JPH10267918A - Solution for chemical analysis of zinc-iron alloy group 2-layer plated steel board, and chemical analysis method using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solution for chemical analysis of a zinc-iron alloy group 2-layer plated steel board, and the chemical analysis method using it wherein a sticking amount of each plated layer and composition are accurately measured by selectively melting lower plated layers in a short time. SOLUTION: In a solution for chemical analysis of a zinc-iron alloy group 2-layer plated steel board, a base material plated layer 12 of a zinc-iron alloy group 2-layer plated steel board 10 which comprises a base metal plated layer 12 with low iron content and a surface part plated layer 11, with high iron content, allocated on the base material plated layer 12 is selectively melted, so that the surface part plated layer 11 is separated from the zinc-iron alloy group 2-layer plated steel board 10. The chemical analysis solution comprises such neutral salt for eluting zinc in the base material plated layer 12, an oxidizer for oxidizing eluted iron ion, and a chelating agent for stabilizing an oxidized iron ion as chelate compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention separates a double-layer plated portion of a zinc-iron alloy-based double-layer plated steel plate and precisely measures the amount of adhesion (also called basis weight) of each plating and its chemical composition. For a chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet and a chemical analysis method using the same.

[0002]

2. Description of the Related Art Steel sheets coated with a zinc-iron alloy are widely used as rust-preventive steel sheets for automobiles because of their excellent corrosion resistance and water resistance. In recent years, in addition to these, in order to improve the chemical conversion property and the weldability, a surface plating layer having a high iron content is formed on the underlying plating layer such as the electroplating layer or the hot-dip plating layer. The technology of layered plating has been developed and put to practical use as an automotive outer panel. Since the product properties such as the weldability and corrosion resistance of the plated steel sheet are affected by the difference in the adhesion amount and composition of each of the plating layers, it is important to accurately grasp these values. As an analysis method used for evaluating the adhesion amount and composition of each plating layer in such a zinc-iron alloy-based double-layer plated steel sheet, for example, the following methods are known. In Japanese Patent Publication No. 6-99825,
In performing the analysis of the plated layer by separating the plated layer of a zinc-based double-layer plated steel sheet having an upper layer having an iron content of 60% or more and a lower layer having an iron content of 25% or less into an upper layer and a lower layer, 50% by weight of alkali metal hydroxide, 0.1 to
Immersion in a solution (solution) containing 90% by volume of triethanolamine and an oxidizing agent dissolves the lower layer of the plating layer, and recovers the lower and upper layers as dissolved and undissolved components, respectively. 2 shows a method of analyzing a plating layer for separating the above.

[0003]

However, the method for analyzing a plating layer described in Japanese Patent Publication No. 6-99825 has the following problems. When measuring the concentration of zinc and / or iron in the solution by atomic absorption spectrometry or emission spectrometry,
The measurement is performed by ejecting the above-mentioned solution as a sample solution from the tip of the nozzle, spraying and vaporizing the solution. However, when an alkaline solution is used, the viscosity of the solution increases, and salt tends to precipitate at the tip of such a nozzle, so that the flow rate of the solution discharged from the nozzle is stabilized. It is difficult to make measurements. And since the fluctuation of a measured value is large, the measuring accuracy of the adhesion amount of a plating layer and its composition will fall. Since the dissolving solution does not sufficiently dissolve the iron in the plating layer, the measurement takes a long time and the measurement cannot be performed efficiently. Since the pH value of the pH value of the solution becomes higher,
Care is required in handling, and the load on facilities and costs is great. Since the alkali metal hydroxide is used, the difference in the solubility of the plating layer due to the difference in the zinc content is small, and in some cases, the upper layer and the portion of the steel sheet are dissolved, which causes a measurement error. The present invention has been made in view of such circumstances, and a zinc-iron alloy that can selectively dissolve a lower plating layer in a short time and accurately measure the amount of adhesion and composition of each plating layer. It is an object of the present invention to provide a solution for chemical analysis of a system double-layer plated steel sheet and a chemical analysis method using the same.

[0004]

According to the present invention, there is provided a semiconductor device comprising:
The solution for chemical analysis of the zinc-iron alloy-based double-layer plated steel sheet according to the present invention includes a base plating layer having a low iron content and a surface plating layer having a high iron content disposed on the base plating layer. A zinc-iron alloy-based steel sheet for separating the surface plating layer from the zinc-iron alloy-based double-layer steel sheet by selectively dissolving the base plating layer of the zinc-iron alloy-based two-layer steel sheet. A solution for chemical analysis of a layer-plated steel sheet, wherein the solution for chemical analysis is a neutral salt that elutes zinc in the base plating layer, an oxidizing agent that oxidizes iron ions that elute, and has been oxidized. A chelating agent for stabilizing the iron ion as a chelating compound. The base plating layer refers to a plating layer that is directly coated on an original steel sheet in order to impart corrosion resistance, water resistance, and the like to the steel sheet. The surface plating layer is
It refers to a surface layer that is overlaid and coated on the base plating layer for the purpose of imparting weldability, chemical conversion treatment, and the like. Neutral salts refer to salts that, when dissolved in an aqueous solution, are formed by the neutralization reaction of the aqueous solution with a neutral acid and base, and include ammonium acetate, ammonium nitrate, and the like. The oxidizing agent refers to a substance for mainly oxidizing ferrous ions (Fe ²⁺ ) to produce ferric ions (Fe ³⁺ ). In addition to hydrogen peroxide (H ₂ O ₂ ), Oxides of elements having higher valences than normal (MnO ₂ , CeO ₂ , PbO ₂ ),
Oxygen acids (nitrite, nitric acid, permanganic acid, chromic acid, chloric acid, hypochlorous acid, perchloric acid) and their salts, hot concentrated sulfuric acid,
Halogen and salts containing high valent metal ions are included.
The chelating agent is an organic compound that forms a chelating compound with ferric ion, such as triethanolamine (TEA) and ethylenediaminetetraacetic acid (EDT).
A), nitrilotriacetic acid (NTA), dimethylglyoxime, acetylacetone, oxine, glycine, ethylenediamine, piperidine, phenanthroline and the like.

A solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to claim 2 is the solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to claim 1, wherein The salt is either ammonium acetate or ammonium nitrate.

The solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to claim 3 is the solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to claim 1 or 2. The contents of the neutral salt and the chelating agent are 1 to 50% by weight and 0.1 to 90% by volume, respectively. When the content of the neutral salt is less than 1% by weight, the effect of dissolving zinc in the base plating layer is extremely reduced, so that the surface plating layer cannot be practically separated from the steel sheet. Further, even if the content of the neutral salt exceeds 50% by weight, the dissolution rate of zinc is not so high, and the solubility exceeds the solubility of the neutral salt, so that zinc is precipitated and cannot contribute to the reaction. If the content of the chelating agent is less than 0.1% by volume, the chelate compound cannot be produced by taking in ferric ions, and the iron ions are deposited as hydroxides to dissolve the underlying plating layer. Is blocked. Further, the content of the chelating agent is 90%.
If the content exceeds the volume%, the solubility of the neutral salt in the solution is significantly reduced, and the dissolution efficiency of the base plating layer is reduced due to the synergistic effect of the chelating agent and the neutral salt.

[0007] The solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to claim 4 is provided by any one of claims 1 to 3.
In the solution for chemical analysis of the zinc-iron alloy-based double-layer plated steel sheet described in the paragraph, the pH value of the hydrogen ion concentration index of the solution for chemical analysis is 8 to 10. PH value of pH value
Is less than 8, it is not preferable because the effect of dissolving the underlying plating layer by the neutral salt is significantly reduced. Conversely, if the hydrogen ion concentration index pH exceeds 10, the selective dissolution effect decreases, and not only the surface plating layer but also the steel sheet itself dissolves,
This is a factor that impairs measurement accuracy.

[0008] The solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to claim 5 is provided by any one of claims 1-4.
In the solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to the above item, the iron content of the base plating layer is 35% by weight or less, and the iron content of the front plating layer is 70% by weight or more. is there. When the iron content of the base plating layer exceeds 35% by weight and the iron content of the surface plating layer is less than 70% by weight, the selective dissolving effect of the dissolving solution is reduced, and the adhesion amount of each plating layer and the chemical amount It becomes difficult to measure the composition precisely.

A chemical analysis method using a solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to claim 6 is characterized in that a base plating layer having a low iron content and a surface plating layer having a high iron content are formed. The zinc-iron alloy-based double-layer plated steel sheet having a neutral salt, an oxidizing agent and a chelating agent is immersed in a solution for chemical analysis having a hydrogen ion concentration index pH of 8 to 10 to form the base plating layer. The surface plating layer is separated from the zinc-iron alloy-based double-layer plated steel sheet by melting.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIGS. 1 (a), (b), (c)
Is a schematic diagram showing an initial state, an intermediate state, and a terminal state of a test piece in a lower layer solution, respectively. FIG. 2 is a diagram showing the relationship between the amount of adhesion and the immersion time in Example 1 of the present invention, and FIG. FIG. 6 is a diagram showing the relationship between the amount of adhesion and the immersion time in Example 2 of FIG.

Zinc is an amphoteric metal and is soluble in both acids and alkalis. On the other hand, iron forms a stable passive film in an alkaline solution having a hydrogen ion concentration index pH of 10 or more.
For this reason, when the zinc-iron alloy plating layer is immersed in an alkaline solution, zinc (Zn) in the plating layer dissolves as ZnO ₂ ^2- ions, but iron (Fe) becomes iron hydroxide and becomes iron hydroxide. The deposition causes problems such as dissolution of the plating layer being hindered and prolonging the dissolution time. Thus, the present inventors have conducted intensive studies and found that, using a neutral salt as a component for dissolving iron, under conditions that do not generate a passive film of iron in the base plating layer, the neutral salt It was found that a plating solution having a specific composition can be selectively and efficiently dissolved by using an aqueous solution containing an oxidizing agent and a chelating agent as a dissolving solution for chemical analysis (hereinafter, referred to as a lower layer dissolving solution), thereby completing the present invention. It has been reached.

First, a chemical analysis method using a solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to an embodiment of the present invention will be described. First, a zinc-iron alloy double-layer plated steel sheet is supplied to a dissolution tank holding a lower layer solution for dissolving a base plating layer (hereinafter, simply referred to as a lower layer 12) of the zinc-iron alloy double-layer plated steel sheet. A test piece 10 cut out to a size is supplied. The lower layer solution is
An aqueous solution of a neutral salt, an aqueous solution of a chelating agent, and an aqueous solution of an oxidizing agent used as an eluent for zinc or the like are each adjusted to a predetermined concentration, and a predetermined amount of these is mixed to form a whole with a predetermined hydrogen ion concentration index pH. The weight ratio or the volume ratio is adjusted. The raw steel plate 13 serving as the substrate of the zinc-iron alloy-based double-layer plated steel plate is a steel plate having an iron content of 99% by weight, and the lower layer 12 formed on the raw steel plate 13 has an iron content of 5 to 20% by weight. And the lower layer 12
The iron content in the surface plating layer (hereinafter, simply referred to as the upper layer 11) formed thereon is 70 to 90% by weight. When forming the lower layer 12 and the upper layer 11 on the raw steel sheet 13, a hot-dip plating method, an electroplating method, or the like can be selected and applied as necessary. Further, in the present embodiment, a zinc-iron alloy-based double-layer plated steel sheet in which the lower layer 12 and the upper layer 11 are formed by an electroplating method is an EL plated steel sheet, the lower layer 12 is formed by a hot-dip plating method, and the upper layer 11 is formed by an electroplating method. The zinc-iron alloy-based two-layer plated steel sheet is referred to as an AS-E plated steel sheet. Then, the test piece 10 formed as shown in FIG. 1A was degreased, and the weight W ₀ of the test piece 10 was measured. 2), the lower layer 12 of the plating layer is selectively dissolved.

After a predetermined immersion time T has elapsed, a predetermined amount of the lower layer solution is extracted from the dissolving tank and diluted, and then the concentrations of Fe and Zn in the lower layer solution are measured by atomic absorption spectrometry. , it can be calculated composition and coating weight W _L in the lower layer 12 based on the measured value of the concentration. In such an atomic absorption spectrometry, a diluted lower layer solution (sample liquid) is directly sprayed into a flame (flame) formed by a combustible gas such as hydrogen or acetylene and a supporting gas such as air or oxygen gas. Or a gas in which a sample liquid has been sprayed into the mixed gas in advance is burned by a burner to generate a flame. Then, light from a light source is allowed to pass through the flame, a specific monochromatic resonance line region set for each target element is selected by a wavelength selector from the spectrum of the transmitted light, and an extinction index in the monochromatic resonance line region is determined. (Absorbance) is measured. Since the extinction index is proportional to the atomic density of the target element in the flame, the concentration in the sample can be determined from this.
When spraying the sample liquid in a mixed gas or flame, when the alkali metal hydroxide is present in the sample liquid and the hydrogen ion concentration index is high as in the related art, the viscosity of the sample liquid is high, Moreover, since salts such as sodium chloride are easily precipitated,
Salt accumulates at the tip of the spray nozzle, making it difficult to stably maintain the flow rate of the sample liquid. However, in the case of a sample solution mainly composed of a neutral salt such as ammonium acetate and ammonium nitrate, such a salt precipitates little, so that fluctuations in the measured value are suppressed and measurement with a small error (standard deviation σ) should be performed. And a neutralization process for stabilizing the flow rate of the sample liquid can be minimized.

Further, the test piece 1 after dissolving the lower layer 12
No. 0 is taken out of the dissolving tank and immersed in a hydrochloric acid solution (hereinafter referred to as an upper layer solution) containing an inhibitor (deterrent agent) for suppressing the elution of iron in the raw steel sheet 13. Then, as shown in FIG. 1 (c), the upper layer 11 attached to the surface of the test piece 10 is scraped off to completely separate the original steel plate 13 and the upper layer 11. Test piece 10 after upper layer 11 was scraped off
Were weighed weight W ₁ of the (original steel plate 13), obtaining the total coating weight W _A (= W ₀ -W ₁₎ the difference between the weight W ₀ of the test piece. Next, the upper layer solution including the scraped upper layer 11 and the partially dissolved upper layer 11 is heated to completely dissolve the solid content in the solution. This upper layer solution was diluted, and the concentrations of iron and zinc in the solution were measured by atomic absorption spectrometry.
And the amount W _U of the composition are determined. Incidentally, the adhesion amount _{W L, W U, W A} ( unit: g) of each test piece 10
Can be used by measuring the total plating adhesion area S of the above and converting it to the adhesion amount per unit area (unit: g / m ² ).

Here, Table 1 shows data indicating the selective solubility of the solution for chemical analysis (lower layer solution) of the zinc-iron alloy-based double-layer plated steel sheet according to the embodiment of the present invention. That is, plating layers having different iron contents were added to the lower layer solution for 12 hours.
It was immersed for 0 minutes, and the amount of iron eluted from the plating layer was measured by a chemical analysis method.

[0016]

[Table 1]

As shown in Table 1, when the iron content in the plating layer is in the range of 100 to 80% by weight, the iron elution amount is 0.0%.
10 to 0.033 g / m ^{2, which} is extremely small, and the amount of iron eluted gradually increases when the iron content is in the range of 65% to 40% by weight, and rapidly elutes when the iron content falls below 35% by weight. You can see that the number increases. In Table 1, the symbol (△) indicates that a part of the plating layer was dissolved, and the symbol (○) indicates that the entire plating layer was dissolved. Thus, in the lower layer solution of the present invention, the steel sheet 13 having an iron content of about 99% by weight is hardly dissolved, and the plating layer having an iron content of 35% by weight or less is selectively formed. Can be dissolved.

[0018]

EXAMPLE 2 Table 2, FIG. 2 and FIG. 3 show the processing conditions and the data of the results in Examples 1 and 2, respectively.
Here, first, a large number of test pieces 10 each made of an EL-plated steel sheet and an AS-E-plated steel sheet are prepared, and the immersion time T of these test pieces 10 in the lower layer solution is 0 to 18;
Various settings are made during 0 minutes. The test piece 10 for each immersion time T, which is the set is removed from the lower lysate applied directly to the above-mentioned measurement method, the adhesion amount W _L (symbol: ○) of the lower layer 12 in Example 1 and Example 2 , The amount of adhesion W _U of the upper layer 11 (symbol: Δ) and the total amount of adhesion W _A (symbol: ●) can be obtained. FIGS. 4 and 5 are graphs showing Comparative Examples 1 and 2 in which the composition of the lower layer solution is different from Examples 1 and 2, respectively, and correspond to Examples 1 and 2, respectively. The comparison data is shown.
Hereinafter, Example 1 and Example 2 will be described with reference to Table 2 and FIGS.

[0019]

[Table 2]

The lower layer solution used in Example 1 was
As shown in Table 2, 13% by weight of ammonium nitrate as an example of a neutral salt as an eluent for zinc and the like, 26% by volume of triethanolamine as an example of a chelating agent, and hydrogen peroxide as an example of an oxidizing agent Was used so as to contain 5% by weight. At this time, the hydrogen ion concentration index pH was 8.5 to 9.5. And test piece 1
For 0, an experiment was performed using an EL-plated steel sheet having the component ranges shown in Table 3 in which the upper layer 11 and the lower layer 12 were each formed by electroplating.

[0021]

[Table 3]

As shown in FIG. 2, the adhesion amount W _{L of} the lower layer 12, the adhesion amount W _U of the upper layer 11, and the total adhesion amount W _A calculated by taking out the test piece 10 at every immersion time T are determined by the immersion time. T
It can be seen that becomes substantially constant after 60 minutes. Therefore, the saturation immersion time T ₀ in this case is 60 minutes. On the other hand, in the case of Comparative Example 1 in which the eluent in the lower layer solution was sodium hydroxide, as shown in FIG. 4, the saturated immersion time T ₀ required to stabilize the adhesion amounts W _L and W _U was About 12
It is 0 minutes, which is twice as long as that of Example 1.

As is apparent from the results of the analysis shown in Table 2, the standard deviation of the iron content of the upper layer 11 and the lower layer 12 in Example 1 finally measured after the saturation immersion time T _0. σ is 0.11 wt% (% by weight) and 0.06 wt%, respectively.
0.38% by weight and 0.08% by weight, data with less precision and excellent accuracy can be obtained.

In Example 2, as shown in Table 2, as a lower layer solution, 12% by weight of ammonium acetate as an example of a neutral salt as an eluent of zinc and the like, and triethanolamine as an example of a chelating agent were used. And an aqueous solution adjusted to contain 25% by volume of hydrogen peroxide and 10% by weight of hydrogen peroxide as an example of the oxidizing agent. PH value of pH value
Was 8.5 to 9.5. An experiment was performed using an AS-E plated steel sheet having a composition range shown in Table 4 for the test piece 10.

[0025]

[Table 4]

As shown in FIG. 3, the weight W _{L of} the lower layer 12, the weight W _U of the upper layer 11, and the total weight W _A of the lower layer 12, which are calculated by taking out the test piece 10 at every immersion time T, are calculated based on the immersion time. T
It turns out that it becomes almost constant after 30 minutes. Therefore, the saturation immersion time T ₀ in this case is 30 minutes. In contrast, when the elution agent in the lower layer solution of Comparative Example 2, sodium hydroxide, coating weight W _L as shown in FIG. 5, W saturated immersion time T ₀ required for certain of the _U is About 90
Minutes, which means that it takes a longer time than in Example 2. In FIGS. 3 and 5, the total adhesion amount (symbol:
●) and the adhesion amount W _L (symbol: ○) of the lower layer 12 are represented by the scale on the left side, while the adhesion amount W of the upper layer 11
_U (symbol: △) is indicated by the scale on the right. Further, as is clear from the results of the analysis treatment shown in Table 2, the standard deviations σ of the iron contents of the upper layer 11 and the lower layer 12 in Example 2 finally measured after the saturation immersion time T ₀ are 0, respectively. .23 wt% and 0.08 wt%, and the corresponding standard deviations σ of the iron contents in Comparative Example 2 were 0.41 wt% and 0.09 wt%, respectively. It can be seen that good results are obtained.

Here, Table 5 shows Examples 1 and 2 and Comparative Example 1.
2 is data showing the difference between the two by calculating the adhesion amounts of the upper layer 11 and the lower layer 12 for each component.

[0028]

[Table 5]

As shown in Table 5, the difference between the measured values of the amounts of adhesion between Examples 1 and 2 and Comparative Examples 1 and 2 corresponding thereto is extremely small. That is, it can be seen that the average value of the measured values of the respective adhesion amounts is substantially equal. Note that both zinc (Zn) and iron (Fe) components are represented by mass per unit area (g / m ² ). Also,
The total adhesion amount is the adhesion amount W _U of the upper layer 11 and the adhesion amount W of the lower layer 12.
The sum of _{L, the} total coating weight W _A is a measured value obtained by measuring the difference in weight of the test piece 10 before and after the treatment of the underlying solution.

The embodiment of the present invention has been described above.
The present invention is not limited to these embodiments, and all changes in conditions without departing from the gist are within the scope of the present invention.

[0031]

In the solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to any one of claims 1 to 5, the chemical analysis solution is capable of converting zinc in the base plating layer to a specific hydrogen ion concentration. Since it contains a neutral salt to be eluted below, it is possible to efficiently dissolve zinc and iron in the base plating layer without forming a passivation film on the portion of the base plating layer where iron exists. it can. And since it has an oxidizing agent that oxidizes the eluted iron ions and a chelating agent that stabilizes the oxidized iron ions as a chelate compound, the eluted iron ions do not precipitate as hydroxides or the like, The saturation immersion time can be reduced. In addition, since the solution for chemical analysis containing the elution component of the base plating layer is an aqueous solution containing a neutral salt, it does not precipitate salts during atomic absorption analysis, emission spectroscopy, etc. under stable conditions. Measurement can be performed and highly accurate measurement data can be obtained. As described above, the dissolution solution for chemical analysis of the present invention selectively dissolves the base plating layer in a short time under conditions that suppress elution from the raw steel sheet and the surface plating layer coated with the plating layer, The adhesion amount and composition can be accurately measured.

In particular, in the solution for chemical analysis of the zinc-iron alloy-based double-layer plated steel sheet according to claim 2, the neutral salt is either ammonium acetate or ammonium nitrate. A more precise analysis can be performed without generating a salt that hinders the measurement of the component concentration. In particular, when ammonium nitrate is used as a neutral salt, a precise analysis result can be obtained without producing a salt that hinders the measurement of the component concentration in the solution for chemical analysis. It is easy to adjust the hydrogen ion concentration index in the solution for use.

In the solution for chemical analysis of the zinc-iron alloy-based double-layer plated steel sheet according to the third aspect, the content of the neutral salt and the content of the chelating agent are each in a specific range. In addition to increasing the elution amount of the plating layer, the elution amount of the surface plating layer and the raw steel sheet can be made substantially negligible, thereby ensuring the selective solubility of the solution for chemical analysis. Further, the zinc of claim 4-
In the solution for chemical analysis of iron alloy-based double-layer plated steel sheets, the pH value of the hydrogen ion concentration index of the solution for chemical analysis is in a specific range, so the selective solubility of the solution for chemical analysis is further enhanced to improve the measurement accuracy. It can be improved and does not cause excessive corrosion of the measuring device.

In the solution for chemical analysis of the zinc-iron alloy-based double-layer plated steel sheet according to the fifth aspect, the iron content of the base plating layer and the iron content of the surface plating layer are specified ranges. In addition, the selective solubility of the solution for chemical analysis with respect to the underlying plating layer can be further enhanced, and highly accurate measurement data can be obtained.

According to a sixth aspect of the present invention, there is provided a chemical analysis method using a solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet, comprising: a base plating layer having a low iron content and a surface plating layer having a high iron content. A zinc-iron alloy-based double-layer plated steel sheet having
Immerse in a solution for chemical analysis of a specific range of hydrogen ion concentration index having a neutral salt, an oxidizing agent and a chelating agent, dissolve the base plating layer, and remove the surface part from the zinc-iron alloy double-layer plated steel sheet. Since the plating layer is separated, no passivation film is formed on the underlying plating layer, zinc and iron in the underlying plating layer are efficiently dissolved, and iron ions oxidized by the oxidizing agent are stabilized as a chelate compound. By doing so, the saturation immersion time during elution can be shortened. Also,
Since the solution for chemical analysis in which the base plating layer is eluted is an aqueous solution containing a neutral salt, salts are less precipitated during processing operations such as atomic absorption spectroscopy or emission spectroscopy, and are performed under stable conditions. Each component can be analyzed and highly accurate measurement data can be obtained.

[Brief description of the drawings]

FIGS. 1A, 1B, and 1C are schematic diagrams respectively showing an initial state, an intermediate state, and a terminal state of a test piece in a lower layer solution.

FIG. 2 is a diagram showing the relationship between the measured value of the amount of adhesion and the immersion time in Example 1 concerning the solution for chemical analysis of the zinc-iron alloy-based double-layer plated steel sheet according to the embodiment of the present invention.

FIG. 3 is a view showing a relationship between a measured value of an attached amount and an immersion time in Example 2;

FIG. 4 is a diagram showing a relationship between a measured value of an attached amount and an immersion time in Comparative Example 1.

FIG. 5 is a diagram showing a relationship between a measured value of an attached amount and an immersion time in Comparative Example 2.

[Explanation of symbols]

Reference Signs List 10 Test piece (Zinc-iron alloy-based double-layer plated steel sheet) 11 Upper layer (surface plating layer) 12 Lower layer (base plating layer) 13 Original steel sheet

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasushi Kawakami 1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works (72) Inventor Koichi Kuwahara Tobata-ku, Kitakyushu-shi, Fukuoka No. 1 town New Nippon Steel Corporation Yawata Works

Claims (6)

[Claims] 1. The undercoating of a zinc-iron alloy-based double-layer plated steel sheet having an undercoat plating layer having a low iron content and a surface plating layer having a high iron content disposed on the undercoat layer. Layer for selectively dissolving the layer, and a zinc-
A solution for chemical analysis of an iron alloy-based double-layer plated steel sheet, wherein the solution for chemical analysis is a neutral salt that elutes zinc in the base plating layer, and an oxidizing agent that oxidizes iron ions that elute, And a chelating agent for stabilizing the oxidized iron ions as a chelate compound. A solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet. 2. The method according to claim 1, wherein the neutral salt is one of ammonium acetate and ammonium nitrate.
A solution for chemical analysis of the zinc-iron alloy-based double-layer plated steel sheet according to the above. 3. The zinc-iron alloy according to claim 1, wherein the contents of the neutral salt and the chelating agent are 1 to 50% by weight and 0.1 to 90% by volume, respectively. Solution for chemical analysis of non-galvanized steel sheet. 4. The chemical analysis solution according to claim 1, wherein the pH value of the hydrogen ion concentration index is 8 to 10.
4. The solution for chemical analysis of the zinc-iron alloy-based double-layer plated steel sheet according to any one of the above items 3. 5. The method according to claim 1, wherein an iron content of the undercoating layer is 35% by weight or less, and an iron content of the surface plating layer is 70% by weight or more. The solution for chemical analysis of a zinc-iron alloy-based double-layer plated steel sheet according to item 1. 6. A zinc-iron alloy-based double-layer plated steel sheet having a base plating layer having a low iron content and a surface plating layer having a high iron content, comprising a neutral salt, an oxidizing agent and a chelating agent. By immersing in a solution for chemical analysis having a hydrogen ion concentration index pH of 8 to 10 to dissolve the base plating layer and separate the surface plating layer from the zinc-iron alloy-based double-layer plated steel sheet, Chemical analysis method of zinc-iron alloy-based double-layer plated steel sheet.