KR101778492B1 - Method of manufacturing electro-galvanized steel sheet and electro-galvanized steel sheet using the same - Google Patents

Abstract

The present invention relates to a method of manufacturing an electro-galvanized steel sheet and an electro-galvanized steel sheet produced therefrom, and more particularly, to a method of manufacturing an electro-galvanized steel sheet by forming a zinc-cobalt alloy plating layer on the surface of a base steel sheet; And forming a zinc-plated layer on the zinc-cobalt alloy plating layer, and to an electro-galvanized steel sheet produced from the method.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing an electro-galvanized steel sheet, and an electro-galvanized steel sheet produced therefrom,

The present invention relates to a process for producing an electroded galvanized steel sheet and an electroded galvanized steel sheet produced therefrom, and to a process for producing an electrodeposited galvanized steel sheet having a poor surface appearance, and to an electroded galvanized steel sheet produced therefrom.

The electro-galvanized steel sheet is used as a material to be applied to home electric appliances and construction materials with a low adhesion amount of 10 to 20 g / m ^{2 because} the surface is beautiful and the amount of deposition is easily controlled. However, the zinc plating layer has a low hardness and has a disadvantage that it is contaminated easily from the outside such as hand marks are easily left when touched by hand.

In order to compensate for this, a zinc fingerprint resin is coated on the zinc plated layer. However, such an electro-galvanized steel sheet undergoes epitaxis growth in which crystal grains are formed depending on the orientation and shape of the base steel sheet, that is, the cold-rolled steel sheet. Therefore, when a cold-rolled steel sheet as a base steel sheet has fine defects, it has a sensitive plating structure in which defects are transferred as they are even after electro-galvanizing. Especially, when the inner fingerprint resin is coated thereon, defects of the plating layer become clearer. Therefore, there should be no defects in the base steel sheet for the production of electro-galvanized steel sheet, and a very beautiful surface can be obtained when such a clean surface is galvanized.

However, the base steel sheet for electro-galvanized steel sheets has a microscale scale that is difficult to be visually recognized or observed, and when zinc plating is performed on the base steel sheet, the steel sheet is immediately smudged and has defects.

In order to solve the above problems, as disclosed in Korean Patent Laid-Open Publication No. 2008-0061458, when zinc plating is performed after thinly plating nickel (Ni) on a pickled cold rolled steel sheet, Although defects in the occurrence of stains are prevented, production cost is increased by using expensive nickel, and the product is classified as a substance causing an allergic reaction to the human body, thereby avoiding products containing Ni in the plating layer.

In addition, there is a case where a single or alloy plating film mainly composed of iron (Fe) is formed, but Fe is very unstable in solution, so that the bivalent iron ions are easily oxidized in three directions, and the hydroxide or oxide is formed in the form of sludge Because it is unstable material is very difficult to manage.

Therefore, it is necessary to minimize defects due to scales generated on the cold-rolled steel sheet without Ni or Fe plating.

An aspect of the present invention is to provide a method for manufacturing a galvannealed steel sheet which prevents defects such as fine scale remaining on a base steel sheet and which has excellent surface appearance.

An aspect of the present invention is to provide an electrogalvanized steel sheet having excellent surface whiteness and excellent surface appearance.

According to the present invention, there is provided a method for manufacturing a zinc-cobalt alloy coating layer, comprising: forming a zinc-cobalt alloy plating layer on a surface of a base steel sheet by electroplating zinc-cobalt alloy at an adhesion amount of 10 to 500 mg / m ² ; And subjecting the zinc-cobalt alloy plating layer to electro-galvanizing to form a zinc-plated layer.

The zinc-cobalt alloy plating layer preferably contains 5 to 15% by weight of cobalt.

Wherein the zinc-cobalt alloy plating layer forming step has a current density of 10 to 100 A / m 2 in a plating bath maintained at a cobalt ion concentration of 10 to 30 g / l, a zinc ion concentration of 40 to 60 g / l, a pH of 4.0 to 6.0, dm < ^{2 &} gt ;.

The zinc plating layer formation step is preferably performed at a current density of 40 to 120 A / dm ² in a sulfuric acid bath maintained at a zinc ion concentration of 50 to 100 g / l, a pH of 0.3 to 1.5 and a temperature of 40 to 60 캜.

Further, the present invention provides a method of manufacturing a steel sheet, A zinc-cobalt alloy plating layer formed on the base steel sheet; And a zinc-plated layer formed on the zinc-cobalt alloy plating layer, wherein the zinc-cobalt alloy plating layer provides an electro-galvanized steel sheet electroplated with zinc-cobalt alloy at an adhesion amount of 10 to 500 mg / m ² on the surface of the base steel sheet do.

The zinc-cobalt alloy plating layer preferably contains 5 to 15% by weight of cobalt.

The base steel sheet is preferably a hot-rolled steel sheet or a cold-rolled steel sheet.

According to the present invention, it is possible to prevent epitaxial growth of zinc crystals upon electro-galvanizing, thereby preventing defects such as fine scale remaining on the base steel sheet and thereby obtaining an electro-galvanized steel sheet having an excellent surface appearance .

1 is a graph showing the results of surface whiteness evaluation of the plating materials 1 to 16.
2 is a graph showing the cathode current efficiency with respect to the deposition film of the plating materials 1 to 15.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

Generally, after hot rolling, scales such as FeO, Fe ₂ O ₃ , Fe ₃ O ₄ and the like are formed thickly, and these scales are removed through pickling process thereafter. However, some of the scales can not be removed, and they are subjected to cold rolling as they are, resulting in a thin and fine scale. At this time, the scale may be reduced or dissolved and removed in the pickling process of the annealing process and the electroplating process, but some of the scale is left as it is, which obstructs the crystal growth during galvanizing or causes a defect in which the color changes.

The inventors of the present invention have made intensive studies on the prevention of defects due to fine scale. As a result, they have found that when a zinc-cobalt alloy plating layer is formed on a base steel sheet before forming an electrogalvanized layer, Galvanized steel sheet having an excellent surface appearance as the zinc-cobalt alloy plating layer is covered with the zinc-cobalt alloy plating layer. Thus, the present invention has been accomplished.

Hereinafter, the present invention will be described in detail.

A method of manufacturing an electro-galvanized steel sheet provided in an aspect of the present invention includes the steps of forming a zinc-cobalt alloy plating layer on the surface of a base steel sheet and forming a zinc plating layer on the zinc-cobalt alloy plating layer According to the above method, an electro galvanized steel sheet having a beautiful surface appearance can be produced.

At this time, the base steel sheet may be any steel sheet for electro-galvanized steel sheet, preferably a hot-rolled steel sheet or a cold-rolled steel sheet, more preferably a cold-rolled steel sheet, most preferably a non- .

As described above, in the present invention, a zinc-cobalt alloy plating layer is formed before electroplating to form a zinc-plated layer, in order to produce an electro-galvanized steel sheet having an excellent surface appearance. That is, a zinc-cobalt alloy electroplating is performed on the surface of the base steel sheet at a deposition amount of 10 to 500 mg / m ² to form a zinc-cobalt-plated alloy layer. If the deposition amount of the zinc-cobalt alloy electroplating is less than 10 mg / m ^2, it is difficult to sufficiently cover defects such as fine scale formed on the base steel sheet. If the deposition amount exceeds 500 mg / m ² , Not only is the effect saturated, it is also uneconomical.

The plating solution for electroplating is not particularly limited, and for example, a sulfuric acid bath, a chloride bath and the like can be applied. In order to prevent cobalt ions from being formed into oxides or hydroxides and changing into sludge, Is preferably maintained at 6.0 or less, and more preferably pH is maintained at 4.0 to 6.0. If the pH of the plating solution is less than 4.0, there is a problem that the amount of hydrogen gas generation is increased and the current efficiency is lowered.

More specifically, the electroplating of zinc-cobalt alloy according to the present invention is carried out in a plating bath maintained at a cobalt ion concentration of 10 to 30 g / l, a zinc ion concentration of 40 to 60 g / l, a pH of 4.0 to 6.0 and a temperature of 30 to 60 ° C And the current density is preferably 10 to 100 A / dm ² .

The zinc ion in the plating bath is preferably added in an amount of 40 to 60 g / l in order to secure an adequate amount of cobalt to be contained in the alloy plating layer. If the content of the zinc ion is less than 40 g / l in the zinc-cobalt alloy plating film The cobalt content is less than 5% by weight when the content of the zinc ion exceeds 60 g / l, and the high current density In the case of plating, the dissolution rate of the plating layer becomes large, and the target amount of adhesion can not be secured, which is not preferable.

If the content of the cobalt ions is less than 10 g / l, the content of zinc in the plating layer exceeds 95% by weight and the plating layer is soft, and the cobalt ions in the plating bath are added in an amount of 10 to 30 g / If the content of the cobalt ions is more than 30 g / l, the content of zinc in the plating layer becomes small, and the coating layer becomes weak and is broken, which is not preferable. .

If the temperature of the plating bath is less than 30 ° C, the electric conductivity of the solution is lowered, and the activity of the ions is lowered. As a result, the plating efficiency is lowered and the salt may be precipitated have. On the other hand, if the temperature exceeds 60 DEG C, the plating solution may evaporate, which is not preferable.

Further, the current density is from 10 to is controlled to 100A / dm ^2, it is difficult that the electric current density of 10A / dm ² lower than if the metal ions are secured at least adhesion amount to the target speed than the plating dissolution rate is further increased to be precipitated, while 100A / dm < ² &^gt; exceeds the critical current density, there is a problem that a blackened surface layer is obtained.

When the zinc-cobalt alloy electroplating is performed according to the above, a zinc-cobalt alloy plating layer having a cobalt (Co) content of 5 to 15 wt% and a zinc (Zn) content of 85 to 95 wt% can be obtained. If the content of cobalt in the zinc-cobalt alloy plating layer is less than 5%, the hardness of the plating layer is low, and when the current density is high, the dissolution rate of the plating layer becomes large and it is difficult to secure the adhesion amount. When the cobalt content exceeds 15% The brittleness of the plated layer is increased, so that it is easily broken and is not economical.

A zinc-cobalt alloy plating layer is formed on the surface of the base steel sheet, and electro-galvanizing is performed on the zinc-cobalt alloy plating layer to form a zinc plating layer.

The zinc plating layer formation step is preferably performed at a current density of 40 to 120 A / dm ² in a sulfuric acid bath maintained at a zinc ion concentration of 50 to 100 g / l, a pH of 0.3 to 1.5 and a temperature of 40 to 60 캜.

Specifically, the zinc ion concentration in the sulfuric acid bath is preferably 50 to 100 g / l, and when the zinc ion concentration is less than 50 g / l, ballistic gold may be generated and the productivity may be lowered. When the zinc ion concentration is 100 g / l, the zinc salt may precipitate when the temperature of the plating solution is lowered, and unnecessary cost may increase because a large amount of metal ions are contained, which is not preferable.

In addition, the pH of the sulfuric acid bath is preferably maintained at 0.3 to 1.5, and if the pH is less than 0.3, the plating efficiency is significantly lowered and redissolving of the plating layer may occur. If the pH exceeds 1.5, It takes a long time and it is difficult to secure zinc ions in the solution, which is not preferable.

The temperature of the sulfuric acid bath is preferably controlled to 40 to 60 DEG C, and if the temperature is lower than 40 DEG C, the electric conductivity is lowered to lower the plating efficiency and the zinc salt can be precipitated. If the temperature exceeds 60 DEG C, It is not preferable because it may evaporate.

When electroplating is carried out in a sulfuric acid bath maintained under the above conditions, the current density may be limited to a range of 40 to 120 A / dm ^{2. If} the current density is less than 40 A / dm ² , productivity may be deteriorated. If the current density exceeds 120 A / dm < ^{2 &} gt ;, the supply of zinc ions to the steel sheet is not smooth and ballistic cracking may occur.

The electro-galvanized steel sheet produced by the method of manufacturing an electro-galvanized steel sheet described above may be subjected to a certain post-treatment process, and there is no particular limitation. For example, a process such as post- have.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electrogalvanized steel sheet manufactured according to a preferred embodiment of the present invention will be described in detail.

The electro-galvanized steel sheet according to the present invention comprises a base steel sheet; A zinc-cobalt alloy plating layer formed on the base steel sheet; And a zinc-plated layer formed on the zinc-cobalt alloy plating layer.

At this time, the base steel sheet may be any steel sheet for the galvanized steel sheet, preferably a hot-rolled steel sheet or a cold-rolled steel sheet, and more preferably a cold rolled steel sheet.

The zinc-plated steel sheet of the present invention includes a zinc-cobalt alloy plating layer between the base steel sheet and the zinc plating layer, thereby preventing defects such as fine scale remaining on the original steel sheet. As a result, an electro-galvanized steel sheet having an excellent surface appearance can be obtained.

The zinc-cobalt alloy plating layer preferably contains 5 to 15% by weight of cobalt (Co) and 85 to 95% by weight of zinc (Zn).

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following examples.

< Example  And Comparative Example >

A cold-rolled steel sheet of 0.7 mmt was cut into 100 × 250 mm as the base steel sheet for the production of galvanized steel sheet. The above ground steel sheet was electro-galvanized on steel sheets treated or not treated with pre-plating of zinc-cobalt alloy electroplating, iron-zinc alloy electroplating or nickel electroplating to produce electrogalvanized steel sheets. In this case, a circulating electroplating apparatus was used for the electroplating, and electrodialyzing was carried out in a sulfuric acid bath maintained at a zinc ion concentration of 50-100 g / l, a pH of 0.3-1.5 and a temperature of 40-60 ° C, and a current density of 40-120 A / dm ² .

Plating materials 1 to 7 were subjected to zinc-cobalt alloy electroplating while changing the plating time at a current density of 50 A / dm ² in a plating bath having a cobalt ion concentration of 20 g / l, a zinc ion concentration of 50 g / l, a temperature of 50 캜 and a pH of 5.0 Galvanized steel sheet so as to have an adhesion amount of 20 g / m &lt; ² &gt;.

Plating materials 8 and 9 were the same as the above plating materials 1 to 7 except that only the plating time (deposition amount) was changed to apply electroplating to the zinc-cobalt alloy, and then electroplated at an adhesion amount of 20 g / m ² To prepare respective electro-galvanized steel sheets

(Plating iron content) and plating time (deposition amount) were changed in a plating bath having an iron ion concentration of 30 g / l, a zinc ion concentration of 10 g / l, a temperature of 50 캜 and a pH of 1.0 for plated materials 10 to 13, -Zinc alloy electroplating, electro galvanizing was carried out at an adhesion amount of 20 g / m &lt; ² &gt; to prepare each electro-galvanized steel sheet.

The plating materials 14 and 15 were subjected to nickel electroplating while changing the plating time (deposition amount) at a current density of 60 A / cm ² in a plating bath having a nickel ion concentration of 40 g / l, a temperature of 60 캜 and a pH of 4, m &lt; ² &gt; to obtain an electro galvanized steel sheet.

For the plating material 16, an electrogalvanized steel sheet was produced by subjecting the base steel sheet to electro-galvanizing immediately with an adhesion amount of 20 g / m ² .

After that, the cathodic current efficiency was calculated from the electrodeposition amount of zinc-cobalt electroplated zinc-cobalt alloy electroplating, iron-zinc alloy electroplating, and nickel electroplating with the actual precipitation amount relative to the theoretical precipitation amount after plating. The results are shown in Table 1. The results are shown in Table 1. The results are shown in Table 1. The results are shown in Tables 1 and 2.

For each of the electro-galvanized steel sheets, the economics and whiteness were measured and evaluated. At this time, the economical efficiency was evaluated as x: low,?: Normal,?: Excellent according to the case where expensive nickel was contained in the plating layer and the plating adhesion amount exceeded the range proposed in the present invention. In addition, whiteness was measured by a colorimeter (Minolta Spectrophotometer CM3700D), and it was judged that the degree of whiteness was 85 or more, and the degree of inferiority was 85 or less. The results are shown in Table 1 and FIG.

Further, before conducting electro-galvanizing, the contents of cobalt, iron or nickel in the alloy plating layers of the plating materials 1 to 15 were analyzed.

Table 1 below shows the current efficiency and cleanliness of the solution in the pre-plating and the economical efficiency and surface whiteness evaluation result of the electro-galvanized steel sheet after the electro-galvanizing.

Plated material
No. Pre-plating Economics surface
Whiteness Remarks Adhesion
(mg / m ² ) Co, Fe, Ni content
(weight%) Cathode current efficiency (%) solution
cleanliness One 10 Co 12 wt% 99 ○ ○ 90 Example 1 2 50 Co 6 wt% 99 ○ ○ 89 Example 2 3 150 Co 8 wt% 98 ○ ○ 88 Example 3 4 300 Co 11 wt% 98 ○ ○ 87 Example 4 5 500 Co 5 wt% 98 ○ ○ 86 Example 5 6 20 Co 15 wt% 99 ○ ○ 87 Example 6 7 400 Co 12 wt% 97 ○ ○ 85 Example 7 8 5 Co 10 wt% 98 ○ ○ 81 Comparative Example 1 9 600 Co 12 wt% 97 ○ △ 88 Comparative Example 2 10 5 Fe 90 wt% 85 × ○ 85 Comparative Example 3 11 300 Fe 100 wt% 83 × ○ 86 Comparative Example 4 12 1000 Fe 95 wt% 86 × ○ 87 Comparative Example 5 13 100 Fe 80 wt% 89 × ○ 86 Comparative Example 6 14 10 Ni 100 wt% 91 ○ × 85 Comparative Example 7 15 300 Ni 100 wt% 90 ○ × 86 Comparative Example 8 16 0 0 - - ○ 80 Comparative Example 9

As shown in Table 1 and FIGS. 1 and 2, zinc-cobalt alloy electroplating was performed on the base steel sheet so that the content of cobalt was 5 wt% to 15 wt% at an adhesion amount of 10 to 500 mg / m ² , In the case of Examples 1 to 7 in which an electrodeposited galvanized steel sheet was produced, the cathodic current efficiency was 97% or more, the solution was also very clean, and the surface whiteness of the galvanized layer was 85 or more, .

On the other hand, the zinc-in Comparative Example 1, subjected to adhesion amount when cobalt alloy electroplating a 5mg / m ^2, there was found to stain defects surface whiteness as low as 81, subjected to coating weight to 600mg / m ² Comparative Example 2 The surface whiteness result was good due to the formation of the alloy plating layer having sufficient cobalt content, but the same effect was obtained even at 500 mg / m ² or less, which is disadvantageous in terms of economy.

In addition, the results of Comparative Examples 3 to 6 in which electroplating of iron-zinc based alloy and electroplating were performed were advantageous in terms of surface whiteness and economical efficiency, but since the pH of the solution had to be controlled to be low, current efficiency was low, Respectively.

In the case of Comparative Examples 7 and 8 in which Ni electroplating was carried out, the surface whiteness was excellent by Ni plating. However, since the current efficiency was low and high-priced Ni was used, it was uneconomical and preferable in view of Ni being harmful to human body I can not.

Further, in Comparative Example 9 in which electro-galvanizing was directly performed without any pre-plating treatment, the surface whiteness was greatly reduced to 80, while it was advantageous in terms of economy, and it was found that a large amount of spot defects occurred on the surface .

According to the above results, when pre-plating with zinc-cobalt alloy electroplating according to the present invention, surface defects can be effectively prevented in the final product, whereby an electro-galvanized steel sheet having an excellent surface appearance can be obtained.

Claims (2)

Forming a zinc-cobalt alloy plating layer by electroplating a zinc-cobalt alloy with an adhesion amount of 10 to 500 mg / m ² on the surface of the base steel sheet; And
And electro-galvanizing the zinc-cobalt alloy plating layer to form an electro-galvanized layer,
The step of forming the zinc-cobalt alloy plating layer may include a step of forming a zinc-cobalt alloy plating layer having a current density of 10 to 30 g / l in a plating bath maintained at a cobalt ion concentration of 10 to 30 g / l, a zinc ion concentration of 40 to 60 g / 100 A / dm &lt; ² &gt;
The step of forming the electroplated zinc layer comprises the steps of: preparing an electrodeposited galvanized steel sheet with a zinc ion concentration of 50 to 100 g / l and a current density of 50 to 120 A / dm ² in a sulfuric acid bath maintained at a pH of 0.3 to 1.5 and a temperature of 40 to 60 캜; Way.
The method of claim 1, wherein the zinc-cobalt alloy plating layer comprises 5 to 15 wt% of cobalt.

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