JP2013166978A - Surface treated steel sheet having good insulation property and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated steel sheet on which an anodic oxidation film having excellent insulation properties and uniformity in film thickness is formed by using a molten Al-based plated steel sheet containing Si and having good workability.SOLUTION: A surface treated steel sheet having good insulation properties is obtained by performing anodic oxidation treatment on a surface layer part of a plating layer of a molten Al-based plated steel sheet having an Si content in the plating layer of 3.0-15.0 mass%, and sequentially includes an Al-Fe-Si-based alloy layer, an Al-based plating layer, and the anodic oxidation film on the surface of a substrate steel sheet, wherein particles of an Si phase are dispersed in the Al-based plating layer and the anodic oxidation film, and the amount of the existing particles of the Si phase, whose length in the through-thickness direction in the Al-based plating layer and the anodic oxidation film in a cross-sectional surface parallel to the through-thickness direction is at least 10 μm, is controlled to be 100 pieces/mm or less per unit length in the direction parallel to the surface of the substrate steel sheet.

Description

  The present invention relates to a surface-treated steel sheet having good insulating properties in which an anodized film having excellent insulating properties is formed on the surface layer portion of an Al-based plating layer, and a method for producing the same.

Anodizing treatment is known as a surface treatment of Al or Al alloy material (hereinafter referred to as “Al-based material”). A film (anodized film) formed by anodizing treatment is mainly composed of Al ₂ O ₃ and has been put into practical use as a means for imparting corrosion resistance, insulating properties, design properties and the like to Al-based materials.

  Techniques for forming an anodized film on the surface layer portion of a molten Al-based plated steel sheet are also known (Patent Documents 1 to 5). As the hot-dip Al-based plated steel sheet, one manufactured using a plating bath containing about 3 to 15% by mass of Si is generally used. By containing Si, the plating bath temperature can be lowered, and the growth of the alloy layer formed between the surface of the base steel plate (plating original plate) and the Al-based plating layer can be suppressed. While this alloy layer plays an important role in securing plating adhesion, it has the disadvantage of being brittle. When a molten Al-based plating bath containing Si is used, a relatively thin Al-Fe-Si-based alloy layer is formed between the base steel plate and the plated layer during plating, and this type of alloy layer is brittle. The workability deterioration of the hot-dip Al-based plated steel sheet is improved. Conventionally, an Al-based plated steel sheet containing Si has been applied as a molten Al-based plated steel sheet for forming an anodized film (Patent Documents 1 to 5).

  On the other hand, even in a plated steel sheet that has been subjected to hot-dip Al-based plating containing Si, when it is subsequently subjected to a process of heating to 500 ° C. or higher, for example, the heating causes a gap between the base steel sheet and the Al-based plating layer. The intervening Al—Fe—Si alloy layer grows. The grown alloy layer may be a factor that impairs workability in applications where bending is performed, which may be a problem. As a technique for solving this problem, a technique of applying a base steel sheet containing a specific amount of solute N is known (Patent Documents 6 to 9).

Japanese Patent Laid-Open No. 63-57995 Japanese Patent Laid-Open No. 64-21094 JP-A-1-263256 Japanese Patent Laid-Open No. 3-104633 JP-A-6-207262 JP 58-224159 A JP 59-177355 A JP-A 61-52356 JP 61-113754 A

  As described above, the generally used hot-dip Al-based plated steel sheet is manufactured using an Al-based plating bath containing about 3 to 15% by mass of Si. Since the plating layer composition of the hot-dip galvanized steel sheet substantially reflects the plating bath composition, the plating layer of a general hot-dip Al-based galvanized steel sheet contains about 3 to 15% by mass of Si.

  FIG. 1 schematically shows a cross-sectional structure of a general molten Al-based plated steel sheet containing Si. An Al-based plating layer 3 is formed on the surface of the base steel plate 1 with an Al-Fe-Si-based alloy layer 2 interposed therebetween. The base of the Al-based plating layer 3 is an Al phase, and particles of an Si phase 4 having a needle shape are distributed therein. In addition, although a small amount of Al—Fe—Si phase may be mixed in addition to the Si phase 4 in the Al-based plating layer 3, the description is omitted.

FIG. 2 schematically shows a cross-sectional structure of a surface-treated steel sheet in which the surface of the Al-based plating layer in FIG. The upper layer portion of the original Al plating layer is changed to the anodic oxide film 5 by the anodic oxidation treatment. That is, the Al-based plating layer 3 (the portion where the original plating layer remains) and the anodized film 5 are present on the surface of the base steel plate 1 via the Al-Fe-Si-based alloy layer 2. The anodized film 5 is grown while forming pores in the depth direction from the surface of the original Al-based plating layer. At that time, the portion of the Al phase constituting the original Al-based plating layer is dissolved and replaced with an oxidizing substance mainly composed of Al ₂ O ₃ , but the metal Si phase is generally maintained in its original form. It remains inside the anodized film 5.

According to the study by the inventors, the anodic oxide film 5 formed on the surface of a molten Al-based plated steel sheet containing Si in the plating layer (hereinafter sometimes referred to as “Si-containing molten Al-based plated steel sheet”) is an aluminum product. As compared with the anodic oxide film formed on the surface, it was found that the insulating property was inferior. The Al ₂ O ₃ based oxide material which can be said to be the base of the anodic oxide film 5 has an insulating property, but the Si phase present therein has a conductivity. Inside the anodized film 5, there are many Si phase 4 particles straddling the boundary with the lower Al-based plating layer 3. Among the particles of the Si phase 4 straddling the boundary, there are particles having a tip located near the surface of the anodic oxide film 5, such as particles denoted by a in FIG. 2. Such Si phase particles reduce the electrical resistance between the vicinity of the surface of the anodic oxide film 5 and the Al-based plating layer 3 and become a factor of deteriorating the insulating properties of the anodic oxide film 5.

  In addition, the needle-like Si phase present in the Al-based plating layer of the Si-containing hot-dip Al-plated steel sheet tends to be an obstacle to stably forming an anodic oxide film having a uniform thickness. The Si phase whose tip is located near the surface of the plating layer causes local current concentration during the anodizing treatment, and causes an anodic oxide film to grow unevenly.

  FIG. 3 schematically shows a cross-sectional structure when the anodized film grows unevenly when the surface of the Al-based plating layer in FIG. 1 is anodized. The anodic oxide film 5 grows rapidly at the location where the current is concentrated, and may reach the Al—Fe—Si alloy layer 2 at an early stage. Where the Al-based plating layer 3 has disappeared, the underlying base steel plate 1 is likely to be eroded, which may lead to a decrease in corrosion resistance and a decrease in the adhesion of the anodized film 5.

  Recently, there is an increasing need to use a metal-based material having flexibility instead of a conventional ceramic or glass material as a substrate material that requires insulation, such as a solar cell substrate. An Al-based material can form an insulating anodic oxide film, and thus can be the above-mentioned substrate material. However, in consideration of material cost, strength, thermal expansion coefficient, etc., molten Al based on a steel material rather than an Al-based material. It is often advantageous to use a galvanized steel sheet. However, since a conventional Si-containing hot-dip Al-based plated steel sheet has the above-described Si phase in the plating layer, the anodized film formed on the upper layer portion is inferior in insulation. Further, depending on the anodizing conditions, there is a problem that uniformity of film thickness and film adhesion are liable to be impaired. A hot-dip Al-plated steel sheet using a pure Al bath containing no Si is liable to grow a brittle Al—Fe-based alloy layer and has poor workability. On the other hand, if a clad material obtained by joining a pure Al sheet to the steel plate surface by clad rolling is used, high insulation can be expected for the anodized film formed on the surface. However, the cladding material does not reach the hot-dip Al-based plated steel sheet in terms of productivity and cost.

  In view of the present situation, the present invention provides a surface-treated steel sheet in which an anodized film excellent in insulation and film thickness uniformity is formed using a hot-worked Al-based plated steel sheet containing Si. It is to try.

  The above object can be realized by subjecting the molten Al-based plated steel sheet obtained by spheroidizing the Si phase particles present in the molten Al-based plated layer to a predetermined shape by heat treatment.

  That is, in the present invention, a surface-treated steel sheet obtained by anodizing the surface layer portion of a hot-dip Al-based plated steel sheet having a Si content of 3.0 to 15.0% by mass, On the surface, an Al—Fe—Si alloy layer, an Al plating layer, and an anodic oxide film are sequentially provided. In the Al plating layer and the anodic oxide film, Si phase particles are dispersed, and the thickness direction The abundance of Si-phase particles having a plate thickness direction length of 10 μm or more in the Al-based plating layer and the anodized film in a cross section parallel to the surface is 100 particles / mm or less per unit length in the direction parallel to the substrate steel plate surface. Provided is a surface-treated steel sheet that is adjusted and has good insulation properties.

  The Al-based plating layer is, for example, in terms of mass%, Si: 3.0 to 15.0%, Sr: 0 to 0.2%, Na: 0 to 0.1%, Ca: 0 to 0.1%, Sb. : 0 to 0.6%, P: 0 to 0.2%, Mg: 0 to 5.0%, Cr: 0 to 1.0%, Mn: 0 to 2.0%, Ti: 0 to 0.0. 5%, Zr: 0 to 0.5%, V: 0 to 0.5%, B: 0 to 0.10%, the balance Al and inevitable impurities.

  In particular, by using a steel plate having an N content of 0.002 to 0.020 mass% as the base steel plate, AlN is precipitated between the base steel plate and the Al—Fe—Si alloy layer. can do. Thereby, even if it is a case where a temperature rise of 500 ° C. or more is involved in, for example, a semiconductor layer deposition process, the growth of the Al—Fe—Si based alloy layer can be remarkably suppressed.

As a manufacturing method of the above surface-treated steel sheet with good insulation,
Forming an Al-based plating layer via an Al-Fe-Si-based alloy layer on the surface of the base steel sheet using a molten Al-based plating bath having the above composition;
By heat-treating the steel sheet on which the Al-based plating layer is formed under the conditions of a heating temperature of 250 to 570 ° C. and a holding time of 0.5 to 50 h, the Si phase present in the Al-based plating layer is spheroidized, and the plate thickness A step of adjusting the abundance of Si phase particles having a plate thickness direction length of 10 μm or more in a cross section parallel to the direction to 100 particles / mm or less per unit length in the direction parallel to the substrate steel plate surface;
Forming an anodized film by anodizing the Al-based plating layer after the heat treatment;
A manufacturing method is provided.

  At that time, a steel plate having an N content of 0.002 to 0.020 mass% is used as the base steel plate, and AlN is formed between the base steel plate and the Al—Fe—Si alloy layer using the heat treatment. Can be deposited.

  According to the present invention, an anodized film excellent in insulation is stably formed using a molten Al-based plated steel sheet produced using a conventional general molten Al-based plating bath containing Si as a material. It became possible. The material on which the anodized film is formed is useful as a flexible substrate material. Moreover, even if it applies to the use with a temperature rise of 500 degreeC or more by the film-forming process of a semiconductor layer etc. by using what contains a predetermined amount of solid solution N as a base-material steel plate, Al-Fe- The growth of the Si-based alloy layer can be remarkably suppressed, and good workability and flexibility are maintained.

The figure which shows typically the cross-sectional structure of the general hot dip Al system plating steel plate containing Si. The figure which shows typically the cross-section of the surface treatment steel plate which performed the anodizing process on the surface of the Al-type plating layer of FIG. The figure which shows typically the cross-sectional structure when the anodized film grows nonuniformly when anodizing is performed on the surface of the Al-based plating layer of FIG. The figure which shows typically the cross-section of the hot-dip Al type plated steel plate in which the form of the Si phase particle in a plating layer was adjusted to the predetermined shape. The figure which shows typically the cross-section of the surface treatment steel plate according to this invention which performed the anodizing process on the surface of the Al type plating layer of FIG. A molten Al-based type in which a steel sheet having an N content of 0.002 to 0.020 mass% is used as the base steel sheet, and AlN is precipitated between the base steel sheet and the Al-Fe-Si alloy layer. The figure which shows typically the cross-section of a plated steel plate. The figure which shows typically the cross-section of the surface treatment steel plate according to this invention which performed the anodizing process on the surface of the Al type plating layer of FIG. The cross-sectional structure photograph of the surface-treated steel sheet which anodized the conventional general Si containing hot-dip Al plating steel sheet. The cross-sectional structure photograph of the surface-treated steel sheet which anodized the conventional general Si containing hot-dip Al plating steel sheet. The cross-section structure | tissue photograph of the surface treatment steel plate according to this invention which performed the anodic oxidation process to the hot-dip Al type plated steel plate in which the Si phase was spheroidized. The cross-section structure | tissue photograph of the surface treatment steel plate according to this invention which performed the anodic oxidation process to the hot-dip Al type plated steel plate in which the Si phase was spheroidized. The cross-sectional structure | tissue photograph of the part which the anodic oxide film grew non-uniformly when anodizing was performed to the conventional general Si containing hot-dip Al plating steel plate. The cross-sectional structure | tissue photograph of the part which the anodic oxide film grew nonuniformly and it melt | dissolved even to the base-material steel plate when anodizing was performed to the conventional general Si containing hot-dip Al plating steel plate. FIG. 14 is a cross-sectional structure photograph when an anodizing treatment of 15 min is attempted on a molten Al-based plated steel sheet having a spheroidized Si phase as in FIG. 13. The figure which shows the circuit structure for measuring the dielectric breakdown voltage of an anodized film.

[Cross-section structure]
FIG. 4 schematically shows a cross-sectional structure of a hot-dip Al-based plated steel sheet applicable to the present invention in which the form of Si phase particles in the plating layer is adjusted to a predetermined shape. The point which has the Al type plating layer 3 on the surface of the base-material steel plate 1 through the Al-Fe-Si type alloy layer 2 is the same as that of the conventional general hot-dip Al type plating steel plate shown in FIG. . However, the particle form of the Si phase 4 dispersed in the Al-based plating layer 3 is different. According to the present invention (FIG. 4), the Si phase 4 particles are spheroidized, and when the length in the plate thickness direction indicated by _{dt in the} drawing is measured for each Si phase 4 particle, The abundance of particles having a length _dt of 10 μm or more is adjusted to 100 particles / mm or less per unit length in the direction parallel to the surface of the base steel plate in a cross section parallel to the plate thickness direction. The abundance is measured within the entire thickness of the plating layer 3 over a length of 1000 μm or more in a direction parallel to the surface of the base steel plate 1 with respect to a cross section parallel to the plate thickness direction as illustrated in FIG. You can ask for it. The average thickness of the Al-based plating layer 3 is preferably more than 10 μm, and may be controlled to 15 μm or more. If the Al-based plating layer 3 is too thin, it may be difficult to form an anodized film that is stable and excellent in insulating properties while leaving the Al plating layer 3 sufficiently in the anodizing process.

FIG. 5 schematically shows a cross-sectional structure of a surface-treated steel sheet according to the present invention in which the surface of the Al-based plating layer in FIG. 4 is anodized. As in the case of FIG. 2, the upper layer portion of the original Al-based plating layer is changed to the anodized film 5 by the anodizing treatment, and the Al—Fe—Si-based alloy layer 2 is interposed on the surface of the base steel plate 1. Al-based plating layer 3 (portion where the original plating layer remains) and anodic oxide film 5 are present. As described above, the anodic oxide film 5 is grown while forming pores in the depth direction from the surface of the original Al-based plating layer, and the portion of the Al phase constituting the original Al-based plating layer is dissolved. As a result, it is replaced by an oxide substance mainly composed of Al ₂ O ₃ , but the Si phase remains in the anodic oxide film 5 while maintaining its original form.

  The average thickness of the anodized film 5 is desirably 5 μm or more for the purpose of insulation. It is more effective to set it to 10 μm or more. However, if a portion where the Al-based plating layer 3 disappears during the anodizing treatment occurs, the underlying base steel plate 1 may be dissolved at that portion, so the average thickness of the remaining Al-based plating layer 3 is 5 μm or more. It is desirable to ensure.

The particles of the Si phase 4 are spheroidized to shorten the plate thickness direction length d _t . There are Si phase particles that straddle the boundary between the anodic oxide coating 5 and the Al-based plating layer 3, but among these particles, the tip reaches the vicinity of the surface of the anodic oxide coating 5 (that is, the thickness of the anodic oxide coating 5. There are very few Si phase particles) that are likely to be a cause of lowering the insulation in the direction. For this reason, the insulation in the thickness direction of the anodic oxide film 5 is maintained high compared to the case of FIG.

It can be considered that the Si phase particles present in the Al-based plating layer and the anodized film after the anodizing treatment generally maintain the original form. Therefore, after the anodizing treatment, the abundance of Si-phase particles having a plate thickness direction length _dt of 10 μm or more in the Al-based plating layer and the anodized film is 100 per unit length in the direction parallel to the substrate steel plate surface. In order to obtain a surface-treated steel sheet having a thickness of / mm or less, as the Al-plated steel sheet before the anodizing treatment, the abundance of Si phase particles having a thickness direction length _dt of 10 μm or more in the Al-based plated layer is What is necessary is just to use what was adjusted to 100 pieces / mm or less per unit length of a parallel direction on the base-material steel plate surface. The abundance of the Si phase particles after the anodic oxidation treatment extends over a length of 1000 μm or more in the direction parallel to the surface of the base steel plate 1 in the cross section parallel to the plate thickness direction as illustrated in FIG. The total thickness of the Al-based plating layer 3 and the anodic oxide film 5 can be measured.

It has been found that the anodized film 5 of the surface-treated steel sheet in which the size of the Si phase particles existing in the Al-based plating layer and the anodized film is optimized as described above exhibits excellent insulating properties. The average thickness of the anodic oxide film 5 is preferably 10 μm or more, but even if the average thickness of the anodic oxide film 5 is about 5 μm, the abundance of Si phase particles having _dt of 10 μm or more is 100. If the particles of the Si phase 4 are spheroidized so as to be equal to or less than / mm, the insulation is greatly improved as compared with the case of using a conventional Si-containing hot-dip Al-based steel sheet. The spheroidization of the Si phase particles can be realized by performing a heat treatment described later after the molten Al-based plating.

  In FIG. 6, a steel sheet having an N content of 0.002 to 0.020 mass% is used as the base steel sheet, and AlN is precipitated between the base steel sheet and the Al—Fe—Si based alloy layer. The cross-sectional structure of the hot-dip Al type plated steel plate applicable to this invention is shown typically. An AlN enriched zone 6 exists between the base steel plate 1 and the Al—Fe—Si alloy layer 2. The AlN enriched zone 6 can be generated using heat treatment for spheroidizing the Si phase 4. The presence of the AlN concentrated zone 6 can be confirmed by an electron beam diffraction by TEM, an analysis method such as EDX, or the like.

  FIG. 7 schematically shows a cross-sectional structure of a surface-treated steel sheet according to the present invention in which the surface of the Al-based plating layer in FIG. 6 is anodized. Except for the presence of the AlN enriched band 6 between the base steel plate 1 and the Al—Fe—Si based alloy layer 2, the structure is the same as in FIG. 5. The AlN concentration band 6 is a barrier that suppresses the reaction of Fe in the base steel sheet 1 with Al and Si in the Al-based plating layer 3 when the steel sheet is subsequently heat-treated at a temperature of about 500 ° C. or higher. And inhibits the growth of the brittle Al—Fe—Si alloy layer 2. Therefore, when it is necessary to form a semiconductor layer or the like on the anodized film 5 at a high temperature of about 500 ° C. or higher, excessive growth of the Al—Fe—Si alloy layer 2 is prevented, and deformation as a substrate is prevented. Performance degradation can be suppressed. The surface-treated steel sheet according to the present invention of the type having the AlN concentrated band 6 is suitable for a device that requires flexibility of the substrate.

[Composition of base steel sheet]
As the base steel plate, various steel types are used depending on the purpose, including steel types that have been conventionally applied as a plating base plate of a molten Al-based plated steel plate. Stainless steel may be used for applications that place importance on corrosion resistance. However, when used for a film formation substrate, ferritic stainless steel is more advantageous than austenitic stainless steel from the viewpoint of thermal expansion coefficient. In addition, when expecting the growth inhibitory effect of the Al-Fe-Si alloy layer by the above-mentioned AlN concentration zone, the steel plate whose N content is 0.002-0.020 mass% is used. If the N content is less than this, it is difficult to sufficiently form an AlN concentrated band by heat treatment for spheroidizing the Si phase in the Al-based plating layer. Conversely, if the N content is excessive, the steel becomes hard, which is not preferable.

[Composition of Al plating]
The hot-dip Al-based plated steel sheet to be applied in the present invention has a Si content in the plating layer of 3.0 to 15.0% by mass. The composition of the molten Al-based plating bath is generally reflected in the composition of the molten Al-based plating layer as it is. If the Si content is too small, the Al—Fe (—Si) -based alloy layer formed at the time of hot dipping is likely to be thick, and cracks are likely to occur in the Al—Fe (—Si) -based alloy layer during processing. Further, the effect of lowering the liquidus temperature of the Al-based plating bath due to the addition of Si is reduced, and the cost for maintaining the plating bath temperature high is increased. On the other hand, when the Si content is excessively high, the liquidus temperature is increased again exceeding the eutectic composition, and the Si phase is coarsened as an initial crystal to impair the workability of the plating layer itself. The Si content in the Al-based plating layer is more preferably 5.0 to 13.0% by mass.

  The molten Al-based plating bath contains Si in the above range. However, Fe is inevitably mixed in the bath from a steel plate as a plating original plate, a constituent member of a pot, or the like. The mixing amount of Fe is allowed up to 3.0% by mass. The plating bath may contain elements other than Si as necessary. For example, in mass%, Si: 3.0 to 15.0%, Sr: 0 to 0.2%, Na: 0 to 0.1%, Ca: 0 to 0.1%, Sb: 0 to 0.6 %, P: 0 to 0.2%, Mg: 0 to 5.0%, Cr: 0 to 1.0%, Mn: 0 to 2.0%, Ti: 0 to 0.5%, Zr: 0 It can be set as a composition which consists of -0.5%, V: 0-0.5%, B: 0-0.10%, remainder Al and an unavoidable impurity. Sr, Na, Ca, Sb, P, Mg, Cr, Mn, Ti, Zr, V, and B are optional additive elements. When one or more of these elements are contained, Sr: 0.005 to 0.2 %, Na: 0.005 to 0.1%, Ca: 0.005 to 0.1%, Sb: 0.005 to 0.6%, P: 0.005 to 0.2%, Mg: 0.00. 05-5.0%, Cr: 0.05-1.0%, Mn: 0.05-2.0%, Ti: 0.005-0.5%, Zr: 0.05-0.5% , V: 0.05-0.5%, B: 0.005-0.10%, it is more effective to secure the content. Further, Mg may be managed within a range of 1.0 mass% or less, and Mn may be managed within a range of 1.0 mass% or less. Of the above elements, Sr, Na, Ca, Sb, and P have the effect of refining the Si phase particles in the plating layer.

〔Production method〕
The Si-containing molten Al-based plated steel sheet as a raw material can be obtained by a conventional general method. The Si content in the molten Al-based plating bath is 3.0 to 15.0% by mass as described above, and Sr, Na, Ca, Sb, P, Mg, Cr, Mn, Ti, Zr, as necessary. One or more of V and B are contained in the above range. The plating adhesion amount (plating layer average thickness) on the side subjected to the anodizing treatment is preferably more than 10 μm, and may be controlled to 15 μm or more.

  As shown in FIG. 1, an acicular Si phase is present in the Al-based plated layer of the obtained Si-containing hot-dip Al-plated steel sheet, and an anodic oxide film excellent in insulation can be stably formed as it is. It is difficult. Therefore, the molten Al-based plated steel sheet is heat treated to spheroidize the Si phase. When a base steel plate containing a predetermined amount of N is used, the above-described AlN enriched zone can be formed simultaneously by this heat treatment.

  In this heat treatment, the abundance of Si phase particles having a plate thickness direction length of 10 μm or more in a cross section parallel to the plate thickness direction is adjusted to 100 particles / mm or less per unit length in the direction parallel to the substrate steel plate surface. This is very important. The optimal heating conditions vary somewhat depending on the Si content in the plating layer and the hot dipping conditions, but according to the study by the inventors, the heating temperature ranges from 250 to 570 ° C. and the holding time ranges from 0.5 to 50 hours. The heating conditions can be set in the inside. In practice, an appropriate heating condition range corresponding to the Si content and the hot dipping conditions may be determined by preliminary experiments. Even when the AlN enriched zone is formed simultaneously, it is possible to find an appropriate heating condition within the range of the heating temperature and holding time.

  The surface-treated steel sheet according to the present invention can be obtained by subjecting the Al-based plating layer of the hot-dip Al-based plated steel sheet in which the size of the Si phase particles is optimized as described above. A well-known anodizing method can be employed. The average thickness of the anodized film is preferably 5 μm or more, more preferably 10 μm.

[Example of cross-sectional structure photograph]
FIG. 8 shows an optical micrograph of a cross section (C cross section) parallel to the plate thickness direction and perpendicular to the rolling direction of a material obtained by anodizing a molten Al-based plated steel plate having a Si content of 9.0 mass%. -Illustrated in FIG. The average thickness of the Al-based plating layer before the anodizing treatment is 37 μm (plating adhesion amount 100 g / m ² ). The anodizing conditions are as follows.
(Anodizing conditions)
・ Treatment solution: 150 g / L sulfuric acid + 5 g / L aluminum
・ Processing temperature: 40 ℃
Current density: 5.0 A / dm ²

  FIG. 8 and FIG. 9 show the conventional general Si-containing hot-dip Al-plated steel sheet subjected to anodizing treatment. The anodizing time is 5 min in FIG. 8 and 10 min in FIG. The base gray-colored portion of the base is a base steel plate, and the white layer above it is an Al-based plating layer. Between the base steel plate and the Al-based plating layer, Al-Fe- that appears slightly darker than the base steel plate There is a Si-based alloy layer. The layer that appears slightly grayer than the pure black on the Al-based plating layer is the anodized film, and the portion that appears black above it is the embedded resin. Particles that appear as dark gray dispersed in the Al-based plating layer and the anodized film are Si phases, and particles that appear lighter in gray (those that appear as gray as the Al-Fe-Si alloy layer) ) Is the phase of the Al-Fe-Si alloy. The appearance of each of the above parts is the same in each photo described later.

  It can be seen that the Si phase has a needle shape in an example using this conventional general Si-containing hot-dip Al-plated steel sheet. They exist in the anodized film while maintaining the original form. The acicular Si phase present in the anodic oxide film is a factor that lowers the insulating properties of the anodic oxide film as described above.

  FIG. 10 and FIG. 11 are surface-treated steel sheets according to the present invention in which a hot-dip Al-based plated steel sheet having a spheroidized Si phase is subjected to anodization. The anodizing time is 5 min in FIG. 10 and 10 min in FIG. The thickness of the Si phase particles is shorter than that of FIGS. 8 and 9, and the abundance of the Si phase particles having a thickness direction length of 10 μm or more is a unit in the direction parallel to the substrate steel plate surface. It is adjusted to 100 pieces / mm or less per length. In the anodized film, the number of Si phase particles reaching from the surface vicinity to the Al-based plating layer is very small. Therefore, the insulating property of the anodized film is maintained high.

  12 and 13 show anodized films grown unevenly when anodizing is performed on a conventional general Si-containing hot-dip Al-plated steel sheet. The anodizing time is 10 min in FIG. 12 and 15 min in FIG. Due to the presence of a long needle-like Si phase, current tends to concentrate locally during anodizing treatment, and the thickness of the anodized film tends to be nonuniform as shown in FIG. If a portion where the Al-based plating layer disappears is generated, the underlying base steel plate may be dissolved as shown in FIG.

  FIG. 14 shows an anodizing process for 15 min which was applied to a hot-dip Al-based plated steel sheet applicable to the present invention in which the Si phase was spheroidized, as in FIG. It can be seen that the anodized film grows very uniformly until just before the Al-based plating layer disappears. This is because the current concentration of the anodizing treatment hardly occurs because there is almost no needle-like long Si phase.

[Example 1]
The steel shown in Table 1 was melted, and a cold-rolled annealed steel sheet having a thickness of 0.8 mm was obtained by processes including hot rolling and cold rolling.

  Using the cold-rolled annealed steel plate as a plating base plate, molten Al-based plated steel plates having various Si contents were produced. Thereafter, heat treatment (Si phase spheroidization treatment) was performed to obtain an anodizing material. For comparison, an anodizing material not subjected to heat treatment was also prepared. A substrate of Si phase particles in which the cross section (C cross section) parallel to the plate thickness direction and perpendicular to the rolling direction of each anodizing material is observed with a microscope, and the plate thickness direction length in the Al-based plating layer is 10 μm or more. The abundance (units / mm) per unit length in the direction parallel to the steel sheet surface was determined. Further, after bending the anodic oxidation material by 2t and bending 180 °, a bending back test was performed, and the workability of the anodic oxidation material was examined by observing the adhesion of the plating layer.

  Next, the surface of the Al plating layer of each anodizing material was anodized to obtain a surface-treated steel sheet having an anodized film on the surface layer portion. The above-mentioned conditions were adopted as the anodizing treatment conditions, and the thickness of the anodized film was adjusted by changing the treatment time. About the obtained surface-treated steel sheet, the abundance (number / mm) of Si phase particles having a plate thickness direction length of 10 μm or more in the Al-based plating layer and the anodized film in a cross section parallel to the plate thickness direction was examined. . As a result, it was almost the same as the measurement result in the original Al-based plating layer.

  Tables 2 and 3 show the plating conditions, heat treatment conditions, the average thickness of the Al-based plating layer before the anodizing treatment, and the base material of the Si phase particles whose length in the plate thickness direction in the Al-based plating layer is 10 μm or more. The abundance (unit / mm) per unit length in the direction parallel to the steel sheet surface, and the average thickness of the anodized film are shown. Since the abundance of the Si phase particles having a plate thickness direction length of 10 μm or more after the anodizing treatment is the same as that before the anodizing treatment, the description is omitted in the table.

For the obtained anodized specimen, a voltage was applied in the thickness direction of the test piece with the circuit configuration shown in FIG. 15 using a withstand voltage / insulation measuring device (manufactured by Kikusui Electronics; TOS9201), A voltage at which a current of 2 mA or more flowed in a voltage application time of 10 sec was obtained by a method of measuring a direct current value while increasing the voltage stepwise, and the voltage was defined as a dielectric breakdown voltage. The electrode was 12φ, the evaluation surface having the anodized film was the positive electrode, the opposite surface was the negative electrode, and the sample surface with which the negative electrode was contacted was the polished surface of the base steel sheet. The plate thickness of the base steel plate is common at 0.8 mm. The applied voltage started from 10V. The test environment is at ambient temperature.
Tables 4 and 5 show the results. In Tables 4 and 5, the workability evaluation was evaluated as ○ (good workability) when no peeling of the Al-based plating layer was observed in the bending test of the above materials, and x (poor workability) otherwise. It is.

  Heat treatment is performed after hot-dip Al-based plating to spheroidize the Si-phase particles in the Al-based plating layer, and the abundance of Si-phase particles having a plate thickness direction length of 10 μm or more per unit length in the direction parallel to the substrate steel plate surface The example of the present invention set to 100 particles / mm or less is dielectric breakdown as compared with No. 28 in which heat treatment is not performed and No. 26 and 27 in which spheroidization of Si phase particles by heat treatment is insufficient. The voltage is significantly improved. Nos. 12-17, 25, 60-65, and 73 using a plating bath containing a small amount of Sr, Na, Ca, Sb, and P were obtained by refining the Si phase in the structure after plating. Compared with Nos. 4 and 53, which have the same content and heat treatment conditions, the abundance of Si phase particles having a length of 10 μm or more in the plate thickness direction is reduced, and accordingly, the breakdown voltage tends to be improved. It was. No. 1 was inferior in workability because an Al-Fe-based alloy layer grew thickly during hot dipping due to the use of a pure Al plating bath. In No. 7, since the Si content was excessive, the Si phase was coarsened as primary crystals, and in this case, the workability was also poor.

[Example 2]
Among the anodized specimens prepared in Example 1, several samples shown in Table 2 and samples using base steel plates containing N shown in Table 3 were 550 ° C. × 60 min. A heating test was performed. The cross section of the sample before and after the heating test was observed, and the change in the average thickness of the Al—Fe—Si based alloy layer was examined. The results are shown in Table 6.

  As can be seen from Table 6, the growth of the Al—Fe—Si alloy layer by the heating test is remarkably suppressed in the case of using the base steel plate (steel B, C) containing a predetermined amount of N. . As a result of analysis by EDX, the above-mentioned sample in which the growth of the Al-Fe-Si alloy layer is remarkably suppressed includes the base steel plate and the Al-Fe-Si alloy at the stage after the Si phase spheroidization treatment. Since enrichment of Al and N was observed in the vicinity of the interface of the layers, it is considered that the AlN enrichment zone functioned as a barrier to suppress the growth of the Al—Fe—Si based alloy layer. A material having such an AlN-concentrated band is deformable (processed) due to the growth of an Al—Fe—Si based alloy layer in applications where film formation is performed at 500 ° C. or higher, for example, when used as a substrate for a CIGS solar cell. This is advantageous in preventing the deterioration of the property. Even when a material having no AlN concentration band is subjected to a film forming process at 500 ° C. or higher, there is no particular problem in applications that do not require special flexibility.

DESCRIPTION OF SYMBOLS 1 Base steel plate 2 Al-Fe-Si type alloy layer 3 Al type plating layer 4 Si phase 5 Anodized film 6 AlN concentration zone

Claims (6)

  A surface-treated steel sheet obtained by anodizing the surface layer part of a hot-dip Al-based plated steel sheet having a Si content of 3.0 to 15.0% by mass. -Fe-Si alloy layer, Al plating layer and anodic oxide film in order, Si phase particles are dispersed in the Al plating layer and anodic oxide film, in a cross section parallel to the plate thickness direction Insulation in which the abundance of Si-phase particles having a plate thickness direction length of 10 μm or more in the Al-based plating layer and the anodized film is adjusted to 100 particles / mm or less per unit length in the direction parallel to the surface of the base steel plate Surface-treated steel sheet with good properties.   The Al-based plating layer is Si: 3.0 to 15.0%, Sr: 0 to 0.2%, Na: 0 to 0.1%, Ca: 0 to 0.1%, Sb: 0% by mass. -0.6%, P: 0-0.2%, Mg: 0-5.0%, Cr: 0-1.0%, Mn: 0-2.0%, Ti: 0-0.5% 2. The insulating property according to claim 1, having a composition comprising: Zr: 0 to 0.5%, V: 0 to 0.5%, B: 0 to 0.10%, the balance Al and inevitable impurities. Good surface treated steel sheet.   A steel plate having an N content of 0.002 to 0.020 mass% is used as the base steel plate, and AlN is precipitated between the base steel plate and the Al-Fe-Si alloy layer. A surface-treated steel sheet having good insulation properties as described in 1. Forming an Al-based plating layer via an Al-Fe-Si-based alloy layer on the surface of the base steel sheet using a molten Al-based plating bath having a Si content of 3.0 to 15.0% by mass;
By heat-treating the steel sheet on which the Al-based plating layer is formed under the conditions of a heating temperature of 250 to 570 ° C. and a holding time of 0.5 to 50 h, the Si phase present in the Al-based plating layer is spheroidized, and the plate thickness A step of adjusting the abundance of Si phase particles having a plate thickness direction length of 10 μm or more in a cross section parallel to the direction to 100 particles / mm or less per unit length in the direction parallel to the substrate steel plate surface;
Forming an anodized film by anodizing the Al-based plating layer after the heat treatment;
A method for producing a surface-treated steel sheet having good insulating properties.   The molten Al-based plating bath contains Si: 3.0 to 15.0%, Sr: 0 to 0.2%, Na: 0 to 0.1%, Ca: 0 to 0.1%, and Sb in mass%. : 0 to 0.6%, P: 0 to 0.2%, Mg: 0 to 5.0%, Cr: 0 to 1.0%, Mn: 0 to 2.0%, Ti: 0 to 0.0. 5. The composition according to claim 4, having a composition comprising 5%, Zr: 0 to 0.5%, V: 0 to 0.5%, B: 0 to 0.10%, the balance Al and inevitable impurities. A method for producing a surface-treated steel sheet with good insulation.   A steel plate having an N content of 0.002 to 0.020 mass% is used as the base steel plate, and AlN is precipitated between the base steel plate and the Al—Fe—Si alloy layer using the heat treatment. A method for producing a surface-treated steel sheet having good insulation properties according to claim 4 or 5.