JPH0129873B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a surface-treated steel material that has stable various color tones and excellent corrosion resistance, and is particularly suitable for unpainted applications. (Prior art and its problems) In recent years, in fields such as home appliances, OA equipment, and automobiles,
There is a movement to reduce costs by omitting painting. For this reason, it is desired that steel materials (including steel strips, steel plates, steel pipes, shaped steel, etc.) have further improved corrosion resistance and better design. Known corrosion-resistant steel materials include: (1) Steel materials that have been subjected to electrical Zn plating and then chromate treatment. (2) Steel material that has been electroplated with Zn, then chromate treated, and then coated with an organic resin of 1 to 3 μm. (3) Among the above (1) and (2), steel materials whose plating is Zn-based alloy plating. (4) Of (2) and (3) above, steel materials coated with a silicate film instead of organic resin. etc. However, these steel materials have a grayish-white or yellow-green appearance, and when used unpainted, their uses are limited in terms of design. On the other hand, known steel materials aimed at design are (5) Pre-painted steel sheets or painted after processing. (6) Black chromate treated steel plate. (7) Colored steel sheets by chlorate immersion, molybdate immersion, etc. (8) Steel material colored by electroplating in a Zn-based plating bath consisting of Co, Ni, additives, etc. (Japanese Patent Application Laid-open No. 58-151490, JP-A No. 58-151491)
etc. However, these steel materials (5) are expensive and cannot be welded. (6) has poor corrosion resistance and is expensive because it uses precious metals such as Ag. In case (7), bath management is troublesome and it is difficult to obtain a stable appearance in a short period of time. (8) has a low degree of color development, and uneven appearance tends to occur due to the influence of the liquid flow rate during plating and anodizing. There are problems such as. That is, the current situation is that there is no known steel material that has a design and corrosion resistance suitable for unpainted applications. (Objective of the Invention) An object of the present invention is to provide a steel material that has stable color tone and excellent corrosion resistance and is suitable for unpainted applications. (Structure of the Invention) The surface-treated steel material of the present invention includes a Zn--Ni alloy plating layer containing 10 to 20 wt% of Ni and consisting of a single γ phase as a first layer on the steel material at a rate of 1 to 50 g/m. ² is formed, and then a passive film (Zn oxide,
containing at least one of Zn hydroxide, Zn sulfide, Ni oxide, Ni hydroxide, Ni sulfide, and metallic Ni) with a thickness of 0.01 to 0.5μ. It is characterized by (Embodiment) The shape of the steel material used in the present invention is not particularly limited. The Zn--Ni alloy plating applied as the first layer on the steel material must consist of a single γ phase and contain 10 to 20 wt% of Ni. Here, the γ layer refers to an intermetallic compound having a composition of Ni ₃ Zn ₂₂ or/and Ni ₅ Zn ₂₁ or/and NiZn ₃ . If the Ni content in the plating layer is less than 10 wt%, the η phase of Zn will appear, which not only impairs corrosion resistance but also makes it impossible to uniformly form a passive film on the upper layer. Furthermore, if the Ni content exceeds 20 wt%, a β phase consisting of Ni _x Zn ₁ will appear, making the plating film hard and susceptible to powdering, which is not preferable. Also, even if Ni is in the range of 10 to 20 wt%,
If the γ phase is not a single phase, a passive film cannot be uniformly formed on the surface. Further, if the amount of the first layer adhered is less than 1 g/m ² , the surface of the steel material cannot be uniformly coated, and if it exceeds 50 g/m ² , the first layer will peel off during processing, which is not preferable. 1st
After forming the plating layer, Zn and/or
Alternatively, a passive film containing at least one of Ni oxides, hydroxides, and sulfides is formed with a thickness of 0.01 to 0.5μ. The method for forming the passive film may be any method such as immersion treatment with an oxidizing solution (nitric acid etching, etc.), anodic treatment, hydrogen sulfide treatment, etc. If the thickness of the passive film is less than 0.01μ, it will not be possible to cover the first layer surface completely uniformly, and
If it exceeds 0.5μ, the passive film tends to peel off due to processing, etc., which is not preferable. The first layer of the present invention is essential for obtaining red rust resistance and forming a passive film, and the passive film further improves red rust resistance, and at the same time, the color tone of the passive film creates a design. It has the effect of increasing sex. The passive film has a color tone such as black for NiO(OH), Ni ₂ S, and Zn oxide, and blue for NiOH, and the design can be controlled by changing its composition. Furthermore, no significant difference is observed in the influence of the composition of the passive film on red rust resistance as long as the film is uniformly formed. This product exhibits a high resistance to the formation of red rust, but under severe corrosive environments white rust will form relatively early. This is thought to be strongly influenced by crystal water (for example, 2NiOOH=Ni ₂ O ₃ .H ₂ O) contained in the passive film, but it is not clear. This product is primarily intended for unpainted applications that require a particularly attractive design. Therefore, the occurrence of white rust is undesirable. Furthermore, since the passive film as it is has some interference color, it is insufficient in terms of design for some uses. The chromate film on the passive film is formed for the purpose of reducing this interference color and further imparting white rust resistance. The amount of chromate film deposited is 10 to 300 mg/m ² , particularly preferably,
It is 15-200mg/ ^m2 . If it is less than 10 mg/m ² , almost no white rust resistance will be obtained, and if it exceeds 300 mg/m ² , the chromate film itself will begin to exhibit interference color. By the way, when using steel without painting, silk printing is often performed directly on the steel, but if the surface of the steel is coated with oxides, hydroxides, sulfides, etc., depending on the type of printing ink, Its adhesion deteriorates significantly. Therefore, it is not preferable for silk printability to have a passive film or a chromate film on the outermost surface. In order to improve this, an organic resin of 0.2% was added as the upper layer of the passive film or chromate film.
Form to a thickness of ~5μ. As the organic resin film, acrylic resin, epoxy resin, and polyester resin are preferable. If the resin film thickness is less than 0.2 μm, not only the silk printability will not be improved, but also the resin film itself will exhibit an interference color, which is not preferable. If it exceeds 5μ, welding becomes impossible and is disadvantageous in terms of cost. Forming a resin film has the advantage that white rust resistance is improved, interference color can be completely eliminated, and variations in appearance due to differences in the conditions for forming the passive film are also significantly reduced. Next, the present invention will be specifically explained using examples. (Example 1) A test material was obtained in which a Zn--Ni alloy plating layer (first layer) consisting of a single γ phase was formed on the surface of a steel plate, and a passive film was further formed on the top layer. At that time, the thickness of the first layer was changed between 0.8 g/m ² and 55 g/m ² ,
The thickness of the first layer, the appearance, and the peeling state of the first layer after processing were tested. The results are summarized in Table 1. However, peeling of the first layer after processing was evaluated by performing cup drawing at a drawing ratio of 2 and then tape peeling.

[Table] ◎ No peeling
○ Almost no peeling
× Severe peeling If the amount of the first layer adhered is outside of 1 to 50 g/ ^m2 , uneven appearance may occur and peeling during processing will increase, but the first layer and the passive film are within the scope of the present invention. Certain test materials have good appearance and corrosion resistance. (Example 2) Test materials (No. 1 to No. 1) in which a Zn-Ni alloy plating layer (first layer) and a passive film were formed on the surface of the steel plate.
7) was created. Passive film is NaNo ₃ 20g/,
It was formed by anodizing in a solution containing 100 g of Na ₂ SO ₄ and 3 g of NaNo ₂ , PH=10, and a solution temperature of 50°C. Corrosion resistance test (SST JIS
Z2371) was carried out. The results are summarized in Table 2. Sample materials No. 2 to No. 4 corresponding to the present invention have a uniform black appearance and exhibit excellent corrosion resistance, but the other sample materials are inferior in color tone and corrosion resistance.

[Table] (Example 3) First layer: Zn88wt%, Ni12wt%, adhesion amount 20
A steel plate with a Zn-Ni alloy plating layer of g/m ² ,
Furthermore, a passive film of varying thickness was applied by nitric acid etching to obtain a test material. Corrosion resistance tests (SST JIS Z 2371) were conducted for each sample material. The results are shown in Figure 1. As is clear from FIG. 1, good corrosion resistance can be obtained when the thickness of the passive film is 0.01 to 0.5 μm. (Example 4) As the first layer, γ phase single phase, Zn87wt%, Ni13wt
Test materials were obtained by forming a passive film with varying film thickness and composition on a steel plate plated with a Zn--Ni alloy with a coating weight of 20 g/m ² . Each sample material was tested for appearance and corrosion resistance (SST JIS Z 2271). The results are summarized in Table 3. As is clear from Table 3, according to the present invention, stable color tone is exhibited,
Moreover, a surface-treated steel material with excellent corrosion resistance can be obtained.

【table】

[Table] (Example 5) The first layer consists of a single γ phase on a steel plate.
20 Zn-Ni alloy plating with Zn88wt% and Ni12wt%
Plated with a coating weight of g/m ² and then coated with a thickness of 0.06μ
A passive film was formed, and on top of that a chromate film was applied in varying amounts to create test materials.
Corrosion resistance tests (SST) were conducted on these test materials.
JIS Z 2371). Corrosion resistance was evaluated by white rust generation time. The results are shown in FIG. From Figure 2, the amount of chromate film deposited is 10 to 300 as Cr.
It can be seen that white rust resistance is good within the mg/m ² range. (Example 6) Zn82wt% and Ni18wt as the first layer on the steel plate
%, Zn-Ni alloy plating consisting of a single γ phase is 20
Plated with a coating weight of g/m ² and then coated with a thickness of 0.04μ
A passive film was formed, and on top of that a chromate film was applied in varying amounts to create test materials.
These test materials were tested for appearance and interference color. The results are summarized in Table 4. It can be seen that when the amount of chromate film deposited is in the range of 10 to 30 mg/m ² as Cr, interference colors are small and a good appearance is exhibited.

【table】

[Table] However, ○ small interference color, △ slightly large interference color, × large interference color (Example 7) On the steel plate, the first layer was γ phase single phase, Zn87wt%,
Zn-Ni alloy plating with Ni13wt% deposited amount 20g/ ^m2
A passive film with a thickness of 0.07 μm was formed as a second layer. Various test materials were prepared by applying a chromate film and an organic resin film to this steel plate.
Each sample material was tested for silk printability. Each sample material was silk-printed to a film thickness of 10μ±2μ, and 100 squares were marked at 1mm intervals.
Evaluation was made based on the residual rate of ink after tape removal. The results are summarized in Table 5. The sample material with the amount of chromate film deposited that corresponds to the present invention and the organic resin film formed thereon exhibits excellent silk printability.

【table】

[Table] (Example 8) On a steel plate, γ phase single phase, Zn86wt%,
Zn-Ni alloy plating with Ni14wt% deposited amount 15g/ ^m2
NiO(OH) 42%, Ni(OH) 2 9%, Zn(OH) 2 49 were plated with NiO(OH) 42%, Ni(OH) ₂ 9%, and Zn(OH) ₂ 49 formed by anodization as the second layer.
% of the passive film was formed with varying thickness.
An epoxy-modified acrylic resin film with a thickness of 2 μm was further formed on this steel plate. In this way, various test materials were prepared, including those in which the thickness of the passive film was varied in the range of 0.01 to 1 μm, and those on which an epoxy-modified acrylic resin film was further formed. Regarding these test materials, L*, a*, and b* were measured using a color difference meter. The results are shown in FIGS. 3, 4, and 5. 3rd~
From FIG. 5, it can be seen that when a resin film is formed, a stable color tone is exhibited regardless of the thickness of the passive film. (Effects of the Invention) According to the present invention, a plated steel material having sufficient corrosion resistance and a color tone with excellent designability can be obtained.

[Brief explanation of drawings]

FIG. 1 is a graph showing the test results of Example 3, FIG. 2 is a graph showing the test results of Example 5, and FIGS. 3, 4, and 5 are graphs showing the test results of Example 8.

Claims (1)

[Claims] 1. A Zn--Ni alloy plating layer containing 10 to 20 wt% Ni and consisting of a single γ phase is formed on the surface of the steel material at an adhesion amount of 1 to 50 g/m ² , and an upper layer is further formed on the surface of the steel material. A passive film containing at least one of zinc oxide, zinc hydroxide, zinc sulfide, nickel oxide, nickel hydroxide, nickel sulfide, and metal nickel is formed with a thickness of 0.01 to 0.5μ. A highly corrosion-resistant surface-treated steel material suitable for unpainted applications. 2. On top of the passive film, add a chromate film,
The steel material according to claim 1, which is formed to have a coating amount of chromium of 10 to 300 mg/m ² . 3. The steel material according to claim 1, further comprising an organic resin film having a thickness of 0.2 to 5 μm formed on the passive film. 4. Claim 2, in which an organic resin film with a thickness of 0.2 to 5 μm is further formed on the chromate film.
Steel materials listed in section.