KR100435473B1 - Method for Manufacturing alloy plating strip having superior surface corrosion resistance - Google Patents

Abstract

The present invention relates to a method for manufacturing a zinc-iron (Zn-Fe) alloy electroplated steel sheet, the purpose of which is to increase the iron content in the zinc-iron plated layer to 14-20% while preventing the occurrence of product surface defects surface corrosion resistance It is to provide a plating method that can be improved.

The present invention for achieving the above object,

Concentration of Zn ^{+ 2} ions: 56-60 g / l, Fe ^{+ 2} ions: 11-13 g / l, Fe ^{+ 3} ions: 1.0 g / l or less, Cl ⁻ ions: 220-240 g / l , Organic additives: 1.5 to 2.5, pH: 1.5 to 2.5, and the solution was passed through a plating bath at a line speed of 75 to 90 mpm at a temperature of 50 to 60 ° C. to form a zinc-iron plated layer of 14 to 20% of iron. The technical gist of the present invention relates to a method for producing a zinc-iron alloy plated steel sheet having excellent surface corrosion resistance including forming.

Description

Method for Manufacturing alloy plating strip having superior surface corrosion resistance}

The present invention relates to a method for manufacturing a zinc-iron (Zn-Fe) alloy electroplated steel sheet, and more particularly, to increase the iron content in the zinc-iron plated layer to 14-20% while preventing the occurrence of product surface defects. It relates to a plating method that can improve the corrosiveness.

Zinc-iron alloy electroplated steel sheet is mainly used for automobile shell, and the most important property is surface corrosion resistance. Surface corrosion resistance is known to be best when the iron content in the zinc-iron alloy layer is maintained at 14-20%. The iron content in the zinc-iron alloy layer is closely related to the plating conditions.

By the way, the conventional method of manufacturing a zinc-iron alloy plated steel sheet has only raised the iron content by about 13%. Occasionally, the iron content in the plating layer is increased to 14-20%, which is only about 3% of the total production. As such, it is difficult to derive the perfect working conditions that can increase the iron content in the zinc-iron plated layer to 14% or more.

The operating conditions of the zinc-iron alloy coated steel sheet include the composition of the solution, the pH of the solution, and the line speed (the feed rate in the plating bath of the steel sheet). The precise control of the zinc-iron alloy plate can increase the iron content in the zinc-iron plated layer. . Increasing the actual line speed also increases the iron content in the zinc-iron plated layer, which may cause arcing due to swelling of the conductive roll rubber, which may cause other defects on the surface of the product. In other words, when the line speed increases, the temperature of the solution rises and the rubber part swells in the conductive roll.As a result, an arc spot occurs due to the separation space from the strip, causing a fatal defect on the surface of the product. do. In addition, sludge containing Fe (OH) ₃ as a main component is generated, which impedes an increase in the iron content in the plating layer.

The present invention provides a plating method capable of stably securing the iron content in the zinc-iron alloy plating layer without occurrence of defects on the surface of the product.

1 is a graph showing the relationship between Fe% content and surface corrosion resistance of zinc-iron alloy plated steel sheets.

Graph

2 is a graph showing the correlation between line speed and current density.

3 shows the relationship between the line speed and the Fe content of the zinc-iron alloy plated steel sheet.

Graph

Method for producing a zinc-iron alloy plated steel sheet of the present invention for achieving the above object, the concentration of Zn ^{+ 2} ions: 56 ~ 60g / l, Fe ^{+ 2} ions: 11 ~ 13g / l, Fe ^{+ 3} ions Concentration: Less than 1.0 g / l, Cl ^- ion concentration: 220-240 g / l, Organic additives: 1.5-2.5, pH: 1.5-2.5 and the solution temperature is 50-60 캜. And a zinc-iron plated layer having an iron content of 14 to 20% by passing at a line speed of 90mpm.

Hereinafter, the present invention will be described in detail.

In the present invention, there is provided a plating method for setting the iron content in the zinc-iron alloy plating layer to 14-20%. If the iron content in the zinc-iron alloy plating layer is 14% to secure the surface corrosion resistance, if it exceeds 20% there is a fear that the plating layer powdering occurs.

The concentration of Zn ⁺² is 56 to 60 g / l, which is less than 56 g / l, which may result in a decrease in the formation of the Zn plated layer, which may cause plating layer powdering. This is because it is difficult to secure the iron content in the plating layer due to the excess of Zn ⁺² ions participating in the plating before the Fe ⁺² .

The concentration of Fe ⁺² ions is 11-13 g / l, which is less than 11 g / l, and it is difficult to set the iron content in the plating layer to 14-20% because the concentration of Fe ions in the solution is small. This is because powdering of the plating layer occurs due to excessive iron content in the plating layer.

Fe ⁺³ ions are generated sludge is mainly composed of Fe (OH) ₃ as shown in the formula (1) below to a large amount present in the plating solution is oxidized by dissolved oxygen, because of the way the securing of an iron content in the coating layer, Fe ⁺ It is preferable that the concentration of ³ ions be less than 1 g / L.

^{Fe +2 → Fe +3 + e -} , Fe +3 + 3OH → Fe (OH) 3

In order to maintain the concentration of Fe ⁺³ ions in the plating solution to less than 1 g / ℓ, Fe powder and HCl are added to the plating solution to reduce Fe ⁺³ to Fe ⁺² as shown in Formula (2).

Powder Fe → Fe ⁺² ↑ + 2e ^-

^{2Fe +3 ↓ + Fe +2 + 2e} - → 3Fe +2

Cl ^- ion is a factor that can help to secure the iron content in the plating solution is Cl ^- is preferred to secure the iron content in the low current density by the addition of an easily together addition of 220~240g / ℓ for this. This is because powdering of the plating layer occurs when it exceeds 240 g / L.

The organic additive (USS-P) is an organic substance that not only makes the plating structure fine but also works to secure the iron content in the plating layer because the deposition and the voltage increase in the plating reaction, and the addition amount is 1.5 to 2.5 g / l. good. If less than 1.5g / ℓ it is difficult to secure the iron content, if it exceeds 2.5g / ℓ there is a problem that the increase in sludge generation, concentration unevenness, waste water treatment load increases.

In addition, the pH of the plating solution is preferably 1.5 to 2.5, which is less than 1.5, but the sludge is reduced in the solution, but plating streaks are easily generated, and the chemical consumption of the anode is increased, resulting in uneven solution concentration. In this case, sludge generation increases, resulting in uneven concentration and increased wastewater treatment load.

It is preferable to set the temperature of the plating solution to 50 to 60 ° C. If the temperature is less than 50 ° C, KCl may be precipitated. If the temperature exceeds 60 ° C, the rubber of the conductive roll may swell and arcing may occur. Because there is.

Line speed is a factor that has a direct relationship with the current density, and as shown in FIG. 2, it can be seen that the current density increases as the line speed increases. In addition, in order to maintain the iron content in the plating layer to 14 to 20%, it is necessary to work at a line speed of 75ppm or more, as shown in Figure 3, but when it exceeds 90mpm, work occurs at the limiting current density, there is a fear of powdering have.

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

EXAMPLE

The plating was performed under the plating conditions as shown in Table 1, and then the Fe content and the plating layer powdering property of the plating layer were measured, and the results are shown in Table 2 below.

division Plating solution (g / ℓ) pH Organic additives Line speed Solution temperature Current density Z ^{n + 2} Fe ⁺² Fe ⁺³ Cl ^- Comparative Example 1 54 9 3.0 200 0.5 0.5 60 45 36 Comparative Example 2 55 10 3.0 210 1.0 1.0 65 45 39.2 Inventive Example 1 56 11 1.0 220 1.5 1.5 75 50 45.2 Inventive Example 2 57 12 0.8 230 1.5 1.5 75 52 45.2 Inventive Example 3 58 12 0.7 230 2.0 2.0 80 54 48.2 Inventive Example 4 59 12 0.7 230 2.0 2.0 80 56 48.2 Inventive Example 5 60 13 0.7 240 2.5 2.5 85 60 51.2 Comparative Example 3 61 14 0.6 250 3.0 3.0 90 62 54.2 Comparative Example 4 62 15 0.6 260 3.0 3.0 90 66 54.2 Comparative Example 5 63 16 0.6 270 3.0 3.0 90 70 54.2

division Fe content (%) Plating Powdering Comparative Example 1 5.0 Not Occurred Comparative Example 2 9.9 Inventive Example 1 14.5 Inventive Example 2 15.2 Inventive Example 3 15.8 Inventive Example 4 18.0 Inventive Example 5 20.0 Comparative Example 3 21.3 Occur Comparative Example 4 22.8 Comparative Example 5 25.0

As shown in Table 2, when the conditions of the present invention are satisfied, the iron content in the plating layer required to secure the surface corrosion resistance satisfies 14 to 20%, and no powdering occurs.

As described above, the present invention has an effect of providing a plated steel sheet having a zinc-iron alloy plated layer having excellent surface corrosion resistance and no plating layer powdering.

Claims (1)

Concentration of Zn ⁺² ions: 56 to 60 g / l, Fe ⁺² ions: 11 to 13 g / l, Fe ⁺³ ions: less than 1.0 g / l, Cl ⁻ ions: 220 to 240 g / l The organic additive: 1.5-2.5, pH: 1.5-2.5, the solution temperature is 50-60 DEG C. The strip is passed at a line speed of 75-90 mpm to form a zinc-iron plated layer of 14-20%. A method for producing a zinc-iron alloy plated steel sheet having excellent surface corrosion resistance including forming.