JPH09235661A - Aluminum-containing hot dip galvanized steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the uniformity of spangles even in the case of a steel sheet in which nonuniformity of steel sheet surface is present and to obtain excellent surface external appearance quality. SOLUTION: After the surface of a steel sheet is ground by >=0.05μm thickness per side, the steel sheet is inserted into continuous hot dipping equipment and a hot dip galvanizing film containing 20-95wt.% Al is formed on the surface of the steel sheet, by which the Al-containing hot dip galvanized steel sheet can be produced. Further, in the case of an Al-containing hot dip galvanized steel sheet, prepared by treating the surface of the Al-containing hot dip galvanized steel sheet produced by the above method with chromating solution, resin- containing chromating solution, etc., excellent surface external appearance quality can be obtained similarly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel sheet containing 20 to 95% by weight of Al and a method for producing the same using a continuous hot dip coating facility.

[0002]

2. Description of the Related Art Since Al-containing hot-dip galvanized steel sheets have a beautiful plating appearance and excellent corrosion resistance, they are subjected to chemical conversion treatment with a chromate solution, a resin-containing chromate treatment solution, etc. Molded and widely used for building roofs, outer walls, etc.

A steel sheet to be hot-dip galvanized containing Al (referred to as a plating base material) is a hot rolled steel sheet after a hot rolling → pickling step or a hot rolling → pickling → cold rolling step. Later cold rolled steel sheet is used. The steel sheet that has undergone these pre-plating steps is inserted into a continuous hot-dip galvanizing facility as shown in FIG. 2, which is disclosed in, for example, JP-A-51-81743.

The inserted steel sheet 1 first enters an annealing furnace 2 having a reducing atmosphere, is heated and reduction-annealed, and then enters the plating bath 5 from a snout 3 whose lower end is immersed in the plating bath 5. Here, the molten metal adheres to the surface of the steel plate 1. After that, the steel plate 1 passes through the sink roll 6 and is discharged from the plating bath 5 so that gas is jetted from the wiping nozzle 7 toward the surface of the steel plate 1 to adjust the amount of coating adhered and the plating film. Is formed.

On the surface of the Al-containing hot-dip galvanized steel sheet produced in this way, a pattern called spangle corresponding to the solidification structure of the molten metal adhered appears. It is known that a plated steel sheet having a good surface appearance quality can be obtained when the size of the spangle becomes uniform (this is said to ensure the uniformity of the spangle).

The size of the spangle is mainly determined by nucleation and dendrite growth in the solidification process of the molten metal attached to the surface of the steel sheet. For this reason, conventionally, efforts have been made to ensure spangle uniformity by accurately controlling the plating operation conditions such as the plating bath composition and the cooling rate after plating within a predetermined control range.

[0007]

However, even if the steel sheets manufactured under the same steel sheet manufacturing conditions are used and the above-mentioned plating operation conditions are accurately controlled, the size of the spangle after plating may be different between coils or between coils. There is a large variation in the position in the coil (width direction and longitudinal direction),
It has been a problem from the past.

The cause of this is the non-uniformity (variation) of the oxidation state and the concentration element that occur on the surface of the steel sheet in the steel sheet manufacturing process of the pre-plating step, and while this non-uniformity exists, Al-containing hot dip galvanizing Then, the size of the spangle varies depending on the non-uniformity of the steel plate surface,
The inventors' investigation revealed that the surface appearance quality deteriorates.

[0009] In addition, as will be described in detail later, when the Al-containing hot-dip galvanizing is applied to the surface of a steel sheet having non-uniformity, when the Al content is 20% by weight or less from the solidification characteristics of the Zn-Al alloy. In comparison with the above, it was revealed by the study by the present inventors that when the Al content is 20% by weight or more, the spangle unevenness is more likely to be promoted and the surface appearance quality is more likely to be deteriorated.

Even if the surface of the Al-containing hot-dip galvanized steel sheet having the above-mentioned non-uniformity is subjected to a chemical conversion treatment with a chromate solution, a resin-containing chromate treatment solution or the like, the surface appearance quality may deteriorate similarly. It was made clear by the investigation by the present inventors.

The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and in the case of applying hot dip galvanizing containing 20% by weight or more of Al, there is unevenness on the surface of the steel sheet. Al-containing hot-dip galvanized steel sheet that ensures good surface appearance quality even when using a steel sheet that is used, as well as Al-containing hot-dip galvanized steel sheet that has been treated with chromate, resin, etc. An object of the present invention is to provide a galvanized steel sheet and a manufacturing method thereof.

[0012]

The invention according to claim 1 is
After the steel plate surface is ground to a thickness of 0.05 μm or more per surface, it is inserted into a continuous hot dip galvanizing equipment to form a hot dip galvanized film containing 20 to 95 wt% of Al on the steel plate surface. It is a manufacturing method of a galvanized steel sheet.

In order to solve the above-mentioned problems, the inventors of the present invention have keenly studied the relationship between the solidification characteristics of Zn-Al alloys and spangles when producing a hot-dip galvanized steel sheet containing 20 to 95% by weight of Al. I conducted a survey and research.

As a result, when the Al content is less than 20% by weight,
The spangle pattern corresponds to the dendrite structure in which Zn solidifies and solidifies Al, and when the Al content is 20% by weight or more, Al is Zn.
A solidified structure corresponding to the solidified dendrite structure is generated. In other words, it was found that different metal solidification structures are formed when the Al content is 20% by weight, and the same spangles have different surface appearance qualities after plating depending on the solidification structure.

As a result, the former plated steel sheet containing less than 20% by weight of Al is inferior in surface appearance quality to the below-mentioned plated steel sheet containing 20% by weight or more of Al and is used for applications in which the appearance is not a problem. In addition, since its corrosion resistance is not sufficient, it is used by painting the surface after plating.

On the other hand, the latter plated steel sheet containing 20% by weight or more of Al has spangles having a beautiful luster, and
Since the Al content is high and the corrosion resistance is good, it is possible to use the spangle pattern itself without designing it, giving it a design property.

If the Al content exceeds 95% by weight, Al
The upper limit is set to 95% by weight, because it becomes closer to plating and the spangle pattern does not appear clearly on the steel plate surface.

From the above description, the problem of nonuniformity of spangle is that the Al content is in the range of 20% by weight to 95% by weight. In the present invention, the Al content is limited to this range. In addition, it is intended to secure the spangle uniformity and obtain a good surface appearance quality by means described later.

Next, the inventors of the present invention determined the range of the oxidation state on the surface of the steel sheet and the nonuniformity of the enriched elements, the steel sheet manufacturing conditions in the pre-plating step, the type of the steel sheet (including alloy elements, etc.). Was investigated variously. As a result, it was found that the range of ordinary cold-rolled steel sheets and pickled hot-rolled steel sheets was at most about 0.05 μm.

After the steel plate surface is ground to a thickness of 0.05 μm or more per one surface, the steel plate from which the nonuniformity of the steel plate surface has been removed is inserted into a continuous hot dip coating equipment. Here, the steel sheet is heated in an annealing furnace having a reducing atmosphere and subjected to reduction annealing. After that, the annealed steel sheet enters a snout arranged behind the annealing furnace, and is inserted into the plating bath via the snout. Since the lower end of the snout is immersed in the plating bath, the surface of the steel sheet after grinding is inserted into the plating bath without being exposed to air and being oxidized. In other words, the steel sheet is inserted into the Al-containing hot dip galvanizing bath while ensuring the uniformity of the steel sheet surface.

From the above, the thickness per surface is 0.05 μ
Even if hot-dip galvanizing containing 20 to 95% by weight of Al is performed by grinding for m or more, the nonuniformity of the steel sheet surface is removed. It is possible to manufacture an Al-containing hot-dip galvanized steel sheet which has good surface appearance quality.

The invention according to claim 2 is characterized in that the surface of the Al-containing galvanized steel sheet produced by the invention according to claim 1 is
A method for producing an Al-containing hot-dip galvanized steel sheet, which comprises performing a chromate treatment.

It is essential to perform chromate treatment on the surface of the Al-containing hot-dip galvanized steel sheet. As described above, the plated steel sheet containing 20 to 95% by weight of Al is often used with the spangle pattern itself having a design property.
After the hot dipping treatment, if the surface is not further treated, rust may occur on the surface of the steel sheet during storage and transportation until the product is used.

In this case, no matter how good the spangle pattern is, the surface appearance quality will deteriorate.

Therefore, the chromate treatment is carried out in order to prevent the generation of rust during storage and transportation.
The chromate treatment method includes a reaction type, a coating type, an electrolytic type and the like, but any method may be used.

The chromate treatment equipment may be installed continuously in the continuous hot dip plating equipment, or may be installed separately from the continuous hot dip equipment.

According to a third aspect of the present invention, in the second aspect of the invention, the chromate treatment is performed with a chromate treatment liquid having a molar ratio of hexavalent chromium content to total chromium content of 0.5 or more. A method for producing a characteristic Al-containing hot-dip galvanized steel sheet.

If the ratio of the hexavalent chromium content to the total chromium content is specified to be less than 0.5, the surface of the steel sheet is likely to turn black during storage and transportation until the product is used. This also leads to deterioration of surface appearance quality.

The invention according to claim 4 is the same as the invention according to claim 2 or 3, after the chromate treatment,
A method for producing an Al-containing hot-dip galvanized steel sheet, which comprises applying a resin.

The application of the resin maintains or complements the effect of the above-mentioned chromate treatment.
The uniformity of the spangle pattern formed on the surface of the Al-containing hot-dip galvanized steel sheet is maintained, and the surface appearance quality is kept good.

Any resin may be used as long as it does not deteriorate the uniformity of the spangle pattern, and an acrylic emulsion resin or the like can be used.

The invention according to claim 5 is the method for producing an Al-containing hot-dip galvanized steel sheet according to the invention according to claim 2 or claim 3, characterized in that chromate treatment is performed with a chromate treatment liquid containing a resin. is there.

As described above, the application of the resin retains or complements the effect of the chromate treatment. Therefore, even if the chromate treatment is performed with a resin-containing chromate treatment liquid, the same effect is obtained. It depends on the effect.

With this, the uniformity of the spangle pattern formed on the surface of the Al-containing hot dip galvanized steel sheet is maintained,
Maintains good surface appearance quality.

The invention according to claim 6 grinds the surface of a steel sheet to a thickness of 0.05 μm or more per one surface, and then inserts it into a continuous hot dip galvanizing facility to form a hot dip galvanized film containing 20 to 95% by weight of Al on the surface of the steel sheet. 2-100 mg / in terms of metallic chromium on the surface of the Al-containing hot-dip galvanized steel sheet produced by forming
Al characterized by forming a chromate film of m ²
It is a hot dip galvanized steel sheet containing.

The reason for forming the chromate film on the surface of the Al-containing hot-dip galvanized steel sheet manufactured as described above is for the reason described in the invention according to claim 2. In this case, it is necessary to form a film having a total chromate deposition amount of ² to 100 mg / m ^{2 in} terms of metal chromium.

The lower limit is set to 2 mg / m ^{2 in} terms of metallic chromium, because if it is less than this, the effect of preventing rust generation during storage and transportation is not sufficient. Setting the upper limit to 100 mg / m ^{2 in} terms of metallic chromium not only becomes economically disadvantageous in terms of manufacturing cost and the like when it is more than this, but also coloring becomes conspicuous, which also deteriorates the surface appearance quality. Is to bring.

The invention according to claim 7 is such that, after the steel plate surface is ground to a thickness of 0.05 μm or more per one surface, the steel plate surface is inserted into a continuous hot dip galvanizing facility, and the steel plate surface contains Al in an amount of 20 to 95% by weight. The Al-containing hot-dip galvanized steel sheet produced by forming the Al-containing hot-dip galvanized steel sheet has a total chromate deposition amount of ² to 100 mg / m ² in terms of metal chromium, and a film containing a resin is formed. It is a galvanized steel sheet.

According to the present invention, a case where a resin film is formed on a chromate film and a case where a film in which a resin and a chromate are mixed are formed can be applied.

In the invention according to claim 2 or claim 3,
This is due to the reason mentioned above. In either case
Mate adhesion amount is 2 to 100 mg / m in terms of metal chromium ^Two
It is necessary to form a film. Request for limitation reason
This is because of the reason described in the invention of item 6.

Any resin may be used as long as it does not deteriorate the uniformity of the spangle pattern, and an acrylic emulsion resin or the like can be used.

The amount of resin usually used is 0.5 to
4.0 g / m ² . If it is less than 0.5 g / m ² , no effect can be expected, and if it exceeds 4.0 g / m ² , the effect is flat.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION The purpose of grinding is to eliminate the non-uniformity of the oxidation state and the thickening element on the surface of the steel sheet, which has occurred in the previous step, and to obtain a uniform surface quality.

As the grinding method, for example, a mechanical grinding method such as a brush roll or a roll having a grindstone provided on the surface thereof is adopted, but a chemical grinding method other than this may be used. Further, the grinding equipment may be installed in front of the continuous hot dip coating equipment for continuous treatment, or the grinding equipment may be ground in another step and then inserted into the continuous hot dip coating equipment. However, in the latter,
Since the surface of the steel sheet is newly oxidized after the grinding to cause nonuniformity, a preventive measure is required. Therefore, the former is more advantageous in productivity, cost, work management and the like.

The upper limit of the grinding amount is not specified. However, in order to increase the grinding amount, it is necessary to increase the grinding equipment or reduce the line speed, which leads to an increase in cost and a decrease in productivity. Further, even if the grinding amount is increased more than necessary, the effect on the spangle uniformity is saturated. Furthermore, as the grinding amount increases, the reduction in plate thickness due to grinding becomes a non-negligible amount. Considering such a situation comprehensively, we think that a thickness of up to about 5 μm per side is practical.

Further, in the present invention, after the steel sheet surface is ground to a thickness of 0.05 μm or more per surface, the steel sheet surface is inserted into a continuous hot dip galvanizing facility to form a hot dip galvanized film containing 20 to 95% by weight of Al on the steel sheet surface. The surface of the Al-containing hot dip galvanized steel sheet produced by forming is subjected to chromate treatment, and after chromate treatment, resin is applied, or chromate treatment is performed with a chromate treatment liquid containing resin. .

In this case, the chromate treatment equipment or both the chromate treatment equipment and the resin coating equipment are installed in a continuous hot dip galvanizing equipment to carry out continuously.

In this case, the resin coating equipment may be provided separately from the continuous hot dip coating equipment. Alternatively, both the chromate treatment equipment and the resin coating equipment may be provided separately from the continuous hot dip plating equipment.

When the chromate treatment is carried out with a resin-containing chromate treatment liquid, the chromate treatment equipment can be partially modified for use.

[0050]

【Example】

(Example 1) In order to confirm the effect of the present invention, a surface grinding machine equipped with a brush roll was installed on the inlet side of a continuous hot dip galvanizing equipment, and a hot-dip galvanized steel sheet production test was conducted.
As the plating base material, the plate width is 1050 mm and the plate thickness is 0.27
Cold-rolled steel sheets of low carbon Al killed steel in the range of 1.0 mm were used. The amount of grinding of the steel plate surface was changed in the range of 0 to 1.34 μm, the steel plate after surface grinding was inserted into a continuous hot dip coating facility, heated to 750 ° C. in an annealing furnace, and reduction-annealed.
Then, after cooling the plate temperature to 580 ° C. in the furnace, the plate was inserted into a hot dip bath. Plating bath composition is 55% Al-1.5% Si-Zn,
The coating weight was 150 g / m ² or more on both sides. The other manufacturing conditions were standard conditions for passing the equivalent material.

As for the surface appearance quality after plating, the uniformity of the size and shape of the spangle was evaluated using the "spangle uniformity index" proposed by the present inventors. Here, the "spangle uniformity index" is 10 cm x 10
When arbitrarily selecting 10 locations from a steel plate sample of cm and counting the number of spangles that cross a length of 1 cm, "spangle uniformity index" = "maximum count value" / "minimum count value" is defined. If the "spangle uniformity index" is in the range of 1.0 to 1.5, the spangle uniformity is judged to be good.

Tables 1 and 2 show the test conditions and the results.
Further, FIG. 1 shows the relationship between the grinding amount of the steel plate surface and the spangle uniformity index from Table 1.

[0053]

[Table 1]

[0054]

[Table 2]

From FIG. 1, in the embodiment in which the grinding amount of 0.05 μm or more is secured, the spangle uniformity index is
It was in the range of 1.0 to 1.5, the spangle uniformity was secured, and good surface appearance quality was obtained. But 0.05
In the comparative example of less than μm and the conventional example without grinding, the spangle uniformity index exceeded 1.5, the spangle uniformity was not ensured, and good surface appearance quality was not obtained.

(Example 2) Next, when an Al-containing hot-dip galvanized steel sheet under the same conditions as in Experiment Nos. 13, 14, and 15 shown in Table 1 of Example 1 was used as a test sample and subjected to chromate treatment (corresponding ○), when resin is applied after chromate treatment (corresponding ○ mark), and when chromate treatment is performed with a chromate treatment liquid containing resin (corresponding ○ mark), Al-containing melting The appearance of the galvanized steel sheet was visually evaluated. The visual evaluation of appearance was indicated as good (◯) and poor (x).

The chromate treatment liquid had a molar ratio of the hexavalent chromium content to the total chromium content of 0.75.

The amount of chromate deposited is 15 in terms of metallic chromium.
mg / m ² . Acrylic emulsion resin was used as the resin, and the resin adhesion amount was 2.0 g / m ² .

As a comparative example, Al-containing hot-dip galvanized steel sheets under the same conditions as Experiment Nos. 11 and 12 shown in Table 1 of Example 1 were used as test samples.

Table 2 shows the test conditions and the results.

[0061]

[Table 3]

As is clear from Table 3, in the examples of the present invention,
The appearance visual evaluation was good both in the case where the chromate treatment was performed, in the case where the resin was applied after the chromate treatment was performed, and in the case where the chromate treatment was performed using the chromate treatment liquid containing the resin.

However, in the comparative example, the appearance was visually observed in the case where the chromate treatment was performed, the case where the resin was applied after the chromate treatment, and the case where the chromate treatment was performed with the chromate treatment liquid containing the resin. The evaluation was bad.

[0064]

According to the method of the present invention, the non-uniformity of the steel sheet surface is removed by grinding the thickness of 0.05 μm or more per one surface before inserting it into the continuous hot dip plating equipment.
The spangle unevenness is not promoted, the spangle uniformity index is secured in the range of 1.0 to 1.5, and an Al-containing hot-dip galvanized steel sheet with good surface appearance quality can be manufactured.

Further, Al produced as described above is
The surface of the hot-dip galvanized steel sheet containing 20 to 95% by weight was subjected to a chromate treatment, a chromate treatment, and then a resin coating, or a chromate treatment liquid containing a resin. The Al-containing hot-dip galvanized steel sheet produced in some cases retains the uniformity of the spangle pattern formed on its surface in any case,
The surface appearance quality can be maintained satisfactorily.

[Brief description of drawings]

FIG. 1 is a diagram in which a relationship between a grinding amount of a steel plate surface and a spangle uniformity index is investigated.

FIG. 2 is a diagram showing a situation in which a hot-dip galvanized steel sheet is manufactured using a continuous hot-dip galvanizing facility.

[Explanation of symbols]

 1 Steel Plate 2 Annealing Furnace 3 Snout 4 Plating Bath 5 Plating Bath 6 Sink Roll 7 Wiping Nozzle

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Claims (7)

[Claims] 1. The surface of a steel sheet is ground to a thickness of 0.05 μm or more and then inserted into a continuous hot dip coating facility to form a hot dip galvanized coating containing 20 to 95% by weight of Al on the surface of the steel sheet. And a method for producing an Al-containing hot-dip galvanized steel sheet. 2. Produced by the method of claim 1.
A method for producing an Al-containing hot dip galvanized steel sheet, which comprises subjecting a surface of the Al-containing hot dip galvanized steel sheet to a chromate treatment. 3. The Al-containing hot-dip galvanizing according to claim 2, wherein the chromate treatment is performed with a chromate treatment liquid having a molar ratio of hexavalent chromium content to total chromium content of 0.5 or more. Steel plate manufacturing method. 4. The resin according to claim 2 or 3, wherein the resin is applied after the chromate treatment.
Manufacturing method of Al-containing hot-dip galvanized steel sheet. 5. The method for producing an Al-containing hot-dip galvanized steel sheet according to claim 2, wherein the chromate treatment is performed with a chromate treatment liquid containing a resin. 6. A steel sheet surface is ground to a thickness of 0.05 μm or more per side, and then inserted into a continuous hot dip galvanizing facility to form a hot dip galvanized film containing 20 to 95% by weight of Al on the steel sheet surface. An Al-containing hot dip galvanized steel sheet, wherein a chromate film of ² to 100 mg / m ^{2 in} terms of metallic chromium is formed on the surface of the Al-containing hot dip galvanized steel sheet. 7. A steel sheet surface is ground to a thickness of 0.05 μm or more per one surface and then inserted into a continuous hot dip galvanizing facility to form a hot dip galvanized film containing 20 to 95 wt% of Al on the steel sheet surface. On the surface of the Al-containing hot-dip galvanized steel sheet, the total chromate adhesion amount is 2 to 100 in terms of metallic chromium.
An Al-containing hot-dip galvanized steel sheet characterized in that a film containing a resin is formed at a mg / m ² .