JP2006207033A - Surface-treated steel sheet excellent in workability and corrosion resistance at worked area - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain excellent workability, excellent corrosion resistance at a worked area, and excellent roll formability in a surface-treated steel sheet comprising, as an underlying steel sheet, an Al-Zn dip-plated steel sheet whose plated film contains 20 to 95 mass% Al. <P>SOLUTION: The surface-treated steel sheet has a chemical conversion film comprising a chromate film with a specified Cr deposition amount on a plated steel sheet and a thermosetting organic resin film formed thereon and is desirably such a steel sheet that the plated film experiences at least the following heat histories (a) and (b): (a) a heat history wherein the average cooling rate in the 10-second period just after leaving the plating bath is lower than 11°C/second, and (b) a heat history wherein the average cooling rate during the period in which the sheet is heated to a temperature T (°C) in the range of 130 to 300°C after the coagulation of the plated metal and is then cooled from the temperature T (°C) to 100°C satisfies C (°C/hr) or smaller (wherein C=(T-100)/2 ) and/or a heat history wherein the average cooling rate during cooling from the temperature T (°C) in the range of 130 to 300°C after the coagulation of the plated metal to 100°C satisfies the above C (°C/hr) or smaller. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface-treated steel sheet in which a molten Al—Zn-based plated steel sheet having an Al content in a plating film of 20 to 95 mass% is a base steel sheet.

The hot-dip Al-Zn-based plated steel sheet containing 20 to 95 mass% of Al in the plating film exhibits excellent corrosion resistance as compared to the hot-dip galvanized steel sheet as shown in Patent Document 1, and has recently been focusing on the building material field. Demand is growing.
This plated steel sheet is manufactured as follows in a continuous hot dipping apparatus using a hot-rolled steel sheet pickled and descaled or a cold-rolled steel sheet obtained by further cold rolling the base steel sheet.
Japanese Patent Publication No.46-7161

  In the continuous hot dip plating facility, the base steel sheet was heated to a predetermined temperature in an annealing furnace maintained in a reducing atmosphere, and simultaneously with the annealing, the rolling oil adhered to the steel sheet surface was removed, and the oxide film was reduced and removed. Thereafter, the lower end passes through a snout immersed in the plating bath and is immersed in a hot dip galvanizing bath containing a predetermined concentration of Al. After the steel plate immersed in the plating bath is pulled up above the plating bath via the sink roll, a pressurized gas is sprayed from the gas wiping nozzle arranged on the plating bath toward the surface of the steel plate. The plating adhesion amount is adjusted and then cooled by a cooling device to obtain a molten Al—Zn-based plated steel sheet on which a predetermined plating film is formed.

Operating conditions such as annealing furnace heat treatment and atmosphere conditions, plating bath composition and cooling rate after plating in continuous hot dip plating equipment are accurately controlled within a prescribed control range to ensure the desired plating quality and material. The
The plating film of the plated steel sheet produced as described above is mainly composed of a part where Al containing Zn is supersaturated and dendrite solidified, and the remaining part of the dendrite gap. Laminated. Due to such a characteristic film structure, the molten Al—Zn-based plated steel sheet exhibits excellent corrosion resistance.

  In addition, Si of about 1.5 mass% is usually added to the plating bath, but due to the action of this Si, the molten Al-Zn-based plated steel sheet suppresses the alloy phase growth at the plating film / underlying steel sheet interface, and the alloy The phase thickness is about 1-2 μm. The thinner the alloy phase is, the more portions of the characteristic film structure exhibiting excellent corrosion resistance. Therefore, the suppression of the growth of the alloy phase contributes to the improvement of the corrosion resistance. In addition, since the alloy phase is harder than the plating film and acts as a starting point of cracks during processing, suppressing the growth of the alloy phase reduces the occurrence of cracks and brings about an effect of improving workability. Moreover, since the base steel plate is exposed in the crack portion and the corrosion resistance is poor, reducing the occurrence of cracks also improves the corrosion resistance of the processed portion.

Usually, the plating bath contains unavoidable impurities, Fe eluted from the steel plate and equipment in the plating bath, Si for alloy phase suppression, but some elements may be added in addition to them, In the alloy phase and the plating film, these elements exist in the form of an alloy or a simple substance.
In addition, hot-dip Al-Zn-based plated steel sheets are rarely used as hot-plated as they are put to practical use, and are usually used as surface-treated steel sheets that have been subjected to chemical conversion treatment or coating on the surface of the plated steel sheet. The

The plating film of the above-mentioned molten Al—Zn-based plated steel sheet has the problem that the plating tends to “galling” when it is slid by contact with the mold during roll forming, and the appearance quality is likely to deteriorate. There is. This is because, from the viewpoint of rationalization, when molding without oiling or processing without coolant, the temperature of the mold rises due to continuous processing, which acts as a more severe condition for processing. It is thought that. For the purpose of improving roll forming properties, Patent Document 2 proposes a method of coating the plating surface with a film containing an organic resin. However, according to this method, although the roll forming property is improved to some extent, the improvement effect can be obtained with a good appearance quality without “galling” even under severe processing conditions where the temperature of the mold rises due to processing. It ’s not that.
Japanese Patent Publication No.4-2672

  Moreover, when the above-described molten Al—Zn-based plated steel sheet is subjected to processing such as bending, cracks occur in the plating film of the processed part depending on the degree of processing. In this plated steel sheet, the alloy phase with a thickness of about 1 to 2 μm present at the interface between the plated film and the underlying steel sheet becomes the starting point of cracks, and the dendrite gap of the plated film becomes the propagation path of cracks, so the same degree of processing. Even in the case of performing cracking, cracks tend to open relatively large compared to hot-dip galvanized steel sheets having the same plating film thickness. Therefore, depending on the degree of processing, there is a problem that the crack is visually recognized with the naked eye and the appearance is impaired. Furthermore, as described above, the hot-dip Al-Zn-based plated steel sheet exhibits superior corrosion resistance compared to the hot-dip galvanized steel sheet having the same plating film thickness, but the exposed cracked part of the base steel sheet is compared with the part without cracks. Therefore, there is a problem that the corrosion resistance is remarkably lowered.

For such a problem, for example, Patent Document 3 discloses a method for improving the ductility of a plated steel sheet by subjecting a molten Al—Zn plated steel sheet to a predetermined heat treatment. However, it is difficult to sufficiently improve the ductility of the plating film only by such conventional heat treatment.
Moreover, as above-mentioned, it is normal to use a fusion | melting Al-Zn type plated steel plate as a chemical conversion treatment steel plate which performed the chemical conversion treatment on the surface, and the coated steel plate which gave the coating. And, from the viewpoint of suppressing crack occurrence at the processed part by processing such as bending, even if the ductility of the plating film is improved to some extent as in the above prior art, performance as a product that is practically used, that is, chemical conversion treatment In addition, the workability as a surface-treated steel sheet with coating or the corrosion resistance of the processed part is not immediately improved.
Japanese Patent Publication No. 61-28748

  Therefore, an object of the present invention is to use a molten Al-Zn-based plated steel sheet having an Al content in the plating film of 20 to 95 mass% as a base steel sheet, and obtain excellent workability, processed part corrosion resistance, and roll forming properties that have not been achieved conventionally. The object is to provide a surface-treated steel sheet.

  In order to solve the above-mentioned problems, the present inventors set a viewpoint on the performance as a surface-treated steel sheet obtained by subjecting a practical product, that is, a molten Al-Zn-based plated steel sheet, to chemical processing, workability, corrosion resistance of a processed part, and roll forming property. In order to improve the properties such as the above, we have conducted intensive studies on the optimal plating film and chemical conversion film structure. As a result, by forming a specific chemical conversion treatment film on the plating film surface of the molten Al—Zn-based plated steel sheet, more preferably, the plating film has undergone a specific thermal history, which cannot be achieved conventionally. It has been found that extremely excellent processability, processed part corrosion resistance and roll forming properties can be obtained.

The present invention has been made based on such findings, and the features thereof are as follows.
[1] A surface-treated steel sheet having a chemical conversion coating on the surface of a molten Al-Zn-based plated steel sheet having an Al content in the plated film of 20 to 95 mass%,
The chemical conversion coating, and chromate coating Cr deposition amount is less than 0.1 mg / m ² or more 100 mg / m ² of metallic chromium conversion which is formed on the plating film surface, a coating formed thereon, heat A surface-treated steel sheet excellent in workability and processed portion corrosion resistance, characterized by comprising an organic resin film having a film thickness of 0.1 to 5 μm using a curable organic resin as a film-forming resin.

[2] In the surface-treated steel sheet according to [1], the plated film is a plated film obtained through at least the following thermal history (a) and (b), and has excellent workability and processed part corrosion resistance Surface treated steel sheet.
(A) Thermal history in which the average cooling rate for 10 seconds immediately after the steel sheet exits the hot dipping bath is less than 11 ° C./sec. (B) After the hot dipped plated metal solidifies, it is in the range of 130 to 300 ° C. A heat history that is heated to a temperature T (° C.) and thereafter satisfies an average cooling rate from the temperature T (° C.) to 100 ° C. below C (° C./hr) shown in the following formula (1):
Or / and the average cooling rate from the temperature T (° C.) in the range of 130 to 300 ° C. to 100 ° C. after solidification of the hot-plated plated metal is below C (° C./hr) shown in the following formula (1) Heat history satisfying C = (T-100) / 2 (1)

[3] In the surface-treated steel sheet according to [1] or [2] above, the heat history temperature T (° C.) of (b) is in the range of 130 to 200 ° C. Excellent surface-treated steel sheet.
[4] A coated steel sheet, wherein a single-layer or multi-layer coating film is formed on the surface of the surface-treated steel sheet according to any one of [1] to [3].

  The surface-treated steel sheet of the invention according to claim 1 of the present application is a surface-treated steel sheet whose base steel sheet is a molten Al—Zn-based plated steel sheet having an Al content of 20 to 95 mass% in the plating film, and has an extremely excellent processed portion. Corrosion resistance and roll forming properties. In addition, the surface-treated steel sheet according to claims 2 and 3 of the present application has excellent workability and roll forming property, and particularly excellent processed portion corrosion resistance.

The surface-treated steel sheet of the present invention uses a molten Al-Zn-based plated steel sheet containing 20 to 95 mass% Al in the plating film as a base steel sheet. Moreover, from a viewpoint of corrosion resistance and the like, a preferable range from the amount of Al in the plating film is 45 to 65 mass%. Moreover, the particularly preferable component composition of the plating film is Al: 45 to 65 mass%, Si: 0.7 to 2.0 mass%, Fe: less than 10 mass%, and the balance is substantially Zn containing inevitable impurities. In the case of such a composition, particularly excellent corrosion resistance is exhibited. However, this molten Al—Zn-based plated steel sheet is difficult to obtain high processed part corrosion resistance only by its plating composition, and it is preferable to combine a chemical conversion treatment film of the upper layer, and more preferably to give a thermal history to the plating film described later Only in combination, excellent processed portion corrosion resistance can be obtained.
Moreover, although there is no restriction | limiting in particular in the plating adhesion amount of this fusion | melting Al-Zn type plated steel plate, Generally it is appropriate to set it as about 30-120 g / m < ² > per single side | surface.

In the surface-treated steel sheet of the present invention, the chemical conversion treatment film formed on the plating film surface has a Cr deposition amount in terms of metal chromium formed on the plating film surface of 0.1 mg / m ² or more and less than 100 mg / m ² , preferably A chromate film of 5 mg / m ² or more and 40 mg / m ² or less, and a film formed thereon, and a film thickness of 0.1 to 5 μm, preferably 0.5, using a thermosetting organic resin as a film-forming resin. It consists of an organic resin film of ˜3 μm.

The chromate film has the effect of improving the corrosion resistance by passivating the plating surface. If the chromium adhesion amount in terms of chromium metal of the chromate film is less than 0.1 mg / m ² , the effect of improving the corrosion resistance is insufficient, while if the Cr adhesion amount is 100 mg / m ² or more, the corrosion resistance improvement effect commensurate with the adhesion amount is obtained. Not only cannot be obtained, but the appearance quality deteriorates due to coloring, which is not preferable.

  Silica can be added to the chromate film, thereby improving the adhesion with the upper organic resin film, and performing a heat treatment to give a specific heat history to the plating film after the chemical conversion treatment. The effect which prevents the corrosion-resistant fall of a chemical conversion treatment film is acquired. As for the type of silica to be added, dry silica is more effective in terms of improving the adhesion to the upper resin film, while wet silica is more effective in terms of preventing deterioration in corrosion resistance due to heat treatment. Therefore, what is necessary is just to select the kind of silica added according to the objective. As addition amount of a silica, 1-50 mass% by the ratio of the solid content in a film | membrane, Preferably 5-30 mass% is desirable.

In addition, additives other than silica may be added as appropriate to the chromate film. For example, for the purpose of improving corrosion resistance and preventing coloring, mineral acids, fluorides, phosphoric acid, phosphoric acid compounds, Ni, Co, Metal salts such as Fe, Zn, Mg, and Ca may be added.
In the chromate treatment, after a chromate treatment solution is applied to the surface of the plated steel sheet, it is usually dried by heating at a temperature of 80 to 250 ° C. to form a chromate film.

The organic resin film formed on the chromate film is a film having a film thickness of 0.1 to 5 μm using a thermosetting organic resin as a film-forming resin.
The organic resin in the organic resin film needs to be a thermosetting resin. When continuous roll forming is applied to the surface-treated steel sheet, the roll temperature rises greatly. When the organic resin contained in the chemical conversion coating is a normal thermoplastic resin or general emulsion resin, the roll temperature is increased. The film is damaged by the rise, and the appearance after processing deteriorates. Therefore, as a result of studying to solve such problems, the use of a thermosetting resin as the organic resin for the film dramatically increases the scratch resistance at high temperatures, resulting in continuous roll forming. It was also found that there was no problem in the appearance after processing.

  Here, the thermosetting resin is an addition or condensation reaction between functional side chains of an organic polymer, or between an organic polymer and a curing agent, or a main chain or a side chain by heating during film formation. It is a resin that undergoes a cross-linking reaction such as radical polymerization using a heavy bond. Examples of the thermosetting resin include alkyd resin, polyester resin, polyurethane resin, acrylic resin, epoxy resin, styrene resin, and modified resins thereof. One or more types can be used. Of these, polyester resins, polyurethane resins, and acrylic resins are particularly desirable from the viewpoint of processability. The thermosetting resin as described above includes a water dispersion system and a solvent system, and any of them may be used.

These resins are cured by a crosslinking reaction caused by heating after application of the resin solution. The curing temperature varies depending on the type of resin and the type of curing agent. In the present invention, the type and addition amount of the curing agent, the heating temperature after application of the resin solution, and the heating time are not particularly limited, and the resin solution may be completely cured by heating after application, It may be cured to an appropriate state by heating (a cured state in which the film does not fall off due to contact with a sheet-passing roll) and then completely cured by a subsequent heat treatment.
When the film thickness of the organic resin film is less than 0.1 μm, the roll forming property is insufficient. On the other hand, when the film thickness exceeds 5 μm, the adhesion of the resin to the molding roll increases, which is not preferable.

In the surface-treated steel sheet of the present invention, when heat treatment is performed after the formation of the chemical conversion coating to impart a specific thermal history as described later to the plating film, the characteristics of the organic resin contained in the chemical conversion coating may be impaired. In this case, it is effective to add an inorganic additive (fine particles) to the chemical conversion film (organic resin film). As an inorganic additive, it is possible to mix | blend 1 or more types, such as a silica, a phosphoric acid type compound, and a silicic acid compound (for example, Ca salt, Mg salt).
Further, in the surface-treated steel sheet of the present invention, since the lower layer of the chemical conversion film is a chromate film, the organic resin film does not contain Cr. For this reason, the surface-treated steel sheet has a performance that is particularly excellent in Cr elution resistance.

In the surface-treated steel sheet of the present invention, the plated film of the molten Al-Zn-based plated steel sheet is preferably a plated film obtained through at least the following thermal history (a) and (b), ) And (b), by forming the above-described specific chemical conversion coating on the surface of the plating coating, particularly excellent workability and processed portion corrosion resistance can be obtained.
(A) Thermal history in which the average cooling rate for the first 10 seconds immediately after the steel sheet exits the hot dipping bath is less than 11 ° C./sec. (B) After the hot dipped plated metal solidifies, it is 130 to 300 ° C. A heat history that is heated to a temperature T (° C.) in the range, and thereafter, an average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less shown in the following formula (1):
Or / and the average cooling rate from the temperature T (° C.) in the range of 130 to 300 ° C. to 100 ° C. after the hot-plated plated metal solidifies is below C (° C./hr) shown in the following formula (1) Heat history satisfying C = (T-100) / 2 (1)

In the thermal history of (b) above, a more preferable range of the temperature T (° C.) is 130 to 200 ° C.
Here, the above formula (1) is a detailed study by the present inventors based on experiments on the influence of the heating condition of the plating film and the subsequent cooling conditions and the cooling condition after solidification of the hot-plated plated metal on the plating film. The empirical formula derived as a result.

  By making the plating film have undergone the thermal history of (a) and (b) above, the workability (such as crack resistance) is remarkably improved while it is a molten Al—Zn plating film. The reason why the workability of the plating film is remarkably improved by passing through the thermal history of (a) and (b) is considered as follows. First, immediately after the steel sheet exits the hot dipping bath, the heat history of (a) above, that is, the hot history obtained by sufficiently slowing down the average cooling rate for 10 seconds immediately after the hot dipping bath is obtained, Since the solidification of the alloy becomes closer to the equilibrium state than the solidification by the normal cooling process, the two-phase separation of Al and Zn is promoted by the diffusion in the semi-molten state, and as a result, the plating film becomes soft. Then, the plating film that has undergone such a thermal history is further heated at a temperature range of (b) above, that is, 130 to 300 ° C. (preferably 130 to 200 ° C.) and then gradually cooled under specific conditions. To a plating film at the time of solidification by passing through a thermal history that is gradually cooled under specific conditions from a temperature range of 130 to 300 ° C. (preferably 130 to 200 ° C.) after solidification of the plating film and / or plating film. While the accumulated strain is released, solid diffusion occurs in the plating film, and the two-phase separation of Al and Zn in the plating film caused by the thermal history of (a) is further effectively promoted. As a result, it is considered that the plating film is remarkably softened and its workability is remarkably improved.

  Therefore, the softening of the plating film and the remarkable improvement in workability associated therewith are due to the combined action of the thermal histories (a) and (b) above, and only one of the thermal histories. It is difficult to achieve with.

Hereinafter, the details of the thermal history of the above (a) and (b) will be described.
First, regarding the thermal history of (a) above, the average cooling rate of the plating film for the first 10 seconds immediately after the steel sheet exits the hot dipping bath is less than 11 ° C./sec. Since the solidification of the film becomes closer to the equilibrium state than the solidification by the normal cooling process, the two-phase separation of Al and Zn is promoted by the diffusion in the semi-molten state, thereby softening the plating film. When the average cooling rate in the first 10 seconds immediately after the steel plate exits the hot dipping bath is 11 ° C./sec or more, the solidification rate is too high, so that the hot dipping of the hot dipped coating proceeds in a non-equilibrium state, and in a semi-molten state. Since a certain time is short, the two-phase separation of Al and Zn is not sufficiently promoted, and the softening of the plating film due to the combination with the thermal history of (b) cannot be sufficiently achieved.

FIG. 1 shows the effect of the average cooling rate of the plating film for the first 10 seconds immediately after the steel sheet exits the hot dipping bath on the workability of the surface-treated steel sheet. These are surface-treated steel sheets in which a chemical conversion film satisfying the conditions of the present invention is formed on a plated steel sheet in which the plated film is manufactured through the thermal history of (b) above. The evaluation of workability in this test was performed in accordance with the evaluation of workability in Examples described later.
As shown in FIG. 1, when the average cooling rate of the plating film in the first 10 seconds immediately after the steel plate exits the hot dipping bath is 11 ° C./sec or more, the score of workability in 0T bending is 2 points or less. It is. On the other hand, when the average cooling rate of the plating film is less than 11 ° C./sec, the score of workability is 4 points or more, indicating that the workability is remarkably improved.

  In order for the plating film to have undergone the thermal history described in (a) above, a temperature adjusting device must be installed between the hot dipping bath surface of the continuous hot dipping equipment and the roll where the steel plate that has exited the hot dipping bath first comes into contact. It is necessary to control the cooling rate of the plating film by this temperature adjusting device. As the temperature adjusting device, it is preferable to provide a heating or heat retaining means and a cooling means as necessary. This cooling means cools the plated steel sheet whose plating film cooling rate is controlled by the heating or heat retaining means before it contacts the first roll (top roll, etc.), and picks up on the roll surface. This is intended to prevent the above. For example, an induction heater or a gas heating furnace can be used as the heating or heat retaining means of the temperature adjusting device, and a gas spraying apparatus or the like can be used as the cooling means. However, there are no particular restrictions on the method, shape, scale, etc. of the heating or heat retaining means or cooling means possessed by the temperature adjustment device, and in short, as long as the thermal history of (a) above can be imparted to the plating film Good.

  Next, regarding the thermal history of (b) above, the plating film (plating film after the hot-plated plated metal is solidified) having undergone the thermal history of (a) is 130 to 300 ° C., preferably 130 to 200. The temperature is raised to a temperature T (° C.) in the range of ° C., and then the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less shown in the above equation (1). The cooling rate or the average cooling rate from the temperature T (° C.) in the range of 130 to 300 ° C. to 100 ° C., which is the cooling process of the plated film after the hot-plated plated metal is solidified, is the above (1) By cooling so as to satisfy C (° C./hr) or less shown in the formula, the strain accumulated in the plating film is released as described above, and solid diffusion occurs in the plating film, and the above (a) Al in the plating film caused by the thermal history of Two-phase separation of n can be more effectively promoted. The plating film is remarkably softened by the combined action of the heat history and the heat history (a), and the workability is remarkably improved.

Here, when the heating / heating temperature T of the plating film in the thermal history of (b) is less than 130 ° C., the above effect cannot be obtained sufficiently, while when the heating / heating temperature T exceeds 300 ° C., the base steel plate In order to promote the growth of the alloy phase at the interface between the film and the plating film, the workability is adversely affected. From such a viewpoint, the upper limit of the heating temperature T that is more preferable for improving the workability is 200 ° C.
Moreover, also about the case where it cools on the conditions to which the thermal history of said (b) is provided from the temperature T (degreeC) of the range of 130-300 degreeC which is the cooling process after the hot-plated plated metal solidifies, If the temperature T is less than 130 ° C., the above-described effects cannot be obtained sufficiently.

  Fig. 2 (a) shows the effect of the heating temperature of the plating film on the workability of the surface-treated steel sheet when heat-treating the plated steel sheet after the hot-plated plated metal solidifies. In all of the test materials obtained as a result, the average cooling rate of the plating film from the heating temperature to 100 ° C. is within the condition of the thermal history of (b) above, and the plating film of the above (a) It is the surface treatment steel plate which formed the chemical conversion treatment film which satisfies the conditions of the present invention on the plating steel plate manufactured through heat history. The evaluation of workability in this test was performed in accordance with the evaluation of workability in Examples described later.

  Fig. 2 (b) shows the surface treatment of the average cooling rate of the plating film (average cooling rate from the heating temperature to 100 ° C) when the plated steel sheet after the hot-plated plated metal solidifies is heat-treated. Investigating the effect on the workability of the steel sheet, all of the test materials obtained as a result, the heating temperature of the plating film is within the condition of the thermal history of (b) above, and the plating film Is a surface-treated steel sheet in which a chemical conversion coating is formed on a plated steel sheet produced through the thermal history of (a) above. The evaluation of workability in this test was performed in accordance with the evaluation of workability in Examples described later.

  As shown in FIGS. 2 (a) and 2 (b), when the heating temperature of the plating film is in the range of 130 to 300 ° C., the score of workability of 0T bending is 4 or more, which is a preferable condition. In the range of ˜200 ° C., the workability score is 4 to 5 points. On the other hand, when the heating / heating temperature is outside the range of 130 to 300 ° C., only 3 scores of workability are obtained. In addition, when the difference between the average cooling rate from the heating temperature to 100 ° C. and “C” in the above equation (1) is zero to minus (within the range of the present invention), the 0T bending workability rating is 4 On the other hand, when the difference is plus (outside the scope of the present invention), only 3 points of workability are obtained.

In order for the plating film to have undergone the thermal history of (b) above, a heating or heat retention device for heat-treating or heat-retaining the plating film is provided in the continuous hot-dip plating facility or outside the facility, Heat treatment or heat retention is performed. For example, a heating mechanism (for example, an induction heater, a gas heating furnace, a hot blast furnace, etc.) may be provided in a continuous hot dip plating facility and continuously heated inline, or after being wound on a coil and offline. You may carry out by batch heating. Moreover, you may carry out by heating continuously with a heating mechanism (for example, an induction heater, a gas heating furnace, a hot stove etc.) in the continuous processing equipment outside a plating line. Furthermore, you may perform appropriate heat retention or heat retention after winding the plated steel plate continuously heated by the plating line or the said continuous processing equipment to a coil. Moreover, you may provide the heat retention apparatus which heat-retains a plating film in the cooling process after the hot-plated plating metal solidifies, and can cool gradually.
However, there are no particular restrictions on the system, shape, scale, etc. of the heating or heat retention device, and the point is that it can provide the thermal history of (b) above to the plating film.

Next, the manufacturing method of the said surface treatment steel plate by this invention is demonstrated.
The production method of the present invention uses a molten Al-Zn-based plated steel sheet having an Al content of 20 to 95 mass% in a plated film produced by a continuous hot-dip plating facility as a base steel sheet, and forms a chemical conversion film on the surface. A method for producing a surface-treated steel sheet, the step of imparting at least the following thermal history (a) and (b) to the plating film on the steel sheet that has exited the hot dipping bath, and a specific formation on the surface of the plated steel sheet Forming a treatment film.
(A) Thermal history in which the average cooling rate for 10 seconds immediately after the steel sheet exits the hot dipping bath is less than 11 ° C./sec. (B) After the hot dipped plated metal solidifies, it is in the range of 130 to 300 ° C. Heat history that is heated to a temperature T (° C.), and thereafter the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less shown in the following formula (1):
Or / and the average cooling rate from the temperature T (° C.) in the range of 130 to 300 ° C. to 100 ° C. after the hot-plated plated metal solidifies is below C (° C./hr) shown in the following formula (1) Heat history satisfying C = (T-100) / 2 (1)

Of the thermal histories (a) and (b) given to the plating film, the thermal history (a) is given by controlling the cooling conditions of the plating film immediately after plating.
In order to impart the thermal history of (a) to the plating film, as described above, the temperature adjustment is performed from the hot dipping bath surface of the continuous hot dipping equipment to the roll where the steel plate that has come out of the hot dipping bath first comes into contact. It is necessary to provide a device and control the cooling rate of the plating film by this temperature adjusting device. As described above, the temperature control device preferably includes heating or heat retention means and, if necessary, cooling means. However, the heating, heat retention means and cooling means are specially provided for the system, shape, scale, etc. There is no particular limitation, as long as it can give the thermal history of (a) to the plating film. For example, an induction heater or a gas heating furnace can be used as the heating or heat retaining means of the temperature adjusting device, and a gas spraying apparatus or the like can be used as the cooling means.

  In addition, the thermal history given in (b) above may be applied to the plated steel sheet after the hot-plated plated metal is solidified, or the plated film after the hot-plated plated metal is solidified. This is done by controlling the cooling of the battery by heat retention or the like. In the production method of the present invention, a specific chemical conversion treatment film is formed on the plated film surface of the plated steel sheet. The heat treatment for imparting the thermal history of (b) above to the plating film is carried out by (i) before the formation of the chemical conversion treatment film. , (Ii) during the chemical conversion treatment film drying step, (iii) after the formation of the chemical conversion treatment coating (after the coating of the treatment liquid and the formation of the coating film by the drying step). Moreover, you may carry out in two or more steps of these.

Therefore, the application of the thermal history of (b) to the plating film can be performed in at least one of the following (1) to (4).
(1) Before formation of chemical conversion coating (2) During drying process of chemical conversion coating (3) After formation of chemical conversion coating (4) Cooling process after solidification of hot-plated plated metal Among the methods, the method (i) has the advantage that each condition of the heat treatment step and the chemical conversion treatment step can be optimized independently, and (ii) and (iii)
This method is suitable for performing all treatments in a continuous hot dip plating facility. Further, the method (ii) is particularly economical because the heat treatment is performed using the heating in the drying step of the chemical conversion treatment.

The heat treatment or heat retention for imparting the thermal history (b) is performed by a heating or heat retention device or the like provided in the continuous hot dip plating facility or outside the facility. A heating mechanism (for example, an induction heater, a hot blast furnace, etc.) may be provided in the continuous hot dip plating equipment, and may be continuously heated in-line, or may be batch-heated offline after being wound on a coil. Also good. Moreover, you may carry out by heating continuously with a heating mechanism (for example, an induction heater, a hot stove, etc.) in the continuous processing equipment outside a plating line. Furthermore, you may perform appropriate heat retention or heat retention after winding the plated steel plate continuously heated by the plating line or the said continuous processing equipment to a coil. Moreover, you may provide the heat retention apparatus which heat-retains a plating film in the cooling process after the hot-plated plating metal solidifies, and can cool gradually. However, there are no particular restrictions on the system, shape, scale, etc. of the heating or heat retention device, and the point is that it can provide the thermal history of (b) above to the plating film.
In addition, the preferable plating composition of the molten Al—Zn-based plated steel sheet to be produced, the coating adhesion amount, the reasons for limiting the thermal history of the above (a) and (b), the obtained effects and the like are as described above.

In the production method of the present invention, the surface of the plated steel sheet is subjected to chromate treatment, and the Cr adhesion amount in terms of metal chromium is 0.1 mg / m ² or more and less than 100 mg / m ² , preferably 5 mg / m ² or more and 40 mg / m ² or less. Then, an organic resin film having a film thickness of 0.1 to 5 μm, preferably 0.5 to 3 μm, having a thermosetting organic resin as a film-forming resin is formed thereon.
In the chromate treatment, a chromate treatment solution to which an additive such as silica is added as required is applied to the surface of the plated steel sheet, and usually heated and dried at 80 to 300 ° C. without washing with water.
In order to form the organic resin film, a thermosetting organic resin is used as a film-forming resin, and if necessary, a resin solution containing other additives is applied, and the resin is cured by heat treatment. A film is formed.
The reasons for limiting the film configuration of the chemical conversion coating, the front-rear relationship between the step of forming the chemical conversion coating and the step (b) of applying the thermal history are as described above.

[Example 1]
A cold-rolled steel plate (thickness 0.5 mm) produced by a conventional method was passed through a continuous hot-dip plating facility and hot-dip plated using a 55% Al-1.5% Si-Zn plating bath. The line speed was 160 m / sec, and the amount of single-sided plating was 75 g / m ² .

In the manufacturing process of this plated steel sheet, the steel sheet is given a heat history with an average cooling rate of 10 seconds immediately after the steel sheet exits the plating bath to the plated film, and a chemical conversion treatment is applied to the plated film surface. gave. In the chromate treatment, dry silica, phosphoric acid and chromic acid are mixed in a ratio of dry silica: phosphoric acid: Cr = 1: 1: 1, and a treatment liquid with a Cr reduction rate adjusted to 40% is applied to the surface of the plated steel sheet. The chromate film was formed by drying at a plate temperature of 80 ° C. As the film forming resin for the organic resin film formed on the chromate film surface, the following were used.
(A) Thermosetting resin (main resin: polyester polyol resin, curing agent: diisocyanate curing agent)
(B) Thermosetting resin (main resin: acrylic polyol resin, curing agent: melamine resin (c) thermoplastic resin (MMA-MA acrylic emulsion resin)

The solvent type resin solution containing any one of the above organic resins was applied to the chromate-treated surface with a roll coater and dried by heating at a plate temperature of 160 ° C.
With respect to the surface-treated steel sheet thus produced, the processed part corrosion resistance and roll forming property were evaluated by the following methods.
The results are shown in Table 1 together with the chemical conversion treatment conditions.

(1) Processed section corrosion resistance After the surface-treated steel sheet was bent 5T, it was placed in a salt spray tester and the state of rust generation from the bent section after 500 hours was observed and evaluated according to the following criteria.
A: No abnormality (rust area ratio less than 10%)
○: Mild white rust and black rust generated (rust generation area ratio of 10% or more and less than 25%)
Δ: White rust and black rust are generated (rust generation area ratio is 25% or more and less than 80%)
×: Remarkable white rust and black rust are generated (rust generation area ratio is 80% or more)

(2) Roll forming workability A 30 mm x 300 mm surface-treated steel sheet is subjected to a sliding test using a draw bead testing machine with a die temperature of 120 ° C and a bead pressing load of 100 kg and a 5 mm R tip bead pressed. The appearance of was visually observed and evaluated according to the following criteria.
A: The blackened area is less than 10% and the film peeled material does not adhere to the mold. ○: The blackened area is 10% or more and less than 25%, or the film peeled material adheres to the mold. Slightly △: The blackened area is 25% or more and less than 50%, or the film peeled material is markedly attached to the mold. ×: The blackened area is 50% or more, or marked on the plated steel sheet surface “Kaziri” available

[Example 2]
A cold-rolled steel sheet (thickness 0.5 mm) produced by a conventional method was passed through a continuous hot-dip plating facility, and a 55% Al-1.5% Si-Zn plating bath (No. 1 to Table 5). No. 11, No. 14 to No. 24), 40% Al-1.0% Si-Zn plating bath (No. 12 in Tables 2 and 3) and 70% Al-1.8% Si-Zn plating Hot dip plating was performed using a bath (No. 13 in Tables 2 and 3). The line speed was 160 m / sec, and the amount of single-sided plating was 75 g / m ² .

In the manufacturing process of this plated steel sheet, the thermal history shown in Table 2 and Table 4 was given to the plated film, and a chemical conversion film was formed on the plated film surface. In the chromate treatment, dry silica, phosphoric acid and chromic acid are mixed in a ratio of dry silica: phosphoric acid: Cr = 1: 1: 1, and a treatment liquid with a Cr reduction rate adjusted to 40% is applied to the surface of the plated steel sheet. The chromate film was formed by drying at a plate temperature of 80 ° C. As the organic resin of the organic resin film to be formed on the chromate film surface, the same organic resin as in Example 1 was used, and a solvent type resin solution containing any of the above organic resins was applied to the chromate-treated surface with a roll coater. Heat drying was performed at a temperature of 160 ° C.
The surface-treated steel sheet thus manufactured was evaluated for roll forming property by the same method as in Example 1, and was evaluated for workability (crack resistance) and processed part corrosion resistance by the following methods.
The results are shown in Tables 2 to 5 together with the thermal history and chemical treatment conditions applied to the plating film.

(1) Workability The surface-treated steel sheet was bent 0T, and cracks at the tip of the 0T bending were observed and evaluated according to the following criteria.
No cracks are observed even when observed with a 5:20 magnifier.
4: Cracks are not observed when visually observed, but cracks are observed when observed with a 20-fold magnifier.
3: Cracks are observed by visual observation.
2: Cracks that are greatly opened by visual observation are observed.
1: A crack accompanied by peeling occurs.

(2) Processed part corrosion resistance After the surface-treated steel sheet was bent 1T, it was placed in a combined cycle tester and observed for rust generation from the bent part after 50 cycles, and evaluated according to the following criteria. One cycle of the combined cycle test is [30 ° C., 5% NaCl spray, 0.5 hour] → [30 ° C. wet, 1.5 hour] → [Dry (50 ° C., 2 hours)] → [Dry ( 30 ° C., 2 hours)].
A: No abnormality (rust area ratio less than 10%)
○: Mild white rust and black rust generated (rust generation area ratio of 10% or more and less than 25%)
Δ: White rust and black rust are generated (rust generation area ratio is 25% or more and less than 80%)
×: Remarkable white rust and black rust are generated (rust generation area ratio is 80% or more)

[Example 3]
A cold-rolled steel plate (thickness 0.5 mm) produced by a conventional method was passed through a continuous hot-dip plating facility and hot-dip plated using a 55% Al-1.5% Si-Zn plating bath. The line speed was 160 m / sec, and the amount of single-sided plating was 75 g / m ² .

In the manufacturing process of this plated steel sheet, the thermal history shown in Table 6 was given to the plating film, and the plating film surface was subjected to chemical conversion treatment. The chemical conversion treatment conditions were the same chromate treatment as in Example 2 to form a chromate film having a Cr adhesion amount (converted to metal chromium) of 20 mg / m ² , and then 100 parts by weight of the polyester polyol resin as the main resin. A solvent-type resin solution to which 10 parts by weight of a diisocyanate resin as a curing agent was added was applied to the chromate-treated surface with a roll coater and dried by heating at a plate temperature of 160 ° C. to form an organic resin film having a thickness of 2 μm. The surface-treated steel sheet thus produced was evaluated for workability (crack resistance) and processed part corrosion resistance by the same method as in Example 2. The results are shown in Table 6 together with the thermal history applied to the plating film.

The graph which shows the influence which the average cooling rate of the plating film of the first 10 seconds immediately after the steel plate leaves the hot dipping bath has on the workability of the surface-treated steel plate FIG. 2 (a) is a graph showing the effect of the heating temperature of the plating film on the workability of the surface-treated steel sheet when heat-treating the plated steel sheet after the hot-plated plated metal has solidified, FIG. b), when the plated steel sheet after the hot-plated plated metal solidifies is heat treated, the average cooling rate of the plating film (average cooling rate from the heating temperature to 100 ° C) is the workability of the surface-treated steel sheet Graph showing the effect on

Claims (4)

A surface-treated steel sheet having a chemical conversion film on the surface of a molten Al-Zn-based plated steel sheet having an Al content of 20 to 95 mass% in the plated film,
The chemical conversion coating, and chromate coating Cr deposition amount is less than 0.1 mg / m ² or more 100 mg / m ² of metallic chromium conversion which is formed on the plating film surface, a coating formed thereon, heat A surface-treated steel sheet excellent in workability and processed portion corrosion resistance, characterized by comprising an organic resin film having a film thickness of 0.1 to 5 μm using a curable organic resin as a film-forming resin. The surface-treated steel sheet excellent in workability and processed part corrosion resistance according to claim 1, wherein the plated film is a plated film obtained through at least the following thermal history (a) and (b).
(A) Thermal history in which the average cooling rate for 10 seconds immediately after the steel sheet exits the hot dipping bath is less than 11 ° C./sec. (B) After the hot dipped plated metal solidifies, it is in the range of 130 to 300 ° C. A heat history that is heated to a temperature T (° C.) and thereafter satisfies an average cooling rate from the temperature T (° C.) to 100 ° C. below C (° C./hr) shown in the following formula (1):
Or / and the average cooling rate from the temperature T (° C.) in the range of 130 to 300 ° C. to 100 ° C. after solidification of the hot-plated plated metal is below C (° C./hr) shown in the following formula (1) Heat history satisfying C = (T-100) / 2 (1)   The surface-treated steel sheet excellent in workability and processed part corrosion resistance according to claim 1 or 2, wherein the thermal history temperature T (° C) of (b) is in the range of 130 to 200 ° C.   A coated steel sheet, wherein a single-layer or multi-layer coating film is formed on the surface of the surface-treated steel sheet according to claim 1, 2 or 3.

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