JP3307326B2 - Alloyed hot-dip galvanized steel sheet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvannealed steel sheet having excellent surface slidability and a method for producing the same.

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheets are widely used as various kinds of rust-preventive steel sheets because they have many excellent properties. In order to use this alloyed hot-dip galvanized steel sheet as a rust-preventive steel sheet for an automobile body, it is necessary to have not only excellent corrosion resistance and coating compatibility but also excellent press formability required in the manufacturing process of the automobile body. .

However, conventional alloyed hot-dip galvanized steel sheets have the following problems with respect to press formability as compared with cold-rolled steel sheets. That is, when press-forming an alloyed hot-dip galvanized steel sheet using a cold-rolled steel sheet as a base material, a slide formed between the Fe-Zn alloy plating layer formed on the surface of the base material and the press die. The sliding resistance force applied to the surface is higher than the sliding resistance force between the cold rolled steel sheet as the base material and the press die. Therefore, in the alloyed hot-dip galvanized steel sheet, the steel sheet is less likely to flow into a portion where sliding is severe, such as a sliding surface with a bead, and the steel sheet is easily broken.
As described above, the alloyed hot-dip galvanized steel sheet is more likely to break than the base material cold-rolled steel sheet alone. The reasons why the alloyed hot-dip galvanized steel sheet is inferior in press formability are as described above.

[0004] As a method of improving the press formability of an alloyed hot-dip galvanized steel sheet, conventionally, a high-viscosity lubricating oil has been applied to the surface of an alloyed hot-dip galvanized steel sheet to slide it between a press die. A method of reducing the sliding resistance applied to the moving surface is widely and generally used. However, according to this method, both the operation of applying lubricating oil before press molding and the operation of degreasing lubricating oil after press molding are required. Therefore, there is a problem that the cost is increased and the environment of the press workplace is deteriorated.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 1-319661 discloses an electroplating of a Fe-based alloy on an upper layer of an alloyed hot-dip galvanized layer to thereby provide a sliding between a mold and a plating layer. A method for producing an alloyed hot-dip galvanized steel sheet excellent in surface slidability by reducing dynamic resistance (hereinafter, referred to as “prior art 1”) is disclosed.

Japanese Patent Application Laid-Open No. 7-18400 discloses that a high-frequency induction heating furnace is used to form an alloyed hot-dip galvanized layer mainly composed of a ζ phase, and then the surface is brought into contact with a solution containing metal ions. Method of forming a metal oxide layer of 5 to 500 mg / m ² on a plating layer by heating and drying
(Hereinafter referred to as “prior art 2”).

Further, Japanese Patent Application Laid-Open No. 2-190483 discloses that
By subjecting the galvanized steel sheet to electrolytic oxidation, acid immersion or coating oxidation treatment, an oxide layer made of zinc or iron or the like is formed on the surface of the galvanized steel sheet, or the plating layer surface is in a solid state or A method of improving press formability by forming a specified zinc oxide film by heating to form an oxide film mainly composed of zinc oxide after being alloyed and roughened (hereinafter referred to as “prior art”). 3 ") is disclosed.

[0008]

However, the prior art 1 requires an electroplating facility, and requires a large amount of money to maintain and replace auxiliary facilities such as conductor rolls and electrodes. Will rise significantly.

[0009] Further, the prior art 2 cannot be applied to a plating step employing a C gas furnace because a high-frequency induction heating furnace must be used. In order to improve the surface slidability, it is necessary to lower the oxygen concentration, it is necessary to seal the entire high-frequency induction heating furnace with, for example, nitrogen gas, etc., there is a problem that equipment becomes huge, Realization is difficult.

Further, in the prior art 3, in order to perform electrolytic oxidation, a dedicated electrolytic oxidation facility is required, which increases the cost.
Further, even when a treatment such as acid immersion or acid application is performed, Al is preferentially oxidized due to the high oxidizing ability of Al present on the plating surface layer, and zinc oxide is not generated. Further, a heating facility is required to form an oxide film, which increases costs.

[0011] As described above, in accordance with the conventional methods, in order to significantly increase the production cost, alloyed hot-dip galvanized steel sheets, particularly, alloyed hot-dip galvanized steel sheets for automobiles, for which low cost is strongly demanded, are required. Could not be provided at low cost.

Here, an object of the present invention is to provide an alloyed hot-dip galvanized steel sheet excellent in surface slidability, that is, press formability, at a low cost. An object of the present invention is to provide an alloyed hot-dip galvanized steel sheet having excellent plating adhesion and suitable as a steel sheet for automobiles.

[0013]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, have obtained the following new findings (1) to (4).

(1) Al present in the plating bath is concentrated and oxidized during the alloying process to the plating surface layer, which extends from the outermost surface layer of the plating layer to a depth of about 500 mm in the depth direction.
Usually, 25 to 40% of Al—O is present in the plating surface layer (in this specification, “%” means “% by weight” unless otherwise specified). The Al-O deteriorates the surface slidability of the galvannealed steel sheet. This is because, as shown in FIGS. 2 (a) and 2 (b) which are surface model diagrams of the alloyed hot-dip galvanized steel sheet 1 at the time of pressing, when Al-O is locally present, the pressing die 2 During the pressing by Al, since the existing portion of Al-O has a high melting point, its hardness is different from that of the surroundings, and the (η + ζ) phase is softened but Al-O
Does not change, the resistance is concentrated on the peripheral portion of Al-O, and the metal zinc portion having a relatively low melting point is easily peeled off from the plating layer to be easily seized with the press die, so that the metal zinc portion is burned to the die. Is estimated.

(2) When an alloyed hot-dip galvanized layer is formed with a low degree of alloying in order to maintain powdering resistance, η phase and ζ phase having high sliding resistance remain on the plating surface layer, and Since the friction coefficient increases, the surface slidability of the alloyed hot-dip galvanized steel sheet deteriorates, and press formability decreases. Therefore, in order to improve the surface slidability, it is effective to reduce Al—O in the surface layer and reduce the η phase and ζ phase.

(3) In order to form a stable zinc oxide layer on the surface of the galvannealed steel sheet, it is effective to reduce the amount of Al—O in the surface layer. By immersing in the solution, a zinc oxide layer is formed on the entire surface of the plated steel sheet, and the coefficient of friction of the steel sheet itself can be reduced to improve press formability.

(4) In order to reduce the amount of Al-O present on the plating surface layer, a method of dipping and dissolving in an alkaline solution as a chemical method, and a method of grinding an extreme surface layer using a brush roll or the like as a mechanical method are used. Good. In addition, η
For removing the phase and the ζ phase and forming the zinc oxide layer, immersion in an acid solution, immersion in an oxidizing agent-added solution, and the like are effective. Note that mechanical grinding with η-phase and ζ-phase brush rolls or the like is difficult to realize because of the seizure of brush rolls and the increase in sludge accompanying the increase in the amount of grinding.

The present invention has been made on the basis of the above findings (1) to (4), wherein the amount of Al—O in the surface layer is less than 15% and the amount of the existing η phase and ζ phase is 5
An alloyed hot-dip galvanized steel sheet having excellent surface slidability, characterized by having an Fe-Zn alloy plating layer of less than g / m ² .

[0019] In the galvannealed steel sheet according to the present invention, the term "surface" means a range of 500 Å depth direction from the outermost layer plating layer.

Further, from another aspect, the present invention provides a method for producing a steel sheet according to the present invention, which has a coating weight per side of 20 to 90 g / m ² and a Fe content of 7 to 90 g / m ^2.
An alloyed hot-dip galvanized steel sheet having a 12% Fe-Zn alloy plating layer is brought into contact with an alkaline solution having a pH of 9.0 or more, or the Fe-Zn alloy plating layer is ground with a brush roll to reduce the Fe-Zn alloy plating layer. -The amount of Al-O in the surface layer of the Zn alloy plating layer is reduced to less than 15%, and then the solution is brought into contact with an acid solution having a pH of 3.0 or less, so that the total amount of the η phase and the ζ phase in the surface layer of the Fe-Zn alloy plating layer is reduced. And less than 5 g / m ² in a method for producing an alloyed hot-dip galvanized steel sheet having excellent surface slidability.

Further, from another aspect, the present invention relates to the present invention, wherein the coating weight per one side is 20 to 90 g / m ² and the Fe content is 7
By contacting an alloyed hot-dip galvanized steel sheet having an Fe-Zn alloy plating layer of ~ 12% with an alkaline solution having a pH of 9.0 or more, or by grinding the Fe-Zn alloy plating layer with a brush roll, The surface of the Fe-Zn alloy plating layer is oxidized to an Al-O content of less than 15% and then brought into contact with an acid solution or an oxidizing agent-added aqueous solution having a pH of 3.0 or less to oxidize the surface of the Fe-Zn alloy plating layer. A method for producing an alloyed hot-dip galvanized steel sheet having excellent surface slidability, comprising forming a zinc layer.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) An embodiment of an alloyed hot-dip galvanized steel sheet having excellent surface slidability and a method of manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings. I do.

FIGS. 1 (a) to 1 (c) are explanatory views showing a situation over time and schematically showing the production of the galvannealed steel sheet of the present invention by the production method of the present embodiment. . The galvannealed steel sheet 3 used in the present embodiment is shown in FIG.
As shown in (a), the coating weight per side was 20-90.
It has a Fe / Zn alloy plating layer 4 of g / m ² and an Fe content of 7 to 12%.

The galvannealed steel sheet 3 of the present embodiment 3
Is preferably 20 g / m ² or more per one surface in order to satisfy corrosion resistance. On the other hand, if the coating weight per one side exceeds 90 g / m ² , the powdering property, the melting property, and the like deteriorate. Therefore, the coating weight is
It is preferable to limit the amount to 20 g / m ² or more and 90 g / m ² or less per one surface.

The iron content in the Fe—Zn alloy plating layer 4 of the galvannealed steel sheet 3 of the present embodiment, that is, the degree of alloying is preferably 7% or more and 12% or less. If the alloying degree is less than 7%, the corrosion resistance after painting deteriorates, while if it exceeds 12%, powdering of the plating layer occurs during press forming.

The galvannealed steel sheet 3 of the present embodiment 3
The Fe—Zn alloy plating layer 4 has an η phase, a ζ phase, a δ ₁ phase, and a Γ phase, and 25 to 40% of Al—O is present in the surface layer.

In this embodiment, the galvannealed steel sheet 3 is brought into contact with an alkaline solution having a pH of 9.0 or more, or the surface layer is ground to 1.0 g / m ² or less with a brush roll or the like. As shown in FIG. 1 (b), the Al—O content in the surface layer of the Fe—Zn alloy plating layer 4 is set to less than 15%.

The alkaline solution used need not be limited to a specific type. For example, an alkali metal hydroxide aqueous solution, sodium phosphate and the like can be exemplified. After the contact with the alkaline solution or the mechanical grinding, if the amount of Al-O in the surface layer is 15% or more, the seizure to the mold cannot be sufficiently improved. Therefore, in the present invention, the Al—O content in the surface layer of the Fe—Zn alloy plating layer 4 is reduced to 15%.
%.

Then, the alloyed hot-dip galvanized steel sheet 3 is brought into contact with an acidic solution having a pH of 3.0 or less to etch the η phase and the ζ phase in the Fe—Zn alloy plating layer 4, as shown in FIG. As shown, the total amount of the η phase and the η phase is reduced to less than 5 g / m ² even at a low alloying degree.

If the total amount of the η phase and the ζ phase is 5 g / m ² or more, it is not possible to suppress the flaking of the plating phase during pressing. Therefore, in the present invention, the η phase and the ζ phase
Limit the phase to less than 5 g / m ^{2 in} total.

The acid solution to be used may be an acid such as sulfuric acid, nitric acid, hydrochloric acid, or an aqueous solution containing an oxidizing agent, which has the ability to dissolve both the η phase and the ζ phase. In this way, according to the present embodiment, the plating adhesion amount per one side is reduced.
20 to 90 g / m ² , the Fe content is 7 to 12%, the Al—O content in the surface layer is less than 15%, and the η phase and ζ phase in the surface layer are less than 5 g / m ^{2 in} total. An alloyed hot-dip galvanized steel sheet 3 having a certain Fe-Zn alloy plating layer is provided.

In the alloyed hot-dip galvanized steel sheet 3, since Al—O in the surface layer of the plating, which is a cause of a decrease in surface slidability, is remarkably reduced, the resistance is not concentrated on the periphery of Al—O. The surface slidability is remarkably improved because the metal zinc portion is less likely to seize with the press die.

(Second Embodiment) The galvannealed steel sheet used in this embodiment has a coating weight per one surface.
It has an Fe-Zn alloy plating layer having a Fe content of 7 to 12% with a content of ²⁰ to 90 g / m ² .

The reason for limiting the amount of coating in the galvannealed steel sheet of this embodiment is the same as in the first embodiment. Therefore, the explanation of the limitation reason is omitted. The iron content in the Fe-Zn alloy plating layer of the galvannealed steel sheet of the present embodiment, that is, the degree of alloying is 7%.
It is preferably at least 12%. If the alloying degree is less than 7%, the corrosion resistance after painting deteriorates, while if it exceeds 12%, powdering of the plating layer occurs during press forming.

The alloyed hot-dip galvanized steel sheet of the present embodiment
The Fe—Zn alloy plating layer has an η phase, a ζ phase, a δ ₁ phase, and a Γ phase, and 25 to 40% of Al—O exists in the surface layer.

In this embodiment, the alloyed hot-dip galvanized steel sheet is brought into contact with an alkaline solution having a pH of 9.0 or more, or the surface layer is ground to 1.0 g / m ² or less with a brush roll or the like to reduce the Fe— Al in the surface layer of Zn alloy plating layer
-O content is less than 15%. The alkaline solution used need not be limited to a specific species. For example, an alkali metal hydroxide aqueous solution, sodium phosphate and the like can be exemplified.

Then, the alloyed hot-dip galvanized steel sheet is brought into contact with an acidic solution or an aqueous solution containing an oxidizing agent having a pH of 3.0 or less to form a zinc oxide layer on the surface of the Fe—Zn alloy plated layer. The acid solution to be used may be an acid such as sulfuric acid, nitric acid, hydrochloric acid or an aqueous solution containing an oxidizing agent.

As described above, according to the present embodiment, the coating weight per one side is 20 to 90 g / m ² , the Fe content is 7 to 12%, and the Al—O content in the surface layer is less than 15%. And a galvannealed steel sheet having a zinc oxide layer formed on the surface layer. In this galvannealed steel sheet, since the zinc oxide layer is formed stably on the surface of the plating layer, the surface slidability is significantly improved.

[0039]

Embodiment (First Embodiment) Next, an embodiment of the present invention will be described in detail. Cold rolled steel sheet with a thickness of 0.8 mm (C: 0.001
%, Mn: 0.15%, Si: 0.005%, P: 0.010%, S: 0.
006%, Al: 0.035%, Ti: 0.035%, balance Fe and inevitable impurities) as a plating base material, and a galvannealed galvanized layer having a coating weight per side of 60 g / m ² was applied to a gas burner heating furnace. To form a sample. In addition,
Plating conditions were as follows: plating bath Al composition value: 0.130%, plating bath temperature: 460 ° C, plating bath steel sheet intrusion temperature: 470 ° C, alloying temperature: 500 ° C, and alloying so as to have a predetermined Fe content. The time was adjusted.

These samples were subjected to alkali treatment under the treatment conditions shown in Table 1, followed by washing with water and drying.
Next, the resultant was subjected to an acid treatment, followed by washing with water and drying. In addition,
The amount of Al-O in the outermost layer of the plating layer was measured under the measurement conditions shown in Table 2.
The η-phase and ζ-phase amounts were determined from the electrolysis time by constant current electrolysis.

[0041]

[Table 1]

[0042]

[Table 2]

These samples were subjected to a general-use cleaning oil with a flat-bead at a holding pressure of 8 N / mm ² (Sugimura Chemical Co., Ltd., trade name: 303)
P) was used to perform a pull-out test, and the friction coefficient was determined from the following equation. Coefficient of friction = Pulling load N / 2P Further, plating adhesion was evaluated by powdering property by cylindrical drawing. The processing conditions are summarized in Table 3.

[0044]

[Table 3]

The evaluation criteria for the powdering property were as follows. A tape was adhered to the side wall of the overhang portion formed by performing a cylindrical drawing process, and then peeled off. The peeling amount was measured by a gravimetric method. 20 mg / piece per sample is indicated by a circle as a target value, and 10 mg / piece or less is indicated by a circle as an excellent value,
Further, those exceeding 20 mg / unit were indicated by x marks.

The results are summarized in Table 1. Table 1 shows that irrespective of the amount of Fe in the film, by performing alkali immersion and acid immersion, the friction coefficient is reduced and the press formability is improved.

(Second Embodiment) The same cold-rolled steel sheet as that used in the first embodiment was used as a base metal, and was subjected to a hot-dip galvanizing treatment and an alloying heat treatment by a conventional means. An alloyed hot-dip galvanized steel sheet in which the Fe content was changed in the range of 7 to 12% was produced.

These samples were subjected to alkali treatment under the treatment conditions shown in Table 4, followed by washing with water and drying.
Next, an acid treatment was performed, followed by washing with water and drying. For these samples, the Al—O content, the coefficient of friction, and the plating adhesion in the outermost layer of the plating layer were determined in the same manner as in the first example. The results are summarized in Table 4.

[0049]

[Table 4]

Table 4 shows that regardless of the amount of Fe in the film, the alkali immersion and the acid immersion reduce the coefficient of friction and improve the press formability.

(Third Embodiment) The same cold-rolled steel sheet as that used in the first and second embodiments was used as a plating base material. But
Fe-Zn having a content of 45 to 100 g / m ² and a Fe content of 6 to 13%
An alloyed hot-dip galvanized steel sheet having an alloy plating layer was subjected to alkali treatment A (NaOH-5% aqueous solution (pH = 12), 60 ° C. × 5).
Alkali treatment B (NaOH-0.1% aqueous solution (pH
= 8.5), immersion at 60 ° C for 5 seconds), grinding C (roll diameter: 300m)
m, brush material: Nylon brush with abrasive grains, rotation speed: 70
0 rpm), the Al—O content in the surface layer of the Fe—Zn alloy plating layer is reduced to 12 to 31% by grinding the Fe—Zn alloy plating layer, and then acid treatment A (HCl-5% aqueous solution) (p
H = 1.5), immersion at 60 ° C for 5 seconds) or acid treatment B (HCl-0.2
% Aqueous solution (pH = 3.5), immersion at 60 ° C. for 5 seconds to adjust the amounts of η phase and ζ phase in the surface layer of the Fe—Zn alloy plating layer. Obtained.

With respect to these sample Nos. 1 to 8, powdering properties,
The coefficient of friction and press workability were evaluated. Test results
Table 5 summarizes the test conditions.

[0053]

[Table 5]

In Table 5, Sample No. 3 and Sample No. 6
Satisfies all the conditions of the present invention, so that both the press workability and the powdering property are excellent. Therefore, it can be seen that an alloyed hot-dip galvanized steel sheet suitable as an automobile body panel was obtained.

Sample No. 1 had poor powdering properties because both the coating weight and the degree of alloying were out of the range of the present invention. In Sample No. 2, the degree of alloying was out of the range of the present invention, so that the powdering property was deteriorated.

In Sample No. 4, since the pH of the alkali treatment solution was outside the range of the present invention, the reduction of Al—O in the surface layer was insufficient, and the pressability was deteriorated. Sample No. 5 was acid-treated
Since the pH was out of the range of the present invention, pressability was deteriorated.
Since the sample No. 7 was not subjected to the alkali treatment, the pressability was deteriorated. Further, the pressability of Sample No. 8 was deteriorated because the acid treatment was not performed.

[0057]

As described above in detail, according to the present invention, for example, an alloyed hot-dip galvanized steel sheet having good press-formability within a range in which practical powdering properties are not a problem for automotive body panels. Can be provided at low cost.

[Brief description of the drawings]

FIGS. 1 (a) to 1 (c) are explanatory views showing a situation over time and schematically showing how an alloyed hot-dip galvanized steel sheet of the present invention is manufactured by the manufacturing method of the first embodiment. It is.

2 (a) and 2 (b) are surface model diagrams of an alloyed hot-dip galvanized steel sheet at the time of pressing.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mikihiko Nagaki 3 Oaza Hikari, Kashima City, Ibaraki Prefecture Sumitomo Metal Industries, Ltd. Kashima Works (72) Inventor Yoshizo Hirakawa 3 Oaza Hikari, Kashima City, Ibaraki Prefecture Sumitomo Metal Industries Kashima Works, Ltd. (72) Inventor Toshihiko Nakamura 3, Oji-ko, Kashima City, Ibaraki Prefecture Sumitomo Metal Industries Co., Ltd. (72) Koichi Nishio 3, Koichi Nishio, Kagoshima, Ibaraki Sumitomo Metal Industries, Ltd. (56) References JP-A-6-10156 (JP, A) JP-A-4-224668 (JP, A) JP-A-2-263969 (JP, A) JP-A-5-230612 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (3)

(57) [Claims] 1. A with Al-O amount is less than 15 wt% in the surface layer, eta phase and ζ phase is present in a total amount 5 g / m ²
An alloyed hot-dip galvanized steel sheet having excellent surface slidability, characterized by having an Fe-Zn alloy plating layer that is less than. 2. The coating weight per one side is 20 to 90 g / m ^2.
A galvannealed steel sheet having an Fe-Zn alloy plating layer having an Fe content of 7 to 12% by weight is brought into contact with an alkali solution having a pH of 9.0 or more, or the Fe-Zn alloy steel sheet is coated with a Fe-Zn alloy by a brush roll. By grinding the Zn alloy plating layer, the amount of Al-O in the surface layer of the Fe-Zn alloy plating layer can be reduced.
Less than 15% by weight, and then contact with an acid solution having a pH of 3.0 or less so that the total amount of the η phase and ζ phase in the surface layer of the Fe—Zn alloy plating layer is less than 5 g / m ^2. For producing an alloyed hot-dip galvanized steel sheet having excellent surface slidability. 3. The coating weight per side is 20 to 90 g / m ^2.
A galvannealed steel sheet having an Fe-Zn alloy plating layer having an Fe content of 7 to 12% by weight is brought into contact with an alkali solution having a pH of 9.0 or more, or the Fe-Zn alloy steel sheet is coated with a Fe-Zn alloy by a brush roll. By grinding the Zn alloy plating layer, the amount of Al-O in the surface layer of the Fe-Zn alloy plating layer can be reduced.
To less than 15% by weight, and then contact with an acid solution or an aqueous solution containing an oxidizing agent having a pH of 3.0 or less.
A method for producing an alloyed hot-dip galvanized steel sheet having excellent surface slidability, wherein a zinc oxide layer is formed on the surface of an Fe-Zn alloy plating layer.