JPH083717A - Manufacture of high corrosion resistant zinc-aluminum alloy plated steel strip by spray-plating - Google Patents

Abstract

PURPOSE:To produce a high corrosion resistant plated steel strip having good appearance by keeping the temp. of the steel strip equal to or lower than the m.p. of a molten Zn-Al alloy for plating, spray-plating the alloy and reheating the steel strip at a specific temp. after solidifying the alloy. CONSTITUTION:The molten Zn-Al alloy for plating contains 25-70wt.% Al. The steel strip 1 is heated to a temp. equal to or lower than the m.p. of the Zn-Al alloy with an induction heating device 5 under non-oxidizing atmosphere and fed to a plating chamber 3. A radiation thermo-meter 7 is arranged in front of the plating chamber 3, and the output of the induction heating device 5 is adjusted to control the temp. of the steel strip 1. The molten Zn-Al alloy is sprayed to the steel strip 1 from spraying nozzles 4 in the plating chamber 3 to execute the spray-plating. Successively, the steel strip 1 is introduced into a reheating furnace 6 under non-oxidizing atmosphere and reheated to a temp. in the range of Tmp+170>=T( deg.C)>Tmp, wherein, Tmp is m.p. of the alloy, T, temp. of the steel strip 1 at the time of plating.

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-55 wt% Al alloy plated steel sheet and the like (trade name: Galvalume steel sheet) are known as an example of highly corrosion resistant Zn-Al alloy plating. This steel plate is
It exhibits extremely excellent corrosion resistance as compared with a zinc iron plate (Japanese Patent Publication No. 46-7161). However, since this plated steel sheet has been manufactured by a method of directly immersing a plating base plate in an alloy bath and performing plating, a Zn-55 wt% Al alloy-plated steel sheet having a good appearance is formed by a spray plating method. At present, the method for producing an Al alloy plated steel sheet has not been established.

Conventionally, a spray plating method in which a molten metal such as molten zinc is atomized by spraying, and this is adhered to the surface of a strip-shaped steel sheet which is continuously fed to perform plating, has been conventionally known from JP-A-53-99047. Japanese Patent Laid-Open No. 1-20
It is known from Japanese Patent No. 1456. All of them relate to the method of plating hot-dip zinc, and do not mention the method of plating alloy metal such as Zn-Al alloy. Further, the importance of the strip-shaped steel sheet temperature at the time of plating is not mentioned, and in the case of molten zinc, it is set to about 450 ° C., which is higher than the melting point.

[0004]

However, as in the conventional method, if the temperature of the strip-shaped steel sheet during plating is higher than the melting point of the plated alloy, a uniform plating appearance cannot be obtained. In the case of alloy metal such as Zn-Al alloy, the fluidity in the molten state is significantly inferior to that of molten zinc. Therefore, the molten Zn-Al alloy is solidified everywhere on the steel sheet before it is sufficiently spread on the steel sheet, and microscopic unevenness remains on the surface of the steel sheet. Furthermore, when observed locally,
Al in the molten Zn-Al alloy is not uniformly dispersed in Zn, and the fluidity is not uniform. Therefore, the fluidity changes depending on the dispersed state of Al, and the highly reactive Al
In addition to the phenomenon that the steel sheet is alloyed unevenly, it remains as a spot pattern in some 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, in the conventional hot-dip zinc spray plating method, the temperature of the strip-shaped steel sheet during plating is high. Therefore, even if Zn-Al alloy spray plating is carried out under the same conditions, high corrosion resistance Zn having a good appearance is obtained. -Al alloy plated steel sheet cannot be manufactured. The present invention relates to molten Zn
An object of the present invention is to provide a method for producing a highly corrosion-resistant Zn-Al alloy plated steel sheet having a good appearance by the -Al alloy spray plating method.

[0006]

To achieve this object, the gist of the present invention is that molten Zn is applied in a non-oxidizing atmosphere to the surface of a strip-shaped steel sheet that has been pretreated and continuously fed. -When spray-plating by spraying fine particles of Al alloy, Al 25 wt% or more and 70 wt% or more
A molten Zn-Al alloy containing the following, the balance consisting of zinc and unavoidable impurities, is spray-plated in a state where the temperature of the strip steel plate at the time of plating is lower than the melting point _Tmp of the Zn-Al alloy, and then Zn -After the Al alloy is solidified, the strip steel plate is subjected to a temperature range of _Tmp + 170 ≥ T (° C)> _Tmp (where _Tmp is the melting point of the Zn-Al alloy and T is the strip steel plate temperature during plating). It is a method for producing a Zn-Al alloy plated steel sheet with high corrosion resistance by spray plating, which is characterized by reheating. Further, the molten Zn-Al alloy is Al2
A Zn-Al alloy containing 5 wt% or more and 70 wt% or less, 0.5 wt% or more and 5.0 wt% or less of Si of the Al content, and the balance being zinc and unavoidable impurities. To do.

[0007]

The present inventors first set the temperature of the strip-shaped steel sheet at the time of plating to a temperature not higher than the melting point of the Zn-Al alloy, the spray-plated Zn-Al alloy is solidified on the strip-shaped steel sheet, and It was confirmed that it is possible to obtain a plated strip steel sheet having a uniform appearance on the entire surface of the strip steel sheet, which is free from unevenness in the plating appearance, because the fluidization in the above and the alloying reaction between the strip steel sheet and Al are suppressed. The temperature of the strip steel plate during plating is Zn-A
It should be lower than the melting point of the alloy, but at least 20 ℃
It is desirable to lower it. However, as it is, holes are present in the plating layer and the surface is also uneven. Therefore, by subjecting this plated strip steel sheet to an appropriate reheating treatment, the solidified Zn-Al alloy is uniformly remelted, and high corrosion resistance Zn-Al having a smooth surface with no holes is formed.
The purpose is to obtain an alloy-plated steel sheet. That is, after the Zn-Al alloy is solidified, the temperature of the strip steel sheet is _Tmp + 170 ≧ T.
(° C)> _Tmp temperature range (where _Tmp is the melting point of Zn-Al alloy, T is the strip steel plate temperature at the time of plating), and high corrosion resistance Zn-Al with good plating appearance when reheated
It is possible to manufacture an alloy-plated steel sheet.

When the reheating temperature is T _mp +170 or more, alloying with iron becomes remarkable and the corrosion resistance of the plating is significantly impaired. On the other hand, at T _mp or less, re-melting of the solidified Zn-Al alloy becomes insufficient, unmelted Zn-Al alloy remains, and an appropriate highly corrosion-resistant Zn-Al alloy plated steel sheet cannot be obtained. The temperature of the strip steel sheet during plating is preferably T _mp + 20 ° C. from the viewpoint of productivity.

FIG. 2 shows the influence of the reheating temperature of the Zn-Al alloy spray-plated steel sheet, and the optimum reheating range according to the present invention is shown by hatching. The plot of ◯ in FIG. 2 is a sample value of a highly corrosion-resistant Zn-Al alloy plated steel sheet having a good appearance manufactured by the method of the present invention. Table 1
Table 1 shows the Al content and melting point of each sample. The Δ plot of comparison condition 1 in FIG. 2 indicates alloying with iron,
Alternatively, a sample having poor plating corrosion resistance due to an inappropriate content of Al (shown in FIG. 3) is shown, and the result of comparison condition 2 x
The plot shows a sample in which remelting was insufficient due to an inappropriate reheating temperature, and both are not qualified as a highly corrosion resistant Zn-Al alloy plated steel sheet. In any of the samples, the production range of the highly corrosion-resistant Zn-Al alloy plated steel sheet having a good appearance is the range shown by the above formula.

FIG. 3 shows the results of investigation of the relationship between the Al content in the Zn-Al alloy and the corrosion resistance of the plating. 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, ⊚ indicates a weight loss of 15 g / m ² or less, ∘ indicates a weight loss of 15 g / m ² or more and less than 20 g / m ² , Δ indicates a weight loss of 20 g / m ² or more and less than 30 g / m ² ,
X indicates a weight loss of 30 g / m ² or more. The corrosion resistance of the plating is not problematic if the Al content of the molten Zn-Al alloy is 25 wt% or more, but Al 70 wt
If it exceeds%, the corrosion resistance tends to be rather lowered. Therefore, the Al content in the Zn-Al alloy to be spray-plated is preferably 25 wt% or more and 70 wt% or less.

Preferably, the molten Zn-Al alloy contains 0.5 wt% or more of the Al content of Si to improve the adhesion at the plating interface between the Zn-Al alloy and the strip steel sheet. Corrosion resistance can be further improved. Figure 4 shows the Si content (Z
The result of having investigated (with respect to Al content in n-Al alloy) is shown. The evaluation is based on the 24 month outdoor exposure test described above.
The result was obtained by investigating the change in weight per one surface of the surface layer. In the figure, ⊚ indicates that the corrosion resistance is improved by 15 to 20%, ∘ indicates that the corrosion resistance is improved by 10% or more, and Δ indicates that the corrosion resistance is improved by less than 10%. Showing things. Molten Zn-Al
If the Si content in the alloy is 0.5 wt% or more of the Al content, the effect is exhibited. Even if the Si content exceeds 5.0 wt% of the Al content, the corrosion resistance improving effect is saturated, so the upper limit of the Si content of the present invention is 5.0 wt% of the Al content. Furthermore, the desirable Si content is A
It is about 3.0 wt% of the 1 content. As described above, according to the present invention, a highly corrosion-resistant Zn-Al alloy plated steel sheet having a good appearance can be obtained by the hot-dip Zn-Al alloy spray plating method.

[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 2 to 4. Specific manufacturing methods according to the manufacturing conditions in Tables 2 to 4 are shown below. As a strip steel material, the thickness is 0.75
A cold rolled steel plate of mm × width 500 mm, low carbon Al killed steel was used as a plating original plate. The strip steel plate 1 is, as a pretreatment,
Sufficient degreasing is performed in advance by pickling treatment or hydrogen reduction heating treatment to clean the surface. Next, in the non-oxidizing atmosphere, the induction heating device 5 heats up to a suitable temperature of the strip steel plate below the melting point of the Zn-Al alloy, and then sends it to the plating chamber 3 as it is. The temperature of the strip steel plate during spray plating is Z
In order to suppress the melting point of the n-Al alloy or less, a radiation thermometer 7 is installed at an appropriate position before being sent to the plating chamber 3, the temperature of the strip-shaped steel plate is measured, and the output control device 8 controls the induction heating device. The output of 5 is adjusted to control the temperature of the strip steel sheet. The strip steel plate 1 is sent to the plating chamber 3 via the deflector roll 2. In the plating chamber 3, molten Zn-A
l Alloy spray nozzle 4 melts both sides of the strip steel
Spray n-Al alloy and spray plating. The coating weight of the plating is adjusted by the supply pressure of the molten Zn-Al alloy to the nozzle and the line speed of the strip steel plate.

The temperature of the molten Zn-Al alloy is set differently depending on the Al content, and the melting point T _{mp of the} Zn-Al alloy is
It is set to be 40 ° C. higher than that shown in Table 1. The strip-shaped steel sheet in which the plated molten Zn-Al alloy is solidified is subsequently introduced into the reheating furnace 6 adjusted to a non-oxidizing atmosphere.
In this reheating furnace 6, the temperature of the strip-shaped steel sheet is raised to a predetermined reheating temperature in about 15 seconds, and heat treatment is performed for a predetermined time while keeping this temperature. The reheating method is radiant heating with a radiant tube burner. The reheating time is about 3 seconds to 20 seconds. The reheating temperature is measured by a radiation thermometer installed in the reheating furnace 6, and is adjusted by adjusting the output of the burner and the line speed of the strip steel sheet. Then, cool to room temperature with a jet cooler.

[0014]

[Table 1]

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 spray-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. The results of the investigation are shown in the right columns of Tables 2 to 4. The product produced by the method for producing a hot-dip galvanized steel sheet according to the present invention has the condition N in this table.
o. 1 to No. Listed up to 48, both
It has a good plating appearance. Among them, molten Zn-
As the Al alloy component, the one containing Si in the indicated amount to improve the corrosion resistance is the condition No. 23 to No. Four
4 shows. In addition, the condition No. 45 to No. Fifty
Has an Al content in the molten Zn-Al alloy of 15 to 20 w.
The figure shows the case where t% and 75 wt% or more are used, and the plating appearance is good, but the plating corrosion resistance is slightly deteriorated. Further, the condition No. 51 to No. 6
No. 2 shows the result when spray-plating was performed by increasing the strip-shaped steel plate temperature during plating. In both cases, the plating appearance has a spotted pattern and the plating quality is poor. This table condition No. 63 to No. No. 66 shows the result that the Si content is less than 0.5 wt% of the Al content, and the effect of improving the corrosion resistance by Si is small.

The surface appearance of the plated surface shown in Table 1 was visually evaluated. Further, the plating corrosion resistance was evaluated by the results of examining the weight change per one surface of the surface layer by the above-mentioned 24-month outdoor exposure test. 20 g / m ² of the following weight loss ones as "good", 20 g / m ² or more 30 g / m ²
Those with a weight loss of less than ² were regarded as "slightly poor", and those with a weight loss of 30 g / m ² or more were evaluated as "poor". Also, the improvement of corrosion resistance due to Si was evaluated by the above-mentioned 24-month outdoor exposure test, and it was confirmed that the corrosion resistance was improved by 10% or more, "Yes", and only the improvement of corrosion resistance of less than 10% was recognized. Was set to "none".

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

[Table 4]

[0020]

According to the present invention, a highly corrosion resistant Zn-Al alloy plated steel sheet having a good appearance can be obtained by the hot dip Zn-Al alloy spray plating method.

[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 reheating range of the present invention,

FIG. 3 is a diagram showing the influence of Al content in a molten Zn-Al alloy on corrosion resistance;

[Fig. 4] S for Al content in molten Zn-Al alloy
It is a figure which shows the influence which i content gives to corrosion resistance.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. When 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, Al 25 wt% or more and 70 wt% or less The temperature of the strip-shaped steel sheet at the time of plating a molten Zn-Al alloy containing
Spray plating is performed at a temperature lower than the melting point T _{mp of the} alloy, and then the Zn-Al alloy is solidified, and then the strip steel plate is T _mp +1
Temperature range of 70 ≧ T (° C.)> T _mp (where T _mp is Zn−
The melting point of Al alloy, T is the strip steel plate temperature during plating),
A method for producing a Zn-Al alloy-plated steel sheet with high corrosion resistance by spray plating, which comprises reheating. 2. The molten Zn-Al alloy is Al25 wt%
More than 70 wt% and less than 0.5% of Al content
The Zn-Al alloy plated steel sheet with high corrosion resistance by spray plating according to claim 1, wherein the Zn-Al alloy contains t% or more and 5.0 wt% or less of Si, and the balance is zinc and unavoidable impurities. Manufacturing method.