JP2003183800A - Hot-dip zinc-base coated steel sheet superior in blackening resistance and corrosion resistance, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot-dip zincing and chromated steel sheet which is superior in corrosion resistance, hardly generates blackening, and can be used in service even without being painted, and to provide a simplified method for manufacturing the same. <P>SOLUTION: The zincing and chromated steel sheet comprises containing 2-15 mass% Al on average in the plated layer, and having concentrated Ni and/or Ti on the outermost surface of the plated layer. The manufacturing method is characterized by treating the steel sheet with the chromating liquid containing Cr<SP>3+</SP>, Cr<SP>6+</SP>, and etching ions of a predetermined quantity ratio. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromate-treated hot-dip galvanized steel sheet having excellent blackening resistance and corrosion resistance, which is suitable for use in the fields of building materials, home appliances and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets are widely used in fields such as automobiles, building materials, and home appliances. In the conventional hot-dip galvanized steel sheet, generally, after the hot-dip galvanizing bath containing Al is plated, the zinc adhesion amount is controlled by a gas drawing method or the like. A zinc bath has also been proposed for improving the coating property, corrosion resistance, and workability of such a hot-dip galvanized steel sheet or for imparting them. For example, 1-8
No. 069 contains 0.2 to 17.0% of Al and 0.
A galvanized steel sheet having excellent workability and improved corrosion resistance by using a prior art zinc bath containing 03-0.15%, Cu 0.1-0.3% and Pb 0.02-0.15%. However, if the coating property is insufficient, Al is added to 15 to 2
5 wt%, Mg 0.05-2.0 wt%, Sb 0.00
Z containing 5 to 0.1 wt% and Pb in an amount of 0.01 wt% or less
It has been proposed to use an n-Al-Mg-based plating bath.

By the way, in some applications such as building materials and home appliances,
Although the hot-dip galvanized steel sheet is often used unpainted, the hot-dip galvanized steel sheet has a problem that white rust is likely to occur, and it is also required to have a beautiful appearance when unpainted. Therefore, the surface of the plated steel sheet is generally subjected to a chromate treatment whose main purpose is to prevent the occurrence of white rust. However, it is known that the chromate-treated hot-dip galvanized steel sheet product causes a so-called black discoloration phenomenon in which the surface locally discolors to black gray during storage or transportation, and the plating appearance is significantly impaired.

The black discoloration that occurs in this chromate-treated zinc-based plated steel sheet is mainly due to zinc oxide, and A in the plating layer
This is because l, Pb, etc. diffuse into the plating surface and convert ZnO existing on the plating surface into oxygen-deficient ZnO _1-X , which is visually observed in black gray.
Further, Cu or Mg contained in the zinc bath to improve the corrosion resistance accelerates blackening of the chromate-treated surface.

It has been proposed to carry out a treatment for improving the blackening resistance before or after the chromate treatment. For example, in JP-A-59-177381, a hot-dip galvanized steel sheet is immersed in or sprayed with a solution containing Ni or / and Co ions before being chromated. In this method, blackening resistance is improved, but corrosion resistance is not obtained. In addition, JP-A-4-297562
No. 4.0 to 7.0 wt% Al and 0.01 wt% Pb
% Or less and Sn in an amount of 0.005 wt% or less, after plating using a hot dip galvanizing bath and before chromate treatment,
It has been proposed to prevent blackening by performing a skin pass with an elongation of 0.3 to 2.0%. However, this method has a problem that stable plating appearance and material characteristics cannot be obtained depending on the skin pass reduction ratio.

Al 0.1-0.3 wt% and Pb 0.05-as proposed in JP-A-11-335866.
The plating surface plated with 0.3 wt% zinc bath is 5-5
In the chromate treatment in which the Pb in the outermost layer is controlled to a constant amount by performing the chromate treatment with the amount of 0 mg / m ² , the blackening resistance is improved to some extent, but the corrosion resistance is lowered and white rust is easily generated.

A constant Cr ³⁺ / Cr ⁶⁺ molar ratio
JP-A-7-54156 discloses a method of forming a chromate film by using a chromate solution containing one kind of metal ion such as 1, Ni, Co, etc. to improve the corrosion resistance and the blackening resistance. Depending on the metal ion species, a plating layer and a local battery may be formed, and corrosion resistance may be significantly reduced. Also, a method of drying the chromate film after chromate treatment proposed in JP-A-5-33157 at 150 ° C. or higher, or a reducing agent (ethanol, butanol, hydrogen peroxide, etc.) proposed in JP-A-5-140762. The method of applying / drying an aqueous solution containing is increased in the number of steps and constraints, and improvement in the production line is desired.

[0008]

DISCLOSURE OF THE INVENTION In view of the above-mentioned conventional techniques, the present invention provides a chromate-treated hot dip galvanized steel sheet which is excellent in corrosion resistance, hardly causes blackening, and can be used even without coating, and a steel sheet of the same. It is intended to provide a manufacturing method.

[0009]

The inventors of the present invention have studied the combination of the addition of the third element to the hot dip galvanizing bath and the chromate treatment after plating. Ni and / or selected from metal elements
Alternatively, the chromate-treated hot dip galvanized steel sheet in which Ti is exposed at a specific ratio and integrated with the chromate layer interface is
It was found that it is excellent in blackening resistance and corrosion resistance. In such a chromate-treated hot-dip galvanized steel sheet, hot-dip galvanized plating containing Al and Ni / Ti in specific amounts contains a specific amount ratio of etching ions to trivalent and hexavalent chromium ions. The inventors have found that they can be easily produced by treating with a chromate solution, and have completed the present invention.

That is, according to the present invention, a steel sheet having a hot-dip galvanized layer and then a chromate layer on the surface,
The hot-dip galvanized layer has an average thickness of 2 to 15 ma.
It contains ss% Al, and the outermost surface of the plating layer has
Provided is a chromate-treated zinc-based plated steel sheet in which concentrated Ni and / or Ti is present and which is excellent in blackening resistance and corrosion resistance.

Further, according to the present invention, there is provided a steel sheet having a hot-dip galvanized layer and then a chromate layer on the surface, wherein the hot-dip galvanized layer has a plating layer average of 2 to 15 mass%.
Ni and / or Ti which contains Al and is concentrated to 0.002 to 0.2 mmol / m ² in terms of metal at the outermost surface portion of the plating layer from the interface with the chromate layer to a depth of 50 nm. The present invention provides a chromate-treated zinc-based plated steel sheet which is excellent in blackening resistance and corrosion resistance. The total content of Ni and / or Ti in the plating layer is about 0.003 to 0.15 mass%.

Further, according to the present invention, the steel sheet is made of Al of 2 to 15
mass% and 0.005 to 2 mass% of Ni and / or
Alternatively, plating is performed using a hot dip galvanizing bath containing Ti, and then trivalent and hexavalent chromium ions and etching ions are added at a mass ratio of etching ions / chromium ions of 0.028 to 0.1. Provided is a method for producing a chromate-treated zinc-based plated steel sheet excellent in blackening resistance and corrosion resistance, which is treated with a chromate solution containing the same. The etching ion is preferably one or more selected from the group consisting of sulfate ion, nitrate ion, fluorine ion, chlorine ion, phosphate ion and perchlorate ion.

According to this method, it is possible to form a structure in which Ni and / or Ti are unevenly distributed on the outermost surface of the plating layer as described above. The hot dip galvanizing bath preferably further contains 0.0005 to 0.5 mass% of misch metal.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The chromate-treated zinc-based plated steel sheet according to the present invention has a hot-dip zinc-based plating layer and then a chromate layer on the surface of the steel sheet. The plating layer in the present invention is A
1 to 2 to 15 mass% of the plating layer on average. In addition, the plating layer, together with Al, contains Ni and / or Ti (Ni
It may be abbreviated as / Ti), and it is important that concentrated Ni and / or Ti is present in the outermost surface portion of the plating layer. This ensures the blackening resistance and corrosion resistance of the chromate-treated zinc-based plated steel sheet. Furthermore, the plating layer in the present invention is 50 n from the interface of the plating layer with the chromate layer, as will be described later in detail.
In the outermost surface portion up to the depth of 0.002 to 0.
It is preferable to have an unevenly distributed portion of Ni / Ti concentrated to ² mmol / m ² .

The chromate-treated zinc-based plated steel sheet of the present invention having the above-mentioned structure can be obtained by using a molten zinc-based plating bath having a specific composition and a chromate solution having a specific composition. Hereinafter, the present invention will be described in detail along with the manufacturing method including the above-mentioned configuration. The steel sheet (base material) is not particularly limited as long as it is generally plated with hot-dip zinc.
For example, cold rolled steel sheets, high tensile steel sheets, ultra low carbon steel sheets, etc. can be widely used.

The hot-dip zinc-based plating bath used in the present invention (hereinafter also simply referred to as a plating bath) is 2 to 15 mass% of A.
Including l. If the plating bath contains 2 mass% or more of Al, it is possible to form a eutectic structure in the plating layer and improve the corrosion resistance. When the Al amount exceeds 15 mass%, dross (slag) increases and the plating quality tends to deteriorate.

In the plating layer, together with the above Al,
In order to prevent blackening, 0.005 to 2 mass% of Ni and / or Ti is contained in total. Here, the present inventors have variously studied the behavior of Ni / Ti in the plating layer, and have obtained the following findings. Ni / Ti in plating layer
In order to investigate the concentrated morphology of Ni, the plating layer was analyzed in the depth direction by GDS (Glow Discharge Spectroscopy), taking as an example the case where Ni was contained in the plating layer at an average of 0.05 mass%. The following were sampled for analysis. Plating layer without chromate, Chromate layer on plating layer but poor blackening resistance, Chromate layer on plating layer, good blackening resistance and corrosion resistance

First, the plating layer (without chromate treatment)
Observation of the depth direction of Ni of the Ni (Ti) is 2 near the plating outermost surface and in the vicinity of the substrate (steel plate) -plating interface.
Peaks indicating uneven distribution at the locations were observed. Of these two peaks, a GDS chart in the vicinity of the outermost plating surface (or the chromate layer side) of each sample was measured in order to study the unevenly distributed portion (peak) close to the outermost plating surface. These are shown as FIGS. ~ In any of the samples, Ni is Z near the plating surface.
Although a peak is seen at almost the same position as n, it was found from detailed observation of the figure that the Ni concentration behavior of was different from and.

Specifically, in the sample in which the blackening phenomenon occurs in the chromate layer (FIG. 2), as in the sample only in the plating layer (FIG. 1), the Ni existing position (depth) is higher than the Zn peak. It is a side leaning. On the other hand, in the sample having good blackening resistance and corrosion resistance (FIG. 3), it was observed that the Ni existing position (depth) moved to almost the same position as the Cr peak and was concentrated. That is, in the sample, N
It was found that i was exposed on the outermost surface of the plating and was integrated with the chromate layer.

From the above, it was estimated that the blackening phenomenon depends on the surface condition of the plating layer. Therefore Ni / Ti
However, even if it has a blackening prevention effect, the effect cannot be sufficiently obtained by simply including it in the plating layer, and since Ni / Ti is present on the outermost surface of the plating that can be integrated with the chromate layer, the chromate film It has been found that the composition exhibits stable blackening and exhibits blackening resistance and corrosion resistance for the first time.

Based on this finding, the N
The concentration position and concentration of i (Ti) were examined by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), etc.
(Ti) is within a range of 50 nm from the interface with the chromate layer (between 1 and 500 Å in terms of the plating layer depth, hereinafter the plating depth may be expressed in the conventional Å unit) in terms of metal. It was found that good blackening resistance and corrosion resistance can be obtained by unevenly concentrating to 002 to 0.2 mmol / m ² .

In the sample, the metal conversion amount of Ni at a plating layer depth of 1 to 500 Å is 0.005 to 0.0.
8 mg / m ² (0.08 × 10 ^{−3 to} 0.001 mmol /
m ² ), and concentrated Ni on the outermost surface of the plating layer.
And / or Ti was not present, and was present at a plating layer depth of 500 to 1000 Å (see Comparative Example 3).

Further, in order to achieve the above-mentioned concentration at the outermost surface of the plating in the present invention, the total amount of Ni / Ti in the hot dip galvanizing bath is properly 0.005 to 2 mass%. . In plating, it is necessary to control the concentration of the plating bath sufficiently. The amount of Ni / Ti is 0.005 mass.
If it is less than%, it becomes difficult to make the Ni / Ti concentration unevenly distributed on the outermost surface of the plating (the concentration peak cannot be observed). Further, if it exceeds 2 mass%, the concentration on the outermost surface of the plating is 0.2
If it exceeds mmol / m ² , it tends to form a local battery with Zn and reduce the corrosion resistance.

The present inventor has also found that Ni / Ti contained in the hot-dip galvanizing bath is contained in the plating layer with a yield of about 70%. Therefore, the plating layer obtained by using the plating bath having the above composition is usually N
i / Ti is contained in a total amount of 0.003 to 0.15 mass%.
This amount is an average value for the entire plating layer.

In the plating bath used in the present invention,
Misch metal can be included in an amount of 0.0005 to 0.5 mass%. Misch metal is a semi-finished product of the refining process, is a mixture of rare earth elements of the cerium group, and generally contains Ce and La. By adding the misch metal in the above amount, the anti-plating prevention effect can be maximized, and the coexistence of the misch metal and Ni / Ti is also effective in preventing blackening resistance and forms a glossy and uniform spangle. can do. The balance of the plating bath consists of zinc and inevitable impurities.

In the present invention, the above specified amounts of Al and Ni are used.
The plating method is not particularly limited except that a hot-dip zinc-based plating bath containing / Ti, and more preferably misch metal is used, and plating can be performed according to a general method.
For example, the plating bath temperature is 420 to 500 ° C, the infiltration plate temperature is 400 to 500 ° C, and the cooling rate after plating is 2 to 30 ° C / min.
The conditions of can be adopted. The amount of plating adhered is not particularly limited, but is usually about 40 to 200 g / m ² (per one side), whereby a plating layer is usually formed with a thickness of about 6 to 30 μm.

When chromating the surface of the plating layer as described above, in the present invention, one or more etching properties selected from the group consisting of nitrate ions, sulfate ions and fluorine ions together with trivalent and hexavalent chromium ions. A chromate solution containing ions is used. 3 in chromate
Valent and hexavalent chromium ions are Cr ^{6+ in} corrosive environment
Cr ³⁺ / Cr ⁶⁺ = 0.
It is desirable to be 1 to 0.5 (mass ratio).

In the present invention, the optimum etching ion concentration in the chromate solution is related to the ion concentration, the amount of Ni / Ti in the plating layer, the concentration position, etc., and the effect of blackening resistance and corrosion resistance. As a result of a detailed investigation on the
It is included in an amount of 0.1 (mass ratio). By using such a chromate solution, the effects of blackening resistance and corrosion resistance can be achieved. For example, as described later in Examples, 5
The ΔL value of the blackening resistance (HCT) evaluated by the lightness (L value) by a wet test for 14 days in 0 ° C. × 98% RH is 1
It is possible to obtain a chromate-treated hot-dip galvanized steel sheet which is 0 or less and does not generate white rust and is excellent in both blackening resistance and corrosion resistance.

The etching ion concentration is 0.028.
If it is less than the range, the concentrated uneven distribution of Ni / Ti does not exist on the outermost surface of the plating, and the blackening resistance effect cannot be reliably obtained. In addition, if the etching ion content exceeds 0.1, the etching action is too large to dissolve even Ni / Ti concentrated on the outermost surface of the plating, and the surface oxide film is also dissolved too much, resulting in deterioration in blackening resistance. I will end up.

The chromate treatment in the present invention is not particularly limited except that the chromate solution as described above is used, and can be carried out according to a general method. For example, the chromate solution can be applied by spraying or coating with a roll coater, or by dipping in a chromate treatment solution. At this time, although not particularly limited, usually, as metal Cr, 5 to 100 mg / m ² (per one surface)
A film of a certain degree can be formed. Baking can usually be performed at room temperature to about 200 ° C.

[0031]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited to these examples. (Examples 1 to 6 and Comparative Examples 1 to 3) Plate thickness 0.5 mm,
An unannealed Al-killed steel plate having a plate width of 1500 mm was subjected to continuous hot dip galvanizing, followed by chromate treatment. Table 1 shows the hot dip galvanizing bath and the chromate treatment conditions.
The blackening resistance and corrosion resistance of the obtained chromate-treated hot-dip galvanized steel sheet were evaluated as follows. The Ni / Ti concentration position and the concentration amount of the plating layer were set to AES (vacuum degree: 5 × 10 ⁻¹⁰ Torr (6.67 × 10 ⁻⁸ Pa), electron beam: acceleration voltage 10 kV, −200 nA, ion). (Gun analysis). The results are shown in Table 1. Table 1
The middle and concentrated positions are the depths from the outermost surface of plating, and are indicated by Å.

Blackening resistance (HCT): The lightness (L value) of a sample (chromate-treated hot dip galvanized steel sheet) was measured with a color difference meter. This brightness was set to L ₀ . Then, several samples were stacked and packed, and a wetness tester (50 ° C x 98%
After being left for 14 days in RH), the lightness was measured again with a color difference meter. The lightness at this time was L _14, and the blackness was evaluated as follows by the difference ΔL from the initial lightness L ₀ . ΔL = 1 to 9: resistance to blackening ○ ΔL = 10 to 15: resistance to blackening ΔΔL = 16 or more: resistance to blackening ×

Corrosion resistance (SST 100h): As a corrosion resistance test of a chromate-treated hot dip galvanized steel sheet (70 × 150 mm size), a salt spray test (according to JIS Z2371) was carried out for 100 hours to visually observe the occurrence of white rust. The white rust generation rate was obtained as described below to evaluate the corrosion resistance. White rust occurrence rate 0 to 5%: ○ 6 to 15%: △ 16% or more: ×

[0034]

[Table 1]

[0035]

INDUSTRIAL APPLICABILITY The present invention provides a chromate-treated hot-dip galvanized steel sheet which is excellent in blackening resistance and corrosion resistance and has a beautiful appearance even without being painted. Further, in the present invention, such a steel sheet can be produced by using a plating bath having a specific composition and a chromate solution having a specific composition without particularly performing a pre-process or a post-process, and the production line is simple. Be converted.

[Brief description of drawings]

FIG. 1 is a diagram showing a GDS chart for investigating Ni behavior of a plating layer.

FIG. 2 is a diagram showing a GDS chart for investigating Ni behavior of a plating layer of a chromate-treated hot-dip galvanized steel sheet having poor blackening resistance.

FIG. 3 is a diagram showing a GDS chart for investigating Ni behavior of a plating layer of a chromate-treated hot dip galvanized steel sheet having good blackening resistance and corrosion resistance.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshiki Koshikawa             1025 Hamano-cho, Chuo-ku, Chiba-shi, Chiba River Steel sheet             Chiba factory (72) Inventor Akira Kanegae             1025 Hamano-cho, Chuo-ku, Chiba-shi, Chiba River Steel sheet             Chiba factory (72) Inventor Taisuke Nishie             1025 Hamano-cho, Chuo-ku, Chiba-shi, Chiba River Steel sheet             Chiba factory F term (reference) 4K026 AA02 AA13 AA22 BA06 BA07                       BB08 BB10 CA17 CA19 CA20                       CA26 CA32 CA33 CA34 DA02                       DA03                 4K027 AA05 AA22 AB04 AB05 AB15                       AB43 AB44 AC82 AE03 AE27                 4K044 AA02 AB02 BA02 BA06 BA10                       BB03 BC02 BC09 CA04 CA11                       CA16

Claims (5)

[Claims] 1. A steel sheet having a hot dip galvanized layer and then a chromate layer on the surface thereof, wherein the hot dip galvanized layer has an average plating layer thickness of 2 to 15 ma.
It contains ss% Al, and the outermost surface of the plating layer has
A chromate-treated zinc-based plated steel sheet that has concentrated Ni and / or Ti and is excellent in blackening resistance and corrosion resistance. 2. A steel sheet having a hot-dip galvanized layer and then a chromate layer on the surface, wherein the hot-dip galvanized layer has a plating layer average of 2 to 15 ma.
The outermost surface portion of the plating layer containing ss% Al up to a depth of 50 nm from the interface with the chromate layer of the plating layer had a concentration of Ni of 0.002 to 0.2 mmol / m ² in terms of metal and / or Alternatively, a chromate-treated zinc-based plated steel sheet containing Ti and having excellent blackening resistance and corrosion resistance. 3. The total content of Ni and / or Ti in the plating layer is 0.003 to 0.1.
The chromate-treated zinc-based plated steel sheet according to claim 1 or 2, which is 5 mass%. 4. A steel sheet containing 2 to 15 mass% of Al and 0.005 to 2 mass% in total.
Plating is performed using a hot dip galvanizing bath containing Ni and / or Ti, and then trivalent and hexavalent chromium ions and etching ions are added at a mass ratio of etching ions / chromium ions of 0.028 to A method for producing a chromate-treated zinc-based plated steel sheet having excellent blackening resistance and corrosion resistance, which is treated with a chromate solution containing 0.1. 5. The hot dip galvanizing bath further comprises 0.00
The method for producing a chromate-treated zinc-based plated steel sheet according to claim 4, which contains 05-0.5 mass% misch metal.