JP3404489B2 - Hot dip galvanizing method for steel - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of hot dip galvanizing of steel materials performed in a batch method, and more specifically, it has a short service life such as temporary materials or steel materials not usually plated. The present invention relates to a thin galvanizing method for steel materials, steel parts, etc. that does not require good or long-term corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, there are various methods for rust prevention of steel structures, but as a rust prevention method for steel structures used outdoors, hot dip galvanizing, electrogalvanizing and painting are generally used. It has been subjected.

In the case of hot-dip galvanizing, the thickness of the plated film can be about 100 μm and has long-term corrosion resistance, but it is problematic to apply it to thin plating or plating of products requiring high accuracy. There is. On the other hand, in the case of electrogalvanizing, it is difficult to perform thick plating due to technical restrictions in terms of cost, and basically thin plating, but it is more expensive than hot dip galvanizing. Further, in the case of coating, care must be taken in handling, and further, deterioration of the coating film due to aging and deterioration of adhesion cannot be expected, so reliable corrosion resistance cannot be expected. As described above, since each method has advantages and disadvantages, the rust prevention method is currently selected depending on the service life, shape, size, etc. of the product.

The hot dip galvanizing bath for structural steel contains iron and unavoidable impurities contained in zinc and zinc base metal in a saturated amount. In addition to that, by adding 0.01% by weight or less of aluminum as an additional metal, it is possible to suppress the oxidation of zinc on the surface of the plating bath and obtain a glossy plating film. However, even if plating is performed under the same conditions, the content of elements that promote a zinc-iron alloying reaction such as silicon, phosphorus, and manganese differs depending on the type of steel material, and therefore the plating film thickness and plating appearance may differ greatly. is there. Further, in the case of hot dip galvanizing of structural steel materials or steel parts, since the shape of the product is complicated and has various shapes, the thickness of the plating film such as gas wiping, which is performed on continuously plated steel sheets, is thinned. The method cannot be used, and the plating film thickness is 50 μm or more even if the conventional plating conditions are adjusted. For this reason, hot-dip galvanized products have long-term corrosion resistance, and products that do not require long-term corrosion resistance, such as temporary materials, have problems from the viewpoint of resource saving and energy saving. In addition, there are steel materials that are usually used for non-plating, but this is not because plating is not necessary at all, but because economic efficiency is emphasized rather than corrosion resistance to reduce costs, Needless to say, if it is possible to inexpensively plate the above steel material, that is preferable.

It has been well known that the addition of aluminum to the plating bath is effective as a method for suppressing the formation of the alloy layer in the hot dip galvanizing and suppressing the thickness of the plating film. Is plated in a reducing atmosphere or a non-oxidizing atmosphere in a plating bath containing 0.1 to 0.2% by weight of aluminum. However, in the batch type hot dip galvanizing method, it is necessary to use a flux. According to JIS H 9124 (hot dip galvanizing work standard), 0.1% by weight or less of aluminum is added to the plating bath. However, in reality, when the amount of aluminum added exceeds 0.01% by weight, defects such as non-plating may occur in the conventional flux containing zinc chloride, ammonium chloride alone or in combination thereof.
Practical application of hot-dip galvanizing in an aluminum concentration range of 0.01% by weight or more was impossible.

Therefore, the applicant of the present invention has proposed a flux for hot-dip galvanizing, a hot-dip zinc-aluminum alloy plating, a hot-dip zinc-aluminum alloy plating with various elements added, and a high-aluminum-containing hot-dip galvanizing for good hot-dip aluminum plating. Already developed, Japanese Patent Laid-Open No. 4-20275
It is disclosed in Japanese Patent No. This flux is one or more of zinc chloride, stannous chloride, alkali metal chlorides and alkaline earth metal chlorides, and alkyl quaternary ammonium salts and alkyl amines which are aliphatic nitrogen derivatives. One or two or more of the above are included. As the aliphatic nitrogen derivative, an alkyl quaternary ammonium salt is preferable, and among them, alkyl trimethyl ammonium chloride and dialkyl dimethyl ammonium chloride are particularly preferable.

[0007]

The relationship between the plating film thickness and the service life of a hot-dip galvanized steel structure will be described with reference to FIG. Plating film thickness is 80μ
If it is m, it has a corrosion resistance of 55 years in the countryside and 35 years in the industrial area. In the case of plating a steel structure, the thickness of the coating film is at least 40 μm or more when the usual hot dip galvanizing method is used, so that corrosion resistance of about 30 years in the rural area and about 20 years in the industrial area can be obtained. However, in the case of steel structures with a service life of about 10 years, such as temporary materials,
A plating film thickness of about 20 μm is sufficient.

As described above, for products that do not require long-term corrosion resistance such as temporary materials or steel materials for which plating is not usually applied, conventional plating baths having an aluminum concentration of 0.01% by weight or less are used. As described above, the hot-dip galvanizing has a corrosion resistance for a service life or more, and thus has a problem from the viewpoint of resource saving and energy saving. On the other hand, when the flux for hot-dip galvanizing with a high aluminum content described in the above publication is used, even if the aluminum concentration in the plating bath is 0.01% by weight or more, the alloy layer is appropriately suppressed, and it is necessary and sufficient as a temporary material It was found that a hot-dip galvanized film having excellent corrosion resistance and a beautiful appearance can be obtained.

In view of the above situation, the present invention is to solve the problems described above by using the flux for hot dip galvanized aluminum alloy plating, even though it is performed within the range of plating conditions in the conventional hot dip galvanization. It has been found that the problem of is solved, suppresses the plating film thickness, has a proper and sufficient corrosion resistance necessary as a temporary material, and also imparts appropriate corrosion resistance to steel materials etc. that are not usually plated, An object of the present invention is to provide a thin galvanizing method for steel having good appearance and capable of achieving resource saving and energy saving.

[0010]

In order to solve the above-mentioned problems, the present invention provides a steel material for a steel structure which has been pretreated with chloride.
Lead, stannous chloride, chlorides of alkali metals or alkali
One or more of the chlorides of the earth-earth metals, and
Of quaternary ammonium salts and alkylamines
Type, or a flux treatment step of dipping or applying the flux in a flux for hot-dip zinc aluminum alloy plating mainly containing two or more species, and the steel material subjected to the flux treatment with an aluminum concentration of 0.01 to 0.
1 to 10 minutes in hot dip galvanizing bath prepared to 075 % by weight
The thickness was between immersion provides a plating step of forming a plating film of 20 to 40 [mu] m, the seeding galvanizing method become more steel and the cooling step of cooling the steel material to form a plating film.

The present invention also relates to a pretreated steel structure.
Steel materials, zinc chloride, stannous chloride, alkali metal chlorides
Or one or two of the alkaline earth metal chlorides
In addition to the above, alkyl quaternary ammonium salts and alkyl
The main component is one or more of the mines.
Immersed in molten zinc aluminum alloy plating flux
Alternatively, a flux processing step of applying the flux
And the steel material subjected to the flux treatment, aluminum concentration
Hot-dip galvanized to 0.075-1.0 wt%
Immerse in a bath for 1 to 10 minutes and apply a thickness of 20 to 30 μm
The plating process to form a coating film and the plating film was formed
The thinning and melting of the steel consisting of the cooling step of cooling the steel.
A hot-dip galvanizing method is provided.

Further, the alkyl quaternary ammonium salt is more preferably alkyl trimethyl ammonium chloride or dialkyl dimethyl ammonium chloride.

[0013]

[0014]

The operation of the thin galvanizing method for steel according to the present invention having the above-mentioned contents has the following effects. In other words, the pre-treated steel for steel structures, sub-chloride
Lead, stannous chloride, chlorides of alkali metals or alkali
One or more of the chlorides of the earth-earth metals, and
Of quaternary ammonium salts and alkylamines
The same range as the conventional hot dip galvanization is obtained by performing hot dip galvanization through a flux treatment step of dipping or applying the flux for hot dip aluminum alloy plating containing two or more main constituents . Even with the plating conditions, a thickness of 40μ , which was not possible when using the conventional flux for hot dip galvanizing, which consisted of zinc chloride, ammonium chloride alone or in combination thereof.
Therefore, thinning plating of m or less is possible. Furthermore, aluminum is added to the hot dip galvanizing bath in an amount of 0.01 to 0.075.
By adding 1 % by weight or 0.075 to 1.0% by weight , the growth of the iron-zinc alloy layer formed on the surface of the steel material in the plating bath is suppressed, and the thickness of the plating film becomes appropriate and sufficient as a temporary material. The difference in the plating film thickness depending on the steel type is also reduced, and the amount of dross generated is also suppressed by suppressing the iron-zinc alloying reaction, and the amount of dross formed by air oxidation on the plating bath surface is also suppressed. It is suppressed.

Here, the action of each composition used for the flux will be briefly described. First, zinc chloride or stannous chloride is
It is for dissolving the thin oxide layer remaining on the steel surface and the oxide film formed on the plating bath surface. The alkali metal chloride or the alkaline earth metal chloride is for maintaining the molten state of the flux having an appropriate viscosity at the plating temperature. Then, by using a flux for hot dip galvanized aluminum alloy plating containing one or more of alkyl quaternary ammonium salts and alkyl amines as an aliphatic nitrogen derivative in the flux, hot dip galvanizing of steel materials is performed. When immersed in a bath, Hofmann decomposition on the surface of the steel material causes foaming, and burnt residue of the flux adhering to the surface of the steel material is quickly separated and removed from the surface, and the wettability between the steel surface and the molten metal is good. And the adhesiveness and appearance of the plating film are significantly improved.

FIG. 2 shows that after treating with a flux solution containing 35% by weight of zinc chloride, 5% by weight of sodium chloride, 1% by weight of dimethyl distearyl ammonium chloride and the balance being water, the plating temperature is 450 ° C. Time is 1
In the hot-dip galvanizing performed under the ordinary plating condition for a minute, the relationship between the aluminum concentration in the plating bath and the thickness of the plating film is shown. As can be seen from this relationship, when the aluminum concentration is 0.01% by weight or more, the controllability and controllability of the plating film thickness becomes remarkable, and up to about 0.075% by weight, the plating film increases as the aluminum concentration increases. The thickness decreases, and in the range of about 0.075 to 1.0% by weight, the plating film thickness is suppressed to 20 to 30 μm, which is almost constant.
On the contrary, the controllability of the plating film thickness is reduced. Therefore, when the aluminum concentration is 0.01% by weight or less, the controllability of the plating film thickness is poor, and conversely, the aluminum concentration is 1.0% by weight.
With the above, while suppressing the plating film thickness is saturated,
Since the controllability is lost and it becomes uneconomical, the aluminum concentration is set to 0.01 to 1.0% by weight in the present invention. Further, for the purpose of suppressing and controlling the plating film thickness, the aluminum concentration in the plating bath is 0.01 to 0.0.
The range of 75% by weight is preferable, and on the other hand, the aluminum concentration in the plating bath is preferably in the range of 0.075 to 1.0% by weight for the purpose of stably suppressing the plating film thickness.

Further, FIG. 3 shows the relationship between the aluminum concentration in the plating bath and the iron elution amount in the hot dip galvanizing performed under the above-mentioned plating conditions. When it is higher than 0.01% by weight, the alloying reaction between the steel material and zinc is suppressed, in other words, the amount of dross generated is suppressed. When the aluminum concentration of the present invention is in the range of 0.01 to 1.0% by weight, the iron elution amount decreases as the aluminum concentration increases. Therefore, the higher the aluminum concentration is, the more preferable in terms of suppressing the iron elution amount. However, an upper limit of 1.0% by weight is sufficient from a practical and economical point of view.

[0018]

EXAMPLES The details of the present invention will be further described based on examples. As the flux used in the hot dip galvanizing method of the present invention, various conventionally known fluxes can be adopted as long as they are fluxes for hot dip zinc aluminum alloy plating. For example, a flux mainly composed of a mixed aqueous solution of zinc chloride and ammonium chloride or an aqueous solution containing only ammonium chloride as disclosed in JP-A-58-136759 can be used, but it is large due to drying in the flux treatment step. Is not suitable for the structure. Therefore, a particularly preferable flux in the present invention is composed of at least chloride and an aliphatic nitrogen derivative, and zinc chloride (Z
nCl ₂ ), stannous chloride (SnCl ₂ ), one or more of chlorides of alkali metals and chlorides of alkaline earth metals, and alkyl quaternary ammonium salts and alkyls as aliphatic nitrogen derivatives. One or two or more of the amines are the main constituent components.

As the alkali metal chloride, chlorides of alkali metals such as lithium, sodium and potassium are used, and as the alkaline earth metal chlorides, alkaline earth chlorides such as beryllium, magnesium, calcium, strontium and barium. Metal chlorides are used.

The alkyl quaternary ammonium salt is preferably alkyl trimethyl ammonium chloride or dialkyl dimethyl ammonium chloride,
Particularly, those having an alkyl group having 7 to 18 carbon atoms are preferable. That is, examples of the alkyl group include octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, octadecenyl, octadecadienyl and the like.

Examples of the alkylamines include aliphatic primary amines such as methylamine and ethylamine, secondary aliphatic amines such as dimethylamine and diethylamine, and tertiary aliphatic amines such as trimethylamine and triethylamine. Those having an alkyl group of the number 1 to 18 are preferable.

Specifically, the flux for hot dip zinc aluminum alloy plating contains 10 to 50% by weight of zinc chloride and / or stannous chloride and one or more of alkyl quaternary ammonium salts and alkyl amines. 2 or more 0.1
1 to 20% by weight of one or more of alkali metal chlorides and alkaline earth metal chlorides, and alkyl quaternary ammonium salts and alkylamines. 0.1 to 3 of 1 or 2 or more of
0 to 50% by weight, zinc chloride and / or stannous chloride in an amount of 10 to 50% by weight, and one or more of an alkali metal chloride and an alkaline earth metal chloride.
Those containing 20% by weight and 0.1 to 30% by weight of one or more of alkyl quaternary ammonium salts and alkylamines can be used.

Here, the optimum concentration of zinc chloride and / or stannous chloride is 30 to 40% by weight. For alkali metal chlorides and alkaline earth metal chlorides, for example, the plating temperature is 400 ° C. Within the range of up to 600 ° C., ZnCl ₂ : NaCl = 4: 1 (molar ratio), ZnC
l ₂ : CaCl ₂ = 3: 1 (molar ratio) is preferable, and Zn is used if the plating temperature is in the range of 600 ° C to 700 ° C.
Cl ₂ : NaCl = 3: 1 (molar ratio), ZnCl ₂ : C
aCl ₂ = 2: 1 (molar ratio) is preferable, and 5 to 10% by weight is optimum. Further, the addition amount of the alkyl quaternary ammonium salt and the alkyl amines is optimally 1 to 10% by weight.

The method of thin galvanizing a steel material according to the present invention comprises an ordinary pretreatment step, a flux treatment step with a flux for hot dip aluminum alloy plating, and an aluminum concentration adjusted to 0.01 to 1.0% by weight. The respective steps of a plating step of dipping in the hot dip galvanizing bath and a cooling step are performed. Here, as the steel material, a temporary material having a short service life, a steel material which is not usually plated, or a precision steel part is targeted. Here, the "thinning plating" in the present invention means that the plating film thickness is 60 μm or less, preferably 40 μm, which was impossible by the conventional hot dip galvanizing.
m or less, more preferably 20 to 30 μm.

In the pretreatment process for steel materials, the temperature is kept at 60 as usual.
3 to 10-15% alkali solution (caustic soda + sodium orthosilicate added at a weight ratio of 1: 1) kept at ~ 80 ° C
After soaking for 0 to 60 minutes and washing with water, the temperature is 50 to 70 ° C.
10 to 15% sulfuric acid aqueous solution kept at 0.
5 to 0.7% added) for 30 to 60 minutes to remove scales, red rust and other rust, and then wash with water.

In the flux treatment step, the molten zinc aluminum alloy plating flux is filled at 20 ° C.
The steel material is dipped in the flux tank heated to the appropriate temperature for 1 to 2 minutes to form a flux film layer on the surface of the steel material. Here, there is no problem even if the temperature of the flux liquid is room temperature, but heating the flux liquid to an appropriate temperature results in less carry-out of the flux liquid and better workability.

In the plating process, the flux-treated steel material is drained and then the aluminum concentration is adjusted to 0.01 to
It is a normal process of adjusting the concentration to 1.0% by weight and immersing it in a hot dip galvanizing bath set to a temperature of 400 to 700 ° C. for 1 to 10 minutes. The immersion time depends on the size, shape and thickness of the steel material, but if the immersion time is too long,
Since the alloying reaction of iron and zinc, which are the main components of the steel material, progresses too much, about 1 to 10 minutes is appropriate. Then, the steel material is dipped for a predetermined time and then pulled up at an appropriate speed to drain the molten zinc.

[0028] Finally, the cooling step is to immerse in water having a temperature of 30 to 50 ° C for 1 to 2 minutes, but if the steel material to be plated is a thin plate, rod or the like having a small heat capacity, air cooling is sufficient. As described above, when the cooling is performed by the conventional operation, a plating film having a uniform and beautiful appearance without unplating, roughness, and sagging can be obtained.

(Embodiment) 4.5 mm thick SS400 (1
The test piece (50 × 75 mm) was degreased, washed with acid and washed with water, and then immersed in a flux liquid heated to 50 ° C. for 1 minute. This flux liquid used was 35% by weight of zinc chloride, 5% by weight of sodium chloride, 1% by weight of dimethyl distearyl ammonium chloride, and the balance being water. The flux-treated test piece was dipped in a hot dip galvanizing bath containing 0.2% by weight of aluminum heated to 450 ° C., a saturated amount of lead and iron, and a small amount of cadmium for 1 minute for plating. When the product was pulled up from the plating bath and water-cooled and the appearance was observed, a thin coating film having a smooth surface and a beautiful appearance and a plating film thickness of 23 μm was obtained.

(Comparative Example 1)
After degreasing, pickling and washing in the same manner as in the example, it was immersed in a flux liquid heated to 50 ° C. for 1 minute. The flux liquid used was 14% by weight of zinc chloride, 16% by weight of ammonium chloride, and the balance being water. The flux-treated test piece was dipped for 1 minute in a hot dip galvanizing bath containing 0.1% by weight of aluminum heated to 450 ° C., saturated amounts of lead and iron, and trace amounts of cadmium for plating. When the product was pulled up from the plating bath, water-cooled, and the appearance was observed, non-plating was observed over a wide area on the surface.

(Comparative example 2)
After degreasing, pickling and washing in the same manner as in the example, it was immersed in a flux liquid heated to 50 ° C. for 1 minute. This flux liquid contains 35% by weight of zinc chloride and 5% of sodium chloride.
Used was one containing 1 wt% of dimethyl distearyl ammonium chloride and the balance being water. The flux-treated test piece was plated by immersing it in a hot dip galvanizing bath containing 0.001% by weight of aluminum heated to 450 ° C., a saturated amount of lead and iron, and a small amount of cadmium for 1 minute. When the product was pulled up from the plating bath and water-cooled and the appearance was observed, a thick plating film having a smooth surface and a beautiful appearance but a plating film thickness of 80 μm was obtained.

[0032]

According to the method of hot dip galvanizing of steel material of the present invention as described above, the pretreated steel material for the steel structure is made of zinc chloride, stannous chloride or alkali metal. The chloride
Rui or one or more of alkaline earth metal chlorides
Above, alkyl quaternary ammonium salt and alkylamido
0.01 to 0.A of aluminum through a flux treatment step of dipping or applying a flux for hot-dip zinc-aluminum alloy plating containing at least one of two or more of the above as main constituents . 075 % by weight or
By performing plating in a hot dip galvanizing bath containing 0.075 to 1.0% by weight , zinc chloride, ammonium chloride alone or a mixture thereof can be used even under plating conditions in the same range as conventional hot dip galvanizing. A thickness of 40 which was impossible when using a hot-dip galvanizing flux.
It is possible to perform thin plating with a thickness of μm or less , thereby providing corrosion resistance commensurate with the service life of steel products, which contributes to resource saving and energy saving. That is, aluminum is added to the hot dip galvanizing bath in the range of 0.01 to 1.
By adding 0% by weight, the growth of the iron-zinc alloy layer formed on the surface of the steel material in the plating bath is suppressed, and it is possible to form a plating layer having a proper and sufficient plating film thickness as a temporary material, In addition, the difference in plating film thickness between steel types is reduced, and the amount of dross generated is also suppressed by suppressing the iron-zinc alloying reaction, and the amount of dust formed on the plating bath surface by air oxidation is also suppressed. It is suppressed, and as a result, the surface has a smooth and beautiful appearance. Furthermore,
Adjust the aluminum concentration in the plating bath to 0.01 to 0.075
When prepared in the range of amount%, the aluminum concentration in this range
The thickness of the plating film can be changed by changing the
Control to the range of 20-40 μm, which was impossible with
And can be controlled and also aluminum in the plating bath
When the concentration is adjusted to the range of 0.075 to 1.0% by weight,
Plating even if the aluminum concentration in the plating bath fluctuates slightly
The thickness of the film can be stably controlled to be approximately 20 to 30 μm.
You can

Further, by using a flux for hot-dip zinc aluminum alloy plating containing one or more of alkyl quaternary ammonium salts and alkyl amines as an aliphatic nitrogen derivative in the flux, a plating film is obtained. That is, the adhesiveness and the appearance are significantly improved. Further, as the alkyl quaternary ammonium salt,
The effect is more remarkable when alkyl trimethyl ammonium chloride and / or dialkyl dimethyl ammonium chloride is used.

[0034]

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the plating film thickness of a steel structure and the service life.

FIG. 2 is a graph showing the relationship between the aluminum concentration in the plating bath and the thickness of the plating film.

FIG. 3 is a graph showing a relationship between an aluminum concentration in a plating bath and an iron elution amount.

Continuation of the front page (56) Reference JP-A-4-202751 (JP, A) JP-A-60-125361 (JP, A) JP-A-58-185756 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (3)

(57) [Claims] 1. A steel material for a steel structure which has been pretreated ,
Lead, stannous chloride, chlorides of alkali metals or alkali
One or more of the chlorides of the earth-earth metals, and
Of quaternary ammonium salts and alkylamines
Flux or a flux treatment step of dipping or applying the flux in a hot-dip zinc aluminum alloy plating flux mainly containing two or more species ,
A plating step of 0.01 to 0.075 wt% to dipping with a thickness of 1 to 10 minutes in a molten zinc plating bath was prepared to form a plating <br/>-out film of 20 to 40 [mu] m, forming a plating film And a thinning hot dip galvanizing method for a steel material, comprising: a cooling step of cooling the steel material. 2. A steel material for a steel structure that has been pretreated,
Lead, stannous chloride, chlorides of alkali metals or alkali
One or more of the chlorides of the earth-earth metals, and
Of quaternary ammonium salts and alkylamines
Molten Zinc Al mainly composed of two or more kinds
Immerse in the flux for minium alloy plating or
A flux treatment step of applying a box, the steel material with a flux treatment, the aluminum concentration
Hot dip galvanizing bath adjusted to 0.075 to 1.0% by weight
Plating with a thickness of 20-30 μm by immersing in 1-10 minutes
A thin galvanizing method for steel material , comprising: a plating step for forming a film; and a cooling step for cooling the steel material on which the plating film is formed . 3. The alkyl quaternary ammonium salt comprises :
Alkyltrimethylammonium chloride and / or
Claimed to be dialkyldimethylammonium chloride
Item 3. A thin galvanizing method for a steel material according to Item 1 or 2 .