JPS5867886A - Steel article coated with iron-zinc alloy plating layer having concentration gradient and manufacture thereof - Google Patents

Abstract

PURPOSE:To easily form a plating layer having different concentration gradient and excellent corrosion resistance, in plating the surface of a steel sheet in a Fe-Zn plating bath, by continuously plating the surface with different current densities. CONSTITUTION:A sulfate plating bath containing Zn and Fe ions at the weight ratio of 0.02-0.90 and the total of Zn and Fe sulfates above 100g/l and up to their solubility limits is supplied to continual several plating cells 6-10 under the condition of pH; 0.8-2.3 and the temperature of liquid; 40-80 deg.C from a tank 1 by a pump. An electric current is applied to a steel sheet 3 to be plated between anodes A1-A5, while the steel sheet 3 is being carried from the plating cell 6-10. The anodes A1-A5 hence gradually reduce their surface areas, and current densities are gradually made larger from the anode A1-A5 in inverse proportion to the surface areas, so that an Fe-Zn plating layer having such gradient in the concentration of the two metals that Zn content is gradually reduced from 98%-5% is formed. Consequently, a coated steel sheet having the plating layer excellent in corrosion resistance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel material with excellent corrosion resistance formed with an iron-zinc alloy plating layer having a concentration gradient, and a method for manufacturing the same.

Steel materials (including #l strip, steel plate, #1lIf or shaped steel, etc.)

) is an important metal material because it has high strength, good workability, and can be supplied in large quantities, and is used in large quantities for automobiles, home appliances, etc. However, it has the disadvantage of being easy to rust and corrode, and has poor weldability, workability,
More advanced properties are being required in terms of chemical conversion treatment properties, paintability, etc. For this reason, surface treatment of steel is extremely important, but conventional methods typically involve galvanizing the steel, applying chemical conversion treatment on top of that, and then painting with paint such as electrodeposition paint. It was done. Regarding zinc plating, attempts have recently been made to further improve corrosion resistance, weldability, paintability, etc. by applying Fe-Zn alloy plating on steel materials by electroplating.

However, if we consider the purpose of plating, such as corrosion resistance, chemical conversion treatment properties, paintability, etc., the role of the plating layer in the immediate vicinity of the steel base is primarily the role of the plating layer in the immediate vicinity of the steel substrate. With regard to chemical conversion treatment properties and paintability, it is strongly expected that the topmost layer of the plating layer directly below the chemical conversion coating will play a major role. Therefore, when applying iron-zinc alloy plating on steel materials, different plating baths are used, and for example, the lower layer has a thickness of 5 to 25 g/- and is composed of at least one of the δ, phase, ζ phase, and ζ phase. An iron-zinc intermetallic compound layer with excellent corrosion resistance is applied, and an iron-zinc solid solution alloy layer with a thickness of 0.5 to 7 g/m' and a zinc content of 35% by weight or less is applied as an upper layer. Other methods are also being researched.

However, the method of performing multilayer plating while changing the plating bath requires controlling the concentrations and compositions of several types of baths to be constant, and in practice the operation becomes considerably complicated when the number of layers increases. I don't get it. Furthermore, in order to prevent separation between layers, which is an essential problem in multilayer structures, it is desirable that the layer compositions of adjacent layers be formed so that they change little by little, that is, have a smooth concentration gradient. In that case, it is desirable to increase the number of plating baths, for example to 3 cells or more, preferably 5 cells or more, but there is a limit to the method of changing the bath composition.

As a result of various studies, the present inventor has found that even when the bath composition is constant, the plating composition changes by changing the current density, and that it is particularly true in a continuous high-current plating line with multiple cells that the plating composition is smooth. It was discovered that a plating layer having a concentration gradient is formed, and the present invention was completed. That is, in the present invention, the plating amount is 5 to 50 g/rr.
? , an iron-zinc alloy plated steel material in which an iron-zinc alloy layer is formed, in which the zinc ratio (proportion) in the plating layer is within the range of 5 to 98% by weight and has a sequential zinc concentration gradient in the cross-sectional direction of the plating layer; In a continuous plating line with multi-cells (electrolytic cells), during plating, zn)-t-7Fe++
Using a sulfate bath having a weight ratio of 0.02 to 90 and containing sulfates of both metals at a total concentration of 100 g/1 or more up to the solubility limit, pao, s to 2,3 and a bath temperature of 40 to 8
An iron-zinc alloy plating layer with a concentration gradient in the range of 5 to 98% by weight of zinc is formed on the steel material by using an insoluble anode at a temperature of 0°C and changing the current density sequentially from the first cell. The present invention relates to a method for producing steel material coated with an iron-zinc alloy plating layer.

Is the plating amount of the steel of the present invention 5 to 50 g/lr? The closure was chosen because if it is too thin, it will not be able to maintain corrosion resistance, and if it is too thick, it will not only be uneconomical to achieve the corrosion resistance required for practical use, but also deteriorate workability. . In addition, the zinc ratio in the plating layer was set at 5 to 98% by weight, because if it is less than 5% by weight, zinc will not act as a sacrificial anode, and if it exceeds 98% by weight, it will become almost pure zinc, and the coating after chemical conversion treatment will This is because properties such as blister resistance deteriorate.

The plating layer is sequentially formed to have a zinc concentration gradient within the range of the zinc ratio in the plating layer, but generally, the amount of bare lead in the lower part of the plating layer that adheres to the steel material is increased to improve corrosion protection. The upper part of the plating layer that is in close contact with the chemical conversion treatment layer increases the amount of iron to improve the chemical conversion treatment property 1, and the plating composition is gradually changed during this period to prevent delamination.

In this case, the Zn″+/Fθ masu weight ratio of Rakuchu is 0.02 to 0.
．． 90, sulfate concentration 100g/・1 or more within solubility limit, p
When performing iron-zinc alloy plating using a plating bath with H0.8 to 2.3 and a bath temperature of 40 to 80°C, the higher the current density, the higher the iron content, and the lower the current density, the higher the zinc content. Become. Normal current density is 20-200A/13n",
Preferably 80-2oOA/dff+! Vary within the range of.

The electrolytic bath is an aqueous solution containing zinc sulfate and ferrous sulfate, which is poured into the electrolytic bath to form the bath. In the bath, z
n++7Fe+1-weight ratio. , 02 to 0.90 because an iron-zinc solid solution alloy plating layer with excellent chemical conversion treatment properties is easily formed in the range of 0.02 to 0.15.
．． An intermetallic compound alloy plating layer with excellent corrosion resistance can be formed in the range of 4 to 0.9, and in other ranges depending on the bath composition, Z, -H-/F in the plating layer can be This is because the ratio can be changed by changing the current density.

The reason why the sulfate concentration in Rakuchu should be 100 g// or more within the solubility limit is because if it is less than 100 g/1, the metal ions in the bath are too thin, making it difficult to ensure a current efficiency that is suitable for practical use, and the Zn material in the bath is too thin. This is because not only is it difficult to maintain the /Fθ+1− weight ratio, but also a high current density cannot be maintained. pH0,
The reason why the pH is set at 8 to 2.3 is that if the pH is too low, it becomes difficult to control the bath composition, and the η phase tends to precipitate, resulting in poor chemical conversion treatment properties. On the other hand, if the pH exceeds 2 or 3, iron hydroxide tends to precipitate and the plating bath tends to deteriorate, making it difficult to perform stable high-speed plating. Normally, plating lowers the pH of the bath, and replenishing metal ions returns the pH to its original value, so the bath pH is maintained at a constant value, but if necessary, the pH can be adjusted using sulfuric acid, ammonia, etc. Alternatively, this can be done by replenishing water. p of the plating bath of the present invention
Since H is low, the plating component metal has a considerably high dissolution rate, so replenishment is easy, and the degree of consumption and replenishment of the metal component can be estimated from slight fluctuations in the pH of the plating bath.

It is also necessary to control the bath temperature within the range of 40 to 80°C for the stability of plating. If the temperature is less than 40°C, the adhesion between the plating layer and the steel material will be poor, which is not preferable.

Further, if the temperature exceeds 80°C, evaporation of the liquid will be large and it will also be difficult to select the material of the device, which is not preferable.

Furthermore, in the present invention, it is essential to use an insoluble anode instead of a soluble anode. In the case of a soluble anode, not only is it troublesome to replace the electrode due to wear, but also a phenomenon of electrode passivity occurs under high current density, making high-speed plating impossible. The insoluble anode of the present invention is suitably made of, for example, a lead alloy, a noble metal such as platinum, rhodium, or iridium, or an oxide thereof. When such an insoluble anode is used, a stable plating current can be ensured under high current density, and therefore the control of the plating film becomes extremely easy.

In addition, in the polishing bath of the present invention, a conductivity imparting agent such as ammonium sulfate or aluminum sulfate is added to an amount that does not impair the solubility of iron ions and zinc ions, for example, 5 to Bog/
There is no problem in adding l.

Furthermore, in the present invention, the pH is lowered and the sulfate concentration is increased. One of the reasons for this is to increase the length of bath conductivity, prevent plating baking when high current density is applied, and reduce bath voltage.0 The larger the number of cells, the more discontinuous the concentration gradient Although the current density decreases, it is preferably 3 or more, more preferably 5 or more, and the current density is sequentially changed. For example, in the first cell, 80A/
dm', 100A/convex in the second cell! , 1 in the third cell
120 A/dm', 1aoA/dm' in the 4th cell,
In the fifth cell, a plating layer is formed by passing the steel material through five 160 A/dm' electrolytic cells.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Zn++/Fe++ weight ratio in plating bath is 0.49, p
The iron content in the plating layer was measured by changing the current density with H1.5, bath temperature 60° C., and steel plate speed 200 mpm, and the results shown in FIG. 1 were obtained.

In addition, the Zn/FeF+ weight ratio in the plating bath is 0. O'
7, pH 0.9, bath temperature 60° C., steel plate speed 200 mpm, and the current density was varied to measure the iron content in the plating layer, and the results shown in FIG. 2 were obtained.

Also, FeSO4-7H2O and Zn5O,-'y H,
The total amount with O is -00g / / s (NL)t S
In a plating bath with 30 g of O4/AS pH 1.0 and a bath temperature of 60°C, the current density was set to 80 A/dm'', and Fe in the bath was
When the iron content in the plating layer was measured by changing the ratio (4) of t/Fe+zr+weight, the results shown in FIG. 3 were obtained. In Figure 3, C, R, and L refer to the composition reference line (Composite reference line).
ion Reference Line).

From the results shown in FIGS. 1 and 2, it can be seen that when the current density is increased while the Zn''/Fe+Shigehashi ratio in the bath is constant, the iron content in the plating layer increases.

Moreover, from the results shown in FIG. 3, it can be seen that when the current density is constant and the iron content in the bath is increased, the iron content in the plating layer increases.

Let us now assume that electroplating is carried out using the apparatus whose principle is explained in FIG. In FIG. 4, the plating solution stored in a tank 1 is sent to cells 6 to 0 by a pump 2. No partition walls are provided between each cell, allowing the plating solution to move.

Insoluble anodes A, ~A, are installed in cells 6 to 10,
Their anode lengths are 71~! , and the current density of each cell is DK, ~DK, respectively. here,
! 2. DK,=l,-DK,=mu,DK,=l,-
In order to maintain the product of anode length and current density constant so that DK4=l, , DK, the anode length is sequentially shortened from cell 6 to cell 10. Therefore, the current density increases sequentially. The steel material 3 enters the plating apparatus from the left in FIG. 4, passes between the energized rolls 4, and progresses to the right to be plated. As is clear from FIGS. 1 and 2, the distribution of the plating layer is such that the lower layer near the material has a higher Zn weight %, and the upper layer has a higher Fe weight %.

If the arrangement of the anodes is reversed and the treatment is carried out by lowering the current density sequentially, a plating layer with a high Fe weight % in the lower layer will be obtained.

If the apparatus shown in FIG. 4 is used and the conditions shown in FIG. 1 are followed, the Fe content in the plating layer can be varied from 18 to 53% by weight. If the plating layer thus obtained is plated according to the conditions shown in FIG. 2, Fe in the plating layer will be reduced to 60
It can vary up to 75% by weight. Furthermore, if it is necessary to obtain a plating layer with a slightly different zinc (or iron) ratio, refer to Figure 3 and adjust the Znl+/Fe ratio in the plating solution.
A plating solution with a slightly different weight ratio may be used.

Example 2 Electroplating was carried out using an apparatus similar to that shown in FIG.

The plating bath was Fe2O2.7 Hto 350 g/
l 5ZnSO4・7 HIO150g /l Oyo U (NHn)t SO430g / / s
The pH was 1.5 and the bath temperature was 60°C.

As the steel material, a degreased and pickled thin steel plate was flowed at a flow rate of 30 mpm. Other conditions and results are shown in Table 1.Table 1 Comparative Example 1 Electroplating was carried out using the apparatus shown in FIG. That is, the plating solution is supplied from tanks 11 to 15 to cells 16 to 20, respectively, and then circulated to tanks 11 to 15. The compositions of the plating solutions stored in tanks 11 to 15 are as shown in Table 2, and the compositions of each solution are different. However, the pH was kept constant at 1.2. In addition, anode B,
~B, the anode length was kept constant at 800 fins.

Unlike the apparatus shown in FIG. 4, partition walls 21 are provided between the cells to prevent the plating liquid from moving.

The degreased and pickled thin steel sheet 22 entered the plating device from the left, passed between the energized rolls 23, advanced to the right, and was plated. The current density applied at each anode is 80 A/b”
It was kept constant.

Table 2 shows other conditions and results.

Table 2 shows that the concentration gradient of the Zn/Fe weight ratio in the plating layer is gentle and changes continuously, and that the adhesion of the plating layer is excellent. It can be seen that it can be easily manufactured.

The tests in the above Examples and Comparative Examples were conducted as follows.

(1) 07 bending adhesion: Attach white vinyl tape to the plated surface and perform 07 bending with several sides inside,
Measurements were taken while the plating layer adhering to the tape was being peeled off.

(2) Cation coating - adhesion test: The plated steel plate was immersed in the phosphate treatment agent GrSD-2000 manufactured by Nippon Paint Co., Ltd., and after baking at 120°C for 0 minutes, Nippon Paint Co., Ltd. Power Top I manufactured by Co., Ltd.
Cation electrodeposition coating was performed using J-30 so that the dry film thickness was 20 μm, and baking was performed for 180′×30 minutes. On top of this, Kansai Paint Co., Ltd. Amirac TP-16
R was painted with a dry film thickness of 25 μm and baked at 140” CX for 20 minutes. Furthermore, Kansai Paint Co., Ltd.'s Amirac 030 was painted with a dry film thickness of 30 μm as a top coat, and baked at 140°C for 20 minutes. After this, the steel substrate was reached. A cross cut was made every two fights apart, and it was removed with cellophane tape.

In (1) and (2), ◎ indicates that there was no peeling of the plating layer or paint film, and ○ indicates that slight peeling of the plating layer or paint film was observed.

[Brief explanation of drawings]

1 and 2 are graphs showing the relationship between current density and Fθ content in the plating layer. FIG. 3 is a graph showing the relationship between the F content (% by weight) in the bath and the F content (% by weight) in the plating layer. FIG. 4 is a diagram explaining the principle of the apparatus used in the example. FIG. 5 is a diagram explaining the principle of the device used in the comparative example.
... pump, 3 ... steel material, 4 ... energizing roll, 6
．． 7.8.9.10.1 cell, A3, A2, A8, A... insoluble anode, 11.12.13.14.1
5...tank, 16.1'71.1L 19.20.
... Cell, 21 ... Partition wall, 22 ... Steel material, 23 ...
- Electric roll, B1, B7, B3, B4, B, ... insoluble anode. Agent Masaaki Inoue, Patent Attorney Figure 1 ttEA (A/dm2) Figure 3 Procedural Amendment February 24, 1980 Commissioner of the Patent Office Shima 1) Haruki Tono1, Indication of Case 1988 Patent Application No. 165'739 No. 2, Title of the invention Steel material coated with an iron-zinc alloy plating layer having a concentration gradient and its manufacturing method 3, Relationship with the amended person's case Patent applicant address: 2 Otemachi, Chiyoda-ku, Tokyo Chome 6-3 Name (6
65) Nippon Steel Corporation Representative Takeshi 1) Yutaka 4, Agent Address 1601-63 Nagara, Hayama-cho, Miura-gun, Kanagawa Prefecture, Detailed Description of the Invention Column 6. Contents of Amendment (1) Scope of Claims Correct as shown in the attached sheet. (2) On page 4, line 14 of the specification, "and" is amended to "and". (3) “Electrode passivity phenomenon” on page 8, line 8 of the same page is changed to “
This is corrected as "electrode passivation phenomenon". (4) "Preventing burn-in" in the 3rd line of No. 9 of the same text is amended to "prevent burn-in." Representative Patent Attorney Masaru Inoue Seki Attachment [2, Claim 1, The plating layer is 5 to 50 g/m'', and the zinc proportion in the plating layer is within the range of 5 to 98% by weight, Steel material coated with an iron-zinc alloy plating layer with reduced or increased content. 2. In a continuous plating line with multiple cells, the zn++/Ir6+ weight ratio is 0.02 in the plating bath.
~0.90, and the total concentration of sulfates of both metals is 100.
Using a sulfate bath containing g/fi or more within the solubility limit, p
H0.8~2.3, bath temperature in the range of 40~80"C, using an insoluble anode, changing the current density sequentially from the first cell, and sequentially changing the zinc content within the range of 5~98% by weight. Method for manufacturing steel covered with iron-zinc alloy plating layer with reduced or increased thickness.-1 JP-A-58-67886 (8)

Claims (1)

[Claims] 1. Iron-zinc alloy plating in which the zinc content is sequentially decreased or increased within the range of a plating amount of 5 to 50 g/i and a zinc proportion in the plating layer of 5 to 98% by weight. Steel coated with multiple layers. 2. In a continuous plating line with multiple cells, the weight ratio of Zn/Fe++ in the plating bath is 0.02 to 0.90.
, and the total concentration of sulfates of both metals is 100 g / /
Sulfur contained within the solubility limit #! Using a salt bath, pH 0.8
~2.3, using an insoluble anode in the bath temperature range of 40 to 80 °C, changing the current density sequentially from the first cell, and decreasing the zinc content in the range of 5 to 98% by weight or A method for producing steel coated with multiple layers of increased iron-zinc alloy plating.