JPS61174398A - Manufacture of one-side galvanized steel sheet - Google Patents

Abstract

PURPOSE:To prevent simply and effectively the stain of one side of a steel sheet not to be galvanized when a one-side galvanized steel sheet is manufactured in an acidic bath, by pickling the steel sheet to be one-side galvanized in a pickling bath having a specified Fe<+3> concn. or below before galvanizing. CONSTITUTION:When a one-side galvanized steel sheet is manufactured in an acidic bath, a steel sheet is degreased and pickled in a pickling bath having <=0.5g/l Fe<+3> concn. before galvanizing. Hydrochloric acid, sulfuric acid, phos phoric acid or the like is used as the acid, and the concn. is regulated to 1-20%. The surfaces of the steel sheet may be rubbed by brushing during washing after the pickling.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a zinc-based single-sided electroplated steel sheet.

<Prior art and its problems> In recent years, in order to prevent corrosion of automobile bodies caused by antifreeze agents sprayed on roads, galvanized steel sheets, that is,
The use of galvanized steel sheets or steel sheets coated with alloys such as zinc-nickel and zinc-iron is increasing.

The most severely corroded part of an automobile body is the box structure on the inside of the automobile. These parts are said to be susceptible to corrosion because they are prone to incomplete chemical conversion treatment or painting, and their structure allows salt, water, and debris to accumulate.

In order to strengthen the rust prevention ability of these parts, galvanized steel sheets have come to be used frequently in place of cold-rolled steel sheets. In this case, since double-sided plated steel plates have problems with appearance and weldability after painting, steel plates plated on only one side are often used.

It is desirable that the non-plated surface of a single-sided plated steel sheet has the same performance as a cold-rolled steel sheet, and is required to have excellent chemical conversion treatment properties and paintability. On the other hand, zinc-based electroplating on steel sheet steel plates can be performed at high current densities and the bath composition can be controlled relatively easily.1 Therefore, plating is usually carried out using an acidic bath such as a sulfuric acid bath or a chloride bath. . For this reason, when producing a single-sided plated steel sheet, the non-plated surface is corrosion resistant, but the accumulation of undesirable substances and the precipitation of impurities often cause stains and deterioration of chemical conversion treatment properties.

Defective chemical conversion treatment is generally caused by the formation of localized areas where the phosphate film is not formed, known as sagging, or the formation of uneven coarse crystals, resulting in deterioration in corrosion resistance and adhesion after painting, or in the appearance. This is an important problem in terms of quality because it causes the above-mentioned non-uniformity.

In order to prevent staining of the non-plated surface and to prevent deterioration of chemical conversion treatment properties, it is necessary to reduce the dissolution of Fe. Measures for this purpose include increasing the pH of the plating bath, lowering the bath temperature, or increasing the line speed, but all of these measures have limitations due to plating conditions or equipment.

There is also a method of polishing the non-plated surface with a brush roll after plating, but this method creates a new problem of reducing surface roughness and is not perfect in terms of reducing stains.

In addition, after plating, a method of anodizing the non-plated surface in a neutral salt aqueous solution, so-called electrolytic pickling (Japanese Patent Laid-Open No. 58-1333
No. 95) or a method in which a thin protective plating is applied to the non-plated surface and removed by electrolytic stripping after plating (Japanese Patent Laid-Open No. 5
No. 8-181889) have also been proposed, but these methods require new equipment for electrolytic stripping in addition to the plating equipment.

The present inventors previously investigated the relationship between plating pretreatment and non-plated surface contamination, and proposed a method for suppressing non-plated surface contamination by making the polarity of electrolytic degreasing negative. 149970), and even with this method, a sufficient effect may not be obtained depending on variations in line conditions.There are various ways to prevent stains on non-plated surfaces, but all of them involve some kind of method.
-I have a problem.

<Object of the Invention> In view of the above-mentioned current situation, an object of the present invention is to provide a method for manufacturing a zinc-based single-sided electroplated steel sheet that can simply and effectively prevent staining on the non-plated surface. .

<Structure of the invention> The above object is achieved by the following present invention.

That is, the present invention is characterized in that when manufacturing a zinc-based single-sided electroplated steel sheet in an acid bath, the steel sheet is pickled in a pickling bath with a Fe◆3 ion concentration of 0.5 gel or less before plating. This is a method for producing single-sided electroplated steel sheets.

The present invention also provides that when producing zinc-based single-sided electroplated steel sheets in a pickling bath, the Fe+3 ion concentration is 0.5 before plating.
This is a method for manufacturing a zinc-based single-sided electroplated steel sheet, which is characterized in that the steel sheet is pickled in a pickling bath of g/fL or less, and then the surface of the steel sheet is rubbed.

The method of the invention will be explained in detail below.

Figure 1 shows a 5PCD steel plate with a thickness of 0.7■■ degreased, then pickled in 5% HC1 at room temperature for 30 seconds, washed with water or water-brushed (no abrasive grains, nylon brush), and then 21S04 * 71i, Io 450g
el, pH 1, 8, 90se in Zn plating bath at 55℃
c Fe” ion concentration in the HCI pickling bath when immersed (
Fig. 3 is a diagram showing the relationship between appearance, brightness, and dissolution loss (added as FeCl3);

From Fig. 1a, it can be seen that surface stains become significant when the Fe◆3 concentration in the HCI bath exceeds (L5 ge1). Also, from Fig. 2b, the brightness clearly decreases when the Fe◆3 concentration in the HCI bath exceeds 0.5 gi9. It is clear that there is a clear correlation between the staining on the steel plate surface and the Fe' concentration in the pickling bath, and that it can be effectively suppressed by reducing the Fe' concentration to 0.5 gel or less. However, in order to obtain a surface almost equivalent to that of the original plate, it is more preferable to set the Fe''3 concentration to 0.2 g/41 or less.

It is also clear from FIG. 1 that the surface is further cleaned by applying friction such as brushing during water washing after pickling. Note that the same effect can be obtained by brushing with abrasive grains. In addition to brushing, the friction may be performed using a puff or the like.

From FIG. 1c, it can be seen that when the F""6 degree in the pickling bath is low, the melt loss of the steel plate is also reduced. This is the melting of the steel plate by Fe', that is, Fe+ 2 FeC13--
This is because the reaction of +3 FeC12-(1) decreases. Therefore, it is thought that the reduction in stains due to Fe+3 concentration suppression is due to suppression of smut formation and surface activation due to pickling. In addition, the dissolution of Fe by Fe+3 is extremely remarkable, and even at concentrations of Fe' 1 ge1 or higher, even though HCl 2 degrees is constant,
The amount of dissolved Fe increased linearly as the Fe concentration increased. Such a significant effect was much more pronounced than when the He concentration or bath temperature was increased.

Note that this tendency is observed not only in HCl baths but also in H2SO baths.
4. It was also observed in pickling baths such as H3PO4. therefore,
The present invention does not limit the type of acid, and the pickling conditions are generally implemented conditions, i.e., a concentration of 1 to 20%,
The temperature can be arbitrarily selected within the range of room temperature to 50°C, time of 5 to 90 seconds, etc. If the concentration, temperature, and time are below the lower limits, the plating adhesion will deteriorate due to insufficient pickling, and unplated areas will likely occur, and if the upper limits are exceeded, the non-plated surface will easily become dirty due to over-pickling. It is.

During plating operations, the Fe' ion concentration in the pickling bath inevitably increases as the steel plate melts. A part of this is oxidized by air, and Fe+3 in the bath increases. As mentioned above, this is an important factor in contamination of conventional non-plated surfaces.

To reduce the Fe" ion concentration, there are two methods: replacing part or all of the pickling bath with a new bath, or performing electrolytic reduction. However, the former method requires the disposal of effective acid, increases waste acid treatment costs, and The latter is not very preferable because it requires new equipment and other problems.

The simplest and most effective method for reducing Fe is to add reduced iron powder to the pickling bath. By this method, HCI
The Fe' concentration can be effectively reduced without consuming too much. Note that the reaction in this case is the same as in equation (1).

The steel used in the present invention is not limited in its type or size, and is subjected to pretreatment such as degreasing, pickling, and water washing, followed by single-sided zinc-based electroplating in an acid bath.

The acidic plating bath is a sulfate bath, a chloride bath, or a mixed bath thereof, and is usually used at a pH of 1 to 4 and a bath temperature of 40 to 70°C.

Zinc-based plating includes zinc plating, zinc-nickel, zinc-iron, or Or or No.

It also includes alloy plating containing other metals such as GO.1 In the present invention, the type and content of metals other than zinc in the plating layer are not limited. The conditions are also appropriately selected depending on the type of plating and bath composition, and are not prescribed.

<Example> Examples of the present invention will be specifically described below.

(Example 1) snoring 7 ■small q'pr”n 廝圀柘る1b intestine
At 20℃, 3g of reduced iron powder was added and the Fe◆3 concentration in the bath was lowered to 0.1g/b.
Pickling was carried out for 25 seconds in a 5% HC solution, followed by washing with water, and single-sided Zn plating was carried out at 90 g/2 under the following conditions.

(1) Bath composition: Zn5Oa ・7820400 ge
lNa2 SO43011/1 (2) Plating conditions: pH 1.8, bath temperature 55°C, current density 60 A/da2 After this, the presence or absence of dirt or unevenness on the non-plated surface was visually determined, and the color difference was determined as an index of surface cleanliness. The lightness (L) was measured using a meter.

Further, a chemical conversion treatment was performed by a dip method using a phosphate treatment solution manufactured by Nippon Barker Rising (Bonderai) $3030.

The chemical conversion coating was visually inspected and observed using a scanning electron microscope to determine its uniformity and
In addition to determining the density of the crystals and the presence or absence of scratches, the amount of film was also measured. These results are shown in Table 1 along with other Examples and Comparative Examples.

(Example 2) The same steel plate as in Example 1 was degreased and washed with water, and then prepared as in Example 1.
In the same manner as above, pickling was carried out for 15 seconds in a 5% HC solution at 20°C with the Fe concentration in the bath set to 0.2 gifL.
After that, it was washed with water and coated with 20g/m2 of single-sided Zn under the following conditions.
-X1 alloy plating was performed.

(1) Bath composition: NiSO4・66H2O300/Bun Z
nSO41171 (20140g/fLNa2SO44
0gin (2) Plating conditions: pH 1.8, bath temperature 55°C, current density 40A/d set 2 (Example 3) When washing with water after HCI pickling, plating was carried out using a nylon brush with a wire diameter of 0.5 (no abrasive grains). The same treatment as in Example 1 was performed except for brushing.

(Comparative Example 1) The same treatment as in Example 1 was performed except that HCl was used before the reduced iron powder containing 0.9 gin of Fe+3 was added.

(Comparative Example 2) The same treatment as in Example 2 was performed except that HCI was used before the reduced iron powder containing 1.2 g/4 Fe+3 was added.

From Table 1, which summarizes these results.

It can be seen that by lowering the Fe◆3 concentration in the HC1m washing bath, stains on the non-plated surface are eliminated and the chemical conversion properties are improved. Furthermore, by brushing during water washing after pickling, the surface cleanliness is further improved.

From the above, it can be seen that the method of the present invention is extremely effective in obtaining a Zn-based single-sided electroplated steel sheet that is free from smut stains and has a non-plated surface with excellent chemical conversion treatment properties.

[Brief explanation of the drawing]

Figure 1a is a graph showing the relationship between the Fe concentration in the HCIL pickling bath and the appearance of the steel plate surface, and Figure 1b is the same <Fe'
A graph showing the relationship between the concentration and the brightness of the surface of the steel plate, and FIG. 1c is a graph showing the relationship between the same <Fe' concentration and the amount of dissolution of the steel plate.

Claims (2)

[Claims] (1) When manufacturing zinc-based single-sided electroplated steel sheets in an acid bath, the Fe^+^3 ion concentration is 0.5g/
1. A method for producing a zinc-based single-sided electroplated steel sheet, which comprises pickling the steel sheet in a pickling bath of 1 or less. (2) When manufacturing zinc-based single-sided electroplated steel sheets in a pickling bath, the Fe^+^3 ion concentration is 0.5g/
1. A method for manufacturing a zinc-based single-sided electroplated steel sheet, which comprises pickling the steel sheet in a pickling bath of 1 or less, and then rubbing the surface of the steel sheet.