JP2532999B2 - Highly corrosion resistant surface treated steel sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention has excellent corrosion resistance, workability,
The present invention relates to a high-corrosion-resistant surface-treated steel sheet which has weldability and is suitable as an anticorrosion steel sheet for automobiles.

[0002]

2. Description of the Related Art Conventionally, it is well known that electrogalvanized steel sheets are widely used as surface-treated steel sheets which improve the corrosion resistance of cold-rolled steel sheets and the corrosion resistance after coating and can be mass-produced without impairing workability. Further, in recent years, the use of galvanized steel sheets has been attempted as a rust preventive measure for automobiles against scattered rock salt for road freezing prevention in winter in cold regions, and high corrosion resistance in a severe corrosive environment is required. In order to meet the demand for improving the corrosion resistance of galvanized steel sheets, there is a means of increasing the zinc coating amount (adhesion amount), but this has many problems in terms of weldability and workability. Therefore, many alloy platings have been proposed as a method of suppressing the dissolution of zinc itself and extending the life of zinc plating. Among them, Zn-based alloy plating containing an iron group metal such as Fe, Co, and Ni as an alloy component has been recognized for its excellent bare corrosion resistance and post-coating corrosion resistance, and has been put to practical use. Further, for the purpose of further improving the corrosion resistance, various organic composite type plated steel sheets in which an organic film is provided on these alloy platings have been developed. These are mainly applied to the part where the automobile coating on the inner surface of the car is difficult to stick to and water and salt are likely to accumulate, that is, to the part where perforated rust is a problem, such as the hem part and the mating part. On the other hand, the problem of so-called outer surface rust originating from a damaged portion caused by flying stones while the automobile is running has been solved by applying a plated steel sheet. In order to improve the anticorrosion property on the inner and outer surfaces of the vehicle body, in addition to Zn-plated or Zn-based alloy-plated steel sheets on both sides, which have a large amount of adhesion, one side as disclosed in JP-A-60-50181 There is also disclosed an organic composite type alloy plating, and another type of alloy plating.

[0003]

However, the above-mentioned rust-proof steel sheet is still not sufficient in view of not only corrosion resistance but also workability and weldability required for steel sheets for automobiles. Especially in the case of double-sided plating, not only the workability and weldability become more serious problems, but also a new problem of peeling of the plating layer due to chipping occurs for plating on the outer surface, In order to apply a double-sided plated steel sheet as a steel sheet, it was necessary to solve many problems. In view of such circumstances, the present inventors have keenly aimed to provide a surface-treated steel sheet having excellent corrosion resistance on the inner and outer surfaces of a vehicle body, excellent workability, and weldability when applied as an anticorrosive steel sheet for automobiles. As a result of examination, the present invention has been achieved.

[0004]

The gist of the present invention is as follows. (1) Adhesion amount 10 g / m ² on one side of the steel sheet in order from the steel sheet side
The above Zn-Ni alloy plating layer, the total Cr deposition amount 10 to
Chromate film of 150 mg / m ² , film thickness 0.3-2μ
On the other side, the Ni plating layer with an adhesion amount of 0.05 g / m ² or more, and the adhesion amount of 10 g / m ^{2 in} order from the steel plate side.
Highly corrosion-resistant surface-treated steel sheet, characterized in that a Zn-Ni-based alloy plating layer of m ² or more was formed, (2) An adhesion amount of 0.01 g on one side of the steel sheet in order from the steel sheet side.
/ M ² or more Ni plating layer, adhesion amount 10 g / m ² or more Z
n-Ni alloy plating layer, total Cr deposit 10-150m
A chromate film of g / m ² and an organic film with a thickness of 0.3 to 2μ are formed.
g / m ² or more Ni plating layer, high corrosion resistance surface treated steel sheet, wherein a coating weight 10 g / m ² or more Zn-Ni alloy plating layer is formed, (3) chromate film is water-soluble content Highly corrosion-resistant surface-treated steel sheet of (1) and (2), which is a poorly soluble chromate film of 5% or less. (4) The high corrosion-resistant surface-treated steel sheet according to (1) or (2), wherein the organic coating is an organic coating containing 30 to 70% by weight or more of epoxy resin and 5 to 50% by weight of silica.

[0005]

The structure of the highly corrosion-resistant surface-treated steel sheet of the present invention is shown in FIG. Adhesion amount 10 g / on one side of the steel plate 1 in order from the steel plate side
Zn-Ni-based alloy plating layer of ² or more m ² , chromate film with total Cr adhesion amount of 10 to 150 mg / m ² , film thickness of 0.
An organic film 4 having a thickness of 3 to 2 μ is formed and constitutes the inner surface side of the automobile. The other surface coating weight 0.05 g / m ² or more of the Ni plating layer 5, the adhesion amount 10 g / m ² or more Zn-Ni alloy plating layer 6 is formed, constitutes an outer surface side of the motor vehicle. Adhesion amount 0.0 between the steel plate 1 and the Zn-Ni alloy plating layer 2
You may interpose the Ni plating layer 5'of 1 g / m < ² > or more.

First, one side of the inner surface of the automobile will be described. This one side is composed of a Zn-Ni alloy plating layer as a base, and a thin film type organic composite plating layer having a chromate film and a thin organic film as an upper layer. Zn-
Since the electrochemical potential of Ni-based alloy plating is closer to that of steel base material as compared with Zn plating and other Zn-based alloy plating, the wear rate of plating is low. When this is applied to the underlayer of an organic film, the barrier effect of the organic film further reduces the consumption rate, and even when applied to a severely corrosive environment such as a heme portion or a joint portion, it exhibits excellent corrosion resistance. Such a combination effect is not found in Zn plating or other Zn-based alloy plating, and is an effect unique to Zn-Ni-based alloy plating. The amount of the Zn-Ni alloy plating layer deposited is 10 g /
m ² or more. If it is less than 10 g / m ² , there is a risk of insufficient corrosion resistance. The upper limit is not particularly limited, but 50 g / m ² or less is preferable from the viewpoint of workability and weldability. Where Zn-
Ni-based alloy plating is Zn plating containing mainly Ni, and specifically, Zn-Ni or Zn-N.
i-Co, Zn-Ni-Fe, Zn-Ni-Cr, Z
Zn-Ni such as n-Ni-Fe-Cr containing other metal components. The Ni content is preferably 5 to 20% by weight. If it is less than 5% by weight, corrosion resistance is insufficient, and if it exceeds 20% by weight, workability is deteriorated, which is not preferable. A more preferable range is 7 to 15% by weight. The total amount of metal components other than Ni is preferably less than 5% by weight, and the amount of 5% by weight or more is not preferable because the effect of Ni is diminished. Zn-
The method for forming the Ni-based alloy plating layer may be according to a known method, for example, using a sulfuric acid-acidic plating solution containing Zn ions, Ni ions, and, if necessary, other metal ions, with a current density of 10 to 10. Electrolysis may be performed at 300 A / dm ^{2 using} the steel plate as a cathode for a predetermined time.

Next, a chromate film is formed on the lower layer of Zn--Ni.
While closely adhering the system alloy plating layer and the upper organic film,
It also contributes to corrosion resistance. Chromate coating amount is total C
The amount of r is 10 to 150 mg / m ² . 10 mg /
If it is less than m ² , the adhesion of the organic film is insufficient,
If it exceeds mg / m ² , there is a concern that workability and meltability may decrease. A more preferable range is a total Cr amount of 20 to 100 mg /
m ² . As the method for forming the chromate film, electrolytic type, coating type, and reactive type are conceivable, and any of them can be applied, but from the viewpoint of preventing chromate adhesion to the plating surface on the opposite side, the coating type using a roll coater is used. Chromate is most suitable. In the case of electrolytic type, reactive type, or coating type chromate by dipping or spraying, it is necessary to remove the chromate on the opposite plating surface because adhesion of chromate to the opposite surface is unavoidable. Coating type, the reactive chromate treatment, Cr6 +, as a main component Cr3 +, inorganic colloids such as SiO ₂ or TiO ₂ on the other, acids and their salts such as phosphoric acid and molybdate, fluoride, water-soluble or emulsion Those containing a mold type organic resin can be applied. Further, as the electrolytic chromate treatment,
Cr6 +, as a main component Cr3 +, other or those containing sulfate or halide ions can be applied more inorganic colloids such as SiO ₂ or TiO _2, those containing metal ions such as Co and Zn. Normally, electrolysis is performed using a steel plate as a cathode, but anodic electrolysis or AC electrolysis can be added. The chromate film formed by these methods has a water-soluble content of 5
% Or less, it is preferably a poorly soluble chromate film.
This is to avoid elution of chromium from the chromate film into these treatment liquids during chemical conversion treatment or electrodeposition coating performed during automobile manufacturing. Chromium which is eluted from the chromate film is caused by Cr6 + in the film. Therefore, in order to obtain a poorly soluble chromate film, the electrolytic type or the reactive type in which a chromate film mainly composed of Cr3 + is easily formed is advantageous. However, even in the coating type, a sparingly soluble chromate film can be obtained by devising the treatment bath such as fixing Cr6 + with phosphoric acid or colloids.

Next, the organic film plays an important role in improving the corrosion resistance on the inner surface side. The thickness of the organic film is 0.3-
2μ. If it is less than 0.3 μ, sufficient corrosion resistance cannot be obtained, and if it exceeds 2 μ, workability and weldability are deteriorated. A more preferable range is 0.5 to 1.7μ. The composition of the organic film is 30% by weight or more of epoxy resin and 5% of silica.
Those containing ˜50% by weight are preferred. Epoxy resin is excellent in water resistance and alkali resistance, has good adhesion to the base, and is most suitable for use in the present invention among many organic resins. If the epoxy resin content in the organic film is less than 30% by weight, the film is brittle and the workability is insufficient. As the epoxy resin, a bisphenol type epoxy resin having a number average molecular weight of 300 to 100,000 is optimal. If the number average molecular weight is less than 300 or more than 100,000, a sufficient crosslinking reaction is not carried out, and thus sufficient corrosion resistance cannot be exhibited. Silica has extremely excellent alkali resistance, and when it is contained in the epoxy resin in a dispersed state, it further enhances the corrosion resistance of the organic film. If the silica content in the organic film is less than 5% by weight, the effect on the corrosion resistance is small, and if it exceeds 50% by weight, the workability is deteriorated. A more preferable range is 15 to 30% by weight. The silica used has an average primary particle size of 1 to 1
00 mμ of dry silica is preferred. Dry silica is excellent not only in alkali resistance but also in water resistance, and has good compatibility with epoxy paint. Less than 1mμ, or 100
If it exceeds mμ, sufficient corrosion resistance cannot be obtained. In addition to the above-mentioned epoxy resin and silica, as a component of the organic film, a curing agent such as a polyisocyanate compound or a block polyisocyanate compound for enabling low temperature baking, and a lubricant such as a polyethylene wax for improving processability. May be included. A coating composition is obtained by dissolving or dispersing these components in an organic solvent. As the organic solvent, a ketone type organic solvent is suitable,
The amount of solid content in the paint should be 10-5.
By adjusting to 0% by weight, a uniform thin film can be easily formed. Examples of the ketone-based organic solvent include methyl isobutyl ketone, acetone, cyclohexanone,
Isophorone and the like are exemplified as preferable ones. The method for forming the organic film is not particularly limited, but the roll coating method is most suitable from the viewpoint of uniform coating, and the baking treatment may be performed in a hot air oven or an induction heating oven under conditions of a final temperature of 100 to 200 ° C.

Next, one side of the outer surface of the automobile will be described. This one side has a Ni plating layer and a Zn--Ni layer.
It is composed of a system alloy plating layer. Ni plating layer is steel plate and Z
Strengthens the adhesion with the n-Ni alloy plating layer,
When applied to the outer surface of an automobile, it brings about an improvement in chipping resistance, which is a problem. The Zn-Ni alloy plating layer has a larger internal stress than that of Zn plating, and the plating adhesion is Z.
Lower than n-plating. On the outer surface of the vehicle body, such Zn
-A total of 100μ of 3-coat coating consisting of cationic electrodeposition coating, intermediate coating, and top coating on the Ni-based alloy plating layer
Since the coating is performed with the above thickness, shrinkage stress generated during baking of the coating is further applied. Further, in the cold region in winter, the temperature drops below the freezing point, and the shrinkage of the coating film progresses due to this effect, so that the stress acting on the plating layer is further increased and the plating adhesion is further reduced. Under such conditions, when a vehicle running on a road collides with pebbles or sprayed rock salt that has been flipped up from the road surface, there is a serious drawback that the plating layer peels off due to the impact force. The Ni plating layer is for overcoming this drawback, and first of all, 0.0
Apply a Ni plating layer of 5 g / m ² or more, and then add Zn
When a Ni-based alloy plating layer is applied, excellent chipping resistance can be obtained. The Ni plating layer is also effective in improving the corrosion resistance, especially after coating. It is presumed that this is due to the improvement of the plating adhesion of the Zn-Ni alloy plating layer.
If it is less than 0.05 g / m ² , the Ni plating layer cannot evenly cover the steel sheet surface, resulting in insufficient chipping resistance. The upper limit is not particularly limited from the viewpoint of chipping resistance, but if it exceeds 5 g / m ² , it is not preferable because the concept of deterioration of corrosion resistance occurs. Considering the corrosion resistance after painting,
1-2 g / m ² is more preferable. S in the Ni plating layer
May be contained in an amount of 0.01 to 10% by weight. By doing so, the uniform coating property of the Ni plating layer is improved, and the chipping resistance of the upper Zn-Ni alloy plating layer is improved even if the Ni plating amount is small. If it is good enough, it can be done.
In this case, less than 0.01% by weight is not effective and 1
If it exceeds 0% by weight, there is a fear of adversely affecting the corrosion resistance, which is not preferable. The method for forming the Ni plating layer is not particularly limited, but for the purpose of uniformly coating the surface of the steel sheet with a slight amount of deposition, a sulfuric acid solution is used to obtain a current density of 10 to 100 A /
It is best done at dm ² . Further, in order to contain S, after performing Ni plating using a sulfuric acid acid solution,
Zn-Ni plating may be performed without washing with water, and S
Can be controlled by the current density during Ni plating.

The details of the Zn-Ni alloy plating layer corresponding to the outer surface side are the same as those on the opposite surface side, but in consideration of the peculiarity of the outer surface side, the following outermost surface finishing treatment may be performed. preferable. That is, Zn-N on the outer surface side
On the surface of the i-based alloy plating layer, chromate stain or surface oxidation may occur due to chromate treatment on the opposite surface side or baking of the organic film. Since these may impair the chemical conversion treatment property and the electrodeposition coating property, it is advisable to perform electrolytic treatment such as brushing treatment, electrolytic stripping, electrolytic reduction, etc. as the final finish after baking the organic film. Regarding the brushing treatment, a method of pressing a nylon brush roll, a Scotch bright roll, or the like on the plated surface with a motor load current of 1 to 50 A is simple and reliable. It is more effective to include abrasive grains such as alumina or silicon carbide in the brush. The electrolytic treatment may be carried out by electrolytic stripping using the plated surface as the anode or electrolytic reduction using the cathode in an electrolytic solution containing phosphate of 0.05 to 2 mol / l and having a pH of 4 to 9.
The brushing treatment and the electrolytic treatment may be appropriately combined depending on the condition of the outermost surface of the Zn—Ni based alloy plating. For example, in the case of electrolytic type chromate, since chromate stain is severe, it is necessary to remove the chromate completely by using electrolytic stripping and brushing. Further, although there is no chromate stain, when the organic film is baked for a long time and oxidation is progressing, it is necessary to remove the oxide film by electrolytic reduction. As a matter of course, the chromate stain on the outer surface side is completely avoided by the coating type chromate by the roll coating method, and if the surface oxidation is suppressed by baking the organic film in a short time of 30 seconds or less, the above-mentioned final finish is performed. No need.

In the present invention, a Ni plating layer is indispensable for improving the chipping resistance on one surface constituting the outer surface of the automobile, but a steel plate and a Zn-- layer are formed on the other surface constituting the inner surface of the automobile. A Ni plating layer may be interposed between the Ni-based alloy plating layers. That is, due to the sophistication of required qualities such as workability and strength for automobile steel sheets, ultra-deep drawn steel sheets and high-strength steel sheets have been developed by controlling additive components in steel and manufacturing conditions. These are not necessarily irrelevant to the plating adhesion of the Zn-Ni alloy plating layer, and generally hinder the plating adhesion. Therefore, when these steel sheets are used as the base, it is necessary to improve the plating adhesion of the Zn-Ni alloy plating layer. As an improvement measure, it is effective to form a Ni plating layer between the steel plate and the Zn—Ni alloy plating layer, as with the outer surface side. in this case,
The appropriate range of the amount of Ni plating layer deposited is 0.01 g / m ² or more, and less than 0.01 g / m ² has no effect. The upper limit is not particularly limited from the viewpoint of plating adhesion, but 5
If it exceeds g / m ² , there is a concern that the corrosion resistance may decrease, which is not preferable. Considering the corrosion resistance, the more preferable range is 1
~ ² g / m2. Further, it is more effective to contain 0.01 to 10% by weight of S in the Ni plating layer as in the case of the outer surface side. The composition and the amount of the Zn-Ni alloy plating layers on the inner surface side and the outer surface side do not necessarily have to be the same. It is advantageous to make the same. With the above-described structure, a surface-treated steel sheet that can be applied to the inner and outer surfaces of the vehicle body at the same time can be obtained. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0012]

[Example] A cold-rolled steel sheet was degreased with alkali, pickled with a 5% aqueous solution of sulfuric acid, Ni-plated on one side or both sides, Zn-based dispersion plating on both sides, and then chromate and an organic coating were applied on only one side. Further, a part of the outer surface side on which the organic film was not applied was subjected to a finishing treatment on the outermost surface to obtain surface-treated steel sheets on both surfaces shown in Table 1. The following performance evaluations were performed on these, and the results are summarized in Table 2. The notes in Table 1 are as follows. 1) Inner chromate film ・ Coating type: Cr6 +, Cr3 + as the main component, other than SiO
A treatment solution containing ₂ and phosphoric acid was applied by a roll coating method and baked at a plate temperature of 80 ° C. Water soluble content is Cr6 +,
It was controlled by the ratio of Cr3 + and phosphoric acid. Chromate contamination on the outer plating surface. Electrolytic type: Cathodic electrolysis was performed at a current density of 10 A / dm ² using a treatment liquid containing Cr6 + and Cr3 + as main components and sulfuric acid, and then washed with water and dried. Chromate contamination on the outer plating surface. -Water-soluble content: It was immersed in distilled water at 50 ° C for 30 minutes, and the ratio of the amount of chromium before and after and the ratio of the amount of initial chromium were calculated. 2) Organic film on the inner surface-Type A: Resin is a bisphenol type epoxy resin having a number average molecular weight of 2900, silica is dry silica having an average primary particle size of 8 mμ, and ethyl acetoacetate block of hexamethylene diisocyanate as a curing agent, and Those containing polyethylene wax as a lubricant. Type B: a resin containing a bisphenol type epoxy resin having a number average molecular weight of 900, silica containing dry silica having an average primary particle size of 40 mμ, hexamethylene diisocyanate as a curing agent, and polyethylene wax as a lubricant. -Type C: A resin containing a bisphenol type epoxy resin having a number average molecular weight of 15,000, silica containing dry silica having an average primary particle size of 20 mμ, and hexamethylene diisocyanate as a curing agent. 3) Treatment of the outermost surface ・ Treatment A: Electrolytic stripping treatment at an electric current of 5 C / dm ^{2 in} an aqueous solution of 1 mol / l sodium phosphate at pH 7 and liquid temperature 40 ° C ・ Treatment B: Lightly plated surface with Scotch bright Grinding process-Process C: Electrolytic peeling process + grinding process described above

The evaluation methods in Table 2 are as follows. (1) Corrosion resistance of hem part on the inner surface side A heme model was prepared by using two samples with the surface coated with an organic film as the inner surface, and the immersion phosphate treatment and cationic electrodeposition coating were performed, and the following cycle corrosion test was performed. I went to After 4000 cycles, the hem model was disassembled, and the amount of reduction in plate thickness at the hem portion was investigated and evaluated. ⊚: 0.1 mm or less O: 0.2 mm or less Δ: 0.3 mm or less x: 0.3 mm or more (2) Inner surface side workability Eriksen 9 mm After extrusion, a taping test was performed and evaluated. ⊚: No exfoliation ○: Very slight exfoliation Δ: Mild exfoliation ×: Large exfoliation (3) Chromium elution property on the inner surface side The total amount of Cr exposed in the immersion type phosphate treatment step was evaluated. ◎: 5 mg / m ² or less ○: 10 mg / m ² or less △: 20 mg / m ² or less ×: more than 20 mg / m ² (4) External surface chipping resistance Immersion-type phosphate treatment, cationic electrodeposition coating, and medium Paint,
Top coat is applied to make the total film thickness 100μ, and 250g of JIS No. 7 crushed stone is 150km / hr at a test piece temperature of -30 ° C.
After the taping test, the area of plating peeling was evaluated. ◎: 3% or less ○: 5% or less △: 10% or less ×: more than 10% (5) Corrosion resistance after external surface coating Immersion-type phosphate treatment, cationic electrodeposition coating, and intermediate coating,
A top coat was applied to give a total film thickness of 100 μm, and a cross-cut flaw reaching the base steel was put in, and it was subjected to the following cycle corrosion test. After 100 cycles, the blister width of the cross cut portion was evaluated. ◎: 3 mm or less ○: 5 mm or less △: 8 mm or less ×: Over 8 mm (6) Weldability Using a CF type electrode with a tip diameter of 6 mmφ, a pressing force of 200 k
Continuous spot welding was performed at 10 g of current, 10 kA of current, and 10 cycles of energizing time, and the number of continuous dots was evaluated. ◎: 3000 points or more ○: 2000 points or more △: 1000 points or more ×: Less than 1000 points

The comparative examples of Table 1- (3) and Table 1- (4) will be described. In Comparative Example 1, the amount of Zn-Ni alloy plating layer deposited is small, and therefore the corrosion resistance is poor on both the inner and outer surfaces. In Comparative Example 2, since the amount of chromate film is small, the adhesion of the organic film is insufficient, resulting in poor corrosion resistance and workability on the inner surface. In Comparative Example 3, since the amount of chromate film is too large, the inner surface is processed. And weldability are poor. In Comparative Example 4, since the water-soluble content of the chromate film is too large, the chromium elution property is poor. Since Comparative Example 5 has a small organic film thickness,
The corrosion resistance and workability on the inner surface side are poor, and in Comparative Example 6, the organic film thickness is too large, and thus the inner surface side workability and weldability are poor. In Comparative Example 7, the resin content of the organic coating is small and the amount of silica is too large, so that the inner surface side processability is poor, and in Comparative Example 8, the organic coating has a small amount of silica, and thus the inner surface side corrosion resistance is poor. Further, Comparative Examples 2 to 5 have a small amount of the Ni plating layer on the outer surface side, and Comparative Examples 6 to 10 have no Ni plating layer on the outer surface side, and thus all have poor chipping resistance on the outer surface side. In Comparative Examples 9 and 10, the steel sheets are an ultra-deep drawn steel sheet and a high-tensile steel sheet, respectively, and since there is no Ni plating layer on the inner surface side, the plating adhesion is insufficient, and as a result, the inner surface side workability is poor. Comparative Examples 11 and 12 are Zn plating and Zn-F, respectively.
Although it is based on e-alloy plating, its inner surface corrosion resistance and other properties are poor. In comparison with these, the examples of the present invention showed good results in both the inner surface side and the outer surface side. More specifically, the present invention examples 22 to 25 and 26
Nos. 29 to 29 respectively use ultra-deep drawn steel sheets and high-strength steel sheets as base steel sheets, but since they have a Ni plating layer on the inner surface side, the plating adhesion is good, and as a result, the inner surface side workability is excellent. Those containing S in the Ni plating layers on the inner and outer surfaces are more excellent in workability or chipping resistance even if the Ni plating amount is small. Invention Examples 15 to 21 and 26 to 29
Since the chromate film is electrolytic, Zn-N on the outer surface side
The outermost surface of the i-based alloy plating layer is contaminated with chromate,
Finishing treatment of the outermost surface (Invention examples 15, 17, 20, 2)
6,27) has better corrosion resistance after coating than the untreated one (Invention Examples 16, 18, 19, 21, 28, 29).

[0015]

[Table 1-1]

[0016]

[Table 2]

[0017]

[Table 1-3]

[0018]

[Table 1-4]

[0019]

[Table 2-1]

[0020]

[Table 2-2]

[0021]

As described above, according to the present invention, the Zn--Ni
This is a double-sided, highly corrosion-resistant surface-treated steel sheet that has a chromate film and an organic film on one side, based on a system-based alloy plating, and is excellent not only in corrosion resistance, but also in chipping resistance, workability, and weldability. In particular, it is suitable as an automobile material because it can simultaneously satisfy the required characteristics of the inner and outer surfaces of the automobile body.

[0022]

[Brief description of drawings]

FIG. 1 shows the structure of a highly corrosion-resistant surface-treated steel sheet according to the present invention.

[Explanation of symbols]

1 Steel plate 2 Zn-Ni-based alloy plating layer with an adhesion amount of 10 g / m ² or more 3 Chromate film with a total Cr adhesion amount of 10 to 150 mg / m ² 4 Organic film with a film thickness of 0.3 to ² μ 5 Adhesion amount of 0.05 g / Ni plating layer with m ² or more 5 ′ Ni plating layer with adhesion amount of 0.01 g / m ² or more 6 Zn-Ni alloy plating layer with adhesion amount of 10 g / m ² or more.

Claims (4)

(57) [Claims] 1. A steel sheet for an automobile, wherein the inner surface of the automobile is
A Zn-Ni alloy plating layer having an adhesion amount of 10 g / m ² or more, and a total Cr adhesion amount of 10 to 1 on the one surface side, which is formed, in order from the steel plate side.
A chromate film of 50 mg / m ² and an organic film having a film thickness of 0.3 to ² μ are formed, and the amount of adhesion is 0.05 g / m ² or more in order from the steel plate side on the side opposite to the outer surface of the automobile. Ni
A highly corrosion-resistant surface-treated steel sheet having a plated layer and a Zn-Ni based alloy plated layer having an adhesion amount of 10 g / m ² or more. 2. A steel sheet for an automobile, wherein the inner surface of the automobile is
Adhesion amount 0.01g / m in order from the steel plate side to the one side that constitutes
² or more Ni plating layer, Zn with an adhesion amount of 10 g / m ² or more
-Ni-based alloy plating layer, total Cr deposit 10-150 mg
/ M ² chromate film, an organic film having a film thickness of 0.3 to 2μ is formed, the Ni plating layer having an adhesion amount of 0.05 g / m ² or more in order from the steel plate side on the opposite surface side that constitutes the outer surface of the automobile , A highly corrosion-resistant surface-treated steel sheet having a Zn-Ni alloy plating layer having an adhesion amount of 10 g / m ² or more. 3. The highly corrosion-resistant surface-treated steel sheet according to claim 1, wherein the chromate film is a poorly soluble chromate film having a water-soluble content of 5% or less. 4. The organic film contains 30% by weight of epoxy resin.
The high-corrosion-resistant surface-treated steel sheet according to claim 1 or 2, which is an organic coating containing the above and 5 to 50% by weight of silica.