JPH0688190A - Galvannealed steel sheet having excellent coating finishability, pressability and chemical conversion treatability - Google Patents

Abstract

PURPOSE:To provide a galvannealed steel sheet excellent in coating finishability, press formability and chemical conversion treatability. CONSTITUTION:The surface of the galvannealed steel sheet is coated with an Mn oxide film via an electrogalvanizing layer. The surface of the galvannealed steel sheet is otherwise coated with a P oxide film via the electrogalvanizing layer. The surface of the galvannealed steel sheet is otherwise coated with an Mn-P oxide film via the electrogalvanizing layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvannealed steel sheet having excellent paint finish, pressability and chemical conversion treatment.

[0002]

2. Description of the Related Art Pressability of hot-dip galvanized steel sheet,
In order to improve the chemical conversion treatability, it has been previously filed and published by the present applicant that the surface of the hot-dip galvanized steel sheet is directly coated with an Mn oxide film or an Mn-based oxide film containing P. JP-A-3-183797 and JP-A-3-249182
It is disclosed in Japanese Patent Publication No. However, in such a conventional hot-dip galvanized steel sheet coated with an oxide film on such a surface, although the pressability and chemical conversion treatability have been improved, there is a problem in the finish of the coating, and in particular, electrodeposition There was a problem that craters were generated during coating and the smoothness after coating was poor.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and improves not only pressability and chemical conversion treatability but also paint finish, coating finish, pressability and chemical treatment. It was completed for the purpose of providing a hot-dip galvanized steel sheet having excellent properties.

[0004]

The present invention made to solve the above problems is characterized in that the surface of a hot-dip galvanized steel sheet is coated with an Mn oxide film through an electrogalvanized layer. The first invention is a galvannealed steel sheet having excellent paint finish, pressability, and chemical conversion treatability.
A hot-dip galvannealed steel sheet excellent in paint finish, pressability, and chemical conversion treatment characterized in that the surface of the hot-dip galvanized steel sheet is coated with a P oxide film through an electrogalvanized layer. Of the present invention, characterized in that the surface of the hot-dip galvanized steel sheet is coated with an Mn-P-based oxide film through an electrogalvanized layer, which is excellent in coating finish, pressability, and chemical conversion treatment. A galvanized steel sheet is a third invention.

As the hot-dip galvannealed steel sheet used in the present invention, for example, the Fe content in the plating layer is 8 to 12% (the balance is Zn and impurities) and the adhesion amount is 30 to 10
Those of 0 g / m ² are used. Then, an electrogalvanized layer is formed on the surface of this hot-dip galvanized steel sheet by electroplating to improve the coating finish (suppression of craters in electrodeposition coating). Even when it is applied to, it is possible to ensure a sufficient electrodeposition coating finish. The coating amount of the electrogalvanized layer is preferably in the range of 1 to 5 g / m ^{2 in} terms of surface smoothness required for finishing the coating and economical reasons.

Further, in the present invention, pressability (workability) is improved by coating the surface of the electrogalvanized layer described above with an Mn oxide film, a P oxide film or an Mn-P type oxide film. At the same time, the chemical conversion treatability is also improved. This is because, in a two-layer plated steel sheet obtained by coating the surface of a hot-dip galvannealed steel sheet with an electrogalvanized layer, the upper electrogalvanized layer is soft, and therefore, for example, the electrogalvanized layer during press forming. May adhere to the die (die), the flowability of the steel sheet into the press die may deteriorate, and cracks may occur during pressing. Mn oxide film or P oxide film on the surface or
It is essential to coat the Mn-P based oxide film.

Further, the Mn oxide film, the P oxide film or the Mn-P type oxide film coated on the surface of the electrogalvanized layer becomes a glassy film similar to the chromate film,
Suppresses galling of the plating die during pressing,
In addition to improving the slidability, the Mn oxide film, P oxide film, or Mn-P-based oxide film dissolves in the chemical conversion solution, so a chemical conversion film should be formed unlike the chromate film. You can Furthermore, since both the Mn oxide film and the P oxide film and the Mn-P-based oxide film are components of the chemical conversion treatment film, there is no adverse effect even if they flow out to the chemical conversion treatment liquid.

Although the structure of Mn oxide is not clear, Mn-O
Mainly network consisting of bonds, partially -OH, C
It is presumed that the O ₃ and Pb ₄ groups may have an amorphous macromolecular structure in which the metal supplied from the plating is replaced. The amount of Mn oxide film is 5 to 500 as Mn
It is preferably mg / m ² . That is, in order to improve pressability, Mn should be 5 mg / m ² or more, but if the coating amount exceeds 500 mg / m ² , formation of the chemical conversion coating may be insufficient. Also, such Mn
As a method for producing an oxide film, for example, potassium permanganate: 1 g / l to a solubility limit, a hot-dip galvanized steel sheet coated with an electrogalvanized layer described above in an aqueous solution containing an etching aid (such as sulfuric acid). The desired coating can be easily formed by immersing in, spraying an aqueous solution, or electrolytically treating the steel sheet as a cathode in the aqueous solution.

In the case of coating the P oxide film, the amount of P is preferably 5 to 1000 mg / m ² for the same reason as in the case of the Mn oxide film described above. The structure of the oxide film is BO bond, P-O
Mainly composed of networks, partially -OH, CO
It is presumed that the _three groups and the like may have an amorphous macromolecular structure in which the metal supplied from the plating is replaced. In addition, as a method of forming the P oxide film, for example,
Whether the hot-dip galvanized steel sheet coated with the electrogalvanized layer described above is dipped in an aqueous solution having a pH of 2 to 6 consisting of sodium phosphate 1 to 60 g / l and an etching aid (sulfuric acid, etc.) or sprayed with an aqueous solution. Alternatively, a desired film can be reliably produced by electrolytically treating a steel sheet as a cathode or an anode in an aqueous solution. When the oxide is generated in this way, a part of the electrogalvanized layer and the alloy metal in the plated layer are mixed into the oxide film as other oxide, but this does not cause any problem. It should be noted that such Mn oxide film or P oxide film is an oxide film with excellent oil resistance, and as a result, it does not dissolve even in the oil cleaning process or deoiling process, and the lubrication performance deteriorates. And does not impose a load on other processes.

In order to improve the adhesion and film forming property of the above Mn oxide film or P oxide film, phosphoric acid,
It is effective to add an inorganic acid such as boric acid, sulfuric acid, hydrochloric acid, etc., or a salt thereof, and further, these coatings contain substances contained in the treatment bath or plating as impurities. Well, these impurities include Zn, A
l, Cr, Co, Ni, Pb, Sn, Cu, Ti, Si, B, N, S,
P, Cl, K, Na, Mg, Ca, Ba, In, C, Fe, V, W, Mo
and so on.

Next, the case of coating the Mn-P type oxide film will be described. When phosphoric acid is mixed to improve the adhesion and film-forming property when forming an Mn oxide film, an Mn-P-based oxide film with an extremely uniform film structure is formed, and the film-forming property is improved. It is recognized that the press formability is further improved because the lubricity is further improved as compared with the Mn oxide film, and the chemical conversion treatability is also improved at the same time. This kind of Mn-P-based oxide film can be surely formed by dipping, spraying, cathodic electrolysis, etc. of the hot-dip galvanized steel sheet coated with the electrogalvanized layer in the same manner as when producing the Mn oxide film. Can be generated. At this time, zinc which is a plating metal (zinc and other alloying elements in the case of zinc alloy plating) and impurities in the aqueous solution are mixed as other oxides, but there is no problem.

In the case of coating the above Mn-P type oxide coating, the coating amount range of the coating is 5 as Mn.
It is preferably mg / m ² or more 500 mg / m ² are as described in the case of coating the Mn oxide film described above, 5 to 200 mg of Mn in the case of Mn over P-based oxide film
/ m ² and P is mixed with 1000 mg / m ² or less (not including O), preferably 500 mg / m ² or less of phosphoric acid. It should be noted that when the above oxide film is formed as another oxide, it does not matter that a part of the plating metal or impurities in the aqueous solution are mixed as an oxide.

Specific examples of the method of forming the above Mn-P type oxide film include, for example, potassium permanganate:
The hot-dip galvanized steel sheet coated with the electrogalvanized layer is immersed in an aqueous solution containing 1 g / l to the solubility limit, phosphoric acid: 5 to 60 g / l, and an etching aid (sulfuric acid, etc.), or sprayed with the aqueous solution. Alternatively, a desired Mn-P-based oxide film can be formed by electrolytically treating a steel sheet as a cathode in an aqueous solution.

[0014]

EXAMPLES 0.8mm thick steel plate to 30 to 100 g / m alloying galvannealed plated ^two galvanized steel sheet 1 to 5 g / m ² of electro-galvanized layer (Fe: 10% , Al: 1
0.25%, balance Zn) was prepared by electroplating to prepare an AS steel plate, which was potassium permanganate: 50
g / l, sulfuric acid: 3 g / l, zinc carbonate: 5 g / l solution (30
7 ℃ / dm ² with the steel plate to be treated as the cathode and the Pt electrode as the anode
After conducting electrolysis for 1.5 seconds, it was washed with water and dried to form an Mn oxide film, and various properties were examined as Examples 1 to 15 and the results are shown in Table 1.

Similarly, phosphoric acid: 40 g / l, sulfuric acid: 3 g / l,
Zinc carbonate: A 5 g / l solution (30 ° C.) was used as a cathode for the treated steel sheet and a Pt electrode as an anode at 7 A / dm ² for electrolysis time and solution concentration respectively to form a P oxide film and then washing with water. Table 2 shows the results of examining the properties of the dried product.

Further, potassium permanganate: 50 g / l
, Phosphoric acid: 10 g / l, sulfuric acid: 3 g / l, zinc carbonate: 5 g / l
In the solution (30 ° C.), the steel sheet to be treated was used as a cathode, the Pt electrode was used as an anode, and electrolysis or immersion was performed at 7 A / dm ² for 1.5 seconds, followed by washing with water and drying, and potassium permanganate, phosphoric acid, Table 3 shows the results of examining the respective properties of the Mn-P-based oxide film produced by adjusting the concentrations of sulfuric acid and zinc carbonate, the temperature of the solution, and the immersion time.

In each table, the AS plating amount means the alloying hot dip galvanizing amount, and the Zn plating amount means the electrogalvanizing amount. Further, the test conditions and evaluation methods for each characteristic are as follows. It is as follows. Pressability test conditions and evaluation method From the obtained hot-dip galvanized steel sheet, 17 mm x 300
mm test piece is prepared, tensile speed is 500 mm / min, square beat shoulder R: 1.0 / 3.0 mm, sliding length: 200 mm, oiling: Knoxlast 530F-40 (manufactured by Parker Kosan Co., Ltd.) 1 g / Under the condition of m ² , a several-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. Conditions for chemical conversion treatment test SD5000 for the chemical conversion liquid (zinc-phosphate-fluorine treatment bath)
Using Nippon Paint Co., Ltd., degreasing and surface preparation were performed as prescribed, and then chemical conversion treatment was performed. The chemical conversion coating was judged by SEM (secondary electron beam image) to be ◯ when the film was uniformly formed, and x when the film was not formed. Coating finish Chemical conversion treatment (SD5000: made by Nippon Paint Co., Ltd.) was performed as prescribed, and then cationic electrodeposition coating (U-80: made by Nippon Paint Co., Ltd.) was applied at an electrodeposition coating voltage of 300 V to a film thickness of 20 μm and washed as prescribed. Then, a baking process was performed. Then 1dm
^{When the} number of craters generated per ² (150 × 70) is 0, it is ◎, when it is 1 it is ○, when it is 6-10 it is △,
When 11 or more occurred, it was judged as x.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

As is apparent from the above description, the present invention forms a hot-dip galvannealed layer on the surface of a hot-dip galvannealed steel sheet and then forms an Mn oxide film or a P oxide film or Mn-P. By forming a system, the slidability during press forming can be improved more than that of cold-rolled steel sheet, a chemical conversion treatment film can be reliably formed, and the coating finish can be good. Thus, as a hot-dip galvanized steel sheet having excellent paint finish, pressability, and chemical conversion treatability that eliminates the conventional problems, it is extremely important to contribute to the development of the industry.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication C25D 5/26 C

Claims (3)

[Claims] 1. A hot-dip galvannealed steel sheet coated with an Mn oxide film through an electrogalvanized layer on the surface of the hot-dip galvanized steel sheet, which has excellent coating finish, pressability, and chemical conversion treatability. Plated steel sheet. 2. A hot-dip galvanized steel sheet having a P oxide film coated on the surface of a hot-dip galvanized steel sheet through an electrogalvanized layer, which is excellent in coating finish, pressability and chemical conversion treatment. Plated steel sheet. 3. A hot-dip galvanized steel sheet having a surface coated with an Mn-P-based oxide film via an electrogalvanized layer, which has excellent coating finish, pressability, and chemical conversion treatment. Alloyed galvanized steel sheet.