JPH11310862A - Method for adjusting spangle of molten zinc-aluminum base coating steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply and surely obtain a target spangle grain diameter by adjusting the temp. of molten coating metal and the dew point at a cooling zone or a snout, etc., according to the deviation between the spangle grain diameter and the target value on molten Zn-Al base coating film having specific composition composed of Al, Si and Zn. SOLUTION: A steel sheet 12 heated in an annealing furnace 11 is dipped into the molten Zn-Al base coating metal 15 held in the plating vessel without contacting with the air in the snout 13 and pulled up after founding around an immersion roll 16. This molten coating metal 15 has the composition, by weight, 0.05-70% Al, 0-7.0% Si and the balance Zn with inevitable impurities. The plated steel sheet 12' obtd. in this process, is cooled in the cooling zone 17. The spangle grain diameter S1 generated on the coating film surface in the process is measured by an optical picture processing method, etc., desirably, as quick as possible after cooling. The S1 is compared with the target value S with a computing element 18 to obtain the deviation |S-S1 |. The temp. of the molten coating metal, the dew point at the cooling zone or the snout, cooling speed, etc., are changed so that this deviation becomes <= a prescribed value K1 >0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a spangle pattern at the time of manufacturing a hot-dip Zn-Al-based plated steel sheet suitable for use in building materials, home appliances, automobiles and the like.

[0002]

2. Description of the Related Art Hot-dip Zn-Al-based plating is performed to improve both the corrosion resistance and the weather resistance of a steel sheet, and its application has been increasing in recent years. Typically, Al content is 0.2%
(In the present specification, "%" means "% by weight" unless otherwise specified.) Less than hot-dip galvanizing, Zn-5% Al alloy plating, Zn-55% Al alloy plating, etc. There is. In the present specification, the Al content is 0.
These are collectively referred to as hot-dip Zn-Al-based alloy plating, including hot-dip galvanized that is less than 2%.

[0003] In particular, Zn-55% Al alloy-plated steel sheet is a high-performance plated steel sheet having the durability, heat resistance, and heat reflection properties of aluminum and the sacrificial corrosion resistance of zinc, which are used in building materials, home appliances, and the like. Is widely used for automobile parts and the like. Such a plated steel sheet is typically made of Al: 55
%, Zn: 43.4% and Si: 1.6%. The ratio between Al and Zn is determined in consideration of corrosion resistance, and Si is added in order to suppress an alloying reaction with a steel substrate that inhibits plating adhesion.

[0004] Unlike other Zn-Al alloy-plated steel sheets having a low Al content, this Zn-55% Al alloy-plated steel sheet has a characteristic silver-white spangle pattern on the plating surface, and is made of a fabric due to its design. As it is, it is widely used for roofs and walls of commercial and industrial buildings and general-purpose buildings, or for fixtures and the like.

[0005] The particle size of spangles on the plating surface of a Zn-55% Al alloy-plated steel sheet varies depending on the hot-dip plating conditions, particularly the solidification rate after hot-dip plating, but is generally about 0.8 mm or more on average. The spangle pattern can be visually identified.

[0006] In particular, in recent years, a melt having a spangle pattern
Zn-Al-based alloy-plated steel sheets tend to be used for outer panel panels and the like, and many of them are easily seen by the public.
When delivering products, there is an increasing need to control the size of the spangle pattern.

In general, the spangle particle size of a hot-dip Zn—Al alloy-plated steel sheet becomes smaller when the cooling rate, that is, the solidification rate of the plating film, is increased by increasing the air volume during forced cooling after hot-dip plating, and conversely. It is known that the air volume increases when the air volume is reduced. However, only the forced cooling using the atmosphere has a limited effect on the spangle particle size, and to control the spangle particle size above or below it must be performed by another means. In particular, the following method is generally known in order to make the particle size smaller than the spangle particle size obtained by forced cooling using the atmosphere.

[0008] That is, there is a method of eliminating a spangle pattern by performing skin pass reduction after the plating film is solidified. However, when the spangle is erased by this method, the appearance deterioration due to the remaining spangle and the appearance unevenness after painting are reduced. Easy to occur. In addition, there are also problems that a flaw is generated due to the plating film being picked up by the skin pass roll, and that a spangle pattern easily emerges during press working by a user.

Furthermore, a technique of spraying solid or liquid fine particles onto an unsolidified plating surface immediately after plating of a hot-dip coated steel sheet to uniformly generate a large number of solidification nuclei, and rapidly cooling to refine a spangle pattern. Have also been proposed. Particularly, for hot-dip aluminized steel sheets, see, for example, JP-A-50-38638 and JP-A-63-1432.
No. 49, and further disclosed in JP-A-63-153255.

According to this method, the average spangle particle size of the plating surface of the Zn-55% Al alloy-coated steel sheet is 0.8
Although it can be smaller than mm, the problems such as the brittleness of the plating film and the aging deterioration of the base material itself due to the rapid cooling cannot be solved yet. Further, in order to carry out this method, it is necessary to add an apparatus for spraying fine particles to a conventional hot-dip plating equipment, which increases the cost. On the contrary, in order to increase the spangle particle size, it is necessary to replace the spraying device with the air-cooling zone, which causes a large loss in time.

Japanese Patent Application Laid-Open No. 59-56570 discloses that a molten metal having an extremely fine spangle and excellent corrosion resistance can be obtained by adding 3 to 15% of Si and 3 to 20% of Mg to a plating bath. An invention for producing a Zn—Al-based alloy-plated steel sheet is disclosed. However, with this plated steel sheet, a relatively large amount of Si
Since Mg and coexist in the plating film, there is a problem that workability is deteriorated due to precipitation of Si and Mg in the film. Conversely, to increase the spangle particle size,
It is necessary to reduce the Mg concentration in the plating bath, which causes a loss in time and a loss in production volume.

Further, as disclosed in JP-A-9-25550 and JP-A-9-235661, the uniformity of spangles is improved by controlling the gas atmosphere in the snout and performing surface grinding of the base steel plate. Although methods are also disclosed, these methods are merely methods for suppressing the variation of spangles, and are not control methods for changing the size of spangles. Therefore, even with this proposal, the spangle particle size cannot be kept at a desired value.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming a target spangle grain by simple means without the presence of other elements such as Mg in the plating film and without spraying fine particles. Molten Zn-Al that can reliably obtain the diameter
An object of the present invention is to provide a method for adjusting spangle of a system-plated steel sheet. Another object of the present invention is to provide a method for adjusting spangles of a hot-dip Zn-Al-based alloy-plated steel sheet that enables automation.

[0014]

In order to solve the above-mentioned problems, the present inventor always measures the spangle particle size after plating at an on-line or off-line position, and compares the result with the production conditions of a plated steel sheet. Focusing on the fact that the spangle particle size can be brought closer to the target particle size in a short time by feeding back to the change system of the above, the manufacturing conditions that contribute to the spangle particle size other than air cooling were examined.

Incidentally, hot-dip Zn-Al-based alloy-plated steel sheets are generally produced by a conventional continuous hot-dip galvanizing equipment used for hot-dip galvanizing. In a typical continuous hot-dip coating equipment, a base material steel sheet (cold-rolled steel sheet or hot-rolled steel sheet) annealed in a continuous annealing furnace is immersed in a hot-dip plating bath via a snout without exposure to the atmosphere, and then exits the plating bath. Immediately afterward, control the desired amount of plating by gas wiping,
Temperature at which solidification is completed in a cooling zone (usually air cooling) (Zn-55%
After cooling to about 370 ° C. or less for Al alloy plating), if necessary, lightly roll it down with a leveler or skin pass roll and wind it up.

The present inventors have conducted intensive studies on means for controlling the spangle pattern of a hot-dip Zn—Al alloy plating film by directly using such a conventional continuous hot-dip plating facility. : 0.05-70%, Si:
When the composition is 0 to 7.0%, the balance being Zn and unavoidable impurity elements, immediately after the plated steel sheet passes through the cooling zone,
For example, if the spangle particle size is measured by means of online image processing as shown in Japanese Patent Application No. 10-24910, the time lag can be minimized as much as possible even in the case of feedback control. As a result, it was found that not only the cooling rate in the cooling zone, but also the plating bath temperature and the dew point of the cooling zone or snout could be used as control factors to control the spangle particle size. It has been found that the degree of influence and the responsiveness become smaller in the order of the cooling rate, the plating bath temperature, and the dew point of the cooling zone or snout, and by appropriately combining these controls, the average spangle particle size becomes the desired value. The present inventors have found that it is possible to form a plating film within the range, and have completed the present invention.

Certainly, regarding the spangle pattern, even in the prior art, when winding the steel sheet after plating, it is necessary to confirm the spangle pattern just before winding, and then change the cooling condition of the cooling zone. Is being done. However, in such a conventional method, there is a large time lag for the adjustment of the spangle pattern, there is a risk of producing a large amount of spangle patterns far from the target, and the adjustment of the spangle pattern can be adjusted in a relatively short time. Since the use of only cooling is limited, the adjustment width of the spangle pattern becomes very small. In fact, it cannot be said that the spangle pattern is controlled.

Here, the present invention relates to the following: Al: 0.05-70%, Si:
A hot-dip Zn-Al-based plating bath having a composition of 0 to 7.0%, with the balance being Zn and unavoidable impurity elements, is subjected to hot-dip plating by continuously intruding a steel sheet through a snout into a hot-dip Zn-Al plating bath. Cooled by a cooling device having a cooling zone arranged above the system plating bath, the molten Zn-Al
For producing a deviation | S ₁ | between a spangle particle size S ₁ generated on the surface of a plating film of a plated steel plate and its target particle size S when producing a galvanized steel sheet, and a deviation | S−S
₁ | is less than or equal to a predetermined value K ₁ (where 0 <K ₁ ), the production of the plated steel sheet is continued as it is, and the deviation | SS ₁
| Is when exceeding a predetermined value K _1, by changing any one of a plating bath temperature, and dew point of the cooling zone or snout of the molten Zn-Al-based plating bath, the deviation | S-S ₁ | a predetermined value melt, characterized in that it comprises a K ₁ less Zn-
This is a spangle adjustment method for Al-based plated steel sheets.

In the method for adjusting the spangle of a hot-dip Zn-Al-based plated steel sheet according to the present invention, the feedback control includes a step of measuring the spangle particle size S ₁ as soon as possible after cooling. Is also desirable because the time lag can be made substantially negligible.

In the method for adjusting the spangle of a hot-dip Zn—Al-based coated steel sheet according to the present invention, the deviation | SS ₁ |
There when exceeding a predetermined value K ₁ + K ₂ (provided that _{0 <K 2 <K 1)} , varying the plating bath temperature in addition to the cooling rate after plating, the deviation | S-S ₁ | a predetermined value K ₁ + K ₃
(However, when 0 <K ₃ <K ₁ ), the deviation | S−S is obtained by changing the dew point of the cooling zone or snout in addition to the cooling rate after plating.
It is desirable that ₁ | be equal to or less than a predetermined value K ₁ .

Furthermore, the molten Zn-
In the spangle adjustment method for Al-based plated steel sheet, the deviation | S-
S ₁ | is a predetermined value K ₁ + K ₂ + K ₃ (where 0 <K ₂ <K
When exceeding ₁ ), the cooling rate after plating is controlled, and the grinding amount of the strip surface is reduced to, for example, 0.2 g / m ^{2 in} the step before the strip enters the molten Zn-Al-based plating bath.
By making the above change, the deviation | S−S ₁ | is set to be equal to or less than the predetermined value K _{1. Since} the deviation | S−S ₁ | is large, the cooling rate after plating, the plating bath temperature, and the cooling zone Alternatively, it is effective when the target particle size S cannot be obtained even when the dew point of the snout is changed.

Here, the target spangle particle size S is
For example, assumed to be the average particle diameter of 0.8 mm, the predetermined value K ₁ is 0.
The 3 mm, the predetermined value K ₂ is 0.2 mm, and a predetermined value K ₃ is zero.
15 mm can be exemplified.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. FIG. 1 is a schematic explanatory view of a hot-dip Zn—Al-based plating line 10 for performing a spangle adjusting method according to the present invention.

In FIG. 1, a steel plate (strip) 12 preheated in an annealing furnace 11 passes through a snout 13 without being exposed to the atmosphere, and is exposed to a molten Zn—Al
System, continuously penetrates into the plating bath 15, is immersed in the plating bath 15, is immersed in the plating bath 15, and is pulled out of the plating bath to be a plated steel sheet 12 ′. Then, the plating film is cooled, forms a predetermined spangle pattern, and is sent to a subsequent winding step (not shown) to be wound around a coil.

Here, according to a preferred embodiment of the present invention, the spangle particle size S ₁ is measured off-line or on-line at the time of leaving the cooling zone 17. The data S _{1 at} this time is
It is sent to the arithmetic unit 18 and compared with data S such as the target spangle particle diameter which is input in advance, and the deviation | S-S ₁
| Is required.

In the present invention, (1) the plating bath temperature of the hot-dip Zn—Al-based plating bath 15 and the dew point of the cooling zone 17 or the snout 13 based on the obtained deviation | SS ₁ | (2) Plating bath temperature in addition to cooling rate after plating, (3) Cooling zone in addition to cooling rate after plating
17 or the dew point of the snout 13 and (4) the cooling rate after plating is controlled, and the molten Zn-Al-based plating bath 15
A control signal c for changing the amount of grinding of the surface of the steel sheet 12 in a process before the steel sheet 12 enters the apparatus is output to each device.

As a result, the cooling power for the steel sheet 12 'by the cooling device having the cooling zone 17 is changed, and the spangle diameter of the plated steel sheet 12' at the time of exiting the cooling zone 17 is controlled so as to approach the target value. You.

(Plating Film and Plating Bath Composition) According to the present invention, the composition of the plating bath 15 is as follows: Al: 0.05 to 70%, Si: 0
~ 7.0%, with the balance being Zn and unavoidable impurities. The composition of the plating film obtained is substantially the same as the composition of the plating bath 15.

Al: 0.05 to 70% In the present invention, the Al content of the plating bath 14 is limited to 0.05% or more and 70% or less. If the Al content is less than 0.05%, Zn in the Zn plating bath of the steel sheet 12, which is the base material, tends to alloy in hot-dip galvanizing, and the workability deteriorates. On the other hand, if the Al content exceeds 70%, the Al-rich phase increases, so Zn
The sacrificial corrosion resistance of the steel decreases, and the corrosion resistance decreases again. Therefore, in the present invention, the Al content is limited to 0.05% or more and 70% or less. From the same viewpoint, the Al content is 0.10% or more and 0.20% or more.
% Or less, or 40% or more and 60% or less.

Si: 0-7.0 Si is brittle Fe- formed at the interface between the plating film and the steel sheet 12.
It has been conventionally added to a Zn-Al-based alloy plating bath in order to suppress the development of the Al alloy layer. As mentioned above, Zn-55%
Al alloy hot-dip plating usually contains about 1.6% of Si for this purpose. In the present invention, the Si content is limited to 0 to 7.0% for the following reasons.

In hot-dip Zn plating, Si is not necessary because Al suppresses the development of the Fe—Zn alloy layer. Conversely, when Si is added, the plating bath temperature is lower than that in the case of Zn-55% Al alloy plating, which causes plating defects such as non-plating. On the other hand, in Zn-Al based alloy plating containing high Al, it is appropriate to mix the Si concentration by 2.0 to 7.0% by weight with respect to Al.

For example, in a Zn-55% Al-based alloy plating, the proper amount of Si is 2 to 4%. If it is less than 2%, the brittle Fe-Al alloy layer abnormally develops as described above, which adversely affects workability. On the other hand, if it exceeds 4%, the alloy layer becomes extremely thin, and a large amount of Si needle-like precipitates precipitate in the plating film, thereby deteriorating workability.

Therefore, in the present invention, the Si content is limited to 0% or more and 7.0% or less. From the same viewpoint, the Si content is preferably 0 to 5.0%. In the present invention,
In the case of hot-dip Zn plating, the content of Si is desirably about the unavoidable mixing amount, and in the case of high Al-Zn alloy plating, it is desirable that the Al concentration is 2.0% or more and 3.5% or less.

(Measurement of spangle particle size) Al content of 40 to 70
% Of the Zn—Al-based alloy plating film is a region surrounded by Al-rich primary dendrite crystals (Al primary dendrite crystals) extending from nuclei during solidification. Therefore, in the present invention, the diameter of this region is spangle diameter S _1. The secondary dendrite crystal extends from the primary dendrite crystal.

In the present invention, the measurement of the spangle particle size S _{1 at} the time when the steel sheet leaves the cooling zone 17 is carried out immediately after the plated steel sheet 12 ′ has passed through the cooling zone 17 when measuring offline.
For example, by using an online image processing means (not shown) as shown in Japanese Patent Application No. 10-24910, for example,
It is measured by measuring the number of spangles over a certain distance (for example, 100 mm) using a magnified image of the surface (for example, 3 times magnification) or a magnified image of 2 '. diameter S ₁ is, is calculated soon as possible a period after cooling.

The on-line image processing means disclosed in Japanese Patent Application No. 10-24910 is simply described as capturing an image by taking in only the reflected light from spangles when the plating surface is irradiated with light from a light source. Image processing means for reading the density of each spangle and calculating the average spangle diameter from the particle size distribution with the enlarged still image, and in the enlarged still image, the background of the imaging region is substantially black and only the spangle is substantially Extracted as white. This image processing means, by measuring the spangles diameter S _1, even the feedback control may be as much as possible minimized to the extent that virtually ignore the time lag. Therefore, in addition to the cooling rate in the cooling zone 17 that has been used so far, the plating bath temperature and the dew point of the cooling zone 17 or the snout 13 can also be used as control factors for adjusting the spangle particle size S _1. And

On the other hand, in order to measure the spangle particle size S ₁ at the time of leaving the cooling zone 17 on-line, the average particle size of the spangle surrounded by the dendrite structure is measured by, for example, an optical image processing device (not shown). may be measured such as by measuring the diameter S _1. In addition, the measurement position may be fixed at a certain width position in the width direction of the plated steel sheet 12 ′, may be scanned, or the plated steel sheet 12 ′ may be scanned.
Can be measured as long as the plating layer is solidified and wound up. Desirably, the closer to the solidification position of the plating film, the earlier the feedback to the operation condition change can be made, and the time lag of the feedback control can be minimized, which is effective.

As described above, in the preferred embodiment of the present invention, the spangle particle size S ₁ is measured immediately after the plated steel sheet 12 ′ has passed through the cooling zone 17 and as soon as possible. Thus, the spangle particle size S ₁ measured after cooling.
Is input to an operation system having an arithmetic unit 17 or the like, thereby obtaining a deviation | S−S ₁ | from a target spangle particle size S.
, And according to the magnitude of this deviation | S−S ₁ |
The operating condition is automatically changed by outputting a control signal c from the arithmetic unit 17 to each device, and the measured spangle particle size S
_{The value 1} is converged to the target spangle particle size S.

Deviation from target spangle particle size S | S
-S ₁ | While various some as production conditions to adjust the spangles diameter S ₁ to 0, in the present invention, the influence on spangle diameter S _1, in particular, (1) melting Zn-Al
One of the plating bath temperature of the system plating bath 15 and the dew point of the cooling zone 17 or the snout 13, (2) the plating bath temperature in addition to the cooling rate after plating, and (3) the cooling rate after plating. , Cooling zone 17 or snout 13 dew point, and even
(4) While controlling the cooling rate after plating,
In the process before the steel sheet 12 enters the Al-based plating bath 15,
The amount of grinding on the surface of each is changed.

That is, the degree of influence on the spangle particle size S ₁ is smallest for one of the plating bath temperature and the dew point of the cooling zone 17 or the snout 13. The temperature, the cooling rate after plating, and the dew point of the cooling zone 17 or the snout 13 are substantially equal, and furthermore, the cooling rate after plating, and the steel sheet 12 intruding into the molten Zn-Al-based plating bath 15 In this case, the grinding amount of the surface of the steel plate 12 is the largest in the process before the grinding.

Therefore, in the present invention, the target spangle particle size S is obtained by using any of the above control factors (1) to (4) according to the magnitude of the deviation | S−S ₁ |.
Can always be realized quickly regardless of the magnitude of the deviation | S−S ₁ |.

Here, the reason for changing these manufacturing conditions in the present invention will be described in detail for each condition.

(Plating Bath Temperature of Plating Bath 15) The spangle particle size S ₁ is controlled by changing the temperature of the plating bath 15. However, when the temperature of the plating bath 15 increases, the interface between the steel sheet 12 and the plating layer increases. The alloy layer formed in the first layer tends to grow non-uniformly, and as a result, the dendrite growth of Al is hindered, and the spangle diameter is reduced. Further, in order to cool start temperature (the strip temperature) is higher after plating, nucleation is increased at the time of air cooling, spangle diameter S ₁ is decreased.

Conversely, when the temperature of the plating bath 15 decreases, the alloy layer formed at the interface between the steel sheet 12 and the plating layer grows relatively thinly and uniformly, so that the Al dendrite growth proceeds smoothly, and the spangle grains grow. diameter S ₁ is increased.

The temperature of the plating bath 15 is changed in the range of 585 to 620 ° C., preferably in the range of 590 to 610 ° C. If the temperature of the plating bath 15 exceeds 620 ° C., the alloy layer formed at the interface between the steel sheet 12 and the plating layer becomes too thick, which adversely affects workability. Further, the evaporation amount of Zn in the snout 13 increases, and the Zn may aggregate on the inner wall surface of the furnace and adhere to the surface of the steel sheet 12 before the plating bath 15 enters, thereby causing defects such as non-plating.

On the other hand, when the temperature of the plating bath 15 is lower than 585 ° C., the solidification temperature of the plating bath 15 is approached (570 ° C.), and the reactivity of the plating bath 15 with the interface with the steel sheet 12 is significantly reduced. Adhesion deteriorates. Further, the viscosity of the plating bath 15 also increases, and the surface properties deteriorate.

By adjusting the plating bath temperature of the plating bath 15, in the case of the present invention, the target (for example, the average particle diameter: 0.1.
8mm) can be changed to a spangle diameter of about ± 0.2mm.

(Dew point in cooling zone 17 or snout 13) By changing the dew point in cooling zone 17 or snout 13, a new thin oxide film is newly formed on the surface of reduced steel sheet 12 or plated steel sheet 12 '. And control its thickness.

If the dew point is high, the thickness of the oxide film having micropores formed on the surface of the reduced steel sheet 12 or the plated steel sheet 12 'becomes large, and as a result, an oxide film formed at the interface between the steel sheet 12 and the plating layer is formed. The crystal of the alloy layer becomes small, the Al dendrite growth becomes smooth, and the spangle particle size S
₁ increases. On the other hand, if the dew point is low,
12 or the plated steel sheet 12 ', and as a result, due to the difference in the reactivity between the ferrite grain boundaries and the intragranularity of the steel sheet 12, the alloy layer is unevenly formed, and the dendrite growth of Al is hindered. And the spangle particle size S ₁ becomes smaller.

The range of the dew point to be changed is from -15 ° C to -75 ° C.
And preferably -20 ° C to -70 ° C. Dew point is -15
If the temperature is higher than 0 ° C., the oxide film formed on the surface of the steel sheet 12 becomes too thick, which causes non-plating and an increase in top dross. On the other hand, if the dew point is lower than −75 ° C., the amount of Zn evaporated from the bath surface in the snout 13 increases, and the Zn is agglomerated on the furnace inner wall surface,
It may adhere to the steel sheet 12 before entering the plating bath 15 and induce defects such as non-plating.

By adjusting the dew point in the cooling zone 17 or the snout 13, in the case of the present invention, it is possible to change a spangle particle size of about ± 0.3 mm from a target (for example, an average particle size: 0.8 mm). it can.

(Cooling Rate after Plating) The spangle particle size S ₁ is controlled by changing the cooling rate after plating.
Used as it is as 17. Therefore, to increase the cooling rate after plating, the amount of air in the cooling zone 17 may be increased, and to decrease the cooling rate, the amount of air may be reduced. The cooling capacity of the cooling zone 17 depends on the blowing capacity of the cooling equipment, the distance between the plated steel sheet 12 ', the length, and the like.
It depends on the temperature, thickness, and speed of the plated steel sheet 12 'passing therethrough. During operation, since the conditions such as the thickness and the passing speed of the plated steel sheet 12 'are liable to change, the cooling zone 17 is a facility capable of obtaining a cooling rate of about 30 ° C./s within the operable range. It is desirable that

However, when the cooling rate of the plated steel sheet 12 ′ after plating exceeds 25 ° C./s, it is difficult to reduce the diameter of the spangle (see FIG. 2 described later), and the hardness of the plating itself increases due to rapid cooling. As a result, the workability is deteriorated, and the equipment is enlarged, leading to an increase in cost. Therefore, the capacity of the cooling zone 17 is desirably 25 ° C./s or less.

In such a range of the cooling rate, the spangle particle size capable of rapidly and effectively changing the spangle particle size S ₁ is a target (for example, an average particle size: 0.8 m).
m) is about ± 0.3 mm. Therefore, within ± 0.3 mm of the target spangle particle size, it is effective to control the spangle particle size by adjusting the air volume of the cooling zone 17, which can quickly and effectively change the spangle particle size.

(Amount of Grinding of Surface of Steel Plate 12) Changing the amount of grinding of the surface of steel plate 12 generates a uniform reaction active surface of the surface layer of steel plate 12 and increases the reaction area.

Therefore, an alloy layer at the interface between the steel sheet 12 and the plating layer is uniformly formed, the Al dendrite grows smoothly, and the spangle diameter S ₁ increases. here,
The range of the amount of grinding of the surface of the steel plate 12 to be changed is 0.2 g / m ² or more, preferably 0.5 g / m ² or more and 14 g / m ² or less.
When the grinding amount is smaller than 0.2 g / m ² , the effect of increasing the spangle particle size S ₁ is small because the active surface of the surface appears unevenly on the contrary. When the grinding amount is more than 14 g / m ² , the influence on the spangle particle size S ₁ is reduced, and
The decrease in the thickness of the steel plate 12 is not negligible, and the cost of the grinding brush and the like is increased.

According to the present invention described in detail above, the target spangle particle size can be reliably determined by a simple means without the presence of other elements such as Mg in the plating film and without spraying fine particles. The present invention can provide a method for adjusting the spangle of a hot-dip Zn-Al-based plated steel sheet that can be obtained at a high temperature. In carrying out this method, automatic control can be performed as shown in FIG.

[0058]

[Example 1] In this example, in a continuous hot-dip plating line 10 shown in FIG. 1 having a molten 55% Al-Zn bath 15, a hot-dip galvanizing method having a coating weight per side of 75 mg / m ² was used. After plating, the steel plate 12 having a line speed of 90 m / min was changed at a cooling speed of 15 to 25 ° C./s in a cooling zone 17 and measured to a target spangle particle size Smm (0.8 mm) after plating. and regulatory control than information spangle diameter S _1. In this example,
The resulting spangle particle size S ₁ is K ₁ ≦ | S−S ₁ |
(However, K ₁ = 0.3 mm).

FIG. 2 is a graph showing the results. In FIG. 2 and FIGS. 3 to 5 to be described later, a solid line indicates an example of the present invention in which the cooling capacity of the cooling device is controlled, and a dashed line indicates a conventional example in which the cooling capacity is not controlled. From FIG. 2, it can be seen that according to the example of the present invention, the spangle particle size S
The control accuracy of ( ₁ ) was improved, and it was possible to substantially approach the target spangle particle size S.

Example 2 In this example, a molten 55% Al-Zn bath 15
In the continuous hot-dip coating line 10 shown in FIG. 1, hot-dip galvanizing with a coating weight per side of 75 mg / m ² is performed, and then the steel sheet 12 having a line speed of 90 m / min is cooled in the cooling zone 17. changing at a rate 15-25 ° C. / s, further to a target spangle diameter Smm (0.8 mm), and regulatory control than the measured spangle diameter S ₁ of the information after plating. In addition,
In this example, the obtained spangle diameter S ₁ is K ₁ + K ₂ ≦
| S−S ₁ | (K ₁ = 0.3 mm, K ₂ = 0.2 mm).

The results are summarized in a graph in FIG. From FIG. 3, in comparison with the conventional example, according to the example of the present invention, the control accuracy of the spangle particle size S ₁ was improved, and the spangle particle size S could be made much closer to the target spangle particle size S.

Example 3 In this example, a molten 55% Al-Zn bath 15
In the continuous hot-dip coating line 10 shown in FIG. 1, hot-dip galvanizing with a coating weight per side of 75 mg / m ² is performed, and then the steel sheet 12 having a line speed of 90 m / min is cooled in the cooling zone 17. with changing at a rate 15-25 ° C. / s, by changing the dew point of the snout 13, the spangle diameter S of the target, and regulatory control than the measured spangle diameter S ₁ of the information after plating. In this example, the spangle diameter S ₁ obtained is K ₁ + K ₃ ≦ | S−S ₁ | (K ₁ = 0.3 mm, K ₃
= 0.15mm).

The results are shown in a graph in FIG. From FIG. 4, in comparison with the conventional example, according to the example of the present invention, the control accuracy of the spangle particle size S ₁ was improved, and it was possible to bring the spangle particle size S much closer to the target.

Example 4 In this example, a molten 55% Al—Zn bath 15
In the continuous hot-dip galvanizing line 10 shown in FIG. 1, hot-dip galvanizing with a coating weight per side of 75 mg / m ² is performed, and then the steel sheet 12 having a line speed of 90 m / min is cooled in a cooling zone 17. At a speed of 15-25 ° C / s, the steel plate
Varying the grinding amount with respect to 12, the spangle diameter S of the target, and regulatory control than the measured spangle diameter S ₁ of the information after plating. In this example, the spangle diameter S ₁ obtained is K ₁ + K ₂ + K ₃ ≦ | S−S ₁ | (K ₁ = 0.
3 mm, K ₂ = 0.2 mm, K ₃ = 0.15 mm).

The results are shown in a graph in FIG. As can be seen from FIG. 5, according to the example of the present invention, the control accuracy of the spangle particle size S ₁ was improved, and the target spangle particle size S could be made much closer to the target, as compared with the conventional example.

[0066]

According to the present invention, the conventional continuous hot-dip galvanizing equipment can be used without modification, without deteriorating the workability and corrosion resistance, and the spangles of the hot-dip Zn-Al-based alloy-plated steel sheet targeted at the time of production. It becomes possible to obtain a pattern.

This plated steel sheet has excellent corrosion resistance typified by a Zn-55% Al-based alloy-plated steel sheet, good workability to withstand severe bending, and has a high design appearance. Therefore, it can be used for building materials, home appliances, and other objects without being painted. Further, since the spangle pattern is uniform, it is most suitable for exterior panels such as building materials and home appliances without any painting.

[Brief description of the drawings]

FIG. 1 is a skeleton diagram of a continuous hot-dip plating line to which the present invention is applied.

FIG. 2 is a graph showing a spangle control effect according to the first embodiment together with a comparative example.

FIG. 3 is a graph showing a spangle control effect according to a second embodiment together with a comparative example.

FIG. 4 is a graph showing a spangle control effect according to a third embodiment together with a comparative example.

FIG. 5 is a graph showing a spangle control effect according to a fourth embodiment together with a comparative example.

Claims (6)

[Claims] 1. A steel sheet is continuously introduced through a snout into a hot-dip Zn-Al-based plating bath having a composition comprising Al: 0.05 to 70% by weight, Si: 0 to 7.0% by weight, balance Zn and unavoidable impurity elements. When the hot-dip galvanized steel sheet, and cooled by a cooling device having a cooling zone disposed above the hot-dip Zn-Al-based plating bath, when manufacturing a hot-dip Zn-Al-based steel sheet, Determining a deviation | S−S ₁ | between the spangle particle size S ₁ generated on the surface of the plating film of the plated steel sheet and the target particle size S; and the deviation | S
When −S ₁ | is equal to or less than a predetermined value K ₁ (where 0 <K ₁ ), the production of the plated steel sheet is continued as it is, and the deviation | S
−S ₁ | exceeds the predetermined value K ₁ , the molten Zn
-By changing one of the plating bath temperature of the Al-based plating bath, and the dew point of the cooling zone or the snout,
A method for adjusting the spangle of a hot-dip Zn-Al-based plated steel sheet, comprising the step of making the deviation | S-S ₁ | less than or equal to the predetermined value K ₁ . 2. A further spangle method of adjusting the melting Zn-Al-based plated steel sheet according to claim 1 further comprising the step of measuring the spangles diameter S ₁ to soon as possible a period after cooling. 3. The deviation | S−S ₁ | is a predetermined value K ₁ + K
₂ (where 0 <K ₂ <K ₁ ), the deviation | S−S ₁ | is set to the predetermined value K ₁ or less by changing the plating bath temperature in addition to the cooling rate after plating. Item 3. The method for adjusting spangles of a hot-dip Zn-Al-based plated steel sheet according to claim 1 or 2. 4. The deviation | S−S ₁ | is a predetermined value K ₁ + K
₃ (where 0 <K ₃ <K ₁ ), the deviation | S−S ₁ | is set to the predetermined value by changing the dew point of the cooling zone or the snout in addition to the cooling rate after plating. spangle adjusting method according to claim 1 or molten Zn-Al-based plated steel sheet according to claim 2, wherein a value K ₁ or less. 5. The deviation | S−S ₁ | is a predetermined value K ₁ + K
₂ + K ₃ (provided that 0 <K ₂ <K ₁₎ When more than controls the cooling rate after plating, the molten Zn-Al
By changing the grinding amount of the strip surface in a process before the strip enters the plating bath, the deviation | S
5. The method for adjusting a spangle of a hot-dip Zn—Al-based steel sheet according to claim ₁ , wherein −S ₁ | is equal to or less than the predetermined value K ₁ . 6. The method according to claim 5, wherein the amount of grinding is changed to 0.2 g / m ² or more.