JPH0696785B2 - Galvanized steel sheet with excellent press formability, chemical conversion treatment and weldability - Google Patents

Description

TECHNICAL FIELD The present invention relates to a zinc-based plated steel sheet excellent in press formability, chemical conversion treatment property, and weldability.

(Problems to be solved by the prior art and invention) As a method for improving the press formability of a galvanized steel sheet, for example, as described in JP-A-62-15883, the surface of the plated steel sheet is subjected to electrolytic chromate treatment. , A method of forming an oxide film of Cr ₂ O ₃ and a method of performing iron-zinc alloy plating, as described in JP-A-62-192597, to form a hard film on a zinc-based plated steel sheet and press it. It is disclosed to prevent galling and die galling to improve the lubricity of the press.

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

However, such products have the following inadequate points 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 plate, the chemical conversion treatment film is used in the chemical conversion treatment process. In the case of a steel sheet on which no lubricating oil has been formed and which has been coated with lubricating oil or a lubricating film, the oil does not come out in the cleaning process, so sufficient lubrication performance cannot be exhibited, and moreover the degreasing process before chemical conversion treatment is overloaded. High cost. 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 is higher than that of the electrolytic chromate treatment, and it is possible to perform chemical conversion treatment at low cost, degreasing, etc. It is desired to develop a zinc-based plated steel sheet that is excellent in press formability without imposing a load on the above process. Further, regarding the improvement of the weldability, no measures have been taken in the past, and it is strongly desired to improve the weldability together with the press formability and the chemical conversion treatment property.

It is an object of the present invention to provide a zinc-based plated steel sheet that can advantageously solve such requirements.

(Problems to be Solved by the Invention) The gist of the present invention is that Zn oxide is 3 to 500 mg / m 2.
Zinc-plated steel sheet with excellent press formability, chemical conversion treatability, and weldability obtained by coating the surface with a film consisting of ² (as Zn), Mn oxide 5 to 500 mg / m ² (as Mn) and other oxides. It is in.

The zinc-based plated steel sheet of the present invention, for example, welding 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 containing mainly Zn, such as i, Zn and Mg, to improve various functions such as corrosion resistance.
Etc., containing one or more kinds of alloying elements and impurity elements, fine particles of ceramics such as SiO ₂ and Al ₂ O ₃ , Ti,
Some oxides such as O ₂ and BaCrO ₄ and organic polymers such as acrylic resin are dispersed in the plating layer.The composition varies in the thickness direction of the plating layer, and the composition changes continuously or in layers. In addition, in the case of multi-layer plated steel sheets, in addition to pure Zn as the plating composition, Zn and Fe, Zn and Ni, Zn are used as the plating composition in the uppermost layer.
And Al, Zn and Mn, Zn and Cr, Zn and Ti, Zn and Mg such as Zn and Mg are the main components, and one or more alloy elements and impurity elements are included to improve various functions such as corrosion resistance. SiO ₂ , Al ₂ O ₃
There are ceramic fine particles such as, oxides such as TiO ₂ and BaCrO _4, and organic polymers such as acrylic resin 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 a steel sheet containing zinc as a main component and a metal containing iron or nickel, or an electrogalvanized steel sheet, an electroplated steel sheet such as zinc, nickel or chromium alloy, or a single alloy layer or a multilayer alloy electroplated steel sheet. , Zinc and zinc-containing metal vapor-deposited steel sheets. 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.

As described above, the surface of such a zinc-based plated steel sheet is coated with a film composed of Zn oxide, Mn oxide and other oxides to improve press formability, chemical conversion treatability and weldability. Is.

(Operation) The reason why such an effect can be obtained is as follows.

A method of forming a hard film on the surface of the plated steel sheet is effective for imparting lubricity to the plated steel sheet during press forming. In this respect, electrolytic chromate treatment and iron-zinc alloy plating are effective, but the former cannot form a chemical conversion coating,
The latter requires a large amount of processing and is costly.

To solve these problems, the hard coating on the surface of the plated steel sheet is an oxide coating, and it can be dissolved in a chemical conversion treatment liquid to form a chemical conversion treatment coating, and even if the coating components are dissolved in the chemical conversion treatment fluid It should be one that does not adversely affect the processing.

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

Zn oxide alone is difficult to form a press slidability improving film by a wet method, but in a mixed crystal state with Mn oxide, press slidability can be significantly improved. Further, Zn oxide can also form a chemical conversion treatment film, and there is no adverse effect even if it is eluted into the chemical conversion treatment liquid.

The structure of Mn and Zn oxide films is not clear, but Mn-O, Zn
Mainly network consisting of -O bonds, partly -O
It is presumed that it may have an amorphous macromolecular structure in which H, CO ₃ , PO ₄ groups, etc. are bonded and the metal supplied from plating is substituted.

In addition, since this film is an oxide film, it does not dissolve in the washing process with oil and the degreasing process, so the lubrication performance is reduced and
Does not impose a load on other processes.

In order to improve the adhesion and film-forming property of this film, phosphoric acid,
It is effective to add an inorganic acid such as boric acid, sulfuric acid, nitric acid or hydrochloric acid, or a salt thereof.

Further, the film may contain substances contained in the treatment bath or plating as impurities. These impurities include Zn, Al, Cr, Co, Mn, Pb, Sn, Cu, Ti, Si, B, N, S, P, Cl, K, N.
a, Mg, Ca, Ba, In, C, Fe, V, W, Ni, etc.

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

The amount of this film is Mn in order to improve press formability.
The oxide (as Mn) should be 5 mg / m ² or more, but if the coating amount exceeds 500 mg / m ² , the formation of the chemical conversion coating may be insufficient.

Therefore, the proper amount of Mn oxide film is 5 mg / m ² or more as Mn.
It is 500 mg / m ² or less.

Next, Zn oxide is mixed in to improve weldability. The amount of this oxide produced is 3 to 500 mg / m ² as the amount of Zn (per one surface) in the oxide film. If it is less than 3 mg / m ² , there is no effect, and if it exceeds 500 mg / m ² , it is not preferable because the electrical resistance becomes large, the chip is likely to be softened and deformed, and the chip life becomes short. That is, in welding or the like, the heating causes the plated metal to be in a molten state, and then,
Although progressing to alloying with a steel sheet, when the above-mentioned plated metal comes into direct contact with the electrode tip when it is in a molten state, copper of the chip composition and zinc of the plating composition selectively react, resulting in a hard and brittle copper-
By forming a zinc alloy layer, the tip is worn and the life of the electrode tip is shortened.

The molten plated metal is cut off from the contact with the chip by the oxide film formed on the surface of the plated steel sheet, preventing melting damage due to direct contact with the chip of the plated metal, and the molten state. The plated metal is alloyed with the iron in the steel sheet to form an iron-zinc alloy, which mainly adheres to the tip of the electrode tip through the cracks in the oxide film or together with the oxide film, and accumulates to form the tip of the chip. Although it is a protective metal film and the reason is not clear, the thickness, shape, etc. of the protective film do not change even if welding is continued, and good welding is always possible, and damage to the tip can be prevented. Here, the electrode protective metal is mainly composed of an alloy of plated metal and base iron, and the average concentration of Fe: 20 to 60%, Zn: 40 to 80%.
In many cases, it is preferable that the Fe concentration is high, and it is not preferable especially when the high-concentration Zn portion is locally present. In addition, the electrode protection metal may include a plating metal component, a steel plate component such as Mn and S, and an electrode tip component such as Cu.

In addition, this electrode protection metal film has the effect of keeping the tip shape convex so that even if the tip is softened and damaged to the same extent, welding can be done at a low current, and the tip protection film is 50% of the tip surface. If it is attached to the above area, the life of the electrode tip can be greatly extended. That is, an oxide film mainly composed of ZnO for adhering an electrode protective metal to the galvanized surface is generated, and an alloy of the plated metal and the steel sheet is passed through the oxide film by welding heat, or together with the oxide film. The electrode protection metal is welded while being attached to the electrode tip.

Even if the Mn oxide is combined with the Zn oxide to form a film, the effect of improving the weldability is recognized as in the case of the Zn oxide. Mn-
It is speculated that this is because the electric resistance of the Zn composite oxide does not increase so much.

Thus, by simultaneously forming a film mainly composed of Mn and Zn oxides on a zinc-based plated steel sheet, press formability and weldability can be improved and chemical conversion treatment can be performed.

Next, an example of a method for producing the above Mn oxide and Zn oxide will be described.

Potassium permanganate 1-70 g /, zinc nitrate 100-800 g /
The zinc-based plated steel sheet is contacted with the aqueous solution by dipping or spraying the zinc-based plated steel sheet in the aqueous solution, or by subjecting the zinc-based plated steel sheet to cathodic electrolysis in the aqueous solution, Mn oxide and Zn oxidation at the same time. Products can be mixed and produced.

When the oxide film is formed in this manner, a part of the plating layer and the alloy metal or the like in the plating layer becomes an oxide and is mixed as other oxide.

It is preferable to add 1 to 50 g / type of one or more of sulfuric acid, nitric acid, perchloric acid, phosphoric acid and the like as an etching agent to the above-mentioned aqueous solution, because the adhesion of the resulting oxide film can be improved. .

(Example) Next, an example of the present invention is shown in Table 1 together with a comparative example.

Note 1) Type of galvanized steel sheet: AS: hot-dip galvanized steel sheet (Fe10%, Al0.25%, residual Zn), EG: galvanized steel sheet, G
I: Hot dip galvanized steel sheet (Al0.3%, Fe0.8%, Pb, 0.1%, balance
Zn), HA: Semi-alloyed hot-dip galvanized steel sheet (Fe5%, Al0.3
%, Residual Zn), and steel plate thickness are all 0.8 mm.

Note 2) Press formability (friction coefficient) Sample size: 17mm × 300mm, Peeling speed: 500mm / min, Square bead shoulder R: 1.0 / 3.0mm, Sliding length: 200mm, Oil: Knoxlast 530F40, 1g / m ^Under the condition of No. ² , several points of tests were conducted at a surface pressure of 100 to 600 kgf, the pulling load was measured, and the friction coefficient was obtained from the slope of the surface pressure and the pulling load.

Note 3) Chemical conversion treatment SD5000 (manufactured by Nippon Paint Co., Ltd.) was used as the chemical conversion treatment liquid, and the chemical conversion treatment was performed after degreasing and surface adjustment according to the formulation.
Judgment of chemical conversion treatment film is made by SEM (secondary electron beam image)
A film having a uniform film was evaluated as ◯, a film having a partial film formed was evaluated as Δ, and a film having no film formed was evaluated as x.

Note 4) Manufacturing conditions are potassium permanganate 5g /, etchant (phosphoric acid) 10g /, zinc nitrate 350g /, liquid temperature 40
Electrolytic treatment (8A / d
The electrolysis time was adjusted to m ² ) or dipping treatment was performed in the aqueous solution to coat the oxide film.

Note 5) Welding conditions Welding conditions are as follows.

1) Pressurizing force: 250kgf 2) Initial pressurizing time: 40Hr 3) Energizing time: 12Hr 4) Holding time: 5Hr 5) Welding current: 11kA 6) Tip diameter: 5.0φ (conical head type) 7) Electrode life end Judgment: Number of dots that can secure a nugget diameter of 3.6 mm at 85% of welding current 8) Electrode material: Cu-Cr (generally used) Welding is performed with one side of the plated steel sheet facing up and the other side facing down. Two sheets were piled up and the number of consecutive points was taken.

Note 6) Oxides are measured by GDS (Glow Discharge Spectroscopy), ICAP
(Ion plasma issue analysis method).

(Effects of the Invention) According to the present invention, in press forming, the slidability can be improved more than that of a cold-rolled steel sheet, a chemical conversion treatment film can be formed, and the weldability can be improved. it can. As a result, excellent effects such as a lower cost than before, a load on a user's process can be reduced, and productivity can be improved, are exhibited.

Claims (1)

[Claims] (As Zn) 1. A Zn oxide 3~500mg / m ^2, (as Mn) Mn oxide 5 to 500 mg / m ² and the press formability made by coating the surface of the film comprising other oxides, Zinc-based plated steel sheet with excellent chemical conversion treatment and weldability.