JP3219035B2 - Manufacturing method of hot-dip Zn-Al-based alloy plated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-dip Zn-Al-based alloy-plated steel sheet having a beautiful spangle particle size on the surface.

[0002]

2. Description of the Related Art Hot-dip Zn-Al alloy plating is performed to improve the corrosion resistance and weather resistance of a steel sheet as a plating base material. In recent years, the production of hot-dip Zn-Al-based alloy plated steel sheets on which the hot-dip Zn-Al-based alloy plating has been performed has been increasing. As a typical example, a Zn-55% Al alloy-plated steel sheet (in this specification, unless otherwise specified, "%"
Means “% by weight”. )It has been known.

[0003] This Zn-55% Al alloy-plated steel sheet is a high-performance plated steel sheet having the durability, heat resistance, and heat reflection properties of Al and the sacrificial corrosion protection of Zn, for example, for building materials, home appliances, and the like. Is widely used in automobiles and the like.

[0004] A Zn-55% Al alloy-plated steel sheet is typically manufactured using a hot-dip plating bath composed of 55% Al, 43.4% Zn, and 1.6% Si. The content of each of Al and Zn in the hot-dip plating bath is determined in consideration of corrosion resistance, and the content of Si is determined in consideration of suppression of alloy reaction with a steel base material that inhibits plating adhesion.

[0005] In particular, a Zn-55% Al alloy-plated steel sheet is different from other Zn-Al-based alloy-plated steel sheets having a low Al content.
A characteristic silver-white color with an average particle size of 0.5 on the plating surface
It has a spangle of a size that can be visually identified as ~ 1.5 mm, and because of its design, it is widely used for roofs and walls of commercial and industrial buildings and general buildings, as well as for objects. I have.

In the spangle, when Zn is solidified, a supercooling phenomenon occurs due to an element which lowers the solidification point of Zn among the trace elements contained in Zn, and dendritic crystals grow around the solidification nucleus. In the process, it is considered that this occurs because the crystal grows while maintaining the molten state until the end. Based on this spangle generation mechanism, it is known that the particle size of spangles decreases when the cooling rate (that is, the solidification rate of the plating film) is increased by increasing the airflow during forced cooling after hot-dip plating. I have.

However, in an actual production line, the hot rolling conditions and the cold rolling conditions for the plating base material are not constant. And even in the same plated steel sheet, it is not constant in the width direction and the longitudinal direction, and varies to such an extent that it can be visually identified. As described above, simply adjusting the solidification rate after hot-dip plating cannot obtain a beautiful spangle uniformly so as not to be visually discerned.

However, there is an extremely strong demand from users to make the particle diameter of spangles uniform, and in recent years, Zn-55%
This was a major issue for Al alloy plated steel sheets. JP-A-8-49055 discloses that a plating bath contains 0.001 to 0.5%
It has been proposed to further refine the spangle by adding a small amount of Ti.

[0009]

In order to carry out the invention proposed in JP-A-8-49055, it is necessary to use a Ti
It is necessary to increase the content. However, it is difficult to adjust the component concentration of the plating bath in a short time in an actual plating tank, and a certain amount of time is required.
Therefore, it is extremely difficult to quickly and accurately cope with the variation in spangle particle size that occurs in each of the width direction and the length direction in each of the plated steel sheets or the same plated steel sheet during the component concentration adjustment. Therefore, even with this proposal, a beautiful spangle cannot be obtained uniformly to such an extent that it cannot be visually identified.

An object of the present invention is to provide a molten Zn—Al alloy that can make the grain size of spangles uniform for each plated steel sheet or for each part in the width direction and the longitudinal direction of the same plated steel sheet so as not to be visually discerned. An object of the present invention is to provide a method for producing a base alloy plated steel sheet.

[0011]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies using a plating base material having a surface roughness Ra of 0.5 μm or less. As a result, continuous annealing before plating was performed. The hot-dip Zn-Al-based alloy plating with uniform grain size and beautiful spangles by heating the plating base material to 600 ° C or higher with the combustion air ratio of the oxidation zone being 0.95 to 1.30 and annealing in a reducing atmosphere It has been found that a steel sheet can be manufactured. The present inventors have further studied based on this finding, and as a result, completed the present invention.

[0012] Here, the gist of the present invention is that the plating base material is treated by a continuous annealing furnace so that the combustion air ratio of the oxidation zone is reduced.
After heating to 600 ° C. or higher at 0.95 to 1.30 and annealing in a reducing atmosphere, hot-dip plating is performed in a plating bath consisting of Al: 40 to 70%, Si: 0.5 to 2.0%, and the balance of Zn. This is a method for producing a hot-dip Zn-Al-based alloy-plated steel sheet, which is characterized by producing a plated steel sheet having a uniform diameter.

[0013] The "combustion air ratio" in the method for producing a hot-dip Zn-Al-based alloy-coated steel sheet according to the present invention is a ratio of an actual air amount actually used to a theoretical air amount necessary for complete combustion. And is calculated from the actual air amount / theoretical air amount.

In the method for producing a hot-dip Zn—Al-based alloy-coated steel sheet according to the present invention, “grain size” means an average grain size, for example, the number of spangles per unit length. Is calculated by counting.

The term “uniform” in the above-described method for producing a hot-dip Zn—Al-based alloy-coated steel sheet according to the present invention means uniformity that cannot be visually identified. It is exemplified that the deviation σ is 0.15 mm or less.

In the method for producing a hot-dip Zn—Al-based alloy-coated steel sheet according to the present invention, the surface roughness Ra of the base metal is
0.5 μm or less is desirable in order to increase the uniformity of the spangle particle size.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The molten Zn-Al according to the present invention
An embodiment of a method of manufacturing a system alloy plated steel sheet will be described in detail in the order of steps.

(1) Continuous Annealing Step The plating base material is charged into a continuous annealing furnace, heated to 600 ° C. or more at a combustion air ratio of the oxidation zone of 0.95 to 1.30, and annealed in a reducing atmosphere.

The components and manufacturing conditions of the plating base material may be those generally used for plated steel sheets, and are not particularly limited. Examples of the plating base material include a low-carbon aluminum killed steel sheet and an extremely low-carbon steel sheet.

The surface roughness Ra of the plating base material is desirably 0.5 μm or less. If the surface roughness Ra is more than 0.5 μm, the unevenness on the surface of the plating base material is large, and it is difficult to form a uniform Fe oxide layer in the oxidation zone of the continuous annealing furnace, and a beautiful spangle with a uniform grain size is obtained. This is because it is difficult to be performed.

In the present invention, the combustion air ratio in the oxidation zone of the continuous annealing furnace for continuously annealing the plating base material is limited to 0.95 or more and 1.30 or less, and the heating temperature of the plating base material is set to 600 ° C.
Limited to the above.

When the combustion air ratio of the oxidation zone is less than 0.95,
Since the amount of reduced Fe in the plating base material is small, an alloy layer is formed unevenly at the interface between the plating layer and the plating base material under the influence of the crystal grain boundaries in the surface layer portion. For this reason, the particle diameter of the spangle tends to be non-uniform. On the other hand, when the combustion air ratio of the oxidation zone exceeds 1.30, the grain size becomes uniform and a beautiful spangle is obtained, but the Fe oxide layer that cannot be completely reduced by continuous annealing remains at the interface between the plating layer and the plating base material. And
The adhesion of the plating film is reduced, and the plating peels off.
Therefore, in the present invention, the combustion air ratio of the oxidation zone is 0.95 or more and 1.
Limited to 30 or less. This combustion air ratio is preferably 1.00
That is all.

If the heating temperature of the plating base material is lower than 600 ° C., the adherence on the surface of the plating base material will not be removed by burning, so that the adhesion of the plating film will decrease and the plating will peel off. Therefore, in the present invention, the heating temperature of the plating base material is limited to 600 ° C. or higher. Desirably, 620 ℃ or more 700
It is below ° C.

Thus, in the present invention, the amount of the Fe oxide layer in the oxidation zone is set to 0.1 to 2.0 g / m ² and the reduced Fe
The amount increases. In the present invention, other continuous annealing conditions need not be limited, and other continuous annealing conditions may be known conditions. In other words, H ₂
Reduction of the plated base metal surface by -N ₂ atmosphere gas, activation and annealing are carried out.

(2) Hot-dip plating process In the present invention, hot-dip plating is performed after the above-described continuous annealing, and a Zn-55% Al alloy-plated steel sheet is obtained.

Therefore, the plating conditions are Zn-55
Any condition can be used as long as it is a general condition that can obtain a% Al alloy plated steel sheet. That is, Al: 40 to 70%, Si: 0.5 to 2.0
% And the balance Zn. In the present invention, there is no need to limit other hot-dip plating conditions, and other hot-dip plating conditions may be known conditions.

According to the method for producing a hot-dip Zn—Al-based alloy-coated steel sheet according to the present invention, the reduction of the Fe oxide layer in the surface layer of the base metal formed in the oxidation zone of the continuous annealing furnace is promoted, and the reduced Fe The amount increases. Due to the increase in the amount of reduced Fe in this way, due to the crystal grain boundaries of the surface layer of the plating base material,
The effect of the heterogeneous reaction of the alloy layer at the interface between the plating layer and the plating base material is reduced, and the reduced Fe layer is uniformly distributed on the surface layer of the plating base material.

For this reason, in the hot-dip plating performed after the continuous annealing, it is possible to form an alloy layer at the interface between the plating layer and the plating base material in a stable and uniform manner. A hot-dip Zn-Al-based alloy-plated steel sheet having a beautiful spangle with a uniform grain size in each of the width direction and the length direction of the steel sheet can be manufactured.

In the method for producing a hot-dip Zn—Al-based alloy-coated steel sheet according to the present invention, it is not necessary to adjust the component concentration of the plating bath, which requires a certain amount of time. It can be made uniform.

The plated steel sheet obtained by the method for producing a hot-dip Zn—Al-based alloy-coated steel sheet according to the present invention is Zn-55% Al
It is an alloy-plated steel sheet that has both corrosion resistance and good workability that can withstand severe bending, and has excellent appearance design due to small variations in spangle particle size.
Therefore, it can be suitably used not only for building materials, home appliances, and automobiles, but also for fabrics, such as roofs and walls of commercial and industrial buildings and general buildings, and equipment.

[0031]

EXAMPLES The present invention will be described more specifically with reference to examples. (Example 1) Hot dip plating was performed on the plating base material that had been continuously annealed by the continuous annealing furnace under the plating conditions shown in Table 1, and the combustion air ratio in the oxidation zone of the continuous annealing furnace and the Zn-
Table 2 summarizes the relationship between the spangle diameter and the workability of the plating film of the 55% Al alloy-plated steel sheet and the overall evaluation results, and shows the relationship between the combustion air ratio and the standard deviation value of the spangle particle size. FIG. 1 shows a graph.

The spangle diameter in Table 2 is obtained by measuring the number of spangles per 100 mm length using a two-fold enlarged photograph of the surface of the plating layer, and calculating the spangle diameter (mm) by [100 / number of spangles]. Was calculated. The measurement position is 6 places in the width direction and 20 places in the longitudinal direction for each plating base metal, totaling 120 points.
The average value and the standard deviation value of these measured values were calculated.

The workability of the plating film in Table 2 is as follows.
In a 180 ° 2T bending test on a plated steel sheet, the crack width and the number of cracks of the plating film in the bent portion were observed using a scanning electron microscope (SEM). No peeling, ：: Evaluation was based on the evaluation criteria of small cracking and no peeling.

[0034]

[Table 1]

[0035]

[Table 2]

From Table 2 and FIG. 1, Sample Nos. 1 to 5 satisfying the combustion air ratio defined in the present invention have a standard deviation σ of spangle particle size of 0.1 mm and cannot be visually identified. It can be seen that it has a degree of uniformity. Sample No. 1
-Sample No. 5 has excellent plating film workability, and is suitable for use not only in building materials, home appliances and automobiles, but also in roofs and walls of commercial and industrial buildings and general buildings, as well as equipment, etc. It can be seen that this was a hot-dip Zn-Al-based alloy plated steel sheet.

On the other hand, Sample No. 6 and Sample No. 7
Since the combustion air ratio was below the range of the present invention, the standard deviation value σ of the spangle particle size was 0.2 mm, and the spangle particle size was non-uniform enough to be visually discerned. Also, sample
In No. 8, plating flaking occurred because the combustion air ratio was below the range of the present invention. Therefore, it can be seen that any of these is unsuitable for the above use.

(Example 2) Hot dip plating was performed on the plating base material subjected to continuous annealing in a continuous annealing furnace under the plating conditions shown in Table 3, and the surface roughness Ra of the plating base material and the obtained Zn- 55
Table 4 summarizes the relationship between the spangle diameter and the overall evaluation results of the% Al alloy-plated steel sheet, and the graph of FIG. 2 shows the relationship between the surface roughness Ra and the standard deviation value σ of the spangle diameter. Show. The particle size of the spangle was measured in the same manner as in Example 1.

[0039]

[Table 3]

[0040]

[Table 4]

From Table 4 and FIG. 2, Sample No. 1 to Sample No. 5 whose surface roughness Ra satisfies the preferred range of the present invention have a standard deviation σ of spangle particle size of 0.15 mm or less and are visually observed. It can be seen that the film has such a degree of uniformity that it cannot be identified. Therefore, for example, it is a hot-dip Zn-Al-based alloy-plated steel sheet suitable for use not only in building materials, home appliances, and automobiles, but also in roofs, walls, and other objects of commercial and industrial and general buildings. Understand.

On the other hand, Sample No. 6 and Sample No. 7
In each case, since the surface roughness Ra exceeded the preferred range of the present invention, the standard deviation values σ of the spangle particle diameters were 0.16 mm and 0.18 mm, and the particle diameter of the spangle was not uniform enough to be visually identified. Therefore, it can be seen that it is not particularly suitable for uses such as roofs and walls of commercial and industrial buildings and general buildings, and objects.

[0043]

As described in detail above, according to the method for producing a hot-dip Zn—Al-based alloy-coated steel sheet according to the present invention, the spangle pattern can be easily and reliably made uniform regardless of the addition of components to the plating bath. It has become possible to produce a highly plated steel sheet. As a result, the design of each plated steel sheet,
It can be uniformly aligned in the width direction and the longitudinal direction of the same plated steel sheet, and the application of hot-dip Zn-Al alloy plated steel sheets to roofs, walls, and other objects of commercial and industrial buildings and general buildings It has become possible to further increase the performance.
The significance of the present invention having such an effect is extremely remarkable.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a combustion air ratio and a standard deviation value of a spangle particle size in Example 1.

FIG. 2 is a graph showing the relationship between surface roughness Ra and standard deviation of spangle particle size in Example 2.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (2)

(57) [Claims] 1. A plating base material is heated to 600 ° C. or more at a combustion air ratio of 0.95 to 1.30 in a continuous annealing furnace at a combustion air ratio of 0.95 to 1.30, and annealed in a reducing atmosphere.
i: A hot-dip Zn— characterized by producing a coated steel sheet having a uniform spangle particle size by performing a hot-dip plating process in a plating bath consisting of 0.5 to 2.0 wt% and the balance Zn.
Manufacturing method of Al-based alloy plated steel sheet. 2. The plating base material has a surface roughness Ra of 0.5 μm.
The method for producing a hot-dip Zn-Al-based alloy-plated steel sheet according to claim 1, wherein