JP3217561B2 - Zn-Ni alloy plated steel sheet with excellent press formability and powdering properties - Google Patents

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 having excellent press formability and powdering property and suitable as a surface-treated steel sheet used for difficult-to-form products in automobiles and home appliances. is there.

[0002]

2. Description of the Related Art Various types of surface-treated steel sheets have been used as a countermeasure against corrosion of automobile bodies due to scattered rock salt for preventing roads from freezing in winter in cold regions. The simplest surface treated steel sheet is a galvanized steel sheet, but high corrosion resistance is required for automotive applications, so it is necessary to increase the amount of plating, which causes problems in the body assembly stage such as weldability and workability. . Therefore, many alloy platings having high corrosion resistance even with a small plating amount have been proposed.
Zn-based alloy plating containing an iron group metal such as e, Co, and Ni as an alloy component has been widely used because it is recognized that not only corrosion resistance but also weldability and workability are good.

On the other hand, with the diversification of needs for automobiles and home electric appliances, higher and more versatile formability has been required, and various techniques have been used for the material design technology utilizing component design, rolling and annealing conditions. Steel sheets having the following forming characteristics have been developed. However, in the case of a plated steel sheet, even if a plating film is simply provided on a steel sheet which is excellent in forming, since the physical properties of the steel sheet as a base material and the plating film are significantly different, the forming characteristics of the steel sheet itself in the actual forming stage. May not be fully demonstrated. This is because the surface that actually contacts the press die becomes a plating film and the effect of its characteristics becomes large,
When a plated steel sheet is applied to a difficult-to-form product requiring deep drawing or a complicated shape, unexpected forming defects such as cracks and galling tend to occur. In order to solve such a problem, as disclosed in Japanese Patent Application Laid-Open Nos. 2-274853-6, there has been proposed a technique for improving the formability of a galvannealed steel sheet by previously adjusting the roughness of the steel sheet surface, JP-A-214877 discloses a technique for improving the slidability by adding an inorganic compound to the surface of a galvanized steel sheet, but none of these techniques has reached a satisfactory level.

[0004]

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

[0005]

[MEANS FOR SOLVING THE PROBLEMS] Zn-Ni alloy plating
A plurality of recesses are provided on the surface of the steel sheet, and the maximum span length of the recesses
Where d is the cross-sectional area, d is the depth of the recess, h is the steel plate thickness
Is t, steel plate surface 1 mm ^Two When the number of recesses per contact is n,
Steel plate surface 1mm^Two V = S × h ×
V represented by n is 0.8 × 10⁶μm^Three ~ 7.5 × 10⁶
μm^Three And the average Ni content of the total plating thickness is 9 to
15% by weight and 1 to 20% of the total plating thickness
The Ni content of the surface layer consisting of only
1 to 1.75 times, and 100 to 50 per cm
Zn-Ni based alloy with 00 micro cracks formed
Characterized by having a plating layer on both sides or one side of the steel sheet
With excellent press formability and powdering properties
-Ni-based alloy plated steel sheet.

[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 plating 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 as the main component of the alloy is 9 to 15
%, And the surface layer is modified so that the Ni content is higher than the average Ni content. Further, the plating film is characterized in that microcracks are formed.

[0007] The press formability can be greatly improved only by modifying the surface layer. However, as in the present invention, the effect is further enhanced when microcracks are further imparted. The effect will be exhibited up to. As a method for modifying such a plating film, there is a method in which Zn-Ni-based alloy plating is applied, and then Zn in the plating film is preferentially dissolved by immersion in an acidic aqueous solution or anodic electrolysis. The roll reduction may be combined in a range that does not affect the material of the base steel sheet in order to increase the rolling reduction.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 schematically shows a longitudinal section of one side of a plated steel sheet according to the present invention. FIG. 2 schematically shows the plane of the surface of the plated steel sheet with respect to the arrangement of the concave portions 1 in FIG. 1. First, the research results leading 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 very low carbon steel with Ti added was used as a base plate for plating, 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.

[0009] As a press formability test, a punch diameter of 50
A low-viscosity oil was applied under the conditions of mm and a draw ratio of 2.2, and ten cylindrical press moldings were continuously performed. The evaluation was made based on cracking, punch load, and the degree of powdering due to side wall taping of the pressed product. 5: No cracks and punch load was 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. Powdering is minute. 3: There is no crack and the punch load is considerably higher than the original plate. Powdering is a bit more. 2: 6 or less cracks. Lots of powdering. 1: 7 or more cracks. Powdering is remarkably high.

Referring to FIG. 3, the press formability depends on the Ni content. If the Ni content is less than 10%, the plating layer is soft, so that the contact with the tool becomes strong and the frictional resistance increases, so that cracks occur. If the Ni content exceeds 15%, the formability is good, but the powdering is increased, so that the pressing flaw is apt to occur, which is not preferable. In Ni10-15%,
The punch load is at a higher level than the original plate, but there is no practical problem because there is no crack.

FIG. 4 shows the relationship between the surface concave volume of the Zn—Ni alloy-plated steel sheet and the press formability, and the press formability test is the same as that performed in FIG. Referring to FIG. 4, the press formability depends on the volume of the plating surface concave portion, and the volume of the concave portion per 1 mm ^{2 of} the plating surface is 0.8 to 0.8%.
It is good to be in the range of 7.5 × 10 ⁶ μm ³ . The volume of the concave portion per 1 mm ^{2 of the} plating surface is 0.8 × 10 ⁶ μm ³
The reason for exceeding is that if it is less than that, the securing of the lubricant is small, and the effect on moldability and mold galling is small,
If it is less than 7.5 × 10 ⁶ μm ³ , if it is more than 7.5 × 10 ⁶ μm ³ , the number of projections increases, and the generation of plating powder due to damage to the projections is not preferable because a pressing flaw is generated.

Next, the effects of the modification of the surface layer and the micro cracks, which are the most significant features of the present invention, will be described. The modification state of the plating film was confirmed by Auger electron spectroscopy and observation with an electron microscope. First, the modification of the plating film on the surface layer will be described. FIG. 5 shows that the coating amount of the plating film is 20 g / m ² , the average Ni content is 9 to 15% by weight, and the volume of the concave portion on the plating surface is 0.8 × 10 ⁶ μm ³ or more.
Ni% of the surface layer at 7.5 × 10 ⁶ μm ³ (N
i _S ) and the average Ni% (Ni _B ) of the total plating thickness is 0.
4 to 2.3 show the relationship between the press formability and the press formability test, which is the same as that of the embodiment shown in FIG.

Referring to FIG. 5, the press formability is Ni _P
Is preferably in the range of 1.01 to 1.75. Ni _P 1.01
The reason for the above is that if it is less than this, the effect of press formability is small because the hardening rise of the plating surface layer is small, and if it is less than 1.75, the press formability is good if it is more than 1.75, but powdering increases. Is not preferred. In a more preferred range, the thickness of the surface layer is 5 to 15% of the total plating thickness, and the Ni content of the surface layer is 1.1 to 1.5 times. Next, the micro crack will be described.

FIG. 6 shows that the adhesion amount of the plating film is 20 g / m.
^{2. The} average Ni content is 9 to 15% by weight, and the volume of the plating surface recess is 0.8 × 10 ⁶ μm ^{3 to} 7.5 × 10 ⁶ μm.
^3. Ni% (Ni _S ) of surface layer and average Ni of total plating thickness
3 shows the relationship between the microcrack density and the press formability when the ratio (Ni _P ) of% (Ni _B ) is 1.05 to 1.7, and the press formability test is the same as that performed in FIG. .

As apparent from FIG. 6, when the microcrack density is less than 100, there is almost no effect of improving the press formability. Conversely, in a region exceeding 5,000, the press formability is improved, but the corrosion resistance is reduced. For these reasons, the number of micro cracks is limited to 100 to 5,000 per cm. A more preferred range is 500 to 2000. Speaking of the relationship with the average Ni content, the range of 9 to 15% by weight is a good range in which both press moldability and corrosion resistance can be achieved. The shape, width, and depth of the microcracks are not particularly limited, as long as the number of microcracks crossing a length of 1 cm is within a predetermined range.

The object of the present invention is that the average Ni content is 9-1.
5% by weight, which is a Zn—Ni-based alloy-plated steel sheet having a modified surface layer as described above, and in addition to Zn and Ni as plating components, for example, Co, Fe, Mn, Cr,
Pb, a metal such as _{Sn; SiO 2, Al 2 O} 3, BaC
Inorganic compounds such as rO _4, etc .; or those containing one or more organic compounds are included. The total amount of components other than Ni is preferably 5% by weight or less, and within this range, the effects of the present invention can be exhibited without any problem. In the present invention, the amount of plating is not particularly limited, but is preferably 10 to 60 g / m ^{2 in} terms of corrosion resistance and production cost.
Is a practical range. As in the present invention, the Zn—Ni-based alloy plating film having the modified surface layer may be formed on only one side or both sides of the steel sheet, and can be appropriately selected according to the forming object.

[0017]

As described above, the present invention provides a Zn-Ni
By modifying the surface of a system-alloy-plated steel sheet into a surface layer having a high Ni content, the press-formability and powdering properties of the Zn-Ni-based alloy plating can be improved without impairing the originally excellent corrosion resistance. The use of the Zn-Ni-based alloy-plated steel sheet can be expanded to difficult-to-form parts of automobiles and home electric appliances, and is of great industrial value.

[Brief description of the drawings]

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

FIG. 2 is a view showing an example of an arrangement of concave portions in FIG. 1;

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

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

FIG. 5: Ni% in the surface layer of a Zn—Ni alloy plated steel sheet
(Ni _S) and shows the relationship between press formability and powdering resistance to the ratio (Ni _P) of the average Ni% of the total plating thickness (Ni _B),

FIG. 6 shows 1 in a surface portion of a Zn—Ni alloy plated steel sheet.
It is a figure which shows the relationship between the number of microcracks per cm, press formability, and powdering property.

[Explanation of symbols]

To one rolling direction of the cross-sectional area P _1-plated steel sheet of the recess of the maximum points to pass length S plated steel sheet of the recess depth d plated steel sheet of the recess of the plate thickness h plated steel sheet recess t-plated steel sheet plated steel sheet according to the invention Center distance between adjacent recesses Center distance between rows in the rolling direction of P ₂ coated steel sheet

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Katsutoshi Enyama 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside the Nippon Steel Corporation Kimitsu Works (72) Inventor Masayuki Fujii 1 Kimitsu, Kimitsu City, Chiba Prefecture New Japan (56) References JP-A-4-318188 (JP, A) JP-A-2-247398 (JP, A) JP-A-3-281794 (JP, A) JP JP-A-6-227099 (JP, A) JP-A-1-225790 (JP, A) JP-A-4-337099 (JP, A) JP-A-62-297490 (JP, A) A) JP-A-61-30683 (JP, A) JP-A-58-45382 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 5/26 B21B 3/00 B21B 1 / 22 C23C 2/26

Claims (1)

(57) [Claims] 1. A plurality of Zn-Ni-based alloy-plated steel sheet surfaces
Is provided, and the maximum span length of the recess is d.
Is the cross-sectional area of S, the depth of the recess is h, the thickness of the steel sheet is t,
1mm^Two Assuming that the number of recesses per contact is n, the steel sheet surface is 1 mm
^Two V = S × h × n, which is the total volume V
0.8 × 10⁶μm^Three ~ 7.5 × 10 ⁶μm^Three Satisfied
And the average Ni content of the total plating thickness is 9 to 15% by weight.
Yes, and a surface with a thickness of 1 to 20% of the total plating thickness
The Ni content of the layer is between 1.01 and 1.75 of the average Ni content.
Twice as many as 100-5000
The Zn-Ni-based alloy plating layer with
Pre-pressed on both sides or one side of steel plate
Zn-Ni alloy with excellent moldability and powdering properties
Gold plated steel sheet.