JP2003129174A - Surface treated steel sheet superior in rust resistance on end face - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface galvanized steel sheet which does not include inseparable components such as Cu, and has an adequate rust resistance on end faces even of a thick sheet of 1.6 mm or thicker. SOLUTION: This surface treated steel sheet comprises, by mass%, 0.2% or less C, 2.0% or less Si, 3.5% or less Mn, 0.10% or less P, 0.02% or less S, 0.005-0.10% Al, and 0.5-10.0% Cr, and the balance Fe with unavoidable impurities, has an area ratio of a martensite structure of 3% or less to a cross section area of the steel sheet, and a galvanizing layer formed on at least one side of the steel sheet, with a coated Zn amount of 5 g/m<2> or more per one side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet suitable for use in home appliances, office equipment, etc., and particularly not only the corrosion resistance of the steel sheet surface, but also the rust resistance (hereinafter referred to as "rust resistance" at the cut end surface of the steel sheet cut by shearing). , Abbreviated as “end surface rust resistance”).

[0002]

2. Description of the Related Art Zn, Zn-Ni,
Zn-Fe, Zn-Al, Zn-Cr, Zn-Ni-Co, Zn-Al-Cr surface-treated steel sheet subjected to plating treatment has excellent corrosion resistance, so Office equipment, automobiles,
Widely used in the field of architecture. The steel sheet used for these purposes is generally formed into a predetermined shape by mechanical processing such as shearing, punching (blanking), punching (punching), and edging (trimming). These molded products are then subjected to required processing if necessary, and then assembled into a final product by an assembler. When such a process is performed, at least 2-3 months or more often elapses from the processing of the steel sheet to the product assembly.

Although such a zinc-based plated steel sheet has excellent corrosion resistance on the surface, the corrosion resistance of the cut end face where the steel plate base is exposed is poor, and red rust occurs in several days in an environment where dew condensation occurs. Therefore, in the case of a zinc-based plated steel sheet, if the stock period from processing to assembly becomes long, it is necessary to take rust preventive measures such as application of rust preventive oil, end face coating, or storage in a highly airtight container.

Therefore, there has been a demand for a technique for preventing the formation of rust on the cut end surface of a zinc-based plated steel sheet. For example, the following technologies have been proposed. Japanese Examined Patent Publication (Kokoku) No. 5-48313 discloses that C: 0.15% or less and acid-soluble Al: 0.005% by weight.
0.10%, Cr: 1.5-20%, Cu: 0.8% or less, P: 0.15%
Hereinafter, a zinc-based plated steel sheet having a steel sheet containing one or more of Ni: 10% or less as a mother plate is disclosed. However, since this steel sheet contains Cu, it is difficult to separate and remove it when recycling, and there are problems that the addition of P reduces the toughness and the addition of Ni increases the cost. In addition, this steel sheet was not sufficient in end face rust resistance.

In Japanese Patent Laid-Open No. 10-330883, weight% is
C: 0.01 to 0.08%, Si: 0.04% or less, Mn: 0.4% or less,
P: 0.04% or less, S: 0.015% or less, and Mn and S satisfy Mn (%) × S (%) ≦ 0.003, and S and P are S (%) × P ( %) ≦ 0.0003 is disclosed, and a surface-treated steel sheet in which a zinc-based plating layer is formed on the steel sheet is contained. However, this steel sheet does not necessarily have sufficient end face rust resistance, and particularly when the plate thickness exceeds 2.0 mm, the end face rust resistance is not at a satisfactory level. Further, since the upper limits of Mn, P and S are regulated, there is a problem that the manufacturing cost increases.

[0006]

The object of the present invention is to provide good end face rust resistance even when the plate thickness is 1.6 mm or more, and particularly when the plate thickness is more than 2.0 mm. An object of the present invention is to provide a galvanized surface-treated steel sheet.

[0007]

[Means for Solving the Problems] Corrosion of steel sheets in the atmosphere, especially in an indoor environment, is different from corrosion of automobiles caused by the presence of NaCl, etc. Occur. Therefore, there has been a demand for the development of a surface-treated steel sheet having good end face rust resistance even if condensed water is present on the cut end face. As a result of research conducted by the inventors, the end surface rust resistance of a steel sheet is to reduce the content of impurity components and the like that become the starting point of rust (rusting point), and increase the corrosion resistance of the base steel by adding Cr, etc. , Furthermore, by controlling the martensite structure in the steel plate structure to a certain ratio or less so that a local potential difference does not occur, it was found that it is dramatically improved,
The present invention has been completed.

The gist of the present invention developed on the basis of the above findings is as follows: C: 0.2 mass% or less, Si: 2.0 mass% or less, M
n: 3.5 mass% or less, P: 0.10 mass% or less, S: 0.02 mass
% Or less, Al: 0.005 to 0.10 mass%, Cr: 0.5 to 10.0 mass%
Zinc having a balance of Fe and unavoidable impurities, having a martensite structure area ratio of 3% or less in the steel plate cross section, and having a Zn adhesion amount of 5 g / m ² or more per one surface of at least one surface of the steel plate. It is a surface-treated steel sheet excellent in end face rust resistance characterized by having a system plating layer.

The present invention also provides, in addition to the ingredients described above,
Furthermore, Cu: 0.4 mass% or less, Ni: 3.0 mass% or less, Mo: 1.
0 mass% or less, Ca: 0.001 to 0.01 mass%, Sb: 0.002 to 0.5
Any one or two or more selected from 0 mass% and / or Ti: 0.001 to 0.50 mass%, V: 0.001 to
0.50mass%, Nb: 0.001-0.50mass%, B: 0.0001-0.0
050mass%, any one or two selected from
A surface-treated steel sheet containing at least one kind is proposed.

In the present invention, it is preferable to further provide a surface treatment layer on the surface of the zinc-based plating layer of the above surface-treated steel sheet, and it is more preferable to use a chromate film as the surface treatment layer. In the present invention, the surface treatment layer is preferably an aqueous composition film containing the following (a), (b) and (c). (a) a metal compound of Mg, Mn and Al, which is at least one metal compound selected from phosphates, carbonates, nitrates, acetates, hydroxides and fluorides (b) a water-soluble organic resin (c ) Acid Incidentally, the metal compound (a) at this time is other than Zn, Co, Ti and S.
It may contain at least one metal compound selected from n, Ni, Fe, Zr, Sr, Y, Cu, Ca, V and Ba. The water-soluble organic resin (b) is at least one kind of polymer of carboxyl group-containing monomer and / or at least one kind of copolymer of carboxyl group-containing monomer and other polymerizable monomer.
Further, it is preferable that the acid (c) is at least one selected from the group consisting of phosphoric acid, acetic acid, nitric acid and hydrofluoric acid. Further, the above aqueous composition may contain a water-dispersible resin.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the constitution of the present invention will be described below. First, the reasons for limiting the chemical composition of steel will be explained. C: 0.2 mass% or less C lowers the corrosion resistance and also forms a chromium carbide by combining with Cr in the steel to reduce the effective amount of Cr contributing to the corrosion resistance. Therefore, the C content is 0.2 mass% or less, preferably 0.03 mass% or less, more preferably 0.003 mass%
Limited to:

Si: 2.0 mass% or less Si is an effective component for deoxidation, but it makes the ferrite brittle and, in hot dip galvanizing, causes non-plating and deteriorates the surface treatment property. Therefore, the upper limit of Si content is 2.0mass.
s%, preferably 0.15 mass%.

Mn: 3.5 mass% or less Mn, like Si, is an effective component for deoxidation, but if it is contained in a too large amount, it forms MnS, MnO, etc. to deteriorate the corrosion resistance. Therefore, the upper limit of the amount of Mn is 3.5 mass%, preferably 0.3
mass%

P: 0.10 mass% or less P is an effective component from the viewpoint of puncture resistance and weather resistance, but from the viewpoint of rust resistance of the end face in the present invention, a smaller content is advantageous. Is. The reason for this is that when dew condensation occurs on the ruptured portion having irregularities, part of P is dissolved to form a local battery, which becomes a starting point of rust. P is also a component that reduces toughness. Therefore, the amount of P is 0.10 mass% or less,
It is preferably limited to 0.03 mass% or less.

S: 0.02 mass% or less Since S forms MnS and becomes a starting point of rust generation, it is a harmful element for the end face rust resistance. Therefore, the amount of S is 0.02 mass
% Or less, preferably 0.005 mass% or less, and more preferably 0.002 mass% or less.

Al: 0.005 to 0.10 mass% Al is a component necessary for fixing deoxidation and N in steel making, and at least 0.005 mass% is necessary, but if it is contained excessively, toughness is deteriorated. , The upper limit is 0.10mass
%.

Cr: 0.5 to 10.0 mass% Cr is a component useful for enhancing the corrosion resistance and the end surface rust resistance. Necessary to exert such effect
The Cr amount is 0.5 mass% or more, but if the Cr amount is large, the plating adhesion deteriorates and the manufacturing cost also increases. Therefore, the Cr content is 0.5 to 10.0 mass%, preferably 1.0 to
The amount is 7.0 mass%, more preferably 2.5 to 7.0 mass%.

The Cr content in the present invention is 10.0 mass%
Is the upper limit. This content is less than the Cr content of 10.5 mass% or more contained in ordinary stainless steel. It is not always clear why the steel sheet of the present invention is significantly improved in corrosion resistance (end face rust resistance) despite such a small amount of Cr content, but the content of C, Mn, P and S is not clear. I think that this is closely related to the regulation of the amount below a certain amount. That is, these elements are harmful components that form precipitates to serve as rust points and accelerate corrosion. Therefore,
By suppressing the contents of these elements to be low, the amount of precipitates also becomes small and the formation of rust points can be suppressed. In addition, Mn,
P and S are concentrated on the surface of the steel sheet and suppress the formation of Cr oxides. However, in the present invention, since these components are reduced,
Cr oxide is easily formed. Therefore, even with a relatively small amount of Cr of 10.0 mass% or less, a Cr oxide film as a protective film is effectively formed on the cut end surface of the steel sheet, and the rust resistance of the end surface is improved in combination with the sacrificial anticorrosion effect of zinc. .

Next, in addition to the above-mentioned components, the following components are preferably added to the plated steel sheet of the present invention, if necessary, for the purpose of improving the corrosion resistance and workability of the steel sheet. Cu: 0.4 mass% or less, Ni: 3.0 mass% or less, Mo: 1.0 mass
% Or less, Ca: 0.001 to 0.01 mass% and Sb: 0.002 to 0.50
Any one or more selected from mass% Cu, Ni, Mo, Ca and Sb are effective for improving the corrosion resistance. However, when Cu is contained in a large amount, it concentrates on the surface and causes hot brittleness, which causes surface defects.
4mass% or less. Further, if Ni is contained in a large amount, the toughness deteriorates, so the content is made 3.0 mass% or less. Mo is 1.0 mass%
The effect will be saturated even if the content exceeds 1.0m, so 1.0m
Ass% or less. When Ca is included in a large amount, it forms a surface defect such as a beard. Therefore, Ca is contained in the range of 0.001 to 0.01 mass% as needed. Sb has a content of 0.002 mas
If it is less than s%, a sufficient effect of improving corrosion resistance cannot be obtained, while
The effect is saturated even if it exceeds 0.50 mass%. Therefore, Sb
Content is in the range of 0.002-0.50 mass%, preferably 0.008-
The range is 0.02 mass%.

Ti: 0.001 to 0.50 mass%, V: 0.001 to 0.50
mass%, Nb: 0.001 to 0.50 mass%, B: 0.0001 to 0.0050m
Any one or more selected from ass% Ti, V and Nb fix C, N and S, B fixes N and is effective in improving ductility. hand,
Ti, V, and Nb can be contained at 0.001 mass% or more, and B can be contained at 0.0001 mass% or more. However, Ti, V, Nb are 0.
If it exceeds 50 mass%, the workability will deteriorate, so 0.001 ~
It is contained in the range of 0.50 mass%. If B is excessively included,
On the contrary, since it lowers the ductility, it is contained in the range of 0.0001 to 0.0050 mass% as necessary.

Next, the reason for limiting the structure of the steel sheet substrate will be described. When Cr is added to steel, a martensite structure is easily formed in the matrix ferrite structure. When a two-phase mixed structure of martensite and ferrite is formed, a potential difference is generated between the martensite crystal grains and the ferrite crystal grains, which induces and accelerates corrosion. If the area ratio of the martensitic structure exceeds 3% in an arbitrary steel plate cross section, the effect of improving the rust resistance on the end surface due to the addition of Cr disappears. For this reason, the area ratio of the martensitic structure is limited to 3% or less in an arbitrary steel plate cross section.

Next, the surface treatment will be described in detail. In the present invention, zinc-based plating having a sacrificial anticorrosive action on a steel sheet is applied to at least one surface of the steel sheet having the above-described composition. This basically improves the corrosion resistance of the steel sheet. The plating method may be any method such as hot dipping, electroplating and vapor deposition plating. The plating metal is not only Zn single metal but also Zn-Ni, Zn-Fe, Zn-Al,
Binary system such as Zn-Co and ternary system such as Zn-Fe-Al ternary system
Zn alloy or _{Zn-SiO 2, Zn-SiO} 2 -Co,, Zn-SiO
The effect is exhibited by any plating layer containing zinc, such as a Zn-containing compound such as _2- Cr or Zn-resin.

The amount of zinc-based plating applied is required to be 5 g / m ² or more in terms of the amount of Zn applied per surface. When the adhesion amount is less than 5 g / m ² , the sacrificial anticorrosion effect of Zn on the cut end face is insufficient. The upper limit of the adhesion amount is 150g.
Even if it exceeds / m ² , no further effect can be expected, so 150 g /
m ² is sufficient.

The effect of the present invention can be obtained by the above zinc-based plating as it is, but when it is used unpainted, the flat plate part (steel plate surface part having a plating layer which is not the cut end surface) is protected against red rust or painted. In order to improve the corrosion resistance of the flat plate part when it is used after being subjected to a coating treatment such as, or to impart fingerprint resistance in addition to corrosion resistance, after zinc-based plating, inorganic coating such as chromate treatment, or organic coating Or forming an inorganic-organic composite coating in place of the inorganic coating is desirable in order to impart good end face rust resistance and flat plate characteristics. In the fields of home appliances, office equipment, etc., which are the main applications of the steel sheet of the present invention, fingerprint resistance is also one of the important characteristics, and the above chromate treatment is effective.

As the inorganic film formed on the surface of the zinc-based plating layer, a chromate film, particularly, a Cr adhesion amount of 10-80
mg / m ² (metal Cr equivalent), the silica-containing chromate film of silica deposited amount is 50 to 350 mg / m ² is desirable. I mean,
When Cr in the chromate film is less than 10 mg / m ^{2 in} terms of metal Cr, fingerprint resistance is poor, and the white rust suppression effect of zinc plating is poor, and as a result, it tends to deteriorate the sacrificial anticorrosion effect of the end face part. . On the other hand, when it exceeds 80 mg / m ^{2 in} terms of metallic Cr,
The elution amount of hexavalent Cr increases, which contaminates the alkaline degreasing liquid in the product processing manufacturer and is economically disadvantageous. Furthermore, if the silica content is less than 50 mg / m ² , the fingerprint resistance is poor and the white rust suppressing effect of zinc plating is poor, while:
If it exceeds 350 mg / m ² , the amount of hexavalent Cr eluted will be large, and there will be adverse effects such as contaminating the alkaline degreasing liquid of the product processing manufacturer, and it will also be economically disadvantageous.

On the above chromate film, if necessary,
Further, it is also effective to form a resin coating layer. By forming such a resin coating layer, the corrosion resistance and fingerprint resistance of the flat portion are further stabilized for a long period of time. The amount of the resin coating layer deposited is preferably 0.1 to 3.0 g / m ² . 0.
If it is less than 1 g / m ² , the effect of the resin coating layer is not sufficient and 3.0 g / m ²
Even if it is formed over the range, the effect of the resin coating layer is saturated, which is economically disadvantageous. A PCM steel plate may be formed by coating or adhering a polymer film such as vinyl chloride or polyethylene on the chromate film. In order to improve the slidability of the surface-treated steel sheet during press forming, polyethylene wax or the like may be added to the chromate film or the resin coating layer located on the outermost surface of each coating layer described above.

By the way, recently, also in the fields of home appliances and office equipment, in consideration of environmental problems, there is a demand for a surface-treated steel sheet which does not contain hexavalent chromium and has corrosion resistance. In order to meet such requirements, the steel sheet of the present invention does not contain hexavalent chromium on the surface of the zinc-based plating layer, (a)
An aqueous composition film can be formed by applying an aqueous composition containing a metal compound, (b) a water-soluble organic resin and (c) an acid.

Metal compound (a) which is a component of the aqueous composition
Is a metal compound of Mg, Mn and Al, and is at least one selected from phosphates, carbonates, nitrates, acetates, hydroxides and fluorides. That is, Mg, Mn and
The following (a-1) containing Al as an essential component, (a-2) and
Each of the metal compounds (a-3) includes one kind or two or more kinds. (a-1) at least one Mg compound selected from Mg phosphate, carbonate, nitrate, acetate, hydroxide and fluoride (a-2) Mn phosphate, carbonate, nitrate, At least one Mn compound (a-3) selected from acetates, hydroxides and fluorides Al at least one selected from phosphates, carbonates, nitrates, acetates, hydroxides and fluorides Al compound Here, hereinafter, the above-mentioned (a-1) to (a-3) are collectively referred to as "(a-
i) ”.

The aqueous composition contains, as the metal compound (a), in addition to the above metal compound (ai), Zn, Co, Ti and S.
At least one metal compound selected from phosphates, carbonates, acetates, nitrates, hydroxides and fluorides of n, Ni, Fe, Zr, Sr, Y, Cu, Ca, V and Ba (hereinafter, `` (A
-ii) ") is included because it is possible to obtain higher corrosion resistance and alkali resistance of the steel sheet surface.
These metal compounds (a-ii) are added alone or in combination of two or more to the aqueous composition. Among these metal compounds (a-ii), it is preferable to use Zn carbonate, acetate and hydroxide in combination, because it is effective for the formation of stable Zn-based corrosion products described later.

(Ai) of the metal compound in the aqueous composition and
The total content of (a-ii) is 5 to 6 solids in the aqueous composition.
0 mass% is preferable, and a range of 5 to 50 mass% is particularly preferable. When a plurality of metal compounds are used as the metal compound (a), each metal compound is preferably contained in the aqueous composition at a ratio of 1 to 50 mass%. Total content is 5 mass
If it is less than 60%, the surface corrosion resistance tends to be poor, and if it exceeds 60 mass%, the weldability tends to be poor. Furthermore, when the metal compound (a) and (a-ii) are used in combination as the metal compound (a), (ai) /
The ratio of (a-ii) is 0, from the viewpoint of stability in the aqueous composition.
The range of 5 to 5 is preferable, and the range of 0.5 to 4 is particularly preferable.
In the present invention, the effect of these metal compounds (a) on the corrosion resistance of the steel sheet surface is not clear, but in the process of corrosion of the zinc-based plating layer, the action of forming a zinc-based corrosion product a dense and stable protective film. It is estimated that there is.

The water-soluble organic resin which is the component (b) of the aqueous composition is at least one kind of the polymer (b-1) of the carboxyl group-containing monomer and / or the carboxyl group-containing monomer and other polymerization. It is preferably at least one type of copolymer (b-2) with a polymerizable monomer. The copolymer of a carboxyl group-containing monomer and other polymerizable monomers (b-2),
An example is a copolymer of a hydroxyl group-containing monomer and a carboxyl group-containing monomer.

Examples of the carboxyl group-containing monomer include ethylenically unsaturated carboxylic acid and its derivatives. Specific examples of the ethylenically unsaturated carboxylic acid, acrylic acid, methacrylic acid, ethylenically unsaturated monocarboxylic acid such as crotonic acid, itaconic acid, maleic acid, ethylenically unsaturated dicarboxylic acid such as fumaric acid,
As their derivatives, alkali metal salts of carboxylic acids,
Examples thereof include ammonium salts and organic amine salts.
Among these, acrylic acid and methacrylic acid can be preferably used. As the hydroxyl group-containing monomer, for example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 2,2-bis (hydroxymethyl) ethyl acrylate, ( (Meth) acrylic acid 2,3-dihydroxypropyl, (meth) acrylic acid 3-chloro-2-
(Meth) acrylic acid hydroxyesters such as hydroxypropyl, acrylic alcohols and alcohol amides such as N-methylol acrylamide and N-butoxymethylol (meth) acrylamide, etc. and monomers having a reducing hydroxyl group. They can be used alone or in combination of two or more. Among these, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate are preferable.

The composition of the water-soluble organic resin (b) is the copolymer (b-
In the case of 2), the carboxyl group-containing monomer is 0.5 mass%
As described above, those containing 40 to 95.5 mass% are preferable. When the content of the carboxyl group-containing monomer is 40 mass% or more, the denseness of the obtained coating layer is increased, so that the corrosion resistance is improved. On the other hand, when the content of the carboxyl group-containing monomer is 95.5% by mass or less, the association of the carboxyl groups does not particularly occur and the amount of the functional group that effectively acts is maintained, which is preferable. In the case of the copolymer (b-2), it is preferable that the other polymerizable monomer is 0.5 to 60 mass% and the carboxyl group-containing monomer is 40 to 95.5 mass%. When the amount of the other polymerizable monomer is less than 0.5 mass%, the functional groups that contribute to the adhesion between the organic resin layer and the underlayer are insufficient, and the corrosion resistance may deteriorate. On the other hand, other polymerizable monomers are 60 mass%
When it exceeds, the stability as a surface treatment agent tends to be impaired, which is not preferable. The weight average molecular weight of the (co) polymer constituting the water-soluble organic resin is not particularly limited, but is about 10,000 to several hundreds of thousands.

The acid which is the component (c) of the aqueous composition includes phosphoric acid, acetic acid, nitric acid, hydrofluoric acid, oxalacetic acid tricarballylic acid, citric acid, isocitric acid, succinic acid, malic acid and glutanoic acid. Examples thereof include organic acids capable of coordinating with divalent or higher valent metal ions. Among these, at least one selected from the group consisting of phosphoric acid, acetic acid, nitric acid and hydrofluoric acid is preferable. In addition, when an organic acid capable of coordinating with the divalent or higher valent metal ions is used in combination, the etching of the plating surface is promoted, and the metal compound is coordinated, and a more dense film layer can be formed, which is effective. Is.

In the present invention, the acid (c) etches the surface of the zinc-based plated steel sheet, further improves the adhesion of the film to the zinc-based plated steel sheet, prevents the film from peeling, and prevents corrosion and corrosion resistance of the steel sheet surface. It has the effect of improving alkalinity. The content of the acid in the total solid content of the aqueous composition is preferably
It is 1 to 20 mass%, and particularly preferably 5 to 15 mass%. 1 mas
If it is less than s%, the zinc plating will be insufficiently etched and the corrosion resistance will be reduced. On the other hand, if it exceeds 20 mass%, the zinc plating will dissolve too quickly, causing uneven appearance on the plated surface.
When an organic acid capable of coordinating with the above-mentioned divalent or higher valent metal ions is used in combination as the acid, the amount is 1 with respect to the total solid mass.
It is preferable to contain ~ 10 mass%. Content is 1m
If it is less than ass%, the effect is not sufficient, the uncrosslinked points are increased, and the denseness of the coating may be hindered. Further, if it exceeds 10 mass%, the stability as an aqueous composition cannot be maintained.

Further, in the present invention, in addition to the above-mentioned components (a) to (c) of the aqueous composition, a polyhydric phenolcarboxylic acid is used.
Addition of (d) is preferable because the corrosion resistance and alkali resistance can be further improved. As the polyhydric phenolcarboxylic acid, tannic acid, gallic acid and the like are suitable, and it is preferable to add them in a proportion of 0.1 to 20 mass% with respect to the solid content of the aqueous composition.

Here, in the present invention, a metal compound
(a), a water-soluble organic resin (b) and an acid (c), and preferably an aqueous composition containing a polyhydric phenolcarboxylic acid (d), about the reason why a film excellent in corrosion resistance and alkali resistance of the steel plate surface can be formed. Is not necessarily clear, but it is considered as follows. It is generally known that, when an aqueous solution in which a carboxyl group-containing resin, a polyvalent metal salt and an acid coexist, is applied, dried and formed into a film, an ionized metal causes pseudo-crosslinking between resin molecules. Due to the pseudo-crosslinking, the organic resin film containing a highly hydrophilic carboxyl group exhibits water resistance. In the present invention, the pseudo-crosslinking is not only expressed between the resins as in the prior art, but also the plating surface is strongly etched in the presence of a sufficient acid component to generate free metal ions in the vicinity of the plating interface. As a result, the plating surface and the organic resin are pseudo-crosslinked, and the organic resin and the plating layer are firmly adhered. The steel plate according to the present invention achieves high corrosion resistance and high alkali resistance due to such effects and improvement of the denseness of the film itself. At this time, the polyhydric phenolcarboxylic acid is preferentially oriented on the plating surface, and has the function of making the adhesion between the resin layer and the plating layer stronger.
The reason why all of Mg, Mn, and Al are essential as the metal compound (a) is that the coexistence of these three kinds of ions having different coordination constants to the carboxyl group allows pseudo-crosslinking in a wide pH range. This is because it is possible to react, form a denser film more efficiently, and improve alkali resistance.

In addition to coexistence of Mg, Mn and Al ions, the cross-linking ratio by pseudo cross-linking can be adjusted by adjusting the ratio between the carboxyl group content and the metal ion. Since the unreacted functional group has hydrophilicity, it dissolves the film during alkaline degreasing and reduces the corrosion resistance after alkaline degreasing. In the present invention, a sufficient amount of the type of metal ions is added, preferably total metal ions /
The molar ratio of the carboxyl groups is 0.5 to 2, more preferably 1.
By setting it to 0 to 2, it is possible to significantly reduce the amount of unreacted functional groups remaining in the film in the conventional technique, and it is considered that the corrosion resistance after alkaline degreasing is improved.

Further, in the present invention, in addition to the above water-soluble organic resin (b), a water-dispersible resin (e) is added to the aqueous composition.
It is also possible to contain. The water-dispersible resin is not particularly limited as long as it can be stably and uniformly dispersed in an acidic aqueous solution. As the water-dispersible resin, acrylic-styrene-based, polyester-based, acrylic-based, urethane-based, and other resins that have been used for surface treatment of conventional metal materials can be used, and two or more types may be used in combination. Addition of these water-dispersible resins increases the stability of the coating, especially in an alkaline environment, and improves corrosion resistance, alkali resistance, and coating adhesion. As a preferable range of the content,
It is preferable to contain 1 to 10 mass% with respect to the total solid content of the aqueous composition. If the content is less than 1 mass%, the effect is not sufficient and the coating film has a defective portion in an alkaline environment. Further, if it exceeds 10 mass%, the stability as a coating composition cannot be maintained.

Further, in the present invention, the aqueous composition is
In addition to containing a metal compound (a), a water-soluble organic resin (b) and an acid (c), and preferably a polyhydric phenolcarboxylic acid (d) and a water-dispersible resin (e), further coupling The agent is more preferable because it reacts with unreacted functional groups and can further improve the water resistance, corrosion resistance and alkali resistance of the film. The coupling agent is preferably a coupling agent having at least one reactive functional group selected from active hydrogen-containing amino group, epoxy group, vinyl group, mercapto group and methacryloxy group. Particularly preferred are silane coupling agents, titanium coupling agents and zirconium coupling agents. The amount of the coupling agent blended is such that when surface-treating a conventional metal material,
If the amount is the same as that added to the surface treatment agent and paint,
It is enough.

As the silane coupling agent, for example, γ
-Aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-
Aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropylmethyldimethoxysilane, γ
-Glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, β-3,4-epoxycyclohexylethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltris (2-methoxyethoxy) silane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane , Vinyltriacetoxysilane, N- [2- (vinylbenzylamino) ethyl] -3-aminopropyltrimethoxysilane, γ-
Methacryloxypropyltrimethoxysilane and the like can be mentioned. Examples of titanium coupling agents include di-isopropoxybis (acetylacetonato) titanium, dihydroxybis (lactato) titanium, diisopropoxy-bis- (2,4-pentadionate) titanium,
Examples thereof include isopropyl tri (dioctyl phosphate) titanate. Examples of the zirconium coupling agent include acetylacetone zirconium butyrate, zirconium lactate, zirconium acetate and the like.

Furthermore, in order to further improve the adhesion with the top coat applied by the customer and the denseness of this coating,
It is preferable to add a metal oxide to the aqueous composition. Metal oxides, silica _{(SiO 2), MgO, ZrO} 2, Al 2 O 3, Sn
It is at least one selected from the group consisting of O ₂ , Sb ₂ O ₃ , Fe ₂ O ₃ and Fe ₃ O ₄ . Among these, it produces stable corrosion products and is effective in improving corrosion resistance.
Silica is particularly preferred. As the silica, colloidal silica, vapor phase silica and the like are suitable. The particle size of silica is not particularly limited, but the finer the particle, the more finely the particle is mixed with the component of the surface treatment agent, which is preferable. Further, silica is effective when used in combination with a silane coupling agent, because a synergistic effect of improving stability as a dispersion is obtained. A sufficient effect can be exhibited if the compounding amount of the metal oxide is the same as the amount added to the surface treatment agent and the coating material of the conventionally known zinc-based plated steel sheet.

In the present invention, other performances, for example,
In order to impart performances such as fingerprint resistance, slidability, and scratch resistance, various additives that are commonly used in waxes and other surface treatment agents may be added to the aqueous composition that is a surface treatment agent. Further, in order to impart other performance, another coating may be further laminated on the upper layer of the coating layer.

In the steel sheet of the present invention, the thickness of the coating layer is 0.
The thickness is preferably 1 to 5 μm, more preferably 0.3 to 2.0 μm. Especially considering alkali resistance 1.
It is preferably 0 to 2.0 μm. When the thickness exceeds 5 μm, the cost is increased although the corrosion resistance and alkali resistance are improved. On the other hand, if the thickness is less than 0.1 μm,
The effect of improving corrosion resistance and alkali resistance tends to be small.

Next, a method for producing the zinc-plated surface-treated steel sheet of the present invention will be described. A hot-rolled steel sheet or a cold-rolled steel sheet is used as the material for the plated steel sheet of the present invention.
Molten steel having the above composition is melted by a known method such as a converter, an electric furnace, a vacuum melting furnace, etc., and made into a steel material (slab) by a continuous casting method or an ingot making method. This steel material is then heated or directly hot-rolled without heating to obtain a hot-rolled steel sheet. The heating temperature in hot rolling is 1000 to 12
A temperature range of 00 ° C is desirable. Finish rolling temperature is γ
It is preferable that the winding temperature is at the high temperature side of the α single-phase region, with Ar being ₃ points or more in the single-phase region. Because the finish rolling temperature is
This is because if it is less than the Ar ₃ point, it becomes a two-phase region in which the α phase and the γ phase coexist, the carbon is concentrated in the γ phase, and martensite is formed during cooling. In addition, the winding temperature after hot rolling is α
This is because the formation of martensite can be suppressed when the temperature is set to the high temperature side of the single phase region.

The hot-rolled steel sheet obtained by hot rolling is used as a plating material as it is or after pickling.
Alternatively, a cold rolled steel sheet subjected to cold rolling and recrystallization annealing after pickling is used as a plating material. When zinc-based plating is applied to the hot rolled steel sheet, it is preferable to remove the oxide layer such as black skin by pickling. On the other hand, when a cold-rolled steel sheet is used as the material, the cold-rolling reduction ratio is preferably 50 to 95% from the viewpoint of obtaining a uniform processed structure. The annealing method may be either continuous annealing or batch annealing,
Continuous annealing is preferable in terms of productivity. The annealing temperature is preferably performed in the α single phase region. This is because when annealing is performed in the two-phase region in which the α phase and the γ phase coexist, carbon is concentrated in the γ phase and martensite is formed during cooling.

The hot-rolled or cold-rolled steel sheet thus produced is subjected to plating treatment. Zinc-based plating treatment includes hot dipping, electroplating, PVD (physical vapor deposition), and CVD.
Any method such as (chemical vapor deposition) method, sol-gel method, thermal spraying method and mechanical plating method can be applied. The alloying treatment may be performed by heating after plating.

The surface of the steel sheet after the zinc-based plating treatment is further coated with a chromate treatment or an aqueous composition, if necessary, to form a surface treatment layer. The chromate treatment may be performed by a conventionally known conventional method. Further, in order to form an aqueous composition, the above-mentioned aqueous composition is dissolved or dispersed in an aqueous medium, the adjusted surface treatment agent is applied, pressed with a Ringer roll, and dried to form a film layer, The method of curing is common. To apply the surface treatment agent to the steel sheet, methods such as roll coating, spray coating, brush coating, dip coating and curtain flow are used. Further, the coating amount / adhesion amount is adjusted to fall within the above-mentioned range of the film thickness.

[0049]

The present invention will be described in more detail based on the following examples. (Example 1) Steel having a chemical composition shown in Table 1 was melted in a converter,
A slab was made by continuous casting. These slabs at 1150 ° C
Then, it was hot-rolled to a finishing temperature of 850 to 920 ° C and a winding temperature of 650 to 770 ° C to obtain a hot rolled steel sheet of 3.5 to 5.5 mm.
Then, these hot-rolled sheets were pickled in a 10 mass% hydrochloric acid aqueous solution at 80 ° C to remove scales on the steel sheet surface, and then the sheet thickness 1.6
Cold rolled to ~ 3.2 mm. The obtained cold rolled steel sheet, alkaline electrolytic degreasing treatment to remove the rolling oil attached to the surface,
Furthermore, in 5vol% H ₂ -N ₂ atmosphere (dew point -30 ° C.), 790
After heating and holding at ˜860 ° C. for 40 seconds, recrystallization annealing of cooling at 30 ° C./s was performed.

The obtained steel sheet was subjected to a Zn-based plating treatment of the following A to F by an electroplating method, a hot dip coating method, an alloying hot dip galvanizing method in which a heat treatment is performed after the hot dip coating. Furthermore, the following A to E surface treatments were performed on some of the steel plates to form various surface treatment layers. In addition, those not subjected to Zn-based plating (Comparative Examples Nos. 22 to 24) were also prepared.

(1) Zinc-based plating: A to F-Plating A: Electrogalvanized steel sheet-Plating B: Electrogalvanized-nickel plated steel sheet (Ni: 12ma
ss%) ・ Plating C: Hot dip galvanized steel sheet ・ Plating D: Alloyed hot dip galvanized steel sheet (Fe: 10mass
%) ・ Plating E: 5% zinc steel sheet (Al: 5mass%) ・ Plating F: 55% zinc steel sheet (Al: 55mass)
%)

(2) Surface treatment: A to E Surface treatment A: Cr reduction rate (3
Chromate with 40% Cr / total Cr) 40 mg / m in terms of metallic Cr
² Chromate coating applied and baked at 100-300 ° C Surface treatment B: Surface treatment A on the surface of the zinc-based plating layer
Layer, and an organic film composed of a resin layer obtained by applying and baking an aqueous dispersion containing a polyolefin resin containing a carboxyl group and an epoxy resin on the surface thereof, and a surface treatment C: an outermost organic film of the surface treatment B layer. Including polyethylene wax-Surface treatment D: Cr reduction rate (trivalent) on the surface of the zinc-based plating layer.
Cr / total Cr) Chromate solution containing liquid phase silica at 40% is metal C
Chromate film that was applied at 40 mg / m ^{2 in} terms of r and baked at 100 to 300 ° C Surface treatment E: Surface treatment D on the surface of the zinc-based plating layer
Layer, and an organic resin film composed of a resin layer obtained by coating and baking an aqueous dispersion containing a polyolefin resin containing a carboxyl group, an epoxy resin, and colloidal silica on the surface thereof.

Test pieces were sampled from the various surface-treated steel sheets thus obtained, and the end surface rust resistance was evaluated according to the following test method. Further, with respect to the test piece obtained by subjecting the zinc-based plating layer to the surface treatment, the flat plate portion corrosion resistance and fingerprint resistance were further evaluated according to the following test methods. <End surface rust resistance> The test piece was cut by a shearing machine (shearing condition is the ratio of the length of the sheared portion to the plate thickness: 30 to 60%),
The end face rust resistance was investigated. The end face rust resistance test was carried out by placing the cut sample in a well-ventilated warehouse and measuring the red rust occurrence rate (= red rust area of the end face / total tested area of the end face) after 3 months. . If this red rust occurrence rate is less than 1%, ◎, 1
Less than -10% was evaluated as ◯, and 10% or more was evaluated as x. In addition,
The red rust occurrence rate was determined by visual inspection or image analysis of a cross-sectional photograph.

<Corrosion resistance of flat plate portion> Corrosion resistance of the flat plate portion is determined by shearing the test piece into a size of 70 mm × 150 mm, sealing the end face, and conducting a salt spray test (JIS Z 2371) to determine the surface area of each test piece. The time required for white rust to be generated in 5% of the above was measured, and 120 hours or more was evaluated as ⊚, 96 to 119 hours was evaluated as ◯, 72 to 95 hours was evaluated as Δ, and less than 72 hours was evaluated as x.

<Anti-fingerprint resistance> Fingerprint resistance is white on each test piece.
Color vaseline is applied and the color tone before and after application (L value, a value, b
Value change by spectroscopic color difference meter (“SQ2000”, Nippon Denshoku Co., Ltd.)
Manufactured), ΔE = (ΔL^Two+ Δa^Two+ Δb^Two)^1/2 And △ E: 1.0 or less is ◎, △ E: 1.0 to 2.0 or less
○, △ E: More than 2.0 and less than 3.0 △, △ E: More than 3.0 ×
Evaluated as.

The evaluation results are shown in Table 2. The steel sheets conforming to the present invention all have good end surface rust resistance,
Steel plates that deviate from the conditions of the present invention do not have good end face rust resistance. By further forming a surface treatment layer compatible with the present invention on the zinc-based plating, in addition to the end surface rust resistance,
It is clear that good results can also be obtained for the flat plate portion corrosion resistance and fingerprint resistance.

[0057]

[Table 1]

[0058]

[Table 2]

Example 2 A steel sheet was manufactured in the same manner as in Example 1, and after performing zinc-based plating A to F, the following various organic resins A to E or various additives, metal compounds (Al, M
g, Mn, Co, Zn, etc. phosphates, acetates, nitrates, carbonates, hydroxides, fluorides, etc.) and other components in the proportions shown in Tables 3 and 4, and water as a solvent. The water-based composition was applied by roll coating. Then, the steel sheet was heated to 150 ° C. for 20 seconds to form a film having a thickness of 0.5 to 6.0 μm, and a test piece was produced.

(1) Organic resin: AE-Resin A: AA / maleic acid = 90/10 (mass ratio) -Resin B: AA / itaconic acid = 70/30 (mass ratio) -Resin C: methacrylic acid / Itaconic acid = 60/40 (mass ratio) ・ Resin D: Butyl methacrylate / AA / 2HBA = 20
/ 40/40 (mass ratio) -Resin E: 1-hydroxybutyl acrylate / MMA /
BA / styrene / methyl acrylate / organic phosphorus monomer = 35/20/30/40/5/1 (mass ratio) In the organic resin, AA is acrylic acid, BA
Is butyl acrylate, 2HBA is 2-hydroxybutyl acrylate, and MMA is methyl methacrylate.

(2) Metal Compound (2-1) Total Addition Amount of Metal Compound as a Whole: It is described in the weight ratio of solid content in Tables 3 and 4. (2-2) Kind of metal compound P: Phosphate C: Carbonate N: Nitrate A: Acetate H: Hydroxide F: Fluoride (2-3) Addition weight ratio of metal compound as metal component: A ~
E Pattern A: Mg / Mn / Al = 1/1/1 Pattern B: Mg / Mn / Al / Me = 1/1/1/1 Pattern C: Mg / Mn / Al / Me = 2/1/1 / 1 Pattern D: Mg / Mn / Al / Me (I) / Me (II) = 1/1/1/1
/ 1 pattern E: Mg / Mn / Al / Me (I) / Me (II) = 2/1/1/1
-1 Here, Me (I) and Me (II) are the metal compounds shown in Tables 3 and 4 and other elements other than Mg, Mn, and Al are shown in order.

(3) Type of acid: A to D A: Phosphoric acid B: Acetic acid C: hydrofluoric acid D: nitric acid (4) Types of organic acids: AC A: tricarballylic acid B: citric acid C: succinic acid

(5) Polyhydric phenol carboxylic acid: A, B A: Tannic acid B: Gallic acid (6) Water-dispersible resin: A to D A: Styrene-butyl methacrylate copolymer B: Styrene-butyl acrylate copolymer C: Styrene-acrylic acid copolymer D: Styrene-methyl methacrylate copolymer

(7) Coupling agent: A to C A: γ-glycidoxypropyltrimethoxysilane
(“KBM403” (manufactured by Shin-Etsu Chemical Co., Ltd.) B: γ-glycidoxypropylmethyldiethoxysilane
(“KBM402” (manufactured by Shin-Etsu Chemical Co., Ltd.) C: N-β (aminoethyl) γ-aminopropyltrimethoxysilane (“KBM603” (Shin-Etsu Chemical Co., Ltd.)
(8) Metal oxides: A to C A: Colloidal silica ("Snowtex O" manufactured by Nissan Chemical Co., Ltd.) B: Colloidal silica ("Snowtex UL" manufactured by Nissan Chemical Co., Ltd.) C: Gas phase Silica (“Aerosil 130” Nippon Aerosil)
(Made by Co., Ltd.)

The results of the above tests are summarized in Tables 3 and 4. As shown in the table, the steel sheet produced according to the present invention has not only the rust resistance on the edge surface but also the flat plate portion corrosion resistance and fingerprint resistance.

[0066]

[Table 3]

[0067]

[Table 4]

[0068]

As described above, the surface-treated steel sheet according to the present invention has good end face rust resistance, and the effect is that the surface-treated steel sheet having only the zinc-based plating layer, the surface of the zinc-plating layer Furthermore, a surface-treated steel sheet having a chromate film,
Alternatively, the same is obtained in any case of a surface-treated steel sheet having an aqueous composition film formed by applying the aqueous composition on the surface of the galvanized layer. Therefore, according to the present invention, it is possible to suppress the generation of end surface rust without performing special processing such as end surface oiling or end surface coating and storage in a highly airtight container after cutting.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) C23C 22/20 C23C 22/20 22/22 22/22 22/30 22/30 22/34 22/34 22/53 22 / 53 28/00 28/00 C (72) Inventor Chiaki Kato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term in the Technical Research Laboratory of Kawasaki Steel Corporation (reference) 4K026 AA02 AA07 AA12 AA13 AA22 BA01 BA03 BA06 BB08 CA18 CA20 CA23 CA28 CA32 CA36 4K044 AA02 AB02 BA06 BA10 BA12 BA14 BA15 BA17 BA20 BA21 BB03 BC02 CA11 CA13 CA18

Claims (7)

[Claims] 1. C: 0.2 mass% or less, Si: 2.0 mass% or less,
Mn: 3.5mass% or less, P: 0.10mass% or less, S: 0.02mass
s% or less, Al: 0.005 to 0.10 mass%, Cr: 0.5 to 10.0 mass
%, The balance consisting of Fe and unavoidable impurities, the area ratio of the martensitic structure is 3% or less in the steel plate cross section, and the Zn adhesion amount per one surface is 5 g / m ² or more on at least one surface of the steel plate. A surface-treated steel sheet having excellent zinc rust resistance, which has a zinc-based plating layer. 2. In addition to the components according to claim 1, Cu:
0.4 mass% or less, Ni: 3.0 mass% or less, Mo: 1.0 mass% or less, Ca: 0.001 to 0.01 mass%, Sb: 0.002 to 0.50 mass%, and any one or more kinds selected from them are contained. The surface-treated steel sheet excellent in end face rust resistance according to claim 1. 3. In addition to the components according to claim 1 or 2, Ti: 0.001 to 0.50 mass%, V: 0.001 to 0.50 mass%,
Nb: 0.001 to 0.50 mass%, B: 0.0001 to 0.0050 mass%,
The surface-treated steel sheet excellent in end face rust resistance according to claim 1 or 2, containing any one or more selected from the above. 4. The surface-treated steel sheet excellent in end face rust resistance according to any one of claims 1 to 3, wherein a surface treatment layer is further provided on the surface of the zinc-based plating layer. 5. The surface-treated steel sheet having excellent end face rust resistance according to claim 4, wherein the surface-treated layer is a chromate film. 6. The surface treatment layer comprises the following (a), (b) and
The surface-treated steel sheet having excellent rust resistance on the end surface according to claim 4, which is an aqueous composition film containing (c). (a) a metal compound of Mg, Mn and Al, which is at least one metal compound selected from phosphates, carbonates, nitrates, acetates, hydroxides and fluorides (b) a water-soluble organic resin (c )acid 7. The surface-treated steel sheet excellent in end face rust resistance according to claim 6, wherein the aqueous composition film contains a water-dispersible resin.