JPH116047A - Base metal for hot dip zinc alloy coating bath, hot dip coating bath, hot dip zinc alloy coated steel and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high temp. corrosion resistant hot dip zinc alloy coated steel by applying hot dip galvanizing on a steel surface as a substrate plating and forming a hot dip zinc alloy coated layer thereon. SOLUTION: After hot dip galvanizing is applied on a steel surface as a substrate plating, hot dip zinc alloy coating is applied on a surface of a substrate plating layer with using a hot dip zinc alloy coating bath, which has a composition consisting of, by weight, 3-30% Al, 0.7-3.5% in total at least one kind among Cu, Ag, Au and the balance Zn with inevitable impurities. This two step coating has corrosion resistance by a salt spray test equivalent to hot dip aluminizing, crack is not generated at a high temp. corrosion resistance test and is produced at a cost lower than a hot dip aluminized product, a hot dip galvanized-hot dip zinc alloy coated steel having excellent corrosion resistance in a high temp. atmosphere is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a specific composition used in a two-stage hot-dip galvanizing method in which a hot-dip galvanizing is applied to the surface of a steel material to form a base plating layer, and then a hot-dip zinc alloy plating is performed to form a surface plating layer. Hot-dip zinc alloy plating bath, and a metal for the hot-dip zinc alloy plating bath of a specific composition for use in preparing the hot-dip zinc alloy plating bath, furthermore, a high-temperature corrosion-resistant hot-dip zinc alloy-plated steel material and a method for producing the same, The present invention relates to a high-temperature corrosion-resistant hot-dip galvanized steel material in which a base plating layer is provided on a surface of a steel material by hot-dip galvanizing and a surface plating layer is provided on the base plating layer by hot-dip zinc alloy plating, and a method for producing the same. .

[0002]

2. Description of the Related Art Conventionally, as a method of coating the surface of a steel material, for example, the surface of an iron or steel plate, wire, profile, bar, band, pipe, or the like with another metal having good corrosion resistance, for example, zinc is used. A method is used in which a hot-dip plating bath is prepared using a base metal, and a steel material is immersed in the bath to make zinc adhere to the surface of the steel material. However, in order to further improve the corrosion resistance of the plating film rather than hot dip galvanizing, in recent years, instead of pure zinc, zinc-aluminum alloy or aluminum has been hot-dip, or zinc Aluminum alloy is hot-dip plated. Such a technique is disclosed in JP-B-63-50419.
JP, JP-B-63-50421, JP-B-4-1
No. 9299, and the like.

[0003]

The hot-dip galvanized aluminum product developed according to the requirement of high corrosion resistance for steel materials has a higher corrosion resistance than the hot-dip galvanized product in the salt spray test specified in JIS Z 2371. As shown, in the high-temperature corrosion resistance test that has been conducted recently, the value is equal to or less than that of the hot-dip galvanized product, and may be extremely poor. As such a high-temperature corrosion resistance test, when a hot-dip galvanized product and a hot-dip zinc-aluminum product of a steel material are immersed in, for example, 5% salt water at 75 ° C. and examined for high-temperature corrosion resistance, the zinc-aluminum product is plated. Cracks occur at the interface between the coating and the steel material, and a phenomenon in which the plated coating peels appears, and the high-temperature corrosion resistance is remarkably inferior to that of the galvanized product. In addition, the hot-dip aluminum plating method has a problem in that the melting point of aluminum is high, and thus the workability and the life of the hot-dip plating bath are different, and further, the aluminum plating layer does not have a sacrificial corrosion resistance to iron.

[0004] An object of the present invention is to provide a hot-dip galvanizing method for forming a base plating layer on a steel material surface and then forming a surface plating layer by forming a hot-dip zinc alloy coating on the surface of the steel material. Corrosion resistance in the test is molten zinc
A hot-dip galvanized alloy plating bath that is equivalent to an aluminum-plated product and is capable of producing a high-temperature corrosion-resistant film-formed zinc-alloy-coated product that does not crack even in the high-temperature corrosion-resistance test described above at a lower cost than the above-described hot-dip aluminum-plated product, and It is an object of the present invention to provide a metal for a hot-dip zinc alloy plating bath for use in preparing such a hot-dip zinc alloy plating bath.

Another object of the present invention is to provide a steel material, a base plating layer provided on the surface of the steel material by hot-dip galvanizing, and a surface plating layer provided on the base plating layer by hot-dip zinc alloy plating. The corrosion resistance in the above salt spray test is equivalent to that of hot-dip zinc-aluminum-plated steel, and cracks do not occur in the above-mentioned high-temperature corrosion resistance test, and it is manufactured at a lower cost than the above-mentioned hot-dip aluminum-plated steel. It is an object of the present invention to provide a high-temperature corrosion-resistant hot-dip galvanized steel material and a method for producing the same.

[0006]

As a result of various studies to achieve the above object, the present inventors conducted hot dip galvanizing on the surface of a steel material to form a base plating layer, and then performed hot dip zinc alloy plating. A hot-dip galvanizing method using a two-stage hot-dip galvanizing method to form a surface plating layer with zinc, aluminum, and a specific composition containing at least one of copper, silver, and gold as a hot-dip zinc alloy plating bath used in the second stage The present inventors have found that a high-temperature corrosion-resistant coating is formed on the surface of a steel material by using a zinc alloy plating bath, and completed the present invention.

That is, the base metal for a hot-dip zinc alloy plating bath according to the present invention is a two-stage hot-dip galvanizing method in which a hot-dip galvanizing is performed on the surface of a steel material to form a base plating layer and then a hot-dip zinc alloy plating is performed to form a surface plating layer. Aluminum for use in preparing a hot-dip zinc alloy plating bath in the plating method is 3 to 3
0% by weight, at least one of copper, silver and gold is contained in a total amount of 0.7 to 3.5% by weight, with the balance being zinc and unavoidable impurities.

[0008] Further, the plating bath for hot-dip zinc alloy plating of the present invention is a two-step hot-dip galvanizing method for forming a surface plating layer by performing hot-dip galvanizing on the surface of a steel material to form a base plating layer and then performing hot-dip zinc alloy plating. Aluminum for use as a hot-dip zinc alloy plating bath in the plating method
0% by weight, at least one of copper, silver and gold is contained in a total amount of 0.7 to 3.5% by weight, with the balance being zinc and unavoidable impurities.

Furthermore, the high-temperature corrosion-resistant hot-dip zinc alloy-plated steel material of the present invention comprises a steel material, a base plating layer provided on the surface of the steel material by hot-dip galvanizing, and a hot-dip zinc alloy plating on the base plating layer. And a surface plating layer provided by
Hot-dip galvanized using a hot-dip bath containing at least 30% by weight and at least one of copper, silver and gold in a total amount of 0.7-3.5% by weight, with the balance consisting of zinc and unavoidable impurities. Characterized in that:

A high-temperature corrosion-resistant hot-dip galvanized steel material according to the present invention comprises a steel material, a base plating layer provided on the surface of the steel material by hot-dip galvanizing, and a hot-dip zinc alloy plating on the base plating layer. And a surface plating layer provided by
It is characterized in that it is an alloy layer containing up to 30% by weight, at least one of copper, silver and gold in a total amount of 0.7 to 3.5% by weight, with the balance being zinc and unavoidable impurities.

Further, the method for producing a high-temperature corrosion-resistant zinc-alloy-plated steel material according to the present invention comprises forming a base plating layer by hot-dip galvanizing the surface of the steel material, and then forming aluminum on the base plating layer. 3 to 30% by weight and copper,
Forming a surface plating layer by performing hot-dip zinc alloy plating using a hot-dip zinc alloy plating bath containing at least one of silver and gold in a total amount of 0.7 to 3.5% by weight and a balance of zinc and unavoidable impurities It is characterized by doing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, iron or steel plates, wires, profiles, bars, strips, pipes, etc. are used as steel materials for obtaining hot-dip galvanized hot-dip galvanized steel. For example, an iron plate, a steel plate, an iron wire, a steel wire, a shaped steel, a bar, a steel strip, a steel pipe, and the like can be used.

The aluminum in the surface plating layer of the high-temperature corrosion-resistant hot-dip galvanized steel material of the present invention obtained by using the base metal and the plating bath of the present invention has an effect of improving the corrosion resistance of the hot-dip galvanized steel material. However, when the aluminum content is less than 3% by weight, the effect of improving the corrosion resistance is insufficient, so that 3% by weight or more of aluminum is added. Corrosion resistance improves with an increase in the amount of aluminum added, but the temperature of the plating bath also needs to be kept high accordingly. When the aluminum content exceeds 30% by weight, it is necessary to maintain the temperature of the plating bath at a considerably high temperature. Therefore, the Fe-Al-Zn compound, which is a characteristic of zinc-aluminum plating of steel, grows abnormally at the interface between the coating and the steel. Iron is eluted therein to generate an Fe-Al-Zn compound, which floats in the plating bath, which also causes poor appearance of the plated steel material. In addition, there is a problem that the concentration of aluminum in the plating bath is reduced due to the generation of such a compound. Therefore, in the hot-dip galvanized alloy layer of the hot-dip corrosion-resistant hot-dip galvanized steel material of the present invention, the aluminum content is limited to 3 to 30% by weight.

The cause of the cracking of the hot-dip zinc-aluminum-plated steel material at the interface between the plating film and the steel material in a high-temperature corrosive environment is that the compound growing at the interface between the coating film and the steel material has a higher potential than the surroundings. It is thought to be due to the fact that it is in a state of low base. In order to suppress this phenomenon, a potential noble metal is added to the plating film /
The compound growing at the interface of the steel material may be shifted in potential to a noble side to make the interface potential flat. Similar solutions can be used for such phenomena other than plating.

The copper, silver or gold in the hot-dip galvanized steel layer of the hot-dip hot-dip galvanized steel sheet of the present invention is as follows:
An effect of flattening the interfacial potential by making the compound growing on the interface between the plating film of the hot-dip zinc alloy-plated steel material obtained as described above and the steel material interface noble is obtained. However, if the total content of at least one of copper, silver and gold is less than 0.7% by weight, the effect of flattening the interfacial potential is insufficient, so that at least one of copper, silver and gold is attained. Is added in a total amount of 0.7% by weight or more. The effect of flattening the interfacial potential improves with an increase in the amount of copper, silver or gold added. However, when the total amount of at least one of copper, silver and gold exceeds 3.5% by weight, the plating film becomes hard. Become
Cracks and the like may occur in the plating film in post-processing after plating. Therefore, the content of at least one of copper, silver and gold in the hot-dip galvanized steel layer of the hot-dip galvanized steel material of the present invention is limited to a total of 0.7 to 3.5% by weight.

In the method for producing a hot-dip galvanized hot-dip galvanized steel material according to the present invention, the surface of the steel material is hot-dip galvanized to form a base plating layer, and then the hot-dip zinc alloy plating is performed on the base plating layer. Prior to such hot-dip galvanizing, the surface of the steel material is degreased, pickled, and washed prior to hot-dip galvanizing.
Flux and dry. Then, it is immersed in a hot-dip galvanizing bath according to a normal hot-dip galvanizing method, pulled up to form a galvanized coating, and then dipped in a hot-dip zinc alloy plating bath and pulled up to form a zinc alloy plated coating.

As described above, the two-step hot-dip galvanizing method in which a hot-dip galvanizing is performed on the surface of a steel material to form a base plating layer and then a hot-dip zinc alloy plating is performed to form a surface plating layer is used. The plating bath specified in the present invention as a hot-dip zinc alloy plating bath for use in the eyes, that is, containing 3 to 30% by weight of aluminum and at least one of copper, silver and gold.
By using a hot-dip zinc alloy plating bath containing a total of 0.7 to 3.5% by weight of seeds and a balance of zinc and unavoidable impurities, a high-temperature corrosion-resistant coating can be formed on the surface of a steel material. That is, it is possible to manufacture a steel material excellent in high-temperature corrosion resistance by hot-dip zinc alloy plating, and thus to manufacture a high-temperature corrosion-resistant steel material at a lower cost than a high-temperature corrosion-resistant steel material conventionally manufactured by performing hot-dip aluminum plating. And a cost reduction effect can be obtained.

In the hot-dip galvanized hot-dip galvanized steel material of the present invention, diffusion occurs between the molten metal and the underlying metal during the hot-dip plating of the underlying plating layer and the surface plating layer, and the interface between the molten metal and the underlying metal occurs. Causes alloying. Therefore, the respective compositions of the base plating layer and the surface plating layer do not always match the compositions of the respective hot-dip plating baths. The difference in their composition is the temperature of the hot-dip bath,
It depends on the time until cooling and solidification.

As described above, the high-temperature corrosion-resistant hot-dip zinc alloy-plated steel material of the present invention has the same corrosion resistance in the salt spray test as that of the hot-dip zinc-aluminum-plated product, and does not crack even in the high-temperature corrosion resistance test. Since it can be manufactured at a lower cost than the hot-dip aluminized product, it is useful not only as a steel material used in a high-temperature atmosphere, but also as a steel material used at room temperature.

[0020]

The present invention will be more specifically described below with reference to examples and comparative examples of the present invention. Examples 1 to 5 and Comparative Examples 1 to 5 As steel, length 100 mm, width 50 mm, thickness 3.2
mm of a general structural rolled steel sheet (SS41), this steel sheet was subjected to plating pretreatment under the following conditions. 1) Degreasing treatment Using a 20% by weight aqueous solution of sodium orthosilicate, 70%
After treating at 60 ° C. for 60 minutes, it was washed with water at room temperature. 2) Pickling treatment After treatment with 5% HCl at room temperature for 30 minutes, the substrate was washed with water. 3) Flux treatment A 30% by weight aqueous solution of a commercially available flux for Zn-Al plating (also useful for Zn plating) was immersed at 90 ° C for 1 minute, and then dried with hot air at 150 ° C for 3 minutes.

As the hot-dip plating bath, 99.
A hot dip galvanizing bath in which zinc ingot having a purity of 99% by weight or more is melted in a graphite crucible is used.
The composition shown in Table 1 below will be obtained using zinc ingot having a purity of not less than 10% by weight, aluminum ingot having a purity of not less than 99.9% by weight, and copper ingot having a purity of not less than 99.99% by weight. A hot-dip zinc alloy plating bath prepared by dissolving in a graphite crucible was used. Regarding the hot-dip plating conditions, the first stage was performed at a hot-dip bath temperature of 450 ° C. and an immersion time of 10 seconds, and the second stage was performed at a hot-dip bath temperature and an immersion time shown in Table 1. The lifting speed during plating is about 1.5 m / min.
Water cooling was performed 10 to 20 seconds after the lifting.

Examples 1 to 4 of hot-dip plating under the above conditions
5 and the corrosion resistance of each of the plated steel materials of Comparative Examples 1 to 5 were evaluated by the time of occurrence of red rust in accordance with the salt spray test specified in JIS Z 2371, and the high-temperature corrosion resistance was determined in 5% salt water at 75 ° C. Was evaluated by the presence or absence of cracks after immersion for 7 days (salt water immersion test). In addition, the presence or absence of an appearance defect was determined by an appearance inspection after hot-dip plating, and the workability was evaluated by performing a bending test on the plated steel material. The results were as shown in Table 1 below.

Examples 6 to 10 and Comparative Examples 6 to 10 Iron wires having a wire diameter of 3.55 mm (SWRM-6) were used as steel wires.
The steel wire was subjected to a plating pretreatment under the conditions described in Examples 1 to 5 and Comparative Examples 1 to 5. As the hot-dip plating bath, the first stage uses the same hot-dip bath as used in Example 1, and the second stage uses the same base metal used in Example 1 as the second-stage bath. A hot-dip galvanized alloy plating bath dissolved and prepared in a graphite crucible so as to have the composition shown in the table was used. Regarding the hot-dip plating conditions, the first stage was performed at a hot-dip bath temperature of 450 ° C. and an immersion time of 10 seconds, and the second stage was performed at a hot-dip bath temperature and an immersion time shown in Table 1. The lifting speed during plating was about 5 m / min, and water cooling was performed 10 to 20 seconds after the lifting.

Examples 6 to 6 of hot-dip plating under the above conditions
10 and the corrosion resistance of each of the plated steel wires of Comparative Examples 6 to 10 were evaluated by the time of occurrence of red rust in accordance with the salt spray test specified in JIS Z 2371, and the high temperature corrosion resistance was 5% salt water at 75 ° C. It was evaluated by the presence or absence of cracks after immersion for 7 days in water (salt water immersion test). Also,
The appearance was inspected after hot-dip plating to determine the presence or absence of appearance defects, and the self-diameter winding and bending test of the plated steel wire was performed to evaluate workability. The results were as shown in Table 2 below.

[0025]

[Table 1]

[0026]

[Table 2]

As is clear from the data in Tables 1 and 2, when the copper content is 0.0% by weight or 0.5% by weight, the effect of flattening the interface potential is insufficient. Therefore, when the copper content was 4.0% by weight, the plating film was hard and the bending workability was poor because the copper coating was hard. The effect obtained by is not achieved.

Further, the state of the cross section of the plated layer of each of the plated steel materials of Example 1, Comparative Example 1, Example 6, and Comparative Example 6 after the high-temperature corrosion resistance test was examined with SEM photographs.
(1200 times), FIG. 2 (800 times), FIG. 3 (1200 times)
Times) and FIG. 4 (800 times). SE of FIGS. 1 and 3 corresponding to Example 1 and Example 6, respectively.
No crack was observed in the M photograph, but Comparative Example 1
2 and 4 corresponding to Comparative Example 6 and Comparative Example 6, respectively.
In the photograph, cracks are clearly observed at the interface between the plating film and the steel material.

[0029]

As described above, hot-dip galvanizing is performed in a two-stage hot-dip galvanizing method in which a hot-dip galvanizing is performed on the surface of a steel material to form a base plating layer, and then a hot-dip zinc alloy plating is performed to form a surface plating layer. The high-temperature corrosion-resistant hot-dip zinc alloy-plated steel material of the present invention obtained by using the hot-dip zinc alloy plating bath of the present invention as an alloy plating bath has the same corrosion resistance in a salt spray test as a hot-dip zinc-aluminum-plated steel material, Cracks do not occur in the high-temperature corrosion resistance test, and it can be manufactured at a lower cost than the above-mentioned hot-dip aluminized steel material.

[Brief description of the drawings]

FIG. 1 is an SEM photograph showing a state of a cross section of a plated layer after a high temperature corrosion resistance test of a plated steel material of Example 1.

FIG. 2 is an SEM photograph showing a state of a section of a plated layer after a high temperature corrosion resistance test of a plated steel material of Comparative Example 1.

FIG. 3 is an SEM photograph showing a state of a cross section of a plated layer after a high-temperature corrosion resistance test of a plated steel wire of Example 6.

FIG. 4 is an SEM photograph showing a state of a cross section of a plated layer after a high temperature corrosion resistance test of a plated steel wire of Comparative Example 6.

Continuing from the front page (72) Inventor Kenji Ito 2-3-1-14 Nihonbashi Muromachi, Chuo-ku, Tokyo Inside Tokyo Seimitsu Co., Ltd. (72) Inventor Masaaki Tsuchiya 5707 Anakura, Kasumigaura-cho, Shinji-gun, Ibaraki Pref. Inside

Claims (6)

[Claims] 1. A hot-dip galvanizing method for preparing a hot-dip galvanizing bath in a two-step hot-dip galvanizing method in which a hot-dip galvanizing is performed on a surface of a steel material to form a base plating layer and then a hot-dip zinc alloy plating is performed to form a surface plating layer. Containing 3 to 30% by weight of aluminum and at least one of copper, silver and gold.
A metal for a galvanizing alloy plating bath, comprising 0.7 to 3.5% by weight of seeds in total, with the balance consisting of zinc and unavoidable impurities. 2. A hot-dip galvanizing method for a hot-dip galvanizing bath in a two-stage hot-dip galvanizing method in which a hot-dip galvanizing is performed on a surface of a steel material to form a base plating layer and then a hot-dip zinc alloy plating is performed to form a surface plating layer. Three aluminum
For hot-dip zinc alloy plating characterized by containing at least 30% by weight and at least one of copper, silver and gold in a total amount of 0.7-3.5% by weight, with the balance consisting of zinc and unavoidable impurities. Plating bath. 3. A steel sheet comprising: a steel material; a base plating layer provided on the surface of the steel material by hot-dip galvanizing; and a surface plating layer provided by hot-dip zinc alloy plating on the base plating layer. The plating layer is made of aluminum
30% by weight and at least one of copper, silver and gold in a total amount of 0.7 to 3.5% by weight, with the balance being hot-dipped using a hot-dip bath comprising zinc and unavoidable impurities High temperature corrosion resistant hot-dip galvanized alloy-plated steel. 4. A steel plate comprising: a steel material; a base plating layer provided on the surface of the steel material by hot-dip galvanizing; and a surface plating layer provided on the base plating layer by hot-dip zinc alloy plating. The plating layer is made of aluminum
High temperature corrosion resistance characterized by being an alloy layer containing 30% by weight and at least one of copper, silver and gold in a total amount of 0.7 to 3.5% by weight, with the balance being zinc and unavoidable impurities. Hot dip galvanized steel. 5. The steel material is an iron plate, a steel plate, an iron wire, a steel wire, a shaped steel, a steel bar, a steel strip, or a steel pipe.
Or a high-temperature corrosion-resistant hot-dip zinc alloy-plated steel material according to 4; 6. A surface of a steel material is hot-dip galvanized to form a base plating layer, and thereafter, the base plating layer contains 3 to 30% by weight of aluminum and at least one of copper, silver and gold. A total of 0.7 to 3.5% by weight, with the balance being hot-dip zinc alloy plating using a hot-dip zinc alloy plating bath consisting of zinc and unavoidable impurities to form a surface plating layer. Manufacturing method of corrosion-resistant zinc-alloy plated steel.