JP2000282204A - Aluminum plated steel sheet for building material excellent in corrosion resistance in edge face and worked part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the corrosion of a plating layer itself and the generation of red rust from the edge faces and worked part by incorporating an Mg2Si phase into an Al plating layer having a specified compsn. of Mg, Si, and the balance Al with inevitable impurities formed on the surface of a steel sheet. SOLUTION: An Al plating layer is composed of, by weight, 0.5 to 15% Mg, 2 to 15% Si, and the balance Al with inevitable impurities. Then, by making a structure in which Mg2Si is dispersed into the Al plating layer, this Mg2Si is dissolved in the using environment to form Mg protective films on the surface of the plating layer and the surface of ferrite and prevents corrosion both in the plating layer itself and the place to which ferrite is exposed. At the time of producing an Al plated steel sheet, an Al-Fe-Si alloy layer is formed on the boundary between the plating layer and ferrite, and its thickness is preferably controlled to <=5 μm. Moreover, preferably, the hardness of the plating layer is controlled to 40 to 150, and its coating weight is controlled to 20 to 100 g/m2 per side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an aluminum-plated steel sheet having excellent corrosion resistance, particularly for a metal roof and a wall material mainly used for a roof, a wall and the like, particularly at an end face and a processed portion.

[0002]

2. Description of the Related Art Conventionally, Zn-coated steel sheets have been mainly used as surface-treated steel sheets for building materials. Recently, a galvanized steel sheet subjected to a coating treatment or a zinc-aluminum alloy-plated steel sheet having excellent corrosion resistance has been widely used in order to further improve corrosion resistance and design. As a zinc-aluminum alloy plated steel sheet, Zn-5%
Al-based and Zn-55% Al-based products are known, and their production has been increasing recently. In general, a zinc-aluminum alloy-plated steel sheet has better corrosion resistance than a galvanized steel sheet. On the other hand, in a Zn-55% Al-based steel sheet, the corrosion resistance of the ground iron is weakened due to the excellent corrosion resistance of the plating layer. After several months of use, red rust appears on the end face or severely bent parts.

Further, in the case of an aluminum-plated steel sheet having excellent corrosion resistance of a plating layer, there is almost no sacrificial corrosion-preventing action of the base steel in a normal environment, and red rust is generated on the end face within a few days. It is necessary and the work becomes complicated. Alternatively, if the repair coating is insufficient, there is a problem that red rust is generated from the end face to impair the appearance. In order to meet this problem of aluminum-plated steel sheets, the present inventors have disclosed Japanese Patent Application Laid-Open No. Hei 6-330.
Japanese Patent Publication No. 274 discloses a technique for suppressing the generation of red rust from a processed portion. However, although the generation of red rust from the processed part can be suppressed by this, the problem of rust generation from the end face still remains.

[0004]

SUMMARY OF THE INVENTION As has been seen above,
Generally, the corrosion resistance of the plating layer itself on the surface treated steel sheet,
The generation of red rust from the end face and the processed portion is an essentially contradictory problem, and it has been extremely difficult to achieve both. The present invention provides a completely new aluminum-plated steel sheet that can satisfy both of these requirements.

[0005]

Means for Solving the Problems The present inventors systematically investigated the corrosion resistance as a plating layer of an aluminum-plated steel sheet and the generation of red rust from the end face, and as a result of repeating various studies in order to achieve both, the plating was performed. New knowledge has been obtained that it is possible to achieve both of these by adding Mg to the layer. In JP-A-56-127762, the present applicants have already disclosed a method for producing an aluminum-plated steel sheet containing Si and Mg.

[0006] As a result of further detailed examination, it has been found that by adding Mg and Si to the plating bath to generate Mg ₂ Si in the plating layer, the surface-treated steel sheet for building materials exhibits a far superior performance. New knowledge was obtained. That is, the corrosion resistance of the plating layer itself is better than the conventional one, and the end face,
It is also possible to suppress the corrosion of iron from the processed part.
It is presumed that this effect is due to the effect that Mg ₂ Si dissolves in a corrosive environment and forms a dense Mg-based film on the exposed surface of the base iron and the surface of the plating layer. In order to crystallize a desired amount of Mg ₂ Si, it is effective to control the cooling rate. For example, rapid cooling after plating is preferable.

The gist of the present invention is as follows: (1) Mg: 0.5 to 15% by weight on the steel sheet surface;
i: having an aluminum plating layer composed of 2 to 15%, with the balance being Al and unavoidable impurities, wherein Mg ₂ Si
Aluminized steel sheet for building materials with excellent corrosion resistance of the end face and processed part characterized by containing phase. (2) The aluminum-coated steel sheet for building materials excellent in corrosion resistance of the end face and the processed portion according to (1), wherein Mg: 3 to 9% and Si: 6 to 10%. (3) At the interface between the plating layer and the steel sheet, Al-
The aluminum-plated steel sheet for building materials according to the above (1) or (2), which has an Si—Fe-based alloy layer and is excellent in corrosion resistance of the end face and the processed portion.

(4) The aluminum-plated steel sheet for building materials according to (1) to (3), wherein the alloy layer contains Mg, and the end face and the processed portion have excellent corrosion resistance. (5) The aluminum-plated steel sheet for building materials according to (1) to (4), wherein the hardness of the aluminum plating layer is 40 to 150, and the end face and the processed portion have excellent corrosion resistance. (6) The aluminum-plated steel sheet for building materials excellent in corrosion resistance of the end face and the processed portion according to the above (1) to (5), having a resin coating layer of 0.5 μm or more on the surface of the plating layer. (7) The coating weight per side is 20 to 100 g / m ^2.
(1) to (6), wherein the end face, the aluminum plated steel sheet for building materials excellent in corrosion resistance of the processed portion.

Hereinafter, the present invention will be described in detail. First, the reasons for limiting the plating layer will be described. The plating layer is Mg: 0.5-1
5%, Si: 2 to 15%, balance Al and inevitable impurities. By adding Mg and Si in combination, Mg ₂ Si is generated in the plating layer, and the corrosion resistance is greatly improved. Therefore, it is desirable that Mg and Si are added in combination. If Mg is less than 0.5%, the effect of improving corrosion resistance is not exhibited, while if added more than 15%, the hardness of the plating layer is increased and the workability of plating is impaired. Even if Si is added in an amount of less than 2%, the effect of improving corrosion resistance cannot be obtained, and if it exceeds 15%, the workability of plating is impaired. Therefore, the amounts of Mg and Si are limited to this range. More preferably, Mg: 3-9
%, Si: 6 to 10%. The significant feature of the present invention, by a the plating layer is dispersed Mg ₂ Si structure, the Mg ₂ Si dissolves in the environment of use M
A g-based protective film is formed on the surface of the plating layer and the surface of the base iron, and both the plating layer itself and the exposed portion of the base iron are protected. The greater the amount, the greater the effect of improving corrosion resistance.

In the present invention, the method for producing the aluminum-plated steel sheet is not particularly limited, and a melting method, an electric method from a non-aqueous solvent, a vapor deposition method, a cladding method, and the like can be applied. Currently, the most industrially widespread are hot-dip aluminized steel sheets. At this time, an alloy layer composed of an intermetallic compound is generated at the interface between the plating layer and the ground iron. Al by melting method
-Si-Mg plating produces an alloy layer as a matter of course, but at this time, the composition of the alloy layer does not change significantly and Al-F
It is an e-Si system. However, when the amount of Mg increases, Al-Fe
Formation of -Si-Mg based intermetallic compounds is also observed. The thickness of the alloy layer is desirably 5 μm or less. This is because the alloy layer is hard and brittle, and if the alloy layer is thick, the workability of the steel sheet is greatly impaired. By adding Mg to the plating bath, an effect of reducing the thickness of the alloy layer can be obtained, and an alloy layer of 2 μm or less can be obtained.

The hardness of the plating layer is preferably about 40 to 150. The hardness of the plating layer affects the workability. If the hardness is too soft, it adheres to a roll or the like at the time of processing and causes flaws. On the other hand, if it is too hard, it causes peeling of the plating layer. The plating layer hardness is a value when a load of 1 g is applied by a Knoop micro hardness tester. The composition of the plating base sheet to be used is not particularly limited, but low carbon steel such as aluminum killed steel is usually used as a metal building material, and the use of these is also preferred in the present invention.

In the present invention, the post-treatment of plating is not particularly limited, but a chemical conversion treatment such as chromate or phosphate treatment can be performed, and the surface may be coated with a resin. As the chemical conversion treatment, phosphoric acid, silica, or the like can be contained, and an Mg-based compound may be added. Examples of the resin type include acrylic acid or methacrylic acid ester, carboxylic acid vinyl ester, vinyl ether, ethylenically unsaturated compounds such as styrene, acrylamide, acrylonitrile, and vinyl halide, and epoxy, urethane, and polyester. Recently, various post-treatments that do not use Cr are being developed, but it is naturally possible to apply these. The purpose of the coating may be to impart a design property or to make use of the luster of the aluminum itself for the appearance, and may be coated with a transparent resin to impart workability. The resin film thickness at this time is preferably 0.5 μm or more.

The post-treatment of the hot-dip aluminized steel sheet is as follows:
In addition to chemical conversion treatment and resin coating, there may be zero spangle treatment which is an external unification treatment after hot-dip plating, annealing treatment which is a plating modification treatment, temper rolling for adjusting the surface condition and material, etc. In the present invention, these are not particularly limited and can be applied.

Finally, regarding the coating weight, generally,
The surface-treated steel sheet used is zinc-based and both sides are 250g / m^Two , Z
150 g / m for n-Al system^Two 200g with aluminum plating
/ M ^Two Often used with a relatively thick. General
In addition, the service life of the plating layer and the suppression of red rust from
It tends to be suppressed by increasing the amount of deposition. The present invention is an
To achieve corrosion resistance, end face, and processed part corrosion resistance.
Amount is 60g / m on both sides^TwoDemonstrates sufficient performance even to the extent.
Naturally, if the amount of adhesion increases, a further effect of improving corrosion resistance is obtained.
Can be 20g / m per side^Two In the following, it is called long-term durability
There is some anxiety in the meaning, and if the amount of
Since there is a concern that the workability may be impaired, the preferable amount of adhesion is 2 on one side.
0-100g / m^Two It is.

[0015]

Next, the present invention will be described in more detail by way of examples. (Example 1) Steel having the components shown in Table 1 was melted by a normal converter-vacuum degassing process to obtain a billet, which was then subjected to a hot rolling and cold rolling process under normal conditions to obtain a cold rolled steel sheet. (Plate thickness 0.8mm)
I got Using this as a material, hot-dip aluminum plating was performed. For the hot-dip aluminum plating, a non-oxidizing furnace-reduction furnace type line was used, and annealing was also performed in this hot-dip plating line.
The annealing temperature was 800 to 850 ° C. After plating, the amount of plating was adjusted by a gas wiping method. The plating bath composition was an Al-Mg-Si system. At this time, the bath contained about 2% of Fe supplied from the plating equipment or the strip. The bath temperature was a value obtained by adding 60 ° C to the melting point read from the Al-Mg-Si ternary phase diagram. The plating appearance was good with no plating or the like. The thickness of the alloy layer was controlled to be lower by controlling the temperature of the invading plate, the cooling rate after plating, and the like. It was confirmed that Mg ₂ Si was sufficiently crystallized in the plating layer by increasing the cooling rate. Although the plating structure was confirmed by a cross-sectional microscope, the Mg ₂ Si phase was observed as a granular phase of about 1 μm or a coarse phase of about 10 to 20 μm. Table 2 shows the manufacturing conditions at this time. The plating adhesion amount was uniform on both sides, and the indication was the adhesion amount on both sides. The performance of the steel sheet thus manufactured as a building material was evaluated. The evaluation method at this time was as shown below, and the plating conditions and performance evaluation results are also shown in Table 2.

[0016]

[Table 1]

(1) Plating layer, alloy layer composition, thickness analysis method Plating layer: 15% H containing an amine-based inhibitor
The plating layer was dissolved by dipping in a C solution to obtain a composition analysis solution. The analysis of each element was performed by ICP. In addition, Cr, Si
When analyzing a steel sheet which has been subjected to a chemical conversion treatment containing, for example, it is necessary to lightly polish the surface to reduce these effects. Alloy layer thickness: The alloy layer thickness was measured from a 400 times cross-sectional microscopic photograph.

(2) Evaluation of Corrosion Resistance Salt Corrosion Resistance JIS Z 23 for a sample having a size of 70 × 150 mm
A salt spray test in accordance with No. 71 was performed for 40 days, and the corrosion products were peeled off and the corrosion weight loss was measured. The indication of the corrosion weight loss is a value for one side of the plating. [Evaluation Criteria] ◎: corrosion weight loss 5 g / m ² or less ○: less than corrosion loss 10 g / m ² △: Corrosion weight loss 10 to 25 g / m ² ×: corrosion weight loss 25 g / m ² greater

Post-Coating Corrosion Resistance After chromate treatment of a chromic acid-silica system, one of the following two types of resin coatings was applied. The film thickness is a numerical value per one side and is a double-sided coating. α: wax-containing acrylic transparent resin 4 μm β: epoxy-based primer 5 μm + polyester-based top coat 20 μm A cycle corrosion test in which the process shown below is regarded as one cycle is performed 60 times, and the coating film swells from the edge (upper burr). The width was measured. 0.5% salt spray (35 ° C, 4 hours) → drying (70 ° C
30% RH, 4 hr) → wet (50 ° C. 98% RH, 4
hr) → Dry (70 ° C. 30% RH, 4 hr) [Evaluation Criteria] 〇: Swelling width less than 1 mm △: Swelling width 1-3 mm ×: Swelling width more than 3 mm

Outdoor exposure test An outdoor exposure test was carried out at 30 ° on the south side after shearing to dimensions of 50 × 200 mm. After 3 months, the occurrence rate of red rust from the end face and the discoloration of the surface were observed. [Evaluation criteria] 〇: Red rust occurrence rate from the end face is less than 30% Δ: Red rust occurrence rate from the end face is 30 to 80% ×: Red rust occurrence rate from the end face is more than 80%

(3) Workability Bending equivalent to 3t (t: plate thickness) was performed by a roll former, and the plating damage near the processed portion was visually observed. The molding was performed without oil coating. [Evaluation criteria] 〇: No abnormality △: Cracking of plating ×: Peeling of plating

[0022]

[Table 2]

When Mg is not contained as in the comparative example, the corrosion resistance tends to be poor in a severe environment. Galvalume steel sheets, which have recently established a firm position as steel sheets for building materials, also have poor corrosion resistance in severe environments. In the examples of the present invention as well, When the amount of Mg is small as in No. 1, No. 5, the corrosion resistance tends to decrease when the amount of Mg is large, and Mg is preferably about 4 to 9% from the viewpoint of corrosion resistance. In addition, the present invention example No. As in the case of 6, when the amount of Si is low, the alloy layer is easily grown and is slightly inferior in workability.

Inventive Example No. Even if the amount of Si is too large as in 8, the corrosion resistance tends to slightly deteriorate. Invention Example No.
If the amount of plating adhered is too small as in 9 and 10, the corrosion resistance tends to be slightly insufficient. When the amounts of Mg and Si are in appropriate ranges, extremely excellent corrosion resistance and workability are exhibited. In particular, in the present invention, an extremely excellent effect is obtained in that the corrosion resistance of the flat surface is increased as compared with the conventional one while overcoming the end surface rust which was a cry of the conventional aluminum-plated steel plate. As a conventional aluminum plating steel sheet for building materials, the adhesion amount is 200 g /
m ² or more have been used,
It can be reduced to about 0 g / m ² .

(Example 2) The composition of the plating bath and the operating conditions were fixed, and the influence of the original plate was investigated. The plating bath composition was Al-8% -Si-6% Mg-2% Fe, and the coating weight was 120 g / m ^{2 on} both sides. Evaluation items and methods are basically the same as those in the first embodiment. At this time, the composition of the plating layer was approximately 8.5% for Si and 5.7 for Mg.
%, Fe: 0.5%, alloy layer thickness: 1.8 to 2.8 μm
And a numerical value of 125 was obtained as the hardness of the plating layer. The steel types used are shown in Table 3, and the evaluation results at that time are summarized in Table 4. Excellent characteristics were obtained regardless of the type of steel used.

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

The present invention provides a metal building material having extremely excellent corrosion resistance as compared with conventional materials.
According to the present invention, it is expected that further maintenance-free and longer life can be achieved, and the contribution to industry is enormous.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masao Kurosaki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Hisaaki Sato 1- 1 Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture 1 Nippon Steel Corporation Yawata Works F-term (reference) 4K027 AA02 AA22 AB02 AB05 AB26 AB32 AB48 AC82 AE03 AE21 AE23 4K044 AA02 AB02 BA10 BA19 BA21 BB03 BC02 BC05 CA11 CA53 CA62

Claims (7)

[Claims] 1. A steel sheet having a Mg content of 0.5 to 1% by weight on a steel sheet surface.
5%, Si: 2 to 15%, the balance has an aluminum plating layer composed of Al and unavoidable impurities.
An aluminum-plated steel sheet for building materials excellent in corrosion resistance of end faces and processed parts, which contains a g ₂ Si phase. 2. The aluminum-coated steel sheet for building materials according to claim 1, wherein the content of Mg is 3 to 9% and the content of Si is 6 to 10%. 3. The construction material according to claim 1 or 2, wherein the interface between the plating layer and the steel sheet has an Al—Si—Fe alloy layer having a thickness of 5 μm or less. Aluminum plated steel sheet. 4. The aluminum-coated steel sheet for building materials according to claim 3, wherein the alloy layer contains Mg. 5. The aluminum-plated steel sheet for building materials according to claim 1, wherein the hardness of the aluminum-plated layer is 40 to 150. 6. The aluminum-plated steel sheet for building materials according to claim 1, further comprising a resin coating layer having a thickness of 0.5 μm or more on the surface of the plating layer. 7. The coating weight per one side is 20 to 100.
g / m < ² >, The aluminum-coated steel sheet for building materials excellent in corrosion resistance of the end face and the processed part of Claim 1-6 characterized by the above-mentioned.