JPH0696780B2 - Galvanized steel sheet with excellent press formability and chemical conversion treatment - Google Patents

Description

The present invention relates to a zinc-based plated steel sheet having excellent press formability and chemical conversion treatability.

[Prior Art] As a method for improving the pressability of a galvanized steel sheet, for example, as described in JP-A-62-185883, the surface of the plated steel sheet is subjected to electrolytic chromate treatment to form an oxide film of Cr ₂ O _3. As described in Japanese Patent Application Laid-Open No. 62-192597, a method of forming a hard coating on a zinc-based plated steel sheet, such as a method of applying an iron-zinc alloy plating, to prevent galling and die galling during pressing, press It is disclosed to improve the lubricity of the.

Further, as described in JP-A-1-136952, it is disclosed that the surface of a plated steel sheet is coated or coated with an organic material such as an organic lubricating film or lubricating oil to improve pressability.

[Problems to be Solved by the Invention]

However, such products have the following drawbacks when used by automobile users.

The outline of the process used by automobile users consists of the process of washing the steel plate with oil, the pressing process, the degreasing process, the chemical conversion treatment process, and the painting process.In the case of electrolytic chromate treated steel plates, the chemical conversion treatment is performed in the chemical conversion treatment process. In the case of a steel sheet that does not form a film and is coated with lubricating oil or a lubricating film, the oil will drop during the cleaning process and will not exhibit sufficient lubricating performance. Furthermore, the degreasing process before the chemical conversion treatment imposes a load, and the cost increases. On the other hand, the zinc-plated steel sheet subjected to iron-zinc alloy flash plating has a problem that the cost of the steel sheet becomes higher than that of the electrolytic chromate treatment.

In view of the present situation, an object of the present invention is to provide a zinc-based plated steel sheet excellent in press formability that can be produced at low cost, can be subjected to chemical conversion treatment, and does not impose a load on steps such as degreasing. .

[Means for Solving the Problems]

 The gist of the present invention is as follows.

(1) Mn oxide 5 to 500 mg / m ^{2 on the} surface of galvanized steel sheet
(As Mn) and boric acid 1000 mg / m ² or less (as boron)
And a zinc-based plated steel sheet coated with a film made of other oxides, which is excellent in press formability and chemical conversion treatment.

(2) Mn oxide 5 to 500 mg / m ^{2 on the} surface of zinc-plated steel sheet
(As Mn), 1 or 2 kinds of phosphoric acid and boric acid 1000mg / m
A zinc-based plated steel sheet excellent in press formability and chemical conversion treatability coated with a film of ² or less (as P and boron) and other oxides.

[Work]

The zinc-based plated steel sheet of the present invention, for example, hot-dip plating method, electroplating method, vapor deposition plating method, there are those by various manufacturing methods such as thermal spraying method, other than pure Zn as the plating composition, Zn and Fe, Zn and Ni, Zn and Al, Zn and Mn, Zn and Cr, Zn and T
Fe, Ni, Co, Al, Pb, Sn, Sb, Cu, Ti, Si, B, P, N, S, O, etc. are mainly composed of Zn such as i, Zn and Mg to improve various functions such as corrosion resistance. Containing one or more kinds of alloying elements and impurity elements, fine particles of ceramics such as SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaC
Some include oxides such as rO ₄ and organic polymers such as acrylic resin dispersed in the plating layer.Some have a single composition in the thickness direction of the plating layer, and some have a composition that changes continuously or in layers. In addition, in the multi-layer plated steel sheet, the uppermost layer,
The plating composition includes pure Zn, Zn and Fe, Zn and Ni, Zn and Al, Z.
n and Mn, Zn and Cr, Zn and Ti, and Zn etc. Zn and Mg as main components, comprises one or two or more kinds of alloy elements and impurity elements for the improvement of various functions such as corrosion resistance, also, SiO ₂ , Ceramic particles such as Al ₂ O ₃ , oxides such as TiO ₂ and BaCrO _4, and organic polymers such as acrylic resin are dispersed in the plating layer.

For example, hot-dip galvanized steel sheet, vapor-deposited galvanized steel sheet, iron-zinc alloyed hot-dip galvanized steel sheet, aluminum mainly containing zinc, hot-dip galvanized steel sheet of iron or the like, lower layer is alloyed in the plating layer cross-section direction. Alloyed hot-dip galvanized steel sheet (generally called half alloy), single-sided iron-zinc alloyed hot-dip galvanized layer, galvanized steel sheet consisting of other-side hot-dip galvanized layer, zinc on these plated layers by electroplating, vapor deposition plating, etc. , Or steel containing zinc as a main component, a steel sheet plated with a metal containing nickel, or an electrogalvanized steel sheet, zinc, nickel, an alloy electroplated steel sheet such as chromium, a single alloy layer or a multilayer alloy electroplated steel sheet, Examples include vapor-deposited steel plates of zinc and zinc-containing metals. In addition, fine particles of ceramics such as SiO ₂ and Al ₂ O ₃ , Ti
There is a dispersion-plated steel sheet in which fine particles of O ₂ oxide and an organic polymer are dispersed in zinc or zinc alloy plating.

By coating the surface of such a zinc-based plated steel sheet with the Mn-based oxide film as described above, it is intended to improve press formability and chemical conversion treatability.

That is, in order to impart the lubricity of the press to the plated steel sheet, it is effective to form a hard film on the surface of the plated steel sheet. In this respect, electrolytic chromate treatment and iron-zinc alloy plating are effective, but the former cannot form a chemical conversion treatment film, and the latter requires a large amount of treatment, resulting in high cost.

To solve these, as a hard coating on the surface of the plated steel sheet,
It is necessary that it is an oxide film that can be melted in a chemical conversion treatment liquid to form a chemical conversion treatment film, and that the film formation does not adversely affect the chemical conversion treatment even if it dissolves into the chemical conversion treatment liquid. .

From such a viewpoint, the present inventors have found that it is sufficient to form an Mn-based oxide film on the surface of a zinc-based plated steel sheet. The Mn-based oxide film becomes a glass-like film like the chromate film, which suppresses galling of the plating die during pressing and improves slidability. Furthermore, since it dissolves in the chemical conversion treatment liquid, a chemical conversion treatment film can be formed unlike the chromate film, and since it is also a component of the chemical conversion treatment film, there is no adverse effect even if it is eluted into the chemical conversion treatment liquid.

Although the structure of the Mn-based oxide film is not clear, Mn-O bond, B
Mainly network consisting of -O bond and P-O bond,
It is presumed that it may be an amorphous macromolecular structure in which the —OH, CO ₃ groups, etc. are partially replaced by the metal supplied from the plating.

Further, since the Mn-based oxide film is an oxide film, it does not dissolve even in the washing process with oil and the degreasing process, so that the lubricating performance is not deteriorated and no load is applied to other processes.

Boric acid is mixed in to improve the adhesion and film formability of the Mn-based oxide film. Thus, the film structure of the Mn-based oxide is made uniform, the film forming property is improved, the press moldability is further improved, and the chemical conversion treatability can be improved at the same time.

Such an oxide film can be reliably produced by immersing the zinc-based plated steel sheet in an aqueous solution, spraying the aqueous solution, or by cathodic electrolysis in the aqueous solution. In the case of zinc plating metal or zinc alloy plating, zinc, alloy elements (metals), impurities in the aqueous solution, etc. are mixed (produced) as other oxides.

Further, similar effects can be obtained by mixing phosphoric acid in addition to boric acid as described above.

Next, the coating amount range of the coating of the present invention will be described.

The coating amount of Mn oxide may be 5 mg / m ² or more as Mn in order to improve pressability, but if the coating amount exceeds 500 mg / m ² , formation of the chemical conversion coating becomes insufficient. Therefore, the proper coating amount of Mn oxide, 5 mg / m ² or more as Mn 500 mg / m ² or less, preferably 5 to 200 mg / m ^2.

Next, as boric acid, 1000 mg / m ² or less (as boron), preferably 200 mg / m ² or less is good, and when it exceeds 1000 mg / m ² , the chemical conversion processability may deteriorate, which is not preferable, and there is a lower limit. All you have to do is do it.

When phosphoric acid is mixed in the above oxide film, the total amount of boric acid and phosphoric acid (as P and boron) is 1000 mg / m ²
It can be generated as below, 1000mg / m ²
If it exceeds the above range, the chemical conversion treatability may be deteriorated, which is not preferable. The lower limit has to exist, and the total amount is preferably 200 mg / m ² or less.

Next, as a method of forming the oxide film as described above, for example, potassium permanganate 1 g / ~ solubility limit, phosphoric acid 1-6
By dipping the zinc-based plated steel sheet in an aqueous solution consisting of 0 g /, boric acid 1 to 60 g /, an etching aid (sulfuric acid, etc.), spraying the aqueous solution, or electrolytically treating the steel sheet as a cathode in the aqueous solution. The desired film can be reliably produced.

〔Example〕

 Next, examples of the present invention will be given together with comparative examples.

Note 1) Galvanized steel sheet: AS: Hot-dip galvanized steel sheet (Fe10%, Al10.25%, residual Z
n), EG: Electro-galvanized steel sheet, GI: Hot-dip galvanized steel sheet (Al0.3%, Fe0.8%, Pb0.1%, residual Zn), HA: Semi-alloyed hot-dip galvanized steel sheet (Fe5%, Al0 .3%, residual Zn), CR: cold rolled steel, ordinary steel with a steel thickness of 0.8 mm.

Note 2) Pressability (friction coefficient) Sample size: 17mm x 300mm, Peeling speed: 500mm / min, Square beat shoulder R: 1.0 / 3.0mm, Sliding length: 200mm, Lubrication: Knoxlast 530F-40 (Parker Kosan) Co., Ltd.) Under the condition that the amount of oil applied was 1 g / m ² , a point test was conducted at a surface pressure of 100 to 600 kgf, the pull-out load was measured, and the friction coefficient was determined from the slope of the surface pressure and the pull-out load.

Note 3) Chemical conversion treatment: SD5000 for the chemical conversion solution (zinc-phosphoric acid-fluorine treatment bath).
(Manufactured by Nippon Paint Co., Ltd.), degreasing and surface preparation were performed as prescribed, and post-chemical conversion treatment was performed. The chemical conversion coating is judged by SEM (secondary electron image): ○ if a uniform coating is formed, △ if a partial coating is formed, and × if a coating is not formed. It was judged.

Note 4) The amount of oxide film shows Mn oxide: Mn amount, phosphoric acid: P amount, boric acid: B amount, respectively.

Note 5) For oxide formation, potassium permanganate 30g /, phosphoric acid 10g /, boric acid 30g /, sulfuric acid 3g / as an etching aid are selected and synthesized to adjust the dipping time of the zinc-based plated steel sheet. I gave it.

〔The invention's effect〕

According to the present invention, it is possible to provide a zinc-based plated steel sheet in which slidability is improved more than that of a cold-rolled steel sheet in press forming, and a chemical conversion coating can be formed. INDUSTRIAL APPLICABILITY The present invention is extremely useful industrially because it can improve productivity during molding.

Claims (2)

[Claims] 1. Mn oxide 5 to 500 m on the surface of zinc-based plated steel sheet
A zinc-based plated steel sheet with excellent press formability and chemical conversion treatment coated with a film consisting of g / m ² (as Mn), boric acid 1000 mg / m ² or less (as boron) and other oxides. 2. Mn oxide 5 to 500 m on the surface of zinc-based plated steel sheet
g / m ² (as Mn), one or two of phosphoric acid and boric acid 1000
A zinc-based plated steel sheet excellent in press formability and chemical conversion treatment, which is coated with a film containing mg / m ² or less (as P and boron) and other oxides.