KR100554755B1 - Method for Manufacturing Electro-Galvanized Steel Sheets with Superior Surface Hardness and Appearance - Google Patents

Abstract

The present invention relates to a method for producing an electro-galvanized steel sheet having excellent surface hardness and appearance in a hydrochloric acid bath, and using a pulse and a reverse current instead of a conventional direct current and adding a certain amount of tetrabutylammonium chloride to refine the grains and to make them uneven. The plated portion is dissolved by reverse current to provide a method for producing an electro-galvanized steel sheet having excellent surface hardness and appearance.

In the present invention, in producing an electrogalvanized steel sheet in a hydrochloric acid bath, the peak current density in the pulse direction is 300 to 500 A / dm2, the plating time is 0.1 to 1 msec, and the maximum current density in the reverse direction is 100. At 165 A / dm 2, the plating time is set to 0.02 to 0.25 msec, and 0.5 to 2.5 g / l of tetrabutylammonium chloride is added to prepare a plated steel sheet.

Pulse current, reverse current, tetrabutylammonium chloride, surface hardness

Description

Method for Manufacturing Electro-Galvanized Steel Sheets with Superior Surface Hardness and Appearance

1 is a waveform diagram of a current usable in the method of the present invention

The present invention relates to a method for producing an electrogalvanized steel sheet with a hydrochloric acid bath, and more particularly, by using a pulse current, a reverse current, and an additive in the plating process of a zinc hydrochloride bath to refine the crystal grains to nano size and to surface hardness of the plating layer. And it relates to a method for producing an electrogalvanized steel sheet excellent in appearance.

In general, galvanized products are widely used in automobiles, building materials, home appliances. In particular, in the case of home appliances, in addition to the function of improving the corrosion resistance by the sacrificial method of zinc, it has the characteristics of being used immediately without coating, and the appearance after processing or handling is not only important, but also has a function as a decoration, so the appearance is beautiful. Is a factor that increases the value of a product.

However, since zinc is a metal with low hardness, when it is plated on a steel sheet, scratches are easily generated due to external factors, that is, external stresses. Therefore, if possible, it is necessary to improve the hardness of the plating layer in order to reduce the occurrence of scratch marks during processing.

Since the physical properties of the zinc plated layer, that is, the surface hardness, the appearance, and the like depend on the size, shape, orientation, and the like of the grains, the grain size and preferred orientation of the zinc plated layer are determined by the plating conditions. In order to improve the hardness of the plating layer, there is also a method of reducing the basal plane of the plating layer by changing the electrolyte of the plating solution or adding a small amount of inorganic material, which has been pointed out as a problem in terms of cost and efficiency.

The present inventors have proposed the present invention to solve the above problems of the prior art, and the present invention provides a plating condition in the production of electro-galvanized steel sheet in a hydrochloric acid bath using a soluble anode using a radial cell. It is an object of the present invention to provide a method for producing an electro-galvanized steel sheet having excellent surface hardness and appearance, which reduces scratches or improves friction characteristics during galvanized steel sheet processing.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is a method of manufacturing an electrogalvanized steel sheet in a hydrochloric acid bath, the maximum current density in the pulse direction of 300 ~ 500A / dm2, the plating time of 0.1 ~ 1msec, the maximum current density in the reverse direction of 100 ~ 165A It relates to a method for producing an electrogalvanized steel sheet, characterized in that the plating time is set to 0.02 to 0.25 msec, and 0.5 to 2.5 g / l is added to / dm2.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is a pulse and reverse of the square wave instead of the DC current used in the production of galvanized steel sheet conventionally used in the production of galvanized steel sheet in the process of manufacturing a continuous electro-galvanized steel sheet in a hydrochloric acid bath to improve the hardness of the plating layer. The present invention relates to a method for producing an electrogalvanized steel sheet, which is plated by using a current and adding tetrabutylammonium chloride.

In general, zinc has been used for a long time in automotive steel plates or home appliances because it is plated on the surface of the steel sheet to protect the base iron by the anticorrosive action and easy plating.

There are various methods of imparting special properties to the metal surface, such as chemical vapor deposition (CVD), sputtering, vaporization, and electroplating. Of these, the coating layer manufacturing by electroplating is the most economical and easy to install. It is widely used because of its advantages of being simple and easy to work with, and its area is being further expanded. In addition, chromium plating, which is used for industrial and decorative purposes, can be obtained using pulse current to obtain chromium electrodeposition layer without increasing internal stress and cracking.

Until now, the method of plating of pulse and reverse current has a high degree of limitation and complexity in process or manufacturing due to the advantages of forming electrodeposits of fine grains, increasing current efficiency and internal stress, and forming electrodeposits with less cracks. It is widely used in machinery, material industry, etc

In the present invention, using the pulse and reverse current shown in Figure 1 and tetrabutylammonium chloride in the plating cell instead of the direct current used in the conventional galvanized steel sheet manufacturing, the crystal grains are refined by high current density and additives during zinc plating in the plating cell. By melting the irregular plating surface by the reverse pulse to improve the hardness and roughness of the surface of the plating layer. 1 shows a graph showing waveforms of pulses and reverse currents usable in the method of the present invention. 1 shows plating when a pulse current is applied. The pulsed current is plated by intermittently applying current to the specimen, and plating is performed by alternately applying on-time and off-time in a short time. In the plating by applying a pulse current, plating is performed by applying any polarity (constant current) to the steel sheet, and plating by applying the opposite polarity (reverse current) is called a reverse direction. Polarity here means the direction of the current.
In such plating, it is very important to select an appropriate current density, plating time and concentration of the additive.

According to the present invention, in manufacturing an electrogalvanized steel sheet in a hydrochloric acid bath, the peak current density in the pulse direction is 300 to 500 A / dm 2, the plating time is 0.1 to 1 msec, and the maximum current density in the reverse direction is set. 100 to 165 A / dm 2, the plating time is 0.02 to 0.25 msec, 0.5 to 2.5 g / l of tetrabutylammonium chloride is added to provide a method for producing an electro-zinc plated steel sheet to improve the surface hardness and roughness of the plating layer.

In the present invention, the reason for limiting the maximum current density values in the pulse and reverse directions to 300 to 500 A / dm 2 and 100 to 165 A / dm 2, respectively, is that the surface of the plating layer is irregular in the pulse direction 300 A / dm 2 or less and the reverse direction 100 A / dm 2 or less. This is because there is a problem in the surface appearance, and in the pulse direction 500A / dm2 or more and the reverse direction 165A / dm2 or more, the grains are fine and the hardness is improved, but the surface appearance is poor, such as edge burning and excessive dissolution of the uneven plating part. Due to undesirable.

The reason why the plating time is limited to the range of 0.1 to 1 msec in the pulse direction and 0.02 to 0.25 msec in the reverse direction is high when the pulse plating time is 0.1 msec or less and the reverse plating time is 0.02 msec or less. At the current density, the waveform of the square wave does not form a right angle and is incomplete, so that it is difficult to control accurate plating time.In the pulse direction, when the plating time is 1msec or more, the maximum current density value is high when the plating is performed at 300 to 500A / dm2. There is a problem such as burning phenomenon, and if the plating time in the reverse direction is 0.25msec or more, there is a problem of excessive redissolution of the non-uniformly plated portion.

In addition, the reason for limiting the amount of tetrabutylammonium chloride added to 0.5 to 2.5 g / l is that at 0.5 g / l or less, the finely plated structure is mixed to have a small effect of improving hardness, and at 2.5 g / l or more, the same It is because it is not efficient for economic aspect by showing level effect.

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

(Example)

In the experimental procedure of the present invention, first, a low carbon steel cold rolled steel sheet is subjected to a pretreatment step of a degreasing pickling washing process and then plated in an electro zinc plating step. Concentrations and conditions in the plating solution are shown in Table 1 below.

Table 1

Zn ²⁺ (g / l) Cl ^- (g / l) PH Temperature (℃) Coating Weight (g / m2) 80 200 5 60 20

Table 2 below shows the surface appearance and hardness of the plating layer according to the present invention and the conventional plating method. The evaluation criteria of Table 2 are as follows.

Surface appearance: Measure surface color and glossiness using SUGA's color difference meter and gloss meter

Surface hardness: measured by Elionnix nano indentation tester

Table 2

Comparative Example 1 was electroplated only by the conventional plating method, and the glossiness was 10, which is an average value from the hydrochloric acid bath, and the hardness was 53. Comparative Example 2 was plated by using pulse and reverse current, and the highest current density value in the pulse direction was 250A / dm2. Scanning electron microscope observation and surface appearance measurement result showed glossiness and hardness according to the mixture of fine grains depending on the surface part. Although there was an improvement, the improvement over the existing plating material was insignificant. In Comparative Example 3, the maximum current density value in the pulse direction was 510 A / dm 2, and thus the appearance of burning phenomenon was observed at the edge of the steel sheet when the plating was performed using the pulse current, so that the surface appearance was not satisfactory. In Comparative Example 4, the maximum current density value in the reverse direction is 180 A / dm 2, which is not preferable due to poor surface appearance such as excessive dissolution of the plating layer portion. Comparative Example 6 is not suitable in terms of surface appearance due to excessive dissolution of the non-uniform plating layer portion with a current flow time of 0.3 msec in the reverse direction, Comparative Example 7 is the crystal grain addition amount of 0.4 g / l tetrabutylammonium chloride Has less nucleation effect than nuclear growth.

Therefore, as in Inventive Examples 1 to 4, the maximum current density in the pulse direction is 300 to 500 A / dm 2, the plating time is 0.1 to 1 msec, and the maximum current density in the reverse direction is 100 to 165 A / dm 2, and the plating time is 0.02-0.25 msec, and 0.5-2.5 g / l of tetrabutylammonium chloride is added to reduce surface hardness and dissolution of the fine grains and non-uniformly plated portions of the grains when reversed by nuclear current. It can be seen that it is effective in improving the appearance.

As described above, according to the method of the present invention, it is possible to produce an electro-galvanized steel sheet excellent in surface hardness and appearance.

Claims (1)

In the method of manufacturing an electro-galvanized steel sheet in a hydrochloric acid bath, when applying a pulse current to the steel sheet to plate, the maximum current density in the pulse direction (constant current) is 300 ~ 500A / dm 2, the plating time is 0.1 ~ 1msec, The maximum current density in the reverse direction (reverse current) is 100 to 165 A / dm 2, the plating time is set to 0.02 to 0.25 msec, and 0.5 to 2.5 g / l of tetrabutylammonium chloride is added to the hydrochloric acid bath. Galvanized steel sheet manufacturing method.

Images