JP2001303266A - Surface-treated steel sheet and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface-treated steel sheet which has the excellent corrosion resistance of processed parts and flawed parts not obtainable with only the self-repair effect by hexad chromium and further the surface-treated steel sheet which is excellent in the corrosion resistance of the processed parts, the blackening resistance under a moist environment or the corrosion resistance of the processed parts and the blackening resistance in a stacked state. SOLUTION: The film in which (A) the chromium is included at 0.1 to 100 mg/2 and (B) calcium is included at 0.1 to 200 mg/2 is formed on the surface of the galvanized steel sheet. The galvanized steel sheet is a Zn-Al system plated steel sheet containing 4 to 25 wt.% aluminum or over 25 to 75 mass % aluminum. The film is formed by applying a treating liquid which is a treating liquid containing the water-soluble chromium compound and the calcium and containing (i) 0.1 to 50 g/l hexad chromium ions and (ii) 1 to 50 g/l calcium on the surface of the galvanized steel sheet and heating the steel sheet to a range of the ultimate sheet temperature 60 to 300 deg.C without washing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical conversion coating formed on the surface of a galvanized steel sheet used for home appliances, building materials and the like, and more particularly, to an excellent corrosion resistance in a galvanized steel sheet. The present invention relates to a surface-treated steel sheet provided with a surface treatment, a surface-treated steel sheet further excellent in blackening resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a chromate-treated film has been formed on the surface of a zinc-based plated steel sheet as a primary rust preventive treatment until used by a consumer, but in recent years, it exhibits a high degree of corrosion resistance even after processing parts. Function to do so has come to be required.

[0003] Among zinc-based steel sheets, Zn-Al-based steel sheets obtained by alloying Zn and Al have higher corrosion resistance than galvanized steel sheets, and their demand is increasing mainly in the field of building materials. .

[0004] However, with the recent development of high durability and maintenance-free in the field of building materials, various environments,
With respect to the shape, it has been required that the original appearance surface of a Zn-Al-based plated steel sheet can be maintained for a long period of time. Specifically, the Zn-5% Al alloy-plated steel sheet containing about 5% aluminum, compared to the chromate-treated film that has been formed on the surface as a primary rust prevention treatment until it is used by consumers, (a) The function of exhibiting high corrosion resistance even after processing in a corrosive environment (corrosion resistance of the processed part) and (b) The plating surface becomes black when stored outdoors for several days with the sheet material stacked before the enforcement A function of suppressing the blackening phenomenon (blackening resistance during stacking) has been required. Also contains about 55% aluminum
Zn-55% Al alloy coated steel sheet (a) Function to exhibit high corrosion resistance even after processing in corrosive environment (corrosion resistance of processed part)
And (b) a function of suppressing the blackening phenomenon in which the plated surface is blackened in a humid environment (resistance to blackening in a humid environment) has been required.

[0005] Chromate-treated films are roughly classified into three types. Electrolytic chromate-treated films containing a trivalent chromium compound as a main component, reactive chromate-treated films, and 3 types.
It is divided into a coating type chromate treatment film composed of a compound of chromium (VI) and hexavalent chromium.

[0006] In these chromate-treated films, a trivalent chromium compound which is hardly soluble acts as a barrier to corrosion factors such as chloride ions and oxygen (barrier effect). Hexavalent chromium in the film elutes to the part, and has the effect of suppressing corrosion by passivating the damaged part of the film (self-repair effect).

[0007] For this reason, when corrosion resistance of the processed portion is required, a coating type chromate film is often applied.
Hexavalent chromium has a strong oxidizing property and is easily reduced to trivalent chromium over time. In addition, it is water-soluble and elutes out of the system in a humid environment. In many cases, hexavalent chromium sufficient to exert a repair effect does not remain in the coating, and it was not always possible to obtain a satisfactory corrosion resistance in the processed portion.

There are several known techniques for solving this problem, but they can be roughly classified into the following two methods. For example, JP-A-2-34792 discloses a method of adding a fluorocarbon resin in a chromate film to impart lubricity, and JP-A-10-176280 discloses a method of reducing lubricity. A method of containing a thermoplastic elastomer to impart ductility is disclosed. Both methods reduce the degree of film damage caused by sliding such as press working, and provide a self-repair effect with a smaller amount of hexavalent chromium. The purpose is to get. Method to suppress the amount of hexavalent chromium elution in the coating For example, in Japanese Patent Publication No. 9-800337, by dispersing a hardly soluble chromate in the coating, chromium is not eluted in the healthy part of the coating, The purpose is to elute hexavalent chromium by using a corrosion reaction (pH rise) in the damaged part of the film as a trigger to exert a self-repair effect.

According to the above method, the degree of damage to the film can be reduced with respect to press working or bending, and a certain degree of self-repair effect can be exhibited.
The effect of reducing damage to the film cannot be obtained for a portion that is damaged due to contact with a sharp metal piece or the like. Further, the resin to be contained is expensive, and there is a problem in terms of economy and productivity, such as a decrease in the stability of the processing solution.

On the other hand, according to the above-mentioned method, although the sustainability of the self-repair effect is improved as compared with the case where a water-soluble chromic acid is applied and a film is formed, the self-repair effect is poor due to the poor solubility. , At the same level as immediately after the formation of a film containing a highly water-soluble chromium compound, and in general, a film containing chromate is easily colored, and it is remarkable for members used without painting. Problems such as lowering the product value also occur.

On the other hand, a Zn-Al-based plated steel sheet has both a sacrificial corrosion-preventing ability by Zn and a passivation film-forming ability by Al acting synergistically to obtain excellent corrosion resistance. However, since Al is an active metal by nature, when the passive film is damaged, the blackening phenomenon easily occurs in a wet environment.

Zn-Al containing 4 to 25% by weight of aluminum
(1)
After plating, a method of treating with a solution containing Ni ions or Co ions (JP-A-59-177381), (2) a method of heat treatment after skin pass rolling (JP-A-55-131178), (3) )
Cleaning the plating surface with an alkaline aqueous solution
Japanese Patent Application Laid-Open No. 63-166974) and (4) a method of performing blast treatment after plating and before chromate treatment (JP-A-63-166974).

[0013] In fact, by applying the above-mentioned prior art, the blackening resistance of a Zn-Al-based plated steel sheet containing 4 to 25% by weight of aluminum is improved in a normal wet environment. However, Zn-Al containing 4-25% by weight of aluminum
System plated steel sheet, during the construction period of roofs, outer walls, etc.
When stored outdoors in the form of sheets or roll-formed molding materials (stacked state), the surface of the steel sheet becomes wet due to condensation easily in the natural environment. There is a problem that changes.

Further, all of the above-mentioned methods require special processing equipment, and therefore have problems in terms of economy and productivity.

Further, as a method for suppressing the blackening phenomenon of an Al-Zn-based plated steel sheet containing aluminum in an amount of more than 25 to 75% by weight, Japanese Patent Publication No. 1-53353 discloses a method in which chromic acid and resin are mixed at a certain ratio or more. Discloses a method of preventing the chromic acid from directly reacting with the plating by treating with a treatment solution mixed with, and improving the blackening resistance. Also, Zn-5
As a method for suppressing the blackening phenomenon performed on a% Al alloy-plated steel sheet or the like, a pretreatment of performing chromate treatment after plating described in JP-A-59-177381 and JP-A-63-65088 is described. As a method of treating with Ni or Co.

However, the method of treating with a treatment solution in which chromic acid and a resin are mixed at a certain ratio or more is based on a method in which aluminum is used.
Although the effect of improving the blackening resistance of Zn-Al-based plated steel sheets containing ultra-up to 75% by weight is recognized, it is not complete,
Rather, by mixing the resin in a certain ratio or more, the life of the processing solution is remarkably shortened, and the use of a resin that withstands the strong oxidizing power of chromic acid is disadvantageous in terms of cost.

Pretreatment with Ni, Co or the like may improve blackening resistance, but is disadvantageous in terms of cost because an expensive metal is used.

[0018]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned technical problems and provides a surface-treated steel sheet having excellent corrosion resistance at a worked portion and a scratched portion which cannot be obtained only by the self-repair effect of hexavalent chromium. It is an object.

Another object of the present invention is to provide a surface-treated steel sheet which is excellent in corrosion resistance in a processed portion and blackening resistance in a wet environment.

Another object of the present invention is to provide a surface-treated steel sheet which is excellent in corrosion resistance in a processed portion and blackening resistance in a stacked state.

Still another object of the present invention is to provide a method for producing the surface-treated steel sheet.

[0022]

The gist of the present invention for solving the above problems is as follows. (1) 0.1 to 100 mg of (A) chromium on the surface of galvanized steel sheet
/ m ² , (B) a surface-treated steel sheet characterized in that a film containing calcium in the range of 0.1 to 200 mg / m ² is formed (first invention).

(2) A zinc-based plated steel sheet contains 4
The surface-treated steel sheet according to the above (1), wherein the steel sheet is a Zn-Al-based plated steel sheet containing up to 25% by weight.

(3) A zinc-based plated steel sheet
The surface-treated steel sheet according to the above (1), wherein the steel sheet is a Zn-Al-based plated steel sheet containing more than 5 to 75% by weight.

(4) In producing the surface-treated steel sheet according to the above (1) to (3), a treatment liquid containing a water-soluble chromium compound and calcium or a compound thereof on the surface of a galvanized steel sheet, In the treatment liquid, (i) hexavalent chromium ion was added in an amount of 0.1
~ 50g / l, and (ii) applying a treatment liquid containing 1-50g / l calcium, and forming a film by heating at a maximum plate temperature of 60-300 ° C without washing with water. A method for producing a surface-treated steel sheet (fourth invention).

(5) The method for producing a surface-treated steel sheet according to (4), wherein the weight ratio of trivalent chromium ion / (trivalent chromium ion + hexavalent chromium ion) in the treatment liquid is 0.2 to 0.8. (Fifth invention).

(6) In producing the surface-treated steel sheet according to the above (1) to (3), a water-soluble chromium compound comprising a trivalent chromium compound and calcium or calcium or A treatment solution containing a compound,
In the treatment liquid, (i) 0.1 to 50 g / l of trivalent chromium ion;
(ii) Production of a surface-treated steel sheet characterized by applying a treatment liquid containing 1 to 50 g / l of calcium, and forming a film by heating at a maximum sheet temperature of 60 to 300 ° C. without washing with water. Method (sixth invention).

(7) The method for producing a surface-treated steel sheet according to the above (6), wherein the water-soluble chromium compound is chromium carboxylate (seventh invention).

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention and the reasons for limiting the same will be described below. The base zinc-coated steel sheets include zinc-coated steel sheets, Zn-Ni-coated steel sheets, Zn-Fe-coated steel sheets (electroplating, galvannealed), Zn-Cr-coated steel sheets, Zn-Mn-coated steel sheets, and Zn-coated steel sheets. Co-plated steel sheet, Zn-Co-Cr
Alloy-plated steel sheet, Zn-Ni-Cr-plated steel sheet, Zn-Cr-Fe-plated steel sheet, Zn-Al-based plated steel sheet (eg, Zn-5% Al alloy-plated steel sheet, Zn-55% Al alloy-plated steel sheet), Zn- Mg-plated steel sheet, Z
An n-Al-Mg plated steel sheet, or a zinc-based composite plated steel sheet in which a metal oxide, a polymer, or the like is dispersed (for example, Zn-SiO ₂ dispersed plating) can be used. Further, among the above platings, a multi-layer plated steel sheet obtained by plating two or more layers of the same or different types can be used.

Further, Zn- containing 4 to 25% by weight of aluminum
The Al-based plated steel sheet is a Zn-Al plated steel sheet that contains 4 to 25% by weight of Al as an essential component, and further contains trace elements such as La, Ce, Mg, and Si as needed. This includes a so-called Zn-5% Al alloy plated steel sheet.

Also, it contains more than 25 to 75% by weight of aluminum.
A Zn-Al-based coated steel sheet is an alloy containing Al: more than 25 to 75% by weight as an essential component, and further, if necessary, trace amounts of La, Ce, Mg, Si
It is a Zn-Al plated steel sheet that also contains elements such as So-called Zn-55
% Al alloy plated steel sheet is included in this.

As a method for plating the above-mentioned steel sheet, any practicable method among an electrolytic method, a melting method and a gas phase method may be adopted.

When the film of the present invention is applied to these plating surfaces, any alkali degreasing, solvent degreasing, surface conditioning treatment (alkaline treatment) may be applied to the plating surface in advance, as necessary, so that film defects and unevenness do not occur. Surface conditioning treatment, acidic surface conditioning treatment). Also,
From the viewpoint of further improving the blackening prevention effect of the steel sheet on which the film of the present invention is formed in a use environment, an acid or iron containing iron group metal ion (Ni ion, Co ion, Fe ion) may be previously formed on the plating surface as necessary. An alkaline surface conditioning treatment can also be performed. When electrogalvanizing is used as a base, from the viewpoint of further improving the blackening prevention effect,
Iron group metal ions (Ni ion, Co ion,
Fe ions) to contain these metals in the plating film.
1 ppm or more can be contained. In this case, the upper limit of the iron group metal concentration in the plating film is not particularly limited.

A feature of the present invention is that a chemical conversion coating containing a compound formed of (A) chromium having a barrier effect and (B) calcium having a self-repairing function is formed on the surface of a galvanized steel sheet. It is in.

Here, the adhesion amount of chromium in the film is preferably 0.1 mg / m ² or more and 100 mg / m ² or less. If it is less than 0.1 mg / m ² , the barrier effect by chromium is not sufficiently exhibited,
On the other hand, if it exceeds 100 mg / m ² , the effect of improving the barrier effect cannot be expected even though the treatment time is extremely long. Desirably, 10mg
More preferably the / m ² or more 70 mg / m ² or less.

The calcium in the film is not particularly limited. In addition to metallic calcium, calcium oxide, calcium hydroxide, calcium silicate, calcium carbonate, calcium phosphate, calcium molybdate and other simple salts containing only calcium as a cation, , Calcium phosphate / zinc, calcium / magnesium phosphate, calcium / zinc molybdate such as double salts containing cations other than calcium and calcium,
These may be mixed. The mechanism of its development is that at the film damaged part in a corrosive environment or a wet environment, calcium that is more noble than the plating metal elutes preferentially, and while the elution of the plating metal is suppressed, the eluted calcium precipitates at the film damaged part. By doing so, a protective film is formed. It is thought that the Zn-Al-based steel sheet containing 4 to 25% by weight of aluminum and the Zn-Al-based steel sheet containing more than 25 to 75% by weight of aluminum exhibit excellent corrosion resistance and blackening resistance in the processed part. Can be

The amount of calcium adhering to the film was 0.1%.
It is preferably from 1 mg / m ^{2 to} 200 mg / m ² . If it is less than 0.1 mg / m ² , the self-repair effect of calcium will be poor. In addition, in a Zn-Al-based plated steel sheet containing 4 to 25% by weight of aluminum and a Zn-Al-based plated steel sheet containing more than 25 to 75% by weight of aluminum, the effect of exhibiting corrosion resistance and blackening resistance due to calcium in the processed part is poor. If it exceeds 200 mg / m ² , the amount of calcium eluted will be excessive, and the corrosion resistance in the healthy film portion (the portion where the film has not been damaged by processing etc.) will be reduced. More preferably, it is more preferably 10 mg / m ² or more and 100 mg / m ² or less.

Here, by coexisting the above-mentioned compound comprising chromium and calcium, a remarkable effect of improving the corrosion resistance of the processed portion can be expected. Zn-Al-based steel sheet containing 4 to 25% by weight of aluminum, more than 25 to 75 of aluminum
In a Zn-Al-based plated steel sheet containing by weight, a remarkable improvement effect of blackening resistance can be expected.

This mechanism is based on the fact that a hardly soluble film made of chromium not only exhibits a barrier effect but also has an effect of supporting calcium in the film (binder effect), so that calcium is uniformly and strongly contained in the film. As a result, it is considered that the above-described self-repair effect can be more effectively exhibited, and thereby the corrosion reaction can be suppressed earlier. Add 4 to 25 aluminum
Zn-Al plated steel sheet containing 25% by weight, aluminum more than 25 ~ 7
In a Zn-Al-based plated steel sheet containing 5% by weight, the blackening phenomenon can be suppressed.

Further, in addition to the above-mentioned film constituting substances, oxide fine particles such as silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, cerium oxide and antimony oxide can be further contained.

Further, in addition to the above-mentioned film constituting materials, organic polymer resins such as epoxy resins, polyhydroxy polyether resins, acrylic copolymer resins, ethylene-acrylic acid copolymer resins, alkyd resins , Polybutadiene resin, phenol resin, polyurethane resin,
It may contain a polyamine resin, a polyphenylene resin, and the like.

In the present invention, a treatment solution containing a water-soluble chromium compound and calcium or a compound thereof, wherein the treatment solution contains (i) hexavalent chromium ion in an amount of 0.1 to 50 g / l and (i)
i) By applying a treatment liquid containing 1 to 50 g / l of calcium and heating it in the range of the maximum reached plate temperature of 60 to 300 ° C without washing with water to form a chemical conversion treatment film, the corrosion resistance of the processed part is excellent. A surface-treated steel sheet can be manufactured. Also, any of a Zn-Al-based plated steel sheet containing 4 to 25% by weight of aluminum and a Zn-Al-based plated steel sheet containing more than 25 to 75% by weight of aluminum are further improved in blackening resistance.

Here, the hexavalent chromium ion concentration is 0.1 g / l
If the amount is less than 0.5 g / l, the coating amount must be significantly increased in order to obtain a desired chromium adhesion amount, coating unevenness is likely to occur, and if it exceeds 50 g / l, the reactivity of the processing solution is extremely high.
The amount of dissolution of the plating film increases, and the stability of the processing solution is lowered, which is not preferable.

The hexavalent chromium ion species is not particularly limited as long as it is water-soluble.
Ammonium chromate and the like correspond to this, and hardly soluble chromium compounds such as zinc chromate, strontium chromate and barium chromate do not correspond thereto.

In the above water-soluble chromium compound, the weight ratio of trivalent chromium ion / (trivalent chromium ion + hexavalent chromium ion) (in terms of chromium metal) is more preferably 0.2 to 0.8. A surface-treated steel sheet having excellent corrosion resistance can be manufactured. Add 4 aluminum
Up to 25% by weight Zn-Al plated steel sheet, 25 aluminum
Any Zn-Al-based plated steel sheet containing ultra-up to 75% by weight has better blackening resistance.

If the weight ratio of trivalent chromium ion / (trivalent chromium ion + hexavalent chromium ion) (in terms of metallic chromium) is less than 0.2, the hexavalent chromium ion concentration in the film becomes excessive, and the film is hardly soluble. In a corrosive environment, a Zn-Al-based steel sheet containing 4 to 25% by weight of aluminum without contributing to corrosion resistance
In a Zn-Al-based plated steel sheet containing more than 25 to 75% by weight, the amount eluted without contributing to blackening resistance increases, which is not preferable from the viewpoint of economy and environmental compatibility. If it exceeds 0.8, the processing solution is likely to gel, and the stability of the processing solution is significantly reduced.

According to the present invention, there is provided a treatment liquid containing a water-soluble chromium compound composed of a trivalent chromium compound and calcium or a compound thereof.
(i) 0.1 to 50 g / l of trivalent chromium ion and (ii) a treatment liquid containing 1 to 50 g / l of calcium, and heated at a maximum plate temperature of 60 to 300 ° C. without washing with water. By forming the chemical conversion coating, the corrosion resistance of the processed part is excellent, and the Zn-Al-based steel sheet containing 4 to 25% by weight of aluminum and the Zn-Al-based steel sheet containing more than 25 to 75% by weight of aluminum are more resistant. Blackening is also excellent. In the method of the present invention, since the treatment solution does not contain hexavalent chromium ions,
There is no problem of elution of hexavalent chromium out of the system, and high self-repairability can be exhibited without relying on hexavalent chromium.

Here, the trivalent chromium ion concentration is 0.1 g / l
If the amount is less than 0.5 g / l, the coating amount must be significantly increased in order to obtain a desired chromium adhesion amount, coating unevenness is likely to occur, and if it exceeds 50 g / l, the reactivity of the processing solution is extremely high.
The amount of dissolution of the plating film increases, and the stability of the processing solution is lowered, which is not preferable.

The trivalent chromium compound is not particularly limited as long as it is water-soluble. For example, chromium chloride,
Examples thereof include chromium sulfate, chromium acetate, and chromium formate, and particularly, chromium carboxylate such as chromium acetate and chromium formate is preferable.

The calcium or its compound coexisting with the water-soluble chromium compound is not particularly limited.
In addition to calcium oxide and calcium hydroxide, single salts containing only calcium as a cation such as calcium silicate, calcium carbonate, calcium phosphate and calcium molybdate, as well as calcium and zinc such as calcium and zinc phosphate, calcium and magnesium phosphate, and calcium and zinc molybdate Any of double salts containing cations other than the above may be used, and these may be mixed. Further, a reaction product with another compound in the treatment liquid is included in the reaction liquid, and may be calcium or calcium ion.

When the calcium concentration is less than 1 g / l,
Zn-Al-plated steel sheet containing 4 to 25% by weight of aluminum, cannot contain enough calcium to exhibit sufficient self-repair effect in the formed film, more than 25 to 75 of aluminum
In any of the Zn-Al-based plated steel sheets containing wt%, the formed film cannot contain enough calcium to exhibit sufficient corrosion resistance and blackening resistance in the processed portion. Also, if it exceeds 50 g / l,
It is not preferable because the calcium content in the coating becomes extremely high, and the corrosion resistance of the sound coating is reduced.

Further, inorganic acids such as phosphoric acid, polyphosphoric acid, boric acid, sulfuric acid and nitric acid can be contained as a film-forming auxiliary.

As a method of applying the treatment liquid described above,
Although there is no particular limitation, application by a roll coater or a ringer roll, or application by dipping and air knife drawing may be mentioned.

After coating, it is preferable to heat at the maximum temperature of 60 to 300 ° C. without washing with water. Here, if the maximum reached plate temperature is less than 60 ° C., the barrier effect is high.
When the chromium (VI) compound is not sufficiently formed, and at temperatures exceeding 300 ° C., numerous cracks are generated to the extent that the self-repair effect does not reach the coating.In both cases, the corrosion resistance of the processed part and the sound part of the coating is remarkable. Will drop.

[0055]

(Example 1) A zinc-coated steel sheet shown in Table 1 was used as a base plate for processing, and coating was performed with a roll coater under the processing solution composition and drying temperature shown in Tables 2 to 4, It was dried by heating without washing with water to form a chemical conversion coating. The amount of adhesion was controlled by the amount of application, the peripheral speed of the roll coater, the amount of reduction, and the like. The quality evaluation of the obtained surface-treated steel sheet was performed as follows.

Corrosion Resistance of Processed Section A notch reaching the iron base was cut into the sample surface over a width of 0.3 mm and a length of 5 cm with a cutter knife, and the following composite corrosion test was performed for 100 cycles.

3 wt% salt water spray test (30 ° C .; 0.5 hour) ↓ Wet test (30 ° C., 95% RH; 1.5 hours) ↓ Hot air drying test (50 ° C., 20% RH; 2.0 hours) ↓ Hot air drying test (30 (° C, 20% RH; 2.0 hours) The evaluation was performed based on the area ratio of rust generation in a region of 5 mm on both sides of the cut line. The state of rust (color tone)
Depends on the Al concentration of the plating film,
White rust was generated in a Zn-Al-based steel sheet having an Al concentration of 25% by weight or less, and gray to black rust was generated in a Zn-Al-based steel sheet having an Al concentration of more than 25 to 75% by weight.

◎: No rust generation ○ +: Rust generation area rate less than 5% ○: Rust generation area rate 5% or more and less than 10% ○ −: Rust generation area rate 10% or more and less than 25% △: Rust generation area rate 25 % Or more and less than 50% ×: Rust generation area rate 50% or more

The corrosion resistance of the film sound part was evaluated by the same criteria as above based on the rusting area ratio of the sample surface by performing 200 cycles of the above-described complex corrosion test on the sample that had not been subjected to any processing such as scratching or bending. The state of rust is the same as in the case of the above-mentioned evaluation of the corrosion resistance of the processed portion.

Blackening Resistance A Zn-Al-based plated steel sheet containing 4% by weight or more of Al was evaluated for blackening resistance. Specifically, the following according to the Al concentration
Performed in two ways. <Zn-Al-based plated steel sheet with an Al concentration of 4 to 25% by weight: N in Table 1
o.2> Stack the sample that has not been subjected to any processing such as scratching or bending, leave it in a wet test machine (HCT) for 6 days, visually observe the appearance of the sample, and determine the degree of blackening and blackening area. The blackening resistance was evaluated according to the following criteria. ◎: No change in appearance before and after the test. 有 り: Slight change in spot-like appearance after the test (Area: 10%
△: After the test, there is a planar appearance change part (area: 10% or more and 50% or more)
%: ×: There is at least 50% of a black discolored portion or a planar appearance changed portion after the test.

(Zn-Al-based steel sheet having an Al concentration of more than 25 to 75% by weight: No. 3 in Table 1) For a sample that has not been subjected to any processing such as scratching or bending, the temperature is 80 ° C. and the relative humidity is 95% RH. Of whiteness (L value) when left in a constant temperature and humidity controlled atmosphere atmosphere for 24 hours ΔL (L value before test-L value after test)
Was measured and evaluated according to the following criteria. A: ΔL ≧ −1.0 ○: −1.0> ΔL ≧ −2.0 Δ: −2.0> ΔL ≧ −4.0 ×: −4.0> ΔL The evaluation results are shown in Tables 2 to 4.

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

[Table 4]

As shown in Tables 2 to 4, the steel sheet having the coating within the range of the first invention is, as compared with the steel sheet of the comparative example having the coating out of the range of the first invention, of course, having a sound coating portion.
Corrosion resistance in the processed part is significantly improved. Furthermore, the steel sheet containing 4% by weight or more of Al having a film formed within the scope of the first invention is more resistant to blackening than the steel sheet of the comparative example containing 4% by weight or more of Al having a film outside the scope of the first invention. I.e., Al
The Zn-Al-based steel sheet containing up to 25% by weight has improved blackening resistance in a stacked state, and the Zn-Al-based steel sheet containing more than 25 to 75% by weight of Al has improved blackening resistance in a humid environment.

Further, when forming a film within the scope of the first invention, the steel sheet manufactured under the conditions within the range of the fourth invention has good film quality. On the other hand, the steel sheet of the comparative example (No. 61, 64) in which a film was formed at a drying temperature outside the range of the fourth invention,
Poor film quality.

(Example 2) A zinc-coated steel sheet shown in Table 1 was used as a base plate for processing, and was applied by a roll coater under the processing solution composition and drying temperature shown in Tables 5 to 7, and washed with water. Without heating and drying, a chemical conversion coating was formed. The amount of adhesion was controlled by the amount of application, the peripheral speed of the roll coater, the amount of reduction, and the like. The quality evaluation of the obtained surface-treated steel sheet was performed as follows.

Corrosion Resistance of Processed Section A notch reaching the iron base was cut into the sample surface over a width of 0.3 mm and a length of 5 cm with a cutter knife, and a salt spray test in accordance with JIS Z2371 was performed for 120 hours. Evaluation is the rust generation area ratio in the area of 5 mm each side of the score line,
Performed according to the same standard as in Example 1. The state of rust (color)
Is the same as that in the case of the evaluation of the corrosion resistance of the processed portion in Example 1.

Corrosion resistance of sound film in a healthy part The above-mentioned salt water spray test was carried out on a sample which had not been subjected to any processing such as scratching or bending, and evaluated based on the same standard as in Example 1 based on the rust generation area ratio of the sample surface. The state of rust is the same as in the case of the above-mentioned evaluation of the corrosion resistance of the processed portion.

Black Degradation Resistance A Zn-Al-based plated steel sheet containing 4% by weight or more of Al was evaluated for black degradation resistance in the same manner as in Example 1. The evaluation results are shown in Tables 5 to 7.

[0072]

[Table 5]

[0073]

[Table 6]

[0074]

[Table 7]

From Tables 5 to 7, it can be seen that the steel sheet on which the coating within the first invention range is formed has, as a matter of course, not only the film sound portion, but also the steel sheet of the comparative example having the coating outside the first invention range.
Corrosion resistance in the processed part is significantly improved. Furthermore, the steel sheet containing 4% by weight or more of Al having a film formed within the scope of the first invention is more resistant to blackening than the steel sheet of the comparative example containing 4% by weight or more of Al having a film outside the scope of the first invention. I.e., Al
The Zn-Al-based steel sheet containing up to 25% by weight has improved blackening resistance in a stacked state, and the Zn-Al-based steel sheet containing more than 25 to 75% by weight of Al has improved blackening resistance in a humid environment.

When forming a film within the scope of the first invention, the steel sheet formed at a drying temperature within the scope of the fourth invention is the steel sheet of the comparative example formed at a drying temperature outside the range of the fourth invention. Good film quality is obtained compared to (No.61,64). In addition, when the treatment liquid having a Cr reduction rate within the range of the fifth invention is used, a better film quality can be obtained as compared with the case where the treatment liquid having a Cr reduction rate lower than the fifth invention range is used (No. 65). Have been. In the case of the treatment liquid (No. 68) having a Cr reduction ratio exceeding the range of the fifth invention, the treatment liquid gelled, and thus the quality evaluation of the steel sheet was not performed.

(Example 3) A zinc-plated steel sheet shown in Table 1 was used as a base plate for treatment, and a chromium salt shown in Table 8 was used as a trivalent chromium compound. Originally, the composition was applied by a roll coater and dried by heating without washing with water to form a chemical conversion coating. The amount of adhesion was controlled by the amount of application, the peripheral speed of the roll coater, the amount of reduction, and the like. The quality evaluation of the obtained surface-treated steel sheet was performed as follows.

Corrosion Resistance of Processed Parts A cut reaching the iron base was made on the sample surface over a width of 0.3 mm and a length of 5 cm with a cutter knife, and the following composite corrosion test was performed for 100 cycles. 3wt% salt spray test (30 ° C; 0.5 hours) ↓ Wet test (30 ° C, 95% RH; 1.5 hours) The evaluation is based on the rust generation area ratio in the area of 5mm on both sides of the cut line, the same standard as in Example 1. I went in. The state of rust (color tone) is the same as in the case of the evaluation of the corrosion resistance of the processed portion in Example 1.

The corrosion resistance of the sound portion of the film was evaluated by applying the above-mentioned complex corrosion test to the sample which had not been subjected to any processing such as scratching or bending for 200 cycles, and evaluated based on the same criterion as above based on the rust generation area ratio of the sample surface. The state of rust is the same as in the case of the above-described evaluation of the corrosion resistance of the processed portion.

Black Degradation Resistance A Zn—Al-based plated steel sheet containing 4% by weight or more of Al was evaluated for black degradation resistance in the same manner as in Example 1. The evaluation results are shown in Tables 9 to 11.

[0081]

[Table 8]

[0082]

[Table 9]

[0083]

[Table 10]

[0084]

[Table 11]

From Tables 9 to 11, it can be seen that the steel sheet having the coating within the first invention range has not only the sound portion but also the sound portion in comparison with the comparative steel sheet having the coating outside the first invention range. Corrosion resistance in the processed part is significantly improved. No.46,65
As can be seen from the comparison of Nos. To 67, when chromium carboxylate is used as the trivalent chromium compound (Nos. 46 and 67), the corrosion resistance and the blackening resistance are more excellent.

Further, a film within the scope of the first invention was formed.
The steel sheet containing 4% by weight or more of Al has a blackening resistance, that is, Zn-Al containing 4 to 25% by weight of Al, compared to the steel sheet of the comparative example containing 4% by weight or more of Al having a coating outside the scope of the first invention. The resistance to blackening in a stacked state is improved in a system-coated steel sheet, and the resistance to blackening in a wet environment is improved in a Zn-Al-based steel sheet containing more than 25 to 75% by weight of Al.

Further, when forming a film within the scope of the first invention, the steel sheet manufactured under the conditions within the scope of the sixth invention has good film quality. On the other hand, the steel sheets of the comparative examples (Nos. 61 and 64) in which the film was formed at a drying temperature outside the range of the sixth invention were inferior in film quality.

[0088]

According to the present invention, it is possible to obtain a surface-treated steel sheet having excellent corrosion resistance of a worked portion and a flaw, which cannot be obtained only by the self-repair effect of hexavalent chromium.

Also, the zinc-based plated steel sheet converts aluminum
In the case of a Zn-Al-based plated steel sheet containing 4 to 25% by weight, a surface-treated steel sheet having excellent corrosion resistance in a processed portion and further excellent blackening resistance in a stacked state can be obtained.

Further, zinc-coated steel sheet converts aluminum
In the case of a Zn-Al-based plated steel sheet containing more than 25 to 75% by weight, a surface-treated steel sheet having excellent corrosion resistance in a processed portion and further excellent blackening resistance in a humid environment can be obtained.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaaki Yamashita 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term in Nihon Kokan Co., Ltd. 4K026 AA02 AA07 AA09 AA13 AA22 BA06 BB08 BB10 CA16 CA18 CA19 CA20 CA38 DA02 DA11 DA15

Claims (7)

[Claims] To 1. A surface of the galvanized steel sheet, characterized by being formed film contained in (A) chromium 0.1~100mg / m ^2, (B) the range of calcium is 0.1 to 200 mg / m ² And surface treated steel sheet. 2. A galvanized steel sheet containing 4 aluminum.
The surface-treated steel sheet according to claim 1, wherein the steel sheet is a Zn-Al-based plated steel sheet containing up to 25% by weight. 3. A galvanized steel sheet comprising 25 aluminum.
The surface-treated steel sheet according to claim 1, wherein the steel sheet is a Zn-Al-based plated steel sheet containing more than 75% by weight. 4. In the production of the surface-treated steel sheet according to claim 1, a treatment liquid containing a water-soluble chromium compound and calcium or a compound thereof on the surface of a galvanized steel sheet. And (i) hexavalent chromium ion
50 g / l and (ii) applying a treatment liquid containing 1 to 50 g / l of calcium, and forming a film by heating at a maximum plate temperature of 60 to 300 ° C. without washing with water. Manufacturing method of surface treated steel sheet. 5. The method for producing a surface-treated steel sheet according to claim 4, wherein the weight ratio of trivalent chromium ion / (trivalent chromium ion + hexavalent chromium ion) in the treatment liquid is 0.2 to 0.8. 6. A method for producing the surface-treated steel sheet according to claim 1, wherein the surface of the galvanized steel sheet contains a water-soluble chromium compound composed of a trivalent chromium compound and calcium or calcium or a compound thereof. A solution, wherein (i) 0.1 to 50 g / l of trivalent chromium ion is added to the treatment solution;
i) A method for producing a surface-treated steel sheet, comprising applying a treatment liquid containing 1 to 50 g / l of calcium, and forming a film by heating at a maximum sheet temperature of 60 to 300 ° C. without washing with water. . 7. The method for producing a surface-treated steel sheet according to claim 6, wherein the water-soluble chromium compound is chromium carboxylate.