JPH06287772A - Surface treated steel sheet excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To provide a surface treated steel sheet excellent in corrosion resistance. CONSTITUTION:The surface of a steel sheet is applied, as a primary layer, with an Al Mn allay plating film contg. 1 to 50wt.% Mn, and the balance substantial Al by 1 to 40g/m<2>, is applied, as a secondary layer, with a chromate film by 5 to 500mg/m<2> expressed in terms of Cr and is applied, as a third layer, with an organic resin film by 0.1 to 5g/m<2>. The organic resin film is contained in the ratio of 1 to 150 pts.wt. with silica as solid content to 100 pts.wt. of organic resin solid content. In this way, the surface treated steel sheet excellent in corrosion resistance after working and the adhesion of coating material can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet having excellent corrosion resistance.

[0002]

2. Description of the Related Art In recent years, high corrosion resistance of steel sheets for automobiles has attracted attention as a social demand, and various rust-preventing steel sheets have been proposed to meet this problem, and are gradually becoming established.

Hot-dip galvanizing is applied to these rust-preventive steel sheets.
Steel sheets such as hot-dip galvanizing, electrogalvanizing and electrogalvanizing are listed first, but when the steel sheet is applied to the bag structure part or the bent part (hemming part) of the inner plate of the car body, its surface is A high degree of corrosion resistance is required, and the above-mentioned plated steel sheet has a problem that the corrosion resistance is not sufficient.

As a steel sheet having a high degree of corrosion resistance, so-called zinc metal coated with zinc rich coating is known. However, even in this rust-preventive coated steel sheet, there is a problem that the film is peeled off in the processed portion such as press forming, and the corrosion resistance is deteriorated.

Further, for the purpose of improving these, recently, a chromate film and 0.3 to 3 are formed on a zinc-based plating.
A steel sheet coated with an organic thin film of about μm is disclosed, for example, in Japanese Patent Laid-Open No. 62-28.
9274, etc. Although the workability of these steel sheets is improved, the corrosion resistance is slightly sacrificed because the organic resin film is a thin film.

On the other hand, Al-plated steel sheets by hot dipping method, Al-Si alloy-plated steel sheets and the like have been used for building materials, home appliances and the like for a long time, and for the purpose of further improving the corrosion resistance, a chromate film is formed on the upper layer of the Al-plated steel sheet. Further, a steel sheet having an organic resin film is proposed in, for example, JP-A-59-47387. However, when these steel sheets are used as steel sheets for automobiles in a severe corrosive environment, their corrosion resistance is insufficient.

As a high corrosion resistance Al alloy plated steel sheet, Al
A Mn alloy-plated steel sheet has been proposed, for example, in Japanese Examined Patent Publication No. 43-18245, but the corrosion resistance after coating is a problem when it is used after coating for automobiles.

[0008]

SUMMARY OF THE INVENTION As described above, a steel sheet obtained by applying a chromate film and an organic resin film on zinc-based plating or Al plating known so far, or Al-M.
The n-alloy plated steel sheet has insufficient corrosion resistance when used as a steel sheet for automobiles in a severe corrosive environment. An object of the present invention is to provide a surface-treated steel sheet excellent in corrosion resistance, which solves the above-mentioned problems of the conventional art.

[0009]

[Means for Solving the Problems] The present invention that solves the above problems
A surface-treated steel sheet with excellent corrosion resistance is a first layer on the steel sheet.
As Mn as 1 to 50 wt% and the balance is substantially Al
1-40 g / m of Al-Mn alloy plating film²
The second layer has 5 to 500 mg / m in terms of Cr²of
Has a chromate film and an organic resin film as the third layer
0.1-5g / m ²Excellent corrosion resistance characterized by having
Surface treated steel sheet.

Further, the organic resin film has a silica content of 1 to 150 relative to 100 parts by weight of the organic resin solid content.
It is preferable to contain it in a ratio of parts by weight because the corrosion resistance is further improved.

[0011]

The present invention will be described in more detail below. The inventors of the present invention have conducted extensive studies to realize a surface-treated steel sheet having excellent corrosion resistance. As a result, by stacking an Al-Mn alloy plating film, a chromate film, and an organic resin film, an organic resin film is further formed. By including silica in these, it is newly found that these corrosion resistance improving effects exert a highly synergistic effect and exhibit excellent bare corrosion resistance, and this steel sheet also has excellent corrosion resistance after working, and the top layer organic It has also been newly found that the resin film realizes excellent post-painting corrosion resistance by improving the paint adhesion, and has reached the present invention.

Mn of Al-Mn alloy plating film of the first layer
The content is 1 to 50% by weight. If the content is less than 1% by weight, the desired corrosion resistance cannot be obtained, and if it exceeds 50% by weight, the plating film becomes hard, which is not preferable in terms of workability. More preferably, the Mn content is 10 to 40% by weight.

The Al-Mn alloy plating film contains other metals such as Be, Mg, Ca, Sr, Ba and T.
i, V, Nb, Ta, Cr, Mo, W, Fe, Co, N
A small amount of one or more of i, Zn, Si, Sn and Pb may be contained.

The amount of Al-Mn alloy plating film deposited is 1 to
It is 40 g / m ² . If the adhesion amount is less than 1 g / m ² , desired corrosion resistance cannot be obtained, and if it exceeds 40 g / m ² , workability is unfavorable. Adhesion amount is 1 to 20 g / m ²
It is more preferable if

The method for forming the Al-Mn alloy plating film is not particularly limited, and any known method such as electroplating method using molten salt or non-aqueous solvent, vacuum deposition method, thermal spraying method, hot dipping method, etc. can be applied. Is. Among them, the electroplating method using a molten salt is preferable because it is easy to control the operating cost, the film composition, and the amount of adhesion.

The amount of the second chromate film deposited is 5 to 500 mg / m ² in terms of Cr. Adhesion amount is 5 mg / m
^If it is less than ² , the desired corrosion resistance cannot be obtained and 500m
If it exceeds g / m ² , it is not preferable in terms of workability. It is more preferable that the adhesion amount is 10 to 200 mg / m ² .

The chromate film contains silica,
It may contain an inorganic powder such as titania or alumina, or a coupling agent such as a silane coupling agent, a titanium coupling agent, an alumino coupling agent or a chromium coupling agent.

The method for forming the chromate film is not particularly limited, and any known method such as coating type, reaction type and electrolytic type can be applied.

The organic resin film of the third layer may be any organic resin as long as it has good adhesion to the chromate film and can form a uniform film on the surface.
For example, epoxy resin, fluorine resin, polyurethane resin, polyethylene resin, polystyrene resin, polyester resin, polyvinyl chloride resin, polyether resin, polycarbonate resin, polyamide resin, polyimide resin,
Examples thereof include amino resins, acrylic resins, phenol resins, polysiloxane resins and the like. Also these 2
A mixture of two or more species is also applicable.

The amount of the organic resin film deposited is 0.1 to 5 g / m
^{Is 2} . If the adhesion amount is less than 0.1 g / m ² , desired corrosion resistance cannot be obtained, and if it exceeds 5 g / m ² , workability is unfavorable. It is more preferable that the adhesion amount is 0.3 to ² g / m ² .

The method for forming the organic resin film is not particularly limited, and roll coating, spraying, shower coating,
Any known method such as a brush coating method can be applied.

The organic resin film preferably contains silica in a proportion of 1 to 150 parts by weight as a solid content relative to 100 parts by weight of the organic resin solid content because the corrosion resistance is further improved. If the amount of silica compounded is less than 1 part by weight, the effect of improving corrosion resistance cannot be expected, and if it exceeds 150 parts by weight, it is not preferable in terms of paint adhesion and processability. More preferably, the amount of silica compounded is 10 to 150 parts by weight.

Examples of silica to be used include colloidal silica and fumed silica, and any of them may be used.

The surface-treated steel sheet of the present invention described above may have the coating on only one side of the steel sheet, or on both sides.

[0025]

EXAMPLES The present invention will be specifically described below based on examples. (Formation method of first layer Al-Mn alloy plating film) After cold-rolled steel sheet degreased and pickled by a usual method is dried in a non-oxidizing atmosphere and preheated to a plating temperature, the following molten salt Al is used.
Al-Mn alloy plating was performed from the -Mn alloy plating bath. Bath composition: AlCl ₃ 60 mol% NaCl 26 mol% KCl 14 mol% MnCl ₂ 10 to 20000 ppm Bath temperature: 200 ° C. Current density: 1 to 100 A / dm ^{2 In} addition, by changing the addition amount of MnCl ₂ and the current density, Al- By adjusting the Mn content of the Mn alloy plating film and changing the electrolysis time, the amount of the Al-Mn alloy plating film deposited was adjusted.

(Method for forming second layer chromate film) A
A chromate treatment liquid (Bt1414A manufactured by Nippon Parkerizing Co., Ltd.) was applied on the 1-Mn alloy plating film by a roll coater and baked at 140 ° C. for 30 seconds to form a chromate film. The amount of the chromate film adhered was adjusted by changing the dilution rate of the chromate treatment liquid.

(Method for forming third layer organic resin film) On the chromate film, a solution prepared by diluting epoxy resin (Epicoat 1007 manufactured by Shell Chemical Co., Ltd.) with toluene was applied with a bar coater and baked at 150 ° C. for 30 seconds. An organic resin film was formed. When silica is contained in the resin, colloidal silica (NBA-ST manufactured by Nissan Chemical Co., Ltd.) was added in an amount of 1 to 150 parts by weight based on 100 parts by weight of the resin solid content. The amount of the organic resin film deposited was adjusted by changing the resin dilution ratio and the bar coater count.

Table 1 shows the coating composition and the adhesion amount of the steel sheet obtained by the above method. Bare corrosion resistance of these steel sheets,
Workability Corrosion resistance and post-painting corrosion resistance were evaluated by the following methods.

(Evaluation Method of Bare Corrosion Resistance) Salt Spray (5% N
aCl, 35 ° C., 4 hours) → drying (60 ° C., 2 hours) →
1000 cycles of cycle corrosion test with wet (50 ° C., 95% RH, 2 hours) as 1 cycle, bare red when rust occurrence area ratio is less than 5% (good), and bare when 5% or more It was defined as poor corrosion resistance (x).

(Evaluation Method of Corrosion Resistance After Processing) Each test steel plate (90 mmφ) was subjected to cylindrical drawing with a diameter of 50 mmφ and a depth of 25 mm (BHF = lton), and the same cycle corrosion test as the bare corrosion resistance evaluation test was performed 200 times. Do a cycle,
When the area ratio of red rust was less than 5%, the bare corrosion resistance was good (◯), and when it was 5% or more, the bare corrosion resistance was poor (x).

(Evaluation Method of Corrosion Resistance After Painting) Power Top U-100 (manufactured by Nippon Paint Co., Ltd.) is 100 V, 3 mi.
After electrodeposition with a film thickness of 20 μm under conditions of n and 28 ° C., a cross-cut was put in with a cutter knife, and 200 cycles of the same cycle corrosion test as the bare corrosion resistance evaluation test were performed. Good corrosion resistance (∘), 2 mm or more was regarded as poor corrosion resistance after coating (x).

Table 1 shows the evaluation results of bare corrosion resistance, post-processing corrosion resistance and post-coating corrosion resistance. As is clear from Table 1, the surface-treated steel sheet of the present invention exhibits excellent corrosion resistance.

[0033]

[Table 1]

[0034]

As described in detail above, the surface-treated steel sheet of the present invention has an Al-Mn alloy plating film as the first layer, a chromate film as the second layer, and an organic resin as the third layer on the steel sheet. By having a predetermined amount of each film, by further containing a predetermined amount of silica in the organic resin film, it is possible to realize a surface-treated steel sheet having extremely excellent corrosion resistance, and its industrial value is very high. .

Front Page Continuation (72) Inventor Shuji Gomi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Headquarters (72) Inventor Kazuo Mochizuki 1 Kawasaki-cho, Chuo-ku, Chiba Address: Kawasaki Steel Corporation Technical Research Division

Claims (2)

[Claims] 1. A steel sheet having an Al—Mn alloy plating film containing 1 to 50% by weight of Mn as the first layer and the balance substantially consisting of 1 to 40 g / m ^{2 and} having the second layer as the second layer. Cr
Has a chromate film of 5 to 500 mg / m ^{2 in} conversion,
A surface-treated steel sheet having excellent corrosion resistance, which has an organic resin film of 0.1 to 5 g / m ² as a third layer. 2. The organic resin film has an organic resin solid content of 10.
The surface-treated steel sheet having excellent corrosion resistance according to claim 1, wherein silica is contained in a proportion of 1 to 150 parts by weight as solid content with respect to 0 parts by weight.