JP7097491B2 - Surface-treated steel sheet - Google Patents

Description

The present invention relates to a surface-treated steel sheet having stable and excellent corrosion resistance and white rust resistance, as well as good surface appearance.

It is known that hot-dip Al-Zn-based plated steel sheets represented by 55% Al-Zn-based steel sheets exhibit high corrosion resistance among hot-dip galvanized steel sheets because they have both the sacrificial corrosion resistance of Zn and the high corrosion resistance of Al. Has been done. Therefore, due to its excellent corrosion resistance, hot-dip Al-Zn plated steel sheets are mainly used in the field of building materials such as roofs and walls that are exposed to the outdoors for a long period of time, and in the field of civil engineering and construction such as guard rails, wiring pipes, and soundproof walls. .. In particular, there is an increasing demand for materials with excellent corrosion resistance and maintenance-free materials under harsher usage environments such as acid rain due to air pollution, spraying of snowmelt to prevent road freezing in snowy areas, and coastal area development. Therefore, in recent years, the demand for molten Al-Zn-based plated steel sheets has been increasing.

The plating film of the molten Al-Zn-based plated steel sheet is composed of the portion where Al containing Zn in hypersaturation is solidified into a dendrite (α-Al phase) and the Zn-Al co-crystal structure existing in the dendrite gap (interdendrite). It is characterized by having a structure in which a plurality of α-Al phases are laminated in the film thickness direction of the plating film. Due to such a characteristic film structure, the corrosion progress path from the surface becomes complicated, so that the corrosion does not easily proceed, and the hot-dip Al-Zn-based plated steel sheet becomes a hot-dip galvanized steel sheet having the same plating film thickness. It is also known that better corrosion resistance can be achieved.

Attempts have been made to further extend the life of such hot-dip Al-Zn-based plated steel sheets, and molten Al-Zn-Si-Mg-based plated steel sheets to which Mg has been added have been put into practical use.
As such a molten Al-Zn-Si-Mg-based plated steel sheet, for example, Patent Document 1 contains an Al-Zn-Si alloy containing Mg in a plating film, and the Al-Zn-Si alloy is 45 to An alloy containing 60% by weight elemental aluminum, 37-46% by weight elemental zinc and 1.2-2.3% by weight Si, wherein the Mg concentration is 1-5% by weight, molten Al-Zn-Si-. Mg-based plated steel sheets are disclosed.
Further, in Patent Document 2, the plating film contains at least one of 2 to 10% Mg and 0.01 to 10% Ca to improve corrosion resistance and protect the base steel sheet after it is exposed. A hot-dip Al-Zn-Si-Mg-based plated steel sheet for the purpose of enhancing the above is disclosed.
Further, in Patent Document 3, Mg: 1 to 15%, Si: 2 to 15%, Zn: 11 to 25% are contained in mass%, and the balance forms a coating layer composed of Al and unavoidable impurities. , Molten Al-Zn-Si-Mg system with improved corrosion resistance of flat plate and end face by reducing the size of intermetallic compounds such as Mg ₂ Si phase and Mg Zn ₂ phase present in the plating film to 10 μm or less. Plated steel plates are disclosed.

Since the above-mentioned molten Al-Zn-based plated steel sheet has a beautiful appearance with a spangle pattern of white metallic luster, it is often used without painting, and the actual situation is that there is a strong demand for its appearance. be. Therefore, techniques for improving the appearance of hot-dip Al-Zn-based plated steel sheets have also been developed.
For example, Patent Document 4 discloses a molten Al-Zn-Si-Mg-based plated steel sheet in which wrinkle-like unevenness defects are suppressed by containing 0.01 to 10% Sr in the plating film.
Further, Patent Document 5 also discloses a molten Al-Zn-Si-Mg-based plated steel sheet in which mottled defects are suppressed by containing 500 to 3000 ppm of Sr in the plating film.
Further, Patent Document 6 discloses a molten Al-Zn-Si-Mg-based plated steel sheet in which 0.001 to 1.0% of Sr is contained in the plating film to achieve both surface appearance and corrosion resistance.
Further, Patent Document 7 also describes a molten Al-Zn-Si-Mg-based plated steel sheet in which 0.001 to 1.0% of Sr is contained in the plating film to achieve both surface appearance and corrosion resistance between the flat plate portion and the processed portion. Is disclosed.
Furthermore, Patent Document 8 also discloses a molten Al-Zn-Si-Mg-based plated steel sheet that achieves both surface appearance and corrosion resistance by containing 0.01 to 0.2% Sr in the plating film. ..
Further, Patent Document 9 discloses a molten Al-Zn-Si-Mg-based plated steel sheet having improved corrosion resistance by controlling the Si and Mg concentrations in the plating film at a specific ratio.

The above-mentioned molten Al-Zn-based plated steel sheet has a problem that white rust is generated due to corrosion of the plating film when used in a severe corrosive environment. Since this white rust causes deterioration of the appearance of the steel sheet, a plated steel sheet with improved white rust resistance has been developed.
For example, Patent Document 10 describes molten Al-Zn-Si in which the mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer is optimized for the purpose of improving the white rust resistance of the processed portion. -Mg-based plated steel sheets are disclosed.
Further, in Patent Document 11, blackening resistance and white rust resistance are improved by forming a chemical conversion film containing a urethane resin on the plating film of a molten Al-Zn-Si-Mg-based plated steel sheet. The technology is disclosed.

Japanese Patent No. 5020228 Japanese Patent No. 5000039 Japanese Unexamined Patent Publication No. 2002-12959 Japanese Patent No. 3983932 Special Table 2011-514934 International Publication No. 2020/179147 International Publication No. 2020/179148 Japanese Unexamined Patent Publication No. 2020-143370 International Publication No. 2016/140370 Japanese Patent No. 5751093 Japanese Unexamined Patent Publication No. 2019-155872

However, the technique of containing Mg in the plating film as disclosed in Patent Documents 1 to 3 does not always bring about the improvement of corrosion resistance uniquely.
In the molten Al-Zn-Si-Mg-Sr-based plated steel sheets disclosed in Patent Documents 1 to 3, the corrosion resistance is improved only by containing Mg in the plating component, but the metal phase constituting the plating film is formed. -The characteristics of the intermetallic compound phase were not taken into consideration, and it was not possible to uniformly talk about the superiority or inferiority of corrosion resistance. Therefore, even when a molten Al-Zn-Si-Mg-Sr-based plated steel sheet is manufactured using the same plating bath composition, the corrosion resistance varies when the corrosion acceleration test is carried out, and the Al-Zn-based steel sheet to which Mg is not added is present. There was a problem that it was not always superior to the plated steel sheet.
Similarly, in improving the plating appearance, simply adding Sr to the plating film does not necessarily eliminate the wrinkle-like unevenness defects, and the molten Al-disclosed in Patent Documents 4 to 8 can be eliminated. In some cases, the Zn-Si-Mg-Sr-based plated steel sheet could not achieve both corrosion resistance and appearance.

In addition, when the steel sheet is plated with a bath in which Mg is added to the molten Al-Zn-Si bath, Mg ₂ Si phase, Mg Zn ₂ phase, and Si phase are deposited in the plating film in addition to the α-Al phase. It is known. However, the effect of the precipitation amount and abundance ratio of each phase on the corrosion resistance has not been clarified.
In the molten Al-Zn-Si-Mg-based plated steel sheet disclosed in Patent Document 9, the concentration of Si and Mg is controlled at a specific ratio, and the corrosion resistance is improved by eliminating the precipitation of the Si phase in the plating film. However, it cannot always be said that the Si phase can be suppressed, and even if the formation of the Si phase in the plating film can be suppressed, excellent corrosion resistance may not be obtained, which is technically incomplete. Met.

Furthermore, regarding the white rust resistance, it was not possible to sufficiently improve any of the techniques. Regarding the molten Al-Zn-Si-Mg-based plated steel sheet of Patent Document 10, although the improvement of the white rust resistance in the processed portion and the flat plate portion after heating is described, the white rust resistance in the unheated flat plate portion is described. Was not taken into consideration, and the realization of stable white rust resistance was still an issue. Further, the molten Al-Zn-Si-Mg-based plated steel sheet of Patent Document 11 is not always stable and excellent in corrosion resistance and white rust resistance, and further improvement has been desired.

In view of such circumstances, it is an object of the present invention to provide a surface-treated steel sheet having stable and excellent corrosion resistance and white rust resistance, as well as good surface appearance.

As a result of studies to solve the above problems, the present inventors have made Mg ₂ Si phase, Mg Zn ₂ phase, and Si formed in the plating film of the molten Al-Zn-Si-Mg-Sr-based plated steel sheet. Regarding the phase, it was found that the amount of precipitation increases or decreases depending on the balance of each component in the plating film and the formation conditions of the plating film, the abundance ratio changes, and one of the phases may not precipitate depending on the balance of the composition. .. In addition, the corrosion resistance of the molten Al-Zn-Si-Mg-Sr-based plated steel sheet changes depending on the abundance ratio of these phases, and the corrosion resistance is stably improved especially when the Si phase is smaller than that of the Mg ₂ Si phase. I found out that.
However, for these Mg ₂ Si phase and Si phase, a general method such as a scanning electron microscope is used to observe the secondary electron image or backscattered electron image of the plating film from the surface or cross section. It is known that it is very difficult to distinguish the difference between the phases. As a method for more detailed analysis, it is possible to obtain microscopic information by observing with a transmission electron microscope, but Mg ₂ Si phase and Si phase that influence macroscopic information such as corrosion resistance and appearance. It was not possible to grasp the abundance ratio of.
Therefore, as a result of further diligent research, the present inventors focused on the X-ray diffraction method and quantified the phase abundance ratio by using the intensity ratio of specific diffraction peaks for the Mg ₂ Si phase and the Si phase. Furthermore, it was found that stable and excellent corrosion resistance can be realized when the Mg ₂ Si phase and the Si phase satisfy a specific abundance ratio in the plating film.
In addition, the present inventors controlled the abundance ratio of Mg ₂ Si phase, Si phase, etc. in the molten Al-Zn-Si-Mg-Sr-based plated steel sheet, and then controlled the Sr concentration in the bath. It was also found that a plated steel sheet with excellent surface appearance can be obtained by reliably suppressing the occurrence of wrinkle-like uneven defects.

Furthermore, the present inventors have also studied the chemical conversion film formed on the plating film, and by forming the chemical conversion film from a specific resin and a specific metal compound, the plating film of the chemical conversion film can be obtained. It was also found that the affinity of the white rust and the rust preventive effect were enhanced, and the stable improvement of the white rust resistance was improved.

The present invention has been made based on the above findings, and the gist thereof is as follows.
1. 1. A surface-treated steel sheet comprising a plating film and a chemical conversion film formed on the plating film.
The plating film contains Al: 45 to 65% by mass, Si: 1.0 to 4.0% by mass, Mg: 1.0 to 10.0% by mass and Sr: 0.01 to 1.0% by mass, and the balance is composed of Zn and unavoidable impurities. Have,
The diffraction intensity of Si and Mg ₂ Si in the plating film by X-ray diffraction satisfies the following relationship (1).
Si (111) / Mg ₂ Si (111) ≤ 0.8 ・ ・ ・ (1)
Si (111): Diffraction intensity of Si (111) plane (plane spacing d = 0.3135 nm),
Mg ₂ Si (111): Diffraction strength of Mg ₂ Si (111) plane (plane spacing d = 0.3668 nm) The chemical conversion film is made of epoxy resin, urethane resin, acrylic resin, acrylic silicon resin, alkyd resin, polyester resin, etc. At least one resin selected from polyalkylene resin, amino resin and fluororesin, P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti A surface-treated steel sheet containing at least one metal compound selected from a compound and a Ca compound.

2. 2. The surface-treated steel sheet according to 1 above, wherein the diffraction intensity of Si in the plating film due to X-ray diffraction satisfies the following relationship (2).
Si (111) = 0 ・ ・ ・ (2)
Si (111): Diffraction intensity of Si (111) plane (plane spacing d = 0.3135 nm)

3. 3. The surface-treated steel sheet according to 1 or 2, wherein the content of Al in the plating film is 50 to 60% by mass.

4. The surface-treated steel sheet according to any one of 1 to 3, wherein the content of Si in the plating film is 1.0 to 3.0% by mass.

5. The surface-treated steel sheet according to any one of 1 to 4, wherein the content of Mg in the plating film is 1.0 to 5.0% by mass.

According to the present invention, it is possible to stably provide a surface-treated steel sheet having excellent corrosion resistance and white rust resistance, as well as good surface appearance.

It is a figure for demonstrating the flow of the Japanese Automotive Standards Organization compound cycle test (JASO-CCT).

The surface-treated steel sheet of the present invention includes a plating film on the surface of the steel sheet and a chemical conversion film formed on the plating film.

(Plating film)
In the surface-treated steel sheet of the present invention, the plating film contains Al: 45 to 65% by mass, Si: 1.0 to 4.0% by mass, Mg: 1.0 to 10.0% by mass and Sr: 0.01 to 1.0% by mass, and the balance is It has a composition consisting of Zn and unavoidable impurities.

The Al content in the plating film is 45 to 65% by mass, preferably 50 to 60% by mass, in view of the balance between corrosion resistance and operational aspects. This is because if the Al content in the plating film is at least 45% by mass, dendrite solidification of Al occurs, and a plating film structure mainly composed of the dendrite solidified structure of the α-Al phase can be obtained. By adopting a structure in which the dendrite solidified structure is laminated in the film thickness direction of the plating film, the corrosion progress path becomes complicated and the corrosion resistance of the plating film itself is improved. Further, the more the dendrite portions of the α-Al phase are laminated, the more complicated the corrosion progress path becomes, and the more difficult it is for corrosion to reach the base steel sheet. Therefore, the corrosion resistance is improved, and the Al content is 50 mass. % Or more is preferable. On the other hand, when the Al content in the plating film exceeds 65% by mass, most of Zn changes to a structure that is solid-dissolved in α-Al, and the dissolution reaction of the α-Al phase cannot be suppressed, so that Al-Zn -The corrosion resistance of Si-Mg-Sr plating deteriorates. Therefore, the Al content in the plating film needs to be 65% by mass or less, preferably 60% by mass or less.

Si in the plating film mainly suppresses the growth of Fe-Al-based and / or Fe-Al-Si-based interfacial alloy layers generated at the interface with the underlying steel sheet, and does not deteriorate the adhesion between the plating film and the steel sheet. Added for the purpose. When the steel plate is actually immersed in an Al-Zn-based plating bath containing Si, Fe on the surface of the steel plate and Al or Si in the bath undergo an alloying reaction, and Fe-Al-based and / or Fe-Al-Si-based. The metal-metal compound layer is formed at the base steel plate / plating film interface. At this time, the Fe-Al-Si alloy has a slower growth rate than the Fe-Al alloy, so the ratio of the Fe-Al-Si alloy is high. The higher the value, the more the growth of the entire interfacial alloy layer is suppressed. Therefore, the Si content in the plating film needs to be 1.0% by mass or more. On the other hand, when the Si content in the plating film exceeds 4.0% by mass, not only the growth suppressing effect of the above-mentioned interfacial alloy layer is saturated, but also the presence of an excess Si phase in the plating film promotes corrosion. Therefore, the Si content should be 4.0% or less. Further, the content of Si in the plating film is preferably 3.0% or less from the viewpoint of suppressing the presence of an excessive Si phase. The Si content is preferably 1.0 to 3.0% by mass from the viewpoint of easily satisfying the relational expression (1) described later in relation to the Mg content described later.

The plating film contains 1.0 to 10.0% of Mg. By containing Mg in the plating film, the above-mentioned Si can be present in the form of an intermetallic compound of Mg ₂ Si phase, and the promotion of corrosion can be suppressed.
Further, when Mg is contained in the plating film, MgZn ₂ phase, which is an intermetallic compound, is also formed in the plating film, and the effect of further improving the corrosion resistance can be obtained. When the Mg content in the plating film is less than 1.0% by mass, Mg is used for solid solution to the α-Al phase, which is the main phase, rather than the formation of the intermetallic compound (Mg ₂ Si, MgZn ₂ ). Therefore, sufficient corrosion resistance cannot be ensured. On the other hand, when the Mg content in the plating film is large, the effect of improving the corrosion resistance is saturated and the workability is lowered due to the weakening of the α-Al phase, so the content is set to 10.0% or less. Further, the Mg content in the plating film is preferably 5.0% by mass or less from the viewpoint of suppressing the generation of dross during plating formation and facilitating the management of the plating bath. From the viewpoint of easily satisfying the relational expression (1) described later in relation to the Si content, the Mg content is preferably 3.0% by mass, and compatibility with dross suppression is taken into consideration. Then, it is more preferable to set the Mg content to 3.0 to 5.0% by mass.

In the surface-treated steel sheet of the present invention, the diffraction intensities of Si and Mg ₂ Si in the plating film by the X-ray diffraction method need to satisfy the following relationship (1).
Si (111) / Mg ₂ Si (111) ≤ 0.8 ・ ・ ・ (1)
Si (111): Diffraction intensity of Si (111) plane (plane spacing d = 0.3135 nm), Mg ₂ Si (111): Diffraction strength of Mg ₂ Si (111) plane (plane spacing d = 0.3668 nm)

As described above, in the present invention, it is important to control the abundance ratio of the Mg ₂ Si phase and the Si phase generated in the plating film due to the inclusion of Mg and Si to a specific ratio. The effects of these on corrosion resistance are currently being investigated and there are many unclear points, but the following mechanisms are presumed.

When the surface-treated steel sheet is exposed to a corrosive environment, the above-mentioned intermetallic compound dissolves preferentially over the α-Al phase, resulting in an environment rich in Mg in the vicinity of the corrosive product formed. It is estimated that in such an Mg-rich environment, the corrosion products formed are less likely to be decomposed, and as a result, the protective effect of the plating film is enhanced. In addition, the effect of improving the protective effect of the plating film is more reliably expressed when Si in the plating film exists as the Mg ₂ Si phase instead of the Si phase, so that the abundance ratio of the Si phase to the Mg ₂ Si phase is lowered. Is considered to be effective.

The abundance ratio of Mg ₂ Si and Si in the plating film has a relationship (1): Si (111) / Mg ₂ Si (111) ≤ 0.8 using the diffraction peak intensity obtained by the X-ray diffractometry. It is necessary to satisfy, but when the abundance ratio of Mg ₂ Si and Si in the plating film does not satisfy the relationship (1), that is, when Si (111) / Mg ₂ Si (111)> 0.8, the plating is performed. Since the amount of Si phase present in the film increases, the above-mentioned environment rich in Mg cannot be obtained in the vicinity of the corrosion product, and it becomes difficult to obtain the effect of improving the protective effect of the plating film. From the same viewpoint, the abundance ratio of Si to Mg ₂ Si (Si (111) / Mg ₂ Si (111)) is preferably 0.5 or less, more preferably 0.3 or less, and 0.2 or less. Is particularly preferable.
Regarding the abundance ratio of Mg ₂ Si and Si in the plating film, the composition of the plating film tentatively satisfies the range of the present invention (Al: 45 to 65% by mass, Si: 1.0 to 4.0% by mass, Mg: Even if it contains 1.0 to 10.0% by mass and Sr: 0.01 to 1.0% by mass, and the balance consists of Zn and unavoidable impurities), the abundance ratio of Mg ₂ Si and Si does not satisfy the relationship (1). However, the effect of improving the protective effect of the plating film according to the present invention cannot be sufficiently obtained.

Here, in the above relationship (1), Si (111) is the diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135 nm), and Mg ₂ Si (111) is (111) of Mg ₂ Si. ) Diffraction intensity of the plane (plane spacing d = 0.3668 nm).
As a method of measuring Si (111) and Mg ₂ Si (111) by the X-ray diffraction, a part of the plating film is mechanically scraped off and X-ray diffraction is performed in a powdered state (powder X). It can be calculated by the line diffraction measurement method). For the measurement of the diffraction intensity, the diffraction peak intensity of Si corresponding to the surface spacing d = 0.3135 nm and the diffraction peak intensity of Mg ₂ Si corresponding to the surface spacing d = 0.3668 nm are measured, and these ratios are calculated. Si (111) / Mg ₂ Si (111) can be obtained.
The amount of plating film (amount to scrape off the plating film) required for powder X-ray diffraction measurement is 0.1 g or more from the viewpoint of accurately measuring Si (111) and Mg ₂ Si (111). It may be sufficient, preferably 0.3 g or more. Further, when the plating film is scraped off, steel plate components other than the plating film may be contained in the powder, but these intermetallic compound phases are contained only in the plating film, and the above-mentioned peak strength can be obtained. It has no effect. Further, the reason why the plating film is powdered and X-ray diffraction is performed is that when X-ray diffraction is performed on the plating film formed on the plated steel sheet, it is affected by the plane orientation of the solidification structure of the plating film and has the correct phase ratio. This is because it is difficult to perform the calculation.

Further, in the surface-treated steel sheet of the present invention, the diffraction intensity of Si in the plating film by the X-ray diffraction method can satisfy the following relationship (2) from the viewpoint that the corrosion resistance can be improved more stably. preferable.
Si (111) = 0 ・ ・ ・ (2)
Si (111): Diffractive intensity of Si (111) plane (plane spacing d = 0.3135 nm) Generally, in the dissolution reaction of Al alloy in an aqueous solution, the Si phase is present as a cathode site, so that the surrounding area is Since it is known to promote the dissolution of the α-Al phase, reducing the Si phase is also effective from the viewpoint of suppressing the dissolution of the α-Al phase, and among them, Si as described in the relationship (2). A phase-free film (setting the diffraction peak intensity of Si (111) to zero) is the most excellent for stabilizing corrosion resistance.
The method for measuring the diffraction peak intensity of the (111) plane of Si by X-ray diffraction is as described above.

Here, the method for satisfying the above-mentioned relationship (1) and relationship (2) is not particularly limited. For example, in order to satisfy the relationship (1) and the relationship (2), the balance between the Si content, the Mg content and the Al content in the plating film is adjusted to obtain Mg ₂ Si and Si. The abundance ratio (diffraction intensity of Mg ₂ Si (111) and Si (111)) can be controlled. It should be noted that the balance between the Si content, the Mg content and the Al content in the plating film does not necessarily satisfy the relationship (1) and the relationship (2) if the content ratio is set to a certain level. For example, it is necessary to change the content ratio of Mg and Al depending on the content of Si (% by mass).
In addition to adjusting the balance between the Si content, Mg content, and Al content in the plating film, the conditions for forming the plating film (for example, cooling conditions after plating) can be adjusted. , The diffraction intensity of Mg ₂ Si (111) and Si (111) can be controlled so as to satisfy the relationship (1) and the relationship (2).

Further, in the surface-treated steel sheet of the present invention, the plating film contains 0.01 to 1.0% by mass of Sr. When the plating film contains Sr, it is possible to more reliably suppress the occurrence of surface defects such as wrinkle-like uneven defects, and it is possible to realize good surface appearance.
The wrinkle-like defect is a wrinkle-like uneven defect formed on the surface of the plating film, and is observed as a whitish streak on the surface of the plating film. Such wrinkle-like defects are likely to occur when a large amount of Mg is added to the plating film. Therefore, in the hot-dip plated steel sheet, by containing Sr in the plating film, Sr is preferentially oxidized over Mg in the surface layer of the plating film, and the oxidation reaction of Mg is suppressed, thereby causing the wrinkle-like defect. It is possible to suppress the occurrence of.

The plating film contains 0.01 to 1.0% by mass of Sr, but when the Sr content in the plating film is less than 0.01% by mass, the appearance improving effect cannot be obtained, and the Sr in the plating film is not obtained. This is because when the content exceeds 1.0% by mass, Sr is excessively incorporated into the interfacial alloy layer, which adversely affects the plating adhesion and the like. From the same viewpoint, the Sr content in the plating film is preferably 0.05 to 0.5% by mass, more preferably 0.1 to 0.4% by mass.
In the surface-treated steel sheet of the present invention, the abundance ratios of Si and Mg ₂ Si in the above-mentioned plating film satisfy the relationship (1), and the plating film contains 0.01 to 1.0% by mass of Sr. .. Thereby, the effect of improving the surface appearance by the above-mentioned Sr can be further enjoyed. Although the cause of this is not clear, it is presumed that when the amount of Si in the plating film increases, the oxidation of the plating surface layer is difficult to be suppressed in the first place, which affects the effect of improving the appearance when Sr is added. ..

The surface-treated steel sheet of the present invention contains Zn and unavoidable impurities.
Of these, the unavoidable impurity contains Fe. This Fe is inevitably contained in the plating bath due to elution of the steel sheet and the equipment in the bath, and is supplied by diffusion from the base steel sheet at the time of forming the interfacial alloy layer, and as a result, it is inevitably contained in the plating film. Will be included. The Fe content in the plating film is usually about 0.3 to 2.0% by mass. Other unavoidable impurities include Cr, Ni, Cu and the like. The total content of the unavoidable impurities is not particularly limited, but if it is excessively contained, it may affect various characteristics of the plated steel sheet, so that the total content is preferably 5.0% by mass or less.

Further, since the plating film can improve the stability of the corrosion product and delay the progress of corrosion in the same manner as the above-mentioned Mg, Cr and Mn in total of 0.01 to 10% by mass. , V, Mo, Ti, Ca, Ni, Co, Sb and B are preferably selected from one or more. The total content of the above-mentioned components is set to 0.01 to 10% by mass because a sufficient corrosion delay effect can be obtained and the effect is not saturated.

The amount of the plating film adhered is preferably 45 to 120 g / m ² per side from the viewpoint of satisfying various characteristics. When the adhesion amount of the plating film is 45 g / m ² or more, sufficient corrosion resistance can be obtained even for applications that require long-term corrosion resistance such as building materials, and the adhesion amount of the plating film is 120 g / m / m. This is because when m ² or less, excellent corrosion resistance can be realized while suppressing the occurrence of plating cracks during processing. From the same viewpoint, the amount of the plating film adhered is more preferably 45 to 100 g / m ² .

The amount of the plating film adhered is calculated from, for example, the difference in the weight of the steel sheet before and after peeling by dissolving and peeling the plating film of a specific area with a mixed solution of hydrochloric acid and hexamethylenetetramine shown in JIS H 0401: 2013. Can be derived. In order to determine the amount of plating adhesion per one surface by this method, it can be determined by sealing with tape so that the plating surface of the non-target surface is not exposed, and then performing the above-mentioned dissolution.

Further, the component composition of the plating film can be confirmed, for example, by immersing the plating film in hydrochloric acid or the like to dissolve the plating film, and confirming the solution by ICP emission spectroscopic analysis, atomic absorption spectroscopy or the like. This method is merely an example, and any method can be used as long as the component composition of the plating film can be accurately quantified, and the method is not particularly limited.

The plating film of the surface-treated steel sheet obtained by the present invention has almost the same composition as the plating bath as a whole. Therefore, the composition of the plating film can be controlled accurately by controlling the composition of the plating bath.

Further, the base steel sheet constituting the surface-treated steel sheet of the present invention is not particularly limited, and a cold-rolled steel sheet, a hot-rolled steel sheet, or the like can be appropriately used according to the required performance and specifications.

Further, the method for obtaining the base steel plate is not particularly limited. For example, in the case of the hot-rolled steel sheet, a steel sheet that has undergone a hot-rolling step and a pickling step can be used, and in the case of the cold-rolled steel sheet, it can be manufactured by further adding a cold-rolling step. Further, in order to obtain the characteristics of the steel sheet, it is possible to go through a recrystallization annealing step or the like before the hot-dip plating step.

The conditions for forming the plating film when producing the surface-treated steel sheet of the present invention are not particularly limited. For example, it can be manufactured by washing, heating, and immersing the base steel sheet in a plating bath in a continuous hot-dip plating facility. In the heating step of the steel sheet, recrystallization baking is performed to control the structure of the base steel sheet itself, and in order to prevent oxidation of the steel sheet and reduce a trace amount of oxide film existing on the surface, a nitrogen-hydrogen atmosphere, etc. It is effective to heat in the reducing atmosphere of.

As for the plating bath used for forming the plating film, as described above, the composition of the plating film as a whole is almost the same as the composition of the plating bath. Therefore, Al: 45 to 65% by mass. Those containing Si: 1.0 to 4.0% by mass, Mg: 1.0 to 10.0% by mass and Sr: 0.01 to 1.0% by mass, and the balance having a composition of Zn, Fe and unavoidable impurities can be used.

Further, the bath temperature of the plating bath is not particularly limited, but is preferably in the temperature range of (melting point + 20 ° C.) to 650 ° C.
The lower limit of the bath temperature is set to a melting point of + 20 ° C., because the bath temperature must be equal to or higher than the freezing point in order to perform the hot-dip plating treatment. This is to prevent coagulation due to a local decrease in bath temperature. On the other hand, the upper limit of the bath temperature is set to 650 ° C. If the temperature exceeds 650 ° C, rapid cooling of the plating film becomes difficult, and the interfacial alloy layer formed between the plating film and the steel sheet may become thick. Because.

Further, the temperature of the base steel plate that penetrates into the plating bath (penetration plate temperature) is not particularly limited, but from the viewpoint of ensuring the plating characteristics and preventing the change in the bath temperature in the continuous hot-dip plating operation, the plating bath is described. It is preferable to control the temperature within ± 20 ° C.

Further, the immersion time of the steel sheet in the plating bath is 0.5 seconds or more. This is because if it takes less than 0.5 seconds, a sufficient plating film may not be formed on the surface of the base steel sheet. The upper limit of the dipping time is not particularly limited, but it is preferably within 8 seconds because the interfacial alloy layer formed between the plating film and the steel sheet may become thicker if the dipping time is lengthened.

Furthermore, in the cooling process after plating, it is preferable to cool the plate over 3 seconds or more from 520 ° C to 500 ° C. The precipitation start temperature of the simple substance Si phase and Mg2Si in the plating film is 500 to 490 ° C for the simple substance Si phase and 520 to 500 ° C for Mg2Si. Therefore, by increasing the residence time in the temperature range of 520 to 500 ° C where only Mg2Si precipitates, the precipitation of Mg2Si is promoted and the precipitation of the simple substance Si phase is suppressed. This is because it is easier to fill.

(Chemical film)
In the surface-treated steel sheet of the present invention, a chemical conversion film is formed on the above-mentioned plating film.
The chemical conversion film may be formed on at least one side of the surface-treated steel sheet, and may be formed on both sides of the surface-treated steel sheet depending on the application and required performance.

In the surface-treated steel plate of the present invention, the chemical conversion film is at least selected from epoxy resin, urethane resin, acrylic resin, acrylic silicon resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluororesin. One kind of resin and at least one kind of metal selected from P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound and Ca compound. It is characterized by containing a compound and.
By forming the above-mentioned chemical conversion film on the plating film, the affinity with the plating film is enhanced, the chemical conversion film can be uniformly formed on the plating film, and the rust preventive effect of the chemical conversion film is achieved. And the barrier effect can be enhanced. As a result, stable corrosion resistance and white rust resistance of the surface-treated steel sheet of the present invention can be realized.

Here, the resin constituting the chemical conversion film is selected from among epoxy resin, urethane resin, acrylic resin, acrylic silicon resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluororesin from the viewpoint of improving corrosion resistance. At least one selected is used. From the same viewpoint, the resin preferably contains at least one of urethane resin and acrylic resin. The resin constituting the chemical conversion film also includes an addition polymer of the above-mentioned resin.

The epoxy resin is, for example, a glycidyl etherified epoxy resin such as bisphenol A type, bisphenol F type, or novolak type, or a bisphenol A type epoxy resin to which propylene oxide, ethylene oxide, or polyalkylene glycol is added. A glycidyl etherified product, an aliphatic epoxy resin, an alicyclic epoxy resin, a polyether epoxy resin, or the like can be used.

As the urethane resin, for example, an oil-modified polyurethane resin, an alkyd polyurethane resin, a polyester polyurethane resin, a polyether polyurethane resin, a polycarbonate polyurethane resin and the like can be used.

Regarding the acrylic resin, for example, polyacrylic acid and its copolymer, polyacrylic acid ester and its copolymer, polymethacrylic acid and its copolymer, polymethacrylic acid ester and its copolymer, urethane-acrylic acid. Examples thereof include copolymers (or urethane-modified acrylic resins) and styrene-acrylic acid copolymers, and those obtained by modifying these resins with other alkyd resins, epoxy resins, phenol resins and the like can be used.

Examples of the acrylic silicon resin include a resin having a hydrolyzable alkoxysilyl group at the side chain or the end of an acrylic copolymer as a main agent, to which a curing agent is added. Further, when an acrylic silicone resin is used, excellent weather resistance can be expected in addition to corrosion resistance.

Regarding the alkyd resin, for example, an oil-modified alkyd resin, a rosin-modified alkyd resin, a phenol-modified alkyd resin, a styrene-modified alkyd resin, a silicon-modified alkyd resin, an acrylic-modified alkyd resin, an oil-free alkyd resin, a high-molecular-weight oil-free alkyd resin, etc. Can be mentioned.

The polyester resin is a polycondensate synthesized by dehydrating and condensing a polyvalent carboxylic acid and a polyalcohol to form an ester bond. Examples of the polyvalent carboxylic acid include terephthalic acid, 2, 6-Naphthalenedicarboxylic acid and the like are used, and examples of the polyalcohol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Specifically, examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. Further, acrylic-modified polyester resins can also be used.

Regarding the polyalkylene resin, for example, an ethylene-based copolymer such as an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, and a carboxyl-modified polyolefin resin, an ethylene-unsaturated carboxylic acid copolymer, and an ethylene-based ionomer. Further, those obtained by modifying these resins with other alkyd resins, epoxy resins, phenol resins and the like can be used.

The amino resin is a thermosetting resin produced by the reaction of an amine or an amide compound with an aldehyde, and examples thereof include melamine resin, guanamine resin, and thiourea resin, but from the viewpoint of corrosion resistance, weather resistance, adhesion, and the like. , It is preferable to use a melamine resin. The melamine resin is not particularly limited, and examples thereof include a butylated melamine resin, a methylated melamine resin, and an aqueous melamine resin.

Examples of the fluororesin include fluoroolefin polymers and copolymers of fluoroolefins with alkyl vinyl ethers, synchroalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkylallyl ethers, tetrafluoropropyl vinyl ethers and the like. When these fluororesins are used, not only corrosion resistance but also excellent weather resistance and excellent hydrophobicity can be expected.

Further, it is particularly preferable to use a curing agent for the purpose of improving corrosion resistance and processability. Examples of the curing agent include urea resin (butylated urea resin, etc.), melamine resin (butylated melamine resin, butyl etherified melamine resin, etc.), butylated urea / melamine resin, amino resin such as benzoguanamine resin, blocked isocyanate, and oxazoline compounds. A phenol resin or the like can be appropriately used.

Regarding the metal compounds constituting the chemical conversion film, among P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds and Ca compounds. At least one selected from is used. From the same viewpoint, the metal compound preferably contains at least one of a P compound, a Si compound and a V compound.

Here, the P compound can be contained in the chemical conversion film to improve corrosion resistance and sweat resistance. The P compound is a compound containing P, and can contain, for example, one or two or more selected from inorganic phosphoric acid, organic phosphoric acid and salts thereof.

As the inorganic phosphoric acid, the organic phosphoric acid and salts thereof, any compound can be used without particular limitation. For example, the inorganic phosphoric acid includes phosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphite, and subphosphoric acid. It is preferable to use one or more selected from acid salt, hypophosphite, and hypophosphite. Further, as the organic phosphoric acid, it is preferable to use phosphonic acid (phosphonic acid compound). Further, as the phosphonic acid, it is preferable to use one or more selected from nitrilotris methylenephosphonic acid, phosphonobtantricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, and ethylidene diphosphonic acid.
When the P compound is a salt, the salt is preferably a salt of a Group 1 to Group 13 element in the periodic table, more preferably a metal salt, and an alkali metal salt and an alkaline earth. It is preferably one or more selected from among the metal salts.

When the chemical conversion treatment liquid containing the above P compound is applied to a molten Al-Zn-Si-Mg-based plated steel plate, the surface of the plating film is etched by the action of the P compound, and Al, Zn, which are constituent elements of the plating film, A concentrated layer in which Si and Mg are incorporated is formed on the plating film side of the chemical conversion film. By forming the concentrated layer, the bond between the chemical conversion film and the surface of the plating film is strengthened, and the adhesion of the chemical conversion film is improved.
The concentration of the P compound in the chemical conversion treatment liquid is not particularly limited, but may be 0.25% by mass to 5% by mass. If the concentration of the P compound is less than 0.25% by mass, the etching effect is insufficient and the adhesion to the plating interface is lowered, not only the corrosion resistance of the flat surface portion is lowered, but also the plating generated in the defective portion, the cut end face portion, the processing, etc. Corrosion resistance and sweat resistance of damaged parts of the film may also decrease. From the same viewpoint, the concentration of the P compound is preferably 0.35% by mass or more, more preferably 0.50% by mass or more. On the other hand, when the concentration of the P compound exceeds 5% by mass, not only the life of the chemical conversion treatment liquid is shortened, but also the appearance when the film is formed tends to be uneven, and the amount of P eluted from the chemical conversion film. There is a possibility that the amount of blackening will increase and the blackening resistance will decrease. From the same viewpoint, the concentration of the P compound is preferably 3.5% by mass or less, more preferably 2.5% by mass or less. Regarding the content of P compound in the chemical conversion film, for example, by applying and drying a chemical conversion treatment liquid having a concentration of P compound of 0.25% by mass to 5% by mass, P adheres to the chemical conversion film after drying. The amount can be 5 to 100 mg / m ² .

The Si compound is a component that serves as a skeleton for forming a chemical conversion film together with the resin, and can enhance the affinity with the plating film and uniformly form the chemical conversion film. The Si compound is a compound containing Si, and preferably contains, for example, one or more selected from silica, trialkoxysilane, tetraalkoxysilane, and a silane coupling agent.

The silica is not particularly limited and any silica can be used. As the silica, for example, at least one of wet silica and dry silica can be used. As the colloidal silica which is a kind of the wet silica, for example, Snowtex O, C, N, S, 20, OS, OXS, NS and the like manufactured by Nissan Chemical Industries, Ltd. can be preferably used. Further, as the dry silica, for example, AEROSIL 50, 130, 200, 300, 380 manufactured by Nippon Aerosil Co., Ltd. can be preferably used.

As the trialkoxysilane, any one can be used without particular limitation. For example, the general formula: R ₁ Si (OR ₂ ) ₃ (in the formula, R ₁ is a hydrogen or an alkyl group having 1 to 5 carbon atoms, and R ₂ is an alkyl group having the same or different carbon atoms of 1 to 5 carbon atoms. ) Is preferably used. Examples of such trialkoxysilanes include trimethoxysilane, triethoxysilane, and methyltriethoxysilane.

As the tetraalkoxysilane, any one can be used without particular limitation. For example, it is preferable to use a tetraalkoxysilane represented by the general formula: Si (OR) ₄ (where R is an alkyl group having the same or different carbon atoms 1 to 5). Examples of such tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

As the silane coupling agent, any one can be used without particular limitation. For example, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-Aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, and γ-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, γ- Examples thereof include isocyanate propyltriethoxysilane.

By including the Si compound in the chemical conversion film, the Si compound is dehydrated and condensed to form an amorphous chemical conversion film having a siloxane bond having a high barrier effect that shields a corrosive factor. Further, by binding with the above-mentioned resin, a chemical conversion film having a higher barrier property is formed. Furthermore, in a corroded environment, dense and stable corrosion products are formed in the defective parts and damaged parts of the plating and film caused by processing, and the combined effect with the plating film also has the effect of suppressing the corrosion of the underlying steel sheet. be. From the viewpoint of having a high effect of forming a stable corrosion product, it is preferable to use at least one of colloidal silica and dry silica as the Si compound.

The concentration of the Si compound in the chemical conversion treatment liquid for forming the chemical conversion film is 0.2% by mass to 9.5% by mass. When the concentration of the Si compound in the chemical conversion treatment liquid is 0.2% by mass or more, the barrier effect due to the siloxane bond can be obtained, and as a result, in addition to the corrosion resistance of the flat surface portion, the damage caused by the defective portion, the cut portion, the processing and the like can be obtained. Corrosion resistance and sweat resistance in the part are improved. Further, when the concentration of the Si compound is 9.5% by mass or less, the life of the chemical conversion treatment liquid can be extended. By applying and drying a chemical conversion treatment liquid having a Si compound concentration of 0.2% by mass to 9.5% by mass, the amount of Si adhered to the chemical conversion film after drying can be adjusted to 2 to 95 mg / m ² .

By including the Co compound and the Ni compound in the chemical conversion film, blackening resistance can be improved. It is considered that this is because Co and Ni have the effect of delaying the elution of the water-soluble component from the film in a corrosive environment. Further, the Co and the Ni are elements that are less likely to be oxidized than Al, Zn, Si, Mg and the like. Therefore, by concentrating at least one of the Co compound and the Ni compound at the interface between the chemical conversion film and the plating film (forming a concentrated layer), the concentrated layer becomes a barrier against corrosion. As a result, blackening resistance can be improved.

By using a chemical conversion treatment liquid containing the Co compound, Co can be contained in the chemical conversion film and incorporated into the concentrated layer. It is preferable to use a cobalt salt as the Co compound. As the cobalt salt, it is more preferable to use 1 or 2 or more selected from cobalt sulfate, cobalt carbonate and cobalt chloride.
Further, by using a chemical conversion treatment liquid containing the Ni compound, Ni can be contained in the chemical conversion film and incorporated into the concentrated layer. It is preferable to use a nickel salt as the Ni compound. As the nickel salt, it is more preferable to use 1 or 2 or more selected from nickel sulfate, nickel carbonate and nickel chloride.

The concentration of the Co compound and / or the Ni compound in the chemical conversion treatment liquid is not particularly limited, but may be 0.25% by mass to 5% by mass in total. When the concentration of the Co compound and / or the Ni compound is less than 0.25% by mass, the interfacial concentrated layer becomes non-uniform, and not only the corrosion resistance of the flat surface portion is lowered, but also the plating caused by the defective portion, the cut end face portion, the processing, etc. And the corrosion resistance of the damaged part of the film may also decrease. From the same viewpoint, it is preferably 0.5% by mass or more, more preferably 0.75% by mass or more. On the other hand, if the concentration of the Co compound and / or the Ni compound exceeds 5% by mass, the appearance when the film is formed tends to be non-uniform, and the corrosion resistance may decrease. From the same viewpoint, it is preferably 4.0% by mass or less, more preferably 3.0% by mass or less. By applying and drying a chemical conversion treatment solution having a total concentration of the Co compound and / or Ni compound of 0.25% by mass to 5% by mass, the total amount of Co and Ni adhered to the dried chemical conversion film is 5 to 100 mg. Can be / m ² .

By containing the Al compound, the Zn compound and the Mg compound in the chemical conversion treatment liquid, a concentrated layer containing at least one of Al, Zn and Mg can be formed on the plating film side of the chemical conversion coating. .. The formed concentrated layer can improve the corrosion resistance.
The Al compound, the Zn compound, and the Mg compound are not particularly limited as long as they are compounds containing Al, Zn, and Mg, respectively, but are preferably inorganic compounds, and salts, chlorides, and the like. It is preferably an oxide or a hydroxide.

Examples of the Al compound include one or more selected from aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide and aluminum hydroxide.
Examples of the Zn compound include one or more selected from zinc sulfate, zinc carbonate, zinc chloride, zinc oxide and zinc hydroxide.
Examples of the Mg compound include one or more selected from magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide and magnesium hydroxide.

The total concentration of the Al compound, Zn compound and / or Mg compound in the chemical conversion treatment liquid for forming the chemical conversion film is preferably 0.25% by mass to 5% by mass. When the total concentration is 0.25% by mass or more, the concentrated layer can be formed more effectively, and as a result, the corrosion resistance can be further improved. On the other hand, when the total concentration is 5% by mass or less, the appearance of the chemical conversion film becomes more uniform, and the corrosion resistance of the flat surface portion, the defective portion, the damaged portion of the plating or the film caused by processing, etc. is further improved.

When the V compound is contained in the chemical conversion film, V is appropriately eluted in a corrosive environment and combined with zinc ions and the like of plating components that are also eluted in a corrosive environment to form a dense protective film. .. The formed protective film can further enhance the corrosion resistance not only to the flat surface portion of the steel sheet but also to the defective portion, the damaged portion of the plating film caused by processing, the corrosion progressing from the cut end face to the flat surface portion, and the like.

The V compound is a compound containing V, and examples thereof include one or more selected from sodium metavanadate, vanadyl sulfate, and vanadium acetylacetonate.

The V compound in the chemical conversion treatment liquid for forming the chemical conversion film is preferably 0.05% by mass to 4% by mass. When the concentration of the V compound is 0.05% by mass or more, it is easy to elute in a corrosive environment to form a protective film, and the corrosion resistance of the defective part, the cut end face part, and the damaged part of the plating film caused by processing is improved. improves. On the other hand, when the concentration of the V compound exceeds 4% by mass, the appearance when the chemical conversion film is formed tends to be non-uniform, and the blackening resistance is also lowered.

By containing the Mo compound in the chemical conversion film, it is possible to enhance the blackening resistance of the surface-treated steel sheet. The Mo compound is a compound containing Mo and can be obtained by adding one or both of molybdic acid and molybdate to the chemical conversion treatment liquid.
Examples of the molybdate include one or more selected from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate.

The concentration of the Mo compound in the chemical conversion treatment liquid for forming the chemical conversion film is preferably 0.01% by mass to 3% by mass. When the concentration of the Mo compound is 0.01% by mass or more, the formation of oxygen-deficient zinc oxide is further suppressed, and the blackening resistance can be further improved. On the other hand, when the concentration of the Mo compound is 3% by mass or less, the life of the chemical conversion treatment liquid is further extended, and the corrosion resistance can be further improved.

By containing the Zr compound and the Ti compound in the chemical conversion film, it is possible to prevent the chemical conversion film from becoming porous and to densify the film. As a result, the corrosion factor is less likely to permeate the chemical conversion film, and the corrosion resistance can be improved.

The Zr compound is a Zr-containing compound, and for example, one or more selected from zirconyl acetate, zirconyl sulfate, potassium zirconyl carbonate, sodium zirconyl carbonate, and ammonium zirconyl carbonate can be used. Among these, the organic titanium chelate compound is suitable because when the chemical conversion treatment liquid is dried to form a film, the film is densified and more excellent corrosion resistance can be obtained.

The Ti compound is a compound containing Ti, and is one or more selected from, for example, titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octylene glycolate, and titanium ethylacetoacetate. Can be used.

The concentration of the Zr compound and / or the Ti compound in the chemical conversion treatment liquid for forming the chemical conversion film is preferably 0.2% by mass to 20% by mass in total. When the total concentration of the Zr compound and / or the Ti compound is 0.2% by mass or more, the effect of suppressing the permeation of the corrosive factor is enhanced, and not only the corrosion resistance of the flat surface portion but also the defect portion, the cut end face portion, and the plating film damage due to processing are damaged. The corrosion resistance of the part can be further improved. On the other hand, when the total concentration of the Zr compound and / or the Ti compound is 20% by mass or less, the life of the chemical conversion treatment liquid can be further extended.

When the Ca compound is contained in the chemical conversion film, the effect of lowering the corrosion rate can be exhibited.

The Ca compound is a compound containing Ca, and examples thereof include an oxide of Ca, a nitrate of Ca, a sulfate of Ca, and an intermetallic compound containing Ca. More specifically, examples of the Ca compound include CaO, CaCO ₃ , Ca (OH) ₂ , Ca (NO ₃ ) _{2.4H 2 O, CaSO 4.2H 2 O and the} like. The content of the Ca compound in the chemical conversion film is not particularly limited.

The chemical conversion film can contain various known components usually used in the paint field, if necessary. For example, various surface conditioners such as leveling agents and defoamers, dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, silane coupling agents, various additives such as titanate coupling agents, coloring pigments, and extender pigments. , Various pigments such as bright materials, curing catalysts, organic solvents, lubricants and the like.

In the surface-treated steel sheet of the present invention, it is preferable that the chemical conversion film does not contain harmful components such as hexavalent chromium, trivalent chromium and fluorine. This is because the chemical conversion treatment liquid for forming the chemical conversion film does not contain these harmful components, so that the safety is high and the amount is small to the environment.

Further, the amount of the chemical conversion film adhered is not particularly limited. For example, from the viewpoint of preventing the chemical conversion film from peeling off while ensuring corrosion resistance more reliably, the adhesion amount of the chemical conversion film is preferably 0.1 to 3.0 g / m ² , preferably 0.5 to 2.5 g / m ² . It is more preferable to do so. Corrosion resistance can be ensured more reliably by setting the adhesion amount of the chemical conversion film to 0.1 g / m ² or more, and cracking or peeling of the chemical conversion film by setting the adhesion amount of the chemical conversion film to 3.0 g / m ² or less. Can be prevented.
The amount of the chemical conversion film adhered may be obtained by a method appropriately selected from existing methods such as a method of measuring the abundance of an element whose content in the film is known in advance by fluorescent X-ray analysis of the film. ..

The method for forming the chemical conversion film is not particularly limited, and can be appropriately selected depending on the required performance, manufacturing equipment, and the like. For example, a chemical conversion treatment liquid is continuously applied onto the plating film with a roll coater or the like, and then, using hot air or induction heating, the plate temperature reaches about 60 to 200 ° C. (Peak Metal Temperature: PMT). It can be formed by drying. For the application of the chemical conversion treatment liquid, a known method such as an airless spray, an electrostatic spray, a curtain flow coater or the like can be appropriately adopted in addition to the roll coater. Further, the chemical conversion film may be either a single-layer film or a multi-layer film as long as it contains the resin and the metal compound, and is not particularly limited.

Further, the surface-treated steel sheet of the present invention can also form a coating film on the chemical conversion film, if necessary.

(Samples 1-112)
(1) Plating shown in Tables 2 and 3 is performed by using a cold-rolled steel sheet with a thickness of 0.8 mm manufactured by a conventional method as a base steel sheet and performing an annealing treatment and a plating treatment with a hot-dip plating simulator manufactured by Resuka Co., Ltd. A sample of a hot-dip plated steel sheet with film conditions was prepared.
Regarding the composition of the plating bath used for manufacturing the hot-dip plated steel sheet, the composition of the plating bath was Al: 30 to 75% by mass and Si: 0.5 to 4.5 so as to be the composition of the plating film of each sample shown in Table 1. It was varied in the range of% by mass, Mg: 0 to 10% by mass, and Sr: 0.00 to 0.15% by mass. The bath temperature of the plating bath is 590 ° C when Al: 30 to 60% by mass and 630 ° C when Al: more than 60% by mass, and the plating penetration plate temperature of the base steel sheet is the same as the plating bath temperature. It was controlled to be. Furthermore, the plating treatment was carried out under the condition that the plate temperature was cooled to a temperature range of 520 to 500 ° C. in 3 seconds.
The amount of the plating film adhered was controlled to be 85 ± 5 g / m ² per side for samples 1 to 82 and 95 to 112, and 51 to 125 g / m ² per side for samples 83 to 94.
(2) After that, a chemical conversion treatment liquid is applied on the plating film of each sample of the prepared hot-dip plated steel sheet with a bar coater, and dried in a hot air furnace (heating rate: 60 ° C / s, PMT: 120 ° C). A chemical conversion film was formed in 1 and each sample of the surface-treated steel sheet shown in Tables 2 and 3 was prepared.
As the chemical conversion treatment liquid, surface treatment liquids A to F in which each component was dissolved in water as a solvent were prepared. The types of each component (resin, metal compound) contained in the surface treatment liquid are as follows.
(resin)
Urethane resin: Superflex 130, Superflex 126 (Daiichi Kogyo Seiyaku Co., Ltd.)
Acrylic resin: Boncoat EC-740EF (DIC Corporation)
(Metal compound)
P compound: aluminum dihydrogen dihydrogen tripolyphosphate
Si compound: silica
V compound: sodium metavanadate
Mo compound: molybdic acid
Zr compound: Zirconyl potassium carbonate Table 1 shows the composition of the prepared chemical conversion treatment liquids A to F and the amount of the formed chemical conversion film adhered. The concentration of each component in Table 1 of the present specification is the concentration of solid content (mass%).

(evaluation)
The following evaluations were performed on each sample of the hot-dip galvanized steel sheet and the surface-treated steel sheet obtained as described above. The evaluation results are shown in Tables 2 and 3.

(1) Composition of plating film (adhesion amount, composition, X-ray diffraction intensity)
For each sample of hot-dip plated steel sheet, 100 mmφ is punched out, the non-measurement surface is sealed with tape, and then the plating is melted and peeled off with a mixed solution of hydrochloric acid and hexamethylenetetramine shown in JIS H 0401: 2013. The amount of adhesion of the plating film was calculated from the mass difference. As a result of the calculation, the amount of adhesion of the obtained plating film is shown in Tables 2 and 3.
Then, the stripping solution was filtered, and the filtrate and solid content were analyzed respectively. Specifically, components other than insoluble Si were quantified by ICP emission spectroscopic analysis of the filtrate.
The solid content was dried and incinerated in a heating furnace at 650 ° C., and then melted by adding sodium carbonate and sodium tetraborate. Furthermore, insoluble Si was quantified by dissolving the melt with hydrochloric acid and ICP emission spectroscopic analysis of the solution. The Si concentration in the plating film is the sum of the soluble Si concentration obtained by the filtrate analysis and the insoluble Si concentration obtained by the solid content analysis. The composition of the plating film obtained as a result of the calculation is shown in Tables 2 and 3.
Furthermore, for each sample, after shearing to a size of 100 mm × 100 mm, the plating film on the evaluation symmetric plane is mechanically scraped until the underlying steel plate appears, the obtained powder is mixed well, and then 0.3 g is taken out and X is taken out. Using a line diffraction line device (“SmartLab” manufactured by Rigaku Co., Ltd.), X-ray used: Cu-Kα (wavelength = 1.54178Å), Kβ ray removal: Ni filter, tube voltage: 40kV, tube current: 30mA, scanning・ Speed: 4 ° / min, sampling interval: 0.020 °, divergence slit: 2/3 °, solar slit: 5 °, detector: high-speed one-dimensional detector (D / teX Ultra), under the conditions of the above powder A qualitative analysis was performed. The intensity obtained by subtracting the base intensity from each peak intensity is defined as each diffraction intensity (cps), and the diffraction intensity of the (111) plane (plane spacing d = 0.3668 nm) of Mg ₂ Si and the (111) plane (plane spacing) of Si. The diffraction intensity of d = 0.3135 nm) was measured. The measurement results are shown in Tables 2 and 3.

(2) Corrosion resistance evaluation After shearing each sample of hot-dip plated steel sheet and surface-treated steel sheet to a size of 120 mm × 120 mm, the range of 10 mm from each edge of the surface to be evaluated, and the end face and non-target surface of the sample are taped. The sample to be evaluated was used after sealing and exposing the surface to be evaluated in a size of 100 mm × 100 mm. Three identical evaluation samples were prepared.
Corrosion acceleration tests were carried out in the cycle shown in FIG. 1 for all three evaluation samples prepared as described above. The corrosion acceleration test was started from wetting and continued until after 300 cycles, and then the corrosion weight loss of each sample was measured by the method described in JIS Z 2383 and ISO 8407, and evaluated according to the following criteria. The evaluation results are shown in Tables 2 and 3.
⊚: Corrosion weight loss of 3 samples is all 30 g / m ² or less ○: Corrosion weight loss of 3 samples is 50 g / m ² or less ×: Corrosion weight loss of 1 sample or more exceeds 50 g / m ²

(3) White rust resistance For each sample of hot-dip plated steel sheet and surface-treated steel sheet, after shearing to a size of 120 mm × 120 mm, the range of 10 mm from each edge of the surface to be evaluated, and the end face and non-target surface of the sample are examined. The sample to be evaluated was used after sealing with tape and exposing the surface to be evaluated in a size of 100 mm × 100 mm.
Using the above evaluation sample, the salt spray test described in JIS Z 2371 was carried out for 90 hours and evaluated according to the following criteria. The evaluation results are shown in Tables 2 and 3.
◎: No white rust on the flat plate ○: White rust area on the flat plate is less than 10% ×: White rust area on the flat plate is 10% or more

(4) Surface appearance The surface of the plating film was visually observed for each sample of the hot-dip galvanized steel sheet.
Then, the observation results were evaluated according to the following criteria. The evaluation results are shown in Tables 2 and 3.
⊚: No wrinkle-like defect was observed ○: Wrinkle-like defect was observed only in the range of 50 mm from the edge ×: Wrinkle-like defect was observed in the range other than 50 mm from the edge.

(5) Workability Each sample of the hot-dip galvanized steel sheet was sheared to a size of 70 mm × 150 mm, and then subjected to 180 ° bending (8T bending) by sandwiching eight plates of the same thickness inside. After the cellophane tape was strongly attached to the outer surface of the bent portion after bending, it was peeled off. The surface condition of the plating film on the outer surface of the bent portion and the presence or absence of adhesion (peeling) of the plating film on the surface of the used tape were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Tables 2 and 3.
〇: Both cracks and peeling are not observed in the plating film △: There are cracks in the plating film, but peeling is not observed ×: Both cracks and peeling are observed in the plating film

(5) Bath stability During hot-dip plating, the condition of the hot-dip bath surface is visually confirmed, and the hot-dip Al-Zn-based plated steel sheet is used to manufacture the hot-dip Al-Zn-based plated steel sheet. ). The evaluation is performed according to the following criteria, and the evaluation results are shown in Tables 2 and 3.
〇: Similar to the molten Al-Zn-based plating bath (55% by mass Al-remaining Zn-1.6% by mass bath) △: For the molten Al-Zn-based plating bath (55% by mass Al-remaining Zn-1.6% by mass) Compared to more white oxide ×: Formation of black oxide is observed in the plating bath

From the results of Tables 2 and 3, each sample of the example of the present invention is superior in balance in corrosion resistance, white rust resistance, surface appearance, processability and bath stability as compared with each sample of the comparative example. You can see that there is.
Further, from the results in Table 3, it can be seen that the white rust resistance of each sample subjected to the chemical conversion treatments A to D is excellent.

According to the present invention, it is possible to stably provide a surface-treated steel sheet having excellent corrosion resistance and white rust resistance, as well as good surface appearance.

Claims (5)

A surface-treated steel sheet comprising a plating film and a chemical conversion film formed on the plating film.
The plating film contains Al: 45 to 65% by mass, Si: 1.0 to 4.0% by mass, Mg: 1.0 to 10.0% by mass and Sr: 0.01 to 1.0% by mass, and the balance is composed of Zn and unavoidable impurities. Have,
The diffraction intensities of Si and Mg ₂ Si in the plating film, which were measured in a state where a part of the plating film was mechanically cut into powder until the underlying steel plate appeared, had the following relationship. Satisfy (1)
Si (111) / Mg ₂ Si (111) ≤ 0.8 ・ ・ ・ (1)
Si (111): Diffraction intensity of Si (111) plane (plane spacing d = 0.3135 nm),
Mg ₂ Si (111): Diffraction strength of Mg ₂ Si (111) plane (plane spacing d = 0.3668 nm) The chemical conversion film is made of epoxy resin, urethane resin, acrylic resin, acrylic silicon resin, alkyd resin, polyester resin, etc. At least one resin selected from polyalkylene resin, amino resin and fluororesin, P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti A surface-treated steel sheet containing at least one metal compound selected from a compound and a Ca compound. The surface-treated steel sheet according to claim 1, wherein the diffraction intensity of the Si in the plating film by the X-ray diffraction method satisfies the following relationship (2).
Si (111) = 0 ・ ・ ・ (2) The surface-treated steel sheet according to claim 1 or 2, wherein the Al content in the plating film is 50 to 60% by mass. The surface-treated steel sheet according to any one of claims 1 to 3, wherein the content of Si in the plating film is 1.0 to 3.0% by mass. The surface-treated steel sheet according to any one of claims 1 to 4, wherein the content of Mg in the plating film is 1.0 to 5.0% by mass.

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