JPH05239686A - Zn electroplating method for cr steel - Google Patents

Abstract

PURPOSE:To remove a passive film on the surface of a Cr steel and to increase the adhesion of a plating film, before Zn electroplating is applied to a Cr steel, by subjecting the Cr steel to anodic electrolysis in a plating bath of the same kind as that of the plating bath. CONSTITUTION:A steel strip 2 constituted of a Cr steel contg. about >=5wt.% Cr is passed through a plating bath 1 and is continuously applied with Zn electroplating to improve the corrosion resistance of the relatively inexpensive lower Cr steel. In inlet parts 1 to 2 or the like of the plating tank 1 of the continuous electroplating line of the steel strip 2, the steel strip 2 is subjected to anodic electrolysis. This anodic electrolysis is executed preferably under the conditions of >=3V voltage and >=0.4sec electrolyzing time. In this way, a passive film on the surface of the steel strip 2 of the Cr steel is removed in the acidic plating bath. Next, in the remaining zones 3..., the polarity is inverted, and usual electroplating is executed.

Description

Detailed Description of the Invention

[0001]

The present invention relates to SUS410 steel, SU
Zn or Zn-Fe, Zn on Cr steel material such as S304 steel
-Zn to Cr steel for electroplating Zn alloy such as Ni
System electroplating method.

[0002]

2. Description of the Related Art As a steel material having excellent corrosion resistance, SUS30
High-grade Cr steel materials (stainless steel) such as No. 4 steel and SUS310 steel are well known. However, these high-grade Cr steel materials are expensive. Therefore, a relatively inexpensive low-grade Cr steel material such as SUS410, which is electroplated with Zn, has been attracting attention as a substitute for a high-grade Cr steel material. If higher corrosion resistance than high-grade Cr steel is required,
A Zn-based electroplated Cr steel material having a high-grade Cr steel material as a base material can be used.

However, the surface of the Cr steel material is covered with a strong passive film, which hinders the adhesion of the plating film. Therefore, it is necessary to remove the passivation film before plating the Cr steel material, and for this purpose, the passivation dissolution of Cr is utilized. For example, JP-A-2-1732
Japanese Patent No. 91 discloses a method of removing a passive film on the surface of a steel material by subjecting a Cr steel material before Zn-based electroplating to anodic electrolysis in an acidic aqueous solution such as hydrochloric acid.

[0004]

This method is very effective in removing the passive film and contributes to the improvement of the adhesion of the plating film. However, if this is to be carried out, for example, on a continuous electroplating line for steel strips, an acid solution electrolysis facility must be newly installed in the line, which requires a large amount of capital investment.

The object of the present invention is not only to remove the passivation film covering the surface of the Cr steel material to perform plating with excellent film adhesion, but also to perform it at low cost even on a continuous electroplating line for steel strips. Another object of the present invention is to provide a Zn-based electroplating method for Cr steel material which is low in running cost.

[0006]

Z for Cr steel of the present invention
The n-based electroplating method is characterized in that, before performing Zn-based electroplating on a Cr steel material, the Cr steel material is subjected to anodic electrolysis in a plating bath of the same kind as the plating bath used for the electroplating.

When carrying out in a continuous electroplating line for steel strip, anodic electrolysis is carried out at the entrance of the plating tank, and
It is preferable that the voltage in the anodic electrolysis be 3 V or more and the electrolysis time be 0.4 seconds or more.

[0008]

The greatest feature of the method of the present invention is that before electroplating,
The purpose is to perform anodic electrolysis using a plating bath of the same type as the plating. By using a plating bath of the same kind as plating for anodic electrolysis, for example, in a continuous electroplating line for steel strips, anodic electrolysis can be carried out at the inlet portion of the plating bath, thus eliminating the need for new equipment investment. Further, even if an electrolytic bath is newly installed on the entrance side of the plating bath, the bath supply system for the plating bath can be diverted, so that the facility cost is extremely low. In addition, the metal lines present in the plating bath improve the electrical conductivity in the electrolytic bath and reduce the power usage.

FIG. 1 shows a typical embodiment in which the method of the present invention is applied to a continuous electroplating line for steel strips. Plating tank 1
A large number of electrodes are arranged in the longitudinal direction. The inside of the tank is divided into a plurality of zones (12 in FIG. 1) by these electrodes.
Zone). In the method of the present invention, the steel strip 2 passing through the tank is subjected to anodic electrolysis in the zones 1 and 2 at the inlet, that is, in the opposite direction, and electroplating is performed in the remaining zones. By changing the number of electrodes used for anodic electrolysis, the electrolysis time can be adjusted even if the line speed is constant.

In the method of the present invention, the mechanism by which the passivation film covering the surface of the Cr steel material is removed is the same as in the case of normal acid solution electrolysis because the plating bath is a strong acid solution. There is a problem that the surface of the counter electrode (electrode for plating) is plated when anodic electrolysis is performed in the plating bath. However, if the steel plate is usually plated in the plating bath after electrolysis, the metal plated on the counter electrode surface Are easily dissolved and removed.

The current continuous electroplating line has a line speed of 50 m / min or more. When the method of the present invention is carried out in this continuous electroplating line, the time during which the steel strip passes through the plating bath for electrolysis is short. Anode electrolysis is usually 1
V voltage is possible, but in continuous electroplating line,
It is preferable to apply a voltage of 3 V or more because it is not possible to secure a sufficient passage time of the plating bath for electrolysis. In addition, even if a voltage of 3 V or more is applied, if the electrolysis time is less than 0.4 seconds, a passive film may remain, resulting in uneven plating. Therefore, the electrolysis condition in the continuous electroplating line is 3V or more,
4 seconds or more is desirable.

The Cr steel material to which the method of the present invention can be applied is, for example, a thin plate material containing 5% by weight or more of Cr.

Zn-based electroplating refers to pure Zn electroplating and Zn alloy electroplating such as Zn-Ni and Zn-Fe.

The plating bath used for electrolysis and the plating bath used for electroplating are necessarily the same when they are carried out in the same bath. When they are carried out in different tanks, they need not necessarily be the same, and for example, a plating bath in which an electrolyte such as Na ₂ SO ₄ is dissolved to improve electric conductivity can be used for electrolysis. The plating bath may have a metal ion concentration of 0.4 mol / liter.

[0015]

EXAMPLES Examples of the present invention will be described below.

Using a continuous electroplating line,
Zn-based electroplating was performed on a 0.8 mm SUS410L steel strip. The main steps are alkaline degreasing, water washing, anodic electrolysis,
Electroplating. Table 1 shows degreasing conditions, electrolysis conditions, and plating conditions. The electrolysis was performed using the inlet part in the plating bath (see FIG. 1), and the electrolysis time was adjusted by changing the number of electrodes used and a slight change in the line speed. The standard line speed is 60 m / min.

[0017]

[Table 1]

After plating, the adhesion of the plated film was investigated by a cellotape peeling test after overhanging Erichsen 7 mm and evaluated according to the criteria of Table 2. The evaluation results are shown in Table 3.

[0019]

[Table 2]

[0020]

[Table 3]

If anodic electrolysis is not performed before electroplating, the adhesion is extremely poor. If anodic electrolysis is performed before electroplating, the adhesion will be dramatically improved. However, when the electrolysis voltage is less than 4V and the electrolysis time is less than 0.5 seconds, 4V or more,
Adhesion is slightly reduced as compared with 0.5 seconds or longer.

[0022]

As is apparent from the above description, in the Zn-based electroplating method for Cr steel according to the present invention, anodic electrolysis is performed using a plating bath before plating. Anodic electrolysis using a plating bath exhibits the same passivation film removal action as ordinary pickling electrolysis. Therefore, good plating film adhesion can be obtained. In addition, plating equipment can be used for anodic electrolysis, the equipment cost is low, and the electric conductivity during electrolysis is improved by the metal ions in the plating bath, so the running cost is also low.
Therefore, a high quality electroplated Cr steel material can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a schematic view of a continuous electroplating bath showing one embodiment of the method of the present invention.

[Explanation of symbols]

 1 plating tank 2 steel strip

Claims (2)

[Claims] 1. A Zn steel for Cr steel, characterized in that, prior to Zn-based electroplating of Cr steel, the Cr steel is subjected to anodic electrolysis in a plating bath of the same kind as that used for the electroplating. -Based electroplating method. 2. When performing Zn-based electroplating on a steel strip made of a Cr steel material in a continuous electroplating line, the steel strip before plating is subjected to an anode under the condition of 3 V or more and 0.4 seconds or more at the inlet portion in the plating tank. A Zn-based electroplating method for Cr steel, characterized by electrolyzing.