JPS6314892A - Production of multi-ply electroplated steel sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a multi-RC4 electroplated steel sheet suitable as a rust-proof steel sheet for automobiles.

[Conventional technology and its problems]

Automobile bodies are exposed to severe corrosive environments, and are required to have a high degree of corrosion resistance in order to prevent the car bodies from rusting. Z
N-plated steel sheets have been widely used as rust-proof steel sheets, but because Zn is an active metal, they do not exhibit sufficient corrosion resistance in severe corrosive environments. For this reason, a new Z
Rust-proof steel sheets electroplated with Zn-based alloys such as n-Ni, Zn-Fe, and Zn-Co-0r have been developed. Among these, Zn-Ni alloy 1! Plating steel sheet is a rust-preventing steel sheet that exhibits excellent properties such as bare corrosion resistance and blister resistance (ability to suppress paint film blistering caused by sub-paint corrosion), but it has poor rust prevention properties for car bodies. Due to the increasing sophistication of requirements for

The first point is that the pitting corrosion resistance is insufficient.

The Zn-Ni alloy plating film is rapidly coated with Zn when exposed to 13 Meals A and humidity.
is preferentially eliminated, so the plating film has extraordinary electrochemical properties. For this reason, it has poor sacrificial corrosion protection, and tends to cause so-called pitting corrosion, in which the base plate is corroded in the depth direction, in areas with coating film defects.

The second point is that it has poor phosphate treatment properties. Phosphate treatment, which is performed as a base treatment for paint films, improves corrosion resistance after painting.
Zn-Ni plays an important role in controlling paint film adhesion.
The alloy plating film was inert in the phosphate treatment solution, and it was only necessary to obtain the fine and dense phosphate crystals necessary to sufficiently ensure the above-mentioned properties.

Point 13 is that the chipping resistance is poor. In recent years, plated steel sheets with a one-pitch coating on the outer surface have been used as a rust prevention measure for the outer surface of car bodies, but in order for the plated steel sheet to exhibit its rust prevention properties on the outer surface, it must be exposed to chipping such as flying stones. Even if the coating is damaged by 1, the plating film remains on the steel plate surface.
! ! must be dressed. However, since the Zn-Ni alloy plating film has a built-in high tensile internal stress formed during electroplating, not only the coating film but also the plating film is easily damaged at the interface between the plating film and the steel sheet due to chipping. .

The following methods have been proposed to solve this problem.

(1) @Improvement of perforation corrosion: JP-A-59-11639
In No. 3, 2 to 7w1%Ni was applied as the first layer on the surface of the steel plate.
Zn-N1 alloy electroplated layer containing 65 wt% or more of Fe-Z as a second layer thereon
A two-layer plated steel sheet with an n-alloy electroplater has been proposed. In this plated steel sheet, the N1 content in the alloy was lowered from the usual 10 to 2 wt Ni to 2 to 7 wt Ni to increase the sustainability of the sacrificial corrosion protection effect and improve the perforation corrosion resistance. There is. However, when the N1 content is lowered in this manner, the alloy phase changes to one mainly consisting of the l phase, so that the properties of pure Zn become apparent, and there is a problem in particular that the blister resistance decreases.

Moreover, in JP-A-59-162292, the outer layer is 8 to 20
A two-layer plated steel sheet has been proposed, in which the inner layer is a Zn-plated layer, or the Zn alloy-plated I- layer has a more base potential than the outer layer.

This 2rf! In plated steel sheets, the inner Zn plating layer or the Zn alloy layer with a more base potential than the outer layer is used to provide l-corrosion resistance and improve the perforation property. Electrochemical coupling accelerates the wear and tear of the base inner layer, which causes blistering to occur.
It has the disadvantage of reduced blister resistance. Especially when the inner layer is a Zn plating layer, the Zn plating layer itself has poor blister resistance! 7't Blistering property was significantly reduced.

(2) Improvement of phosphate treatment property @: JP-A-56-38495
In this issue, a Ni-plated layer is formed as a first layer on the surface of a steel sheet, and a Zn-plated layer containing 2 to 20 wt% Ni is formed as a second layer on the surface of the steel sheet.
-Ni alloy plating, and a multilayer plated steel sheet having an electrogalvanized layer as the third layer (outermost layer) has been proposed. This multilayer plated steel sheet improves the chemical conversion treatment property of Zn-Ni alloy plating by making active Zn the most active. However, the Zn--Ni plating layer and the lowest N1 layer have poor sacrificial corrosion protection, and therefore, this multilayer plated steel sheet has the disadvantage of poor perforation corrosion resistance.

(3) Improvement in chipping resistance: To ensure good chipping resistance, the plating layer must be in close contact with the underlying steel plate.

A technique related to this is disclosed in Japanese Patent Laid-Open No. 59-200789. According to this, Cr,
Mn, Fe, Co.

Nl, Cu, In, Zn, Cd,
By depositing precipitates consisting of one or more of Sn and Pb in a 1 to 1000 M9/1n* dispersion and forming a Zn-based alloy or composite electroplating film thereon, the fine precipitates can be removed from the initial crystalline surface. The core of this is to improve plating adhesion. However, in this system, there is a problem in that the galvanic current increases the corrosion rate and reduces the corrosion resistance because the plating 1 of the composition is in contact with the metal.

As mentioned above, although Zn-N1 alloy electroplated steel sheet has excellent bare corrosion resistance and blister resistance,
Conventionally, it has been difficult to simultaneously ensure good sealing corrosion resistance, chemical conversion treatment properties, and chipping resistance, and it has not been possible to sufficiently meet the increasingly sophisticated needs for rust prevention.

[Means to solve the problem]

In view of the above-mentioned conventional drawbacks, the present inventors have developed Zn-
The corrosion resistance of Ni alloy electroplated steel sheet and...
Excellent sealing and corrosion resistance while maintaining anti-blister resistance of 1.
We have conducted repeated research on a method for manufacturing a plated steel sheet that has chemical conversion treatment properties and chipping resistance, and as a result, we have discovered that a steel sheet that satisfies the above characteristics can be obtained by the following manufacturing method.

That is, the non-invention is a method for manufacturing a multi-layer electroplated plate using a continuous electroplating line, in which 8 to 15 wt% Ni, 0.01 to 15 wt% Ni is applied to the surface of the steel plate in the first plating bath.
An alloy plating consisting of 0.5 wt% Cr % 1 part Zn is applied with a bond of 0.01 to 117 m'', and in subsequent plating tanks after the second plating tank, 8 to 15 wt% Ni,
Alloy plating consisting of 0.01 to 0.5 wt% Cr and the balance Zn to 5 to 70? Zn plating or Zn-Fe alloy plating containing 60 wt4 or less Fe is applied at 1 to 5 r/m.
Its basic feature is that it can be applied with a coating amount of .

The present invention will be explained in detail below.

In the present invention, in a continuous electroplating line, 8 to 15 wt% Ni and 0.01 to 0.5 w are applied to the surface of a steel plate.
A Zn-Ni-Cr alloy plating film having a composition of t% Cr and the balance Zn is formed, and on top of that (this Zn plating film or a Zn-Fe alloy plating film containing 60 Wt'1 or less Fe) is formed. In the case of the Zn-Ni-Cr alloy plating described above, in the first plating bath of the continuous line,
Plating is applied with a coating weight of 0.01 to 117 m'', and plating is applied with a coating weight of 5 to 70 g/m2 in the subsequent second plating tank and thereafter.

The Zn-Ni-Cr alloy plating film formed on the surface of the steel sheet not only has excellent bare corrosion resistance and anti-blister property, but also has excellent sealing corrosion resistance. This alloy plating film has significantly improved sealing corrosion resistance mainly due to the inclusion of Cr. This is due to the effect that Cr contained in the form of hydroxide partially passivates Zn, thereby inhibiting the rapid disappearance of the Zn component and increasing the sustainability of the termite protection provided by Zn. It is thought that.

The Cr content in the plating film is 0.01 to 0.5w1%. When the Cr content was less than 0.01 wt%, the effect of improving the sealing corrosion resistance was not observed as shown in Figure 2, while when the Cr content was 0.5 wt%, the adhesion of the mating film deteriorated. Put it away.

Further, the N1 content is set to 8 to 15w1%.

If Nl is a wt, it is not possible to obtain sufficient bare corrosion resistance and blister resistance, and if it exceeds 1 5 WL 4 , bare corrosion resistance, plating adhesion, and the box deteriorate, and as shown in Figure 1, the sealing The corrosion resistance also deteriorates.

In the present invention, it is possible to form a Zn-N1-Cr alloy film having such a composition, and in particular, the coating amount in the first plating bath is limited to a predetermined range, and in addition, the coating amount in the second and subsequent plating baths is The total adhesion amount is also regulated within a predetermined range. The present inventors have discovered that the chipping resistance of the alloy plating film is dominated by the alloy plating film formed in the first plating of a continuous electroplating line equipped with multiple plating baths, and Plating No. 0. 1 in the range of O1 to O12
Excellent chipping resistance by limiting till limit? 4
I found out that it can be maintained.

Although the reason for this is not necessarily clear, it is presumed that it is due to a lack of information. In other words, the plating amount is 1
At 91 m'' or less, the plating layer becomes a planarly discontinuous film. On the other hand, when the applied M amount exceeds 196", the plating layer becomes a planarly continuous film. Therefore, first 19
After plating a length of 1 m" or less, when electricity is started again and plating is performed over 117 m", a continuous film is formed on a discontinuous film. When an external force is applied to a coating with high internal tension (tensile force) such as the one made from this alloy, cracks occur in the plating layer, and this causes the plating to peel off at the plating/steel plate interface. However, if the plating film in contact with the interface with the steel plate is discontinuous, interfacial peeling tends to stop at the discontinuous point, making it difficult for peeling to propagate at the interface. Therefore, even if an external force such as chipping is applied, macro plating does not peel off, and the plating film is retained on the steel plate surface. If the amount of the discontinuous plating film is significantly reduced, it will actually be equivalent to a continuous film being formed on the surface of the steel sheet, making it easier for the plating to peel off. The lower limit at which the discontinuous plating film can demonstrate its function is 0.0191 m.
”.

In continuous electroplating lines, usually 1 plating tank per tank.
Although plating exceeding t/- is performed, in the present invention, the first
By setting the plating amount in the plating tank to 0.01 to 117 m'', a discontinuous plating film is formed on the steel plate surface,
A continuous plating film will be formed on top of it.

The alloy plating film applied in the first plating tank and the alloy plating film applied in the second and subsequent plating tanks can have different compositions within a specified range.

Since these films have almost the same electrochemical properties within the above composition range, no galvanic current will flow even if there is a difference in composition. Therefore, no decrease in corrosion resistance occurs.

The level of corrosion resistance is controlled by the alloy plating film formed in the plating baths after the second plating bath. / or more, the practical rust prevention requirement level is satisfied. On the other hand, as the amount of plating increases, the internal stress of the plating film increases, making it easier for the plating film to peel off due to chipping. Second
If the plating amount of the alloy plating film formed in the plating tanks after the plating tank exceeds 70t/-, the effect of improving chipping resistance due to regulating the plating amount in the first plating tank will be offset. . Therefore, the total amount of Zn--Ni--Cr alloy plating deposited in the second and subsequent plating baths is in the range of 5 to 70 f/-.

In the above Zn-Ni-Cr alloy plating layer, the surface activity is lowered by Cr than that of the Zn-N1 alloy plating layer, and when phosphate treatment is performed, coarse phosphate crystals are formed sparsely. It ends up. Therefore, Zn-Nl-Cr
When the alloy plating layer is present in the outermost layer, phosphate treatability is further reduced. The above-mentioned Zn plating or Zn-Fe alloy plating containing 60 wt% or less of Fe is performed on the Zn-Ni-Cr alloy plating film in order to ensure the above-mentioned chemical conversion properties.

Therefore, the amount of plating required to form phosphate crystals is sufficient, and the required amount of plating is 1 to 5 tA-.

If the coating weight is less than 1 f/-, fine and dense phosphate crystals cannot be obtained, while if the coating weight exceeds 527♂, phosphate crystals and Zn-Ni-Cr alloy plating will not be obtained. f
f! A Zn plating layer or a Zn-Fe alloy plating layer remains between the two. Remaining of such a plating layer reduces the blister resistance when the plating layer is a Zn plating layer, and reduces the bare corrosion resistance of the unpainted part when the plating layer is a Zn-Fe alloy plating layer. become. The Fe content of the Zn-Fe alloy plating film was set to 60 wt% or less because as the Fe content increases, the internal stress of the Zn-Fe alloy increases. This is because cracks generated in the plating film propagate to the underlying Zn-Ni-Cr alloy plating film and reach the underlying layer.

〔Example〕

A single-layer plated steel plate was prepared under the following conditions (1) and (2), and the following tests were conducted.

■Plated lead plates were subjected to phosphate treatment under the following conditions (3), and phosphate treatment properties and freeze corrosion resistance were evaluated.

(2) Electrodeposition coating was applied to the above-mentioned salt-treated product under the following conditions (4), and blister resistance and perforation corrosion resistance were evaluated.

■Top: Self-painted (this) Furthermore, under the conditions of (4), an intermediate coat and top layer were applied, and the chipping resistance was evaluated.

Table 1 shows the coating conditions and test results for each plated plate.

(1) Melting bath composition a, plating bath Z for Zn-Ni-Cr alloy plating film
nSO4'7HtO: 150? /1NiSO,-6
H, O: 350 titNa, So, :
60? /1CrO1: O~4 f/L pit = 1.3 b-Plating bath for second layer 1) Electric Zn plating bath ZnSO4.7H,O: 450r/l Na! So: 60? /lpH=2
．． □ ii) Zn-Fe alloy plating bath Zn5O, 7H, O: 20-180P/1FeS
O, 7H, 0: 270~430? /LN&,SO
, : 30? /L CH,C00NaiH! O: 20 f/LCsHaO
y: 5? /lpH=2.5 (2) Plating conditions 8.1! Flow density C1 Plating bath temperature: 50'0 (3) Phosphate treatment Using a dip type phosphorus barley salt treatment solution (Bt3080 manufactured by Nippon Parriki Rising Co., Ltd.), phosphate treatment was carried out under standard conditions.

(4) Painting a. Cationic electrodeposition coating Nirekron 9400 manufactured by Kansai Paint Co., Ltd. Electrodeposition coating and baking using A coating film with a thickness of 20μ was formed.

b. Intermediate coating Uses intermediate coating paint manufactured by Kansai Paint Co., Ltd. A 35 μm intermediate coating film was applied to the standard coating. After the spray painting and firing process Formed.

C1 top coat Uses top coat paint manufactured by Kansai Paint Co., Ltd. A 35μm topcoat film was applied to the standard coating. After the spraying and baking process, Formed.

(5) Performance Evaluation Test a: Bare Corrosion Resistance A salt spray test in accordance with JIS Z2371 was conducted, and the following rankings were conducted based on red rust generation time.

X: 100 hours or less ○: 100-300 hours ◎: 300 hours or more Blister resistance Cross-cutting with a knife on an electrocoated plate Compliant with JIS Z2371 after adding The salt spray test lasted for 1000 hours. No, the bulge at the cross cut part ( One side) was evaluated.

×: 4fm or more O: 41 unused C0 perforation corrosion resistant Cross-cutting with a knife on an electrocoated plate Salt water spray test 9-Drying- Combined cycle corrosion consisting of wet tests The exam took place for two months. paint film, rot Remove the food products from the test piece and By measuring the corrosion depth of steel plates The perforation corrosion resistance was evaluated.

X: 0.3 w or more Δ: Less than 0.2 to 0.3 ○: 0.1 to less than 0.2 ◎: Less than 0.111 m d, phosphate treatment SEM of phosphate, clear crystal The state of production was observed and evaluated.

X: Coarse crystal ○: Fine and dense crystals e.Chipping resistance Injection air pressure 4s/α1, distance 30m, Gravelometry under the condition of 500f of crushed stone Chipping is performed using a The plating film is removed and the underlying steel sheet is exposed. Count the number of scratches and check the chip resistance. The performance was evaluated.

×: 11 or more Δ: 6 to 10 pieces ○: 5 or less /′

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between the Ni content in the film and the perforation corrosion resistance, and Fig. 2 is the same (a graph showing the relationship between the Cr content and the perforation corrosion resistance). Patent Applicant Nippon Steel Co., Ltd. Inventor Sagiyama Kosuma Omura Kosuma
Shun Honma 2nd generation
Satoshi Koike, Patent Attorney
Sho Yoshihara Sando Toshido Tomabechi Attorney Hiro Yoshihara Children
1 Figure 2r:! 5

Claims (1)

[Claims] In a method for producing a multilayer electroplated steel sheet using a continuous electroplating line, 8 to 15 wt% Ni and 0.01 to 0.5 wt% Ni are applied to the surface of the steel sheet in a first plating bath.
0.01-1g of alloy plating consisting of %Cr and balance Zn
/m^2, and in subsequent plating tanks after the second plating tank, 8 to 15 wt% Ni, 0.01 to 0.5 wt% Cr
, an alloy plating with the balance consisting of Zn is applied at a coating weight of 5 to 70 g/m^2, and then Zn plating or a Zn-Fe alloy plating containing 60 wt% or less of Fe is applied at a coating weight of 1 to 5 g/m2. A method for producing a multi-layer electroplated steel sheet, characterized in that the coating is applied with a coating weight of ^2.