JPH0754163A - Zn-ni based alloy plated steel sheet excellent in press formability - Google Patents

Abstract

PURPOSE:To develop a Zn-Ni based alloy platd steel sheet excellent in both of formability and corrosion resistance by providing the surface of a steel sheet with a Zn-Ni based alloy plating layer having many recessed parts with a specified shape. CONSTITUTION:The surface of a steel sheet is plated with a Zn-Ni based alloy, and the average Ni content of the full thickness is regulated to 9-15wt.%, and the Ni content in the surface layer of the plating layer is regulated to 1.01-1.75 times the total average value of the plating layer. This Zn-Ni alloy plated steel sheet is immersed in a weak acidic aq. soln. or is subjected to anodic electrolytic treatment to form plural recessed parts on the surface of the steel sheet. At that time, in the case the maximum diameter is defined as (d), the cross-sectional area as S, the depth of the recessed parts as (h), the thickness of the steel sheet as (t) and the number of the recessed parts per mm<2> of the surface of the steel sheet as (n), the total (V) of the volumes of the recessed parts per mm<2> of the surface of the steel sheet, V=SXhXn satisfies 0.8X10<6> to 7.5X10<6>mum<3>, by which the Zn-Ni based alloy plated steel sheet excellent in both of corrosion resistance and press formability can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Zn-Ni alloy plated steel sheet which has excellent press formability and corrosion resistance and is suitable as a surface-treated steel sheet used for difficult-to-form articles in automobiles and home appliances.

[0002]

2. Description of the Related Art A wide variety of surface-treated steel sheets are used as measures against corrosion of automobile bodies by sprayed rock salt for preventing road freezing in winter in cold regions. Galvanized steel sheets are listed as the simplest surface-treated steel sheets, but high corrosion resistance is required for automotive applications, so it is necessary to increase the amount of plating, which causes problems such as weldability and workability at the vehicle body assembly stage. . Therefore, many alloy platings have been proposed that have high corrosion resistance even if the plating amount is thin.
Zn-based alloy plating containing an iron group metal such as e, Co, or Ni as an alloy component has been found to have good corrosion resistance as well as weldability and workability, and is widely used.

On the other hand, in automobiles and home electric appliances, with the diversification of needs, higher and more versatile formability is required, and a technique for manufacturing a material making full use of component design, rolling and annealing conditions. Have developed steel sheets with various forming characteristics. However, in the case of a plated steel sheet, even if a plating film is simply applied onto a steel sheet that is excellent in forming, the physical properties of the steel sheet that is the base material and the plating film are significantly different, so the forming characteristics of the steel sheet itself may differ in the actual forming stage. It may not be fully exerted. This is because the surface that actually contacts the press die becomes a plating film and the effect of its characteristics increases.
If you try to apply a plated steel sheet to a difficult-to-form product that requires deep drawing or a complicated shape, unexpected forming defects such as cracks and mold galling are likely to occur. To solve such a problem, as disclosed in JP-A-2-274853-6, a technique for improving the formability by previously adjusting the roughness of the steel sheet surface in the galvannealed steel sheet, and JP-A-4-27453. As disclosed in JP-A-214877, a technique is disclosed in which an inorganic compound is added to the surface of a zinc-based plated steel sheet to improve slidability, but none of them has been satisfactory.

[0004]

As described above, Zn-based alloy-plated steel sheets have excellent corrosion resistance, but their applications are limited in terms of press formability and are not fully utilized at present. . In particular, Zn-Ni alloy-plated steel sheets are thin and have excellent corrosion resistance, so that there is a great need for expanding applications to automobiles and home appliances, and improvement in press formability is desired. An object of the present invention is to provide a Zn-Ni alloy-plated steel sheet which can satisfy a high degree of press formability mainly for automobiles and home appliances.

[0005]

[Means for Solving the Problems] Zn-Ni alloy plating
Multiple recesses are provided on the steel plate surface, and the maximum transfer length of the recesses
Where S is d, the sectional area is S, the depth of the recess is h, and the steel plate thickness
T, steel plate surface 1 mm ² When the number of recesses per hit is n,
Steel plate surface 1 mm² The total V of the concave volume per hit is V = S × h ×
V represented by n is 0.8 × 10⁶ μm³ ~ 7.5 x 10⁶ 
μm³ And the average Ni content of the entire plating thickness is 9 to
15% by weight and the Ni content of the surface layer is average Ni
Zn-Ni based alloy having a content ratio of 1.01 to 1.75 times
Characterized by having a plating layer on both sides or one side of the steel sheet
Zn-Ni alloy plated steel with excellent press formability
It is a plate.

[0006]

The Zn-Ni alloy-plated steel sheet having excellent press formability according to the present invention is provided with a plurality of recesses on the plated surface, and the volume of the recesses is 0.8 to 7.5 × 10 ⁶ μm ³ per 1 mm ^2.
And the average content of Ni, which is the main component of the alloy, is 9 to 15
It is characterized in that the surface layer is modified so that the Ni content of the surface layer is higher than the average Ni content. As a method for modifying the plating film, a method of preferentially dissolving Zn on the plating surface by dipping in a weakly acidic aqueous solution or anodic electrolysis after applying Zn—Ni alloy plating, and plating with a high Ni content on the plating surface are used. The former method is more advantageous in terms of stability and economic efficiency.

The present invention will be described in detail below with reference to the drawings. FIG. 1 schematically shows a longitudinal cross section of one side of a plated steel sheet according to the present invention, and FIG. 2 schematically shows a plane surface of the plated steel sheet for the arrangement of the recesses 1 in FIG. First, the research results up to the present invention will be described. FIG. 3 shows the relationship between the average Ni content of the Zn-Ni alloy plated steel sheet and press formability. The test conditions are as follows. A Ti-added ultra-low carbon steel was used as a plating original plate, and Zn-Ni alloy plating with an adhesion amount of 20 g / m ² and a Ni content of 5 to 20% by weight was applied to the plate and subjected to a press formability test.

As a press formability test, a punch diameter of 50
A low-viscosity oil was applied under the conditions of mm and a drawing ratio of 2.2, and 10 cylindrical press moldings were continuously performed, and evaluated by cracking, punch load, and powdering degree by side wall taping of the pressed product. 5: There is no crack and the punch load is almost at the original plate level. No powdering occurred. 4: There is no crack and the punch load is slightly higher than the original plate. The powdering is very small. 3: There is no crack and the punch load is considerably higher than the original plate. There is a lot of powdering. 2: 6 or less cracks. There is a lot of powdering. 1: 7 or more cracks. There is a lot of powdering.

Referring to FIG. 3, the press formability depends on the Ni content. When the Ni content is less than 10%, the plating layer is soft, so that the adhesion to the tool becomes strong and the friction resistance increases, causing cracking. Further, if the Ni content exceeds 15%, the formability is good, but since powdering increases, push defects are likely to occur, which is not preferable. With Ni 10-15%,
The punch load is higher than that of the original plate, but there is no crack and there is no practical problem.

FIG. 4 shows the relationship between the surface recessed volume of the Zn—Ni alloy-plated steel sheet and the press formability, and the press formability test is the same as in FIG. Referring to FIG. 4,
The press formability depends on the volume of the recess on the plating surface, and the volume of the recess per 1 mm ^{2 of} the plating surface is 0.8 to 7.5 × 10.
A range of ⁶ μm ³ is preferable. Plating surface 1mm ²
The reason why the volume of the concave portion per contact is set to more than 0.8 × 10 ⁶ μm ³ is that if it is less than that, the lubricant is less secured, and the effect on moldability and mold scoring is small.
It is not preferable that the particle size is less than × 10 ⁶ μm ³ because the number of protrusions is larger than that, and plating powder is generated due to damage of the protrusions, which causes a flaw.

Next, the effect of modifying the surface layer, which is the greatest feature of the present invention, will be described. FIG. 5 shows that the coating amount of the coating film is 20 g / m ² , the average Ni content is 9 to 15% by weight, and the volume of the recess on the plating surface is 0.8 × 10 ⁶ μm ^{3 to} 7.5 × 1.
The relationship between the Ni% (Ni _S ) in the surface layer and the average Ni% (Ni _B ) of the total plating thickness (Ni _P ) at 0 ⁶ μm ³ and the formability is shown.

Referring to FIG. 5, the formability is Ni._PIs 1.
The range of 01 to 1.75 is preferable. Ni _PTo 1.01 or more
The reason is that if it is less than that, the hardening increase of the plating surface layer is small.
The effect of moldability was small, and it was set to 1.75 or less.
Over that, moldability is good, but powdering increases
However, it is not preferable. A more preferable range is the surface layer
Thickness is 5 to 15% of total plating thickness, Ni content of surface layer
Is 1.1 to 1.5 times.

The object of the present invention is that the average Ni content is 9 to 1
It is 5% by weight, and is a Zn-Ni alloy plated steel sheet having the above-mentioned modified surface layer, and in addition to Zn and Ni as plating components, for example, Co, Fe, Mn, Cr,
Metals such as Pb and Sn; SiO ₂ , Al ₂ O ₃ and BaC
Inorganic compounds having poor solubility such as rO ₄ ; or those containing one or more organic compounds are included. The total content of components other than Ni is preferably 5% by weight or less, and within this range, the effects of the present invention are exhibited without any trouble. In the present invention, the coating amount is not particularly limited, but from the viewpoint of corrosion resistance and manufacturing cost, it is 10 to 60 g / m ^2.
Is a practical range. The Zn—Ni alloy plating film having the modified surface layer as in the present invention may be formed on only one side or both sides of the steel sheet, and can be appropriately selected according to the object to be formed.

[0014]

As described above, according to the present invention, the Zn--Ni
By reforming the surface of the Ni-based alloy plated steel sheet into a surface layer having a high Ni content, the press formability of the Zn-Ni alloy plating was successfully improved without impairing the excellent corrosion resistance originally possessed by the Zn-Ni alloy plating. Zn-Ni
The applications of the alloy-based alloy plated steel sheet can be expanded to difficult-to-form parts such as automobiles and home appliances, and it has great industrial utility value.

[Brief description of drawings]

FIG. 1 is a longitudinal section of a Zn—Ni alloy plated steel sheet according to the present invention,

FIG. 2 is a diagram showing an example of an array of recesses in FIG.

FIG. 3 is a diagram showing the relationship between the average Ni content of Zn-Ni alloy plated steel sheet and press formability.

FIG. 4 is a diagram showing the relationship between the volume of surface recesses of a Zn—Ni alloy plated steel sheet and press formability;

FIG. 5: Ni% of the surface layer portion of a Zn-Ni alloy plated steel sheet
It is a diagram showing the relationship between the molding against (Ni _S) and the average Ni% of the total plating thickness ratio _{(Ni B) (Ni P)} .

[Explanation of symbols]

1 Recessed portion of plated steel sheet according to the present invention, t Thickness of plated steel sheet, h Depth of recessed portion of plated steel sheet, d Maximum length of recessed portion of plated steel sheet, S Cross-sectional area of recessed portion of plated steel sheet, P ₁ plating Center distance between recesses adjacent to each other in the rolling direction of the steel sheet, center distance between rows in the rolling direction of the P ₂ plated steel sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsutoshi Enyama 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Steel Co., Ltd. (72) Inventor Masayuki Fujii 1 Kimitsu, Chiba Shin-Nihon Kimitsu Steel Works, Ltd.

Claims (1)

[Claims] 1. A Zn-Ni alloy-plated steel plate surface is provided with a plurality of recesses, and the cross-sectional area is S, the recess depth is h, and the steel plate thickness is S when the maximum transfer length of the recesses is d. t, where the number of recesses per 1 mm ^{2 of} the steel plate surface is n, the steel plate surface is 1 m
The total V of the concave volume per m ² is expressed by V = S × h × n V
Satisfies 0.8 × 10 ⁶ μm ^{3 to} 7.5 × 10 ⁶ μm ³ , the average Ni content of the entire plating thickness is 9 to 15% by weight, and the Ni content of the surface layer is the average Ni content. Rate 1.
A Zn-Ni alloy-plated steel sheet having excellent press formability, which has a Zn-Ni alloy-plated layer of 01 to 1.75 times on both sides or one side of the steel sheet.