JPH0892720A - Production of high corrosion resistance zinc-aluminium alloy plated steel sheet by double layer spray plating - Google Patents

Abstract

PURPOSE: To improve the appearance of a steel sheet and the adhesive strength of a coating film after coating by spray-plating a hot-dip Zn-Al alloy having a specified compsn. to a belt-like steel sheet and thereafter spray-plating it with a hot-dip Zn-Al alloy in which the content of Al is limited. CONSTITUTION: The surface of a belt-like steel sheet is spray-plated with a hot-dip Zn-Al alloy contg., by weight, 3.5 to 10% Al, and the balance Zn with inevitable impurities in a nonoxidizing atmosphere in such a manner that the temp. of the belt-like steel sheet is regulated to the range of 430 to 600 deg.C to form a primary plating layer. Next, it is spray-plated with a hot-dip Zn-Al alloy in which the content of Al is limited to <=0.08% to form a secondary plating layer. By the same double layer hot-dip Zn-Al alloy spray plating method, the plated steel sheet having a good appearance and adhesion and excellent in corrosion resistance can be obtd.

Description

Detailed Description of the Invention

[0001]

The present invention relates to Zn-A for strip steel plate.
TECHNICAL FIELD The present invention relates to a spray plating method for 1-alloy, and particularly to a plating method capable of obtaining a high-quality strip steel plate.

[0002]

2. Description of the Related Art Zn-5.0 wt% Al-0.1 wt% Mg alloy plated steel sheet and the like (trade name: Superzing steel sheet) are known as an example of Zn-Al alloy plating having high corrosion resistance. Compared with zinc-iron plate, this steel plate is superior in bare corrosion resistance and can suppress the generation of spangles, so that it has the feature that the appearance after painting can be kept uniform and smooth (special characteristics). JP-A-54-33223).
However, this plated steel sheet is usually manufactured by a method in which the original plating plate is directly immersed in an alloy bath for plating. On the other hand, a spray plating method, in which a molten metal such as molten zinc is atomized by spraying and deposited on the surface of a strip-shaped steel sheet that is continuously fed, is conventionally
JP-A-53-99047 and JP-A-1-201245
It is known from publication No. 6. However, all of them are related to the method of plating hot-dip zinc, and the appearance of Zn-5.0wt% Al-0.1wt% is good by spray plating.
At present, a method for producing a Zn-Al alloy plated steel sheet such as a Mg alloy plated steel sheet has not been established.

[0003]

In the case of alloy metal such as Zn-Al alloy, generally, if the Al content in the molten Zn-Al alloy is low, the fluidity of the molten Zn-Al alloy is very good. Therefore, it is known that a plated steel sheet having a uniform appearance can be obtained. However, high corrosion resistance Zn-A
Al in hot-dip Zn-Al alloy like alloy plated steel sheet
When the content is high, the fluidity of the molten Zn-Al alloy is significantly deteriorated. Therefore, molten Zn-A can be found throughout the steel sheet.
The l-alloy solidifies before it fully spreads on the steel sheet, leaving microscopic unevenness on the surface of the steel sheet. Furthermore, when locally observed, Al in the molten Zn-Al alloy is not uniformly dispersed in Zn, and the fluidity is also non-uniform. For this reason,
The fluidity changes depending on the dispersed state of Al, and in addition to the phenomenon that highly reactive Al and the steel sheet are nonuniformly alloyed, spots remain in places. Therefore, it is extremely difficult to obtain a highly corrosion-resistant Zn-Al alloy plated steel sheet having a uniform appearance on the entire plated surface by the same method as the conventional hot-dip zinc spray plating method.

As described above, a high corrosion-resistant Zn-Al alloy-plated steel sheet having a good appearance is produced even if the conventional hot-dip zinc spray plating method is used to perform the Zn-Al alloy spray plating under the same conditions. You cannot do it. The present invention provides a highly corrosion-resistant Zn-Al alloy-plated steel sheet having a good appearance by a hot-dip Zn-Al alloy spray plating method, and further, a Zn-Al alloy-plated steel sheet having excellent coating film adhesion after coating. It aims at providing the manufacturing method of.

[0005]

To achieve this object, the gist of the present invention is to provide fine particles of molten Zn--Al alloy on the surface of a strip-shaped steel sheet that has been pretreated and continuously fed. In producing a hot-dip Zn-Al alloy-plated steel sheet by spray-coating by spraying, Al3.
A molten Zn-Al alloy containing 5 wt% or more and 10 wt% or less and the balance zinc and unavoidable impurities is spray-plated at a temperature of a strip steel plate of 430 to 600 ° C during plating. After forming the plating layer, A
l content is limited to 0.08 wt% or less, and the second plating layer is formed by spray-plating a molten Zn-Al alloy having the balance zinc and unavoidable impurities to form a second plating layer. It is in a method for manufacturing a Zn-Al alloy plated steel sheet.

[0006]

The inventors of the present invention firstly apply A to the molten zinc to be sprayed.
Molten Z containing 1 to 3.5 wt% or more and 10 wt% or less
It was confirmed that by spray-plating fine particles of the n-Al alloy, it is possible to manufacture a hot-dip Zn-Al alloy-plated steel sheet having excellent plating adhesion and excellent corrosion resistance. However, the plating adhesion and corrosion resistance are extremely good, but as it is, the fluidity of the molten Zn-Al alloy is poor, and the molten Zn-Al alloy is solidified before fully spreading on the steel sheet, and the steel sheet surface Microscopic unevenness remains. Further, since the alloying reaction proceeds nonuniformly, spotted patterns are formed everywhere, and the plating appearance is extremely poor.

Therefore, the inventors of the present invention further applied molten Z on the plated layer with an Al content of 0.08 wt% or less.
It was confirmed that by spray-plating n, it is possible to manufacture a hot-dip Zn-Al alloy-plated steel sheet having an excellent plating appearance and excellent corrosion resistance. Since molten Zn having an Al content of 0.08 wt% or less has extremely good fluidity, the molten Zn fine particles spread rapidly on the strip-shaped steel sheet, and the particles are well overlapped with each other, and the plated steel sheet has a uniform appearance. This is because Further, since the first plating layer (lower layer) is a Zn-Al alloy plating layer having a high Al content, the alloying reaction between molten zinc and iron can be appropriately suppressed. Therefore, even if molten Zn with a low Al content is sprayed onto the second plating layer (upper layer), the excessive alloying reaction of molten zinc and iron that adversely affects the plating adhesion is suppressed in the first plating layer (lower layer). Therefore, the excellent adhesion between the first plating layer and the steel sheet is not impaired.

As described above, the lower layer (first plating layer) is made of Al.
Molten Zn- with a content of 3.5 wt% or more and 10 wt% or less
Excellent plating appearance is obtained by spray-plating an Al alloy to ensure excellent plating adhesion, and by spray-plating molten Zn with an Al content of 0.08 wt% or less on the upper layer (second plating layer). Can be secured. Furthermore, as a result of examining the influence of other contained components, as the molten Zn of the second plating layer, the Al content was set to 0.
Molten Zn- containing less than 08 wt% and balance Zn
It has been confirmed that the above-mentioned characteristics are exhibited with an Al alloy. Molten Z for plating the first plating layer and the second plating layer
There is no problem if the unavoidable impurities in the n-Al alloy are 0.01 wt% or less.

Further, the inventors investigated the influence of the steel plate temperature when spray-plating a molten Zn-Al alloy.
FIG. 2 shows the influence of the steel plate temperature during plating on the corrosion resistance of the Zn-Al alloy layer forming the first plating layer, and the optimum steel plate temperature range of the present invention is shown by hatching. Plots in FIG. 2 are sample values of the highly corrosion-resistant Zn-Al alloy-plated steel sheet having a good appearance produced by the method of the present invention. From this figure, the molten Zn-Al alloy layer formed by spray plating in the state where the steel plate temperature at the time of spray plating the first plating layer is in the temperature range of 430 to 600 ° C,
It can be seen that the plating layer has extremely good plating adhesion and excellent corrosion resistance. When the steel sheet temperature is 600 ° C. or higher, alloying with iron becomes remarkable and plating corrosion resistance is significantly impaired. This state is represented by the Δ plot of comparative condition 1 in FIG. On the other hand, at 430 ° C. or lower, holes are present in the Zn—Al alloy plating layer, and the plating adhesion and corrosion resistance are significantly deteriorated. This state is represented by a cross plot of comparative condition 2 in FIG. Therefore, by setting the temperature of the strip-shaped steel sheet at the time of spray-plating the first plating layer to a temperature range of 430 to 600 ° C., it is possible to manufacture a hot-dip Zn—Al alloy-plated steel sheet having excellent plating adhesion and excellent corrosion resistance.

Furthermore, the inventors investigated the effect of Al in the molten Zn-Al alloy forming the first plating layer. FIG. 3 shows Al in the molten Zn-Al alloy used for the first plating layer.
The results of investigating the influence of the content on the plating adhesion are shown below. It can be seen that the plating adhesion is good if the Al content in the molten zinc used in the first plating layer is 0.2 wt% or more, and the higher the Al content, the better.
Even if Al is contained in an amount of more than 1.2 wt%, the margin for improving the adhesiveness does not increase. Further, FIG. 4 shows the results of investigation on the influence of the Al content in the molten Zn-Al alloy on the plating corrosion resistance. It is the result of investigating the weight change per one side of the surface layer by the 24-month outdoor exposure test. ◎ in the figure
Is a weight loss of 20 g / m ² or less, ◯ is a weight loss of 20 g / m ² or more and less than 30 g / m ² , and Δ is 30 g / m ² or more 4
Weight loss of less than 0 g / m ² and x indicate weight loss of 40 g / m ² or more, respectively. Plating corrosion resistance is hot Zn
It is understood that the Al content of the -Al alloy is 3.5 wt% or more, but the higher the Al content, the better. However, when Al exceeds 10 wt%,
The amount of improvement in corrosion resistance is small, and a large amount of Al-Zn alloy (top dross) is produced in the molten Zn-Al alloy bath, which is not desirable in operation. Therefore, the Al content in the Zn-Al alloy to be spray-plated is 3.5 wt% or more and 10
It should be less than wt%.

Further, FIG. 5 shows the results of investigation on the influence of the Al content in the molten Zn used for the second plating layer on the appearance of the plating. It can be seen that the appearance of the plating is satisfactory if the Al content in the molten Zn used for the second plating layer is 0.08 wt% or less, but the lower the Al content, the better. The Al content in the molten Zn used for the second plating layer is preferably kept as low as possible and 0.01 wt% or less. Further, it is most preferable to set the Al content in the molten Zn to 0.0 wt%, that is, to use pure molten zinc. The temperature of the steel sheet when the molten zinc is sprayed to form the second plating layer may be the melting point of zinc, usually 420 ° C. or higher. Usually, since the first plating layer and the second plating layer are continuously treated, the steel sheet temperature during the formation of the second plating layer is almost the same as that during the formation of the first plating layer, as shown in the examples.

[0012]

FIG. 1 shows an example of a manufacturing process for carrying out the present invention. In this example, a highly corrosion resistant Zn-Al alloy plated steel sheet was manufactured according to the manufacturing conditions shown in the left columns of Tables 1 to 4. Specific manufacturing methods according to the manufacturing conditions in Tables 1 to 4 are shown below. As the strip-shaped steel sheet, a cold rolled steel sheet of low carbon Al killed steel having a thickness of 0.75 mm and a width of 500 mm was used. The strip-shaped steel sheet 1 is sufficiently degreased in advance by a pickling treatment or a hydrogen reduction heating treatment to clean the surface. Next, the temperature of the strip-shaped steel sheet 1 at the time of plating is heated to a predetermined temperature equal to or higher than the melting point of the molten Zn-Al alloy by the induction heating device 5 in a non-oxidizing atmosphere, and the deflector is maintained while maintaining the non-oxidizing atmosphere. It is sent to the plating chamber 3 via the roll 2. Regarding the temperature of the strip steel sheet, a radiation thermometer 7 is installed at an appropriate position before being sent to the plating chamber 3, the temperature of the strip steel sheet is measured, and the output of the induction heating device 5 is adjusted by the output control device 8. And control.

Next, in the plating chamber 3, molten Zn-A is used.
l Alloy spray nozzle 4 melts both sides of the strip steel
Spray n-Al alloy and spray plating. At this time, as the Zn-Al alloy material to be sprayed, the first plating layer contains molten Zn-Al alloy adjusted to a predetermined Al content.
An alloy was used, and a zinc ingot having an Al content of 0.0 wt% which is commonly used for electrogalvanizing was used for the second plating layer. The steel plate temperature during spray plating is shown in Tables 1 to 4 as the temperature of the strip steel plate during plating. Molten Zn
The -Al alloy spray nozzle 4 is a gas atomization system, that is, a system in which a molten Zn-Al alloy is atomized with nitrogen gas, and atomizes to a cumulative weight average particle size of 50 μm or less. The coating weight of each layer is determined by the amount of molten Zn-
It is adjusted by the supply pressure of the Al alloy, the line speed of the strip steel plate, and the number of nozzles arranged in the longitudinal direction of the strip steel plate. Then 2
After maintaining the strip steel plate temperature in the heat retention furnace 6 for about 3 seconds,
Cool quickly to room temperature with a gas jet cooler.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

According to the manufacturing process of FIG. 1, the plating quality of the product manufactured by the manufacturing method of the hot-dip Zn-Al alloy plated steel sheet of the present invention and the comparative material manufactured by the hot-dip Zn-Al alloy spray plating method of the comparative method ( Plating corrosion resistance,
The results of the investigation of plating appearance and plating adhesion) are shown in the right columns of Tables 1 to 4. This table condition No. 1 to No. It has been described up to 36, and all have good plating corrosion resistance, plating appearance and plating adhesion. In addition, condition N in this table
o. 37 to No. 52 is molten Zn- of the first plating layer
The case where the Al content in the Al alloy is in the range of 0.0 to 3.0 wt% is shown, and the plating durability becomes poor.

Next, in the condition No. of this table. No. 53 to No. 61
Until, the temperature of the steel plate during spraying of the first plating layer was 430 ° C.
The following cases are shown, and condition No. 6
2 to No. Up to 73, the steel plate temperature at the time of spraying the first plating layer is 600 ° C. or higher, and in both cases, the plating durability is poor. In addition, condition N in this table
o. 77 to No. Up to 82, the molten Z of the second plating layer
Al content in the n-Al alloy is 0.01 to 5.0 wt%
It shows the case of using the one in the range of, and the plating appearance becomes poor. Thus, according to the present invention, two-layer fused Zn
-A molten Z having a good appearance and adhesion by an Al alloy spray plating method and having good plating corrosion resistance
An n-Al alloy plated steel sheet can be obtained.

[0020]

According to the present invention, a two-layer hot-dip Zn-Al alloy spray plating method is used to obtain hot-dip Zn-Al having good appearance and adhesion and good plating corrosion resistance.
An alloy plated steel sheet can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a manufacturing process for carrying out the present invention,

FIG. 2 is a diagram showing an optimum steel plate temperature range and Al content during first layer spray plating of the present invention,

FIG. 3 is a diagram showing the influence of the Al content in the molten Zn—Al alloy of the first plating layer on the plating adhesion,

FIG. 4 is a diagram showing the influence of the Al content in the molten Zn—Al alloy of the first plating layer on the plating durability,

FIG. 5 is a diagram showing the influence of the Al content in molten Zn of the second plating layer on the plating appearance.

[Explanation of symbols]

 1 strip steel plate 2 deflector roll 3 plating chamber 4 spray nozzle 5 induction heating device 6 heat-retaining furnace 7 radiation thermometer 8 output control device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanori Hoshino 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division

Claims (1)

[Claims] 1. When producing a steel sheet by spray plating by spraying fine particles of a molten Zn—Al alloy in a non-oxidizing atmosphere onto the surface of a strip-shaped steel sheet that has been pretreated and continuously fed, Al3 0.5 wt% or more and 10 wt%
A molten Zn-Al alloy containing the following and the balance consisting of zinc and unavoidable impurities was spray-plated at a temperature of the strip steel plate at the time of plating to a temperature range of 430 to 600 ° C to form a first plating layer. After that, the Al content is 0.08 wt
% Or less, and the second plating layer is formed by spray-plating molten Zn whose balance is zinc and unavoidable impurities to form a second plating layer. A method for producing a highly corrosion-resistant Zn-Al alloy-plated steel sheet by two-layer spray plating. .