JPH08134686A - Zinc-nickel alloy plated low carbon steel sheet excellent in press formability - Google Patents

Abstract

PURPOSE: To produce a Zn-Ni alloy plated low carbon steel sheet excellent in press formability by providing the surface of a starting sheet, having a specific composition consisting of C, Si, Mn, P, S, Al, Ti, and Fe, with a specific Zn-Ni alloy plating layer having an Ni-concentrated surface layer. CONSTITUTION: As a starting sheet before plating, a low carbon steel sheet, having a composition consisting of, by weight, <=0.10% C, <=0.5% Si, 0.05-1.0% Mn, <=0.15% P, <=0.02% S, 0.01-0.07% Al, 0.005-0.11% Ti, and the balance Fe with inevitable impurities and further containing, if necessary, 0.002-0.20% Nb and/or <=0.001% B, is used. Both sides or one side of this steel sheet is provided with a Zn-Ni alloy plating layer in which the average Ni content of the whole plating thickness is regulated to 5-15%. Further, the Ni content in the surface layer having a thickness 1-20% of this plating layer is regulated to a value 1.10 to 1.75 times the average Ni content. This Ni concentration can be done by preferentially dissolving the Zn in the surface by means of a weakly acidic aqueous solution.

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 having high corrosion resistance have been proposed 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, automobiles and home electric appliances are required to have higher and more versatile formability in accordance with the diversification of needs, and various types can be obtained by the material design technology utilizing the component design and rolling and annealing conditions. A steel sheet having the forming characteristics of is developed. However, in the case of a plated steel sheet, even if a plating film is simply applied on 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.
When attempting 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 adjusting the roughness of the steel sheet surface in advance in an alloyed hot-dip galvanized steel sheet, and JP-A-4-27453. As disclosed in JP-A-214877, a technique for imparting an inorganic compound to the surface of a zinc-plated steel sheet to improve slidability is disclosed, but none of them has reached a satisfactory level.

[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]

(1) The original plate before plating is% by weight, C: 0.10% or less Si: 0.5% or less Mn: 0.05 to 1.0% P: 0.15% or less S: 0.02% or less Al: 0.01 to 0.07% Ti: 0.005 to 0.11%, balance Fe and unavoidable impurities, the average Ni content of the entire plating thickness is 9 to 15% by weight, and Ni of the surface layer having a thickness of 1 to 20% of the total plating thickness
Zn-N excellent in press formability, characterized by having a Zn-Ni alloy plating layer having a content of 1.10 to 1.75 times the average Ni content on both sides or one side of a steel sheet.
i-based alloy plated low carbon steel sheet.

(2) The original plate before plating is% by weight, C: 0.10% or less Si: 0.5% or less Mn: 0.05 to 1.0% P: 0.15% or less S: 0.0. 02% or less Al: 0.01 to 0.07% Ti: 0.005 to 0.11%, Nb: 0.002 to 0.20%, B: 0.001%
One or two of the following are included, the balance is Fe and unavoidable impurities, and the average Ni content of the total plating thickness is 9 to
The Ni content of the surface layer having a thickness of 15% by weight and 1 to 20% of the total plating thickness has an average Ni content of 1.1.
A Zn-Ni alloy plated low carbon steel sheet having excellent press formability, which has a Zn-Ni alloy plated layer of 0 to 1.75 times on both sides or one side of the steel sheet.

[0007]

The Zn-Ni alloy-plated steel sheet having excellent press formability of the present invention has an average Ni content of 9 to 15% by weight, which is the main component of the alloy, and an average Ni content of its surface layer. It is characterized in that it is modified to have a higher content than the Ni content. As a method of modifying the plating film, Zn-N
A method of preferentially dissolving Zn on the plating surface by dipping or anodic electrolysis after applying the i-based alloy plating, and a method of re-plating the plating surface with a high Ni content are mentioned. Is a more advantageous method in terms of stability and economy.

The present invention will be described in detail below. FIG. 1 schematically shows a vertical cross section of one side of a plated steel sheet according to the present invention. Reference numeral 1 is a Zn-Ni alloy-plated low-carbon steel sheet according to the present invention, reference numerals 2 and 3 are Zn-Ni alloy plated layers, and reference numeral 3 is a plating modified layer. The research results up to this point will be described. First, according to the present invention, the reasons for limiting the components of the steel for imparting the press formability to the low carbon steel sheet are as follows. C is 0.
If it exceeds 10%, the weldability will deteriorate, so the C content must be 0.10% or less. If Si increases, it hardens and the workability deteriorates. Therefore, it is necessary to set Si to 0.5% or less. Since Mn deteriorates the r value, it must be 1.0% or less. The lower limit is 0.05% or more in order to prevent S hot brittleness.

If P exceeds 0.150%, it hardens and the workability deteriorates, so P must be made 0.150% or less.
If S exceeds 0.02%, the workability is deteriorated, so
0.02% or less is good. Al is an element necessary for non-aging, but if its content is less than 0.01%, its effect cannot be expected, so 0.01% or more is required. However, if the amount is too large, it hardens and the press formability is impaired, so the content is made 0.07% or less. Ti is an element that improves press formability,
If less than 0.005%, no effect can be expected, so 0.00
If it is 5% or more, and if it is contained in a large amount, the precipitation strengthening element becomes large and the quality of the material is deteriorated.

Nb is effective for further improving the drawability of the low carbon steel sheet of the present invention. In that case, Nb.
02 to 0.20% is desirable. In this case, 0.002%
If less than 0.20%, no effect can be expected, so 0.002% or more, and if over 0.20%, no effect can be expected, so N
The b amount is 0.20% or less. Moreover, when secondary workability of the low carbon steel sheet of the present invention is required, B is 0.0
1% or less is desirable. In this case, if it is contained in a large amount, it hardens and the material deteriorates, so the content is made 0.001% or less.

Next, the relationship between the Ni% in the Zn-Ni alloy plated layer and the press formability was investigated, and the appropriate Ni content was examined. The investigation conditions are shown in Table 1. Each of the low carbon steel steel sheets, which are various test materials shown in Table 1, has a chemical composition value of 20 g / m ² , and a Ni content of 5 to 20 wt% is plated on each of the steel sheets, followed by press forming. It was subjected to a sex test. The press formability test is a cylindrical press in which a low-viscosity oil is applied under the condition that the punch diameter is 50 mm and the drawing ratio (blank diameter / punch diameter) is 2.0, 2.1 or 2.2 depending on the material. Continuous molding 10
A score of 1 to 5 was given according to the individual operation, cracking, punch load, and powdering degree by the 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. Here, in judging the quality of the moldability, a rating of 3 or more was rated as good (◯), and a rating of less than 3 was rated as bad (x).

[0013]

[Table 1]

The results are shown in Table 2. Table 2 shows Zn-Ni
The relationship between the average Ni content and the press formability of the system alloy plated steel sheet is shown. When Table 2 is described, it was found that the press formability depends on the average Ni content. That is, the test materials A1, B1, C1, D1, E1, F1,
When the Ni content of G1, H1, and I1 is less than 9%, the plating layer is soft, so that the adhesion to the tool becomes strong and the frictional resistance increases, causing cracks, and the test materials A4, B4,
When the Ni content of C4, D4, E4, F4, G4, H4, and I4 exceeds 15%, the moldability is good, but the powdering increases, so that a flaw easily occurs, which is not preferable. With 9 to 15% of the other test materials, the punch load is higher than that of the original plate, but there is no crack and there is no practical problem.

[0015]

[Table 2]

Next, the effect of modifying the surface layer, which is the greatest feature of the present invention, will be described. Table 3 shows the Ni% (Ni _S of the surface layer portion in the surface layer having a deposition amount of the plating film of 20 g / m ² , an average Ni content of 9 to 15% by weight, and a thickness of 0.5 to 22% of the total plating thickness. ) And the average Ni% of the total plating thickness
The relationship between the (Ni _B ) ratio (Ni _P ) and the formability is shown. Table 3
From the result, the modified surface layer thickness is 1 to 20 of the total plating thickness.
%, Ni _P of 1.10 to 1.75 was found to be excellent in moldability. Table 3 will be described in detail. First, if the thickness of the modified surface layer is less than 1% of the test materials A8 and B8, the modified layer is small and the formability is not effective. If the thickness of the test materials F8, G8 and I8 exceeds 20%, the operation efficiency deteriorates. , Not preferable. Also N
When i _P is less than 1.1 for the test materials C8 and H8, the hardening increase is small, and there is no formability effect.
If it exceeds 5, powdering will increase and deteriorate. Furthermore, all the other test materials satisfied the formability. A more preferable range is that the surface layer thickness is 5 to 15% of the total plating thickness,
The Ni content of the surface layer is 1.2 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 , BaC
It includes a poorly soluble inorganic compound such as rO ₄ , or a compound containing one or more organic compounds. 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.

[0018]

[Table 3]

[0019]

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-based 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 view showing a vertical section of a Zn—Ni alloy plated steel sheet according to the present invention.

[Explanation of symbols]

 1 Zn-Ni system alloy plating low carbon steel steel plate 2 Zn-Ni system alloy plating layer 3 Surface modification layer 4 Base metal according to the present invention

Claims (2)

[Claims] 1. The original plate before plating is% by weight, C: 0.10% or less Si: 0.5% or less Mn: 0.05 to 1.0% P: 0.15% or less S: 0.02 % Or less Al: 0.01 to 0.07% Ti: 0.005 to 0.11%, balance Fe and unavoidable impurities, and the average Ni content of the total plating thickness is 9 to 15% by weight. And Ni of the surface layer having a thickness of 1 to 20% of the total plating thickness
Zn-N excellent in press formability, characterized by having a Zn-Ni alloy plating layer having a content of 1.10 to 1.75 times the average Ni content on both sides or one side of a steel sheet.
i-based alloy plated low carbon steel sheet. 2. The original plate before plating is% by weight, C: 0.10% or less Si: 0.5% or less Mn: 0.05 to 1.0% P: 0.15% or less S: 0.02 % Or less Al: 0.01 to 0.07% Ti: 0.005 to 0.11%, Nb: 0.002 to 0.20%, B: 0.001%
One or two of the following are included, the balance is Fe and unavoidable impurities, and the average Ni content of the total plating thickness is 9 to
The Ni content of the surface layer having a thickness of 15% by weight and 1 to 20% of the total plating thickness has an average Ni content of 1.1.
A Zn-Ni alloy plated low carbon steel sheet having excellent press formability, which has a Zn-Ni alloy plated layer of 0 to 1.75 times on both sides or one side of the steel sheet.