JP2002275659A - Surface treated steel sheet having excellent workability and corrosion resistance of worked portion, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent workability, corrosion resistance of worked portions and roll formability of a surface treated steel sheet consisting of an Al-Zn hot dip coated steel sheet of 20 to 95 mass% in Al content in a plating film as a substrate steel sheet. SOLUTION: The plating film is obtained by undergoing a heat history of at least the following (a). This steel sheet has a chemical conversion treated film containing prescribed amounts of Cr and a thermosetting organic resin obtained by subjecting the surface of the plating film described above the chromate treatment under specific conditions: (a) The heat history in which the plating metals subjected to hot dip plating is warmed up and heated to temperature T( deg.C) of the range from 130 to 300 deg.C after solidifying and thereafter the average cooling rate form the temperature T( deg.C) to 100 deg.C satisfies C( deg.C/hr) expressed by the following equation (1) or below and/or the heat history in which the average cooling rate from the temperature T( deg.C) of 130 to 300 deg.C after the solidification of the plating metals subjected to the hot dip plating to 100 deg.C satisfies C( deg./hr) expressed by the following equation (1) or below: C=(T-100)/2...(1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing A
The present invention relates to a surface-treated steel sheet using a hot-dip Al-Zn-based plated steel sheet having an l content of 20 to 95 mass% as a base steel sheet and a method for producing the same.

[0002]

2. Description of the Related Art Al in a plating film is 20 to 95 mass%.
The hot-dip Al-Zn plated steel sheet contained is
As shown in No. 7161, since it exhibits superior corrosion resistance as compared with hot-dip galvanized steel sheet, in recent years, demand has been increasing mainly in the field of building materials. The plated steel sheet is produced as follows in a continuous hot-dip plating facility using a hot-rolled steel sheet subjected to pickling descaling or a cold-rolled steel sheet obtained by further cold-rolling the hot-rolled steel sheet as a base steel sheet.

In a continuous hot-dip plating apparatus, a base steel sheet is heated to a predetermined temperature in an annealing furnace maintained in a reducing atmosphere to remove rolling oil and the like adhering to the steel sheet surface simultaneously with annealing.
After the oxide film is reduced and removed, the lower end is immersed in a hot-dip galvanizing bath containing a predetermined concentration of Al through a snout immersed in the plating bath. After the steel sheet immersed in the plating bath is lifted above the plating bath via the sink roll, by injecting pressurized gas toward the surface of the steel plate from the gas wiping nozzle arranged on the plating bath The coating weight was adjusted, and then cooled by a cooling device to form a molten Al-
A Zn-based plated steel sheet is obtained.

The operating conditions such as the heat treatment conditions and atmosphere conditions of the annealing furnace in the continuous hot-dip plating equipment, the plating bath composition, and the cooling rate after plating are controlled within predetermined control ranges in order to ensure desired plating quality and material. Well managed. The plating film of the plated steel sheet manufactured as described above is mainly composed of a portion where Al containing Zn in supersaturation is dendrite solidified and a portion of the remaining dendrite gap, and the dendrite is in the thickness direction of the plating film. Laminated. With such a characteristic film structure, molten Al-
Zn-based plated steel sheets exhibit excellent corrosion resistance.

[0005] In addition, usually about 1.5 mass% of Si is added to the plating bath, and the action of the Si suppresses the growth of the alloy phase at the interface between the plating film and the base steel sheet in the molten Al-Zn-based plated steel sheet. And the alloy phase thickness is about 1 to 2 μm. The thinner the alloy phase, the greater the number of characteristic film structures exhibiting excellent corrosion resistance. Therefore, suppressing the growth of the alloy phase contributes to the improvement of the corrosion resistance. Further, 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 has an effect of improving workability. In addition, since the cracked portion is inferior in corrosion resistance because the base steel sheet is exposed, reducing the occurrence of cracks also improves the corrosion resistance of the processed portion.

[0006] Usually, the plating bath contains unavoidable impurities, Fe eluted from a steel plate or equipment in the plating bath, and Si for suppressing an alloy phase. These elements are present in the alloy phase or plating film in the form of an alloy or a simple substance. In addition, hot-dip Al-Zn-based coated steel sheets are rarely used as they are when they are put to practical use, and are usually used as surface-treated steel sheets that have been subjected to chemical conversion treatment or painting on the surface of the coated steel sheets. You.

[0007]

SUMMARY OF THE INVENTION Molten Al as described above
-There is a problem that the plating film of a Zn-based plated steel sheet is liable to be "galling" when it is slid by contact with a mold during roll forming, and the appearance quality is likely to be deteriorated. This is because, from the viewpoint of rationalization, when performing molding without oiling or processing without coolant, the temperature rise of the mold due to continuous processing acts as a more severe condition for processing. It is considered to be. In order to enhance roll forming properties, Japanese Patent Publication No. Hei 4-2672 proposes a method of coating a 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 effect of the improvement is that a good appearance quality without "galling" can be obtained even under severe processing conditions in which the temperature of the mold is increased by the processing. Not that.

[0008] Further, when the above-described hot-dip Al-Zn-based plated steel sheet is subjected to processing such as bending, cracks occur in the plated film of the processed portion depending on the degree of processing. In this plated steel sheet, about 1
Since the alloy phase with a thickness of ~ 2 µm becomes the starting point of cracks and the dendrite gap of the plating film becomes the propagation path of cracks, even when the same processing is performed, compared with the hot-dip galvanized steel sheet with the same plating film thickness Cracks tend to open relatively large. For this reason, there is a problem that the crack is visually recognized depending on the degree of processing and the appearance is impaired. Furthermore, as described above, the hot-dip Al-Zn coated steel sheet exhibits superior corrosion resistance as compared with a hot-dip galvanized steel sheet having the same plating film thickness, but the exposed cracked portion of the base steel sheet is compared with a crack-free portion. Therefore, there is also a problem that the corrosion resistance is significantly reduced.

In response to such a problem, for example,
JP-A-28748 discloses a method of improving the ductility of a plated steel sheet by subjecting a hot-dip Al-Zn-based plated steel sheet to a predetermined heat treatment. However, as described above, a hot-dip Al-Zn-based plated steel sheet is generally used as a chemical conversion-treated steel sheet whose surface has been subjected to a chemical conversion treatment or a coated steel sheet which has been coated. From the viewpoint of suppressing cracking in a processed portion by simply bending or the like, even if the ductility of the plating film is improved to some extent as in the above-described conventional technology, the performance as a product to be practically used, that is, It does not immediately improve the workability as a coated surface-treated steel sheet or the corrosion resistance of the processed part.

[0010] Accordingly, an object of the present invention is to use a hot-dip Al-Zn plated steel sheet having an Al content of 20 to 95 mass% in a plating film as a base steel sheet, and to provide unprecedented excellent workability, corrosion resistance in a processed portion, and roll forming property. And to provide a method for producing the same.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have determined the viewpoint of the performance as a practical product, that is, a surface-treated steel sheet obtained by subjecting a hot-dip Al-Zn-based plated steel sheet to a chemical conversion treatment. In order to improve the properties such as corrosion resistance, corrosion resistance of the processed part, roll forming property, etc., the intensive study was carried out on the optimal composition of the plating film and the chemical conversion treatment film. As a result, by forming the plating film of the hot-dip Al-Zn-based plated steel sheet through a specific heat history, and forming a specific chemical conversion coating film on the plating film surface, extremely excellent processing which could not be achieved by the conventional method. It has been found that the properties, corrosion resistance of the processed part and roll forming property 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 conversion coating on the surface of a hot-dip Al-Zn-based coated steel sheet having an Al content of 20 to 95 mass% in the plating film, wherein the plating film has at least the following thermal history (a): A plating film obtained through the above, wherein the chemical conversion treatment film is a chromic acid, a chromate compound, at least one selected from chromic acid compounds in which a part of chromic acid is reduced, and a thermosetting organic resin. Is a film obtained by applying a chromate treatment solution containing, and drying at a plate temperature of 130 to 300 ° C, the amount of organic resin (A) contained in the film and the amount of Cr in terms of metallic chromium. (B) A workability characterized by comprising a coating having a mass ratio (A) / (B) of 1 or more to less than 200 and a Cr content in terms of metal chromium of 0.1 mg / m ² or more and less than 100 mg / m ² . Surface treated steel sheet with excellent corrosion resistance in the processed part. (a) After the hot-dip plated metal solidifies, 130
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history,
And / or from a temperature T (° C.) in the range of 130 to 300 ° C. after solidification of the hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Heat history that satisfies the following: C = (T-100) / 2 (1)

[2] The Al content in the plating film is 20 to 9
A surface treated steel sheet having a chemical conversion treatment film on the surface of a 5 mass% hot-dip Al-Zn-based plated steel sheet, wherein the plating film is a plating film obtained through at least the following thermal history (a), The film is a chromate film formed on a plating film surface and a film formed thereon, and is selected from chromic acid, a chromate compound, and a chromic acid compound obtained by partially reducing chromic acid. After applying a chromate treatment solution containing at least one or more kinds of thermosetting organic resin and drying at a plate temperature of 130 to 300 ° C., the amount of the organic resin (A) contained in the film and the metal chromium conversion Ratio (A) / (B) of Cr amount (B) is 1 or more and 20
0 less, surface-treated steel sheet Cr amount is excellent in workability and the processing unit corrosion, characterized in that comprising a 0.1 mg / ^{m 2} or more 100 mg / ^{m 2} less than a is film of metal chromium conversion. (a) After the hot-dip plated metal solidifies, 130
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history,
And / or from a temperature T (° C.) in the range of 130 to 300 ° C. after solidification of the hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Heat history that satisfies the following: C = (T-100) / 2 (1)

[3] The workability and workability of the surface-treated steel sheet according to the above [1] or [2], wherein the temperature T (° C.) of the heat history of (a) is in the range of 130 to 200 ° C. Surface treated steel sheet with excellent corrosion resistance. [4] A coated steel sheet comprising a surface-treated steel sheet according to any one of the above [1] to [3], wherein a single- or multi-layer coating film is formed on the surface.

[5] The Al content in the plating film is 20 to 9
A method for producing a surface-treated steel sheet having a chemical conversion coating on the surface of a 5 mass% hot-dip Al-Zn-based coated steel sheet, wherein at least the following thermal history (a) is applied to the plating film of the steel sheet that has left the hot-dip coating bath. And (a) after the hot-dip plated metal solidifies, is heated to a temperature T (° C.) in the range of 130 to 300 ° C., and then heated to a temperature T (° C.)
The average cooling rate from to 100 ° C is C shown in the following formula (1).
(° C./hr) Heat history satisfying the following condition, and / or 130 to 300 after solidification of hot-dip plated metal
Heat history C = (T-100) / 2 where the average cooling rate from the temperature T (° C.) in the range of ° C. to 100 ° C. satisfies C (° C./hr) or less shown in the following equation (1). ) After applying a chromate treatment solution containing at least one selected from chromic acid, a chromate compound, and a chromic acid compound obtained by partially reducing chromic acid, and a thermosetting organic resin to the surface of a plated steel sheet A film obtained by drying at a sheet temperature of 130 to 300 ° C., wherein the mass ratio (A) / (A) of the amount of organic resin (A) contained in the film and the amount of Cr (B) in terms of chromium metal (B) is less than 200 1 or more, the workability and the processing unit which Cr of the metal chromium conversion is characterized by having a step of forming a chemical conversion film is less than 0.1 mg / ^{m 2} or more 100 mg / ^{m 2} Manufacturing method of surface treated steel sheet with excellent corrosion resistance.

[6] The Al content in the plating film is 20 to 9
A method for producing a surface-treated steel sheet having a chemical conversion coating on the surface of a 5 mass% hot-dip Al-Zn-based coated steel sheet, wherein at least the following thermal history (a) is applied to the plating film of the steel sheet that has left the hot-dip coating bath. And (a) after the hot-dip plated metal solidifies, is heated to a temperature T (° C.) in the range of 130 to 300 ° C., and then heated to a temperature T (° C.)
The average cooling rate from to 100 ° C is C shown in the following formula (1).
(° C./hr) Heat history satisfying the following condition, and / or 130 to 300 after solidification of hot-dip plated metal
Heat history C = (T-100) / 2 where the average cooling rate from the temperature T (° C.) in the range of ° C. to 100 ° C. satisfies C (° C./hr) or less shown in the following equation (1). ) A chromate film is formed on the surface of the plated steel sheet, and then the upper layer of the chromate film is thermoset with at least one selected from chromate, a chromate compound, and a chromate compound obtained by partially reducing the chromate. A coating obtained by applying a chromate treatment solution containing a reactive organic resin and then drying at a plate temperature of 130 to 300 ° C., wherein the amount of the organic resin (A) contained in the coating and the metal chromium conversion And the mass ratio (A) / (B) of the Cr content (B) is 1 or more and less than 200, and the Cr content in terms of metallic chromium is 0.1 mg / m ² or more and 100 mg / m ^2.
A method for producing a surface-treated steel sheet having excellent workability and corrosion resistance in a processed portion, comprising a step of forming a chemical conversion treatment film for forming a film having a thickness of less than 10%.

[7] In the method of the above-mentioned [5] or [6],
(a) A method for producing a surface-treated steel sheet having excellent workability and corrosion resistance in a processed portion, wherein the temperature T (° C.) of the heat history is in the range of 130 to 200 ° C. [8] In the manufacturing method according to any one of the above [5] to [7], the heat history of (a) is applied to the plating film in at least one of the following steps (1) to (4). A method for producing a surface-treated steel sheet having excellent workability and corrosion resistance in a processed portion. (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-dip plated metal [9] Above [5] ] To [8], further comprising a step of applying one or more coats on the surface of the chemical conversion coating film.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The surface treated steel sheet of the present invention has a molten Al-Z containing 20 to 95 mass% of Al in a plating film.
The n-based plated steel sheet is used as a base steel sheet. Further, from the viewpoint of corrosion resistance and the like, a more preferable range than the amount of Al in the plating film is 45 to 45.
It is 65 mass%. Further, particularly preferred component compositions of the plating film are: Al: 45 to 65 mass%, Si: 0.7 to
2.0 mass%, Fe: less than 10 mass%, and the balance being substantially Zn containing unavoidable impurities. In such a composition, particularly excellent corrosion resistance is exhibited. However, this molten Al
-It is difficult for a Zn-based plated steel sheet to obtain high corrosion resistance in a processed portion only by its plating composition, and excellent corrosion resistance in a processed portion can be obtained only after undergoing a heat history described below and in combination with an upper chemical conversion coating. Although there is no particular limitation on the coating weight of the hot-dip Al-Zn-based plated steel sheet, it is generally appropriate to set the coating weight to about 30 to 120 g / m ² per one surface.

Further, the plating film of the hot-dip Al—Zn-based plated steel sheet must be a plating film obtained through at least the following thermal history (a). (a) After the hot-dip plated metal solidifies, 130
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history,
And / or from a temperature T (° C.) in the range of 130 to 300 ° C. after solidification of the hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Heat history satisfying the following: C = (T-100) / 2 (1) In the heat history of (a), the more preferable range of the temperature T (° C.) is 130 to 200 ° C. Where
Equation (1) is based on experiments conducted by the present inventors to study in detail the effects of the heating condition of the plating film and the subsequent cooling conditions and the cooling conditions after the solidification of the hot-dip plated metal on the plating film, based on experiments, and as a result, It is a derived empirical formula.

By forming the plating film through the heat history of the above (a), the workability (crack resistance and the like) is greatly improved even though it is a molten Al-Zn plating film. The workability is improved as described above because the plating film is heated to a temperature range of 130 to 300 ° C. (preferably 130 to 200 ° C.) and then gradually cooled under specific conditions and / or 130-300 after solidification of plating film
Through the thermal history of slow cooling under specific conditions from a temperature range of 130 ° C. (preferably 130 to 200 ° C.), strain accumulated in the plating film at the time of solidification is released, and solid diffusion in the plating film is performed. Occurs, and Al and Z in the plating film
It is considered that the two-phase separation of n is effectively promoted, so that the plating film is softened.

In the heat history (a), the plating film (the plating film after the hot-dip plated metal solidifies) is heated to a temperature T (° C.) in the range of 130 to 300 ° C., preferably 130 to 200 ° C. After heating, the average cooling rate from the temperature T (° C.) to 100 ° C. is C
(° C./hr) or a plating film after solidification of the hot-dip plated metal is cooled to a temperature T in the range of 130 to 300 ° C., which is the cooling process.
Cooling is performed so that the average cooling rate from (° C.) to 100 ° C. satisfies C (° C./hr) or less in the above equation (1).

In the heat history of (a), if the heating temperature T of the plating film is lower than 130 ° C., the above-mentioned effect cannot be sufficiently obtained. In order to promote the growth of the alloy phase at the interface between the steel sheet and the plating film, it adversely affects the workability. Further, from such a viewpoint, the upper limit of the heating temperature T, which is more preferable for improving the workability, is 200 ° C. Also, the cooling process after the hot-dip plated metal solidifies is 1
Even in the case where cooling is performed from the temperature T (° C.) in the range of 30 to 300 ° C. under the condition that the heat history of (a) is imparted, the above-described effect is sufficiently obtained when the temperature T is lower than 130 ° C. Absent.

FIG. 1 (a) shows the effect of the heating temperature of the plating film on the workability of the surface-treated steel sheet when the hot-dip coated steel sheet is heat-treated after solidification of the hot-dip plated metal. In the test materials obtained from these results, the plated steel sheet in which the average cooling rate of the plating film from the heating temperature to the heating temperature of 100 ° C. is within the conditions of the heat history of the above (a), the condition of the present invention. It is a surface-treated steel sheet on which a chemical conversion treatment film satisfying the above is formed. The evaluation of the workability in this test was performed according to the evaluation of the workability in Examples described later.

FIG. 1 (b) shows the average cooling rate (average cooling rate from the heating temperature to 100 ° C.) of the plating film when the plated steel sheet after the hot-dip plating metal is solidified is heat-treated. The effect of this on the workability of the surface-treated steel sheet was investigated, and the test materials for which these results were obtained show that the heating temperature of the plating film is within the range of the heat history of (a) above. This is a surface-treated steel sheet in which a chemical conversion coating satisfying the conditions of the present invention is formed on a steel sheet. The evaluation of the workability in this test was performed according to the evaluation of the workability in Examples described later.

As shown in FIGS. 1 (a) and 1 (b), when the heating temperature of the plating film is in the range of 130 to 300 ° C., the workability of the 2T bending is 4 or more, and preferable conditions are satisfied. In the range of 130 to 200 ° C., the workability score was 4 to 5 points. On the other hand, when the heating temperature is 13
Outside the range of 0 to 300 ° C., only three points of workability were obtained. When the difference between the average cooling rate from the heating temperature and 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 workability of 2T bending is 4 points. If the difference is plus (outside the scope of the present invention), the workability score is only 3 points.

In order to make the plating film go through the heat history of the above (a), a heating or heat retaining device for heat-treating or keeping the plating film in or out of the continuous hot-dip plating equipment is provided. A predetermined 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 to perform continuous heating in-line, or may be performed offline after winding on a coil. It may be performed by batch heating. In addition, a heating mechanism (for example, an induction heater, a gas heating furnace,
The heating may be performed by continuous heating using a hot air oven or the like. Furthermore, after the plated steel sheet continuously heated in the plating line or in the above-described continuous processing equipment is wound around a coil, appropriate heat retention or heat retention may be performed. In addition, a heat retaining device may be provided so that the plating film can be cooled and gradually cooled in a cooling process after the hot-dip plated metal solidifies. However, there is no special restriction on the method, shape, scale, etc. of the heating or heat retaining device, and it is essential that the heat treatment of (a) be given to the plating film.

By forming a specific chemical conversion treatment film on the surface of the plating film having undergone the heat history of (a) as described above,
This surface-treated steel sheet exhibits excellent workability, corrosion resistance in the processed part, and roll forming property. The chemical conversion film formed on the plating film surface is composed of chromic acid, chromate compound,
It is obtained by applying a chromate treatment solution containing at least one selected from chromic acid compounds in which a part of chromic acid has been reduced and a thermosetting organic resin, followed by drying at a plate temperature of 130 to 300 ° C. Wherein the mass ratio (A) / (B) of the amount of organic resin (A) contained in the film to the amount of Cr (B) in terms of metallic chromium is 1 or more and less than 200, preferably 50 or more and 150 or less. Hereinafter, the amount of Cr in terms of metallic chromium is 0.1 mg /
m ² or more and less than 100 mg / m ² , preferably 5 mg / m ²
It is necessary that ^two or more 40 mg / ^{m 2} or less of the chemical conversion film.

If the Cr content in terms of metallic chromium in the chemical conversion coating is less than 0.1 mg / m ² , the corrosion resistance of the processed portion is not sufficiently improved, while if the Cr content is 100 mg / m ² or more, the effect of improving the corrosion resistance of the processed portion is not obtained. Not only saturates, but also lowers the Cr fixation rate due to an increase in the amount of Cr, thereby impairing environmental harmony.

In the present invention, an organic resin is incorporated into the chemical conversion coating for the purpose of improving the corrosion resistance of the processed portion, and the organic resin needs to be a thermosetting organic resin. When continuous roll forming is performed on a surface-treated steel sheet, the roll temperature rises significantly, and when the organic resin contained in the chemical conversion coating is a normal thermoplastic resin or a general emulsion resin, the roll temperature is increased. The rise causes scratches on the film and deteriorates the appearance after processing. Therefore, as a result of studying to solve such a problem, the use of a thermosetting resin as a resin to be blended in the film dramatically improves the scratch resistance at high temperatures, and as a result,
It was found that there was no problem in appearance after processing even in continuous roll forming processing.

Here, the thermosetting resin refers to 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, when heated during film formation. A resin that undergoes a cross-linking reaction such as radical polymerization utilizing a chain double bond. Examples of the thermosetting resin include alkyd resins, polyester resins, polyurethane resins, acrylic resins, epoxy resins, styrene resins, and modifications thereof. One or more kinds of resins and the like can be used. Among these, polyester resin, polyurethane resin and acrylic resin are particularly desirable from the viewpoint of workability. Further, the above-mentioned thermosetting resins include an aqueous dispersion type and a solvent type, and any of them may be used.

The amount of the organic resin in the chemical conversion coating (A)
And mass ratio (A) of Cr amount (B) in terms of metallic chromium (A) /
When (B) is less than 1, the effect of improving the corrosion resistance of the processed portion by the organic resin cannot be sufficiently obtained. On the other hand, the mass ratio (A) /
(B) If it is 200 or more, the effect of improving the corrosion resistance of the processed portion by Cr cannot be sufficiently obtained. In addition, when the drying temperature after applying the chromate treatment liquid at the time of forming the chemical conversion treatment film is less than 130 ° C. at the plate temperature, an appropriate chemical conversion treatment film is not formed because the temperature is low. The organic resin is liable to be thermally degraded, and further heat is applied to the plating film, so that the alloying reaction is accelerated, and the workability may be reduced.

In the surface-treated steel sheet of the present invention, a general chromate film may be formed on the plating film surface, and the above-mentioned specific chemical conversion film may be formed thereon. In this case, the chemical conversion film is composed of two layers. It will be composed of a film,
Further improvement in corrosion resistance can be expected. In this case, the composition of the chromate film formed on the lower layer side is not particularly limited, and may be a known composition usually applied to a plated steel sheet. It is optional to add an organic resin to the chromate film, but usually it does not contain an organic resin.

In the surface-treated steel sheet of the present invention, when heat treatment is performed after formation of the chemical conversion coating in order to impart a specific thermal history to the plating coating, the properties of the organic resin contained in the chemical conversion coating may be impaired. In some cases, it is effective to add an inorganic additive (fine particles) to the chemical conversion coating. As inorganic additives, silica,
Phosphoric acid compounds, silicate compounds (for example, Ca salt, Mg
Salt) or the like.

Next, a method of manufacturing the above-mentioned surface-treated steel sheet according to the present invention will be described. The production method of the present invention uses a hot-dip Al-Zn-based plated steel sheet having an Al content of 20 to 95 mass% in a plating film manufactured by a continuous hot-dip plating facility or the like as a base steel sheet, and forms a chemical conversion coating on the surface thereof. A method of producing a surface-treated steel sheet that has been subjected to a step of imparting at least the following (a) heat history to the plating film of the steel sheet that has exited the hot-dip plating bath, and forming a specific chemical conversion treatment film on the surface of the plated steel sheet. And a step of causing (a) After the hot-dip plated metal solidifies, 130
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history,
And / or from a temperature T (° C.) in the range of 130 to 300 ° C. after solidification of the hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Heat history that satisfies the following: C = (T-100) / 2 (1)

The heat history of (a) may be applied by subjecting the plated steel sheet after the hot-dip plated metal has solidified to a specific heat treatment, or This is performed by controlling the cooling of the film by heat retention or the like. In the production method of the present invention, a specific chemical conversion treatment film is formed on the plating film surface of the plated steel sheet, but the heat treatment for imparting the thermal history of (a) to the plating film is performed before the formation of the chemical conversion treatment film, During the step of drying the film, the step may be performed at any stage after the formation of the chemical conversion treatment film (after the application of the treatment liquid and the formation of the film by the drying step). Moreover, you may perform in two or more steps of these.

Therefore, the application of the thermal history (a) to the plating film can be performed in at least one of the following steps (1) to (4). (1) Before forming 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-dip plated metal Among the methods, the method has the advantage that each condition of the heat treatment step and the chemical treatment step can be independently optimized, and the method of and is suitable for performing all the processing in the continuous hot-dip plating equipment. . In addition, since the heat treatment is carried out by utilizing the heating in the drying step of the chemical conversion treatment, the method is particularly economical.

The heat treatment or heat preservation for imparting the heat history of (a) is performed by a heating or heat preserving device provided inside or outside the continuous hot-dip plating equipment. A heating mechanism (e.g., induction heater, hot blast stove, etc.) may be provided in the continuous hot-dip plating equipment to perform continuous heating in-line, or to perform batch heating offline after winding on a coil. Is also good. Further, the heating may be performed by continuous heating using a heating mechanism (for example, an induction heater or a hot blast stove) in a continuous processing facility outside the plating line. Furthermore, after the plated steel sheet continuously heated in the plating line or in the above-described continuous processing equipment is wound around a coil, appropriate heat retention or heat retention may be performed. Also,
In the cooling process after the hot-dip-plated metal is solidified, a heat retaining device may be provided so as to keep the plating film heated and gradually cooled. However, there is no special restriction on the method, shape, scale, etc. of the heating or heat retaining device, and it is essential that the heat treatment of (a) be given to the plating film. The preferable plating composition, the coating weight, the reason for limiting the heat history of the above (a), the obtained effects, and the like of the manufactured hot-dip Al-Zn-based plated steel sheet are as described above.

[0038] In the production method of the present invention, the thermosetting organic material is coated with at least one selected from chromic acid, a chromate compound, and a chromate compound in which a part of the chromic acid is reduced, on the plating film surface of the plated steel sheet. After applying the chromate treatment liquid containing the resin, the mass of the amount of the organic resin (A) contained in the film and the amount of Cr (B) in terms of metallic chromium by drying at a plate temperature of 130 to 300 ° C. the ratio (a) / (B) is less than 200 1 or more, preferably 50 or more 150 or less, Cr of the metal chromium conversion is 0.1 mg / ^{m 2} or more 100 mg / m
A chemical conversion coating of less than ² , preferably 5 mg / m ² or more and 40 mg / m ² or less is formed. In this chromate treatment, a chromate treatment solution is applied to the plated steel sheet surface, and usually,
Dry without washing.

The reasons for limiting the composition of the chemical conversion coating and the drying temperature, and the relationship between the step of forming the chemical conversion coating and the step (a) of imparting the thermal history are as described above. . In the production method of the present invention, it is also possible to apply a general chromate treatment to the plating film surface and then form a film by the above-mentioned specific chromate treatment on the upper layer. A treatment film is formed. In this case, the lower layer side chromate treatment may be performed under a known treatment condition that is usually applied to a plated steel sheet.

[0040]

[Example 1] A cold-rolled steel sheet (sheet thickness: 0.5 mm) manufactured by a conventional method was passed through a continuous hot-dip plating facility, and 55%
Al-1.5% Si-Zn plating bath (N in Tables 1 to 4
o. 1 to No. 19, no. 22, no. 23), 40
% Al-1.0% Si-Zn plating bath (No. 20 in Tables 3 and 4) and 70% Al-1.8% Si-Zn plating bath (No. 21 in Tables 3 and 4). Hot-dip plating. The line speed was 160 m / sec, and the single-side plating adhesion amount was 75 g / m ² .

In the manufacturing process of the plated steel sheet, a heat history shown in Tables 1 and 3 is imparted to the plating film,
A chemical conversion treatment was applied to the plating film surface. The following were used as the organic resin for chemical conversion treatment film addition. (a) Thermosetting resin (main resin: polyester urethane emulsion resin, curing agent: isocyanate curing agent) (b) Thermosetting resin (main resin: acrylic emulsion resin having tertiary amino group and carboxyl group, cured Agent: epoxy silane compound having both alkoxysilyl group and epoxy group) (c) Thermoplastic resin (MMA-MA acrylic emulsion resin) (d) Thermoplastic resin (polyester urethane emulsion resin)

A treatment solution obtained by mixing any one of the above organic resins and chromic acid at a predetermined ratio is applied to a plated steel sheet surface with a predetermined Cr content.
Coating was carried out so as to obtain an adhesion amount, and drying treatment was performed at a maximum reached plate temperature of 160 ° C. The workability (crack resistance), the corrosion resistance of the processed part, the roll forming property, and the Cr fixing rate of the surface-treated steel sheet manufactured as described above were evaluated by the following methods. The results are shown in Tables 1 to 4 together with the thermal history and chemical conversion treatment conditions applied to the plating film.

(1) Workability The surface-treated steel sheet was bent by 2T, cracks at the tip of the 2T bending were observed, and evaluated according to the following criteria. No cracks were observed even when observed with a 5:20 loupe. 4: No crack is observed when visually observed, but 20
Cracks are observed when observed with a double magnifier. 3: Cracks are observed by visual observation. 2: A large opening crack is observed by visual observation. 1: A crack accompanied by peeling has occurred.

(2) Corrosion resistance of the processed part After the surface-treated steel sheet was bent by 2T, it was placed in a wet tester at 50 ° C. and 98% RH or more, and the state of rust generation from the bent part after 1000 hours had passed was observed. Evaluation was made according to the following criteria. ◎: No abnormality (Rust generation area rate less than 10%) ○: Mild white rust or black rust generation (Rust generation area rate 10%)
Δ: less than 25%) Δ: White rust and black rust occurred (rust generation area ratio 25% or more: 8)
X: Significant white rust and black rust occurred (rust generation area ratio 80%)
that's all)

(3) Roll forming workability A 30 mm × 300 mm surface-treated steel sheet was subjected to a flat plate sliding test using a draw bead tester at a mold temperature of 120 ° C. and a bead pressing load of 75 kg, and the appearance after drawing was visually observed. And evaluated according to the following criteria. ◎: The blackened area is less than 10% and there is no adhesion of the film peeling to the mold. ○: The blackening area is 10% or more and less than 25%, or the adhesion of the film peeling to the mold is insufficient. Slightly present △: Blackening area is 25% or more and less than 50%, or there is remarkable adhesion of a film exfoliated substance to a mold ×: Blackening area is 50% or more, or remarkable on the surface of a plated steel sheet There is "biting"

(4) Cr fixation rate The surface-treated steel sheet was sprayed with hot water at 60 ° C. for 120 seconds, and the amount of Cr adhering before and after the spraying was measured by X-ray fluorescence, and the residual Cr rate (%) was measured as the Cr fixation rate. And evaluated according to the following criteria. ◎: Cr residual rate of 95% or more ：: Cr residual rate of 85% or more and less than 95% Δ: Cr residual rate of 75% or more and less than 85% ×: Cr residual rate of less than 75%

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

[Table 4]

Example 2 A cold-rolled steel sheet (sheet thickness 0.5 mm) manufactured by a conventional method was passed through a continuous hot-dip plating apparatus,
Hot-dip plating was performed using a 1.5% Al-1.5% Si-Zn plating bath. The line speed was 160 m / sec, and the single-side plating adhesion amount was 75 g / m ² .

In the manufacturing process of the plated steel sheet, a thermal history shown in Table 5 was imparted to the plating film, and a chemical conversion treatment was applied to the plating film surface. The chemical conversion treatment conditions were as follows: the resin (b) used in Example 1 (10 parts by weight of a curing agent was added to 100 parts by weight of the base resin) and chromic acid were an organic resin / Cr = 1.
/ 100 is applied to the coated steel sheet surface
r The coating amount was 20 mg / m ^2, and the coating was dried at a maximum temperature of 160 ° C. With respect to the surface-treated steel sheet manufactured in this manner, workability (crack resistance) and corrosion resistance of the processed portion were evaluated in the same manner as in Example 1. Table 5 shows the results together with the thermal history applied to the plating film.

[0053]

[Table 5]

[0054]

As described above, the surface-treated steel sheet according to the present invention is a very highly treated steel sheet having an Al content in a plating film of 20 to 95 mass% as a base steel sheet. Has excellent workability, corrosion resistance in the processed part, and roll forming property. Further, according to the manufacturing method of the present invention, such a surface-treated steel sheet can be manufactured stably and with high productivity.

[Brief description of the drawings]

FIG. 1 (a) is a graph showing the effect of increasing the heating temperature of a plating film on the workability of a surface-treated steel sheet when a plated steel sheet after solidification of a hot-dip plated metal is heat-treated. FIG. 1 (b) shows the average cooling rate of the plating film (from the heating temperature to the heating temperature of 1%) when the plated steel sheet after the hot-dip plating metal is solidified is heat-treated.
Graph showing the effect of average cooling rate to 00 ° C) on the workability of surface-treated steel sheet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 2/28 C23C 2/28 22/28 22/28 // B05D 7/14 B05D 7/14 A (72 Inventor Toshihiko Ooi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Keiji Yoshida 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Junichi Inagaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside Nihon Kokan Co., Ltd. (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Inventor Yasuhiro Majima 6-1 Mizue-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside NKK Steel Sheet Co., Ltd. (72) Inventor Nobuyuki Ishida 6-1 Mizue-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa NKK Steel Inside Plate Co., Ltd. (72) Inventor Yuichi Fukushima 6-1 Mizue-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa F-term in KK Steel Sheet Co., Ltd. (Reference) 4D075 AB03 BB24X BB74X BB87Z BB93Z CA33 DA06 DB02 DC10 EA06 EB01 4F100 AA22C AB03A AB10B AB18B AK01C AK51 BA03 BA07 BA10A BA10C EH46 EH71 EH71B EJ68C GB90 JB02 JB13C JL01 YY00B 4K026 AA02 AA07 AA09 AA13 AA22 BA06 BB08 BB09 CA16 CA18 CA20 CA22 CA23 CA27 CA02 AC05 AB04 AC02 AB05 AC02 BA21 BB02 BB11 BC02 BC05 CA11 CA16 CA53

Claims (9)

[Claims] An aluminum content in a plating film is 20 to 95.
A surface-treated steel sheet having a chemical conversion treatment film on the surface of a hot-dip Al-Zn-based plated steel sheet of mass%, wherein the plating film is a plating film obtained through at least the following thermal history (a); After applying a chromate treatment liquid containing at least one selected from chromic acid, a chromate compound, and a chromic acid compound obtained by partially reducing chromic acid, and a thermosetting organic resin, the film is heated to a plate temperature of 130. A film obtained by drying at a temperature of from about 300 ° C. to a mass ratio (A) / (B) of the amount of organic resin (A) contained in the film and the amount of Cr (B) in terms of metallic chromium There than 200 1 or more, Cr amount is 0.1 mg / ^{m 2} or more 100 mg / ^m surface-treated steel sheet with excellent worked portion corrosion resistance and workability characterized by comprising less than ² in a film of metallic chromium conversion. (a) After the hot-dip plated metal solidifies, the temperature T in the range of 130 to 300 ° C.
(° C.), and then the temperature T (° C.)
The average cooling rate to 0 ° C is C (° C / h
r) The thermal history that satisfies the following, and / or the average cooling rate from temperature T (° C.) in the range of 130 to 300 ° C. to 100 ° C. after solidification of the hot-dip plated metal is as follows:
Thermal history satisfying C (° C./hr) or less as shown in equation (1) C = (T−100) / 2 (1) 2. An aluminum content in a plating film of 20 to 95.
a surface-treated steel sheet having a chemical conversion treatment film on the surface of a hot-dip Al-Zn-based plated steel sheet of mass%, wherein the plating film is a plating film obtained through at least the following thermal history (a); The film is a chromate film formed on a plating film surface and a film formed thereon, which is selected from chromic acid, a chromate compound, and a chromic acid compound obtained by partially reducing chromic acid. After applying a chromate treatment liquid containing at least one seed and a thermosetting organic resin,
The mass ratio (A) / (B) of the amount of organic resin (A) obtained by drying at a temperature of 0 to 300 ° C. and contained in the film and the amount of Cr (B) in terms of metallic chromium is 1 or more and 200 Less than 0.1mg / m ² Cr 100mm
A surface-treated steel sheet having excellent workability and corrosion resistance in a processed portion, comprising a film having a g / m ^{2 or} less. (a) After the hot-dip plated metal solidifies, 130
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history, and / or temperature T (° C.) in the range of 130 to 300 ° C. after solidification of hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Heat history that satisfies the following: C = (T-100) / 2 (1) 3. The temperature T (° C.) of the thermal history of (a) is 130 to
3. A temperature range of 200 [deg.] C.
Surface treated steel sheet excellent in workability and corrosion resistance in the processed part described in 4. 4. A coated steel sheet comprising a surface-treated steel sheet according to claim 1, wherein a single-layer or multi-layer coating film is formed on the surface. 5. An Al content in a plating film of 20 to 95.
A method for producing a surface-treated steel sheet having a chemical conversion treatment film on the surface of a hot-dip Al-Zn-based plated steel sheet having a mass of at least the following (a): And (a) after the hot-dip plated metal solidifies,
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history, and / or temperature T (° C.) in the range of 130 to 300 ° C. after solidification of hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Thermal history that satisfies the following: C = (T-100) / 2 (1) The surface of the plated steel sheet is selected from chromate, a chromate compound, and a chromate compound in which a part of the chromate is reduced. A film obtained by applying a chromate treatment liquid containing at least one kind of thermosetting organic resin and drying at a plate temperature of 130 to 300 ° C., wherein the amount of organic resin contained in the film (A ) and the amount of Cr reckoned as metal chromium weight ratio of (B) (a) / ( B) is less than 200 1 or more, Cr content of the metal chromium conversion is less than 0.1 mg / ^{m 2} or more 100 mg / ^{m 2} Chemical A method for producing a surface-treated steel sheet having excellent workability and corrosion resistance in a processed portion, comprising a step of forming a treated film. 6. An Al content in a plating film of 20 to 95.
Chemical conversion treatment on the surface of mass% hot-dip Al-Zn plated steel sheet
A method for producing a surface-treated steel sheet having a coating, the method comprising:
Both the following (a) the step of imparting the heat history, (a) after the hot-dip plated metal solidified, 130
And heated to a temperature T (° C.) in the range of
After that, the average cooling rate from temperature T (° C) to 100 ° C decreases
Thermal history that satisfies C (° C./hr) or less shown in equation (1), and / or after the hot-dip plated metal solidifies
A temperature T (° C.) in the range of 130 to 300 ° C. to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Thermal history satisfying the following: C = (T-100) / 2 (1) A chromate film is formed on the surface of the plated steel sheet.
Chromic acid, chromic acid
Salt compounds, chromic acid compounds that have partially reduced chromic acid
Containing at least one selected from the group consisting of a thermosetting organic resin and
After applying the romate treatment liquid, the plate temperature is 130 to 300 ° C.
A film obtained by drying at a temperature, which is contained in the film.
Of organic resin (A) and Cr in terms of chromium metal
(B) mass ratio (A) / (B) of 1 to less than 200, gold
0.1mg / m Cr content of genus chromium ²More than 100m
g / m²Of a chemical conversion coating to form a coating that is less than
Processability and process part resistance characterized by having a forming step
A method for producing surface-treated steel sheets with excellent corrosion properties. 7. The temperature (T) of the heat history of (a) is 130 to
7. The temperature range of 200 [deg.] C.
3. A method for producing a surface-treated steel sheet having excellent workability and corrosion resistance in a processed part according to the above. 8. The method according to claim 5, wherein the application of the thermal history of (a) to the plating film is performed in at least one of the following steps (1) to (4). A method for producing surface-treated steel sheets with excellent workability and corrosion resistance in the processed part. (1) Before chemical conversion coating formation (2) During chemical conversion coating drying process (3) After chemical conversion coating formation (4) Cooling process after solidification of hot-dip plated metal 9. The method according to claim 5, further comprising the step of applying one or more coats to the surface of the chemical conversion coating in addition to the steps of the manufacturing method according to claim 5, 6, or 7. Manufacturing method of painted steel sheet.