JPS6077988A - Manufacture of galvanized steel sheet with blackening resistance - Google Patents

Abstract

PURPOSE:To obtain a galvanized steel sheet preventing a blackening phenomenon during storage by adding specified times as much Ni ions as Pb ions contained in a galvanizing bath to the bath, galvanizing a steel sheet in the bath, and chromating it. CONSTITUTION:To a galvanizing bath are added 5-500 times as much Ni ions as Pb ions contained in the bath as an impurity. The amount of Ni ions to be added is <=1/25 time the amount of Zn ions and <=10g/l. A steel sheet is galvanized in the electrolytic bath, and it is chromated in an aqueous soln. contg. Cr<+6> as the principal component. When a galvanized steel sheet obtd. by this method is stored in a piled state in a wet atmosphere at a high temp., the blackening phenomenon of the surface is remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention provides high mj! ia This article describes a method for manufacturing electrolytic Zn-plated steel sheets that prevents the blackening phenomenon that mainly occurs in electrolyzed Zn-plated steel sheets that are stacked and stored in harsh environments.

(Prior art) Electric Zn-plated pan steel sheets are manufactured using chromate treatment to completely prevent zero rust (improved corrosion resistance) that occurs when exposed to corrosive atmospheres, or to completely improve paint adhesion. . However, when electrolytic Zn-plated steel sheets are stacked and stored in a high-temperature, humid, corrosive environment, a phenomenon in which part or all of the steel surface turns black or brown (blackening phenomenon) occurs, which significantly reduces the commercial value. There was a problem. This blackening phenomenon occurs due to the accumulation of electrical Zn.
It is thought to be caused by oxygen concentration cells that have entered the minute gaps between the plated steel plates, and is said to be more likely to occur in thin-layer Zn-plated areas of electrolytic Zn-plated steel plates that have been generally chromate-treated. The blackening phenomenon is also caused by the rise in temperature and humidity during storage of steel sheets.

This is further promoted by anions in the electrolytic Zn plating (804-', C1-, etc.) or impurity ions IS04'rGZ-, etc. in the chromate solution remaining in the coating on the surface of the copper plate. However, as measures to prevent blackening of electrolytic Zn-plated steel sheets, measures have been taken to strengthen the edges of the electrolytic Zn-plated plate and impurity ions in the chromate solution. However, such a blackening prevention effect is not necessarily sufficient, and is not satisfactory when stored in a highly humid environment or in a region.

(Purpose of 'i?+light) In consideration of the above facts, the present invention has developed an electric Zr+plated steel frame that completely prevents the blackening phenomenon. l! ! The purpose is to provide all drawing methods.

(11 Features and Effects of the Invention) However, the inventors of the present invention aimed to manufacture electric Zn-plated steel sheets that suffer from the blackening phenomenon in high-humidity environments, etc. Regarding the factors of fi′! i
As a result of careful consideration, we found that 7j+ was largely influenced by Pb ions contained in the Zn plating electrolytic bath. Figure 1 shows the effect of Pb ions contained in a plating bath on the blackening of an electrolytically Zn-plated steel sheet.
The blackening resistance is improved by reducing the content to 2 ppm or less (preferably 0.1 ppm or less). In addition, in the first section, electrolytic galvanized steel sheets manufactured by fR using a plating bath containing Pb ions as impurities were treated with chromate treatment.
After each nodule was stacked and stored at 70°C for 24 hours,
The plated gun plate surface is L″'a based on JIS Z8730.
A "b" color yarn was used, and the degree of blackening was evaluated based on lightness (L"). Such an improvement is due to the fact that the P3jF is parallel to the plate surface of the plated steel plate, as shown in Figure 2, which compares the preferential crystal orientation of the plated layer when each electrolytic Zn-plated steel sheet is manufactured using a Zn plating bath with different P3jF. This can occur by increasing the total preferred orientation of the (0002) plane.I'l
) Ions are introduced when the electrode is dissolved in the plating bath, and even the high-purity electrical Zn metal used for soluble Zn electrodes contains about 20p pnl of PB, and even insoluble PB. 8: Pb-S used as electrode material
Even in n-type materials, trace amounts of Pb dissolution are considered unavoidable.

Furthermore, the present inventors have also discovered from experiments conducted with the addition of various metal ions that the (0002) plane, which has been reduced due to the dissolution of Pb ions, can be recovered by the addition of Ni ions.

The present invention was constructed based on these findings, and its gist is that all 4 surfaces of the steel plate were cleaned.
5 to 50 of the amount of Pb ions contained as impurities
Electrolytic Zn plating is carried out in a Zn plating electrolytic bath containing 725 or less of Zn ion amount and 10' / less at 0 times,
This is a method for manufacturing a blackening-resistant electrolytic Zn-plated steel sheet, which is then subjected to chromate treatment in an aqueous solution containing Or'fc as a main component.

The present invention will be explained in more detail below.

The steel plate used as the plated plate is degreased, washed with water, and pickled.

The steel sheet is cleaned and activated through the usual pretreatment process such as washing with water, and then placed in a zinc oxide-conductive salt (sodium sulfate, ammonium, etc.) plating bath. The present invention is not limited to such plating baths, however,
Pb contained in the electrolytic Zn plating bath is a harmful component that enters from the electrode and reduces the preferred crystal orientation of the (0002) plane, causing blackening. In the present invention, 1. In order to completely solve this problem, we have developed a Zn plating bath (
Add CNi ions. Table 1 shows the results of investigating the preferential precipitation of the (0002) plane by X-ray analysis when 80% of metal ions were added to the electrolytic Zn plating bath. In other words, the addition of Ni ions completely suppresses the influence of P b ions (
0002) It is an effective component for restoring the preferred orientation of the plane, but its effect f(j4) corresponds to the I゛1] ion-containing material, and there is a fee to add Ni ions, which is a little less than 5 times. A significant amount of N1 ion cannot be obtained, but an excessive amount of N1 exceeding 500 times
For ions, the saturation point of the effect is reached, and Zn and N
A local battery is generated during the period i, which inhibits the corrosion resistance of the Zn plating layer and also the insolubilization reaction during chromate treatment, thereby degrading the corrosion resistance of the chromate coating. Furthermore, the present invention 1d, Ni
In order to prevent deterioration of corrosion resistance due to addition, it is necessary to set an upper limit of 10'/25 or less of the amount of IZn ions. When Ni ions are added to the Zn plating bath in excess of these upper limits of 7, Z
An n-plated layer is electrodeposited. As a result, blackening resistance is improved, but local battery formation deteriorates corrosion resistance in a corrosive environment, local deterioration of corrosion resistance due to uneven romate coating (white rust occurs), and further deterioration of phosphoric acid treatment. This is not desirable as it causes many problems such as

Further, a Zn-plated steel sheet electrodeposited using a Zn-plating electrolytic bath regulated under the conditions described above is subjected to a chromate treatment using an aqueous solution containing Cr''k as a main component after washing with water.

This chromate treatment is carried out for the purpose of improving the corrosion resistance of boxes and Zn-plated steel sheets, especially preventing the occurrence of white rust when exposed to corrosive environments, and improving paint adhesion.In the present invention, this chromate treatment condition is is not particularly specified, but for example, as shown in 1 below, it is difficult to use the entire Lomate bath.

(3) 5-50 /10r03 bath, (bl (10-1
00/l) Or('3(IQ ~300/1)
Treatment baths such as silica sol-based baths, (c) (10-100'/l) ammonium chromate-water-soluble resin (e.g., copolymer of polystyrene-maleic acid, etc.) baths are used. Electrolytic Zn-plated steel sheets Using these chromate baths, immersion treatment, spray treatment, 'FL solution treatment,
The treatment is carried out at a temperature of ~80°C.

After this treatment, a chromate adhesion control process is performed to remove excess chromate by using +C, O-lue aperture or high-pressure gas to reduce the Cr adhesion to a predetermined level. 50C~1.80 in vain
A dry plating treatment is carried out at a temperature of 8 degrees Celsius, and the product is washed.

〔Example〕

In order to clarify the effects of the method of the present invention, the following examples are shown.

Cold-rolled steel sheet metal with a thickness of 0.8 mm, degreased in 3% sodium silicate at a current density of 7.5"+Jn? for 3 seconds, using a 7.5% 112 SO4 bath for the water washing ridge, After carrying out the entire pickling process for 5 seconds at room temperature, and after the activation pretreatment which is normally carried out in electrolytic Zn plating, the method of the present invention was carried out under the conditions shown in Table 2, and its performance was evaluated. Please compare this with a comparative example using the conventional method.

As a result, as shown in Table 2, the performance improvement effect achieved by the method of the present invention was remarkable.

(Effects of the Invention) As described above, when the electrolytic Zn-plated field boards manufactured by the method of the present invention are stored in a stacked state in a high humidity atmosphere, the surface blackening phenomenon occurs. is significantly reduced.

[Brief explanation of the drawing]

Figure 1 is a graph showing the influence of black discoloration on the amount of Pl) ions contained in the Zn plating bath. 2 is a graph showing the results of X-ray diffraction on the preferred crystal orientation of the plating layer. Agent Patent attorney Masamitsu Akizawa and 2 othersContinued from page 1 ■Inventor Masatsugu HorishitaTo Kitakyushu City 1-1-1 Edamitsu, Hatto-ku Inside Nippon Steel Corporation's Hakake Steel Works

Claims (1)

[Claims] (1) Surface-cleaned steel sheet i, 5 to 500% of the amount of PB ions contained in the Zn plating bath with Ni ions as impurities.
The amount of Zn ions is /2. A blackening-resistant electrolytic Zn-plated steel sheet characterized by electrolytic Zn peeling in a Zn plating electrolytic bath containing 10'/ or less, and then chromate treatment in an aqueous solution containing Or''k as a main component. fR
Construction method.