01 BA10 BA19 BA21 BB01 BB03 BC02 CA02 CA53 CA62

Claims (5)

[Claims] 1. An Al—Mg—Si alloy coated steel wire containing 3 to 9% by mass of Mg and 2 to 10% by mass of Si and the balance of Al and unavoidable impurities. Al-Mg-S having excellent corrosion resistance, characterized in that the coating layer contains plate-like particles of Mg ₂ Si phase.
i-based alloy coated steel wire. 2. The Al—Mg—Si alloy coated steel wire having excellent corrosion resistance according to claim 1, wherein the average value of the maximum diameter of the plate-like particles of the Mg ₂ Si phase is 20 μm or less. 3. An Al-Mg-Si based alloy coating layer,
It consists of a baking type composition and has a degree of cure of 80 after baking.
% Or more, wherein the coating has an organic synthetic resin coating layer of at least 10% by weight.
g-Si alloy coated steel wire. 4. The steel sheet according to claim 1, wherein the surface of the steel wire is coated with an Al—Mg—Si alloy coating layer simultaneously with the drawing by extrusion.
A method for producing a Mg-Si alloy coated steel wire. 5. The method according to claim 4, wherein all of the steps are performed at 500 ° C. or lower.
Production method of system alloy coated steel wire.