WO2020255437A1 - Chemically-treated steel sheet and method for manufacturing same - Google Patents

Abstract

Provided are: a chemically-treated steel sheet which has superior corrosion resistance even in a flat section and in which degradation of corrosion resistance is unlikely to occur at a portion that has been machined; and a method for manufacturing the same. The chemically-treated steel sheet (1) comprises a Zn-plated steel sheet (10) and a chemically-treated film (20). The chemically-treated film (20) has, as a portion of a matrix formed via a metal oxide polymer (25) that is a polymer of a Group IV metal oxoacid, a heterogeneous structural part (30) dispersed and present in the matrix. The heterogeneous structural part (30) is a salt in which a Group IV metal (M) and a specific oxoacid have been bonded.

Description

Chemical conversion steel sheet and its manufacturing method

The present invention relates to a chemical conversion-treated steel sheet in which a chemical conversion-treated film is formed on the surface of a Zn-based plated steel sheet, and a method for producing the same.

Zn-based galvanized steel sheets are used in a wide range of applications such as automobiles, building materials, and home appliances. Normally, the surface of a plated steel sheet is subjected to a chrome-free chemical conversion treatment in order to impart corrosion resistance without oiling. Chromium-free chemical conversion treatment is roughly divided into organic treatment and inorganic treatment.

Conventionally, as a chemical conversion treatment liquid used for inorganic treatment, titanium-based, zirconium-based, molybdenum-based, and composite systems thereof have been developed depending on the difference in rust preventive. Further, in order to enhance corrosion resistance, chemical conversion treatment solutions of a system to which a silane coupling agent, silane, etc. are further added have also been developed (see, for example, Patent Documents 1 to 4).

Japanese Patent Publication "Japanese Patent Laid-Open No. 2003-055777" Japanese Patent Publication "Patent No. 5638191" Japanese Patent Publication "Patent No. 5317516" Japanese Patent Publication "Patent No. 5431721"

However, since the chemical conversion-treated film mainly composed of inorganic components is relatively hard, cracks are likely to occur in the processed portion when the chemical conversion-treated steel sheet having the chemical conversion-treated film is processed (bending, etc.). Therefore, when the processed steel sheet for chemical conversion is used outdoors, for example, white rust may occur in the processed portion at an early stage.

In particular, in a chemical conversion-treated steel sheet formed by forming a chemical conversion-treated film mainly composed of an inorganic component on the surface of a Zn-based plated steel sheet containing Mg in the plating layer, the plating layer is also hard, so that the chemical conversion-treated steel sheet can be used. When processed, cracks are likely to occur not only in the chemical conversion coating but also in the plating layer. As a result, the occurrence of white rust in the processed portion may become more remarkable.

Patent Document 1 describes a chromate-free hot-dip Zn—Al alloy-plated steel sheet having a film containing a zirconium compound and a vanadyl compound. Further, Patent Document 2 describes a chemical conversion-treated metal plate in which a film containing a compound of a Group 4 element (Group 4 metal) is formed on the metal plate. Further, Patent Documents 1 and 2 show that the samples obtained by using these techniques are excellent in the corrosion resistance of the processed portion subjected to the Eriksen processing. However, since the film of the sample is hard, the corrosion resistance of the processed portion may deteriorate as described above when severe processing (for example, 180 ° bending processing) is performed.

Further, Patent Documents 3 and 4 describe a chemical conversion-treated steel sheet having a chemical conversion-treated film mainly composed of an organic resin or an organic substance. However, such a chemical conversion-treated film cannot be applied to applications for spot welding because the film has poor conductivity. Further, as in the cited documents 1 and 2, the corrosion resistance of the processed portion may deteriorate when severe processing is performed in these techniques as well.

One aspect of the present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a chemical conversion-treated steel sheet which is less likely to deteriorate in corrosion resistance in a processed portion and has excellent corrosion resistance even in a flat portion. The purpose is to provide the manufacturing method.

As a result of diligent studies, the present inventors have stated that the generation of cracks during processing can be suppressed by forming a chemical conversion treatment film so that structures that can act as stress relaxation points are dispersed in the matrix. With new knowledge, the invention of the present application was conceived.

That is, the chemical conversion-treated steel sheet according to one aspect of the present invention includes a Zn-based plated steel sheet having a Zn-based plating layer on the surface of the base steel sheet and a chemical conversion-treated film formed on the surface of the Zn-based plating layer. Then, in the chemical conversion coating, as a part of the matrix formed by the metal oxide polymer which is a polymer of at least one group 4 metal oxo acid, (i) the group 4 metal contained in the group 4 metal oxo acid. (Ii) A salt in which a specific oxo acid is bonded is dispersed and present in the matrix.

Further, in the method for producing a chemical conversion-treated steel sheet according to one aspect of the present invention, with respect to a Zn-based plated steel sheet having a Zn-based plated layer on the surface of the base steel sheet, (i) at least one kind of Group 4 metal oxoate And (ii) a chemical conversion treatment liquid coating step of applying a chemical conversion treatment liquid containing both a salt containing a specific oxo acid, and the chemical conversion treatment with a standing time of 35 seconds or less immediately after the chemical conversion treatment liquid coating step. The heat-drying of the liquid is started, the temperature rise time until the temperature of the Zn-based plated steel sheet reaches 80 ° C. is set to 1 second or more and 10 seconds or less, and the maximum reaching temperature is set to 170 ° C. or lower to dry the chemical conversion treatment liquid. It includes a heat-drying step of forming a chemical conversion treatment film on the surface of the Zn-based plated steel sheet.

According to one aspect of the present invention, it is possible to provide a chemical conversion-treated steel sheet having excellent corrosion resistance even in a flat portion and a method for producing the same, in which deterioration of corrosion resistance does not easily occur in the processed portion.

It is sectional drawing which shows typically the chemical conversion treatment steel sheet in one Embodiment of this invention. It is a schematic diagram for demonstrating the structure of the chemical conversion treatment film which the chemical conversion treatment steel sheet has in one Embodiment of this invention. It is a schematic diagram for demonstrating the specific example of the dissimilar structure part contained in the chemical conversion treatment film which the chemical conversion treatment steel sheet has in one Embodiment of this invention. It is a table which shows the result of having measured the XPS spectrum about the chemical conversion-treated film of the chemical conversion-treated steel sheet in one Embodiment of this invention, and the result of having calculated the atomic ratio based on the measurement result. It is a flowchart which shows typically an example of the manufacturing method of the chemical conversion-treated steel sheet in one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described. The following description is intended to better understand the gist of the invention, and does not limit the present invention unless otherwise specified. Further, in the present specification, "AB" indicates that it is A or more and B or less.

<Summary explanation of findings of the invention>
First, the outline of the findings found by the present inventors is as follows.

The group 4 metal oxoate is easily polymerized as an inorganic polymer, and by using a chemical conversion treatment solution containing the group 4 metal oxoate, a chemical conversion treatment film having a dense three-dimensional structure can be formed by the compound of the group 4 metal. .. Therefore, in general, Group 4 metal oxoacid salts are often used as raw materials for chemical conversion treatment.

However, in general, a chemical conversion-treated film formed from a Group 4 metal oxoate is vitreous and extremely hard. Therefore, inevitably, when a chemical conversion-treated steel sheet having the chemical conversion-treated film is bent, for example. Is prone to cracks in the bent portion.

The present inventors have diligently studied to realize a chemical conversion-treated steel sheet in which the occurrence of cracks in the case of bending is effectively suppressed, and as a result, the following findings have been obtained and the present invention has been conceived. ..

First, when a chemical conversion-treated steel sheet is produced using a chemical conversion-treated liquid containing a Group 4 metal oxoacid salt, it is considered that the following reactions generally occur.

That is, as the chemical conversion treatment liquid dries on the original plate (for example, Zn-based plated steel plate) coated with the chemical conversion treatment liquid, the group 4 metal oxoacids are polymerized (typically dehydrated and condensed) to be multimerized. .. As a result, a vitreous polymer (amorphous polymer) having a bond between the Group 4 metal and oxygen is formed, and this polymer forms a matrix in the chemical conversion treatment film.

For example, in general, when a chemical conversion treatment liquid containing a group 4 metal oxo acid salt and a phosphate is used to prepare a chemical conversion treatment film, it is known that these components cooperate to form a dense chemical conversion treatment film. ing. In this case, in the above polymer, the oxo acid of the Group 4 metal and the phosphoric acid are complexly polymerized, or the polymer mainly composed of the Group 4 metal oxo acid and the polymer mainly composed of phosphoric acid are present. It is considered that they exist in a complex manner. In a chemical conversion-treated film in which such an internal structure is relatively homogeneously formed, cracks are likely to occur when bending is performed.

The present inventors performed bending processing by dispersing and present a partial structure in the chemical conversion treatment film that functions to interrupt the hard continuous film (that is, cut the repeating structure of the polymer). It was found that the occurrence of cracks in the case can be suppressed. It is considered that this is an action caused by the partial structure acting to relieve the stress generated in the chemical conversion coating. In the process of forming a chemical conversion coating, a continuous coating is usually likely to be formed as described above. On the other hand, as a result of detailed examination of the film forming conditions of the chemical conversion treatment, the present inventors have formed the above-mentioned partial structure (hereinafter, may be referred to as stress relaxation point) in the chemical conversion treatment film. It is possible to disperse and make it exist favorably.

More specifically, the polymerization of the Group 4 metal oxoate in the reaction field generated during the drying of the chemical conversion treatment solution containing the Group 4 metal oxoacid and a salt containing a specific oxo acid (for example, a phosphate). The film formation conditions are set so that the reaction proceeds at an appropriate rate (state). As a result, a chemical conversion-treated film can be produced so that the salt (X) in which a Group 4 metal and a specific oxo acid are bonded, which acts as a stress relaxation point as described above, is dispersed and present in the matrix. it can.

For example, if the drying rate of the chemical conversion treatment liquid is slowed down, a dense matrix is easily formed by the polymerization of the group 4 metal oxo acid salt, and it becomes difficult for the salt (X) to be contained in the matrix. In addition, shrinkage stress is likely to be accumulated in the matrix due to the progress of the (slow) polymerization reaction at a relatively low temperature, and as a result, the chemical conversion coating is hardened.

On the other hand, if the drying rate of the chemical conversion treatment liquid is increased, the salt (X) is easily incorporated into the matrix. However, the faster the drying rate of the chemical conversion treatment liquid is, the easier it is for the salt (X) having a small solubility product to precipitate (precipitate) in the chemical conversion treatment liquid. As a result, a polymer of a specific oxo acid is more likely to be formed in the chemical conversion coating than the salt (X) is incorporated into the matrix, and in this case, the corrosion resistance of the flat portion before processing may be lowered. If the drying rate of the chemical conversion treatment liquid is too fast, the stress relaxation points dispersed in the matrix are reduced, and in this case, cracks are likely to occur in the bent portion that has been subjected to the bending process.

The chemical conversion-treated steel sheet and the manufacturing method thereof according to one aspect of the present invention will be described in detail below.

<Chemical conversion steel sheet>
FIG. 1 is a cross-sectional view schematically showing a chemical conversion-treated steel sheet according to one aspect of the present invention. As shown in FIG. 1, the chemical conversion-treated steel sheet 1 in the present embodiment has a Zn-based plated steel sheet 10 having a Zn-based plated layer 12 on the surface of the base steel sheet 11 and the surface of the Zn-based plated layer 12 (that is, Zn-based plating). It has a chemical conversion treatment film 20 formed on the surface of the steel plate 10).

(Zn-based galvanized steel sheet)
In one aspect of the present invention, a Zn-based galvanized steel sheet 10 having excellent corrosion resistance is used as the original plate (chemical conversion treatment original plate) to be subjected to chemical conversion treatment. The “Zn-based plated steel sheet” in the present embodiment means a plated steel sheet having a Zn-based plated layer 12 on the surface of the base steel sheet 11.

The Zn-based plating layer 12 preferably contains 40% by mass or more of Zn in order to improve the adhesion between the Zn-based plating layer 12 and the chemical conversion treatment film 20. This is because the Zn-based plating layer 12 contains 40% by mass or more of Zn, so that the proportion of the Zn-containing phase on the surface of the Zn-based plating layer 12 on which the chemical conversion coating 20 is formed increases, and the Zn-based plating This is because sufficient adhesion can be obtained between the layer 12 and the chemical conversion coating film 20.

Further, the Zn-based plating layer 12 may contain at least one selected from the group consisting of Al, Mg, Si, Ti and B. The Zn-based plating layer 12 of the Zn-based plated steel sheet 10 in the present embodiment may have an Al content of 0.1% by mass or more and 55.0% by mass or less, and a Mg content of 0.2% by mass or more and 10. It may be 0% by mass or less. Further, the Zn-based plating layer 12 may contain Si in the range of 0.005% by mass or more and 2.0% by mass in order to improve the adhesion between the base steel plate 11 and the Zn-based plating layer 12. .. Further, the Zn-based plated layer 12 contains 0.001% by mass or more and 0.1% by mass of Ti in order to suppress the formation and growth of the Zn ₁₁ Mg _2- phase, which adversely affects the appearance and corrosion resistance of the Zn-based plated steel sheet 10. It is preferable that B is contained in the following range and in the range of 0.0005% by mass or more and 0.045% by mass or less.

The Zn-based plated steel sheet 10 may be manufactured under general manufacturing conditions such as a hot-dip galvanizing method and an electroplating method. The type of the base steel sheet 11 of the Zn-based plated steel sheet 10 is not particularly limited, and for example, ordinary steel, low alloy steel, stainless steel, and the like can be used.

(Chemical conversion coating)
The chemical conversion treatment film 20 is a film for improving the corrosion resistance of the Zn-based plated steel sheet 10. As used herein, the term "corrosion resistance" is used to include both processed portion corrosion resistance and flat portion corrosion resistance. The “processed portion corrosion resistance” is the corrosion resistance of the portion (processed portion) of the chemical conversion-treated steel sheet 1 that has been subjected to processing (for example, bending) to deform the chemical conversion-treated steel sheet 1, and is particularly 180 ° in the present specification. Corrosion resistance of the processed part when severe bending such as bending is applied. “Flat portion corrosion resistance” is the corrosion resistance of a portion of the chemical conversion-treated steel sheet 1 other than the processed portion.

The chemical conversion treatment film 20 of the present embodiment is a reaction layer (first chemical conversion treatment layer) located on the surface of the Zn-based plated steel plate 10 formed by the reaction of (i) the chemical conversion treatment liquid and the surface of the Zn-based plated steel plate 10. ) 21 and (ii) a chemical conversion treatment layer (second chemical conversion treatment layer) 22 mainly composed of a polymer which is a polymer of a group 4 metal oxo acid formed on the upper layer of the reaction layer 21. Here, the susceptibility to cracks in the case of bending processing is mainly related to the properties of the chemical conversion treatment layer 22. Further, the chemical conversion-treated film 20 in the present embodiment is a very thin film (for example, a thickness of 1 μm or less), and the reaction layer 21 is even thinner and has a small volume ratio to the chemical conversion-treated film 20. Therefore, in the following, for the sake of clarity of explanation, the chemical conversion treatment film 20 will be described without distinguishing between the reaction layer 21 and the chemical conversion treatment layer 22, but the following description is mainly related to the chemical conversion treatment layer 22. To do.

The chemical conversion treatment film 20 of the present embodiment will be described below together with the components of the chemical conversion treatment liquid used to form the chemical conversion treatment film 20.

In the chemical conversion treatment film 20 in the present embodiment, a chemical conversion treatment liquid containing at least both (i) at least one group 4 metal oxo acid salt and (ii) a salt containing a specific oxo acid is applied to the Zn-based plated steel plate 10. By coating and drying the chemical conversion treatment liquid, it is formed on the surface of the Zn-based plated steel plate 10.

There are various types of Group 4 metal oxoacids, but one type of compound selected (specified) from the compound group of Group 4 metal oxoacids is referred to in the present specification as "Specific Group 4 metal" for convenience of explanation. Sometimes referred to as "oxoacid".

In the method for producing the chemical conversion-treated steel sheet 1 of the present embodiment, the drying conditions are controlled so that the drying (reaction) of the chemical conversion-treated liquid proceeds appropriately, as will be described in detail later. The chemical conversion treatment film 20 thus obtained has the following structure.

FIG. 2 is a schematic diagram for explaining the structure of the chemical conversion treatment film 20 in the present embodiment. The figure shown by reference numeral 2001 in FIG. 2 schematically shows the internal structure in the region 20P in which the inside of the chemical conversion treatment film 20 is locally enlarged.

The chemical conversion coating 20 has a matrix formed of the metal oxide polymer 25. The metal oxide polymer 25 has a three-dimensional structure having a bond between a specific group 4 metal (M in the figure) and oxygen (O in the figure) formed by polymerization of a specific group 4 metal oxoate. It is a polymer in a vitreous state. Such a metal oxide polymer 25 is described as having a structure (polyacid-like structure) in which polyoxometallate (also called polyacid) known as a polymer (cluster) of metal oxometalate is further multimerized. can do. Further, the metal oxide polymer 25 can also be expressed as an amorphous metal oxide. In the present specification, the basic structure (basic structure) is a structure in which oxygen (O in the figure) is bonded to a specific group 4 metal (M in the figure) (typically four oxygen atoms are bonded to one metal element). It is called 26. The main structure of the metal oxide polymer 25 is a structure in which a large number of basic structural portions 26 are bonded (repeatedly repeated many times) to form a three-dimensional network.

Here, in the conventional chemical conversion-treated steel sheet in which the metal oxide polymer 25 is homogeneously formed in the chemical conversion-treated film 20, cracks are likely to occur in the chemical conversion-treated film 20 when it is bent or the like. On the other hand, as shown by the reference numeral 2002 in FIG. 2, the chemical conversion treatment film 20 in the present embodiment is designated as the specific group 4 metal M as a part of the matrix formed by the metal oxide polymer 25. The salt bound to the oxo acid is dispersed and present in the matrix. The salt is a portion having a structure different from the main structure (structure in which the basic structure portion 26 is a monomer unit) in the metal oxide polymer 25, and in the present specification, the salt is referred to as a heterologous structure portion (first heterogeneous structure). Part) 30. The heterogeneous structure portion 30 is formed by combining a specific group 4 metal M and an anion species (specific oxo acid) 31 in which a salt containing a specific oxo acid is ionized. The dissimilar structure portion 30 is one end of the metal oxide polymer 25, and the anion species 31 is bonded to one specific group 4 metal M.

In other words, the metal oxide polymer 25 contains a heterogeneous structure portion 30 composed of a salt in which a specific oxo acid and a specific Group 4 metal M are bonded at the end of the polymer structure, and also contains the specific Group 4 metal M and oxygen O. Heterogeneous structural parts 30 are dispersed and exist in a three-dimensional structure having a bond with and as a main skeleton.

In practice, it is not easy to specify the specific structure in the chemical conversion coating film 20 in detail by using some measuring method, but the chemical conversion steel sheet of the present embodiment has superior corrosion resistance in the processed portion as compared with the conventional one. ing. From this and the results of the structural analysis described later, it is considered that the heterogeneous structural portions 30 are dispersed and exist in the matrix so as to form discontinuous portions in the continuous film (metal oxide polymer 25).

It is considered that this causes the dissimilar structure portion 30 to act so as to relax the contraction stress generated by the polymerization reaction during matrix formation. Further, the dissimilar structure portion 30 acts as a stress relaxation point for relaxing the stress generated when the chemical conversion-treated steel sheet 1 is processed, and also acts to prevent the growth (propagation) of cracks generated in the chemical conversion-treated film 20. It is thought to play.

(Basic structure)
The basic structural portion 26 of the metal oxide polymer 25 is formed from the specific group 4 metal oxoacid salt contained in the chemical conversion treatment liquid. The specific group 4 metal oxoate is a component for forming a dense chemical conversion-treated film, and improves the corrosion resistance of the chemical conversion-treated steel sheet 1. The Group 4 metal is not particularly limited, and for example, titanium (Ti), zirconium (Zr), or hafnium (Hf) can be used.

In the specification of the present application, "oxo acid" and "oxo acid salt" are used in the meaning defined in IUPAC NIC 1990. In addition, the group 4 metal oxoacid salt is a group 4 metal oxoacid ion having a structure in which a plurality of (typically 4, 5, or 6) oxygen atoms are coordinated around the nucleus which is a group 4 metal element. And a salt consisting of some cation species.

In the present specification, the specific group 4 metal M is a metal of the same type as the group 4 metal contained in the "specific group 4 metal oxoacid" in the chemical conversion treatment liquid used for producing the chemical conversion-treated steel plate 1 in the present embodiment. Is. For example, when the specific Group 4 metal oxoacid is ammonium carbonate, the specific Group 4 metal is zirconium. The main structure of the metal oxide polymer 25 is, for example, a multi-nuclide structure having a single specific group 4 metal as a nuclide (however, it is allowed to contain a different group 4 metal as an unavoidable impurity). The metal oxide polymer 25 may have a multi-nuclide structure having a plurality of types of metals as nuclides, which further contains a metal different from the specific group 4 metal as a nuclide. In this case, a plurality of metals contained in the main structure. It is preferable that 80% or more (atomic ratio) of the metal species is a specific group 4 metal.

The group 4 metal oxo acid salt is a group 4 metal oxo acid, for example, a hydride, an ammonium salt, an alkali metal salt, an alkaline earth metal salt, or the like. The group 4 metal oxoacid salt is preferably an ammonium salt of the group 4 metal oxoacid from the viewpoint of corrosion resistance, and ammonium zirconium carbonate is particularly preferable. The specific group 4 metal oxo acid salt is preferably Zr oxo acid salt. That is, the specific group 4 metal is preferably Zr.

When a chemical conversion treatment solution containing Zroxoate is used, the basic structural part 26 has a Zr—O bond. In the basic structure portion 26, for example, two O's may be arranged in parallel between the two Zr's to form a Zr—O bond.

(Heterogeneous structure part)
The heterogeneous structure portion 30 in the metal oxide polymer 25 is formed as a salt in which an anion species 31 derived from a salt containing a specific oxo acid contained in a chemical conversion treatment liquid and a specific group 4 metal M are bonded. The dissimilar structure portion 30 forms one terminal group in the three-dimensional structure of the metal oxide polymer 25, and the anion species 31 is bonded only to the specific group 4 metal M.

The anion species 31 in the present embodiment is a specific oxo acid, and in the present specification, the “specific oxo acid” is a “specific oxo acid” in the chemical conversion treatment liquid used for producing the chemical conversion-treated steel sheet 1 of the present embodiment. It is a substance similar to the counter anion (also called counter anion) in "salt containing oxo acid". For example, if the salt containing the particular oxoacid is diammonium hydrogen phosphate, the particular oxoacid is phosphoric acid. In this case, more specifically, the dissimilar structure portion 30 may be, for example, a dihydrocarbonate phosphate of the specified group 4 metal M, or a monohydrogen phosphate salt.

The salt containing a specific oxoacid contained in the chemical conversion treatment liquid is at least a salt of a type different from the specific group 4 metal oxo acid salt contained in the chemical conversion treatment liquid. In other words, the specific oxo acid as the anion species 31 forming the heterologous structure portion 30 is at least the oxo contained in the specific group 4 metal oxo acid constituting the specific group 4 metal oxo acidate contained in the chemical conversion treatment liquid. It is a different kind of acid.

The salt containing a specific oxo acid is, for example, a phosphate, a group 5 metal oxo acid salt, or a group 6 metal oxo acid salt (excluding Cr oxo acid salt). Since all of these salts are components that easily form an inorganic polymer, it is considered that they are likely to polymerize with a specific group 4 metal oxoate to form a matrix.

The type of phosphate is not particularly limited, and inorganic phosphate or organic phosphate can be used. Specific examples of the inorganic phosphate include alkali metal phosphates (eg, sodium diphosphate, potassium diphosphate, sodium tripolyphosphate), alkaline earth metal phosphates (calcium diphosphate, etc.), ammonium phosphate (eg, calcium diphosphate). For example, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, triammonium phosphate, etc.) and the like. Specific examples of the organic phosphate include 1-hydroxyethane-1,1-diphosphonic acid, nitrilotris (methylene-phosphonic acid) and the like.

The group 5 metal oxo acid salt is, for example, a chlorate, hydride, sulfate, nitrate, phosphate, ammonium salt, alkali metal salt, alkaline earth metal salt, etc. of the group 5 metal oxo acid. In particular, from the viewpoint of corrosion resistance, an ammonium salt of a group 5 metal oxoacid is preferable. The Group 5 metal is not particularly limited, and V, Nb, or Ta can be used. When the Group 5 metal is V, the Group 5 metal oxoacid salt is preferably vanadate from the viewpoint of corrosion resistance.

The group 6 metal oxo acid salt is, for example, a chlorate, hydride, sulfate, nitrate, phosphate, ammonium salt, alkali metal salt, alkaline earth metal salt, etc. of the group 6 metal oxo acid. In particular, from the viewpoint of corrosion resistance, an ammonium salt of a Group 6 metal oxoacid is preferable. As the Group 6 metal, Mo or W can be used. Since the chemical conversion treatment that is the subject of the present invention is a chromium-free treatment, Cr is excluded from the Group 6 metal.

FIG. 3 is a diagram for explaining a specific example of the heterogeneous structure portion 30. As shown by reference numeral 3001 in FIG. 3, in one example, the heterogeneous structure portion 30 is a salt in which a specific group 4 metal M and a phosphate ion 31A are bonded. In another example, as shown by the reference numeral 3002 in FIG. 3, the heterogeneous structure portion 30 is a salt in which the specific group 4 metal M and the sulfate ion 31B are bonded. In yet another example, as shown by reference numeral 3003 in FIG. 3, the heterogeneous structure portion 30 is a salt in which the specific group 4 metal M and the nitrate ion 31C are bonded.

Further, as shown by the reference numeral 3004 in FIG. 3, in the dissimilar structure portion 30, the specific group 4 metal M and the phosphoric acid compound ion 31D of a metal (for example, Zn) other than the specific group 4 metal M are bonded. It may be salted salt. That is, the chemical conversion-treated film 20 may further contain a phosphate of a metal other than the specific group 4 metal M (for example, a phosphate of Zn) in the matrix. In this case, usually, the chemical conversion treatment film 20 is derived from the phosphate ion contained in the chemical conversion treatment liquid, and also contains a phosphate of the specific group 4 metal M as a heterogeneous structure portion 30.

Although not shown, the anion species 31 may be at least one of a group 5 metal oxo acid and a group 6 metal oxo acid (excluding Cr oxo acid). In this case, the specific group 4 metal M and the group 5 metal oxo acid (for example, molybdic acid) or the group 6 metal oxo acid (for example, vanadic acid) are bonded to each other to form the heterogeneous structural portion 30.

When the abundance of the dissimilar structure portion 30 in the chemical conversion treatment film 20 is small, the chemical conversion treatment film 20 becomes hard and the corrosion resistance of the processed portion is lowered. On the other hand, if the abundance of the dissimilar structure portion 30 in the chemical conversion treatment film 20 becomes too large, the barrier property of the corrosion factor is lowered, and the corrosion resistance of the flat portion of the chemical conversion treatment steel sheet 1 is lowered.

Therefore, among the Group 4 metals contained in the chemical conversion coating film 20, the atomic ratio of the Group 4 metal forming the basic structure portion 26 is combined with X and the anion species 31 to form the heterogeneous structure portion 30. Assuming that the atomic ratio of the Group 4 metal is Y and Y / (X + Y) = α, the appropriate value of α is 0.1 or more and 0.6 or less. If the value of α is less than 0.1, the chemical conversion coating film 20 tends to be too hard and the corrosion resistance of the processed portion tends to decrease. On the other hand, when the value of α exceeds 0.6, it becomes difficult for the chemical conversion coating film 20 to form a continuous film, and the corrosion resistance of the flat portion tends to decrease.

A general method may be used for measuring the atomic ratio as described above. For example, the above X and Y can be calculated using the result of measuring the XPS spectrum of the chemical conversion-treated film 20 using a photoelectron spectroscopic analyzer. The XPS spectrum shows information about the state of each element near the surface (typically several nm in depth) on the surface of an object irradiated with X-rays. Before measuring the XPS spectrum, the sample to be measured is pretreated to obtain a clean sample surface.

As an example, the specific group 4 metal is Zr, and the atomic ratio is calculated based on the results of measuring the XPS spectrum and the measurement results of the chemical conversion-treated film 20 containing Zr phosphate and Zr sulfate as the heterogeneous structural part 30. The results are shown in FIG.

As shown in FIG. 4, for example, for the 3d3 / 2 spectrum of Zr in the measured XPS spectrum, peak separation is performed based on the peak position (binding energy) corresponding to each bond. Then, the atomic ratio X and the atomic ratio Y are calculated based on the area (peak area) of each separated peak. In this example, the value of α is 0.65.

(Second heterogeneous structure part)
The chemical conversion-treated film 20 in the present embodiment has the above-mentioned heterogeneous structural portion 30, and the specific group 4 metal oxoate and the group 5 metal oxoate or the group 6 metal oxoate are polymerized. Therefore, a group 5 metal or a group 6 metal may be contained as a part of the metal oxide polymer 25. In other words, the Group 5 metal or the Group 6 metal may be present in the metal oxide polymer 25 by substituting a part of the specific group 4 metal M contained in the metal oxide polymer 25. In this case, the metal oxide polymer 25 contains a monomer unit of a group 5 metal or a group 6 metal having a size different from that of the basic structural portion 26, and the monomer unit is referred to as a second heterogeneous structural portion in the present specification. Refer to.

The chemical conversion coating 20 contains, for example, a phosphate of a specific Group 4 metal M as a heterologous structure portion 30, and in the matrix, more specifically in the main structure, a Group 5 metal oxo acid and a Group 6 metal oxo acid ( However, at least one of (excluding Cr oxo acid) may be further contained. The second heterogeneous structural part, the Group 5 metal oxoacid or the Group 6 metal oxoacid in the main structure, can function as stress relaxation points. Therefore, the chemical conversion-treated steel sheet 1 containing the second dissimilar structure portion is excellent in corrosion resistance of the processed portion.

(Group 1 metal)
Further, the chemical conversion treatment liquid used for producing the chemical conversion-treated steel sheet 1 may contain a Group 1 metal, and in this case, the chemical conversion-treated film 20 contains a Group 1 metal. The Group 1 metal may be added to the chemical conversion treatment liquid as a phosphoric acid compound of the Group 1 metal or another compound (for example, a hydroxide).

By containing a Group 1 metal in the chemical conversion treatment film 20, the number of hydroxyl groups in the chemical conversion treatment film 20 increases. As a result, a bond is likely to occur between the chemical conversion coating 20 and the Zn-based plated steel sheet 10. As a result, the adhesion between the chemical conversion coating 20 and the Zn-based plated steel sheet 10 can be improved. Further, when the number of hydroxyl groups in the chemical conversion treatment film 20 increases, it is suppressed that water is removed from the chemical conversion treatment film 20 when the chemical conversion treatment liquid is dried. As a result, it is possible to prevent cracks from being generated in the chemical conversion coating film when the chemical conversion coating film 20 is formed. As a result, the corrosion resistance of the manufactured chemical conversion-treated steel sheet 1 can be improved.

Group 1 metals also have the function of improving the long-term storage stability (treatment liquid stability) of the chemical conversion treatment liquid. This is because the inclusion of the Group 1 metal in the chemical conversion treatment liquid increases the amount of hydroxyl groups in the chemical conversion treatment liquid, so that the binding of the Group 4 metal and phosphorus can be suppressed. That is, by including the Group 1 metal in the chemical conversion treatment liquid, it is possible to suppress the chemical conversion treatment liquid from becoming a gel, that is, to improve the long-term storage property of the chemical conversion treatment liquid.

(Other substances)
The amount of the chemical conversion-treated steel sheet 1 at the time of processing is such that the adhesion between the chemical conversion-treated film 20 and the Zn-based plated steel sheet 10 is not deteriorated and the effect of the chemical conversion-treated steel sheet 1 in the present embodiment is not hindered. A wax or an organic resin may be contained in the chemical conversion coating film 20 in order to impart lubricity.

(About molar ratio)
The molar ratio of the specific group 4 metal oxoacid salt and the like contained in the chemical conversion treatment liquid used for producing the chemical conversion treatment steel sheet 1 of the present embodiment will be described as follows.

For example, when the chemical conversion treatment liquid contains a phosphate as a salt containing a specific oxo acid and also contains a group 1 metal, the chemical conversion treatment liquid has a molar ratio of phosphorus to the group 4 metal of 0.5 to 4. It is preferable that the molar ratio of the Group 1 metal to the Group 4 metal is 0.02 to 0.8, and the molar ratio of the Group 1 metal to phosphorus is 0.01 or more.

When the molar ratio of phosphorus to Group 4 metal in the chemical conversion treatment liquid is less than 0.5, and when the molar ratio of phosphorus to Group 4 metal is larger than 4, the chemical conversion treatment film is corroded by chloride ions and the like. Since the film is easy to permeate the factors, the corrosion resistance of the chemical conversion-treated steel sheet is lowered.

When the molar ratio of Group 1 metal to Group 4 metal or phosphorus in the chemical conversion treatment liquid is smaller than the above value, the number of hydroxyl groups derived from Group 1 metal is not sufficient in the formed chemical conversion treatment film. Therefore, the number of bonds between the chemical conversion-treated film containing Group 4 metal and phosphorus as main components and the Zn-based plated steel sheet is reduced. As a result, the adhesion between the chemical conversion coating and the Zn-based plated steel sheet becomes insufficient.

When the molar ratio of the Group 1 metal to the Group 4 metal in the chemical conversion treatment liquid is larger than 0.8, the chemical conversion treatment film is easily decomposed by the corrosion factor, so that the corrosion resistance of the chemical conversion treatment steel sheet is lowered.

From the viewpoint of long-term storage of the chemical conversion treatment liquid, the molar ratio of the Group 1 metal to the Group 4 metal is 0.5 or more, and the molar ratio of the Group 1 metal to phosphorus is 0.18 or more. Is preferable.

The chemical conversion treatment liquid of the present embodiment has, for example, a group 4 metal concentration of 5 to 35 g / L, a phosphorus concentration of 0.8 to 60 g / L, and a group 1 metal concentration of 0.2 g / L or more. Further, the chemical conversion treatment liquid of the present embodiment may contain an amine, a silane coupling agent, or the like in addition to the above-mentioned substances. The amine dissolves a salt containing vanadium in a chemical conversion treatment solution while maintaining the valence of V at a pentavalent value, and forms a pentavalent or hexavalent Mo composite oxoacidate from the molybdate. The amine is preferably a low boiling point amine having a molecular weight of 80 or less. As the amine, for example, ethanolamine, 1-amino-2-propanol, ethylenediamine and the like can be used.

If the concentration of the Group 4 metal in the chemical conversion treatment liquid is higher than 35 g / L, the Group 4 metals will bond with each other while the chemical conversion treatment liquid is being stored, and the chemical conversion treatment liquid will gel. Therefore, the chemical conversion treatment film 20 cannot be formed satisfactorily. That is, the chemical conversion treatment liquid of the present embodiment has high long-term storage stability by setting the concentration of the Group 4 metal to 35 g / L or less.

The pH of the chemical conversion treatment liquid is preferably in the range of 7 or more and 9 or less, and in this case, the polymerization of the group 4 metal oxo acid salt proceeds preferably.

Further, it has been confirmed that the composition of the chemical conversion treatment liquid in the present embodiment and the composition of the chemical conversion treatment film 20 formed by applying the chemical conversion treatment liquid and drying it are substantially the same as each other.

(About hardness)
In the chemical conversion-treated steel sheet 1 of the present embodiment, the hardness of the chemical conversion-treated film 20 is 70 HV 0.01 or more and 200 HV 0.01 or less (Vickers hardness). This Vickers hardness is a value measured on the surface of the chemical conversion-treated steel sheet according to the Vickers hardness test method specified in JIZ Z 2244.

(Production method)
Hereinafter, a method for producing the chemical conversion-treated steel sheet 1 according to one aspect of the present invention (hereinafter, may be simply referred to as “the present production method”) will be described with reference to FIG. Along with the description of the present production method, the preparation of the chemical conversion treatment liquid will also be described.

As shown in FIG. 5, in the present manufacturing method, roughly, first, a Zn-based plated steel sheet 10 as a chemical conversion-treated original plate is prepared (S1: original plate preparation step). Next, a pretreatment for appropriately applying the chemical conversion treatment to the Zn-based plated steel sheet 10 is performed (S2: pretreatment step). In the pretreatment step S2, the pretreatment generally performed in the chemical conversion treatment may be performed, and roughly, a treatment for cleaning the surface of the Zn-based plated steel sheet 10 is performed.

Next, in the stage immediately before the chemical conversion treatment liquid is applied (S3: the step immediately before the treatment liquid is applied), the plate temperature of the Zn-based plated steel sheet 10 after the pretreatment is set to 60 ° C. or lower, preferably 50 ° C. or lower. It is preferable that the plate temperature of the Zn-based plated steel sheet 10 after the pretreatment is room temperature. This is because if the plate temperature immediately before applying the chemical conversion treatment liquid is too high, the drying of the chemical conversion treatment liquid (that is, the reaction in the chemical conversion treatment liquid) is promoted, so that the chemical conversion treatment film 20 having a desired structural structure is formed. This is because it is difficult to obtain.

Here, the chemical conversion treatment liquid for coating on the Zn-based plated steel sheet 10 is prepared in advance (S10: chemical conversion treatment liquid preparation step). In order to obtain the chemical conversion treatment film 20 in the present embodiment, the composition of the chemical conversion treatment liquid is important. The solvent of the chemical conversion treatment liquid is typically water.

The group 4 metal compound used as a raw material for preparing a chemical conversion treatment solution is required to be soluble in water, and for example, fluoride salts, carbonates, peroxoates and the like can be used. As the group 4 metal compound, a carbonate is preferable.

Examples of the salt containing a specific oxoacid used as another raw material for preparing the chemical conversion treatment liquid include a nitrate of a group 4 metal and a sulfate of a group 4 metal, and further, a group 4 metal oxo when dried. Examples thereof include phosphates that easily form compounds with acid salts.

Further, a method of using a group 5 metal oxo acid salt or a group 6 metal oxo acid salt as a raw material can be mentioned. The salt containing a specific oxo acid is not particularly limited as long as it is possible to suppress the generation of cracks in the film during processing, that is, to form the heterogeneous structural portion 30 in the matrix of the chemical conversion-treated film 20. However, in order to sufficiently secure the corrosion resistance of the processed portion and the flat portion, it is not preferable that the corrosive factor is present in the film. Therefore, as the raw material, phosphate, group 5 metal oxoacid, or 6 Group metal oxoacids are preferred.

The Group 4 metal used for producing the chemical conversion coating film 20 is preferably Zr. When Ti is used, the water-soluble compound is a fluoride salt, and the storage stability tends to decrease as described above. Further, since Hf is expensive, the cost of the chemical conversion coating film 20 is high.

In order to prepare the chemical conversion treatment liquid, a group 4 metal oxoacid salt and a substance other than the group 4 metal oxoacid salt may be mixed as a raw material for the group 4 metal, but in that case, the treatment liquid is stored. Stability can be poor. Further, a chemical conversion treatment solution containing a group 4 metal oxoacid salt and a group 4 metal fluoride salt may be used, but the plating layer is dissolved by the fluoride and the plating layer component is mixed in the treatment solution. This can lead to poor storage stability.

In order to adjust the above-mentioned value of α in the chemical conversion treatment film 20, it is important to control the reaction in the drying process of the treatment liquid. As a production condition, when the temperature of the chemical conversion treatment liquid applied to the Zn-based plated steel sheet 10 is relatively high, the drying time of the chemical conversion treatment liquid becomes short. Further, as described above, even when the plate temperature of the Zn-based plated steel sheet 10 is relatively high, the drying time of the chemical conversion treatment liquid is shortened.

Here, the film thickness of the chemical conversion coating film 20 is about 1 μm or less, and the reaction that occurs on the surface of the Zn-based plated steel sheet 10 is greatly affected by changes in the film forming conditions. As the drying of the chemical conversion treatment solution progresses, various reactions including the polymerization reaction of the group 4 metal oxoate compete with each other in the process of gelation and solidification of the chemical conversion treatment solution to form the chemical conversion treatment film 20. To proceed.

When the temperature of the chemical conversion treatment liquid or the plate temperature of the Zn-based plated steel sheet 10 is relatively high, the anion species 31 (for example, phosphoric acid) is polymerized and precipitated, or reacts with the Zn-based plated layer 12 to react with the reaction layer 21. It thickens to. As a result, the abundance of the dissimilar structure portion 30 becomes smaller (the atomic ratio Y of the group 4 metals forming the dissimilar structure portion 30 becomes smaller, and therefore the value of α becomes smaller).

Therefore, when the chemical conversion treatment liquid is applied to the surface of the Zn-based plated steel sheet after the pretreatment (S4: chemical conversion treatment liquid application step), the liquid temperature of the chemical conversion treatment liquid is 55 ° C. or lower, preferably 50 ° C. or lower. The liquid temperature of the chemical conversion treatment liquid is preferably room temperature, for example.

In the chemical conversion treatment liquid application step S4, methods such as a roll coating method, a spin coating method, and a spray method can be used. The amount of the chemical conversion-treated film adhered to the surface of the Zn-based plated steel sheet 10 is preferably in the range of 50 to 1000 mg / m ² . If the amount of adhesion is less than 50 mg / m ^2, the thickness of the chemical conversion coating film 20 becomes thin, so that sufficient corrosion resistance cannot be obtained. On the other hand, if the amount of adhesion is more than 1000 mg / m ² , the thickness of the chemical conversion coating film 20 becomes too thick, and the corrosion resistance becomes excessive. Considering the spot weldability, the amount of the chemical conversion coating 20 adhered to the surface of the Zn-based plated steel sheet 10 is more preferably in the range of 50 to 500 mg / m ² .

Next, the Zn-based plated steel sheet 10 coated with the chemical conversion treatment liquid is allowed to stand for a short time from immediately after coating to the start of drying (referred to as setting time in the present specification) (S5). : Short-term standing step). The longer the settling time, the more the reaction in the chemical conversion treatment liquid proceeds, and the higher the atomic ratio X of the Group 4 metal forming the basic structural portion 26 becomes.

However, if the settling time is too long, the basic structural portion 26 forms a dense film, and as a result, the chemical conversion treatment film 20 after heat drying may not contain the heterogeneous structural portion 30 in the metal oxide polymer 25. is there. Therefore, the setting time is preferably 35 seconds or less, and more preferably 2 seconds or more and 30 seconds or less. This is because the settling time is preferably 2 seconds or more in order to secure the reaction time between the chemical conversion treatment liquid and the Zn-based plated steel sheet 10.

It should be noted that the drying of the chemical conversion treatment liquid progresses to some extent even in the short-time standing step S5. The drying at this stage is affected by the plate temperature of the Zn-based plated steel sheet 10 and the liquid temperature of the chemical conversion treatment liquid.

Next, the Zn-based plated steel sheet 10 coated with the chemical conversion treatment liquid on the surface is heated to further dry the chemical conversion treatment liquid (S6: heat drying step). In the heat-drying step S6, the reaction in the chemical conversion treatment liquid is allowed to proceed at an appropriate rate so that the desired chemical conversion treatment film 20 can be obtained. By setting an appropriate drying rate, it is possible to obtain a chemical conversion-treated film 20 in which the different structural portions 30 that are a part of the metal oxide polymer 25 are dispersed in the matrix. However, if the drying rate is too fast, a reaction in which the reaction product of the Group 4 metal and the anion species 31 having a small solubility product in the chemical conversion treatment liquid is precipitated is more likely to occur than the reaction generated by the basic structure part 26. ..

Therefore, the temperature rise time until the temperature of the Zn-based galvanized steel sheet coated with the chemical conversion treatment liquid on the surface reaches 80 ° C. is set to 1 second or more and 10 seconds or less, preferably 2 seconds or more and 7 seconds or less.

Further, when the maximum temperature reached by the Zn-based plated steel sheet 10 is high, dehydration of the film progresses too much, the film becomes hard, and the corrosion resistance of the processed portion may deteriorate. Therefore, the maximum temperature reached is 170 ° C. or lower, preferably 160 ° C. or lower. In the heating / drying step S6, heating is performed in an air atmosphere using, for example, an electric furnace. Further, for example, when the chemical conversion treatment liquid contains a nitrogen compound, if the maximum temperature reached by the Zn-based plated steel sheet 10 is too low, the corrosion resistance of the flat portion is deteriorated due to the residual nitrogen remaining in the chemical conversion treatment film 20. Can be reduced. From this point of view, for example, the maximum temperature reached may be 70 ° C. or higher. If the chemical conversion-treated steel sheet in the present embodiment can be obtained, the maximum temperature reached may be less than 70 ° C.

Next, the chemical conversion-treated steel sheet 1 having the chemical conversion-treated film 20 formed on the surface of the Zn-based plated steel sheet 10 is cooled (S7: cooling step). As a result, the chemical conversion-treated steel sheet 1 of the present embodiment is obtained.

(Modification example)
The chemical conversion-treated steel sheet 1 in the present embodiment has a chemical conversion-treated film 20 formed on the surface of the Zn-based plated steel sheet 10, but is not limited thereto. For example, the Zn-based plating layer 12 may be formed on an upper layer of another type of plating layer (for example, an Al-based plating layer) applied to the surface of the base steel plate 11. That is, the chemical conversion-treated steel sheet in another aspect of the present invention may be manufactured by using a multi-layer plated steel sheet as the chemical conversion-treated original plate.

[Appendix]
The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the claims, and the present invention also relates to an embodiment obtained by appropriately combining the technical means disclosed in the above description. It is included in the technical scope of the invention.

Hereinafter, examples of the chemical conversion-treated steel sheet according to one aspect of the present invention will be described, but the present invention is not limited to these examples.

In this embodiment, using a steel strip of ultra-low carbon Ti-added steel having a plate thickness of 0.5 mm as a base material, Zn is contained in an amount of 40% by mass or more using a continuous hot-dip galvanizing production line under the conditions shown in Table 1. A Zn-based galvanized steel sheet is produced, and the original plate No. It was set to 1 to 14. Further, using the same steel strip as a base material, a pure galvanized steel strip was produced by an electrogalvanizing method, and the original plate No. It was set to 15. This No. The Zn-based plating layer of the Zn-based plated steel sheet of No. 15 is pure zinc except for unavoidable impurities.

In this example and comparative example, water-soluble zirconium ammonium carbonate was used as the specific group 4 metal oxo acid salt, and diammonium hydrogen phosphate was used as the salt containing the specific oxo acid. Ammonium zirconium carbonate and diammonium hydrogen phosphate were dissolved in water to prepare a chemical conversion treatment solution having a Zr concentration of 10 g / L and a phosphorus concentration of 1.7 g / L. The chemical conversion treatment liquid was applied to various original plates shown in Table 1 and dried to prepare a chemical conversion treatment steel sheet.

Table 2 is a table showing various manufacturing conditions used for manufacturing the chemical conversion-treated steel sheets of Examples and Comparative Examples of the present invention. The manufacturing conditions No. 2 shown in Table 2 below. No. 12 was heated under a drying condition in which it took 5 seconds for the plate temperature to reach 80 ° C., and the heating was stopped when the plate temperature reached 70 ° C. The time until the reaching plate temperature reaches 80 ° C. corresponds to the rate of temperature rise of the plate temperature during heating and drying.

Table 3 is a table showing the composition and physical properties of the chemical conversion coating film in the chemical conversion-treated steel sheets of Examples and Comparative Examples of the present invention, and the test results of the corrosion resistance of the chemical conversion-treated steel sheet.

In the examples and comparative examples shown in Table 3, the plating No. of Table 1 was used as the original plate of the chemical conversion-treated steel sheet. Using the Zn-based plated steel sheet subjected to the hot-dip Zn-based plating shown in No. 1, the chemical conversion-treated steel sheet No. 1 to 27 were prepared. Specifically, first, the surface of the original plate of the chemical conversion-treated steel sheet was degreased and dried. Next, the above chemical conversion treatment liquid was applied to the surface of the original plate, and immediately after that, the temperature of the original plate was raised to a predetermined temperature using an automatic discharge type electric hot air oven and dried by heating. As a result, a chemical conversion-treated film is formed on the surface of the original plate, and the chemical conversion-treated steel sheet No. 1 to 27 were prepared.

Note that the chemical conversion treated steel sheet No. No. 19 used ammonium titanium fluoride as the specific group 4 metal oxoacid salt. Chemical conversion treated steel sheet No. No. 20 was prepared using a chemical conversion treatment solution containing ammonium zirconium carbonate but not diammonium hydrogen phosphate. In addition, chemical conversion treated steel sheet No. No. 23 was prepared using a chemical conversion treatment solution containing vanadium pentoxide without containing ammonium zirconium carbonate and diammonium hydrogen phosphate. Chemical conversion treated steel sheet No. No. 24 was prepared using a chemical conversion treatment solution containing ammonium molybdate and vanadium pentoxide without containing ammonium zirconium carbonate and diammonium hydrogen phosphate.

In the above series of steps, various conditions were set based on the method for producing a chemical conversion-treated steel sheet according to one aspect of the present invention described in the above-described embodiment. The specific temperature of the chemical conversion treatment liquid, the temperature of the steel sheet at the time of coating, the setting time (time from application to the start of drying), and the drying conditions are as shown in Table 2.

(Analysis of metal in chemical conversion coating)
For the chemical conversion-treated steel sheet, a metal element present in the chemical conversion-treated film was identified by a glow discharge emission spectrophotometer (SPECTRUMA ANALYTIK GmbH; GDA750).

(Composition of chemical conversion coating)
The prepared chemical conversion-treated steel sheet was analyzed with an X-ray source MgKα using a photoelectron spectroscopic analyzer (Shimadzu Seisakusho Co., Ltd./KRATOS Co., Ltd .; ESCA-3400). The XPS spectrum due to the binding energy of the Group 4 metal (eg Zr) was measured. Then, the peak area due to the binding energy of the Group 4 metal forming the basic structural part in the matrix in the chemical conversion treatment film and the binding energy of the Group 4 metal forming a different structural part by bonding with the anion species. The peak area caused by the above was calculated. As a result, among the group 4 metals contained in the chemical conversion treatment film, the atomic ratio of the group 4 metal forming the basic structural part and the heterogeneous structural part 30 are formed by combining with the anion species 4 The atomic ratio of group metals was calculated. FIG. 4 can be referred to as an example of the calculation result.

(Corrosion resistance of flat parts of chemical conversion treated steel sheet)
Corrosion resistance tests were carried out on the chemical conversion treated steel sheets 1 to 27 as follows. First, the end face of a 70 mm × 150 mm test piece of a chemical conversion-treated steel sheet was sealed, and a salt spray test was carried out for 120 hours in accordance with JIS Z2371. Next, white rust generated on the surface of the test piece was observed. Table 3 shows the results of the corrosion resistance test. In this corrosion resistance test, when the area ratio of white rust is 5% or less, it is "◎", when it is larger than 5% and 10% or less, it is "○", and when it is larger than 10% and less than 30%, it is "△". If it was 30% or more, it was evaluated as "x", and if it was "Δ" or more, it was passed.

(Corrosion resistance of processed steel sheet of chemical conversion treatment)
In the corrosion test of the processed part, the test piece was bent 180 degrees so as to have an inner radius of 1 mm in accordance with JIS Z2248, and then the same salt spray was continued for 24 hours. Then, the area of white rust generated on the surface of the processed portion is measured, and the area ratio of white rust on the surface of the processed portion is "◎" for 5% or less, "○" for 5 to 10%, and "○" for 10 to 30%. The corrosion resistance of the processed portion was evaluated with "Δ", 30 to 50% as "black coating Δ", and 50% or more as "x", and "black coating Δ" or more was accepted.

(Test results)
As shown in Table 3, the chemical conversion-treated steel sheet Nos. of Examples produced under appropriate film formation conditions using a chemical conversion-treated liquid containing both a group 4 metal oxoacid salt and a salt containing a specific oxoacid. 1 to 19 showed the following results. That is, as a part of the matrix formed by the metal oxide polymer, dissimilar structural parts were dispersed in the matrix and appropriately present, and excellent flat portion corrosion resistance and processed portion corrosion resistance were exhibited.

Comparative example of chemical conversion treated steel sheet No. In No. 20, a dense chemical conversion treatment film is formed by using a chemical conversion treatment solution containing ammonium zirconium carbonate, but the chemical conversion treatment film does not contain different structural parts, so that the corrosion resistance of the processed portion is inferior.

Comparative example of chemical conversion treated steel sheet No. In No. 21, the manufacturing condition No. 21 Since the drying rate in No. 18 was too fast, the chemical conversion treatment film (at least the surface layer of the chemical conversion treatment film measured by XPS) was formed by the phosphate of Zr, and the basic structural part of Zr was not formed. In this case, Y used to calculate the α value is the atomic ratio of the Group 4 metal bonded to phosphoric acid, which is an anionic species, among the Group 4 metals contained in the chemical conversion coating, which was calculated by XPS measurement. Represents.

On the other hand, the chemical conversion-treated steel sheet No. of the comparative example. In No. 22, the manufacturing condition No. 22 Since the drying rate in No. 19 was too slow, heterogeneous structural parts were not formed in the chemical conversion treatment film (at least the surface layer of the chemical conversion treatment film measured by XPS). In this case, since P is detected not only by Zr but also by GDS, it is considered that P is contained in the chemical conversion coating in some form other than the heterogeneous structure.

Comparative example of chemical conversion treated steel sheet No. In 25 to 27, different structural parts were not formed in the chemical conversion coating because any of the setting time, the temperature rising time, and the reaching plate temperature was unsuitable. For example, it is considered that P was concentrated in the reaction layer directly above the Zn-based plating layer without forming different structural parts.

As described above, when a chemical conversion treatment film containing both a specific group 4 metal oxoacid salt and a salt containing a specific oxo acid is used to prepare a chemical conversion treatment film, the film forming conditions have a very sensitive effect. You can see that it has an effect. By setting the film forming conditions such as settling time, temperature rising time, and reaching plate temperature within an appropriate range, a chemical conversion-treated steel sheet having a chemical conversion-treated film in which dissimilar structural parts are dispersed in a matrix and appropriately present is obtained. be able to.

Next, the plating No. in Table 1 Chemical conversion-treated steel sheet No. 2 was used in the same manner as above except that each Zn-plated steel sheet shown in 2 to 14 was used. 31 to 43 were prepared. Table 4 shows the chemical conversion treated steel sheet Nos. It is a table which shows the film composition, physical property, and corrosion resistance of a chemical conversion-treated steel sheet of 31-43.

Example of chemical conversion-treated steel sheet No. Similarly, in Nos. 31 to 44, different structural parts are dispersed in the matrix and appropriately present as a part of the matrix formed of the metal oxide polymer, and excellent flat portion corrosion resistance and processed portion corrosion resistance are exhibited. It was.

Also, the plating No. in Table 1 Using the Zn-based plated steel sheet shown in No. 1, the chemical conversion-treated steel sheet No. 1 was used in the same manner as above except for the following. 51 to 64 were prepared. Zirconium sulfate or zirconium nitrate was used as the Group 4 compound used in the chemical conversion treatment liquid. Ammonium molybdate was used as the group 5 metal oxoate, and vanadium pentoxide was used as the group 6 metal oxoate. Sodium sulfate, potassium nitrate, or sodium pyrophosphate was used as the Group 1 containing compound. Chemical conversion treated steel sheet No. For 53 to 55, 59 and 60, diammonium hydrogen phosphate was added to the chemical conversion treatment solution. Table 5 shows the chemical conversion treated steel sheet Nos. It is a table regarding the film composition, physical properties and corrosion resistance of the chemical conversion-treated steel sheet of 51 to 64.

Chemical conversion treated steel sheet No. In 51 and 52, Zr sulfate or Zr nitrate as different structural parts were dispersed in the matrix and showed high corrosion resistance in the processed part.

Chemical conversion treated steel sheet No. 53-55 and No. At 59 and 60, vanadate or molybdate is considered to be included in the chemical conversion treated steel sheet as a first heterogeneous structural part or a second heterogeneous structural part. As a result, the chemical conversion treated steel sheet No. 53-55 and No. In 59 and 60, a high corrosion resistance of the processed portion was exhibited and a very high corrosion resistance of the flat portion was exhibited.

Chemical conversion treated steel sheet No. In Nos. 56 to 58, not only the dissimilar structure portion had a structure dispersed in the matrix, but also the chemical conversion treatment film contained the Group 1 metal, so that the processed portion showed extremely high corrosion resistance.

Chemical conversion treated steel sheet No. In 61 to 63, it is considered that vanadate or molybdic acid is combined with Zr to form the first heterogeneous structural part. As a result, a very high flat portion corrosion resistance was exhibited.

Chemical conversion treated steel sheet No. In 64, phosphate, vanadate, and molybdate are contained in the chemical conversion coating as a first heterogeneous structure or a second heterogeneous structure, and a group 1 metal is contained in the chemical conversion coating. .. As a result, a very high flat portion corrosion resistance and a very high processed portion corrosion resistance were exhibited.

1 Chemical-treated steel sheet 10 Zn-based plated steel sheet 11 Base steel sheet 12 Zn-based plated layer 20 Chemical-treated film

Claims (11)

1. A Zn-based plated steel sheet having a Zn-based plated layer on the surface of the base steel sheet,
   It has a chemical conversion treatment film formed on the surface of the Zn-based plating layer.
   In the chemical conversion treatment film, as a part of the matrix formed by the metal oxide polymer which is a polymer of at least one group 4 metal oxo acid, (i) the group 4 metal contained in the group 4 metal oxo acid (i). ii) A chemical conversion-treated steel plate characterized in that a salt bonded to a specific oxo acid is dispersed and present in the matrix.
2. The chemical conversion treatment film according to claim 1, wherein the Vickers hardness measured according to the Vickers hardness test method specified in JIZ Z 2244 is 70 HV 0.01 or more and 200 HV 0.01 or less. Treated steel plate.
3. Among the group 4 metals contained in the chemical conversion treatment film, the atomic ratio of the group 4 metal forming the basic structure of the metal oxide polymer is set to X, and the salt is formed by binding with the specific oxo acid. Assuming that the atomic ratio of the formed Group 4 metal is Y,
   The chemical conversion-treated steel sheet according to claim 1 or 2, wherein the chemical conversion-treated film is Y / (X + Y) = 0.1 to 0.6.
4. The chemical conversion-treated steel sheet according to any one of claims 1 to 3, wherein the group 4 metal is Zr.
5. The specific oxo acid is phosphoric acid,
   Any of claims 1 to 4, wherein the chemical conversion-treated film further contains at least one of a group 5 metal oxo acid and a group 6 metal oxo acid (excluding Cr oxo acid) in the matrix. The chemical conversion-treated steel sheet according to item 1.
6. The chemical conversion-treated steel sheet according to any one of claims 1 to 5, wherein the chemical conversion-treated film further contains a Group 1 metal.
7. The chemical conversion-treated steel sheet according to any one of claims 1 to 6, wherein the chemical conversion-treated film further contains a phosphate of a metal other than the group 4 metal in the matrix.
8. The chemical conversion according to any one of claims 1 to 7, wherein the specific oxo acid is at least one of a group 5 metal oxo acid and a group 6 metal oxo acid (excluding Cr oxo acid). Treated steel plate.
9. The chemical conversion-treated steel sheet according to any one of claims 1 to 8, wherein the Zn-based plating layer contains 40% by mass or more of Zn.
10. For a Zn-based plated steel sheet having a Zn-based plated layer on the surface of the base steel sheet, both (i) at least one group 4 metal oxoacid salt and (ii) a salt containing a specific oxo acid are added. The chemical conversion treatment liquid application step of applying the chemical conversion treatment liquid containing, and
    Immediately after the chemical conversion treatment liquid application step, the heat drying of the chemical conversion treatment liquid is started with a standing time of 35 seconds or less, and the temperature rise time until the temperature of the Zn-based plated steel sheet reaches 80 ° C. is 1 second or more. The chemical conversion treatment comprises 10 seconds or less, a maximum reaching temperature of 170 ° C. or less, and a heat-drying step of drying the chemical conversion treatment liquid to form a chemical conversion treatment film on the surface of the Zn-based plated steel sheet. Steel plate manufacturing method.
11. The method for producing a chemical conversion-treated steel sheet according to claim 10, wherein the Zn-based plating layer contains 40% by mass or more of Zn.

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