JPH09228067A - Surface treated steel sheet excellent in resistance against environmental pollution and corrosion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated steel sheet containing no hexavalent chromium and having excellent preventing property against the environmental pollution which is advantageous for the global environment and shows a corrosion resistance same as or higher than a conventional chromate treatment. SOLUTION: After the surface of a steel sheet or galvanized steel sheet is subjected to Zn-Cr alloy plating (Cr= 7 to 40%), the surface of the sheet is coated with a film containing no hexavalent chromium but containing an insoluble salt-forming anion, or a film containing no hexavalent chromium but containing an insoluble saltforming anion and oxide colloid and/or cations. The obtd. surface treated steel sheet has excellent preventing property against the environmental pollution and excellent corrosion resistance.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a surface-treated steel sheet having excellent environmental pollution resistance and corrosion resistance.

[0002]

2. Description of the Related Art A plated steel sheet is used in the fields of automobiles, home appliances, building materials, etc. due to its excellent corrosion resistance. Chromate-treated steel sheets that have been subjected to a treatment such as chromate treatment for the purpose of preventing white rust of plating and improving corrosion resistance on the plated steel sheets, and further, subjecting the chromate-treated surface to a resin layer are well known. . This method is widely used because it is inexpensive and has excellent corrosion resistance. These chromate-treated steel sheets are treated with a liquid containing hexavalent chromium such as chromic acid and dichromic acid, and the chromate film also contains hexavalent chromium.

It is due to the self-healing effect of hexavalent chromium that the chromate-treated plated steel sheet is very excellent in corrosion resistance not only on a plain plate but also after drawing. Hexavalent chromium is highly oxidative and highly reactive, and is soluble in water, and the trivalent chromium oxide produced by the reduction of hexavalent chromium forms a glass-like hardly soluble film and is resistant to corrosion. Is high. Chromate treatment uses this principle, and hexavalent chromium dissolved in water in the corrosive environment redox-reacts on the exposed zinc part of the chromate film in the corroded and processed parts, and the film is constantly recreated. .

However, since hexavalent chromium is harmful, a chromate treatment technique which is an alternative to hexavalent chromium has been desired from the viewpoint of pollution prevention, and in recent years, from the viewpoint of protecting the global environment, a chromate substitute free of hexavalent chromium has been further developed. Technology is being coveted. Various attempts have been made as chromate substitution techniques to meet these social demands. These can be roughly divided into three groups. For example, as the first, JP-A-50-28449 and JP-A-55-21.
529, JP-A-63-50484, JP-A-63-227786, and JP-A-59-133373.
As disclosed in Japanese Patent Publication, etc., it is difficult to dissolve a plated steel sheet containing a phosphate coating, silica, a metal oxide sol such as alumina, silicates, and even water-soluble resins and mixtures thereof. Aiming for film coating with salts.

Second, JP-A-54-32140, JP-A-58-199873, JP-A-61-583, 62-274077, and JP-A- 64-277.
Such as Mg, Mo, W, V, Ti, Zr,
The aim is to perform a treatment similar to that of chromate by subjecting the plated steel sheet to a treatment containing metals such as Co, Mn, and Ni around Cr in the periodic table, that is, metal ions having properties close to Cr, metal oxide ions, and the like.

Third, JP-A-54-128950, JP-A-55-148773, and JP-A-58-1.
9481, JP-A-63-18084, hydroxylamines, tannic acids, pyrazole derivatives,
It is disclosed that a substance such as containing an organic nitro compound is applied to a zinc-based plated steel sheet, and attention is paid to the adsorptivity, metal complexing property, and oxidative property of these compounds, and the aim is to suppress the corrosion reaction of the zinc plating surface. . However, according to these techniques, although the corrosion resistance is improved as compared with the plated steel sheet which is not subjected to the chromate treatment, it is the current situation as compared with the chromate treatment.

[0007]

In view of the above situation, the present inventors have no hexavalent chromium at all, are excellent in environmental pollution resistance, are advantageous to the global environment, and have corrosion resistance equal to or higher than that of the existing chromate treatment. The purpose is to provide a surface-treated steel sheet.

[0008]

The features of the present invention are as follows. (1) Zn--containing Zn as a main component and Cr as a second component in an amount of 7% or more and 40% or less on the surface of a steel plate or a plated steel plate;
Excellent in environmental pollution resistance and corrosion resistance, characterized in that a Cr-based alloy plating is applied, and a coating containing a sparingly soluble salt-forming anion containing no hexavalent Cr is applied on the surface of the Zn-Cr-based alloy plating. Surface treated steel sheet. (2) Zn-Cr alloy plating is mainly composed of Zn and Cr
Is a second component, and a third component group is a Zn-Cr-based alloy containing 0.5% or more of Ni, Fe, Co, and Mn in a proportion of not more than the Cr content of the second component and 0.5% or more. A surface-treated steel sheet having excellent environmental pollution resistance and corrosion resistance as described in (1) above, which is a plating.

(3) The film on the surface of the Zn-Cr alloy plating contains a sparingly soluble salt-forming anion, and as a cation species, in addition to the Zn-Cr alloy alloy element component, Co, Ni, M
n, Fe, Mg, Ca, Sr, Al, 1 of lanthanoid
The surface-treated steel sheet excellent in environmental pollution resistance and corrosion resistance according to the above (1) or (2), characterized in that the surface-treated steel sheet contains one or more kinds. (4) The above-mentioned (1), (2) or (3), wherein the coating film on the surface of the Zn-Cr alloy plating contains a sparingly soluble salt-forming anion and an oxide colloid. It is a surface-treated steel sheet with excellent environmental pollution resistance and corrosion resistance.

The inventors of the present invention have diligently studied, and as a result, the inventors of the present invention have for many years been involved in the development of a Zn-Cr type plated steel sheet. Zn-
Cr-based alloy-plated steel sheets have remarkably excellent corrosion resistance as compared with conventional Zn-based plated steel sheets as known from JP-A-1-55397 and JP-A-1-191977. However, although the Zn-Cr alloy plated steel sheet is certainly superior in terms of rust prevention of the steel sheet, it is compared with the chromate treated material in terms of white rust occurrence time which is Zn rust at the initial stage of corrosion. Fast. It is presumed that this is because Zn-Cr plating forms a highly corrosion-resistant film by a network of trivalent chromium in the initial corrosion and achieves long-term rust prevention thereafter. The inventors of the present application paid attention to this characteristic,
If high corrosion resistant film formation of n-Cr plating can be formed in an extremely short period at the beginning of corrosion, white rust which is the initial rust of corrosion does not occur even if hexavalent Cr is completely absent, and it is equivalent to the chromate treated material. We came to the knowledge that the above performance can be obtained,
It is the invention.

First, the plated steel sheet to be subjected to Zn-Cr plating in the present invention is preferably a plated steel sheet having a base potential lower than that of the steel sheet. Precious electroplating, eg Au, N
A steel plate on which a general plating such as i, Cr plating, Sn plating, or Pb plating is applied has a large potential difference between the Zn-Cr plating layer and the lower plating layer, and the effect of the present invention is small. Plating with a base potential lower than that of the steel plate has a high sacrificial and anticorrosion effect on the steel plate, but since the plating itself is inherently active, chromate or other treatment is performed in the current technology in order to suppress corrosion rust. Of. Specific examples of the plated steel sheet having such a base potential include an electrogalvanized steel sheet, a Zn-Ni electric alloy plated steel sheet, a Zn-Fe electric alloy plated steel sheet, a Zn-Mn electric alloy plated steel sheet, and a hot dip galvanized steel sheet. , Galvannealed steel sheet, Zn-Al plated steel sheet, and dispersion plated steel sheet in which oxides or resin polymers such as SiO ₂ , Al ₂ O ₃ and TiO ₂ are dispersed in the plated steel sheet, Al plated steel sheet and the like. .

Next, the composition of the plating applied to the surfaces of these plated steel sheets or steel sheets (hot rolled steel sheets, cold rolled steel sheets) is as follows. Must have Zn as a main component. The second component, Cr, forms a highly corrosion resistant film during corrosion,
In order to exert the corrosion resistance effect, 7% or more is required.
The effect of corrosion resistance is improved by increasing the content rate, but 40%
If it exceeds the range, the plating layer becomes hard and the adhesion of the plating during processing deteriorates, which is not practical.

Further, as a third component group, Ni, Fe,
Inclusion of one or more of Co and Mn in a range not exceeding the second component enhances the reaction with the plating layer in the treatment of the poorly soluble salt forming film applied to the upper layer of the plating layer and fixes the film. Is effective in. If the total amount of the third element component group is less than 0.5%, the effect is small, and there is no difference in the fixed effect from the case of not containing Ni, Fe, C.
It is preferable to contain 0.5% or more of o and Mn. If the total content of the third component elements exceeds the chromium content, the formation of a highly corrosion-resistant film by Cr is reduced, and the effect of corrosion resistance is reduced, which is not preferable.

It should be noted that SiO ₂ , Ti and
Even if an oxide colloid such as O ₂ or Al ₂ O ₃ is dispersed, in addition, inevitable impurities during plating, such as Pb,
Sn, Sb, Mo, Na, K, Li, B, P, Mg, C
Even if a small amount of u, Ag, Cd, C, etc. is contained, the effect of preventing hexavalent chromium in the present invention from the initial rust does not essentially change.

When the Zn-Cr alloy plating amount is 3 g / m ² or more on the cold-rolled steel sheet, not only the initial rust prevention effect but also the same or more rust prevention effect as that of ordinary zinc plating can be obtained. The amount necessary for preventing the initial occurrence of white rust is 0.5 g / m ² or more, and the plating layer base is an electrogalvanized steel sheet, a Zn-Ni electroalloy-plated steel sheet, Z
Even if it is a galvanized steel sheet such as an n-Fe electric alloy plating, a hot dip galvanized steel sheet, an alloyed hot dip galvanized steel sheet, a Zn-Al galvanized steel sheet, a dispersion galvanized steel sheet, an Al galvanized steel sheet,
The essence of the present invention does not change in terms of suppressing the initial occurrence of white rust. Regarding the crystal structure of the plating layer of the Zn-Cr alloy plating, when the η layer showing pure Zn is not recognized, the effect of preventing the initial rust of the present invention is greater depending on the amount of Cr.
If the composition is 7% or more, even if the η layer is recognized, it has the same or more initial rust prevention effect as that of chromate.

Next, a film containing a sparingly soluble salt-forming anion formed on the Zn-Cr alloy plating layer will be described. The sparingly soluble salt-forming anion is an anion that forms a sparingly soluble salt with Cr ^3+, and refers to a small anion product having a solubility product of about 10 ⁻¹⁰ or less in terms of anhydrous normal salt. Examples of such anion species include phosphates such as phosphate ion, pyrophosphate ion, triphosphate ion, and polyphosphate ion, boric acid, molybdic acid, vanadic acid,
There are tungstic acids and the like, and these are particularly preferable because they have no possibility of oxidizing Cr to hexavalent. Permanganates also form a sparingly soluble salt and are effective as an effect of preventing initial rust, but they are not desirable because they have high oxidizing power and have the possibility of oxidizing trivalent chromium to hexavalent chromium.

Although chromic acids similarly form sparingly soluble salts, they are contrary to hexavalent chromium-free, which is the gist of the present invention, and are not within the scope of the present invention. As a precaution, as the soluble salt-forming anion species that does not form a hardly soluble salt, there are chloride ions, fluoride ions, nitrate ions, sulfate ions, etc. When the salt-forming anion species is the main component and is used as an etching agent or the like for forming the film and the soluble salt-forming anion species is contained in the film, the effects of the present invention are exhibited and are within the scope of the invention.

The coating amount of the hardly soluble salt-forming anion species varies depending on the kind of the element, but the effect is exhibited when the amount of the element is 5 mg / m ² or more, and preferably 20 mg / m ² That is all. The upper limit is not particularly specified, but the effect is saturated at 200 mg / m ² or more. When the above-mentioned sparingly soluble salt-forming anionic species are present on the surface of the Zn-Cr plating, not only in the unprocessed part but also in the film of the ironing part such as the cup drawing process as well as the chromate material of the zinc-based plating. It is presumed that the effect of preventing the initial occurrence of white rust is exhibited even in the damaged portion as follows.

These sparingly soluble salt-forming anions are dissolved and dissociated in water in a corrosive environment, although in very small amounts.
For this reason, the Zn-Cr plating layer which is the base reacts with trivalent Cr ions generated by a slight amount of corrosion, which favors the deposition of trivalent chromium salt. For this reason, the highly corrosion-resistant coating film of trivalent chromium is formed at an early stage and exhibits the rust preventive effect, so that the initial rust can be suppressed. Even if the film is damaged due to processing and corrosion processes, the trivalent chromium film is similarly regenerated and a self-repairing action is exhibited. Since the formed film is a chromate film or a trivalent chromium film which is made of stainless steel and functions as an anticorrosion film, it is presumed that the anticorrosion effect is sufficient.

Further, in a film containing a sparingly soluble salt-forming anionic species, Co, Ni, Mn, Mg, Ca, Sr,
Inclusion of one or more cations of Al and lanthanoid as the cation strengthens the Zn oxide film, and these cations themselves also tend to form a sparingly soluble salt with the sparingly soluble salt forming anion. Since it also has an effect of retaining the soluble salt-forming anion for a long period of time against the corrosion time, the effect of fixing the hardly soluble salt-forming anion to the film is enhanced and the initial rust suppressing effect is further exerted.

When the amount of the cation species is less than 3 mg / m ^{2 in} terms of the elemental metal element, the effect is small, and the difference in the fixing effect is small when it is not contained, so that it is preferably 3 mg / m ² or more. The upper limit is not particularly specified, but the effect is saturated at 200 mg / m ² or more. In addition, oxide colloids (eg, SiO ₂ , Ti
O ₂ , Sb ₂ O ₅ , ZrO, Al ₂ O ₃ and other colloids) increase the thickness of the coating film and suppress the penetration of corrosion-promoting substances into the coating film. It is considered that it will also act as a trap site when the Cr corrosion product from the Zn-Cr-based alloy plating layer of the underlayer penetrates and elutes, so that the initial rust suppressing effect of the surface-treated steel sheet is remarkably improved.

The effect of these oxide colloids is recognized at 20 mg / m ² or more in terms of oxide. There is no particular upper limit to the corrosion resistance, but if it is 2000 mg / m ² or more, the workability deteriorates and the insulating property increases, and the weldability deteriorates, which is not practical. If the amount is less than 20 mg / m ² , the effect is small, and the effect is not different from the effect of the film containing only the hardly soluble salt-forming anion species as described above.
0 mg / m ² is preferred. It should be noted that the inclusion of both the above-mentioned cations and oxide colloids in the hardly soluble salt-forming anion-containing film is presumed to have independent actions, so that the initial rust suppressing effect is synergistically exhibited. It should be noted that ions that are inevitably mixed during the film formation, such as Na,
Even if an alkali metal ion such as K or Ba is contained in the film, the effect of suppressing the initial rust of the present invention does not change.

The present invention is intended to further improve the corrosion resistance, lubricity, coating adhesion, and fingerprint resistance, and atomizes colloids, acrylic and epoxy resins, and waxes such as polyoxyethylene. It is possible to add a class to the coating of the invention or to coat it on the coating of the invention without departing from the invention. Further, addition of inhibitors such as tannic acid and amines to the film of the present invention is not particularly hindered. Even if an element added or contained in the underlying Zn—Cr-based plating reacts in the film of the present invention during the treatment and is contained as a part of the film-forming component, as long as it is within the component range of the present invention, the present invention The effect of is demonstrated.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described. The Zn-Cr alloy plating can be produced by a known method, for example, an acidic bath containing Zn ²⁺ ions, Cr ³⁺ ions and a polyoxyalkylene derivative. A method for forming a film containing a sparingly soluble salt-forming anion is described in Z
A solution containing a sparingly soluble salt-forming anion is applied to a steel plate or a plated steel plate on the surface of which an n-Cr alloy plating is applied, by dipping, spraying, coating with a method such as roll, electrolysis, It can be reacted and produced.
Of course, rinsing and / or drying may be performed after bringing the steel sheet into contact with the solution containing the sparingly soluble salt-forming anion.

Co, Ni, Mn, Mg, Ca, Sr, A
It is advantageous in terms of production process to mix lanthanoid cations and oxide colloids into the hardly soluble salt-forming anion-containing film in a treatment solution containing the hardly soluble salt-forming anion. Alternatively, they may be applied separately. In this case, the film may have two or more layers, but the mechanism that the sparingly soluble salt-forming anion elutes in the water in a corrosive environment and acts on the corrosion point of the plating is the same. The effect of suppressing rust does not change. Similarly, the order of the treatment of the hardly soluble salt-forming anion, cations, and oxide colloids on the plating surface does not particularly affect the effect.

[0026]

EXAMPLES Next, examples of the present invention, along with comparative examples, are shown in Tables 1 and 2 for conditions of treated steel sheet, Zn—Cr alloy plating and hardly soluble salt forming film. List its performance. Example Nos. 27 to 37 are the same as the invention of claim 1,
Example Nos. 38 to 47 are the same as those of the invention of claim 2
Nos. 9 to 22 are the same as the invention of claim 3 and are Nos.
26 corresponds to the invention of claim 4. The present invention can exhibit corrosion resistance equal to or higher than that of the current chromate-treated material (Comparative Example 1) both in the non-processed part and the processed part, and the elution of Cr is much less than in the chromate material and traced. is there. Comparative Example 2 is a Zn-Cr plating only, Comparative Examples 3 and 6 are those without a Zn-Cr plating layer, Comparative Example 4
Is a Zn-Cr plated layer having a low Cr composition, Comparative Example 5
Is an anion species of NO ₃ and does not become a hardly soluble salt. In each case, the effect of suppressing the initial rust is less than that of the chromate material. The inventions of claims 2 and 3 exhibit the improvement of the fixing rate of the coating and the corrosion resistance, and the invention of claim 4 dramatically shows the improvement of the corrosion resistance.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

Note that notes 1 to 4 in the table indicate the following items. Note 1) Treated steel sheet A normal cold-rolled steel sheet having a plate thickness of 0.8 mm and various zinc-based plated steel sheets were prepared and used according to actual equipment or a known preparation method. The meanings of the symbols in the table are as follows. CR: Cold rolled steel sheet, EG: Electrogalvanized steel sheet, GA: Alloyed hot-dip galvanized steel sheet (Fe: 8%), GI: Hot-dip galvanized steel sheet (Al: 0.3%, Pb: 0.15%, balance) Zn), Zn-Ni: Zn-Ni electroalloy-plated steel sheet (20 g / m ² , Ni: 11%, residual Zn), Zn-F
e: Zn-Fe electric alloy plated steel sheet (20 g / m ² , F
e: 15%, residual Zn), Zn-Al: Zn-Al plated steel sheet (Al: 5%, Mg: 0.5%, residual Zn 40 g / m
_{^{2), Zn-SiO 2:}} SiO 2 dispersed electro-galvanized steel sheets _{^{(20g / m 2, SiO 2}} : 3%, residual Zn), Zn-
Co: Zn-Co electroalloy-plated steel sheet (20 g / m ² ,
Co: 12%, residual Zn), Zn-Ni-SiO 2: Si
O ₂ -dispersed Zn-Ni electroalloy-plated steel sheet (20 g /
m ² , SiO ₂ : 3%, Ni: 11%, residual Zn), Zn
-Fe-SiO _2: SiO ₂ dispersed Zn-Fe electrical alloy plated steel sheet _{^{(20g / m 2, SiO 2}} : 3%, Fe: 15
%, Residual Zn), Al: hot dip aluminum plated steel sheet (6
0 g / m ² , Si: 5%, balance Al)

Note 2) Zn-Cr alloy electroplating Zn-Cr alloy electroplating was prepared according to a known method (for example, JP-A-1-5539). Zn ²⁺ : 5
0 to 100 g / l, Cr ³⁺ : 30 to 60 g / l, polyethylene glycol (molecular weight 1500): 1 to 2 g / l,
Na ⁺ : 5 to 20 g / l, pH: 0 to 3, temperature: 50 ° C
Was prepared at a current density of 50 to 200 A / dm ² and a relative flow rate of 60 to 200 m / mim. The plating containing the third element group is performed by adding Ni ²⁺ , Fe ²⁺ , C to the above plating solution.
O ³⁺ and Mn ²⁺ sulfates were appropriately added and prepared. Third
Notation of group elements, for example, Mn, Fe, Ni 0.2, 0.
4, 0.5 are Mn = 0.2%, Fe = 0.4%, Ni
= 0.5% is shown. The amount of coating was determined by chemical analysis, glow discharge analysis and fluorescent X-ray method.

Note 3) Hardly soluble salt forming film The following chemicals were used as anions. PO_Four: Phosphoric acid and its K, Na salts, P_TwoO₇: Piro
Phosphoric acid and its K, Na salts, P_ThreeO_Ten: Triphosphoric acid
And its Na salt, BO_Three: Boric acid and its Na salt, M
o₇O_{twenty four}: Ammonium molybdate, VO_Three: Banaj
Acid Na, NH _FourSalt, WO_FourThe following agents were used as Na tungstate cations. Co, Ni, Fe, Mg, Al, CO_Three, SO_Four, NO
_ThreeSalt, Ca, Sr, CO _Three, NO_Three, Cl salt, rare earth element
Elementary: CO_Three

Commercially available oxide colloids were used as the oxides. The treatment method depends on the coating method and the amount of water film is 0.5 to 3 cc / m.
^{Using an} air knife type or roll type coater in the range of the coating amount of ² , the aim was to prepare an aqueous solution having a concentration corresponding to the coating amount with the above chemicals. After coating, the plate was dried at a plate temperature of 60 to 200 ° C. The immersion method was performed by adding an etching agent to an aqueous solution (anion salt 10 to 150 g / l) adjusted to pH 2 to 4 and a temperature of 40 ° C. and immersing it for 3 seconds to 5 minutes. If necessary, it was washed with water and dried. The electrolysis method is pH
Aqueous solution adjusted to 2-10 (anion salt 20-200g
Cations are added to 1 / l) at a temperature of 40 ° C for 3 to 1
The cathode or anode was electrolyzed at 0 A / dm ² , 3 sec to 1 min, and electrolysis was performed, followed by washing with water and drying if necessary. A chemical analysis method and a fluorescent X-ray method were used for the film amount. The amount of coating is converted to a single element for both anions and cations (for example, PO ₄ is P,
Mo ₇ O ₂₄ is converted to Mo etc.). Oxide colloids are converted to oxides listed in the table.

Note 4) Performance Corrosion resistance No processing: Salt spray test on a flat plate (JIS standard Z23
71) was performed, and the time until white rust generation was 2% was evaluated. Corrosion resistance processing: 80 mm blank, 42 mm punch, 20 mm high cup shape was drawn, salt spray test (JIS standard Z2371) was performed, and the time until white rust occurrence of 2% on the processed outer surface was evaluated. . Evaluation is unprocessed,
With processing, 2% white rust occurrence time is 24 hours or less XX, 24
Over 48 hours or less ×, over 48 hours and 72 hours or less △, over 72 hours and 120 hours or less ○, over 120 hours 24
◎ indicates less than 0 hours and ☆ indicates more than 240 hours. Cr elution amount: Treated steel plate (40 cm ² ) with boiling water (50 m
l) soak for 30 min, analyze the aqueous solution, and elute C
The elution amount of r was evaluated. Tr is below the detection limit (equivalent to the strength of ion-exchanged water) Elution rate: Treated steel sheet with boiling water in the same manner as in Cr elution amount measurement 3
Immersion was carried out for 0 min, the aqueous solution was analyzed, and the elution ratio with respect to the total amount of the film-constituting elements shown in the table was obtained to evaluate the film fixing property. Tr is below detection limit (equivalent to ion exchange water strength)

[0036]

According to the present invention, it is possible to achieve corrosion resistance equal to or higher than that of the chromate-treated material of the plated steel sheet not only in the non-processed portion but also in the processed portion without containing hexavalent chromium at all. Since the present invention does not contain hexavalent chromium at all, even when using this steel sheet in home appliances, automobiles, building materials, etc., there is concern about environmental pollution due to hexavalent chromium and the environment of hexavalent chromium due to the disposal of these products and products. There is no concern about pollution, and it is very beneficial not only to industry but also to society. Further, even when the steel sheet of the present invention is transported, it is possible to avoid hexavalent chromium elution stains due to dew condensation or water wetting, thereby increasing the commercial value. In addition, this technology
Since a strong oxidizing agent such as chromic acid is not used, reducing agents such as wax and resins, which could not be added to the chromate treatment solution in the past, can be added to this film treatment solution for easy lubrication. It is easy to improve stain resistance and stain resistance such as fingerprints, and has great industrial utility.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Arai 5-3 Tokai-cho, Tokai-shi, Aichi Prefecture Nippon Steel Co., Ltd. Nagoya Steel Works (72) Inventor Tatsuya Kanemaru 5-3 Tokai-cho, Tokai-shi, Aichi Prefecture Nippon Steel Co., Ltd. Nagoya Steel Works

Claims (4)

[Claims] 1. A Zn—Cr based alloy plating containing Zn as a main component and 7% or more and 40% or less of Cr as a second component is applied to the surface of a steel plate or a plated steel plate, and the Zn—Cr alloy is further plated.
A surface-treated steel sheet excellent in environmental pollution resistance and corrosion resistance, characterized in that a coating containing a sparingly soluble salt-forming anion containing no hexavalent Cr is applied to the surface of a system alloy plating. 2. Zn-Cr based alloy plating, wherein Zn is a main component, Cr is a second component, and a third component group has a Cr content of the second component or less and Ni, Fe, Co, and Mn are 1 or less. The surface-treated steel sheet excellent in environmental pollution resistance and corrosion resistance according to claim 1, wherein the surface treated steel sheet is Zn-Cr alloy plating containing 0.5% or more of two or more kinds. 3. A coating film on the surface of a Zn—Cr alloy plating,
Contains a sparingly soluble salt-forming anion and contains Z as the cation species.
Co, Ni, Mn, F
The surface-treated steel sheet excellent in environmental pollution resistance and corrosion resistance according to claim 1 or 2, containing one or more of e, Mg, Ca, Sr, Al, and lanthanoid. 4. A film on the surface of a Zn—Cr alloy plating,
The surface-treated steel sheet excellent in environmental pollution resistance and corrosion resistance according to claim 1 or 2 or 3, containing a sparingly soluble salt-forming anion and an oxide colloid.