JP2619440B2 - Surface-treated steel sheet with excellent workability and paintability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a surface-treated steel sheet having excellent paintability and workability such as phosphatability and cationic electrodeposition paintability. It relates to a suitable surface-treated steel sheet.

<Prior art and its problems> Conventionally, various surface-treated steel sheets have been used for the purpose of preventing corrosion of automobile bodies in so-called salt-affected zones such as North America and Canada.

Various properties required for surface-treated steel sheets for automobile bodies are diverse, such as phosphatability, paintability, post-paint corrosion resistance, bare corrosion resistance, weldability, workability, and surface properties. However, conventional surface-treated steel sheets have advantages and disadvantages, and researches and developments have been made on solving these disadvantages and various new surface treatments.

In particular, Zn-plated and Zn-based alloy-plated steel sheets have excellent sacrificial corrosion protection and are used in large quantities to prevent perforations on the inner surface of automobile bodies. The coating properties and press workability are not always sufficient, and it is desired to improve these properties.

Particularly, in recent years, measures to prevent external rust on the outer surface of an automobile body have been promoted. For this reason, it is particularly important to improve the above-described phosphating property, cationic electrodeposition coating property, press workability, and the like.

In addition, even when a non-plated surface of a cold-rolled steel sheet or a surface-treated steel sheet is used on the outer surface of an automobile body, the above-mentioned phosphating property, cationic electrodeposition coating property, press workability, etc., have better performance. Things are desirable.

Even on the non-plated surface of a cold-rolled steel sheet or a surface-treated steel sheet, depending on the processing conditions and the press mold, poor phosphatability and press workability may occur. If the performance can be improved and stabilized by performing a surface treatment such as plating on the non-plated surface of the steel sheet, a great merit can be obtained.

As a method of improving the cationic electrodeposition coating property and the water-resistant secondary adhesion, which are disadvantages of the Zn-based plated steel sheet, a method of performing Fe plating on the Zn-based plated steel sheet is disclosed in, for example, JP-A-57-6719.
No. 5, No. 57-198293, No. 58-34192, etc., but the phosphatability is poor because pure Fe plating delays the generation of phosphate nuclei.

In addition, the present inventors have already disclosed in JP-A-59-211592, an improvement in phosphatability by Fe-P plating and an improvement in cationic electrodeposition coating properties. However, when this Fe-P plating was performed, although the effect of P was certainly recognized, the improvement effect was sometimes insufficient.

<Object of the Invention> The present invention solves the above-mentioned problems of the prior art, and is excellent in workability and coating properties, such as excellent phosphatability, cationic electrodeposition coating property and press workability. It is to provide a steel plate.

<Structure of the Invention> The present inventors have conducted intensive studies on the improvement of the phosphatability and the cationic electrodeposition coating property using the above-described Fe-based plating, and have also studied the improvement effect on the press workability. As a result of intensive studies, they have found that the addition of O and further P to the Fe-based plating improves their performance, leading to the present invention.

That is, according to the first aspect of the present invention, at least one surface is provided with an Fe—O plating layer having an O content of 0.2 to 5.0 wt% or more in an amount of 0.01 g / m ² or more. Provided is a surface-treated steel sheet having excellent paintability and paintability.

According to the second aspect of the present invention, at least one surface has an O content of 0.2 to 5.0 wt% and a P content of 0.003 to 0.003 wt%.
A surface-treated steel sheet excellent in workability and coatability, characterized by being provided with a 5.0 wt% Fe-OP plating layer of 0.01 g / m ² or more, is provided.

Further, according to the third aspect of the present invention, on at least one surface, a Zn or Zn-based alloy plating layer is provided as a lower layer, an O content is 0.2 to 5.0 wt% as an upper layer, and an adhesion amount is 0.5 g / m 2. A surface-treated steel sheet excellent in workability and coatability characterized by providing ^two or more Fe—O plating layers is provided.

According to the fourth aspect of the present invention, a Zn or Zn-based alloy plating layer is formed as a lower layer on at least one surface, and an O content of 0.2 to 5.0 wt% and a P content of 0.003 to 5.0 are formed as an upper layer.
Provided is a surface-treated steel sheet having excellent workability and coatability, characterized by being provided with an Fe-OP plating layer having a coating amount of 0.5 g / m ² or more in terms of wt%.

Hereinafter, the surface-treated steel sheet of the present invention will be described in detail.

In the Fe—O plating layer or the Fe—OP plating layer in the present invention, it is preferable that O is contained in an amount of 0.2 to 5.0 wt%. The reason is described below.

FIG. 1 shows the relationship between the O content in the Fe—O plating layer and the initial number of crystal nuclei generated during the phosphate treatment. The Fe—O plating layer used was one containing 0.2 wt% of P and one containing no P at all. The number of initial nuclei generated here is a value obtained by counting the number of crystal nuclei of phosphate 5 seconds after the phosphate treatment by SEM photograph.

As is clear from the figure, the number of phosphate-treated crystal nuclei changes depending on the O content in the Fe—O plating layer, and the O content is reduced.
It is understood that the number of crystal nuclei significantly increases at 0.2 wt% or more. Preferably, the content is 1.0% by weight or more. O content is about 5wt%
If the number exceeds 3, no crystal nucleus is observed, and the phosphatability is rather deteriorated. The O content is preferably 4.0 wt% or less.

If the O content is too high, the phosphatability is rather degraded for the following reasons.

That is, FIG. 2 shows the result of identification of the Fe—O plating layer by X-ray diffraction. In the figure, the horizontal axis indicates the X-ray diffraction angle, and the vertical axis indicates the arbitrary intensity.

As apparent from the figure, Fe-O plating layer although alpha-Fe is mainly, Fe ₃ since the weak peaks of O ₄ is present, Fe-O at least a portion of O in the plating layer of Fe _It can be seen that it is ₃ O ₄ . When Fe-O compounds such as Fe ₃ O ₄ are dispersed, they function as a cathode, so that a large number of microcells are formed, the phosphating reaction is accelerated, and the phosphating property is improved. It is considered something. However, if the O content in the Fe—O plating layer is too high, the surface is covered by the Fe—O compound, and the phosphate treatment property is considered to be rather deteriorated.

Next, by adding P to the above-described Fe—O plating layer, the number of initial crystal nuclei of phosphatability can be further increased.

The effect of the addition of P is recognized for the Fe-O plating layer having any O content in the range of 0.2 to 5.0 wt%, and the P content is 0.1%.
In the range of 003 to 5.0% by weight, there is an effect of reducing phosphate crystals. The P content is more preferably 0.05 to 1.0 wt.
% Is good.

It is considered that P improves phosphatability in order to improve acid solubility.

In the present invention, the addition of P to the Fe—O plating layer is limited.
s, Sb, Bi, B, Cr, Ni, Co, etc. may be contained.

When these Fe—O plating layers or Fe—O—P plating layers are applied directly on a steel sheet, the adhesion amount is required to be 0.01 g / m ² or more. If it is less than 0.01 g / m ² , the above effect is small because the steel sheet surface cannot be uniformly coated.

More preferably, it is 0.01 g / m ² or more.

Thus for effective even with a small amount of coating weight, good Zn ₃ Fe (PO ₄₎ of the performance of the phosphating crystal 2 _· 4H ₂ O
This is because Fe ²⁺ necessary to form (Phosphophyllite) is supplied from the base steel.

By the way, when a phosphate treatment is applied to Zn or a Zn-based alloy-plated steel sheet, the generated phosphate film is Zn ₃ (P
O ₄ ) Since ₂ · 4H ₂ O (Hopeite) is generated, it is inferior in water-resistant secondary adhesion after 3 coats and corrosion resistance after coating. Also, the crater resistance at the time of cationic electrodeposition coating is poor.

Therefore, by applying the Fe—O plating or the Fe—OP plating of the present invention to the surface of the Zn or Zn-based alloy plated steel sheet, Zn ₂ Fe (PO ₄ ) ₂ .4H ₂ O (Phosphophy
llite) phosphate film can be formed. Therefore, it has excellent water resistance secondary adhesion, corrosion resistance after coating, and crater resistance during cationic electrodeposition coating. For this purpose, the amount of Fe—O plating or Fe—OP plating is 0.5 g / m ² or more, preferably 1.5 g / m ² , more preferably
2.5 g / m ² or more is required. This is about 1g /
This is because dissolution of the plating layer of about m ² occurs, and Hopeite is more likely to be generated as the amount of adhesion is smaller.

Figure 3 is, Ni content of 8 wt%, the improvement effect of press formability when subjected to Fe-O plating or Fe-O-P plating Zn-Ni alloy electroplated steel sheet coating weight 20 g / m ² FIG. The press workability was determined using an Erichsen cup tester, and the critical drawing ratio (LDR) was determined at a punch diameter of 33 mm and a wrinkle holding pressure of 300 kg.

As is evident from the figure, the critical draw ratio is remarkably poor in the Zn-Ni alloy electroplated steel sheet with a Ni content of 8 wt%,
When Fe—O plating is applied on this Zn—Ni alloy plating layer, the limit drawing ratio is improved, and it is found that the O content increases further. Further, it can be seen that when Fe-OP plating is applied, the limit drawing ratio is further improved as compared with Fe-O plating even with the same O content.

The Zn or Zn-based alloy plating is applied as the lower layer because the sacrificial corrosion protection function of Zn is required, so the amount of Fe-O or Fe-OP plating without sacrificial corrosion protection is small. Is more preferable, and 9 g / m ² or less is appropriate.

<Example> Hereinafter, the present invention will be described in more detail based on examples.

The Fe-O plating and Fe-OP are applied to the cold rolled steel sheet which has been subjected to electrolytic degreasing and pickling according to a conventional method under the conditions shown in (1) below.
Plating was applied.

Zn plating, Zn-Ni plating, Zn-Fe plating, alloying melting
When the Zn plating layer is the lower layer, after normal immersion degreasing,
After performing light pickling with 0.1% HCl and 5 sec, similarly (1)
The Fe-O and Fe-OP plating were performed under the following conditions.

In addition, about Zn plating, Zn-Ni plating, Zn-Fe plating, and alloying hot-dip Zn plating, what was manufactured by the general method was used.

In order to contain O in Fe plating, the Fe plating solution contains
Fe ³⁺ is contained. The O content can be changed by changing the pH, bath temperature, and current density using this solution.

(1) Plating bath composition (1-1) Fe-O plating bath composition _{FeCl 2 · nH 2 O 180g /} FeCl 3 · 6H 2 O 20g / KCl 180g / (1-2) Fe-O-P plating bath composition FeCl _{2 · nH 2 O 180g / FeCl} 3 · 6H 2 O 20g / KCl 180g / NaH 2 PO 2 · H 2 O 0.01~5g / (1-3) electrolysis conditions pH 1.0 to 2.5 bath temperature 25 to 85 ° C. current density 5 150150 A / dm ² (2) Phosphate treatment As a comparative example of a dip type, phosphate treatment was performed by a conventional method using Granodine SD-2000 (manufactured by Nippon Paint).

(3) Phosphate treatment film amount Measured by a dissolution weight loss method using a 5% chromic acid solution.

(4) P ratio P ratio was determined from the peak heights of Phosphophyllite and Hopeite in X-ray diffraction by a conventional method.

(5) Phosphate crystal size An average crystal size was measured by a 1000 × SEM photograph.

(6) Number of initial crystal nuclei The number of phosphate-treated crystals after 5 seconds of phosphate treatment was counted by SEM photograph.

(7) Crater resistance of cationic electrodeposition coating Using Power Top U-30 (manufactured by Nippon Paint Co., Ltd.), perform quick electrodeposition to 300V and perform 180 electrodeposition coating.
After baking at 30 ° C. for 30 minutes, the number of crater-like defects was evaluated.

(8) Water-resistant secondary adhesion Phosphate treatment solution: Granodine SD-2000 (Nippon Paint) Cationic electrodeposition coating: Powertop U-30 (Nippon Paint) 20 μm Intercoat: Amirac chipping sealer N3 (Kansai) Paint) 35μm Top coat: Neoamirac B002 (Kansai Paint) 35μ
m After the above three coats were applied, the coating was immersed in deionized water at 50 ° C. for 10 days, and 100 squares of 2 mm square were cut within 10 minutes after being pulled up, and the tape was peeled off. Evaluation was made based on the coating film remaining ratio.

(9) Corrosion resistance after painting Phosphate treatment solution: Granozin SD-2000 (made by Nippon Paint) Cationic electrodeposition coating: Power Top U-30 (made by Nippon Paint) 20 μm After the above electrodeposition coating, a cross cut was performed. A salt spray test (JISZ2371) was performed. Evaluation was made based on the blister width (mm) of the wound after 20 days.

(10) Press workability Using an Erichsen cup drawing tester, punch diameter 33
m, LDR (limit drawing ratio) was determined at 300 kg of wrinkle pressure.

Tables 1 and 2 show the results of the tests performed under the above conditions.
Shown in Table 1 shows that the Fe-O plating layer or Fe
Examples and comparative examples in which the -OP plating layer is directly provided are shown in Table 2, and Table 2 shows the results on Zn or Zn-based alloy plated steel sheets.
This is an example and a comparative example in which an Fe—O plating layer or an Fe—OP plating layer is provided.

As is clear from Tables 1 and 2, Fe-O plating with an O content of 0.2 to 5.0 wt% or an O content of 0.2 to 5.0 according to the present invention.
It can be seen that the phosphatability is improved by Fe-OP plating with wt% and a P content of 0.003 to 5.0 wt%. In addition, it can be seen that the crater resistance during the cationic electrodeposition coating, the corrosion resistance after coating, the secondary water resistance, and the press workability are improved.

<Effects of the Invention> As described in detail above, according to the present invention, the Fe-O plating layer having an O content of 0.2 to 5.0 wt% or the O content
Fe-OP with 0.2-5.0wt%, P content 0.003-5.0wt%
By providing a plating layer of 0.01 g / m ² or more, it is possible to provide a surface-treated steel sheet excellent in press workability, phosphate treatment property, and the like, and thus has an effect that it can be widely applied to automobile bodies and the like.

In addition, the O content on Zn or Zn-based alloy-plated steel sheet is 0.
2-5.0wt% Fe-O plating layer or O content 0.2 ~
5.0 wt%, by being provided P content of the Fe-O-P plating layer of 0.003~5.0wt% 0.5g / m ² or more, excellent in press formability, phosphating resistance and electrodeposition coatability, etc. Since the present invention can provide a surface-treated steel sheet, it can be widely applied to automobile bodies and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the O content in the Fe—O plating layer and the number of phosphate-treated crystal nuclei in the initial stage (after 5 seconds) after the phosphate treatment. FIG. 2 is a graph showing the results of identification of the Fe—O plating layer by X-ray diffraction. Fig. 3 shows the F content of a Zn-Ni plated steel sheet with a Ni content of 8 wt%.
It is a graph which shows the influence which an e-OP plating layer gives to a limit drawing ratio.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-56600 (JP, A) JP-A-49-31549 (JP, A)

Claims (4)

(57) [Claims] 1. The method according to claim 1, wherein at least one surface has an O content of 0.2 to 0.2.
Excellent surface treated steel sheet in workability and coating properties of the Fe-O-plated layer of 5.0 wt% and characterized in that provided 0.01 g / m ² or more. 2. The method according to claim 1, wherein at least one surface has an O content of 0.2 to 0.2.
A surface-treated steel sheet having excellent workability and paintability, characterized by comprising an Fe-OP plating layer of 5.0 wt% and a P content of 0.003 to 5.0 wt% provided in an amount of 0.01 g / m ² or more. 3. A Zn or Zn-based alloy plating layer as a lower layer and an O content of 0.2 to 5.0 as an upper layer on at least one surface.
A surface-treated steel sheet having excellent workability and coatability, characterized by being provided with an Fe-O plating layer having a coating amount of 0.5 g / m ² or more in wt%. 4. At least one surface has a Zn or Zn-based alloy plating layer as a lower layer and an O content of 0.2 to 5.0 as an upper layer.
wt%, P content is 0.003-5.0wt%, and adhesion amount is 0.5g / m ²
A surface-treated steel sheet having excellent workability and coatability, characterized by comprising the above Fe-OP plating layer.