JP2010121198A - Surface-treated steel sheet and housing of electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated steel sheet which is remarkably superior in the electroconductivity, corrosion resistance and flaking resistance of a formed and worked part, and has a chemical conversion coating film containing no hexavalent chromium formed on a hot-dip galvannealed steel sheet. <P>SOLUTION: This surface-treated steel sheet has a hot-dip galvannealed layer which is substantially formed of a Γ phase and a δ1 phase and includes 10.5-15 mass% Fe and 0.15-0.30 mass% Al, formed on both sides of a base steel sheet; and has a conversion treatment film on at least one surface of the hot-dip galvannealed layer. The conversion treatment film includes a zirconium compound (a), fine particles of silica (b), a component (c) derived from a silane coupling agent, a vanadate compound (d), a phosphate compound (e), a nickel compound (f) and an acrylic resin (g); and has a Zr deposition amount controlled to 40-1,200 mg/m<SP>2</SP>and a film thickness controlled to 0.1-3 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes hexavalent chromium on the surface of an alloyed hot-dip galvanized layer, which is suitable for use in a casing of an electronic device that shields electromagnetic waves, and has excellent conductivity, corrosion resistance, and flaking resistance of a molded portion. The present invention relates to a surface-treated steel sheet subjected to no chemical conversion treatment. The present invention also relates to a housing of an electronic device that is formed using the above-mentioned surface-treated steel sheet and that is remarkably excellent in electromagnetic wave shielding properties and corrosion resistance.

  Suppressing electromagnetic waves generated from components mounted on electronic devices such as flat-screen TVs and personal computers from leaking from the housing and affecting the human body, or malfunctioning electronic devices due to electromagnetic waves entering from the outside In order to prevent this, the casings of these electronic devices (hereinafter referred to as electronic device casings) are required to have electromagnetic shielding properties.

  It is well known that electromagnetic waves can be shielded by making the electronic device casing made of metal. Further, when the conductivity of the metal constituting the electronic device casing is increased, the shielding property of electromagnetic waves is also improved. However, since a metal electronic device casing is generally manufactured by fastening a molded metal plate via a flange, it has many seams and joints. There was a problem that electromagnetic waves leaked or invaded from the gaps present in the joint. As a method of preventing leakage or intrusion of electromagnetic waves from this gap, the gasket method of filling the gap by inserting a gasket at the joint or joint, and further improving the conductivity of the metal plate constituting the electronic device casing, There is a non-gasket method that further enhances the electromagnetic wave absorbing ability of the metal plate and prevents electromagnetic waves from leaking or entering even if there are gaps in the joints or joints. In recent years, the non-gasket method has been preferred because the use of gaskets causes an increase in the number of parts constituting the electronic device casing and leads to an increase in the manufacturing cost of the electronic device casing.

Conventionally, a surface-treated steel sheet (hereinafter referred to as a chromate-treated zinc-based plated steel sheet) having a chromate-treated film on a zinc-based plated layer has been widely used as a metal plate of an electronic device casing. Since the chromate-treated film is thin, the conductivity of the chromate-treated galvanized steel sheet was hardly inhibited. However, since the chromate treatment liquid contains hexavalent chromium, which is an environmental load substance, the use of chromate-treated zinc-based plated steel sheets has been restricted. Accordingly, a surface-treated steel sheet (hereinafter referred to as a chromate-free chemical conversion-treated zinc-based plated steel sheet) that does not contain hexavalent chromium on the zinc-based plated layer and has a so-called chromate-free chemical conversion-treated film has come to be used. However, since the chromate-free treated coating with the same corrosion resistance as the chromate-treated coating is thick, the conductivity of the chromate-free chemically treated zinc-coated steel sheet is low, and it is manufactured using a chromate-free chemically treated zinc-coated steel sheet. In many cases, the electronic device casing cannot shield electromagnetic waves unless a gasket is used.
In addition, “so-called chromate-free that does not contain hexavalent chromium” does not mean that even a very small amount of hexavalent chromium that exists as an unavoidable impurity is included, and the inclusion of trivalent chromium as necessary. It shall be allowed.

  As a method for improving the conductivity of the chromate-free chemical conversion-treated zinc-based plated steel sheet, there is a technique of forming a chromate-free chemical conversion-treated film on a zinc-based plating layer having fine irregularities on the entire surface. In the surface-treated steel sheet according to such a technique, the thickness of the chromate-free chemical conversion coating film is locally thick at the concave portion of the zinc-based plating layer, and the convex portion from the chromate-free chemical conversion coating film is local at the convex portion of the zinc-based plating layer. By exposing these fine recesses and projections to the entire surface of the zinc-based plating layer, the surface treated steel sheet with a thick chromate-free chemical conversion coating can be used for corrosion resistance. On the other hand, the protrusions locally exposed from the chromate-free chemical conversion coating function as conduction points and have the same corrosion resistance and conductivity as the chromate-treated galvanized steel sheet. Therefore, an electronic device casing manufactured using a surface-treated steel sheet having a chromate-free chemical conversion coating on a zinc-based plating layer having fine irregularities on the entire surface can ensure a certain electromagnetic shielding property. It was.

  However, when the surface of the galvanized layer is formed with fine irregularities after the galvanized steel sheet is plated, and in the case of electrogalvanization, before the plating, the steel sheet is tempered and rolled with a dulled roll. In addition to increasing the manufacturing cost, the non-gasket method electronic equipment casing using the surface-treated steel sheet with the chromate-free chemical conversion coating manufactured in this way meets the increasingly demanding electromagnetic shielding properties. It was becoming impossible. Therefore, it has been desired to further increase the conductivity of the chromate-free chemical conversion-treated galvanized steel sheet at low cost.

As a technique for solving such a problem, for example, in Patent Document 1, on a plated film on at least one surface of an alloyed hot-dip galvanized steel sheet (hereinafter referred to as an alloyed hot-dip galvanized steel sheet), A surface-treated steel sheet having a chromate-free rust-proof coating is disclosed.
JP 2006-257456 A

  The surface-treated steel sheet disclosed in Patent Document 1 improves conductivity by utilizing fine irregularities peculiar to the surface of an alloyed hot-dip galvanized layer that cannot be crushed even if temper rolled with a dulled roll or the like. It has been made.

However, in the surface-treated steel sheet described in Patent Document 1, after the chemical conversion film is formed on the Zn-rich FeZn ₁₃ columnar crystals (ζ phase), the protrusions exposed from the chemical conversion film layer are formed. The ratio of the conductive part that is easily deformed by sliding and exposed from the film surface is low, and the conductivity is not sufficiently improved.

  Moreover, since the surface-treated steel sheet described in Patent Document 1 has low reactivity between the rust-proofing treatment liquid and the alloyed hot-dip galvanized layer, the adhesion between the antirust-treated film and the alloyed hot-dip galvanized layer is low, It was inferior in corrosion resistance.

  Since the electronic component casing is manufactured by forming a steel sheet, when using a surface-treated steel sheet with a rust-proof coating on the alloyed hot-dip galvanized steel sheet, the alloyed hot-dip galvanized layer has a high anti-flame resistance. Must have king characteristics. However, in the case of the surface-treated steel sheet described in Patent Document 1, since the alloyed hot-dip galvanized layer has a ζ phase, the anti-flaking property was inferior.

  Therefore, the inventors have provided an alloyed hot-dip galvanized layer substantially composed of a Γ layer and a δ1 phase on both surfaces of a base steel sheet described in Japanese Patent Application No. 2008-222320, and the alloyed hot-dip galvanized steel. The Fe content and the Al content of the layer are limited to a certain range, and a chemical conversion treatment film not containing hexavalent chromium is formed in a certain film thickness range on at least one surface of the alloyed hot dip galvanized layer. We proposed a surface-treated steel sheet with excellent conductivity, corrosion resistance and flaking resistance of the processed parts.

  However, the surface-treated steel sheet described in the specification of Japanese Patent Application No. 2008-222320 is excellent in conductivity, corrosion resistance and flaking resistance of the formed portion, and is suitable for use in an electronic device casing. When high surface pressure is applied to the steel plate, flaking occurs in the plating layer, or the plating projections compressively deform and the conduction point density decreases, resulting in insufficient conductivity of the formed parts There is. When the flaking is severe, the corrosion resistance of the molded portion is also insufficient. In the future, the design of electronic equipment casings will become more important, and the steel plates used in electronic equipment casings will often be formed into complex shapes, requiring better anti-flaking resistance. It becomes. Furthermore, the emphasis is placed on the design of the electronic device casing, so that the structure of the entire electronic device casing becomes complicated and the steel plate used for the electronic device casing needs to have better conductivity. Become. That is, as the steel sheet used for the electronic device casing, a surface-treated steel sheet that is superior in terms of conductivity, corrosion resistance, and flaking resistance of the formed portion is desired.

Further, the inventors have disclosed a zirconium compound (a), fine particle silica (b), a silane coupling agent-derived component (c), and vanadic acid on the surface of a zinc-based plated steel sheet described in Patent Document 2. A chromate-free chemical conversion coating (hereinafter referred to as chemical conversion coating A) containing a compound (d), a phosphoric acid compound (e), a nickel compound (f), and an acrylic resin (g) so as to satisfy certain conditions. The surface-treated steel sheet has been proposed, which has excellent corrosion resistance, blackening resistance, and appearance and durability after press molding.
JP 2008-169470 A

  However, the surface-treated steel sheet described in Patent Document 2 is intended to improve corrosion resistance, flat plate portion corrosion resistance, blackening resistance, and appearance and corrosion resistance after press molding. Has not been considered. In addition, the surface-treated steel sheet described in Patent Document 2 is an electrogalvanized steel sheet, a hot-dip galvanized steel sheet, a Zn-Ni alloy-plated steel sheet, a molten Zn-5 mass% Mg alloy-plated steel sheet, and a molten Zn- This is mainly for Mg alloy-plated steel sheets, and studies on alloyed hot-dip galvanized steel sheets have not been sufficient.

  In an example of Patent Document 2, as a zinc-based plated steel sheet, a surface-treated steel sheet in which a chemical conversion coating A is formed on the surface of an alloyed hot-dip galvanized steel sheet in which the Fe content of the alloyed hot-dip galvanized layer is 10 mass%. Although described, since the Fe content is 10 mass%, it is considered that the galvannealed layer contains a ζ phase. Therefore, the case where the alloyed hot-dip galvanized layer is formed with the chemical conversion coating A on the surface of the alloyed hot-dip galvanized steel sheet substantially composed of the Γ phase and the δ1 phase has not been studied.

  Even if the same chromate-free chemical conversion treatment solution is used, the surface treatment of the alloyed hot-dip galvanized layer and the chromate-free chemical conversion coating formed on the surface-treated steel sheet, even when the same chromate-free chemical conversion treatment solution is used. Varies greatly depending on the film thickness. Therefore, alloyed hot-dip galvanized layers consisting essentially of a Γ layer and δ1 phase are provided on both sides of the base steel sheet, and the alloyed hot-dip galvanized layers are limited to a certain range in terms of Fe content and Al content. In the surface-treated steel sheet in which the chemical conversion coating A is formed on the surface of the galvanized surface, investigations and examinations on the conductivity, corrosion resistance, and flaking resistance of the formed portion have not been sufficient.

The present invention solves the above-mentioned problems, and provides a surface-treated steel sheet in which a chromate-free chemical conversion coating film is formed on an alloyed hot-dip galvanized steel sheet that is remarkably excellent in conductivity, corrosion resistance, and flaking resistance of a molded portion. The purpose is to provide.
It is another object of the present invention to provide an electronic device casing that is formed using the surface-treated steel sheet of the present invention and that is remarkably excellent in electromagnetic wave shielding properties and corrosion resistance of components.

In order to solve the above situation, the inventors formed various alloyed hot-dip galvanized layers on both surfaces of the base steel sheet, and further made various chromate-free chemical conversions on at least one surface of the alloyed hot-dip galvanized layer. A surface-treated steel sheet with a treated film was prepared, and the conductivity, corrosion resistance, and flaking resistance of the molded portion were intensively investigated.
As a result, the alloyed hot-dip galvanized layer does not contain a ζ phase, substantially comprises a Γ phase and a δ1 phase, the content of Fe and Al in the alloyed hot-dip galvanized layer is within a certain range, and The surface-treated steel sheet in which the chemical conversion coating A is formed on at least one surface of the alloyed hot-dip galvanized layer with a predetermined coating thickness has markedly improved conductivity, corrosion resistance, and flaking resistance of the formed portion, and is also high. It has been found that it also has a thermal emissivity.

  The present invention has been made by further studying the above knowledge, and the gist of the present invention is as follows.

1. On both sides of the base steel sheet, an alloyed hot-dip galvanized layer consisting essentially of a Γ phase and a δ1 phase is provided,
The alloyed hot-dip galvanized layer contains 10.5 to 15% by mass of Fe, 0.15 to 0.30% by mass of Al, and
At least one surface of the alloyed hot-dip galvanized layer has a zirconium compound (a), fine-particle silica (b), a silane coupling agent-derived component (c), a vanadate compound (d), and a phosphate compound. A coating containing (e), a nickel compound (f), and an acrylic resin (g) so as to satisfy the following conditions (1) to (6) and having a Zr adhesion amount of 40 to 1200 mg / m ² A surface-treated steel sheet having a chemical conversion film having a thickness of 0.1 to 3 μm.
(1) Mass ratio (b) / (a) = 0.1 to 1.2 of fine particle silica (b) and Zr equivalent amount of zirconium compound (a)
(2) Mass ratio (Si) / (a) = 0 of the total amount (Si) of Si in the fine particle silica (b) and the silane coupling agent-derived component (c) and the amount of Zr in the zirconium compound (a) .15-1.0
(3) Mass ratio (d) / (a) = 0.02 to 0.15 of V converted amount of vanadic acid compound (d) and Zr converted amount of zirconium compound (a)
(4) Mass ratio (e) / (a) = 0.03 to 0.30 of P equivalent of phosphoric acid compound (e) and Zr equivalent of zirconium compound (a)
(5) The mass ratio (f) / (a) between the Ni conversion amount of the nickel compound (f) and the Zr conversion amount of the zirconium compound (a) is 0.005 to 0.10.
(6) Mass ratio (g) / (x) = 0.005 to 0.18 of acrylic resin (g) and total amount (x) of solid content of film

2. 2. The surface-treated steel sheet according to 1 above, wherein the chemical conversion film further contains wax (h) so as to satisfy the following condition (7).
(7) Mass ratio (h) / (x) = 0.01-0.10 of wax (h) and total amount (x) of film solids

3. The surface of the alloyed hot-dip galvanized layer has an arithmetic average roughness: Ra of 0.5 to 1.5 μm, and the number of peaks per length of 25.4 mm in the average line direction of the roughness curve: PPI of 150 The surface-treated steel sheet according to 1 or 2 above, which satisfies -350.

4). 4. The surface-treated steel sheet according to any one of 1 to 3 above, wherein an average aspect ratio of crystals on the surface of the alloyed hot-dip galvanized layer is 3 or less.

5. 5. An electronic device casing formed by using the surface-treated steel sheet according to any one of 1 to 4 above.

ADVANTAGE OF THE INVENTION According to this invention, the surface treatment steel plate which gave the chemical conversion treatment which does not contain hexavalent chromium to the alloyed hot-dip galvanized steel plate which is remarkably excellent in the electroconductivity of a shaping | molding process part, corrosion resistance, and flaking resistance can be obtained.
Moreover, the electronic device housing formed by using the surface-treated steel sheet of the present invention is remarkably excellent in electromagnetic wave shielding properties and corrosion resistance.

The details of the present invention and the reasons for limitation will be described below.
The surface-treated steel sheet of the present invention comprises an alloyed hot-dip galvanized layer substantially composed of a Γ phase and a δ1 phase on both surfaces of the base steel sheet, and the alloyed hot-dip galvanized layer contains 10.5 to 15 mass of Fe. %, Al is contained in an amount of 0.15 to 0.30% by mass, and at least one surface of the alloyed hot-dip galvanized layer has a zirconium compound (a), fine-particle silica (b), and a silane coupling agent. The derived component (c), vanadic acid compound (d), phosphoric acid compound (e), nickel compound (f), and acrylic resin (g) so as to satisfy the following conditions (1) to (6) It is a surface-treated steel sheet having a chemical conversion treatment film with a film thickness of 0.1 to 3 μm and a Zr adhesion amount of 40 to 1200 mg / m ² .
(1) Mass ratio (b) / (a) = 0.1 to 1.2 of fine particle silica (b) and Zr equivalent amount of zirconium compound (a)
(2) Mass ratio (Si) / (a) = 0 of the total amount (Si) of Si in the fine particle silica (b) and the silane coupling agent-derived component (c) and the amount of Zr in the zirconium compound (a) .15-1.0
(3) Mass ratio (d) / (a) = 0.02 to 0.15 of V converted amount of vanadic acid compound (d) and Zr converted amount of zirconium compound (a)
(4) Mass ratio (e) / (a) = 0.03 to 0.30 of P equivalent of phosphoric acid compound (e) and Zr equivalent of zirconium compound (a)
(5) The mass ratio (f) / (a) between the Ni conversion amount of the nickel compound (f) and the Zr conversion amount of the zirconium compound (a) is 0.005 to 0.10.
(6) Mass ratio (g) / (x) = 0.005 to 0.18 of acrylic resin (g) and total amount (x) of solid content of film
Hereinafter, the explanation will be divided into the base steel plate, the galvannealed layer and the chemical conversion coating A.

(Base steel plate)
The type of the base steel plate is not particularly limited as long as it has a strength that does not cause cracks when the electronic component housing is formed, but a mild steel plate equivalent to a tensile strength (TS) of 270 MPa is preferable. Further, when forming into a shape with a large drawing ratio, a steel plate equivalent to an ultra-low carbon IF steel with good workability is preferable.

(Alloyed hot-dip galvanized layer)
An alloyed hot-dip galvanized layer is formed on both surfaces of the base steel plate. The alloyed hot-dip galvanized layer is formed by subjecting a base steel sheet to hot-dip galvanizing and then alloying treatment, but the alloyed hot-dip galvanized layer of the surface-treated steel sheet of the present invention is substantially Γ. Alloying is performed so as to be composed of a phase (Fe ₃ Zn ₁₀ ) and a δ 1 phase (FeZn ₇ ). If the alloying treatment is insufficient, the ζ phase (FeZn ₁₃ ) remains on the surface of the alloyed hot-dip galvanized layer. The conductivity of the surface-treated steel sheet in which a chromate-free chemical conversion coating film is formed on the alloyed hot-dip galvanized layer with the ζ phase remaining on the surface is at a sufficient level. However, after the molding process, the conductivity of the sliding portion during molding is inferior. This is because the ζ phase is a Zn-rich phase and flexible compared to the Γ phase and δ1 phase, and the convex portions are crushed and deformed easily by sliding during molding, and a sufficient conduction point cannot be secured. Therefore, an electronic device casing produced by forming such a surface-treated steel sheet is inferior in electromagnetic shielding properties.

  Also, the alloyed hot-dip galvanized layer with the ζ phase remaining on the surface is a chromate-free chemical conversion treatment performed after the alloying treatment, and the reactivity between the ζ phase and the chromate-free chemical conversion treatment solution is not good. The adhesion between the free chemical conversion coating and the galvannealed coating is inferior, resulting in a decrease in corrosion resistance. In addition, when a surface-treated steel sheet with a chromate-free chemical conversion coating formed on an alloyed hot-dip galvanized layer containing a ζ phase is formed, the Zn-rich ζ phase is more flexible than the Γ phase and δ1 phase. Peeling called king is likely to occur. Further, since the ζ phase is flexible, the dynamic friction coefficient at the time of molding becomes high and the moldability deteriorates.

  On the other hand, if the alloying treatment is excessive, an alloyed hot-dip galvanized layer having a small δ1 phase and a large Γ phase is obtained. When a surface-treated steel sheet in which a chromate-free chemical conversion coating film is formed on an alloyed hot-dip galvanized layer having many Γ phases, powdering due to the Γ phase, which is a Fe-rich and brittle phase, is likely to occur.

  Therefore, the alloyed hot-dip galvanized layer is composed of a Γ phase and a δ1 phase mainly composed of a Γ1 phase (18.5 to 23.5 mol% Fe). In addition, the inclusion of a trace amount of alloy phase that is inevitably formed is allowed. In the present invention, the fact that it substantially consists of a Γ phase and a δ1 phase is determined by the peak intensity ratio of the Γ phase, δ1 phase, and ζ phase of X-ray diffraction described later.

Furthermore, the Fe content and the Al content in the galvannealed layer of the surface-treated steel sheet according to the present invention must satisfy the following conditions.
-Fe content: 10.5-15 mass%
If the Fe content is less than 10.5% by mass, it becomes an alloyed hot-dip galvanized layer containing a ζ phase, which not only deteriorates the flaking resistance, but also causes cracks and wrinkles during molding due to insufficient sliding. On the other hand, when the Fe content exceeds 15% by mass, an alloyed hot-dip galvanized layer in which the Γ phase is excessively formed is obtained, and powdering properties are deteriorated. In addition, it is necessary to increase the alloying temperature during the alloying treatment, and a long alloying time is required. This results in a decrease in line speed and hinders productivity. Therefore, the Fe content is in the range of 10.5 to 15% by mass. Preferably, it is the range of 11.0-14.0 mass%.

-Al content: 0.15-0.30 mass%
When the Al content is less than 0.15% by mass, the ζ phase is thermodynamically stable, and not only the ζ phase is easily generated but also the control of the Fe content is difficult due to the high alloying speed. Become. On the other hand, if the Al content exceeds 0.30% by mass, alloying becomes extremely slow, so that it is necessary to increase the alloying temperature and lengthen the alloying time, thereby inhibiting productivity. Furthermore, it becomes difficult to control for uniform alloying, and a problem arises that the η phase remains in a part of the steel sheet, resulting in a so-called burnt state. Accordingly, the Al content is in the range of 0.15 to 0.30 mass%. Preferably, it is the range of 0.18-0.25 mass%.

  Next, alloying treatment conditions will be described. In order to obtain an alloyed hot-dip galvanized layer substantially consisting of a Γ phase and a δ1 phase and having an Fe content and an Al content within the above ranges, when the base steel plate is mild steel, the alloying treatment conditions are as follows: It is preferable to do so.

-Zinc adhesion amount: 25-60 g / m ² per side
The amount of zinc deposited has a great influence on the alloying rate. When the zinc coating weight is less than one side per 25 g / m ^2, fast progress of alloying, Fe content in the coating layer becomes excessive, powdering resistance of the plating layer is deteriorated, whereas, per side 60 g / beyond m ^2, the progress of alloying is slow, Fe content in the coating layer becomes insufficient, anti-flaking property is deteriorated. Therefore, the zinc adhesion amount is preferably in the range of 25 to 60 g / m ² per side. In particular, considering use as an electronic device casing, the range of 35 to 50 g / m ² is preferable.

-Alloying temperature: 450-530 ° C
When the alloying treatment temperature is less than 450 ° C., the ζ phase is likely to be generated, the anti-flaking resistance is deteriorated, and the alloying speed is slow. Therefore, in order to obtain a desired Fe content, a long time is required. Alloying treatment is required. Moreover, the problem that the η phase remains in a part of the steel plate also occurs. On the other hand, when the alloying temperature exceeds 530 ° C., the Fe content tends to be high due to rapid alloying, the amount of Γ phase generated becomes excessive, and the powdering resistance deteriorates. Therefore, the alloying treatment temperature is preferably in the range of 450 to 530 ° C. More preferably, it is the range of 470-510 degreeC. The heat source used for the alloying treatment is preferably induction heating capable of rapid heating in order to shorten the alloying time in a low temperature range where the η phase is easily generated.

The fact that the alloyed hot-dip galvanized layer alloyed under the above conditions is substantially composed of a Γ phase and a δ1 phase is determined by X-ray diffraction by a diffractometer method, and d (Å) = 2.592 of the Γ phase. (Where d (Å) is the lattice spacing), and the peak intensity (cps) of δ1 phase d (Å) = 2.136 and ζ phase d (Å) = 3.025, respectively, Ia, Ib and When Ic
Ib / Ia> 50 and Ic / Ia <1.2
Can be confirmed.

(Chemical conversion coating A)
At least one surface of the galvannealed layer of the surface-treated steel sheet according to the present invention has a chemical conversion coating A. When the requirement for corrosion resistance is not so high, the chemical conversion film A can be formed only on one surface, and can be provided as a surface-treated steel sheet that is particularly excellent in electromagnetic shielding properties. On the other hand, when the requirement for corrosion resistance is very high, by forming the chemical conversion treatment film A on both sides, it can be provided as a surface-treated steel sheet that is particularly excellent in corrosion resistance.

Next, the aqueous chromate-free chemical conversion treatment solution used when forming the chemical conversion coating A will be described.
This aqueous chromate-free chemical conversion treatment solution uses water as a solvent, a water-soluble zirconium compound (A), water-dispersible fine particle silica (B), a silane coupling agent (C), a vanadate compound (D), It contains a phosphoric acid compound (E), a nickel compound (F), and an acrylic resin emulsion (G), and preferably contains these components (A) to (G) as main components. In addition, the aqueous chromate-free chemical conversion treatment liquid can further contain a wax (H) as necessary.
The water-soluble zirconium compound (A) is not particularly limited, and examples thereof include zirconium nitrate, zirconium oxynitrate, zirconyl acetate, zirconyl sulfate, zirconyl ammonium carbonate, zirconyl potassium carbonate, and zirconyl sodium carbonate. One or more types can be used. Here, even when an inorganic fluorine-containing compound such as zircon hydrofluoric acid or a salt thereof is included, it is a water-soluble zirconium compound and can be used as long as the solution is compatible. Since the treatment liquid contains silica as an essential component, the stability of the liquid is often impaired when an inorganic fluorine-containing compound is contained. Therefore, zircon hydrofluoric acid or a salt thereof is not so preferable.

The water-dispersible fine particle silica (B) is not particularly limited in particle size or type, but colloidal silica or dry silica can be used. Examples of colloidal silica include Snowtex (registered trademark) O, C, N, 20, OS, OXS (all trade names) manufactured by Nissan Chemical Co., Ltd., and examples of dry silica include Japan. Aerosil Co., Ltd. AEROSIL50, 130, 200, 300, 380 (all are brand names) etc. are mentioned, One or more of these can be used.
The mixing ratio of the water-dispersible fine particle silica (B) is 0.1 to 1 in mass ratio (B) / (A) between the water-dispersible fine particle silica (B) and the Zr equivalent amount of the water-soluble zirconium compound (A). .2. If (B) / (A) is less than 0.1, the corrosion resistance and the flaking resistance are reduced due to the fact that the chemical conversion coating is easily cut during press molding, while the mass ratio (B) / (A) is 1. If the ratio exceeds 2, the film cannot be formed properly and the corrosion resistance is lowered. From such a viewpoint, the more preferable mass ratio (B) / (A) is 0.2 to 1.0, and particularly preferably 0.3 to 0.8.

  Examples of the silane coupling agent (C) include vinyl methoxy silane, vinyl ethoxy silane, vinyl trichloro silane, vinyl trimethoxy silane, vinyl triethoxy silane, β- (3,4 epoxy cyclohexyl) ethyl trimethoxy silane, γ -Glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β (amino Ethyl) γ-aminopropylmethyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyltrimethoxysilane, γ-methacryloxy Propylmethyldiethoxysilane, γ-methacryloxypropylmethyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyltrimethoxysilane, p-styryltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, γ-chloropropyltrimethoxysilane, bis (triethoxysilylpropyl) tetrasulfide, γ-isocyanatopropyltriethoxysilane, γ-triethoxy Cisilyl-N- (1,3-dimethyl-butylidene) propylamine, N- (vinylbenzylamine) -β-aminoethyl-γ-aminopropyltrimethoxysilane, and the like, and one or more of these should be used Can do.

  The mixing ratio of the silane coupling agent (C) is 0.5 to 3.0 in terms of a mass ratio (C) / (A) between the silane coupling agent (C) and the Zr equivalent amount of the water-soluble zirconium compound (A). And If the mass ratio (C) / (A) is less than 0.5, the corrosion resistance and the flaking resistance will be reduced due to the fact that the chemical conversion film is easily cut during press molding. On the other hand, if it exceeds 3.0, the film is suitable. Therefore, the corrosion resistance is lowered and the stability of the treatment liquid is also lowered. From such a viewpoint, the more preferable mass ratio (C) / (A) is 1.0 to 2.5, and particularly preferably 1.2 to 2.0.

Examples of the vanadic acid compound (D) include ammonium metavanadate and sodium metavanadate, and one or more of these can be used. Here, V of the vanadic acid compound is pentavalent, but corrosion resistance cannot be ensured with a tetravalent vanadium compound.
The compounding ratio of the vanadic acid compound (D) is 0.02 to 0 in mass ratio (D) / (A) of the V converted amount of the vanadic acid compound (D) and the Zr converted amount of the water-soluble zirconium compound (A). .15. When the mass ratio (D) / (A) is less than 0.02, the corrosion resistance is lowered. On the other hand, when it exceeds 0.15, the film is colored and the appearance is impaired. From such a viewpoint, the more preferable mass ratio (D) / (A) is 0.04 to 0.12, and particularly preferably 0.05 to 0.10.

The phosphoric acid compound (E) is not particularly limited as long as it is compatible with the liquid. Examples of the phosphoric acid compound include phosphoric acid, primary phosphate, secondary phosphate, and tertiary phosphate. Salt, pyrophosphate, pyrophosphate, tripolyphosphate, condensed polyphosphate such as tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid, hypophosphite, phosphonic acid, phosphonate Can be mentioned. Examples of the phosphonate include nitrilotrismethylenephosphonic acid, phosphonobutanetricarboxylic acid, ethylenediaminetetramethylenephosphonic acid, methyldiphosphonic acid, methylenephosphonic acid, ethylidenediphosphonic acid, and ammonium salts and alkali metal salts thereof. Etc. One or more of these phosphoric acid compounds can be used.
The mixing ratio of the phosphoric acid compound (E) is 0.03 to 0 in mass ratio (E) / (A) between the P equivalent amount of the phosphoric acid compound (E) and the Zr equivalent amount of the water-soluble zirconium compound (A). .30. When the mass ratio (E) / (A) is less than 0.03, the corrosion resistance is lowered. On the other hand, when it exceeds 0.30, the flaking resistance of the press-formed part is lowered. From such a viewpoint, the more preferable mass ratio (E) / (A) is 0.06 to 0.20, and particularly preferably 0.10 to 0.18.

The nickel compound (F) is not particularly limited as long as it is compatible with the liquid, and examples thereof include nickel nitrate, nickel sulfate, nickel carbonate, nickel chloride, nickel phosphate, and one or more of these. Can be used.
The mixing ratio of the nickel compound (F) is 0.005 to 0.10 in mass ratio (F) / (A) between the Ni conversion amount of the nickel compound (F) and the Zr conversion amount of the water-soluble zirconium compound (A). And When the mass ratio (F) / (A) is less than 0.005, the blackening resistance decreases, whereas when it exceeds 0.10, the corrosion resistance decreases. From such a viewpoint, (F) / (A) is more preferably 0.01 to 0.08, and particularly preferably 0.02 to 0.06.
The sum (SI) of the Si-converted amount of the water-dispersible fine particle silica (B) and the silane coupling agent (C) is the mass ratio (SI) / (A) with the Zr-converted amount of the water-soluble zirconium compound (A). 0.15-1.0. If the mass ratio (SI) / (A) is less than 0.15, the corrosion resistance and the flaking resistance decrease due to the fact that the chemical conversion film is easily cut during press molding, while if it exceeds 1.0, the corrosion resistance is reduced. descend. From such a viewpoint, the more preferable mass ratio (SI) / (A) is 0.25 to 0.85, and particularly preferably 0.30 to 0.68.

The acrylic resin emulsion (G) is an aqueous emulsion resin obtained by emulsion polymerization of vinyl monomers such as acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, and styrene. Although there is no restriction | limiting in particular in a kind, Especially, a nonionic emulsifier can be applied suitably. Among nonionic emulsifiers, those having a structure having polyethylene oxide or polypropylene oxide can be particularly suitably applied.
The blending ratio of the acrylic resin emulsion (G) is 0 in mass ratio (G) / (X) between the solid content of the acrylic resin emulsion (G) and the total amount (X) of the solid content in the aqueous chromate-free chemical conversion treatment liquid. 0.005 to 0.18. When the mass ratio (G) / (X) is less than 0.005, the corrosion resistance is lowered. On the other hand, when it exceeds 0.18, the chemical conversion film is easily scraped due to an increase in the organic component, so that the flaking resistance is lowered. . From such a viewpoint, the more preferable mass ratio (G) / (X) is 0.01 to 0.16, and particularly preferably 0.02 to 0.14.

The acrylic resin constituting the acrylic resin emulsion (G) preferably has a glass transition temperature (Tg) calculated by the following formula (1) of 10 to 30 ° C. The following equation (1) is generally called a FOX equation.
1 / Tg = Σ (Wi / Tgi) (1)
Where Wi: weight fraction of component i Tgi: Tg of component i
If the Tg of the acrylic resin is less than 10 ° C., the chemical conversion film is easily scraped, so that the anti-flaking property is lowered. On the other hand, if the Tg exceeds 30 ° C., the corrosion resistance tends to be lowered.

  The pH of the aqueous chromate-free chemical conversion treatment liquid of the present invention is not particularly limited, but is preferably pH 6 to 11 and more preferably pH 8 to 10 from the viewpoint of the stability of the treatment liquid. When the pH of the treatment liquid is less than 6, the stability of the treatment liquid is lowered, and the corrosion resistance and the appearance of the film are lowered. On the other hand, when the pH exceeds 11, etching of zinc becomes remarkable, and the appearance of the film also deteriorates and the corrosion resistance tends to decrease. As the alkali used for adjusting the pH, ammonia and amine are preferable, and as the acid, a phosphoric acid compound is preferable.

The water-based chromate-free chemical conversion treatment liquid as described above is applied to the surface of the zinc-based plated steel sheet and dried by heating to form the chemical conversion treatment film A. The adhesion amount of the chemical conversion film A after the heat drying is 40 to 1200 mg / m ^{2 in} terms of Zr equivalent of the zirconium compound in the film. When the adhesion amount is less than 40 mg / m ² , sufficient corrosion resistance cannot be obtained. On the other hand, when it exceeds 1200 mg / m ² , the coating film is thick and the appearance and corrosion resistance after press molding are lowered. From such a viewpoint, a more preferable adhesion amount is 80 to 600 mg / m ² , and particularly preferably 120 to 320 mg / m ² .
The film thickness of the chemical conversion film A after heating and drying is as follows under the condition that the Zr adhesion amount falls within the above range. As described above, since there is no ζ phase on the surface of the alloyed hot-dip galvanized layer of the surface-treated steel sheet according to the present invention, the reactivity with the chromate-free chemical conversion treatment liquid described above is good. When the film thickness of the chemical conversion film A formed by these treatments is less than 0.1 μm, it is disadvantageous for corrosion resistance, whereas when it exceeds 3 μm, it is disadvantageous for electromagnetic wave shielding properties. Therefore, the film thickness of the chemical conversion film A is in the range of 0.1 to 3 μm. Preferably, it is in the range of 0.2 to 1.5 μm, more preferably in the range of 0.3 to 0.8 μm.

As a method for forming the chemical conversion coating A by applying a water-based chromate-free chemical conversion treatment liquid to the surface of the zinc-based plated steel sheet, a conventional method may be used. For example, the surface of a zinc-based plated steel sheet is treated with a water-based chromate-free chemical conversion treatment solution by a coating method, a dipping method, or a spray method, followed by heat drying. As a coating method, any method such as a roll coater (for example, a 3-roll system, a 2-roll system), a squeeze coater, a bar coater, or a spray coater may be used. In addition, after the coating process using a squeeze coater or the like, or the dipping process or the spray process, the coating amount may be adjusted, the appearance may be made uniform, or the film thickness may be made uniform by an air knife method or a roll drawing method.
The heating means for performing heat drying is not particularly limited, and a dryer, a hot air furnace, a high frequency induction heating furnace, an infrared furnace, or the like can be used. The heating and drying temperature is preferably 50 to 250 ° C. as the ultimate plate temperature. If it exceeds 250 ° C., cracks may occur in the coating and the corrosion resistance may be reduced. On the other hand, when the temperature is lower than 50 ° C., the moisture remaining in the film increases, and the corrosion resistance may also decrease. From such a viewpoint, a more preferable heating and drying temperature is 60 to 200 ° C, and particularly preferably 60 to 180 ° C.

Next, the surface-treated steel sheet of the present invention obtained using the above aqueous chromate-free chemical conversion treatment liquid will be described.
This surface-treated steel sheet has a zirconium compound (a), fine-particle silica (b), a silane coupling agent-derived component (c), and a vanadate compound (d) on the surface of the above-described alloyed hot-dip galvanized steel sheet. The chemical conversion film A includes a phosphoric acid compound (e), a nickel compound (g), and an acrylic resin (g), and preferably contains these as a main component. Moreover, you may mix | blend wax (h) with this chemical conversion treatment film A further as needed.

The zirconium compound (a) is a component derived from Zr in the water-soluble zirconium compound (A) blended in the treatment liquid, and details of the water-soluble zirconium compound (A) are as described above.
The fine particle silica (b) is derived from the water dispersible fine particle silica (B) blended in the treatment liquid, and details of the water dispersible fine particle silica (B) are as described above.
The content ratio of the fine particle silica (b) in the film is 0.1 to 1.2 in terms of the mass ratio (b) / (a) between the fine particle silica (b) and the Zr equivalent amount of the zirconium compound (a). . If (b) / (a) is less than 0.1, the corrosion resistance and the flaking resistance are lowered due to the chemical conversion coating being easily cut, while the mass ratio (b) / (a) is 1.2. If it exceeds 1, the film cannot be formed properly and the corrosion resistance is lowered. From such a viewpoint, the more preferable mass ratio (b) / (a) is 0.2 to 1.0, and particularly preferably 0.3 to 0.8.

The component (c) derived from the silane coupling agent is derived from the silane coupling agent (C) blended in the treatment liquid, and details of the silane coupling agent (C) are as described above.
Here, the sum (Si) of the Si equivalent amount of the particulate silica (b) and the silane coupling agent-derived component (c) is the mass ratio (Si) / (a) with the Zr equivalent amount of the zirconium compound (a). 0.15-1.0. If the mass ratio (Si) / (a) is less than 0.15, the corrosion resistance and the flaking resistance are lowered due to the chemical conversion coating being easily scraped. On the other hand, if it exceeds 1.0, the corrosion resistance is lowered. From such a viewpoint, the more preferable mass ratio (Si) / (a) is 0.25 to 0.85, and particularly preferably 0.30 to 0.68.

The vanadic acid compound (d) is derived from the vanadic acid compound (D) blended in the treatment liquid, and details of the vanadic acid compound (D) are as described above.
The content ratio of the vanadic acid compound (d) in the film was 0.02 in terms of the mass ratio (d) / (a) of the V converted amount of the vanadic acid compound (d) and the Zr converted amount of the zirconium compound (a). To 0.15. When the mass ratio (d) / (a) is less than 0.02, the corrosion resistance is lowered. On the other hand, when it exceeds 0.15, the film is colored and the appearance is impaired. From such a viewpoint, the more preferable mass ratio (d) / (a) is 0.04 to 0.12, and particularly preferably 0.05 to 0.10.

The phosphoric acid compound (e) is derived from the phosphoric acid compound (E) blended in the treatment liquid, and details of the phosphoric acid compound (E) are as described above.
The content ratio of the phosphoric acid compound (e) in the film was 0.03 in mass ratio (e) / (a) between the P equivalent amount of the phosphoric acid compound (e) and the Zr equivalent amount of the zirconium compound (a). ~ 0.30. When the mass ratio (e) / (a) is less than 0.03, the corrosion resistance is lowered. On the other hand, when it exceeds 0.30, the appearance of the film is lowered. From such a viewpoint, the more preferable mass ratio (e) / (a) is 0.06 to 0.20, and particularly preferably 0.10 to 0.18.

The nickel compound (f) is derived from the nickel compound (F) blended in the treatment liquid, and details of the nickel compound (F) are as described above.
The content ratio of the nickel compound (f) in the film is 0.005 to 0 in mass ratio (f) / (a) between the Ni conversion amount of the nickel compound (f) and the Zr conversion amount of the zirconium compound (a). .10. When the mass ratio (f) / (a) is less than 0.005, the appearance of the film is deteriorated, whereas when it exceeds 0.10, the corrosion resistance is deteriorated. From such a viewpoint, (f) / (a) is more preferably 0.01 to 0.08, and particularly preferably 0.02 to 0.06.

The acrylic resin (g) is derived from the acrylic resin emulsion (G) blended in the treatment liquid, and the details of the acrylic resin emulsion (G) and the acrylic resin are as described above.
The content ratio of the acrylic resin (g) in the film is 0.005 to 0.18 in terms of mass ratio (g) / (x) between the acrylic resin (g) and the total amount (x) of the solid content of the film. . When the mass ratio (g) / (x) is less than 0.005, the corrosion resistance is lowered. On the other hand, when it exceeds 0.18, the chemical conversion film is easily scraped due to an increase in the organic component, so that the flaking resistance is lowered. . From such a viewpoint, the more preferable mass ratio (g) / (x) is 0.01 to 0.16, and particularly preferably 0.02 to 0.14.

In the surface-treated steel sheet obtained by the present invention, the reason why excellent flat plate portion corrosion resistance and corrosion resistance after press forming are obtained is not necessarily clear, but is considered to be due to the following mechanism.
First, a film skeleton is formed by a water-soluble zirconium compound, water-dispersible fine particle silica, and a silane coupling agent. The water-dispersible fine particle silica is considered to maintain its shape even in the dried film. Moreover, when a silane coupling agent is dissolved in water, silanol and alcohol are produced by hydrolysis. The resulting silanol is dehydrated and condensed into polysiloxane. This polysiloxane is considered to be dispersed in water in a double structure with the core as the core and an alkyl group on the outside.

  The water-soluble zirconium compound penetrates between the double structure containing fine particle silica (particles) and polysiloxane, and acts as a binder in the dried film to connect the double structure containing fine particle silica and polysiloxane. To form a film. The inorganic film formed in this way is hard, but is easily crushed by the stress during press molding, and does not have adhesiveness like organic polymers. On the other hand, since such a film is fragile with less stress, it may be difficult to obtain anti-flaking properties. However, in the present invention, the film receives a certain amount of a specific resin (acrylic resin). Stress can be relaxed, and stable flaking resistance can be obtained.

  As mentioned above, water-soluble zirconium compound, water-dispersible fine particle silica, silane coupling agent and acrylic resin are components that form the skeleton of the film, and once dried, do not dissolve in water again and have a barrier effect. It is done. On the other hand, the vanadic acid compound and the phosphoric acid compound are uniformly dispersed in the film and exist in a form that is easily soluble in water, and have an inhibitory effect during so-called zinc corrosion. That is, the vanadic acid compound suppresses the corrosion of zinc itself by a passivating action, and the phosphoric acid compound etches zinc when coming into contact with zinc to form a slightly soluble metal salt with dissolved zinc, or When zinc corrosion occurs, it is considered that zinc ions are trapped in the film and further corrosion is suppressed. Thus, since the inhibitors having different corrosion inhibiting mechanisms are used in combination, not only excellent flat plate portion corrosion resistance but also excellent corrosion resistance after press molding can be obtained.

  The above is the basic configuration of the surface-treated steel sheet of the present invention, but the following configuration may be added as necessary.

Wax (H) can be added to the aqueous chromate-free treatment liquid of the present invention in order to further improve the lubrication performance during press molding.
The wax (H) is not particularly limited as long as it is compatible with the liquid. For example, polyolefin wax such as polyethylene, montan wax, paraffin wax, microcrystalline wax, carnauba wax, lanolin wax, silicon wax , Fluorine wax, and the like, and one or more of these can be used. Examples of the polyolefin wax include polyethylene wax, polyethylene oxide wax, and polypropylene wax, and one or more of these can be used.
The blending ratio of the wax (H) is 0.01 to 0 as a mass ratio (H) / (X) of the solid content of the wax (H) and the total amount (X) of the solid content in the aqueous chromate-free chemical conversion treatment liquid. 10 is preferable. When the mass ratio (H) / (X) is less than 0.01, the effect of improving the lubricity, particularly the lubricity during press molding, is not seen. On the other hand, when the ratio exceeds 0.10, this effect is saturated. Conversely, corrosion resistance may be reduced. From such a viewpoint, a more preferable mass ratio (H) / (X) is 0.02 to 0.08.

The chemical conversion film A formed with the water-based chromate-free chemical conversion treatment liquid to which the wax (H) is added further contains the wax (h) and improves the lubricating performance during continuous high-speed press molding. This is derived from the wax (H) blended in the treatment liquid, and the details of the wax (H) are as described above.
The content ratio of the wax (h) in the film may be 0.01 to 0.10 in mass ratio (h) / (x) between the wax (h) and the total amount (x) of the film solids. preferable. When the mass ratio (h) / (x) is less than 0.01, the effect of improving the lubricity, particularly the lubricity at the time of press molding, is not seen. On the other hand, when the ratio exceeds 0.10, this effect is saturated, Conversely, corrosion resistance may be reduced. From such a viewpoint, a more preferable mass ratio (h) / (x) is 0.02 to 0.08.

As described above, the amount of chemical conversion coating A deposited is in the range of 40 to 1200 mg / m ^{2 in} terms of Zr of the zirconium compound in the coating. More preferably 80~600mg / ^{m 2,} particularly preferably at 120~320mg / ^{m 2.} Similarly, the thickness of the surface treatment film is in the range of 0.1 to 3 μm. More preferably, it is in the range of 0.2 to 1.5 μm, and further preferably in the range of 0.3 to 0.8 μm.

  The above is the basic configuration of the surface-treated steel sheet of the present invention, but the following configuration may be added as necessary.

The surface of the alloyed hot-dip galvanized layer of the surface-treated steel sheet according to the present invention has an arithmetic average roughness: Ra of 0.5 to 1.5 μm, and a peak per length of 25.4 mm in the average line direction of the roughness curve. The number of PPI is preferably 150 to 350 in terms of PPI. Moreover, it is preferable that the average aspect ratio of the crystal on the surface of the alloyed hot-dip galvanized layer is 3 or less.
Hereinafter, the reason for limiting the average aspect ratio of the crystal on the surface of the alloyed hot-dip galvanized layer of arithmetic average roughness: Ra, the number of peaks per 25.4 mm in the length of the average line direction of the roughness curve: PPI will be described. To do.

(Arithmetic mean roughness: Ra 0.5-1.5 μm)
Arithmetic average roughness: Ra shall conform to JIS B 0601-1994. When Ra is less than 0.5 μm, the coating rate of the plating projections in a state where the chemical conversion coating A is applied is increased, so that there is a problem that the conduction point ratio is lowered and the conductivity is deteriorated. On the other hand, when Ra exceeds 1.5 μm, the exposed rate of the plating projections in a state where the chemical conversion film A is applied is high, and thus the conductivity is good, but the deterioration of the corrosion resistance becomes a problem. Therefore, Ra is preferably in the range of 0.5 to 1.5 μm. More preferably, it is the range of 0.7-1.3 micrometers.

(Number of peaks per 25.4 mm length in the average line direction of the roughness curve: PPI 150-350)
Number of peaks per 25.4 mm length in the average line direction of the roughness curve: PPI is called the peak count index, and is defined by the US SAE standard. It means that the cross-sectional area (vertical cross-sectional area) becomes large. Fig. 1 shows the roughness of the surface roughness when measuring the PPI defined by the US Engineering Society for Advancing Mobility Land Sea Air and Space: SAE J911-JUN 86 “SURFACE TEXTURE MEASUREMENT OF COLD ROLLED SHEET STEEL”. The height curve is shown. In FIG. 1, a constant reference level H is provided in both positive and negative directions from the average line of the roughness curve. After exceeding the negative reference level, one count is made when the positive reference level is exceeded. This count is repeated until the evaluation length: Ln is reached, and the displayed number is designated as PPI. In the present invention, Ln is 25.4 mm (1 inch) and 2H (peak count level: width between positive and negative reference levels) is 1.27 μm (50 microinches).

  When PPI is less than 150, the plating coverage in a certain area of the surface to which the chemical conversion coating A is applied is high, so that the conductivity is deteriorated. On the other hand, when the PPI exceeds 350, the plating exposure rate within a certain area of the surface to which the chemical conversion coating A is applied is high, so that the conductivity is good but the corrosion resistance is deteriorated. Accordingly, the PPI is preferably in the range of 150 to 350. More preferably, it is the range of 170-330.

(Average aspect ratio of crystals on alloyed hot-dip galvanized layer surface: 3 or less)
Among the crystals existing on the surface of the alloyed hot-dip galvanized layer, when observed from the vertical direction using a scanning electron microscope (SEM), the aspect ratio (longest side length / shortest side length) is 10 Individual crystals are selected, and the average value of the aspect ratios of the ten crystals is defined as the average aspect ratio. FIG. 2 is a photograph showing the result of observing the surface of the alloyed hot-dip galvanized layer before forming the chemical conversion coating A at 1000 times using a scanning electron microscope (SEM), (a) (B) is a figure which shows an example in which the average aspect-ratio of the crystal | crystallization of an alloying hot-dip galvanization layer surface is 3 or less, and (b) shows an example in which the average aspect-ratio of the crystal | crystallization of an alloying hot-dip galvanization layer surface exceeds 3.

  If the average aspect ratio of the crystal on the surface of the alloyed hot-dip galvanized layer exceeds 3, a Zn-rich and soft ζ phase is present in the alloyed hot-dip galvanized layer. Since the material is crushed and easily deformed, there is a problem that the conductivity of the molded portion becomes insufficient. Therefore, the average aspect ratio of crystals on the surface of the alloyed hot-dip galvanized layer is preferably 3 or less. More preferably, it is 2 or less. In addition, there is no restriction | limiting in particular about the lower limit of the average aspect-ratio of the crystal | crystallization of an alloying hot-dip galvanization layer surface.

  In addition, the place mentioned above is only an example of embodiment of this invention, and can change variously in a claim.

  Next, examples will be described. Each sample was produced as shown below. First, steel plate No. S1-S20 galvanized steel sheets were prepared. As the type of zinc plating, steel plate No. S1 to S15 are alloyed hot dip galvanized steel plate Nos. S16 is electrogalvanized steel plate No. S17 is hot dip galvanized (no alloying treatment), steel plate No. S18 is Zn—Ni alloy plating (Ni: 12 mass%), steel plate No. S19 is a hot-dip Zn-5 mass% Al-0.5 mass% Mg alloy plating and steel plate No. S20 was Zn—Mg alloy plating (Mg: 0.5 mass%).

(Steel plate Nos. S1 to S12)
An ultra-low carbon IF steel plate having a thickness of 1.0 mm prepared as a base steel plate was infiltrated into a hot dip galvanizing bath, and the amount of zinc adhered was adjusted to 40 g / m ² per side by gas wiping. The amount of dissolved Al in the plating bath is 0.110 to 0.150% by mass so that the Al content in the galvannealed layer is in the range of 0.10 to 0.40% by mass shown in Table 1. The range was changed. The temperature of the plating bath was 500 ° C.

  Next, the alloying treatment was performed by using an induction heating device as a heat source and setting the alloying treatment temperature within a range of 470 to 500 ° C. as shown in Table 1.

(Steel plate Nos. S13 and S14)
The amount of zinc adhered was measured using steel plate No. S13 is 70 g / m ² per side, steel plate No. S14 is steel plate No. except that it is adjusted to 30 g / m ² per side. Samples were prepared in the same manner as in S1.

(Steel plate No. S15)
Except for the fact that the galvannealed layer has a ζ phase, the steel plate No. In the same manner as in S1, the steel plate No. S15 was produced.

(Steel plate Nos. S16 to S20)
As a reference example, zinc-based plating other than the alloyed hot-dip galvanized layer was formed on both surfaces of the base steel plate. In addition, steel plate No. The type of the zinc-based plating layer formed in S16 to S20 is described in the column of “Alloyed hot dip galvanizing” in Table 1.

  In preparing each steel plate, the identification of the alloy phase, the Fe content and the Al content in the galvannealed layer were measured as follows. In addition, the arithmetic average roughness of the surface of the alloyed hot-dip galvanized layer: Ra and the number of peaks per length of 25.4 mm in the average line direction of the roughness curve: PPI were measured as follows. Furthermore, the average aspect ratio of crystals on the surface of the alloyed hot-dip galvanized layer was measured as follows.

(Identification of alloy phase in alloyed hot-dip galvanized layer)
Prior to forming the chromate-free chemical conversion coating film, the alloy phase in the alloyed hot-dip galvanized layer was identified for each sample after the alloying treatment by X-ray diffraction using a diffractometer method. The X-ray diffraction conditions are as follows.
Equipment: RU-300 manufactured by Rigaku Corporation
X-ray source: Co-Kα
Tube voltage: 30 kV
Tube current: 100 mA
Irradiation time: 30 minutes Speed: 2 deg / min Step: 0.05
Slit: DS = SS = 1 °, RS = 0.3 °
Rotation: None Peak intensity: Maximum value Background processing: Smoothing

  The peak intensity of the alloy phase was measured by the method described above, and d (Å) = 2.592 for Γ phase, d (Å) = 2.136 for δ1 phase, and d (Å) = 3.025 for ζ phase. When the peak intensities of Ia, Ib and Ic are respectively satisfied and Ib / Ia> 50 and Ic / Ia <1.2 are satisfied, the alloyed hot-dip galvanized layer has substantially only a Γ phase and a δ1 phase. Was present and judged not to contain a ζ phase.

(Fe content and Al content in alloyed hot-dip galvanized layer)
A sample is cut out from each sample before the alloying treatment is completed and a chromate-free chemical conversion treatment film is formed, and JIS H 0401: 2007,5. Amount of Fe in alloyed hot-dip galvanized layer by wet chemical analysis (ICP analysis) of solution in which alloyed hot-dip galvanized layer is dissolved using test solution specified in 5.2 Indirect Method And the Al content was measured.

(Arithmetic mean roughness: Ra)
About each sample which completed the alloying process, arithmetic mean roughness: Ra was measured based on JISB0601-1994, before forming a chromate-free chemical conversion treatment film.

(Number of peaks per 25.4 mm length in the average line direction of the roughness curve: PPI)
Before forming a chromate-free chemical conversion coating film for each sample that has been alloyed, the number of peaks per 25.4 mm in length in the average line direction of the roughness curve in accordance with the SAE standard described above: PPI Was measured.

(Average aspect ratio of crystals on alloyed galvanized layer surface)
Before forming the chromate-free chemical conversion coating film, the average aspect ratio of each sample that had been alloyed was determined as follows.
Of the crystals present on the surface of the alloyed hot-dip galvanized layer, the aspect ratio (longest side length / shortest side length) is large when observed at 1000 times using a scanning electron microscope (SEM) from the vertical direction. Ten crystals were selected from the above, and the average value of the aspect ratios of the ten crystals was defined as the average aspect ratio.

Next, the chromate-free chemical conversion treatment will be described.
Water-soluble zirconium compound shown in Table 2, water-dispersed fine particle silica shown in Table 3, silane coupling agent shown in Table 4, vanadic acid compound shown in Table 5, phosphate compound shown in Table 6, nickel compound shown in Table 7, Using the acrylic resin emulsion (nonionic acrylic resin emulsion) shown in Table 8 and the wax shown in Table 9, these components were appropriately blended in water to prepare aqueous chromate-free chemical conversion treatment solutions shown in Tables 10 to 13. The pH of the treatment liquid was appropriately adjusted with ammonia and phosphoric acid.

  Steel plate No. 1 shown in Table 1. After applying alkaline degreasing treatment to S1 to S20, washing with water and drying, the aqueous chromate-free chemical conversion treatment solution is applied to one surface of the steel plate with a bar coater, and when the chemical conversion treatment film is applied to both surfaces, In the same manner, the surface of the steel sheet was coated in the same manner, and then immediately dried by heating so that the surface temperature of the steel sheet reached a predetermined temperature in several seconds to several tens of seconds to form a chemical conversion coating A, and each sample was produced. The film thickness of the chemical conversion coating A was adjusted by the concentration of the aqueous chromate-free chemical conversion treatment solution, and the Zr adhesion amount of the coating was determined by quantifying Zr with a fluorescent X-ray analyzer.

  The film thickness of the chemical conversion coating A is measured by preparing a cross-section sample using a focused ion beam (FIB) processing apparatus (“FB2000A” manufactured by Hitachi, Ltd.) and an attached microsampling apparatus, and then using a transmission electron microscope. (Transmission Electron Microscope: TEM) was used. Prior to FIB processing, a carbon (C) protective film is flash-deposited to a thickness of about 200 nm on the surface of the sample piece of the surface-treated steel sheet for preparing the cross-section sample to protect it from damage caused by ion beam irradiation. Further, a protective film of gold (Au) was sputter coated thereon. After setting the test material with the surface protected in this manner to the FIB processing apparatus, the chemical vapor deposition (CVD) mechanism of the FIB processing apparatus is further used at the sampling position of the cross-sectional sample. A carbon protective film having a thickness of about 500 nm was coated, and a cross-sectional sample was cut out by an ion beam. A cross-section sample (width direction about 20μm, depth direction about 10μm) taken out using a microsampling device is fixed to a straight part of a molybdenum meniscus special mesh using a CVD mechanism, and then cut out by an ion beam. To a thickness suitable for TEM observation (about 0.1 μmt). Thereafter, the cross-sectional sample was observed with a TEM at an accelerating voltage of 200 kV, and the film thickness at three locations was measured in the range of about 10 μm, and the average value was taken as the film thickness.

  For each sample thus obtained, a) conductivity of the molded part, b) corrosion resistance of the flat part, c) corrosion resistance of the press-molded part, d) anti-flaking, e) powdering resistance and f) heat radiation The rate was evaluated as follows.

a) Conductivity of molded part The surface resistance values of both surfaces of each sample on which the chromate-free chemical conversion coating was formed were measured, and the conductivity of each sample was evaluated by the average value of the surface resistance values of each surface. Specifically, the surface resistance value of each sample surface was measured using a low resistance measuring device (Loresta GP: manufactured by Mitsubishi Chemical Corporation: ESP probe). At that time, the load applied to the probe tip was changed, and the load during conduction was measured. Further, after sliding with a flat mold at a pressure of 196 kPa (2 kgf / cm ² ) and a sliding speed of 20 mm / s, the surface resistance was measured in the same manner. The evaluation criteria are as follows.
A: 2.9 N (300 gf) or less O: Over 2.9 N (300 gf) and 4.9 N (500 gf) or less Δ: Over 4.9 N (500 gf) and 6.9 N (700 gf) or less X: 6.9 N (700 gf) ).

b) Corrosion resistance of flat part About one side of each sample in which the chromate-free chemical conversion treatment film was formed, a salt spray test (JIS-Z-2371) was performed, and the white rust resistance after 240 hours was evaluated. The evaluation criteria are as follows.
◎: White rust area ratio less than 5% ○: White rust area ratio 5% or more and less than 10% ○-: White rust area ratio 10% or more and less than 25% △: White rust area ratio 25% or more and less than 50% × : White rust area ratio 50% or more

c) Corrosion resistance of press-molded part For each sample on which a chromate-free chemical conversion coating film was formed, a punch cup diameter: 33 mm, wrinkle holding load: 19.6 kN (2 tf), die diameter: 66 mm, molding speed: 300 mm / s, cylindrical cup A squeeze test was conducted, a salt spray test (JIS Z 2371) was performed, and white rust resistance after 48 hours was evaluated.
◎: White rust area ratio less than 5% ○: White rust area ratio 5% or more and less than 10% ○-: White rust area ratio 10% or more and less than 25% △: White rust area ratio 25% or more and less than 50% × : White rust area ratio of 50% or more d) Flaking resistance Flaking resistance was evaluated by a limit drawing ratio. If the alloyed hot-dip galvanized layer contains a large amount of ζ phase with a lower Fe content than the Γ phase or δ1 phase, the coefficient of friction between the mold die and the surface of the alloyed hot-dip galvanized layer will increase during molding. Since the king occurs, the limit drawing ratio decreases.
About each sample in which the chromate-free chemical conversion treatment film was formed, the same cylinder cup squeeze test was conducted at a punch diameter: 33 mm, a crease pressing load: 19.6 kN (2 tf) and a molding speed of 300 mm / s, and the limit squeeze ratio was investigated. The evaluation criteria are as follows.
A: 2.0 or more
○: 1.9 or more and less than 2.0 △: 1.8 or more and less than 1.9 ×: 1.7 or more and less than 1.8

e) Powdering resistance For each sample on which a chromate-free chemical conversion coating was formed, a cellophane adhesive tape with a width of 40 mm was applied, and a 90-degree bending mold (irregularity) with a tip R of 0.5 mm was used. The cellophane adhesive tape is peeled off and the adhering matter adhering to the cellophane adhesive tape is measured using a fluorescent X-ray analyzer, and the Zn K _α intensity ( cps) was multiplied by 25 to obtain a powdering index, and the powdering resistance was evaluated. The evaluation criteria are as follows.
◎: 3000 or more and less than 4000 ○: 4000 or more and less than 5000 Δ: 5000 or more and less than 6000 ×: 6000 or more

f) Thermal emissivity For each sample on which a chromate-free chemical conversion coating was formed, using a Bruker Optics infrared absorption spectrum measuring apparatus (IFS66 / S), a spectral reflectance spectrum in a wavelength region of 2.5 to 25 μm. (R (λ)) was measured. An integrating sphere was used for the measurement. This spectral reflection spectrum (R (λ)) was substituted into the following equation to obtain thermal emissivity.

  The evaluation results of a) to f) are shown in Tables 14 to 17 together with the production conditions. In addition, in the film | membrane structure of the surface treatment zinc-plated steel plate shown in Table 14-Table 17, mass ratio (b) / (a) of fine particle silica (b) and Zr conversion amount of a zirconium compound (a), vanadate compound (D) Mass ratio (d) / (a) of V conversion amount of zirconium compound (a) and Zr conversion amount of zirconium compound (a), P conversion amount of phosphoric acid compound (e) and Zr conversion amount of zirconium compound (a) Mass ratio (e) / (a), mass ratio (f) / (a) of Ni conversion amount of nickel compound (f) and Zr conversion amount of zirconium compound (a), acrylic resin (g), and coating solid For the mass ratio (g) / (x) to the total amount (x) of the minute and the mass ratio (h) / (x) of the total amount (x) of the wax (h) to the coating solids, see Table 10 The mass ratio (B) / (A) of the composition of the aqueous chromate-free chemical conversion treatment solution shown in Table 13, Equivalent to the quantity ratio (D) / (A), mass ratio (E) / (A), (F) / (A), mass ratio (G) / (X), mass ratio (H) / (X), respectively. Therefore, it was not described in Tables 14-17.

As is apparent from Tables 14 to 17, all of the surface-treated steel sheets of the present invention shown in the invention examples are remarkably excellent in small surface resistance value, that is, in electrical conductivity, and in anti-flaking and powdering resistance. It was confirmed that it was excellent. In particular, it was confirmed that the surface-treated steel sheet of the present invention was not deteriorated in conductivity before and after forming. Moreover, it has also confirmed having a high thermal emissivity.
On the other hand, in the comparative example and the reference example, it was confirmed that at least one of conductivity, corrosion resistance, flaking resistance, powdering resistance and thermal emissivity was inferior.

ADVANTAGE OF THE INVENTION According to this invention, the surface treatment steel plate which gave the chemical conversion treatment which does not contain hexavalent chromium to the alloyed hot-dip galvanized steel plate which is remarkably excellent in the electroconductivity of a shaping | molding process part, corrosion resistance, and flaking resistance can be obtained.
Moreover, the electronic device housing formed by using the surface-treated steel sheet of the present invention is remarkably excellent in electromagnetic wave shielding properties and corrosion resistance.

It is a graph which shows the roughness curve of the surface roughness regarding the definition of PPI defined by the SAE standard. It is a photograph which shows the result of having observed the surface of the alloying hot-dip galvanization layer before forming the chemical conversion treatment film A of the surface treatment steel plate according to this invention in 1000 time using the scanning electron microscope (SEM).

Claims (5)

On both sides of the base steel sheet, an alloyed hot-dip galvanized layer consisting essentially of a Γ phase and a δ1 phase is provided,
The alloyed hot-dip galvanized layer contains 10.5 to 15% by mass of Fe, 0.15 to 0.30% by mass of Al, and
At least one surface of the alloyed hot-dip galvanized layer has a zirconium compound (a), fine-particle silica (b), a silane coupling agent-derived component (c), a vanadate compound (d), and a phosphate compound. A coating containing (e), a nickel compound (f), and an acrylic resin (g) so as to satisfy the following conditions (1) to (6) and having a Zr adhesion amount of 40 to 1200 mg / m ² A surface-treated steel sheet having a chemical conversion film having a thickness of 0.1 to 3 μm.
(1) Mass ratio (b) / (a) = 0.1 to 1.2 of fine particle silica (b) and Zr equivalent amount of zirconium compound (a)
(2) Mass ratio (Si) / (a) = 0 of the total amount (Si) of Si in the fine particle silica (b) and the silane coupling agent-derived component (c) and the amount of Zr in the zirconium compound (a) .15-1.0
(3) Mass ratio (d) / (a) = 0.02 to 0.15 of V converted amount of vanadic acid compound (d) and Zr converted amount of zirconium compound (a)
(4) Mass ratio (e) / (a) = 0.03 to 0.30 of P equivalent of phosphoric acid compound (e) and Zr equivalent of zirconium compound (a)
(5) The mass ratio (f) / (a) between the Ni conversion amount of the nickel compound (f) and the Zr conversion amount of the zirconium compound (a) is 0.005 to 0.10.
(6) Mass ratio (g) / (x) = 0.005 to 0.18 of acrylic resin (g) and total amount (x) of solid content of film The surface-treated steel sheet according to claim 1, wherein the chemical conversion film further contains a wax (h) so as to satisfy the following condition (7).
(7) Mass ratio (h) / (x) = 0.01-0.10 of wax (h) and total amount (x) of film solids   The surface of the alloyed hot-dip galvanized layer has an arithmetic average roughness: Ra of 0.5 to 1.5 μm, and the number of peaks per length of 25.4 mm in the average line direction of the roughness curve: PPI of 150 The surface-treated steel sheet according to claim 1 or 2, which satisfies -350.   The surface-treated steel sheet according to any one of claims 1 to 3, wherein an average aspect ratio of crystals on the surface of the galvannealed layer is 3 or less.   An electronic equipment casing formed by using the surface-treated steel sheet according to any one of claims 1 to 4.