JP2023038245A - Surface-treated steel sheet and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated steel sheet stably excellent in corrosion resistance and white rust resistance.

SOLUTION: A surface treated steel sheet includes a plating film and a chemical conversion coating formed on the plating film. The plating film has a composition including Al:45 to 65 mass%, Si:1.0 to 4.0 mass%, Mg:1.0 to 10.0 mass% and a balance consisting of Zn and inevitable impurities; a Ni content in the inevitable impurities is 0.010 mass% or less to the total mass of the plating film; and the chemical conversion coating includes at least one kind of resins selected from an epoxy resin, an urethane resin, an acrylic resin, an acrylic silicon resin, an alkyd resin, a polyester resin, a polyalkylene resin, an amino resin and a fluororesin and at least one kind of metal compounds selected from a P compound, a Si compound, a Co compound, a Ni compound, a Zn compound, an Al compound, a Mg compound, a V compound, a Mo compound, a Zr compound, a Ti compound and a Ca compound.

SELECTED DRAWING: None

COPYRIGHT: (C)2023,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a surface-treated steel sheet having stably excellent corrosion resistance and white rust resistance, and a method for producing the same.

Hot-dip Al-Zn coated steel sheets, represented by 55% Al-Zn, are known to 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. It is Therefore, due to its excellent corrosion resistance, hot-dip Al-Zn coated 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 guardrails, wiring and piping, and soundproof walls. . In particular, the demand for materials with excellent corrosion resistance and maintenance-free materials is increasing in harsher usage environments such as acid rain due to air pollution, spraying of snow-melting agents to prevent road freezing in snowy areas, and development of coastal areas. Therefore, the demand for hot-dip Al-Zn coated steel sheets is increasing in recent years.

The coating film of the hot-dip Al-Zn coated steel sheet consists of the Zn-Al eutectic structure existing in the dendrite-like solidified portion (α-Al phase) and the dendrite interstices (interdendrites) containing supersaturated Zn. 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. This characteristic film structure complicates the path of progression of corrosion from the surface, making it difficult for corrosion to progress easily. It is also known that it is possible to achieve superior corrosion resistance.

Attempts have been made to extend the service life of such hot-dip Al-Zn-coated steel sheets, and Mg-added hot-dip Al-Zn-Si-Mg-coated steel sheets have been put to practical use.
As such a hot-dip Al-Zn-Si-Mg plated steel sheet, for example, Patent Document 1 includes an Al-Zn-Si alloy containing Mg in the plating film, and the Al-Zn-Si alloy has a Molten Al-Zn-Si- alloy containing 60% by weight elemental aluminum, 37-46% by weight elemental zinc and 1.2-2.3% by weight Si, the concentration of Mg being 1-5% by weight A Mg-based plated steel sheet is disclosed.
In addition, in Patent Document 2, by including one or more of 2 to 10% Mg and 0.01 to 10% Ca in the plating film, corrosion resistance is improved, and the protective effect after the base steel plate is exposed A hot-dip Al-Zn-Si-Mg coated steel sheet is disclosed for the purpose of increasing the
Furthermore, in Patent Document 3, a coating layer containing Mg: 1 to 15%, Si: 2 to 15%, Zn: 11 to 25% by mass, and the balance being Al and unavoidable impurities is formed. , A molten Al-Zn-Si-Mg system that improves the corrosion resistance of flat plates and end faces by reducing the size of intermetallic compounds such as Mg ₂ Si phase and MgZn ₂ phase in the plating film to 10 μm or less. A plated steel sheet is disclosed.

The hot-dip Al-Zn coated steel sheet described above has a beautiful appearance with a spangle pattern with a white metallic luster. be. Therefore, techniques for improving the appearance of hot-dip Al-Zn coated steel sheets have also been developed.
For example, Patent Document 4 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet in which wrinkle-like irregularities are suppressed by containing 0.01 to 10% Sr in the plated film.
Further, Patent Document 5 also discloses a hot-dip Al-Zn-Si-Mg plated steel sheet in which 500 to 3000 ppm of Sr is contained in the plated film to suppress mottling defects.

In addition, the hot-dip Al-Zn-coated steel sheet described above has a problem that when used in a severely corrosive environment, white rust occurs due to corrosion of the coating film. Since this white rust causes deterioration of the appearance of steel sheets, development of plated steel sheets with improved white rust resistance is underway.
For example, in Patent Document 6, for the purpose of improving the white rust resistance of the processed part, the mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the coating layer is optimized. A -Mg-based plated steel sheet is disclosed.
In addition, in Patent Document 7, blackening resistance and white rust resistance are improved by forming a chemical conversion film containing a urethane resin on the plating film of a hot-dip Al-Zn-Si-Mg plated steel sheet. Techniques are disclosed.

Japanese Patent No. 5020228 Japanese Patent No. 5000039 JP-A-2002-12959 Japanese Patent No. 3983932 Japanese Patent Publication No. 2011-514934 Japanese Patent No. 5751093 JP 2019-155872 A

However, the technique of incorporating Mg into the plating film as disclosed in Patent Documents 1 to 3 does not necessarily uniquely improve corrosion resistance.
In the hot-dip Al-Zn-Si-Mg-coated steel sheets disclosed in Patent Documents 1 to 3, corrosion resistance is improved only by including Mg in the coating components, but the above four elements (Al, Zn, The influence of ingredients other than Si and Mg) and the characteristics of the metallic phase and intermetallic compound phase that make up the plating film were not considered, and it was not possible to uniformly talk about the superiority or inferiority of corrosion resistance. Therefore, even when a hot-dip Al-Zn-Si-Mg-coated steel sheet is produced using a plating bath composition in which the contents of the above four element components are the same, the corrosion resistance varies when an accelerated corrosion test is performed. There is a problem that it is not necessarily superior to Al-Zn plated steel sheets to which Mg is not added.
Similarly, in improving the appearance of the plating, it is not always possible to eliminate the wrinkle-like unevenness defects by simply adding Sr to the plating film. For Zn-Si-Mg plated steel sheets, there were cases where both corrosion resistance and appearance could not be achieved. In addition, since Mg is an element that is easily oxidized, the Mg contained in the plating bath generates oxides (top dross) near the bath surface. Fe-Al compounds (bottom dross) containing iron unevenly distributed in the middle or bottom may occur, and these dross adheres to the surface of the plating film and causes convex defects, which may affect the appearance of the plating film surface. There was also the danger of damaging the
In addition, when a steel plate is plated in a molten Al-Zn-Si bath with Mg added, in addition to the α-Al phase, the Mg ₂ Si phase, MgZn ₂ phase, and Si phase precipitate in the plating film. It is known. However, it has not been clarified how the precipitation amount and abundance ratio of each phase affect the corrosion resistance.
Furthermore, with respect to white rust resistance, none of the techniques have been able to achieve sufficient improvement. Regarding the hot-dip Al-Zn-Si-Mg plated steel sheet of Patent Document 6, it is described that the white rust resistance is improved in the processed part and the flat plate part after heating, but the white rust resistance in the unheated flat part was not considered, and the realization of stable white rust resistance was still an issue. Moreover, the hot-dip Al-Zn-Si-Mg-coated steel sheet of Patent Document 7 does not necessarily provide stable and excellent corrosion resistance and white rust resistance, and further improvements have been desired.

In view of such circumstances, an object of the present invention is to provide a surface-treated steel sheet having stably excellent corrosion resistance and white rust resistance, and a method for producing the same.

The inventors of the present invention conducted studies to solve the above problems, and found that the composition of the plating film of the hot-dip Al-Zn-Si-Mg-coated steel sheet can be obtained only by controlling the concentrations of Al, Zn, Si and Mg. Focusing on the fact that it is important to control the concentration of elements contained as impurities, among them, it is possible to effectively suppress the deterioration of corrosion resistance by appropriately controlling the content of Ni. We have found that the deterioration of corrosion resistance can be more effectively suppressed by appropriately controlling the size and distribution of Ni-based compounds present as impurities in the plating film.
In addition, regarding the Mg ₂ Si phase, MgZn ₂ phase, and Si phase formed in the plating film of the hot-dip Al-Zn-Si-Mg steel plate, precipitation depends on the balance of each component in the plating film and the conditions for forming the plating film. Depending on the compositional balance, some phases may not be precipitated. In particular, it was found that the corrosion resistance is stably improved when the _MgZn2 phase is large compared to the _Mg2Si phase and Si phase. However, for these Mg ₂ Si phase, MgZn ₂ phase and Si phase, general techniques such as scanning electron microscopy are 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 between the phases even if the corrosion resistance is measured. However, it was not possible to ascertain the abundance ratios of the Mg ₂ Si, MgZn ₂ and Si phases, which affect the macroscopic information such as appearance and surface appearance.
Therefore, the inventors of _the present invention conducted further extensive research, _and focused on the X-ray diffraction method. The presence ratio can be quantified, and if the Mg ₂ Si phase and MgZn ₂ phase satisfy a specific content ratio in the plating film, excellent corrosion resistance can be stably achieved, and dross generation can be suppressed. It was found that good surface appearance can also be ensured.
In addition, the present inventors controlled the Ni content and film structure in the plating film described above, and controlled the Sr concentration in the plating bath to reliably suppress the occurrence of wrinkle-like uneven defects. It was also found that a plated steel sheet with excellent surface appearance can be obtained.

Furthermore, the present inventors also studied the chemical conversion film formed on the plating film, and found that the chemical conversion film is composed of a specific resin and a specific metal compound, thereby forming a chemical conversion film and a plating film. It has also been found that the affinity for and the antirust effect are enhanced, and the stable improvement of white rust resistance is improved.

The present invention was made based on the above findings, and the gist thereof is as follows.
1. A surface-treated steel sheet comprising a plating film and a chemical conversion film formed on the plating film,
The plating film has a composition containing 45 to 65% by mass of Al, 1.0 to 4.0% by mass of Si, and 1.0 to 10.0% by mass of Mg, with the balance being Zn and unavoidable impurities,
Ni content in the unavoidable impurities is 0.010% by mass or less with respect to the total mass of the plating film,
The chemical conversion film includes at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluorine resin, P compound, and Si compound. , and at least one metal compound selected from Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds. , surface-treated steel plate.

2. The surface-treated steel sheet according to 1 above, wherein the plated film contains a Ni-based compound, and the major axis of the Ni-based compound is 4.0 μm or less.
3. 3. The plating film according to 1 or 2, wherein the plating film contains a Ni-based compound, and the number of the Ni-based compounds present in a direction parallel to the surface of the base steel sheet is 5/mm or less. Surface treated steel plate.
4. 2. The surface-treated steel sheet according to 1 above, wherein the plated film does not contain a Ni-based compound.

5. 5. The surface-treated steel sheet according to any one of 1 to 4 above, wherein diffraction intensities of Mg ₂ Si and MgZn ₂ in the plated film by an X-ray diffraction method satisfy the following relationship (1).
_Mg2Si (111)/ _MgZn2 (100)≦2.0 (1)
Mg ₂ Si (111): diffraction intensity of the (111) plane of Mg ₂ Si (d = 0.3668 nm),
MgZn ₂ (100): Diffraction intensity of the (100) plane of MgZn ₂ (interplanar spacing d = 0.4510 nm)

6. 6. The surface-treated steel sheet according to any one of 1 to 5, wherein the diffraction intensity of Si in the plated film by an X-ray diffraction method satisfies the following relationship (2).
Si (111) = 0 (2)
Si (111): Diffraction intensity of the (111) plane of Si (d = 0.3135 nm)

7. 7. The surface-treated steel sheet according to any one of 1 to 6 above, wherein the plated film further contains Sr: 0.01 to 1.0% by mass.

8. 8. The surface-treated steel sheet according to any one of 1 to 7 above, wherein the Al content in the plating film is 50 to 60% by mass.

9. 9. The surface-treated steel sheet according to any one of 1 to 8, wherein the Si content in the plating film is 1.0 to 3.0% by mass.

10. 10. The surface-treated steel sheet according to any one of 1 to 9 above, wherein the plating film has a Mg content of 1.0 to 5.0% by mass.

11. A method for producing a surface-treated steel sheet comprising a plating film and a chemical conversion film formed on the plating film,
The chemical conversion film includes at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluorine resin, P compound, and Si compound. , at least one metal compound selected from Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds and Ca compounds,
The plating film is formed in a plating bath containing 45 to 65% by mass of Al, 1.0 to 4.0% by mass of Si, and 1.0 to 10.0% by mass of Mg, with the balance being Zn and unavoidable impurities. , comprising a hot-dip plating process in which the base steel plate is immersed, and the Ni content in the inevitable impurities of the plating bath is controlled to 0.010% by mass or less with respect to the total mass of the plating bath. A method for producing a treated steel sheet.
12. 11. The method for producing a surface-treated steel sheet according to 10 above, wherein the plating bath further contains Sr: 0.01 to 1.0% by mass.

ADVANTAGE OF THE INVENTION According to this invention, the surface-treated steel plate which has excellent corrosion resistance and white rust resistance stably, and its manufacturing method can be provided.

It is a figure for demonstrating the flow of the combined cycle test (JASO-CCT) of a Japanese automobile standard.

<Surface treated steel plate>
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 45 to 65% by mass of Al, 1.0 to 4.0% by mass of Si, and 1.0 to 10.0% by mass of Mg, and the balance is Zn and unavoidable impurities. have

The Al content in the plating film is 45 to 65% by mass, preferably 50 to 60% by mass, from the viewpoint of the balance between corrosion resistance and operational aspects. This is because when 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 a dendritic solidification structure of the α-Al phase can be obtained. Since the dendrite solidification structure is laminated in the film thickness direction of the plating film, the corrosion progression path becomes complicated, and the corrosion resistance of the plating film itself is improved. In addition, the more the dendrite part of this α-Al phase is laminated, the more complicated the corrosion progression path becomes, and the more difficult it is for the corrosion to easily reach the base steel plate, so the corrosion resistance is improved. % or more. On the other hand, when the Al content in the plating film exceeds 65% by mass, most of the Zn changes into a solid solution structure in α-Al, the dissolution reaction of the α-Al phase cannot be suppressed, and Al-Zn - Corrosion resistance of Si-Mg system plating deteriorates. Therefore, the Al content in the plating film should be 65% by mass or less, preferably 60% by mass or less.

Si in the plating film mainly suppresses the growth of Fe-Al and/or Fe-Al-Si interfacial alloy layers generated at the interface with the base steel sheet, and does not deteriorate the adhesion between the plating film and the steel sheet. added for a purpose. Actually, when a steel sheet is immersed in an Al-Zn-based plating bath containing Si, Fe on the surface of the steel sheet and Al and Si in the bath undergo an alloying reaction, resulting in Fe-Al and/or Fe-Al-Si An intermetallic compound layer is formed at the base steel plate/plated film interface, but at this time, the growth rate of Fe-Al-Si alloys is slower than that of Fe-Al alloys, so the ratio of Fe-Al-Si alloys is The higher it is, the more the growth of the entire interfacial alloy layer is suppressed. Therefore, the Si content in the plating film should 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 does the effect of suppressing the growth of the interfacial alloy layer saturate, but the excessive Si phase in the plating film promotes corrosion. Therefore, the Si content should be 4.0% or less. Furthermore, the Si content in the plating film is preferably 3.0% or less from the viewpoint of suppressing the existence 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% Mg. By containing Mg in the plated film, the above-mentioned Si can be present in the form of an intermetallic compound of the Mg ₂ Si phase, and promotion of corrosion can be suppressed.
In addition, when the plating film contains Mg, an intermetallic compound, MgZn _2- phase, is also formed in the plating film, which has the effect of further improving corrosion resistance. When the Mg content in the plating film is less than 1.0% by mass, Mg is used for solid solution in the α-Al phase, which is the main phase, rather than for forming the intermetallic compounds (Mg ₂ Si, MgZn ₂ ). Therefore, sufficient corrosion resistance cannot be secured. On the other hand, when the Mg content in the plating film increases, the effect of improving the corrosion resistance becomes saturated and the workability decreases due to the weakening of the α-Al phase. Furthermore, the Mg content in the plating film is preferably 5.0% by mass or less from the viewpoint of suppressing dross generation during plating formation and facilitating plating bath management. In terms of the relationship with the Si content, the content of Mg is preferably 3.0 mass% from the viewpoint of easily satisfying the relational expression (1) described later, considering compatibility with dross suppression. Therefore, it is more preferable to set the content of Mg to 3.0 to 5.0% by mass.

Moreover, the plating film contains Zn and unavoidable impurities. Among these, the unavoidable impurities contain Fe. This Fe is inevitably included in the plating bath due to elution of the steel sheet and bath equipment into the plating bath, and as a result of being supplied by diffusion from the base steel sheet during the formation of the interfacial alloy layer. to 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. These components are eluted into the plating bath from the base steel plate and stainless equipment in the bath, and are contained as impurities in the metal lumps that are the raw materials of the plating bath. It is inevitably included in the plated film by manufacturing using the same pot or equipment in the bath used in the manufacturing of the plated steel sheet to which it is added.

The surface-treated steel sheet of the present invention is characterized in that the Ni content in the unavoidable impurities is 0.010% by mass or less with respect to the total mass of the plating film. Since Ni contained in the plating film may deteriorate the corrosion resistance of the hot-dip Al-Zn-Si-Mg plated steel sheet, the content of Al, Zn, Si and Mg in the plating film described above is Deterioration of corrosion resistance can be suppressed by appropriately controlling and further suppressing the Ni content as an unavoidable impurity. From the same point of view, the Ni content in the unavoidable impurities is preferably 0.005% by mass or less with respect to the total mass of the plating film.

When Ni is contained in the inevitable impurities, the plating film of the hot-dip Al-Zn-Si-Mg plated steel sheet may contain the Ni-based compound as an impurity. Here, the Ni-based compound mainly includes Ni-based compounds such as binary intermetallic compounds such as Ni-Al compounds and ternary intermetallic compounds such as Ni-Al-Fe compounds. That is. Examples of Ni-Al compounds include intermetallic compounds such as _NiAl3 , and examples of Ni-Al-Fe compounds include intermetallic compounds such as (Ni,Fe) _Al3 , in which part of Ni in _NiAl3 is replaced with Fe. Compounds can be exemplified, but are not limited to these compounds.
Here, the presence of the Ni-based compound in the plating film can be determined by, for example, using a scanning electron microscope, observing the plating film from the surface or cross section with a secondary electron image or a backscattered electron image, and energy dispersive X-ray spectroscopy. It can be confirmed by analyzing by the method (EDS). For example, arbitrarily select 5 to 10 locations on a 100 μm plating cross section, observe and perform elemental mapping analysis at an accelerating voltage of 5 kv or less for each, and further perform point analysis on the areas where Ni is detected to detect Ni content. The composition of the object can be confirmed. This method is merely an example, and any method can be used as long as the presence of the Ni-based compound can be confirmed, and the method is not particularly limited.

Moreover, when the plating film contains a Ni-based compound, the major axis of the Ni-based compound is preferably 4.0 μm or less.
The Ni-based compound present in the plating film functions as a cathode in a corrosive environment and forms a local cell with the surrounding solidified structure, which may cause deterioration of corrosion resistance. In particular, when coarse Ni-based compounds are present in the plating film, the corrosion resistance of the hot-dip Al-Zn-Si-Mg-based plated steel sheet may be remarkably lowered. Therefore, in order to obtain a hot-dip Al-Zn-Si-Mg coated steel sheet having better corrosion resistance, it is effective to control the size of the Ni-based compound contained as an impurity in the coating film to be small. Therefore, the major axis of the Ni-based compound is preferably 4.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less.
In addition, the major axis of the Ni-based compound is, for example, using a scanning electron microscope, observing the plated film with a backscattered electron image from the cross section, and confirming that it is a Ni-based compound by EDS. It can be measured by observing a backscattered electron image with an enlarged observation field. The major axis of the Ni-based compound is the maximum major axis of the Ni-based compound confirmed in the observation field of the plating film.

Furthermore, when the plating film contains a Ni-based compound, it is effective to reduce the amount of the Ni-based compound that causes corrosion from the viewpoint of obtaining high corrosion resistance more stably. Specifically, the number of particles of the Ni-based compound in the plating film is preferably 5/mm or less in a direction parallel to the surface of the base steel sheet, more preferably 2/mm or less, and 0 pcs/mm (absent) is most preferred.
Therefore, by suppressing the abundance of the compound containing Ni in the plating film, deterioration of the corrosion resistance of the hot-dip Al-Zn-Si-Mg plated steel sheet can be suppressed more reliably. In order to obtain such a film structure (a film structure containing no Ni-based compounds), it is necessary to reduce the Ni content in the unavoidable impurities. It is important to make it 0.005% by mass or less with respect to
Regarding the number of particles of the Ni-based compound, for example, using a scanning electron microscope, a cross section parallel to the surface of the base steel sheet of the plating film is continuously observed with a backscattered electron image at a length of 1 mm or more, and EDS By dividing the number of Ni-based compounds confirmed by the measured length (mm), the number of Ni-based compounds existing within a length range of 1 mm can be calculated.

Furthermore, the total content of unavoidable impurities in the plating film is not particularly limited, but if it is contained excessively, it may affect various characteristics of the plated steel sheet, so the total content is 5.0% by mass or less. It is preferable to

In the surface-treated steel sheet of the present invention, the concentration of Al, Zn, Si, Mg, and Ni as an unavoidable impurity can be controlled, and the corrosion resistance can be improved more stably. It is preferable that the diffraction intensities of Mg ₂ Si and MgZn ₂ in the X-ray diffraction method satisfy the following relationship (1).
_Mg2Si (111)/ _MgZn2 (100)≦2.0 (1)
Mg ₂ Si (111): Diffraction intensity of the (111) plane of Mg ₂ Si (d = 0.3668 nm) MgZn ₂ (100): Diffraction of the (100) plane of MgZn ₂ (d = 0.4510 nm) Strength

As described above, in the present invention, it is important to control the existence ratio of intermetallic compounds such as Mg ₂ Si and MgZn ₂ that are generated in the plating film due to the inclusion of Mg to a specific ratio. The effects of these factors on corrosion resistance are currently being investigated, and there are many unclear points, but the following mechanism is presumed.

When the surface-treated steel sheet is exposed to a corrosive environment, the above intermetallic compounds dissolve preferentially over the α-Al phase, resulting in an Mg-rich environment in the vicinity of the formed corrosion products. In such a Mg-rich environment, it is assumed that the formed corrosion products are difficult to decompose, and as a result, the protective effect of the plating film increases. In addition, since _MgZn2 is more effective in improving the protective action of this plating film than _Mg2Si , it is considered effective to increase the existence ratio of _MgZn2 in the intermetallic compounds present in the plating film. be done.

Further, the existence ratio of Mg ₂ Si and MgZn ₂ in the plating film was calculated using the diffraction peak intensity obtained by the X-ray diffraction method, and the relationship (1): Mg ₂ Si (111)/MgZn ₂ (100 )≦2.0. When the existence ratio of Mg ₂ Si and MgZn ₂ in the plating film does not satisfy the relationship (1), that is, Mg ₂ Si (111)/MgZn ₂ (100)>2.0, Since there is a large amount of Mg ₂ Si in the intermetallic compound, the above-mentioned Mg-rich environment cannot be obtained in the vicinity of the corrosion product, and the effect of improving the protective action of the plating film is difficult to obtain. There is a risk.

Here, in the relationship (1), Mg ₂ Si (111) is the diffraction intensity of the (111) plane of Mg ₂ Si (d = 0.3668 nm), and MgZn ₂ (100 ₎ is the This is the diffraction intensity of the (100) plane (d = 0.4510 nm).
As a method for measuring Mg ₂ Si (111) and MgZn ₂ (100) by X-ray diffraction, a part of the plating film is mechanically scraped off and powdered, and X-ray diffraction is performed (powder X-ray diffraction measurement method). For measurement of diffraction intensity, measure the diffraction peak intensity of Mg ₂ Si corresponding to the interplanar spacing d = 0.3668 nm and the diffraction peak intensity of MgZn ₂ corresponding to the interplanar spacing d = 0.4510 nm, and calculate the ratio of these. can obtain Mg ₂ Si (111)/MgZn ₂ (100).
In addition, the amount of plating film required when performing powder X-ray diffraction measurement (the amount of plating film scraped off) is 0.1 g from the viewpoint of accurately measuring Mg ₂ Si (111) and MgZn ₂ (100). 0.3 g or more is preferable. In addition, when the plating film is cut out, the powder may contain steel sheet components other than the plating film, but these intermetallic compound phases are contained only in the plating film, and the above-mentioned peak strength No effect. Furthermore, the reason why the plating film is powdered and subjected to X-ray diffraction is that when X-ray diffraction is performed on the plating film formed on the plated steel sheet, the correct phase ratio is affected by the plane orientation of the solidification structure of the plating film. This is because it is difficult to calculate.

In addition, in the surface-treated steel sheet of the present invention, the concentrations of Al, Zn, Si, Mg, and Ni as an unavoidable impurity can be controlled, and the corrosion resistance can be improved more stably. It is preferable that the diffraction intensity of Si in the plating film by the X-ray diffraction method satisfies the following relationship (2).
Si (111) = 0 (2)
Si (111): Diffraction intensity of the (111) plane of Si (d = 0.3135 nm) 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. It is most excellent for stabilizing the corrosion resistance to form a film in which no phase exists (the Si(111) diffraction peak intensity is set to zero).
As for the method for measuring the diffraction peak intensity of the (111) plane of Si by X-ray diffraction, the same method as the method for measuring Mg ₂ Si (111) and MgZn ₂ (100) described above can be used.

Here, there is no particular limitation on the method for satisfying the relationship (1) and relationship (2) described above. For example, in order to satisfy the relationship (1) and the relationship (2), by adjusting the balance of the Si content, Mg content and Al content in the plating film, Mg ₂ Si, MgZn ₂ and Si abundance ratio (diffraction intensity of Mg ₂ Si (111), MgZn ₂ (100) and Si (111)) can be controlled. The balance of the Si content, the Mg content, and the Al content in the plating film does not necessarily satisfy the relationship (1) or the relationship (2) if it is set to a constant content ratio. It is necessary to change the content ratio of Mg and Al depending on the content (% by mass).
In addition to adjusting the balance of the Si content, Mg content and Al content in the plating film, by adjusting the conditions during plating film formation (for example, cooling conditions after plating) , the diffraction intensity of Mg ₂ Si (111), MgZn ₂ (100) and Si (111) can be controlled so as to satisfy the relationship (1) or (2).

Moreover, in the surface-treated steel sheet of the present invention, the plating film preferably contains 0.01 to 1.0% by mass of Sr. By containing Sr in the plating film, it is possible to more reliably suppress the occurrence of surface defects such as wrinkle-like irregularities, and to realize good surface appearance.
The wrinkle-like defects are wrinkle-like irregularities formed on the surface of the plating film, and are observed as whitish streaks on the surface of the plating film. Such wrinkle-like defects tend to occur when a large amount of Mg is added to the plating film. Therefore, in the hot-dip plated steel sheet, by including 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, so that the wrinkle-like defects It is possible to suppress the occurrence of

In the surface-treated steel sheet of the present invention, the existence ratio of Mg ₂ Si and MgZn ₂ in the plating film described above satisfies the relationship (1), and the plating film contains 0.01 to 1.0% by mass of Sr. is preferred. This is because the effect of improving surface appearance due to Sr described above can be more enjoyed. The reason for this is not clear, but it is presumed that when the amount of Mg ₂ Si in the plating film increases, it is difficult to suppress the oxidation of the plating surface layer in the first place, which affects the effect of improving the appearance when Sr is added. be done. If the Sr content in the plating film is less than 0.01% by mass, it is difficult to obtain the effect of suppressing the occurrence of wrinkle-like defects described above, and the Sr content in the plating film exceeds 1.0% by mass. In this case, Sr is excessively incorporated into the interfacial alloy layer, which may affect plating adhesion beyond improving appearance. Therefore, the Sr content in the plating film is 0.01 to 1.0% by mass. is preferred.

In addition, the plating film has the effect of improving the stability of corrosion products and delaying the progress of corrosion in the same manner as Mg described above, so that the total content of Cr, Mn , V, Mo, Ti, Ca, Co, Sb and B are preferably further contained. The reason why the total content of the above components is set to 0.01 to 10% by mass is that a sufficient corrosion retarding effect can be obtained and the effect will not be saturated.

From the viewpoint of satisfying various characteristics, the coating weight of the plating film is preferably 45 to 120 g/m ² per side. When the coating weight 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. This is because, when it is m ² or less, it is possible to achieve excellent corrosion resistance while suppressing the occurrence of plating cracks and the like during processing. From the same point of view, it is more preferable that the coating amount of the plating film is 45 to 100 g/m ² .

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

In addition, the component composition of the plating film can be confirmed by immersing the plating film in hydrochloric acid or the like to dissolve it and confirming the solution by ICP emission spectrometry, atomic absorption spectrometry, etc., as with the Ni content described above. This method is merely an example, and any method may be used as long as it can accurately quantify the component composition of the plating film, and is not particularly limited.

In addition, 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 accurately controlled 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 standards.

Furthermore, the method for obtaining the base steel sheet is not particularly limited. For example, in the case of the hot-rolled steel sheet, a hot-rolled steel sheet and a pickling process may be used, and in the case of the cold-rolled steel sheet, a cold-rolling process may be further added. Furthermore, in order to obtain the characteristics of the steel sheet, it is also possible to undergo a recrystallization annealing process or the like before the hot dip plating process.

Regarding the plating film forming conditions when producing the surface-treated steel sheet of the present invention, there is no particular limitation in performing the hot-dip plating step of immersing the base steel sheet in the plating bath. The hot-dip plating treatment step includes, for example, continuous hot-dip plating equipment, washing the base steel plate,
It can be carried out by heating and immersion in a plating bath. In the heating process of the steel sheet, recrystallization annealing or the like is performed to control the structure of the base steel sheet itself, and a nitrogen-hydrogen atmosphere or the like is applied to prevent oxidation of the steel sheet and reduce a small amount of oxide film existing on the surface. Heating in a reducing atmosphere is effective.

Further, with respect to the plating bath used in the hot-dip plating process, as described above, the composition of the plating film as a whole is almost the same as the composition of the plating bath, so Al: 45 to 65% by mass, Si: A composition containing 1.0 to 4.0% by mass and 1.0 to 10.0% by mass of Mg, with the balance being Zn and unavoidable impurities can be used.

In the hot-dip plating step, the Ni content in the unavoidable impurities in the plating bath should be controlled to 0.010% by mass or less with respect to the total mass of the plating bath. As described above, Ni contained in the plating film may deteriorate the corrosion resistance of the hot-dip Al-Zn-Si-Mg plated steel sheet. Deterioration of corrosion resistance can be suppressed by appropriately controlling the Ni content and further suppressing the Ni content as an unavoidable impurity.
Also, the content of Ni as an unavoidable impurity in the plating bath should be controlled to 0.010% by mass or less, preferably 0.005% by mass or less, relative to the total mass of the plating bath. If the Ni content in the plating bath exceeds 0.005% by mass, the corrosion resistance of the produced hot-dip Al-Zn-Si-Mg-coated steel sheet may deteriorate. This is because there is a possibility that There is no lower limit for the Ni content, which adversely affects corrosion resistance.

Here, the means for reducing the Ni content in the plating bath is not particularly limited.
For example, since it is effective to suppress the elution of stainless steel in-bath equipment into the plating bath, it is preferable to treat the surface of the in-bath equipment with a thermal spray coating or the like. This is because the formation of the thermal spray coating or the like makes it possible to impart corrosion resistance to the plating bath to the in-bath equipment and to suppress elution of the in-bath equipment into the plating bath. The type of the thermal spray coating is not particularly limited, but a coating having heat resistance and corrosion resistance such as a WC-based or MoB-based coating can be selected. It is also more effective to use in-bath equipment made of heat-resistant materials that do not contain Ni. In this case, even if the device in the bath is eluted, the Ni content can be prevented from increasing.

Moreover, as another means for reducing the Ni content in the plating bath, it is preferable to use a metal ingot with a low Ni content in the impurities as the raw material of the plating bath.
Furthermore, it is also effective not to use the pots and equipment in the bath used for the production of plated steel sheets to which Ni is intentionally added for the production of hot-dip Al-Zn-Si-Mg-based plated steel sheets. This is because it is possible to suppress dissolution of Ni-containing metal lumps adhering to the pot and the equipment in the bath and mixing into the plating bath.

Furthermore, although the bath temperature of the plating bath is not particularly limited, it is preferably in the temperature range of (melting point +20°C) to 650°C.
The reason why the lower limit of the bath temperature is set to the melting point +20°C is that the bath temperature must be higher than the freezing point in order to perform the hot-dip plating process. This is to prevent coagulation due to a local temperature drop in the bath. On the other hand, the upper limit of the bath temperature is set to 650°C because if it 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. It's for.

In addition, the temperature of the base steel sheet that enters the plating bath (immersion plate temperature) is not particularly limited. It is preferable to control the temperature within ±20°C.

Furthermore, it is preferable that the immersion time of the base steel sheet in the plating bath is 0.5 seconds or longer. This is because if the time is 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 immersion time is not particularly limited, but if the immersion time is long, the interfacial alloy layer formed between the plating film and the steel sheet may become thicker, so it is more preferably 8 seconds or less.

(Chemical film)
The surface-treated steel sheet of the present invention has a chemical conversion film formed on the plating film described above.
The chemical conversion coating 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 sheet of the present invention, the chemical conversion film is at least selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluorine resin. 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 and a compound.
By forming the above-described chemical conversion film on the plating film, it is possible to increase the affinity with the plating film and uniformly form the chemical conversion film on the plating film. In addition, the corrosion prevention effect of the chemical conversion film and the barrier effect can be enhanced. As a result, it becomes possible to realize stable corrosion resistance and white rust resistance of the surface-treated steel sheet of the present invention.

Here, from the viewpoint of improving corrosion resistance, 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. At least one selected is used. From the same point of view, the resin preferably contains at least one of urethane resin and acrylic resin. In addition, addition polymers of the resins described above are also included in the resin constituting the chemical conversion film.

Regarding the epoxy resin, for example, bisphenol A type, bisphenol F type, novolac type epoxy resin, etc. are glycidyl etherified, propylene oxide, ethylene oxide or polyalkylene glycol is added to bisphenol A type epoxy resin, Glycidyl-etherified ones, aliphatic epoxy resins, alicyclic epoxy resins, polyether epoxy resins, and 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, or the like can be used.

For 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), styrene-acrylic acid copolymers, and the like, and those obtained by modifying these resins with other alkyd resins, epoxy resins, phenol resins, etc. can also be used.

Examples of the acrylic silicone resin include those obtained by adding a curing agent to a resin having a hydrolyzable alkoxysilyl group at the side chain or terminal of an acrylic copolymer as a main agent. Moreover, when an acrylic silicon resin is used, excellent weather resistance can be expected in addition to corrosion resistance.

Examples of the alkyd resins include oil-modified alkyd resins, rosin-modified alkyd resins, phenol-modified alkyd resins, styrenated alkyd resins, silicon-modified alkyd resins, acrylic-modified alkyd resins, oil-free alkyd resins, and high molecular weight oil-free alkyd resins. can be mentioned.

The polyester resin is a polycondensate synthesized by dehydrating and condensing a polycarboxylic acid and a polyalcohol to form an ester bond. Examples of the polycarboxylic acid include terephthalic acid, 2, 6-naphthalenedicarboxylic acid and the like are used, and polyalcohols include, for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Specifically, the polyester includes polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and the like. In addition, acrylic-modified polyester resins can also be used.

Examples of the polyalkylene resin include ethylene-based copolymers such as ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, and carboxyl-modified polyolefin resins, ethylene-unsaturated carboxylic acid copolymers, and ethylene-based ionomers. and the like, and those obtained by modifying these resins with other alkyd resins, epoxy resins, phenol resins or the like can also be used.

The amino resin is a thermosetting resin produced by a reaction between an amine or an amide compound and an aldehyde, and includes melamine resin, guanamine resin, thiourea resin and the like. , it is preferable to use a melamine resin. The melamine resin is not particularly limited, and examples thereof include butylated melamine resin, methylated melamine resin, aqueous melamine resin and the like.

Examples of the fluororesin include fluoroolefin polymers and copolymers of fluoroolefins with alkyl vinyl ethers, synchroalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkyl allyl 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.

Furthermore, it is preferable to use a curing agent as the resin constituting the chemical conversion film, in order to improve corrosion resistance and workability. Curing agents include urea resins (butylated urea resins, etc.), melamine resins (butylated melamine resins, butyl-etherified melamine resins, etc.), butylated urea/melamine resins, amino resins such as benzoguanamine resins, blocked isocyanates, oxazoline compounds, A phenol resin or the like can be used as appropriate.

In addition, 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 point of view, the metal compound preferably contains at least one of P compound, Si compound and V compound.

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

Any compound can be used as the inorganic phosphoric acid, organic phosphoric acid, and salts thereof without particular limitation. For example, the inorganic phosphoric acid includes phosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphate, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphorous It is preferable to use one or more selected from acid salt, hypophosphorous acid, and hypophosphite. Phosphonic acid (phosphonic acid compound) is preferably used as the organic phosphoric acid. Furthermore, as the phosphonic acid, it is preferable to use one or more selected from nitrilotrismethylene phosphonic acid, phosphonobutanetricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, and ethylidenediphosphonic acid.
When the P compound is a salt, the salt is preferably a salt of an element of Groups 1 to 13 in the periodic table, more preferably a metal salt, an alkali metal salt and an alkaline earth metal salt. It is preferably one or more selected from metal salts.

When the chemical conversion treatment solution containing the P compound is applied to a hot-dip Al-Zn-Si-Mg plated steel sheet, the surface of the plating film is etched by the action of the P compound, and the constituent elements of the plating film, Al, Zn, 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 thickened 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 solution is not particularly limited, but can 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, the adhesion to the plating interface is reduced, and the corrosion resistance of the flat surface is reduced. Corrosion resistance and perspiration resistance of the damaged part of the film may also decrease. From the same point of view, 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, if the concentration of the P compound exceeds 5% by mass, not only will the life of the chemical conversion treatment solution be shortened, but also the appearance of the formed film will tend to be uneven, and the amount of P elution from the chemical conversion film will be reduced. increases, and there is a possibility that blackening resistance may decrease. From the same point of view, 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 the P compound in the chemical conversion film, for example, a chemical conversion treatment solution with a P compound concentration of 0.25% by mass to 5% by mass is applied and dried to reduce the adhesion of P in the chemical conversion film after drying. Amounts can be from 5 to 100 mg/m ² .

The Si compound is a component that forms a skeleton for forming a chemical conversion film together with the resin, and can enhance affinity with the plating film and form a uniform 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.

Any silica can be used without particular limitation. As the silica, for example, at least one of wet silica and dry silica can be used. As the colloidal silica, which is a type of wet silica, for example, Snowtex O, C, N, S, 20, OS, OXS, NS manufactured by Nissan Chemical Industries, Ltd. can be suitably used. As the dry silica, for example, AEROSIL 50, 130, 200, 300, 380 manufactured by Nippon Aerosil Co., Ltd. can be preferably used.

Any trialkoxysilane can be used without particular limitation. For example, the general formula: R ₁ Si(OR ₂ ) ₃ , where R ₁ is hydrogen or an alkyl group having 1 to 5 carbon atoms, and R ₂ is the same or different alkyl group having 1 to 5 carbon atoms. ) is preferably used. Such trialkoxysilanes include, for example, trimethoxysilane, triethoxysilane, methyltriethoxysilane, and the like.

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

Any silane coupling agent 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- isocyanatopropyltriethoxysilane and the like.

By including the Si compound in the chemical conversion film, the Si compound undergoes dehydration condensation to form an amorphous chemical conversion film having siloxane bonds with a high barrier effect to shield corrosion factors. Also, by combining with the above-mentioned resin, a chemical conversion film having higher barrier properties is formed. Furthermore, in a corrosive environment, dense and stable corrosion products are formed in defective parts and damaged parts of the plating and film caused by processing, etc., and the effect of suppressing corrosion of the base steel plate is also obtained by the combined effect with the above-mentioned plating film. be. At least one of colloidal silica and dry silica is preferably used as the Si compound from the viewpoint of being highly effective in forming stable corrosion products.

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. If the concentration of the Si compound in the chemical conversion treatment solution is 0.2% by mass or more, a barrier effect due to the siloxane bond can be obtained. Corrosion resistance and perspiration resistance in the part are improved. Moreover, if the concentration of the Si compound is 9.5% by mass or less, the life of the chemical conversion treatment solution can be extended. By applying and drying a chemical conversion treatment solution with a Si compound concentration of 0.2 mass % to 9.5 mass %, the amount of Si attached to the chemical conversion film after drying can be 2 to 95 mg/m ² .

The Co compound and the Ni compound are contained in the chemical conversion film, thereby improving resistance to blackening. This is probably because Co and Ni have the effect of delaying the elution of water-soluble components from the film under corrosive environments. In addition, Co and 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 thickened layer), the thickened layer serves as a barrier against corrosion. As a result, blackening resistance can be improved.

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

The concentration of the Co compound and/or Ni compound in the chemical conversion treatment solution is not particularly limited, but can be 0.25% by mass to 5% by mass in total. If the concentration of the Co compound and/or Ni compound is less than 0.25% by mass, the interfacial thickened layer becomes non-uniform and the corrosion resistance of the flat surface is lowered. There is also a risk that the corrosion resistance of the damaged part of the coating will also decrease. From the same point of view, 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 of the formed film tends to be non-uniform, and corrosion resistance may decrease. From the same point of view, 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 in which the total concentration of the Co compound and/or Ni compound is 0.25% by mass to 5% by mass, the total amount of Co and Ni deposited in the chemical conversion film after drying is 5 to 100 mg. / ^m2 .

By including the Al compound, the Zn compound, and the Mg compound in the chemical conversion treatment solution, a concentrated layer containing at least one of Al, Zn, and Mg can be formed on the plating film side of the chemical conversion film. . The formed thickened layer can improve 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, such as salts, chlorides, It is preferably an oxide or 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 solution 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 coating becomes more uniform, and the corrosion resistance of flat portions, defective portions, and damaged portions of the plating and coating caused by processing is further improved.

When the V compound is contained in the chemical conversion film, V moderately elutes in a corrosive environment, and likewise bonds with zinc ions, which are plating components that elute in a corrosive environment, to form a dense protective film. . The formed protective film can further improve corrosion resistance not only on the flat surface of the steel sheet, but also against defects, damaged parts of the plating film caused by processing, corrosion progressing from the cut end surface to the flat surface, 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 content of 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. If the concentration of the V compound is 0.05% by mass or more, it is likely to dissolve in a corrosive environment and form a protective film, and the corrosion resistance of defective parts, cut edges, and damaged parts 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 of the formed chemical film tends to be non-uniform, and the resistance to blackening is lowered.

By being contained in the chemical conversion film, the Mo compound can 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 a chemical conversion treatment solution.
The molybdate includes, for example, 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 blackening resistance can be further improved. On the other hand, if the concentration of the Mo compound is 3% by mass or less, the life of the chemical conversion treatment solution can be further extended, and the corrosion resistance can be further improved.

By containing the Zr compound and the Ti compound in the chemical conversion film, the chemical conversion film can be prevented from becoming porous and the film can be densified. As a result, it becomes difficult for corrosive factors to permeate the chemical conversion coating, and the corrosion resistance can be enhanced.

The Zr compound is a compound containing Zr, 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 preferable because it densifies the film when the chemical conversion treatment solution is dried to form the film, thereby obtaining more excellent corrosion resistance.

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

The total concentration of the Zr compound and/or Ti compound in the chemical conversion treatment liquid for forming the chemical conversion film is preferably 0.2% by mass to 20% by mass. If the total concentration of the Zr compound and/or Ti compound is 0.2% by mass or more, the effect of suppressing permeation of corrosion factors is enhanced, and not only the corrosion resistance of the flat surface but also the plating film damage caused by defects, cut edges, and processing. The corrosion resistance of the part can be further improved. On the other hand, if the total concentration of the Zr compound and/or Ti compound is 20% by mass or less, the life of the chemical conversion treatment solution can be further extended.

By being contained in the chemical conversion film, the Ca compound can exhibit the effect of reducing the corrosion rate.

The Ca compound is a compound containing Ca, and examples thereof include oxides of Ca, nitrates of Ca, sulfates of Ca, and intermetallic compounds containing Ca. More specifically, the Ca compound includes 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 coating is not particularly limited.

The chemical conversion film may contain various known components commonly used in the paint field, if necessary. For example, various surface conditioners such as leveling agents and antifoaming agents, dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, various additives such as titanate coupling agents, coloring pigments, and extender pigments. , various pigments such as glittering agents, curing catalysts, organic solvents, lubricants, and the like.

In addition, in the surface-treated steel sheet of the present invention, the chemical conversion coating preferably does not contain harmful components such as hexavalent chromium, trivalent chromium and fluorine. This is because the chemical conversion treatment solution for forming the chemical conversion film does not contain these harmful components, so that it is highly safe and environmentally friendly.

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

The method for forming the chemical conversion film is not particularly limited, and can be appropriately selected according to the required performance, manufacturing equipment, and the like. For example, on the plating film, the chemical conversion treatment solution is continuously applied with a roll coater or the like, and then hot air or induction heating is used to achieve a peak metal temperature (PMT) of about 60 to 200 ° C. It can be formed by drying. For applying the chemical conversion treatment liquid, known methods such as an airless spray, an electrostatic spray, and a curtain flow coater can be appropriately employed in addition to the roll coater. Furthermore, the chemical conversion film may be either a single layer film or a multilayer film as long as it contains the resin and the metal compound, and is not particularly limited.

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

<Method for producing surface-treated steel sheet>
A method for producing a surface-treated steel sheet according to the present invention is a method for producing a surface-treated steel sheet including a plating film and a chemical conversion film formed on the plating film.
In the production method of the present invention, the chemical conversion film is at least one selected from epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins and fluorine resins. and at least one metal compound selected from 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. and contains
The plating film is formed in a plating bath containing 45 to 65% by mass of Al, 1.0 to 4.0% by mass of Si, and 1.0 to 10.0% by mass of Mg, with the balance being Zn and unavoidable impurities. and a hot-dip plating step of immersing the substrate steel sheet, and controlling the Ni content in the inevitable impurities of the plating bath to 0.010% by mass or less.

As described above, Ni contained in the plating film may deteriorate the corrosion resistance of the hot-dip Al-Zn-Si-Mg plated steel sheet. Deterioration of corrosion resistance can be suppressed by appropriately controlling the Ni content and further suppressing the Ni content as an unavoidable impurity.

The conditions of the hot-dip plating process are the same as those described in the plating film of the surface-treated steel sheet of the present invention.
Also, the structure of the chemical conversion coating is the same as that described for the chemical conversion coating of the surface-treated steel sheet of the present invention.

(Samples 1-148)
(1) A cold-rolled steel sheet with a thickness of 0.8 mm manufactured by a conventional method was used as the base steel sheet, and the coating shown in Tables 2 and 3 was obtained by performing annealing and plating using a hot-dip plating simulator manufactured by Lesca Co., Ltd. A sample of a hot-dip plated steel sheet was prepared under coating conditions.
Regarding the composition of the plating bath used in the production of the hot dip plated steel sheet, the composition of the plating bath was adjusted to Al: 5 to 75% by mass and Si: 0.0 so that the composition of the plating film of each sample shown in Tables 2 and 3 was obtained. ~4.5% by mass, Mg: 0~10% by mass, Ni: 0.000~0.025% by mass. The bath temperature of the plating bath is 450°C for Al: 5% by mass, 480°C for Al: 15% by mass, 590°C for Al: 30 to 60% by mass, and more than 60% by mass for Al. In the case of , the temperature was set to 630° C., and the temperature of the base steel sheet in which the plating penetrated was controlled to be the same temperature as the plating bath temperature. Furthermore, in the case of Al: 30 to 60% by mass, plating was performed under the condition that the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds.
The amount of plating film deposited was 85±5 g/m ² per side for samples 1-118 and 131-148, 50±5 g/m ² per side for samples 119-120, and 100±5 g per side for samples 121-122. /m ² , 125 g/m ² ±5 g/m ² per side for samples 123-124, and 70 ± 5 g/m ² per side for samples 125-130.

(2) After that, apply a chemical conversion treatment solution on the plated film of each sample of the hot-dip plated steel sheet with a bar coater and dry it with a hot air oven (heating rate: 60 ° C / s, PMT: 120 ° C). to form a chemical conversion film, and prepare each sample of surface-treated steel sheets shown in Tables 2 and 3.
As the chemical conversion treatment liquid, surface treatment liquids A to F were prepared by dissolving each component in water as a solvent. 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 tripolyphosphate
Si compound: silica
V compound: sodium metavanadate
Mo compound: molybdic acid
Zr compound: Potassium zirconyl carbonate Table 1 shows the compositions of the prepared chemical conversion solutions A to F and the amounts of chemical conversion films formed. In addition, the concentration of each component in Table 1 of this specification is the concentration (% by mass) of the solid content.

(evaluation)
Each sample of the hot-dip plated steel sheet and the surface-treated steel sheet obtained as described above was evaluated as follows. Evaluation results are shown in Tables 2 and 3.

(1) Plating film (composition, coating amount, Ni-based compound, X-ray diffraction intensity)
For each sample of the hot-dip plated steel sheet, a 100 mmφ was punched, and the non-measurement surface was sealed with tape. The adhesion amount of the plating film was calculated from the mass difference. Tables 2 and 3 show the adhesion amount of the plating film obtained as a result of the calculation.
After that, the stripping liquid was filtered, and the filtrate and the solid content were analyzed. Specifically, components other than insoluble Si were quantified by subjecting the filtrate to ICP emission spectroscopic analysis.
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 subjecting the solution to ICP emission spectroscopic analysis. The Si concentration in the plating film was obtained by adding the insoluble Si concentration obtained by solid content analysis to the soluble Si concentration obtained by filtrate analysis. Tables 2 and 3 show the compositions of the plating films obtained as a result of the calculation.
Furthermore, after shearing each sample to a size of 15 mm × 15 mm, it was embedded in a conductive resin so that the cross section of the steel plate could be observed, and then mechanically polished and then subjected to a scanning electron microscope (ULTRA55 manufactured by Carl Zeiss). Backscattered electron images were continuously taken at a width of 100 μm under the condition of an acceleration voltage of 3 kv for a continuous cross section of an arbitrarily selected plating film having a length of 2 mm or more in the direction parallel to the surface of the base steel sheet. Furthermore, in the same equipment, using an energy dispersive X-ray spectrometer (Oxford Instruments Ultim Extreme), elemental mapping analysis of each cross section (Al, Zn, Si, Mg, Fe, Sr , and Ni) were performed. The part where Ni intensity was detected to be high in this analysis was subjected to point analysis using the same spectrometer under the condition of an acceleration voltage of 3 kv, and the substance was identified from the obtained semi-quantitative values of the components. The major axis was measured for all Ni-based compounds confirmed in the observation field, and the maximum major axis was determined. In addition, by counting the number of all Ni-based compound particles present in the observed continuous cross section and dividing by the observed cross-sectional length (mm), the number of Ni-based compound particles per 1 mm parallel to the surface of the base steel sheet The number of particles (particles/mm) was calculated. The part where Ni intensity was detected to be high in this analysis was subjected to point analysis using the same spectrometer under the condition of an acceleration voltage of 3 kv, and the substance was identified from the obtained semi-quantitative values of the components. Analysis results are shown in Tables 2 and 3.
In addition, for each sample, after shearing to a size of 100 mm × 100 mm, the plating film on the evaluation symmetrical surface was mechanically scraped until the base steel plate appeared, and the obtained powder was mixed well, then 0.3 g was taken out, X-rays used: Cu-Kα (wavelength = 1.54178 Å), removal of Kβ rays: Ni filter, tube voltage: 40 kV, tube current: 30 mA, Scanning speed: 4°/min, sampling interval: 0.020°, divergence slit: 2/3°, solar slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra) qualitative analysis was performed. _Each diffraction intensity ₍ cps) is obtained by subtracting the base intensity from each peak intensity. = 0.4510 nm) and the diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135 nm). The measurement results are shown in Tables 2 and 3.

(2) Corrosion resistance evaluation For each sample of hot-dip plated steel sheet and surface-treated steel sheet, after shearing to a size of 120 mm × 120 mm, a range of 10 mm from each edge of the evaluation target surface, and the end surface of the sample and the non-evaluation surface were taped. A sample with a size of 100 mm×100 mm exposed to be evaluated was used as a sample for evaluation. In addition, three identical evaluation samples were produced.
Accelerated corrosion tests were performed on the three samples for evaluation produced as described above with the cycle shown in FIG. The accelerated corrosion test was started from wet and after 300 cycles, the corrosion weight loss of each sample was measured by the method described in JIS Z 2383 and ISO8407, and evaluated according to the following criteria. Evaluation results are shown in Tables 2 and 3.
◎: Corrosion weight loss of all 3 samples is 30 g/m ² or less ○: Corrosion weight loss of all 3 samples is 75 g/m ² or less ×: Corrosion weight loss of 1 or more samples exceeds 75 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 evaluation target surface, the end surface of the sample and the non-evaluation surface A sample with a size of 100 mm×100 mm and an evaluation target surface exposed by sealing with tape was used as an evaluation sample.
Using the evaluation samples, a salt spray test described in JIS Z 2371 was performed for 90 hours and evaluated according to the following criteria. Evaluation results are shown in Tables 2 and 3.
◎: No white rust on the flat plate part ○: Less than 10% white rust generated area on the flat plate part ×: 10% or more white rust generated area on the flat plate part

(4) Surface Appearance For each sample of the hot-dip plated steel sheet, the surface of the plated film was visually observed.
The observation results were evaluated according to the following criteria. Evaluation results are shown in Tables 2 and 3.
◎: No wrinkle-like defects were observed ○: Wrinkle-like defects were observed only in the range of 50 mm from the edge ×: Wrinkle-like defects were observed outside the range of 50 mm from the edge

(5) Workability Each sample of the hot-dip plated steel sheet was sheared into a size of 70 mm x 150 mm, and then subjected to 180° bending (8T bending) with eight sheets of the same thickness sandwiched inside. Cellotape (registered trademark) was strongly adhered to the outer surface of the bent portion after bending, and then 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 tape used were visually observed, and workability was evaluated according to the following criteria. Evaluation results are shown in Tables 2 and 3.
○: Both cracks and peeling are not observed in the plating film △: There are cracks in the plating film, but no peeling is observed ×: Both cracks and peeling are observed in the plating film

(5) Bath stability During hot-dip plating, the state of the bath surface of the plating bath is visually checked, and the bath surface of the plating bath used when manufacturing hot-dip Al-Zn coated steel sheets (bath surface without Mg-containing oxides) ). Evaluation was performed according to the following criteria, and evaluation results are shown in Tables 2 and 3.
〇: Same as hot dip Al-Zn plating bath (55 mass% Al-balance Zn-1.6 mass% bath) △: Hot dip Al-Zn plating bath (55 mass% Al-balance Zn-1.6 mass% bath) There are many white oxides compared to ×: Formation of black oxides is observed in the plating bath

From the results in Tables 2 and 3, the samples of the invention examples are superior to the samples of the comparative examples in terms of corrosion resistance, white rust resistance, surface appearance, workability and bath stability in a well-balanced manner. I know there is.
Also, from the results in Table 3, it can be seen that the samples subjected to the chemical conversion treatments A to D exhibited particularly excellent white rust resistance.

ADVANTAGE OF THE INVENTION According to this invention, the surface-treated steel plate which has excellent corrosion resistance and white rust resistance stably, and its manufacturing method can be provided.

Claims (12)

A surface-treated steel sheet comprising a plating film and a chemical conversion film formed on the plating film,
The plating film has a composition containing 45 to 65% by mass of Al, 1.0 to 4.0% by mass of Si, and 1.0 to 10.0% by mass of Mg, with the balance being Zn and unavoidable impurities,
Ni content in the unavoidable impurities is 0.010% by mass or less with respect to the total mass of the plating film,
The chemical conversion film includes at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluorine resin, P compound, and Si compound. , and at least one metal compound selected from Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds. , surface-treated steel plate. 2. The surface-treated steel sheet according to claim 1, wherein the plated film contains a Ni-based compound, and the major axis of the Ni-based compound is 4.0 μm or less. 3. The plating film according to claim 1 or 2, wherein the plating film contains a Ni-based compound, and the number of the Ni-based compounds present in a direction parallel to the surface of the base steel sheet is 5/mm or less. surface-treated steel plate. The surface-treated steel sheet according to claim 1, wherein the plated film does not contain a Ni-based compound. The surface according to any one of claims 1 to 4, wherein the diffraction intensities of Mg ₂ Si and MgZn ₂ in the plating film by an X-ray diffraction method satisfy the following relationship (1): treated steel plate.
_Mg2Si (111)/ _MgZn2 (100)≦2.0 (1)
Mg ₂ Si (111): diffraction intensity of the (111) plane of Mg ₂ Si (d = 0.3668 nm),
MgZn ₂ (100): Diffraction intensity of the (100) plane of MgZn ₂ (interplanar spacing d = 0.4510 nm) The surface-treated steel sheet according to any one of claims 1 to 5, wherein the diffraction intensity of Si in the plated film by an X-ray diffraction method satisfies the following relationship (2).
Si (111) = 0 (2)
Si (111): Diffraction intensity of the (111) plane of Si (d = 0.3135 nm) The surface-treated steel sheet according to any one of claims 1 to 6, wherein the plated film further contains Sr: 0.01 to 1.0% by mass. The surface-treated steel sheet according to any one of claims 1 to 7, 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 8, wherein the Si content in the plated film is 1.0 to 3.0% by mass. The surface-treated steel sheet according to any one of claims 1 to 9, characterized in that the content of Mg in said plating film is 1.0 to 5.0% by mass. A method for producing a surface-treated steel sheet comprising a plating film and a chemical conversion film formed on the plating film,
The chemical conversion film includes at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluorine resin, P compound, and Si compound. , at least one metal compound selected from Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds and Ca compounds,
The plating film is formed in a plating bath containing 45 to 65% by mass of Al, 1.0 to 4.0% by mass of Si, and 1.0 to 10.0% by mass of Mg, with the balance being Zn and unavoidable impurities. , A surface treatment comprising a hot-dip plating step of immersing a base steel sheet, and controlling the Ni content in the inevitable impurities of the plating bath to 0.010% by mass or less with respect to the total mass of the plating bath. A method of manufacturing a steel plate. 12. The method for producing a surface-treated steel sheet according to claim 11, wherein the plating bath further contains Sr: 0.01-1.0% by mass.

Images