JP6146541B2 - Plated steel sheet and manufacturing method thereof - Google Patents

Description

The present invention relates to a plated steel sheet having excellent corrosion resistance and a method for producing the same.
This application claims priority on November 10, 2014 based on Japanese Patent Application No. 2014-228436 for which it applied to Japan, and uses the content here.

  In steel plate products for cans, in order to ensure properties such as corrosion resistance, rust resistance and paint adhesion (coating film adhesion), Sn, Zn, Ni, etc. present directly on the steel plate surface or on the steel plate surface A chromate film is formed on the plating. This chromate film is made of metallic chromium and oxide chromium, and is formed by subjecting a steel sheet to cathodic electrolysis (electrolytic chromic acid treatment) in a treatment solution containing hexavalent chromium. On the other hand, since hexavalent chromium is harmful to the environment, in recent years, development of a technology that replaces chromate treatment with surface treatment that does not use hexavalent chromium has progressed.

  As one type of surface treatment of steel sheets, chemical conversion treatment using a treatment liquid containing a phosphate and a zirconium compound is known. For example, Patent Documents 1 and 2 disclose that a strip steel is subjected to a cathodic electrolytic treatment in a treatment solution containing zirconium ions, fluoride ions and phosphate ions, and the strip steel is coated with a chemical conversion treatment film. Yes.

  In Patent Documents 3, 4, 5, and 6, after forming a phosphate film in one bath containing a phosphate solution, a zirconium film is formed in the other bath containing a solution containing zirconium ions. A method is disclosed.

Japanese Unexamined Patent Publication No. 2009-84623 International Publication 2011/118588 Pamphlet Japanese Unexamined Patent Publication No. 2009-256726 International Publication No. 2008/123632 Pamphlet Japanese Unexamined Patent Publication No. 2009-249691 Japanese Unexamined Patent Publication No. 2014-95123

  However, the chemical conversion treatment film disclosed in Patent Documents 1 to 6 described above has only relatively good corrosion resistance when a coating film (painted film) is formed on the chemical conversion treatment film. On the other hand, when a coating film is not formed on the chemical conversion coating, when the highly corrosive contents are put in the container and this container is used in a harsh environment, these chemical conversion coatings have performance such as corrosion resistance. Cannot be fully utilized. The present inventors recognize that the chemical conversion treatment film disclosed in Patent Documents 1 to 6 does not give sufficient corrosion resistance to the steel sheet under the condition that there is no coating film on the chemical conversion treatment film, and increase the amount of zirconium oxide. Thus, it has been found that there is a possibility that sufficient corrosion resistance can be obtained even when a coating film is not formed on the chemical conversion coating. However, in the case where no coating film is formed on the chemical conversion coating film, sufficient corrosion resistance cannot be obtained only by increasing the amount of zirconium oxide. In addition, when the amount of zirconium oxide is increased, aggregated zirconium oxide is generated in the chemical conversion coating when a load is applied to the surface of the chemical conversion coating, and the coating film peels off during processing starting from the aggregated zirconium oxide. It was. As a result, the paint adhesion decreased and the corrosion resistance after processing decreased. Therefore, in the prior art (for example, Patent Document 4), if a coating film is formed on the chemical conversion coating, the amount of zirconium oxide is reduced so that sufficient corrosion resistance can be obtained even after processing. For this reason, even when the coating film is not formed on the chemical conversion coating, the present inventors consider the necessity of examining a chemical conversion coating that can provide sufficient corrosion resistance to the plated steel sheet and maintain sufficient coating adhesion. Recognized for the first time.

  Moreover, since the manufacturing method disclosed by patent document 3, 4, 5, 6 forms the chemical conversion treatment film using two baths, manufacturing time is long and productivity is low. On the other hand, when a chemical conversion film is formed on a plated steel sheet by cathodic electrolysis using one bath, it is possible to control the cation to some extent, but the chemical conversion film is plated using two baths. Compared with the case where it forms on the top, the control conditions of the quality of a chemical conversion treatment film become fewer.

  Therefore, the present invention solves the above-mentioned problems of the prior art, is excellent in coating film adhesion, and not only under conditions where there is a coating film on the chemical conversion treatment film but also under conditions where there is no coating film on the chemical conversion treatment film. It aims at providing the plated steel plate excellent in corrosion resistance, and its manufacturing method.

  The present inventors have intensively studied the above-mentioned problems and constructed a chemical conversion treatment film in a tin-plated steel sheet capable of obtaining excellent coating adhesion and extremely good corrosion resistance, and a method for realizing the chemical conversion treatment film. did.

That is, the gist of the present invention is as follows.
(1) The plated steel plate according to the first aspect of the present invention includes a steel plate, a plated metal layer including a Sn plating layer, and a chemical conversion treatment layer, and the plated metal layer is present on the surface of the steel plate. the chemical conversion treatment layer, the present on the surface of the Sn-plated layer, in the chemical conversion treatment layer, P amount is is a 3 to 20 mg / ^{m 2,} Zr amount is 5 mg / ^{m 2} ultra and 30 mg / ^{m 2} or less The ratio P / Zr of the P amount and the Zr amount is 0.35 to 1.00, and the chemical conversion treatment layer contains tin phosphate and zirconium oxide (IV),
In the chemical conversion treatment layer, the area ratio having an intensity of 50% or less of the average intensity of Zr obtained by mapping analysis of a field emission electron beam microanalyzer is 0.1 to 10%.
(2) In the plated steel sheet according to (1) above, the Sn plating layer may be present on the surface of the steel sheet.
(3) In the plated steel sheet according to (1), the plated metal layer further includes an alloy layer, the alloy layer is present on the surface of the steel sheet, and the Sn plated layer is formed of the alloy layer. The alloy layer that exists on the surface may include at least one chemical element selected from the group consisting of Sn and Ni, and Fe.
(4) In the plated steel sheet according to (3), the alloy layer is selected from the group consisting of a FeSn ₂ phase, a Ni ₃ Sn ₄ phase, an α phase in a Fe—Ni system, and a γ phase in a Fe—Ni system. At least one alloy may be included.
(5) In the plated steel sheet according to any one of (1) to (4), the Zr amount may be 6 mg / m ² or more.
(6) In the plated steel sheet according to any one of (1) to (4), the Zr amount may be 8 mg / m ² or more.
(7) The method for producing a plated steel sheet according to the above (1) to (6) includes a Sn plating process for plating Sn on the steel sheet; and after the Sn plating process, an anodic electrolytic treatment for the steel sheet in the chemical conversion solution anodic electrolytic treatment step and performing; after the anodic electrolytic treatment step, the chemical conversion treated liquid and a cathode electrolytic treatment step performing cathodic electrolysis treatment to the steel sheet; consist, the chemical conversion treatment liquid, the 100ppm~10000ppm Containing zirconium ions, 100 ppm to 10000 ppm fluoride ions, 100 ppm to 3000 ppm phosphate ions, and 100 ppm to 30000 ppm nitrate ions, the temperature of the chemical conversion treatment solution being 20 ° C. to 60 ° C., and the chemical conversion treatment layer P content in the in the range of 3 to 20 mg / ^{m 2,} the chemical conversion Zr amount of processing layer is in the range of 5 super to 30 mg / ^{m 2,} before The conditions of the anodic electrolytic treatment in the anodic electrolytic treatment step and the cathodic electrolytic treatment in the cathodic electrolytic treatment step so that the ratio P / Zr of the P amount and the Zr amount is in the range of 0.35 to 1.00. Control the conditions.
(8) The method for producing a plated steel sheet according to (7) described above includes Ni-containing plating for plating the steel sheet with at least one metal selected from the group consisting of Ni and Fe—Ni before the Sn plating step. A process may be further included.
(9) The method for producing a plated steel sheet according to (7) or (8) described above is a pretreatment electrolysis in which a cathode electrolytic treatment is performed on the steel sheet in the chemical conversion solution before the anodic electrolytic treatment step. A process may be further included.
(10) In the pretreatment electrolysis step in the method for producing a plated steel sheet according to (9) above, the current density during the cathodic electrolysis is 0.1 to 10 A / dm ² , and the energization amount due to the cathodic electrolysis 1-10 C / dm < ² > may be sufficient.
(11) In the anodic electrolytic treatment step in the method for producing a plated steel sheet according to any one of (7) to (10), a current density during the anodic electrolytic treatment is 0.1 A / dm ^{2 to 2} A /. an dm ^2, the amount of current by the anodic electrolysis treatment may be ^{0.1C / dm 2 ~2C / dm 2} .
(12) In the cathode electrolytic treatment step in the method for producing a plated steel sheet according to any one of (7) to (11), a current density during the cathode electrolytic treatment is 1 to 20 A / dm ² . 5-50 C / dm < ² > may be sufficient as the energization amount by the said cathode electrolytic treatment.
(13) In the method for producing a plated steel sheet according to any one of (7) to (12), the Zr amount may be 6 mg / m ² or more.
(14) In the method for producing a plated steel sheet according to any one of (7) to (13), the amount of Zr may be 8 mg / m ² or more.
(15) In the method for producing a plated steel sheet according to any one of (7) to (14) above, the chemical conversion solution may have a pH of 3 to 4.

  According to the present invention, it is possible to provide a plated steel sheet having coating film adhesion and extremely good corrosion resistance and a method for producing the same.

It is the schematic of the layer structure of the plated steel plate which concerns on one Embodiment of this invention. It is the schematic of the layer structure of the plated steel plate which concerns on another embodiment of this invention. It is the schematic of the layer structure of the plated steel plate which concerns on another embodiment of this invention. It is the schematic of the layer structure of the plated steel plate which concerns on another embodiment of this invention. It is a figure which shows an example of the relationship between P / Zr ratio and corrosion resistance. It is a figure which shows the outline of the order of a manufacturing process. It is a figure which shows the outline of the order of a chemical conversion treatment process.

  Below, the plated steel plate concerning the embodiment of the present invention is explained in detail.

(Plating steel plate 1)
As shown in FIGS. 1 to 4, the plated steel sheet 1 according to this embodiment includes a steel sheet 2, a plated metal layer 3 on the surface of the steel sheet 2, and a chemical conversion treatment layer 4 on the surface of the plated metal layer 3. . The plated metal layer 3 includes an Sn plated layer 3a, and in some cases includes an alloy layer 3b. That is, the plated metal layer 3 may be composed of the Sn plated layer 3a or may be composed of the Sn plated layer 3a and the alloy layer 3b. Therefore, the plated metal layer 3 contains Sn. 2 and 4, the chemical conversion treatment layer 4 includes a first chemical conversion treatment layer 4a on the surface of the plating metal layer 3 and a second chemical conversion treatment layer 4a on the surface of the first chemical conversion treatment layer 4a. You may provide the process layer 4b.

  For example, like the plated steel plate 1 according to one embodiment of the present invention shown in FIG. 1, the plated steel plate 1 includes the steel plate 2, the Sn plating layer 3 a, and the chemical conversion treatment layer 4 in this order. Further, for example, like a plated steel plate 1 according to another embodiment of the present invention shown in FIG. 2, the plated steel plate 1 includes a steel plate 2, a Sn plating layer 3 a, a first chemical conversion treatment layer 4 a, and a second chemical conversion treatment layer 4 a. The chemical conversion treatment layers 4b are provided in this order. Moreover, like the plated steel plate 1 according to another embodiment of the present invention shown in FIG. 3, the plated steel plate 1 further includes an alloy layer (alloyed layer) 3b between the steel plate 2 and the Sn plating layer 3a. Also good. The Sn plating layer 3 a exists between the steel plate 2 and the chemical conversion treatment layer 4. As shown in FIG. 1, when the plated steel plate 1 does not include the alloy layer 3 b, the Sn plated layer 3 a exists on the surface of the steel plate 2. As shown in FIG. 3, when the plated steel plate 1 includes the alloy layer 3b, the alloy layer 3b exists on the surface of the steel plate 2, and the Sn plating layer 3a exists on the surface of the alloy layer 3b. This alloy layer 3b contains Fe and at least one chemical element selected from the group consisting of Sn and Ni.

Moreover, when the chemical conversion treatment layer 4 includes the first chemical conversion treatment layer 4a and the second chemical conversion treatment layer 4b, the first chemical conversion treatment layer 4a exists on the surface of the Sn plating layer 3a, and the second chemical conversion treatment layer 4a. The chemical conversion treatment layer 4b exists on the surface of the first chemical conversion treatment layer 4a. The chemical conversion treatment layer 4 contains tin phosphate and zirconium oxide (IV). Moreover, in the chemical conversion treatment layer 4, the amount of P is 3 to 20 mg / m ² , and the amount of Zr is more than 5 mg / m ^{2 and not} more than 30 mg / m ² . Furthermore, the ratio (P / Zr) of the P amount to the Zr amount in the chemical conversion treatment layer 4 is 0.35 to 1.00.

  The plated steel sheet 1 according to this embodiment is preferably used for containers such as beverage cans and food cans. However, the plated steel plate 1 according to the present embodiment is not limited to the use as a container.

(Steel 2)
In this embodiment, various steel plates can be used as the steel plate 2 without limitation. For example, when the plated steel plate 1 is used for a container, a conventionally used steel plate such as aluminum killed steel or low carbon steel can be used as the steel plate 2 without any problem. Moreover, what is necessary is just to select grades, such as the thickness of a steel plate, and a tempering degree, according to the intended purpose.

(Plating metal layer 3)
The amount of the alloy layer 3b and the amount of the Sn plating layer 3a are not limited because they may be appropriately selected according to the purpose of use. Generally, the alloy layer 3b is often composed of a phase containing Sn and Fe in order to reduce the potential difference between the Sn plating layer and the steel sheet and reduce the corrosion current. Thus, when the alloy layer 3b contains Sn, it is common that the amount of Sn in the alloy layer 3b is 0.1-1.6 g / m < ² >. When a heating step (reflow treatment) for melting Sn after Sn plating is performed, Sn in an amount of at least 0.1 g / m ² is inevitably included in the alloy layer 3b. When the amount of Sn in the alloy layer 3b is 1.6 g / m ² or less, minute cracks are hardly generated in the alloy layer 3b during processing such as bending and curling, and the starting point (crack) of corrosion can be reduced. . Since the melting point of Sn is 232 ° C., the maximum reflow temperature is 232 ° C. to 300 ° C. or less. In this reflow process, an FeSn ₂ phase is mainly formed.

In the Sn plating layer 3a, the amount of metal tin (substantially monometallic tin, that is, excluding tin dissolved in an intermetallic compound and other metals) is generally 0.2 to 12 g / m ^2. It is. When the amount of metal tin is 0.2 g / m ² or more, the frequency of local overheating by wire seam welding for manufacturing a can body is reduced, and the scattering of molten metal called chilli can be suppressed. It becomes easy to obtain a sufficient welding proper current range. When the amount of metallic tin is 12 g / m ² or less, weldability per unit weight of metallic tin is increased, and material costs and scarce resources can be saved.

Moreover, the alloy layer 3b may contain Ni. As the amount of Ni ₃ Sn ₄ increases, the amount of FeSn ₂ decreases. Therefore, when the alloy layer 3b contains Ni, excessive generation of the Fe—Sn alloy in the alloy layer 3b is suppressed, and minute cracks are hardly generated in the alloy layer 3b during processing such as bending and curling. When the amount of Ni in the alloy layer is 2 mg / m ² or more, the generation of cracks during the above processing can be more reliably suppressed. On the other hand, when the amount of Ni is 100 mg / m ² or less, excessive formation of a Ni—Sn alloy (Ni ₃ Sn ₄ phase) in the alloy layer 3b is suppressed, so that a minute amount in the alloy layer 3b during processing is suppressed. The generation of cracks can be suppressed. Therefore, the alloy layer 3b contains Fe and at least one chemical element selected from the group consisting of Sn and Ni. For example, the alloy layer 3b is a layer of Fe—Sn alloy (FeSn ₂ phase in Fe—Sn system), a layer of Fe—Ni alloy (α phase, γ phase in Fe—Ni system), Fe—Ni—Sn alloy (Fe -Ni-Sn based FeSn ₂ phase, Ni ₃ Sn ₄ phase mixed phase) may be at least one layer selected from the group consisting of layers.

(Chemical conversion treatment layer 4)
The chemical conversion treatment layer 4 located on the Sn plating layer 3a contains tin phosphate and zirconium oxide (IV). Moreover, this chemical conversion treatment layer 4 may be comprised from the lower layer (1st chemical conversion treatment layer 4a) containing a tin phosphate, and the upper layer (2nd chemical conversion treatment layer 4b) containing a zirconium oxide (IV). . Tin phosphate has a role as a binder for bonding zirconium oxide (IV) to the Sn plating layer 3a. When the chemical conversion treatment layer 4 contains tin phosphate and zirconium oxide (IV), the surface of the Sn plating layer 3a can be appropriately covered with the chemical conversion treatment layer 4 by controlling the surface structure. Improves.

The amount of P in the chemical conversion treatment layer 4 needs to be 3 to ²⁰ mg / m ² . If the amount of P is less than 3 mg / m ² , the chemical conversion treatment layer 4 cannot properly cover the plated metal layer 3, and the corrosion resistance of the plated steel sheet 1 decreases. On the other hand, when the amount of P exceeds 20 mg / m ² , the chemical conversion treatment layer 4 is destroyed by aggregation of the phosphoric acid compound, and the corrosion resistance of the plated steel sheet 1 is lowered. In order to further improve the corrosion resistance of the plated steel sheet 1, the amount of P in the chemical conversion layer 4 is preferably 4 mg / m ² or more, and more preferably 5 mg / m ² or more. In order to further suppress the aggregation of the phosphoric acid compound in the chemical conversion treatment layer 4 and further increase the corrosion resistance of the plated steel sheet 1, the amount of P in the chemical conversion treatment layer 4 is preferably 15 mg / m ² or less, preferably 10 mg / m 2. More preferably, it is ² or less. For example, the amount of P is more preferably 5 to 10 mg / m ² .

In some cases, zirconium oxide (IV) is present on the surface of the plated steel sheet 1 except for the coating film formed on the plated steel sheet 1. Zirconium oxide (IV) is stably present as a passive substance in a relatively wide pH range, and exhibits high corrosion resistance against various contents in contact with the inner surface of the can. In order for the chemical conversion treatment layer 4 containing zirconium oxide (IV) to properly coat the plated metal layer 3, the amount of Zr in the chemical conversion treatment layer 4 needs to be within a predetermined range. That is, the amount of Zr (in terms of metal Zr) in the chemical conversion treatment layer 4 needs to be more than 5 mg / m ^{2 and not} more than 30 mg / m ² . When the amount of Zr is 5 mg / m ² or less, the surface of the plated metal layer 3 is not properly covered with the chemical conversion treatment layer 4, so that sufficient corrosion resistance is not ensured. On the other hand, when the amount of Zr exceeds 30 mg / m ² , the chemical conversion treatment layer 4 is destroyed by aggregation of zirconium (IV) oxide, and the corrosion resistance of the plated steel sheet 1 is lowered. In order to enhance the barrier property of the chemical conversion treatment layer 4 and further increase the corrosion resistance of the plated steel sheet 1, the amount of Zr is preferably 6 mg / m ² or more, or 8 mg / m ² or more, preferably 9 mg / m ² or more or 10 mg / m. More preferably, it is ² or more. In order to further suppress the aggregation of zirconium (IV) in the chemical conversion treatment layer 4 and further increase the corrosion resistance of the plated steel sheet 1, the amount of Zr is preferably 25 mg / m ² or less, and 20 mg / m ² or less. It is more preferable. For example, the amount of Zr is more preferably 8 to ²⁰ mg / m ² . Moreover, the chemical conversion treatment layer 4 may contain F.

  When the P / Zr ratio is less than 0.35, the amount of tin phosphate is insufficient with respect to the amount of zirconium (IV) oxide. Therefore, the role of tin phosphate as a binder for bonding zirconium oxide (IV) to the Sn plating layer 3a is not sufficient, and the chemical conversion treatment layer 4 is brittle. Therefore, the plated steel sheet 1 does not have sufficient corrosion resistance, and the appearance of the plated steel sheet 1 may deteriorate. When the P / Zr ratio exceeds 1.00, tin phosphate is excessive with respect to zirconium (IV) oxide. Therefore, the effect of increasing the corrosion resistance of zirconium (IV) oxide is reduced by tin phosphate. Therefore, the plated steel sheet 1 does not have sufficient corrosion resistance, and the appearance of the plated steel sheet 1 may deteriorate.

  FIG. 5 shows an example of the relationship between the P / Zr ratio and the corrosion resistance. In FIG. 5, the plated steel sheet having sufficient corrosion resistance has a corrosion resistance of 3 or more. As shown in FIG. 5, when the P / Zr ratio is 0.35 to 1.00, the corrosion resistance of the plated steel sheet is sufficiently high even when there is no coating or with coating. On the other hand, if the P / Zr ratio is less than 0.35 or more than 1.00, sufficient corrosion resistance may be obtained when there is paint, but when there is no paint as can be understood from the arrows in FIG. Does not provide sufficient corrosion resistance. As described above, by controlling the P / Zr ratio appropriately, it is possible to obtain a superior and excellent effect that has not been recognized in the past. In order to obtain higher corrosion resistance more stably, the P / Zr ratio is preferably 0.95 or less, and more preferably 0.90 or less or 0.85 or less. Similarly, the P / Zr ratio is preferably 0.38 or more, and more preferably 0.40 or more or 0.50 or more.

  Further, in order to stably and sufficiently obtain the corrosion resistance of the plated steel sheet 1 without forming a coating film on the chemical conversion treatment layer 4, the surface structure of the chemical conversion treatment layer 4 containing zirconium (IV) oxide and tin phosphate ( For example, it is preferable that the thickness is properly controlled.

  Conditions regarding the structure of the chemical conversion treatment layer 4 can be evaluated using a field emission electron beam microanalyzer (FE-EPMA). The area ratio (area ratio of the low Zr region) of the region having an intensity level of 50% or less of the average strength level of Zr, obtained by analyzing the surface of the plated steel sheet 1 by this FE-EPMA mapping analysis is 0. It is preferable that the chemical conversion treatment layer 4 has a surface structure of 1 to 10%. In this case, if the range of the P / Zr ratio satisfies the above-described conditions, it can be determined that the chemical conversion treatment layer 4 properly covers the plated metal layer 3, which is stable and sufficient for the plated steel plate 1. Corrosion resistance can be imparted. For example, if the area ratio of the low Zr region is 10% or less, the corrosion region can be reliably limited to a radius of 35 μm or less. In this case, since the change of the plated steel sheet 1 due to corrosion cannot be visually confirmed, it can be regarded as having practically sufficient corrosion resistance. Also, for example, if the area ratio of the low Zr region is 0.1% or more, the chemical conversion coating 4 forms an appropriate surface structure with zirconium (IV) oxide and tin phosphate, so that it has practically sufficient corrosion resistance. Can be regarded as having stable. In addition, since such a surface structure is strong against stress, even when stress is applied to the coating film when the plated steel sheet 1 includes the coating film, it is possible to stably prevent cohesive failure of the chemical conversion coating 4. it can. Thus, the greater the uniformity and thickness of the chemical conversion layer 4, the more the corrosion resistance of the plated steel sheet 1 is not stably improved. Therefore, by controlling not only the amount of P and the amount of Zr but also the range of P / Zr and the surface structure of the chemical conversion treatment layer 4, it is possible to further improve the corrosion resistance or to stably obtain high corrosion resistance. In order to obtain higher corrosion resistance more stably, the area ratio of the low Zr region is more preferably 0.2% or more. Similarly, the area ratio of the low Zr region is more preferably 9% or less, and most preferably 8% or 6% or less.

(Measuring method)
The amount of metal Sn in the Sn plating layer 3a is measured by an electrolytic stripping method based on ASTM A630. In this electrolytic stripping method, a plated steel plate 1 to be measured is used for the anode, and a platinum plate is used for the cathode. A constant current is passed through these anodes and cathodes in 1N hydrochloric acid to create a potential-time curve, and then the amount of metal Sn is calculated according to Faraday's law. Further, the amount of Fe, Ni, and Sn in the alloy layer 3b is determined by the fluorescent X on the surface (peeled surface) of the steel plate obtained by peeling the metal Sn from the plated steel plate 1 by the electrolytic peeling method in accordance with the above ASTM A630. Analyzed and measured by X-ray elemental analysis (XRF). Furthermore, the FeSn ₂ phase, the Ni ₃ Sn ₄ phase, the α phase, and the γ phase in the alloy layer 3b are identified by a thin film X-ray diffraction method.

  The amount of P and the amount of Zr in the chemical conversion treatment layer 4 are measured by fluorescent X-ray elemental analysis (XRF). The measurement region is a region having a diameter of 20 mm or more on the surface of the plated steel sheet 1 (the surface of the chemical conversion treatment layer 4). For quantification of the P amount and the Zr amount, a calibration curve prepared in advance, that is, a relational expression between the P amount and the fluorescent X-ray intensity (CPS) of the wavelength corresponding to P, and the wavelength corresponding to the Zr amount and Zr are used. The relationship between the fluorescent X-ray intensity (CPS) is used. This calibration curve is obtained by measuring the X-ray fluorescence intensity (CPS) of a known sample whose P amount and Zr amount have been previously measured with an ICP emission spectrometer by XRF. In addition, if a fluorescent X-ray apparatus can measure P and Zr, a general commercial item can be used as a fluorescent X-ray apparatus without limiting a model.

  Furthermore, an X-ray photoelectron spectrum is measured by X-ray photoelectron spectroscopy (XPS), and this measurement is repeated in the thickness direction (depth direction) of the chemical conversion treatment layer 4. By analyzing the presence state of the chemical element from the obtained X-ray photoelectron spectrum, the layer structure of the chemical conversion treatment layer 4 is identified, and the compounds present in the chemical conversion treatment layer 4 are detected. The Sn ion in the chemical conversion layer 4 is identified from the amount of chemical shift in the Sn spectrum, and the phosphate ion in the chemical conversion layer 4 is identified from the amount of chemical shift in the P or O spectrum. When both Sn ions and phosphate ions are identified in the chemical conversion treatment layer 4, it is considered that tin phosphate is present in the chemical conversion treatment layer 4. Further, the zirconium (IV) oxide in the chemical conversion treatment layer 4 is identified from the amount of chemical shift in the Zr spectrum. The spectrum of P is obtained from the region of binding energy of 130 to 140 eV, the spectrum of Zr is obtained from the region of binding energy of 176 to 188 eV, and the spectrum of Sn is obtained from the region of binding energy of 482 to 490 eV. . Note that the analysis of the chemical conversion treatment layer 4 ends when the magnitude (height) of the spectrum of Sn existing as the metal Sn becomes substantially constant in the depth direction. The amount of each element (P amount, Zr amount, Sn amount) can be calculated from the area of the spectrum. When the area of the spectrum is 0, the amount is regarded as 0, and when the area of the spectrum is the maximum in the depth direction, the amount is regarded as 100, and the amount of P in the thickness direction of the chemical conversion layer 4 is Zr. Amount, Sn amount is determined. Here, since the thickness of the chemical conversion treatment layer 4 is very small compared to the roughness of the surface of the plated metal layer 3, the surface of the chemical conversion treatment layer 4 has a certain degree of roughness. Therefore, when the amount of P increases, the amount of Zr decreases, and the amount of Sn increases from the surface of the chemical conversion treatment layer 4 to a certain depth toward the inside, the chemical conversion treatment layer 4 is converted into the first chemical conversion treatment layer 4a. And the second chemical conversion treatment layer 4b existing on the surface of the first chemical conversion treatment layer 4a.

As described above, the distribution of zirconium oxide (IV) in the vicinity of the surface of the plated steel sheet 1 is obtained by analyzing the surface of the plated steel sheet 1 with a field emission electron beam microanalyzer (FE-EPMA). The Zr intensity level in a square area of 200 μm on one side of the surface of the plated steel sheet 1 is mapped at a pitch of 1 μm (200 × 200, 40,000 points). An average intensity level of Zr is calculated from the mapping data of the intensity level of Zr, and points having an intensity level of 50% or less of the average intensity level of Zr are counted. By dividing the number of obtained points by 40,000, which is the total number of data, the area ratio of a region having an intensity level of 50% or less of the average intensity level of Zr is calculated. Mapping analysis is performed once for any three positions on the surface of the plated steel sheet 1, and the area ratio of the area having an intensity level of 50% or less of the average intensity level of Zr by averaging the obtained three area ratios. To decide. That is, since the total number of data is 120,000 points, if the point having an intensity level of 50% or less of the average intensity level of Zr is 12,000 points or less, the intensity of 50% or less of the average intensity level of Zr The area ratio of the region having the level is considered to be 10% or less. For example, when the amount of Zr is 5 mg / m ² , the average intensity level of Zr can be regarded as 5 mg / m ² , so the amount of Zr corresponding to 50% of the average intensity level of Zr amount is 2.5 mg / m ^2. Can be considered. Under the measurement conditions described above, the region where the Zr amount is 2.5 mg / m ² or less is 10% or less, and when the region is considered to be circular, the radius of the region is about 35 μm or less. If the corrosion area is 35 μm or less, the change in the plated steel sheet 1 due to corrosion cannot be visually confirmed, so the above measurement conditions must be adopted.

(Production method)
Next, the manufacturing method of the plated steel plate which concerns on embodiment of this invention is explained in full detail.

  The process before plating a steel plate is not specifically limited. As pretreatment, for example, the steel sheet may be subjected to degreasing with electrolytic alkali and pickling with dilute sulfuric acid.

  Before the Sn is plated on the steel plate, the steel plate may be plated with Ni or an Fe—Ni alloy. In this case, as the Ni plating bath, for example, a watt bath mainly composed of nickel sulfate, nickel chloride, boric acid, a strike bath mainly composed of nickel chloride, or a total sulfuric acid bath mainly composed of nickel sulfate may be used. it can. Examples of the Fe-Ni alloy plating bath include a bath in which iron sulfate or iron chloride is added to the watt bath, a bath in which iron chloride is added to the strike bath, or a bath in which iron sulfate is added to the total sulfuric acid bath. Can be used. Further, after plating the steel plate with Ni, the Ni-plated steel plate may be heated to diffuse Ni into the steel plate surface layer, thereby forming a Fe—Ni alloy layer on the steel plate surface.

  The method of Sn plating is not particularly limited. For example, an acidic Sn plating bath such as a phenol sulfonic acid bath or a sulfuric acid bath containing a gloss additive can be used. When electric Sn plating is applied to the steel sheet in such an acidic Sn plating bath, good Sn plating can be obtained.

The steel plate after Sn plating may be dipped in a bath containing water or a diluted solution of Sn plating solution and dried. Then, you may reflow-process with respect to Sn plating steel plate. The reflow process is a step of heating the Sn-plated steel sheet to 232 ° C. or higher, which is the melting point of Sn, in order to impart gloss to the surface of the Sn-plated steel sheet. When this heating temperature is 300 ° C. or lower, generation of an excessive alloy layer can be suppressed. The heating means is not particularly limited. For example, electrical resistance heating, induction heating, or a combination thereof can be used as the heating means. Moreover, by quenching the Sn-plated steel sheet immediately after the reflow treatment, it is possible to prevent the FeSn ₂ phase and Ni ₃ Sn ₄ phase in the alloy layer and the tin oxide on the surface of the Sn plating layer from being excessively generated. it can. The Sn-plated steel sheet in which tin is melted can be quenched by immersing it in water.

  A chemical conversion treatment is performed on the Sn-plated steel sheet by the method described below.

  The feature of this method is that a chemical conversion treatment layer containing tin phosphate and zirconium (IV) oxide is formed using one bath. If a chemical conversion treatment layer containing two compounds that are difficult to produce at the same time is formed using two baths, two baths must be prepared, which is more expensive than one bath. In addition, operating conditions need to be constrained to avoid the adverse effects caused by the ingredients in the first bath being mixed into the next bath. For example, it is necessary to slow down the production line as one of the production conditions. In addition, when the plated steel sheet is washed when transferring the plated steel sheet from the first bath to the next bath in order to avoid mixing of components, a compound such as a hydroxide may be generated. Forming a chemical conversion treatment layer with only one bath not only reduces the cost and eases operating conditions, but also avoids the formation of intermediate by-products that adversely affect the surface structure of plated steel sheets. There are also merits.

The concentration of each ion in the chemical conversion solution will be described.
The zirconium ion concentration in the chemical conversion solution is 100 ppm to 10000 ppm. When the zirconium ion concentration is less than 100 ppm, the zirconium ions in the chemical conversion treatment solution necessary for nucleation and growth are insufficient, and a chemical conversion treatment layer containing a sufficient amount of zirconium (IV) oxide cannot be obtained. On the other hand, when the zirconium ion concentration exceeds 10,000 ppm, the chemical conversion treatment layer grows extremely and induces excessive unevenness in the chemical conversion treatment layer.

  In order to obtain higher barrier properties, the concentration of zirconium ions in the chemical conversion solution is preferably 500 ppm or more, and more preferably 1500 ppm or more. In addition, the zirconium ion concentration decreases, the unevenness of the chemical conversion treatment layer decreases, and the amount of deformation when the chemical conversion treatment layer breaks increases. Therefore, the zirconium ion concentration in the chemical conversion treatment liquid is preferably 9500 ppm or less, and more preferably 9000 ppm or less.

  Moreover, the fluoride ion density | concentration in a chemical conversion liquid is 100 ppm-10000 ppm. The fluoride ion forms a stable complex with zirconium ion (IV) to stabilize zirconium ion (IV) in the chemical conversion solution. In addition, fluoride ions improve the wettability and lyophilicity of the plated steel sheet, and the surface of the plated steel sheet is appropriately activated. When the fluoride ion concentration is less than 100 ppm, a complex of fluoride ion and zirconium ion (IV) is not sufficiently formed in the chemical conversion treatment solution, and a sufficient amount of stable zirconium ion (IV) is obtained. I can't.

On the other hand, when the fluoride ion exceeds 10,000 ppm, the fluoride ion and zirconium ion (IV) form a complex, whereby the zirconium ion (IV) is excessively stabilized. Usually, cathodic electrolysis increases the pH in the vicinity of the surface of the plated steel sheet, and the hydrolysis of the complex proceeds with this increase in pH. However, if the complex is overly stabilized, the rate of hydrolysis will decrease. Therefore, the responsiveness of the amount of Zr with respect to the cathode current density and the electrolysis time during the cathodic electrolysis treatment is remarkably lowered, and the time required for the cathodic electrolysis is remarkably increased. Further, when cathodic electrolysis is performed for a long time, excessive unevenness may be induced in the chemical conversion treatment layer.

  In order to stably obtain a chemical conversion treatment layer containing a higher amount of zirconium oxide, the concentration of fluoride ions in the chemical conversion treatment solution is preferably 500 ppm or more, and more preferably 1500 ppm or more. In order to improve the appearance of the plated steel sheet, the fluoride ion concentration is preferably 9500 ppm or less, and more preferably 9000 ppm or less.

  Moreover, the phosphate ion density | concentration in a chemical conversion liquid is 100 ppm-3000 ppm. When the phosphate ion concentration is 100 ppm to 3000 ppm, a chemical conversion treatment layer containing a sufficient amount of phosphate groups can be obtained. If the phosphate ion concentration is less than 100 ppm, a chemical conversion treatment layer containing a sufficient amount of phosphate groups cannot be obtained. That is, the phosphate ion concentration is required to be 100 ppm or more in order to react Sn ions eluted from the Sn plating layer and phosphate ions during the anodic electrolysis treatment and to add tin phosphate to the surface of the plated steel sheet. . When the phosphate ion concentration exceeds 3000 ppm, an insoluble matter that is considered to be composed of zirconium ions and phosphate ions may be easily generated in the chemical conversion solution. Therefore, effective zirconium ions and phosphate ions may decrease at the same time as insoluble substances contaminate the chemical conversion solution.

  In order to stably obtain a chemical conversion treatment layer containing a higher amount of tin phosphate, the concentration of phosphate ions in the chemical conversion treatment solution is preferably 300 ppm or more, and more preferably 1000 ppm or more. Further, in order to more optimally control the amount of P in the chemical conversion treatment layer or to more efficiently use the chemical conversion treatment solution, the concentration of phosphate ions is preferably 2800 ppm or less, and preferably 2500 ppm or less. It is more preferable.

  Moreover, the nitrate ion density | concentration in a chemical conversion liquid is 100 ppm-30000 ppm. When the nitrate ion concentration is 100 ppm to 30000 ppm, the electrical conductivity necessary for the anodic electrolysis treatment and the cathodic electrolysis treatment can be maintained, and a chemical conversion treatment film can be formed on the surface of the plated steel sheet. If the nitrate ion concentration is less than 100 ppm, the conductivity necessary for the electrolytic treatment cannot be obtained, and a chemical conversion coating is not formed. When the nitrate ion concentration exceeds 30000 ppm, the chemical conversion film is formed even with a minute current. Therefore, it is difficult to control the generation rate of the chemical conversion coating so that local growth and the like can be suppressed.

  In order to use the current more efficiently, the nitrate ion concentration in the chemical conversion treatment liquid is preferably 500 ppm or more, and more preferably 2000 ppm or more. Further, in order to further reduce the unevenness of the chemical conversion treatment film, the nitrate ion concentration in the chemical conversion treatment solution is preferably 25000 ppm or less, and more preferably 22000 ppm or less.

  Furthermore, it is preferable that pH of a chemical conversion liquid is 3 or more. When the pH of the chemical conversion treatment solution is 3 or more, hydrolysis of a complex formed by fluoride ions and zirconium ions (IV) is easily promoted when the pH in the vicinity of the surface of the plated steel sheet increases during cathodic electrolysis. Moreover, it is preferable that the pH of a chemical conversion liquid is 4 or less. When the pH of the chemical conversion solution is 4 or less, a complex formed by fluoride ions and zirconium ions (IV) can be stably obtained. Moreover, when the pH of the chemical conversion treatment liquid is 4 or less, it can be prevented that zirconium oxide (IV) is generated in the chemical conversion treatment liquid and the amount of zirconium ions (IV) is lowered. Therefore, it is preferable that pH of a chemical conversion liquid is 3-4. Nitric acid may be used to lower the pH, and ammonia water may be used to raise the pH.

  Moreover, the temperature of the chemical conversion liquid at the time of an electrolytic process is 20 to 60 degreeC. In this temperature range, the complex formed by fluoride ions and zirconium ions (IV) is stabilized in the chemical conversion solution. In addition, at a temperature of less than 20 ° C., insoluble matter that is considered to be composed of zirconium ions and phosphate ions tends to be generated in the chemical conversion treatment liquid. At a temperature higher than 60 ° C., a complex formed by fluoride ions and zirconium ions (IV) becomes unstable in the chemical conversion solution. Moreover, since a chemical conversion liquid tends to evaporate, a chemical conversion liquid cannot be used for a long time.

  The most significant feature of this method is that anodic electrolysis and cathodic electrolysis are performed in this order in one bath (one kind of chemical conversion solution), and tin phosphate, zirconium oxide (IV) and Forming a chemical conversion treatment layer containing

  Next, conditions for electrolytic treatment will be described. The amount of P and the amount of Zr in the chemical conversion treatment layer are not limited to the following conditions because they vary depending not only on the electrolytic treatment conditions but also on the surface properties of the plated steel sheet before the electrolytic treatment. However, it is preferable to select the following conditions so that the predetermined P amount and Zr amount can be stably obtained while avoiding the influence of the surface properties of the plated steel sheet.

In order to reduce oxides near the surface of the plated metal layer (for example, tin oxide formed near the surface of Sn plating by reflow treatment), in some cases, cathodic electrolysis is added as a pretreatment before anodic electrolysis You may do it. In this pretreatment (cathodic electrolytic treatment), the cathode current density is preferably 0.1 to 10 A / dm ² , and the energization amount is preferably 1 to 10 C / dm ² . When the cathode current density is 0.1 A / dm ² or more, tin oxide generated by the reflow treatment can be sufficiently reduced.

On the other hand, when the cathode current density in this pretreatment is 10 A / dm ² or less, it is possible to more reliably prevent substances that inhibit the formation of tin phosphate from adhering to the surface of the plated steel sheet. In order to reduce the amount of such substances, the cathode current density is preferably 1 A / dm ² . When the energization amount is 1 C / dm ² or more, tin oxide generated by the reflow treatment can be sufficiently reduced. On the other hand, when the energization amount is 10 C / dm ² or less, not only the tin oxide generated by the reflow process can be efficiently reduced, but also zirconium (IV) oxide is hardly generated. Even if the pretreatment by the cathodic electrolysis is performed before the anodic electrolysis, Sn in the Sn plating cannot be eluted, so that tin phosphate is not formed.

The anodic electrolysis treatment is a step of imparting tin phosphate to the surface of the plated steel sheet by combining Sn ions generated by slowly dissolving tin plating in the chemical conversion treatment solution with phosphate ions in the chemical conversion treatment solution. . In the anodic electrolysis treatment, the anode current density of ^{0.1A / dm 2 ~2A / dm 2} , the energization amount preferably a ^{0.1C / dm 2 ~2C / dm 2} . When the anode current density is 0.1 A / dm ² or more, Sn can be dissolved at a sufficiently high rate, and a sufficient amount of tin phosphate is added for a suitable time to impart sufficient corrosion resistance to the plated steel sheet. Can be obtained within.

On the other hand, when the anode current density is 2 A / dm ² or less, tin can be dissolved at a sufficiently stable rate, so that dense and tough tin phosphate is produced. Therefore, the chemical conversion treatment layer is not easily destroyed by aggregation of tin phosphate, and sufficient corrosion resistance can be stably imparted to the plated steel sheet. When the energization amount is 0.1 C / dm ² or more, a sufficient amount of tin phosphate can be adhered to the surface of the plated steel sheet. On the other hand, when the energization amount is 2 C / dm ² or less, it is possible to prevent a large amount of Sn from eluting from the Sn plating layer, and it is possible to sufficiently maintain the Sn plating layer effective for barrier-type anticorrosion.

Cathodic electrolysis is performed after the anodic electrolysis, and zirconium (IV) oxide is formed on the surface of the plated steel sheet formed with tin phosphate. In this cathodic electrolysis treatment, the cathode current density is preferably 1 to 20 A / dm ² and the energization amount is preferably 5 to 50 C / dm ² . When the cathode current density is 1 A / dm ² or more, the pH in the vicinity of the surface of the cathode is sufficiently increased, and zirconium (IV) oxide can be generated at a sufficient rate, so that productivity is high.

On the other hand, when the cathode current density is 20 A / dm ² or less, it is possible to prevent a region where the current density is locally increased or to generate hydrogen gas, so that zirconium (IV) oxide can be prevented. Can be more reliably eliminated. When the energization amount is 5 C / dm ² or more, it is possible to stably ensure a sufficient amount of zirconium oxide (IV) to obtain sufficient corrosion resistance. On the other hand, it can prevent that a chemical conversion treatment layer peels in a chemical conversion liquid as the energization amount is 50 C / dm < ² > or less. Moreover, since zirconium oxide (IV) can be efficiently produced in a short time, the amount of zirconium oxide (IV) can be controlled with higher productivity.

The amount of P, the amount of Zr, and the ratio P / Zr in the chemical conversion treatment layer can be controlled by the composition and temperature of the chemical conversion treatment solution, the conditions of anodic electrolysis, and the conditions of cathodic electrolysis. In this embodiment, P in the chemical conversion treatment layer is mainly derived from tin phosphate. On the other hand, in the present embodiment, Zr in the chemical conversion treatment layer is mainly derived from zirconium (IV) oxide. The ratio P / Zr can be controlled by controlling the amount of P (mainly tin phosphate) and the amount of Zr (mainly zirconium (IV) oxide). Specifically, the P amount in the chemical conversion treatment layer is in the range of 3 to ²⁰ mg / m ² , the Zr amount in the chemical conversion treatment layer is in the range of more than 5 to 30 mg / m ² , and the ratio P between the P amount and the Zr amount P The conditions of anodic electrolysis in the anodic electrolysis process and cathodic electrolysis in the cathodic electrolysis process are controlled so that / Zr is in the range of 0.35 to 1.00.

In order to increase the amount of P in the chemical conversion treatment layer, for example, the phosphate ion concentration and the nitrate ion concentration in the chemical conversion treatment solution, the current density of the anodic electrolysis and the energization amount are increased within the above ranges.
In order to increase the amount of Zr in the chemical conversion treatment layer, for example, the zirconium ion concentration and nitrate ion concentration in the chemical conversion treatment solution, the current density of the cathodic electrolysis, and the energization amount are increased within the above ranges.

  The manufacturing process in this embodiment will be described consistently. If necessary, the oil and scale adhering to the surface of the original steel plate are removed (cleaning step). Next, Ni-based plating is applied to the surface of the steel sheet as necessary (pre-plating step). Next, Sn is plated on the surface of the steel plate (electrical Sn plating step). Next, if necessary, Sn in the Sn plating layer is melted and solidified by water cooling (reflow process). Next, a chemical conversion treatment layer is formed on the Sn plating layer by chemical treatment (after anodic electrolytic treatment and cathodic electrolytic treatment) (chemical conversion treatment step). Finally, rust preventive oil is applied to the surface of the chemical conversion treatment layer as necessary. FIG. 6 shows an outline of the order of the manufacturing process, and FIG. 7 shows an outline of the order of the chemical conversion treatment process. In FIGS. 6 and 7, a process surrounded by a broken line indicates a process performed as necessary (a process that can be skipped if necessary), and a process surrounded by a solid line indicates an essential process. .

  Examples according to the present invention will be described below.

  A steel strip having a plate thickness of 0.18 mm and a tempering degree of T-4CA was used as a steel plate (original plate). This steel strip is obtained by continuously annealing a low carbon cold-rolled steel strip and then temper rolling. Prior to plating, the steel strip was electrolytically degreased in a 10 mass% sodium hydroxide solution and then pickled with 5 mass% dilute sulfuric acid.

  Some steel strips were subjected to Fe—Ni alloy plating or Ni plating. In a part of the steel strip subjected to Ni plating, Ni was diffused in the steel strip by annealing to form an Fe—Ni alloy layer.

Next, electrotin plating was applied to the steel strip using a ferrostan bath. The surface of the steel strip was subjected to cathodic electrolysis at a cathode current density of 20 A / dm ² in a tin plating solution at 50 ° C. containing 20 g / L of tin ions, 75 g / L of phenolsulfonic acid ions and 5 g / L of surfactant. As the anode, platinum-plated titanium was used. The amount of tin plating was adjusted to 2.8 g / m ² by adjusting the electrolysis time. After tin plating, the tin-plated steel sheet was immersed in a solution obtained by diluting the above tin-plating solution 10 times, and the liquid adhering to the surface of the tin-plated steel sheet was removed with a rubber roll. Thereafter, the tin-plated steel sheet was dried with cold air. Furthermore, the tin-plated steel sheet was heated from room temperature to 250 ° C. for 10 seconds by energization heating to reflow the tin. Immediately after the tin reflowed, the tinned steel sheet was quenched with 80 ° C. water.

  Subsequently, a chemical conversion treatment film was formed on the aforementioned Sn-plated steel sheet under the conditions shown in Tables 1-5. Regarding the items of “pre-plating” and “electrolytic pattern” in Tables 1 to 5, “−” indicates that the corresponding treatment was not performed. In addition, in the item of “electrolysis pattern”, the electrolytic treatment was sequentially performed from the left to the right. The obtained plated steel sheet with a chemical conversion treatment film was evaluated as follows. Moreover, pH of the chemical conversion liquid was adjusted to 3.8.

<Sample for analysis of chemical conversion coating>
Samples for analysis of chemical conversion coatings were separated from each edge in the plate width direction of the plated steel plate by a distance of 1/4 of the plate width (2 locations), and the center of the plate width of the plated steel plate (1 location) From. Further, this sampling position was 1 m or more away from the edge in the rolling direction of the plated steel sheet.

<Analyzing method of chemical conversion coating>
The amounts of Zr and P were measured by fluorescent X-ray elemental analysis. For the preparation of the calibration curve, a known sample whose Zr amount and P amount were previously measured with an ICP emission spectrometer was used. The measurement area was 20 mmΦ. In addition, the presence state of elements in the depth direction was analyzed by XPS. In XPS, Quantum 2000 manufactured by ULVAC-PHI was used. The measurement conditions are as follows.
X-ray source: AlKα
X-ray output: 15 kV, 25 W
Measurement area: 100μmΦ
Degree of vacuum: 2.1 × 10 ⁻⁷ Pa
Sputtering speed: 17.6 nm / min (Sputtering speed in terms of SiO ₂ )

  Furthermore, the strength level of Zr in a square region of 200 μm on one side of the surface of the plated steel plate was measured with FE-EPMA at a pitch of 1 μm, and this strength level was mapped (40,000 points of 200 × 200). From this mapping data, the area ratio of a region having an average intensity level of Zr and an intensity level of Zr equal to or less than 50% of the average intensity level of Zr was obtained. The “area ratio of the low Zr region” in Tables 1 and 2 indicates the area ratio of a region having an intensity level of Zr that is 50% or less of the average intensity level of Zr.

<Testing method for corrosion resistance>
<Corrosion resistance without painting>
As the corrosion resistance test solution, an aqueous solution in which a 0.1% sodium thiosulfate aqueous solution and 0.1N sulfuric acid were mixed at a volume ratio of 1: 2 was used. A circular test piece having a diameter of 35 mm was cut out from the plated steel plate, and the test piece was placed and fixed on the mouth of a heat-resistant bottle containing a corrosion resistance test solution. After heat-treating the heat-resistant bottle at 121 ° C. for 60 minutes, the corrosion area of the test piece was measured. Corrosion resistance was evaluated from the ratio of the corrosion area of the test piece to the area of the mouth of the heat-resistant bottle. The area of the mouth of the heat-resistant bottle means the area where the test piece comes into contact with the corrosion resistance test solution.

  Corrosion resistance was evaluated with a score of 1 to 5 according to the ratio of the corrosion area. The larger this score, the smaller the corrosion area. A steel strip having a rating of 3 or more was regarded as a plated steel plate having good corrosion resistance.

<Corrosion resistance with paint>
In order to evaluate the corrosion resistance of the evaluation material (plated steel plate) on the surface corresponding to the inner surface of the can, a UCC (under cutting corrosion) test was performed. An epoxy phenol-based paint was applied to the surface of the plated steel sheet at 50 mg / dm ^{2 and} baked at 205 ° C. for 10 minutes. Furthermore, the baking was performed at 180 ° C. for 10 minutes. A sample having a size of 50 mm × 50 mm was cut out from the coated plate. A cross-cut (grid-like cut) such that the cutter blade reaches the ground iron was put in the coating film on the sample surface, and the end surface and back surface of the sample were sealed with paint. Thereafter, the sample was immersed in a test solution at 55 ° C. composed of 1.5% citric acid and 1.5% sodium chloride for 96 hours under open air. Immediately after washing and drying the sample, a tape was applied to the sample so as to include the vicinity of the cut portion and the flat portion, and the tape was peeled off from the sample. Then, in order to evaluate corrosion resistance, the cut part vicinity and the plane part were observed, and it was confirmed whether there was pitting corrosion in the cut part vicinity, and whether the coating film of the plane part was peeled off.

  Samples that were neither stripped nor corroded by the tape were scored 4 (very good). A sample in which the area where the coating film was peeled off by the tape was 0 mm or more and less than 0.2 mm from the cut portion and a sample in which only slight corrosion that could not be visually confirmed was given 3 points (good). Two points (slightly poor) were given to the sample in which the area where the coating film was peeled off by the tape was 0.2 mm or more and 0.5 mm or less from the cut part and the sample where corrosion was visually observed. One point (defect) was given as a score to a sample in which the area where the coating film was peeled off by the tape was more than 0.5 mm from the cut part. A steel strip having a rating of 3 or more was regarded as a plated steel plate having good corrosion resistance.

<Coating film adhesion (T peel test)>
An epoxyphenol-based paint was applied to the plated steel sheet at 5 g / m ^{2 and} baked so that the maximum temperature reached 180 ° C. Two test pieces having a size of 5 mm × 100 mm were cut out from the plated steel sheet. A nylon adhesive film having a size of 5 mm × 90 mm × 0.05 mm was sandwiched between the two test pieces, and the coated surface of the test piece and the nylon adhesive film were bonded by heating and pressure. As a result, an area without the nylon adhesive film remained at the longitudinal ends of the two test pieces. Each of these regions is perpendicular to the longitudinal direction of the specimen (longitudinal direction of the nylon adhesive film) and the specimen is T-shaped in a cross section perpendicular to the width direction of the specimen (width direction of the nylon adhesive film). The regions were bent to form a shape. The region was grasped with a chuck of a tensile tester and pulled at 200 mm / min to measure peel strength (T peel strength). This T peel strength is the strength per 5 mm width of the test piece. When the T peel strength exceeded 4 kgf (4 kg / 5 mm), it was determined that the coating film adhesion of the plated steel sheet was high. On the other hand, when the T peel strength was 4 kgf (4 kg / 5 mm) or less, it was determined that the coating film adhesion of the plated steel sheet was low.

  As a result, in some plated steel sheets, the T peel strength was 2 to 4 kgf, and in the remaining plated steel sheets, the T peel strength was 6 kgf or more. In the plated steel sheet having a T peel strength of 2 to 4 kgf, the peel surface of one test piece had a dull metallic luster, and the peel surface of the other test piece was covered with a coating film. When the peeled surface of these test pieces was analyzed by an electron beam microanalyzer (EPMA), Zr was detected in both test pieces. That is, in the plated steel sheet having a T peel strength of 2 to 4 kgf, the adhesion of the coating film was lowered due to the cohesive failure of the chemical conversion coating. On the other hand, in the plated steel sheet having a T peel strength of 6 kgf or more, both peeling surfaces of the test pieces were covered with the coating film. When the peeled surface of these test pieces was analyzed by an electron beam microanalyzer (EPMA), Zr was not detected in both test pieces. This means that cohesive failure does not occur in the chemical conversion coating.

  In Table 1, the influence which the composition of a chemical conversion liquid has on the corrosion resistance of a plated steel sheet is shown. In Table 2, the influence which the temperature of a chemical conversion liquid has on the corrosion resistance of a plated steel plate is shown. Tables 3 to 5 show the influence of the electrolytic treatment conditions on the corrosion resistance of the plated steel sheet. In addition, with respect to the items of “area ratio of low Zr region” and “corrosion resistance” in Tables 1 and 2, “−” indicates that a chemical conversion treatment layer could not be formed (a precipitate is generated in the chemical conversion treatment solution and the chemical conversion treatment solution Indicates that the corresponding item was not evaluated. Further, regarding the items of “Zr amount” and “P / Zr” in Table 4, “ND” indicates that Zr could not be detected, and “−” indicates that the value of P / Zr cannot be calculated. .

  From Tables 1 to 5, it is clear that in the invention examples, the plated steel sheet has excellent corrosion resistance. Moreover, from the measurement result by XPS, the chemical conversion treatment layer contained Sn phosphate (tin phosphate) and zirconium oxide (IV) in all the conditions of the inventive examples. In some of the inventive examples, two layers were clearly recognized in the chemical conversion treatment layer. On the other hand, in the comparative example, the corrosion resistance of the plated steel sheet was insufficient. Among these comparative examples, under condition 71, since anodic electrolysis was not performed, phosphoric acid Sn was not recognized in the chemical conversion treatment layer. Under condition 72, no cathodic electrolysis was performed, and therefore no zirconium compound such as zirconium oxide (IV) was found in the chemical conversion treatment layer. In both conditions 71 and 72, two layers were not recognized in the chemical conversion treatment layer.

  Table 6 shows the corrosion resistance of the plated steel sheet (condition 82) manufactured under the same manufacturing conditions as the steel sheet 8 of Patent Document 2. Under this condition 82, sufficient corrosion resistance was obtained when the plated steel sheet was coated. However, when the plated steel sheet is not coated, the plated steel sheet under condition 82 did not have sufficient corrosion resistance. Moreover, under this condition 82, phosphoric acid Sn was not recognized in the chemical conversion treatment layer.

Furthermore, in Table 7 and Table 8, the corrosion resistance and coating-film adhesiveness of the plated steel plate (conditions 83 and 84) manufactured on the manufacturing conditions similar to Example 9, Example 27, and Comparative Example 9 of patent document 4 are shown. . That performs a cathodic electrolysis treatment and anodic electrolysis treatment in some bath containing the phosphate salt solution, then under negative electrode electrolytic treatment in a separate bath containing the aqueous solution containing zirconium ion, forming a chemical conversion treatment layer did. Moreover, the conditions in Example 9 and Example 27 of Patent Document 4 were changed as appropriate to change the amounts of P and Zr in the chemical conversion treatment layer. Under these conditions 83 and 84, sufficient corrosion resistance could not be obtained both when the plated steel sheet was coated and when the plated steel sheet was not coated. Also, the coating film adhesion evaluated by the T peel test was not sufficient. On the other hand, sufficient coating film adhesion was obtained in all the conditions of the inventive examples in Tables 1 to 4. Table 9 shows a part of the coating adhesion results obtained from the plated steel sheets of the inventive examples.

  Since the present invention provides a plated steel sheet having a very good corrosion resistance and a manufacturing method thereof, the industrial applicability of the present invention is clear.

DESCRIPTION OF SYMBOLS 1 Plated steel plate 2 Steel plate 3 Plating metal layer 3a Sn plating layer 3b Alloy layer (alloying layer)
4 Chemical conversion layer (chemical conversion coating)
4a First chemical conversion treatment layer (first chemical conversion treatment film)
4b 2nd chemical conversion treatment layer (2nd chemical conversion treatment film)

Claims (15)

Steel sheet,
A plating metal layer including a Sn plating layer;
With a chemical conversion treatment layer,
The plated metal layer is present on the surface of the steel plate,
The chemical conversion treatment layer exists on the surface of the Sn plating layer,
Wherein in the chemical conversion treatment layer, a P amount is 3 to 20 mg / ^{m 2,} Zr amount is less 5 mg / ^{m 2} Ultra and 30 mg / ^{m 2,}
The ratio P / Zr of the P amount and the Zr amount is 0.35 to 1.00,
The chemical conversion treatment layer viewed contains a phosphoric acid-tin oxide and zirconium oxide (IV),
In the chemical conversion treatment layer, an area ratio having an intensity of 50% or less of an average intensity of Zr obtained by mapping analysis of a field emission electron beam microanalyzer is 0.1 to 10%. Plated steel sheet. The plated steel sheet according to claim 1 , wherein the Sn plating layer is present on a surface of the steel sheet. The plated metal layer further comprises an alloy layer,
This alloy layer is present on the surface of the steel sheet,
The Sn plating layer is present on the surface of the alloy layer,
2. The plated steel sheet according to claim 1 , wherein the alloy layer includes at least one chemical element selected from the group consisting of Sn and Ni, and Fe. The alloy layer includes at least one alloy selected from the group consisting of a FeSn ₂ phase, a Ni ₃ Sn ₄ phase, an α phase in an Fe—Ni system, and a γ phase in an Fe—Ni system. Item 4. A plated steel sheet according to item 3 . The said Zr amount is 6 mg / m < ² > or more, The plated steel plate as described in any one of Claims 1-4 characterized by the above-mentioned. The said Zr amount is 8 mg / m < ² > or more, The plated steel plate as described in any one of Claims 1-4 characterized by the above-mentioned. An Sn plating step of plating Sn on the steel sheet;
An anodic electrolytic treatment step of performing an anodic electrolytic treatment on the steel sheet in the chemical conversion solution after the Sn plating step;
A cathodic electrolysis process of performing a cathodic electrolysis process on the steel sheet in the chemical conversion solution after the anodic electrolysis process;
Consists of
The chemical conversion treatment solution includes 100 ppm to 10000 ppm of zirconium ions, 100 ppm to 10000 ppm of fluoride ions, 100 ppm to 3000 ppm of phosphate ions, and 100 ppm to 30000 ppm of nitrate ions, and the temperature of the chemical conversion treatment solution is 20 ℃ -60 ℃,
Range P content of 3 to 20 mg / ^{m 2} of the chemical conversion layer, in the range Zr amount of 5 super to 30 mg / ^{m 2} of the chemical conversion treatment layer, the P content and the Zr amount ratio P / Zr The conditions of the anodic electrolysis treatment in the anodic electrolysis treatment step and the cathodic electrolysis treatment conditions in the cathodic electrolysis treatment step are controlled so as to be within a range of 0.35 to 1.00. The manufacturing method of the plated steel plate as described in any one of 1-6. The plated steel sheet according to claim 7 , further comprising a Ni-containing plating step of plating the steel plate with at least one metal selected from the group consisting of Ni and Fe-Ni before the Sn plating step. Manufacturing method. Before performing the anodic electrolysis treatment step, manufacture of the plated steel sheet according to claim 7 or 8, wherein the method further comprises a pretreatment electrolysis step of performing cathodic electrolysis treatment to the steel sheet in the chemical conversion treatment solution Method. The current density during the cathodic electrolysis in the pretreatment electrolysis step is 0.1 to 10 A / dm ² , and an energization amount by the cathodic electrolysis is 1 to 10 C / dm ^2. The manufacturing method of the plated steel plate of 9 . In the anodic electrolytic treatment step, the current density during the anodic electrolytic treatment is 0.1 A / dm ^{2 to 2} A / dm ² , and the energization amount by the anodic electrolytic treatment is 0.1 C / dm ^{2 to 2} C / dm ² . method for producing a plated steel sheet according to any one of claims 7 to 10, characterized in that. In the cathode electrolytic treatment step, the current density in the cathode electrolytic treatment is 1 to 20A / dm ^2, claim 7 energization amount by the cathodic electrolysis treatment is characterized by a 5~50C / dm ² ~ The manufacturing method of the plated steel plate as described in any one of 11 . Method for producing a plated steel sheet according to any one of claims 7 to 12, wherein the Zr amount is 6 mg / ^{m 2} or more. Method for producing a plated steel sheet according to any one of claims 7 to 12, wherein the Zr amount is 8 mg / ^{m 2} or more. Method for producing a plated steel sheet according to any one of claims 7 to 14, wherein the pH of the chemical conversion treatment solution is 3-4.

Images