KR20160078670A - HOT DIP Zn ALLOY PLATED STEEL WIRE HAVING EXCELLENT ANTI-CORROSION AND METHOD FOR MANUFACTURING THE STEEL WIRE USING THE SAME - Google Patents

Abstract

A hot dip zinc alloy plated steel wire having excellent corrosion resistance according to an embodiment of the present invention includes a matrix steel wire and a hot dip zinc alloy plated layer. A composition of the hot dip zinc alloy plated layer includes aluminum (Al): 0.5-15 wt%, magnesium (Mg): 0.5-3 wt%, the remaining zinc (Zn) and inevitable impurities. The hot dip zinc alloy plated layer has a metal structure wherein a Zn single phase structure, a Zn/MgZn_2 binary process structure, an MgZn_2 single phase structure and a Zn/Al/MgZn_2 triple process structure are mixed. An area ratio of the Zn/MgZn_2 binary process structure and the MgZn_2 single phase structure observed at a cross section in a linear particle size direction of the hot dip zinc alloy plated layer may be 50% or more.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot dip galvanized steel wire having excellent corrosion resistance,

The present disclosure relates to a hot-dip galvanized steel wire having excellent corrosion resistance and a method of manufacturing the same.

In general, Zn plating is performed for a steel wire requiring corrosion resistance. However, as the use environment of the steel wire becomes severe, development of a wire having high corrosion resistance is required. Also, the necessity of high corrosion resistant steel wire for the improvement of the corrosion resistance and the service life according to the high strength of the steel wire is steadily increasing.

Although plating of steel wire has improved corrosion resistance compared to Zn plating material by using Zn-Al plating method, it is required to develop a plating wire of higher corrosion resistance as the number of customers demanding high corrosion resistance is increased.

In recent years, Al and Mg have been added to a Zn plating bath as a zinc alloy plating material to secure a manufacturing technique of a coated steel sheet for improving the corrosion resistance of a coated steel sheet.

However, the Zn-Al Mg based hot-dip galvanizing technique was not applied to steel wire plating.

Since the volume of the steel wire is very small as compared with the steel sheet, the steel wire plating has a different plating structure depending on the pre-plating pretreatment, the composition of the plating bath, and the cooling rate.

In particular, the composition of the plating bath and the cooling condition have a great influence on the composition ratio of the intermetallic compound and the area fraction of the Mg alloy in the plated layer plated on the steel wire. The metal structure and the area fraction of the plating layer greatly affect the characteristics of the plated steel wire.

Therefore, there is a need for a technique for securing high corrosion resistance of a plated steel wire by controlling the element content of the Zn-Al Mg based hot dip galvanized layer.

The following Patent Document 1 relates to a hot-dip galvanized steel wire and a manufacturing method thereof.

Japanese Laid-Open Patent No. 2001-107213

An embodiment of the present disclosure is to provide a hot-dip galvanized steel wire having excellent corrosion resistance and a method of manufacturing the same.

A hot dip galvanized steel wire having excellent corrosion resistance according to an embodiment of the present disclosure includes a base steel wire and a hot-dip galvanizing layer, and the composition of the hot-dip galvanized layer is 0.5 to 15% by weight of aluminum (Al) ): 0.5 to 3% by weight, the balance zinc (Zn) and other including unavoidable impurities, and the molten zinc alloy plating layer is Zn phase, Zn / MgZn ₂ 2 won process organization, MgZn ₂ phase organization and Zn / Al / MgZn ₂ 3 won process organization having the mixed metal structure, the molten zinc alloy plating layer has an area fraction of the line diameter Zn / MgZn _{2 2} won process organization and MgZn ₂ phase tissue observed in the cross section of the number is more than 50%.

A method of manufacturing a hot dip galvanized steel wire having excellent corrosion resistance according to an embodiment of the present disclosure includes the steps of: 0.5 to 15% by weight of aluminum (Al), 0.5 to 3% by weight of magnesium (Mg) Preparing a molten zinc alloy plating bath containing impurities; Immersing the ground steel wire in the molten zinc alloy plating bath and performing plating to produce a plated steel wire; And gas wiping and cooling the plated steel wire, wherein the cooling is performed at a cooling rate of 3 to 10 DEG C / sec.

According to one embodiment of the present disclosure, it is possible to control the content of the metal structure through adjustment of the range of the component content, and to provide a hot-dip galvanized coated steel wire excellent in corrosion resistance and a method of manufacturing the same.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an electron microscope photograph showing a metal structure of a plating layer according to an embodiment of the present disclosure; FIG.

Preferred embodiments of the present disclosure will now be described with reference to the accompanying drawings.

However, the embodiments of the present disclosure are provided to more fully describe the present disclosure to those skilled in the art.

The embodiments of the present disclosure can be modified into various other forms, and the scope of the present disclosure is not limited to the embodiments described below.

In addition, to include an element throughout the specification does not exclude other elements unless specifically stated otherwise, but may include other elements.

Hereinafter, the molten zinc alloy plated steel wire excellent in corrosion resistance according to the present disclosure will be described in detail.

A hot dip galvanized steel wire having excellent corrosion resistance in one embodiment of the present disclosure includes a base steel wire and a hot-dip galvanizing layer, and the composition of the hot-dip galvanizing layer is 0.5 to 15% by weight of aluminum (Al) Wherein the molten zinc alloy plating layer comprises a Zn single phase, a Zn / MgZn ₂ binary raw structure, a MgZn ₂ single phase structure, and a Zn / Al / MgZn ₂ 3: 0.5 to 3 wt.%, The balance zinc and other inevitable impurities. having a source process tissue are mixed with the metal structure, and the Zn / MgZn _2, MgZn 2 circle process organization and area fraction of the _second phase observed in the tissue-ray particle diameter of cross section of the molten zinc alloy plating characterized in that 50% or more.

Hereinafter, an alloy element of the plating layer of the present disclosure will be described.

magnesium( Mg ): 0.5 to 3 wt%

The Mg is an element that plays a major role every week to improve the corrosion resistance of the plating layer.

The Mg can be inhibited from growing zinc oxide-based corrosion products which are contained in the plating layer and which are less effective in improving the corrosion resistance in a severe corrosive environment, and can be stabilized on the surface of the plating layer with a zinc hydroxide- .

The content of Mg may be 0.5 wt% to 3 wt%.

If the content of Mg is less than 0.5% by weight, the amount of the Zn-Mg-based compound to be formed is small and the effect of improving the corrosion resistance may be very small.

If the content of Mg exceeds 3 wt%, the effect of improving the corrosion resistance is saturated and the oxidative dross of Mg rapidly increases on the bath surface of the plating bath, so that the plating workability can be greatly reduced.

aluminum( Al ): 0.5 to 15 wt%

The Al is an element added to reduce the dross generated by the oxidation reaction of Mg in the molten zinc alloy plating bath to which Mg is added.

The Al can be combined with zinc (Zn) and magnesium (Mg) to improve the corrosion resistance of the coated steel wire.

The content of Al may be 0.5 wt% to 15 wt%.

If the content of Al is less than 0.5% by weight, the effect of preventing the oxidation of the surface layer of the plating bath by Mg addition may be insufficient and the effect of improving the corrosion resistance may be insufficient.

If the content of Al exceeds 15 wt%, the amount of Fe elution of the steel wire immersed in the plating bath sharply increases, so that Fe alloy type dross can be formed, and a Zn / Al binary vacancy phase is formed in the plating layer, It is possible to reduce the effect of improving the corrosion resistance of Mg to the part and the coated part.

The plating layer of the hot-dip galvanized steel wire having excellent corrosion resistance in one embodiment of the present disclosure may further contain 0.0001 to 1% by weight in total of at least one element selected from the group consisting of Ru, Rh and Pd.

Element of the Ru, Rh, and Pd is the melting point (Tm) of each of 2334 ℃, 1985 ℃ and very high as 1554.9 ℃, the first coagulation than cooling when Zn, Al and Mg Zn-MgZn _{2 2} precipitation of the original process organization and It can play a role of inducing coarse conversation.

The steel wire of the present disclosure includes the remainder zinc (Zn) and other unavoidable impurities.

Impurities that are not intended from the raw material or the surrounding environment can be inevitably incorporated in the ordinary steel manufacturing process and can not be excluded.

All of these impurities are not specifically mentioned in the present disclosure, as they are known to anyone skilled in the art of steel making.

The molten zinc alloy plating layer has a metal structure in which a Zn single phase structure, a Zn / MgZn ₂ binary source structure, a MgZn ₂ single phase structure and a Zn / Al / MgZn ₂ 3 source process structure are mixed.

When the end face of the plating material is exposed to the corrosive environment, Mg ^{2 +} cations are eluted from the coarse Zn / MgZn ₂ binary structure or the MgZn ₂ single phase structure at the end face of the plating layer.

The eluted Mg ^{2 +} cations and mobile parts of the cathode (Cathode) region of the plating layer cross-section, to form a dense and stable corrosion product and improves the corrosion resistance of the plated steel wire cross-section portion.

According to this disclosure, it is preferable that the Zn / MgZn _2, MgZn 2 won process organization and area fraction of the _second phase observed in the tissue-ray particle diameter of cross section of the molten zinc alloy plating layer to secure 50% or more.

If the area fraction of the Zn / MgZn ₂ binary structure and the MgZn ₂ single phase structure is less than 50%, the Mg ²⁺ cation elution amount is not sufficient and the effect due to the formation of a stable corrosion product may be reduced, The effect of improving the corrosion resistance of the steel wire may be insufficient.

The formation of such a metal structure in the plating layer can be greatly affected not only by the composition of the plating bath but also by the cooling rate in the cooling step of the coated steel wire.

The molten zinc alloy plating layer may have a plating amount of 10 to 600 g / m ² .

If the plating amount of the plating layer is less than 10 g / m < ² >, it may be difficult to expect a corrosion resistance characteristic.

If the plating amount of the plating layer exceeds 600 g / m ² , the economical efficiency of the plated steel wire can be reduced.

Hereinafter, a method for manufacturing a hot-dip galvanized steel wire having excellent corrosion resistance according to the present disclosure will be described in detail.

A method of manufacturing a hot dip galvanized steel wire having excellent corrosion resistance according to an embodiment of the present disclosure includes the steps of: 0.5 to 15% by weight of aluminum (Al), 0.5 to 3% by weight of magnesium (Mg) Preparing a molten zinc alloy plating bath containing impurities; Immersing the ground steel wire in the molten zinc alloy plating bath and performing plating to produce a plated steel wire; And gas wiping and cooling the plated steel wire, wherein the cooling is characterized by cooling at a rate of 3 to 10 DEG C / sec.

When plating is carried out by immersing the base steel wire in a molten zinc alloy plating bath, the plating bath temperature at the time of the ordinary hot-dip galvanizing can be applied, preferably at a plating bath temperature ranging from a melting point to 450 ° C Can be performed.

Generally, if the content of Al in the components of the plating bath is increased, the melting point of the plating bath must be increased to increase the temperature of the plating bath.

However, if the temperature of the plating bath is increased, the internal equipment of the base material steel wire and the plating bath may be eroded, shortening the life of the equipment, increasing the Fe alloy dross in the plating bath, Lt; / RTI >

In the present invention, since the content of Al is controlled to be relatively low as 0.5 to 15 wt%, it is not necessary to set the temperature of the plating bath to be high, and it is preferable to apply the ordinary plating bath temperature.

After completion of the plating, the plating line can be controlled by applying a gas wipe to the steel wire having the plating layer formed thereon.

The gas wiping is for adjusting the plating adhesion amount, and the method is not particularly limited.

At this time, air or nitrogen (N ₂ ) may be used as the gas to be used, and it may be preferable to use nitrogen.

When air is used, Mg oxidation may occur preferentially on the surface of the plating layer, which may cause surface defects of the plating layer.

After the plating adhesion amount of the plating layer is adjusted by the treatment of the gas wiping, the coating is cooled at a temperature of 320 to 400 ° C at a rate of 3 to 10 ° C / sec.

Unlike a conventional hot-dip galvanizing layer in which the solidification reaction is terminated at 420 ° C, solidification of Zn-Al-Mg ternary alloy plating layer starts at a low temperature of 400 ° C or lower and solidification is terminated at 320 ° C.

Therefore, when the cooling rate in the temperature range from 400 deg. C at which solidification of the plating layer starts to 320 deg. C at which solidification ends is different, a different metal structure can be obtained even with a plated steel wire having the same composition and composition ratio.

If the cooling rate is less than 3 占 폚 / sec, the area fraction of the Zn single phase structure becomes large and corrosion resistance may be deteriorated.

If the cooling rate exceeds 10 ° C / sec, the Zn single phase structure is coarsened, and the exposure amount on the surface portion is drastically increased, and the surface portion corrosion resistance may be lowered.

As the cooling method during cooling, a conventional cooling method that can cool the plating layer can be used. For example, an air jet cooler, N ₂ wiping, water fog, Cooling can be performed.

In order to secure a metal structure containing Zn single phase structure, Zn / MgZn ₂ binary structure, MgZn ₂ single phase structure and Zn / Al / MgZn ₂ three-element process structure in the plating layer, Control is very important.

Hereinafter, the present disclosure will be described in more detail by way of examples. However, the following embodiments are only examples for explaining the present disclosure in detail, and do not limit the scope of the present disclosure.

(Example 1)

In order to observe the microstructure of the plating layer according to the plating bath component, a steel wire having a diameter of 4 mm was prepared as a base steel wire with a plating bath test piece, the base steel wire was immersed in acetone and ultrasonically cleaned to remove foreign substances such as rolling oil Respectively.

Before plating, all specimens were subjected to a reducing atmosphere heat treatment at 750 ° C to ensure the mechanical properties of the steel wire at the general hot dip galvanizing site.

The plating conditions after the heat treatment were the same in all plating baths except for the plating bath temperature, and the plating bath temperature was adjusted to 450 ° C in consideration of the increase of the melting point according to the Al content.

After completion of the plating, the plating adhesion amount was adjusted to 250 g / m ² using N ₂ gas wiping, and the coating was cooled at the same rate of 8 ° C / sec in the temperature range of 320 to 400 ° C.

Thereafter, the microstructure of the plated layer was observed and analyzed, and the results are shown in Table 1 below. The microstructure of the plated layer was observed by FE-SEM (SUPRA-55VP, ZEISS) and FE-TEM (JEM-2100F, JEOL) and the alloy phase fraction of the intermetallic compound in the plated layer was analyzed using analySIS Respectively.

division Composition of plating layer
(weight%) Area fraction (%) of microstructure of plating layer Al Mg Zn Zn /
MgZn ₂ Zn / Al / MgZn ₂ MgZn ₂ Zn /
25% Al Zn /
45% Al Zn /
MgZn ₂
+ MgZn ₂ Comparative Example 1 0.2 0 100 0 0 0 0 0 0 Comparative Example 2 2 One 73 11 13 0 3 0 11 Comparative Example 3 3.2 3.5 12 32 56 0 0 0 32 Comparative Example 4 15 3.2 6 0 9 15 48 22 15 Comparative Example 5 17 0 0 0 0 0 12 88 0 Example 1 1.5 2.7 20 37 28 15 0 0 52 Example 2 2 2.3 32 28 15 25 0 0 53 Example 3 3 1.5 37 22 2 36 3 0 58 Example 4 5 2.8 11 46 25 12 6 0 58 Example 5 12 2.9 8 53 18 16 5 0 69 Example 6 14 2.8 7 29 10 23 21 10 52

As shown in Table 1, Examples 1 to 6 all Zn / MgZn observed in the line diameter cross section of the plating layer ₂₂ won process organization and MgZn ₂ phase organization which satisfies the composition range and the composition ratio of Al and Mg in the disclosure Was 50% or more.

1 is an electron micrograph of a plated layer of Example 1. Fig.

When Fig. 1, see Example 1 was confirmed to have a roughness of Zn / MgZn _{2 2} won process organization.

In Comparative Examples 1 to 5, which do not satisfy the composition ranges or the composition ratios of Al and Mg of the present disclosure, all of the Zn / MgZn ₂ binary structure and the MgZn ₂ single phase structure in the cross section of the plating layer in the line- .

(Example 2)

In order to observe the microstructure of the plating layer according to the cooling rate in the cooling step of the coated steel wire in the production of the coated steel wire, the cold-rolled steel wire of 3 mm diameter was immersed in acetone and ultrasonically cleaned to remove foreign substances and oil And the sample was prepared.

The hot dip test for this example was annealed and plated using a hot dip simulator.

The annealing atmosphere gas in the annealing condition was a reducing atmosphere composed of 10% of hydrogen and 90% of nitrogen, and the annealing heat treatment cycle was heat-treated at 700 to 820 캜 in accordance with required mechanical properties.

The specimens heat-treated in the reducing atmosphere were immersed for about 5 seconds in a molten alloy containing 2.3 wt% of Al and 3 wt% of Mg, satisfying the composition and composition ratios of Al and Mg of the present invention, And the adhesion amount of the alloy plating layer was adjusted to 250 g / m ² .

To observe the cooling rate and temperature change of the steel wire, a thermocouple was contacted to the steel wire to monitor the micro temperature change of the steel wire during the cooling process.

The moving speed of the steel wire was controlled at 100 to 500 mm / s under the same cooling gas flow rate in order to observe the variation of the coating layer characteristics according to the cooling rate of the test piece.

In order to control the formation of Zn single phase structure having the highest solidification completion temperature among the tissues formed by the addition of Al and Mg, the cooling rate from the plating layer temperature of 400 ° C to the solidification end point of 320 ° C was finely monitored.

Thereafter, the microstructure of the plated layer was observed and analyzed, and the results are shown in Table 2 below.

division Cooling rate (° C / sec) Zn / MgZn ₂ + MgZn ₂
Cross-sectional area fraction (%) Comparative Example 1 2.5 29.3 Comparative Example 2 12.5 40.7 Example 1 3.7 80.2 Example 2 9.4 69.8

Embodiment satisfying the cooling rate range of the disclosure Examples 1 and 2 were found to be Zn / MgZn _2, MgZn 2 won process organization and area fraction of the _second phase tissue it is 50% or more is observed in the particle size of the line cross section of the plating layer.

In Comparative Example 1 in which the cooling rate was less than 3 ° C / sec, the area fraction of the Zn / MgZn ₂ binary structure and the MgZn ₂ single phase structure was decreased due to the coagulation of Zn single phase structure from the low- And less than 50%.

In Comparative Example 2 in which the cooling rate exceeds 10 ° C / sec, the Zn single phase structure coagulates and coarsens from the surface portion of the plating layer together with the volume increase and miniaturization of the Zn / Al / MgZn ₂ three- , Zn / MgZn ₂ 2 original structure and MgZn ₂ single phase structure were less than 50%.

(Example 3)

In order to evaluate the corrosion resistance of the steel wire according to the area fraction of the Zn / MgZn ₂ binary structure and the MgZn ₂ single phase structure observed in the cross-section of the line width of the zinc-zinc alloy plating layer, the specimen having the composition and microstructure shown in Table 1 , And the results are shown in Table 2 below. Specific test methods and evaluation criteria are as follows.

Corrosion resistance of the steel wire was evaluated by performing a corrosion promotion test with a salt spray test (salt spray standard test according to KS-C-0223) at a plating amount of 10 to 600 g / m ² for each plating material, The elapsed time was measured until it reached 5%.

◎: When exceeding 1500 hours

○: 500 to 1500 hours.

?: 200 to 500 hours.

X: less than 200 hours.

division
Composition of plating layer Area fraction of Zn / MgZn ₂ + MgZn ₂ (%)
Plated
Corrosion resistance Al Mg Comparative Example 1 0.2 0 0 × Comparative Example 2 2 One 11 △ Comparative Example 3 3.2 3.5 32 △ Comparative Example 4 15 3.2 15 ○ Comparative Example 5 17 0 0 ○ Example 1 1.5 2.7 52 ◎ Example 2 2 2.3 53 ◎ Example 3 3 1.5 58 ◎ Example 4 5 2.8 58 ◎ Example 5 12 2.9 69 ◎ Example 6 14 2.8 52 ◎

As shown in Table 3, all of the plating materials containing Mg and Al (Examples 1 to 6 and Comparative Examples 2 to 5), in relation to the corrosion resistance of the coated steel wire, Which is about 4 ~ 10 times higher than that of the conventional one.

The above Examples 1 to 6 satisfy the content ranges of Al and Mg of the present disclosure and satisfy the requirements that the area fraction of the Zn / MgZn ₂ binary structure and the MgZn ₂ single phase structure satisfy 50% or more, It was confirmed that the corrosion resistance was excellent.

It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure, Should be interpreted on the basis of.

Claims (8)

A base steel wire, and a hot-dip zinc alloy plating layer,
The composition of the molten zinc alloy plating layer includes 0.5 to 15 wt% of aluminum (Al), 0.5 to 3 wt% of magnesium (Mg), zinc (Zn) and other unavoidable impurities,
The molten zinc alloy plating layer has a metal structure in which a Zn single phase, a Zn / MgZn ₂ binary process structure, a MgZn ₂ single phase structure, and a Zn / Al / MgZn ₂ three-
A hot-dip zinc-plated galvanized steel wire having excellent corrosion resistance with an area fraction of Zn / MgZn ₂ binary structure and MgZn ₂ single phase structure observed in the cross-section of the molten zinc alloy plating layer in the line diameter direction of 50% or more.
The method according to claim 1,
Wherein the molten zinc alloy plating layer further comprises 0.0001 to 1 wt% of at least one element selected from the group consisting of Ru, Rh and Pd in total.
The method according to claim 1,
Wherein the hot-dip galvanized steel sheet has a plating amount of 10 to 600 g / m ² and is excellent in corrosion resistance.
Preparing a molten zinc alloy plating bath comprising 0.5 to 15 wt% of aluminum (Al), 0.5 to 3 wt% of magnesium (Mg), zinc (Zn) and other inevitable impurities;
Immersing the ground steel wire in the molten zinc alloy plating bath and performing plating to produce a plated steel wire; And
Gas wiping and cooling the plated steel wire,
Wherein the cooling is performed at a rate of 3 to 10 占 폚 / sec.
5. The method of claim 4,
Wherein the composition of the molten zinc alloy plating bath comprises 2.0 to 3.0% by weight of aluminum (Al), in terms of% by weight, of the molten zinc alloy plated steel wire.
5. The method of claim 4,
Wherein the plating bath further comprises 0.0001 to 1% by weight of at least one element selected from the group consisting of Ru, Rh and Pd in total.
5. The method of claim 4,
Wherein the bath temperature of the molten zinc alloy plating bath is higher than or equal to the melting point of 450 占 폚 or less.
5. The method of claim 4,
Wherein the gas used in the gas wiping is nitrogen (N ₂ ).

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