KR100909692B1 - Manufacturing method of electro galvanized steel sheet with excellent surface hardness and surface appearance - Google Patents

Abstract

In manufacturing an electro galvanized steel sheet in a chloride bath, the front cell is plated by DC, which is a conventional plating method, and the rear cell has a peak current of 300 to 500 A / dm2, plating time of 0.1 to 0.3 ms, and down time. In the method for producing an electro galvanized steel sheet having excellent surface hardness and surface appearance by improving the surface appearance according to the refinement of the plating crystal grains and the surface hardness of the plating layer by using a DC & pulse current having a pulse of 1 to 5 ms or less. It is about.

Description

A manufacturing method of zinc-plated steel plate with superior surface hardness and clean surface}

1: Waveform diagram of direct current & pulse current usable in the method of the present invention

Figure 2: Schematic diagram showing a conventional electro galvanized steel sheet manufacturing process

Figure 3: Schematic diagram showing a process for producing an electrogalvanized steel sheet according to the present invention

<Description of the symbols for the main parts of the drawings>

1: apparatus for unwinding steel sheet 2: degreasing 3: pickling

4: flushing 5: plating ZONE 5-1: front end plating ZONE

5-2: Back end plating ZONE 6: Water washing and post treatment 7: Winding plated steel plate

The present invention improves the surface hardness of the coating layer during electro-galvanizing in a zinc hydrochloric acid bath so that there is no scratches when the galvanized steel sheet is processed, and the electro-galvanized steel sheet having excellent surface hardness and surface appearance to improve friction characteristics. It relates to a method for producing. More specifically, the surface hardness and surface appearance are reduced by reducing the grain size and changing the orientation of the crystal surface to the pyramid surface by using a pulse current instead of a direct current in the plating cell of the rear end in the plating process of the zinc hydrochloride bath. The present invention relates to a method for producing an excellent galvanized steel sheet.

Zinc is a metal with low hardness, so when zinc is plated on a steel plate, 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. The physical properties of the galvanized layer, ie hardness, surface appearance, etc. depend on the size, shape, and orientation of the grains, so the grain size or preferred orientation is determined by the plating conditions. In order to improve the hardness of the plating layer, there is 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 is pointed out as a problem of high cost and inefficiency.

The present invention improves the surface hardness of the plating layer during electrogalvanization in hydrochloric acid bath using a soluble anode using a radial cell in order to solve the above problems, reducing scratches or friction during processing of galvanized steel sheet An object of the present invention is to provide a method for producing an electrogalvanized steel sheet excellent in surface hardness and surface appearance which improves characteristics.

In order to achieve the above object, the present invention is a method for manufacturing a galvanized steel sheet by electro-galvanization, the front cell is plated with a direct current of the conventional plating method and the rear end cell is peak current density (peak current) Is plated using a DC & pulse current of 300 to 500 A / dm 2, plating time 0.1 to 0.3 ms, and rest time 1 to 5 ms or less, and the deposition amount of the plating layer formed in the rear end cell is 4 g / m 2 or more. Provided is a method for producing an electrogalvanized steel sheet having excellent surface hardness and surface appearance.

The method for improving the hardness of the galvanized layer in the process of producing a continuous galvanized steel sheet will be described in more detail. In the method for producing an electrogalvanized steel sheet in which zinc is plated on a steel sheet in a hydrochloric acid bath, The pre-treatment step includes the front end plating step using the existing DC current and the post step plating step of plating the steel sheet through the front end plating step using pulse wave current of square wave. Provided is a method for producing an electrogalvanized steel sheet, comprising the step of: / m 2 or more. The deposition amount of the plating layer to be plated at the rear end provides a method of manufacturing an electro galvanized steel sheet having excellent surface hardness after galvanizing by managing the finer grains in the plating layer to 4 g / m 2 or more.

In other words, the present invention is a method of manufacturing a mixed zinc plating of direct current + pulse current is galvanized using a direct current at the front end and plated using a pulse current of a square wave at the rear end.

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 and is easily plated. There are several methods for imparting specific properties to metal surfaces, including CVD, sputtering, evaporation, and electroplating. Of these, the coating layer manufacturing by electroplating is widely used because it has the advantages of being the most economical, the device is simple, and the operation is easy, and its area is being expanded. In addition, it is possible to obtain a chromium electrodeposition layer free of internal stress and cracks by chromium plating used for industrial and decorative purposes using pulse current. Until now, the advantages of the plating method of the pulse current include high electrodeposition speed and high electrodeposition speed due to the increase of electrodeposition speed, formation of fine grain electrodeposition, increase of current efficiency, and formation of electrodeposition layer with less internal stress and cracking. It is widely used in the electronics industry, machinery and materials industries that require the limitation and complexity.

In the present invention, using the direct current and pulse current shown in FIG. 1 instead of the direct current used in the manufacture of the conventional galvanized steel sheet, the crystal grains are refined by high current density during zinc plating in the plating cell at the rear end, and thus the surface of the plating layer. It is to improve the value of hardness. 1 is a graph showing waveforms of direct current & pulse current usable in the method of the present invention. When plating the rear end, it is important to select an appropriate current density and plating time.

In the present invention, the reason that the peak current density value of the rear end cell (peak current) is 300 to 500 A / dm 2 is the reason that the maximum current density value of 300 A / dm 2 or less is formed by mixing the existing plating structure size and micronized plating structure. Therefore, it is observed that there is a part having excellent hardness and a part having the same hardness value as the existing plating structure depending on the plating site, and thus it is difficult to obtain a uniform fine plating layer. Under the condition that peak current is 500A / dm2, the grain size is fine and the hardness is improved, but it is not preferable due to the surface appearance defect such as the phenomenon of edge burning. The reason for limiting the plating time to 0.1 to 0.3 msec idle time is in the range of 1 to 5 msec. At the plating time of 0.1 msec and the idle time 1 msec or less, the waveform of the square wave becomes incomplete and it is difficult to control the accurate plating time. If the plating time is 0.3msec or more, there is a problem such as burning phenomenon due to the high current density when the peak current is 300 ~ 500A / dm2, and the line speed of the continuous electroplating process is more than 5msec. It is not preferable in terms of plating efficiency in view of this. The reason why the amount of adhesion by pulse is more than 4g / m2 in the plating cell at the rear end is that the adhesion amount must be at least 4g / m2 in order to show the effect of hardness improvement due to the miniaturization of plating grains. It was observed that there was a uniform hardness improvement effect throughout.

Hereinafter, an Example is given and this invention is demonstrated in detail.

<Example>

The experimental procedure of the present invention is first subjected to a pretreatment step of a degreasing pickling washing process of a cold rolled steel sheet of general low carbon steel, and plated in the electrogalvanization step. The concentration and conditions in the plating solution are shown in Table 1.

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

Table 2 shows the results of hardness and surface appearance of the conventional plating method and the present invention.

Evaluation criteria of Table 2 are as follows.

Surface appearance: Using SUGA's color difference meter and gloss meter

Measure surface color and glossiness.

Surface hardness: measured by Elionnix nano indentation tester

Amount of zinc deposited at the front plated cell (g / m2) Amount of zinc deposited on the back end plating cell (g / m2) Peak current (A / dm2) Energization time (msec) Downtime (msec) Surface appearance Hardness Comparative Example 1 20 0 - - - 2 70 Comparative Example 2 17 3 250 3 One One 75 Comparative Example 3 14 6 520 0.3 One 5 97 Comparative Example 4 16 4 300 0.05 0.5 3 77 Inventive Example 1 10 10 300 0.1 5 One 96 Inventive Example 2 5 15 400 0.2 0.3 One 95 Inventive Example 3 16 4 500 0.3 One One 98 Inventive Example 4 2 18 350 0.1 3 One 96

* Rating: Good 1 ~ 6 Poor

In Comparative Example 1, only the existing plating method was electroplated, and 70, which is an average surface hardness value in a hydrochloric acid bath, was obtained. In Comparative Example 2, the plated portion was plated using pulse current at the rear end, and the plating deposition amount at the rear end was 3g / m2 and the maximum current density was 250A / m2. The grain size and hardness were uneven so that the variation of the surface hardness according to the surface area could still be seen. In Comparative Example 3, the peak current density value of the rear end cell is 520A / dm2, and the burning phenomenon is observed at the edge of the steel sheet when the plating is performed using the pulse current, which is effective in improving the hardness, but the surface appearance is not satisfactory. In Comparative Example 4, the energization time and the rest time are so short that the waveform of the square wave becomes incomplete and incomplete, so that it is difficult to accurately control the plating time.

Therefore, the shear cell presented in the invention example is the same as the existing plating method, and the peak current density of the rear cell is 300 ~ 500A / dm2, plating time 0.1 ~ 0.3ms, and downtime is 1 ~ 5 ms or less. It is effective to improve the surface appearance and the surface hardness of the plating layer according to the refinement of the crystal grains appearing when the ratio of nucleation to nuclear growth is increased by using a direct current & pulse current.

In manufacturing an electrogalvanized steel sheet in a chloride bath according to the present invention as described above, the front cell is the same as the existing plating method and the peak current density of the rear end cell is 300 ~ 500A / dm2, plating time 0.1 Electrolytic galvanized steel sheet with excellent surface hardness and surface appearance by improving the surface appearance and the surface hardness of the plated layer by using a DC & pulse current having a sintering time of ~ 0.3 ms and a rest time of 1 to 5 ms or less It can manufacture.

Claims (2)

In the method of manufacturing a galvanized steel sheet by electro-galvanization, the front cell is plated with DC current, which is a conventional plating method, and the rear cell is the peak current density 300 ~ 500A / dm 2, plating time 0.1 ~ 0.3 ㎳, the method of producing an electrogalvanized steel sheet having excellent surface hardness and surface appearance, characterized in that the adhesion amount of the plating layer formed on the rear end cell by plating with a pulse current under the conditions of 1 to 5 휴지 of rest time is 4 g / m 2 or more. delete

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