JP2002212757A - Galvanized steel sheet having excellent corrosion resistance after working and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubrication treated steel sheet having high workability and high corrosion resistance which can not be obtained in a GA steel sheet and good surface quality free from rugged defects which can not be obtained in a GI steel sheet compatibly, and further having corrosion resistance after working and adhesion, and to provide a production method therefor. SOLUTION: A galvanizing coating film provided on the steel sheet contains, by mass, 0.20 to 1.0% Al and 0.5 to 6.0% Fe. The surface thereof is provided with a chromate film, and the surface of the film is provided with a silica- containing lubricating organic resin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a component of an electric appliance,
The present invention relates to a hot-dip galvanized steel sheet used for a steel sheet for automobiles, building materials and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a hot-dip galvanized steel sheet, Al
Galvanized steel sheet (hereinafter referred to as GI steel sheet) obtained by performing plating in a plating bath containing about 0.13% by mass or more, adjusting the coating weight, and not heating, and 0.15% by mass
Plating in a plating bath containing a smaller amount of Al,
There is an alloyed hot-dip galvanized steel sheet (hereinafter referred to as GA steel sheet) in which a plated steel sheet is heated after adjusting the amount of plating applied and the plating film is alloyed so that the Fe in the plating film becomes 8 to 12% by mass. .

[0003] GA steel sheets have a galvanized coating within the above-mentioned range.
Because it is alloyed with Fe, it has excellent resistance weldability compared to GI steel sheet, and has excellent adhesion of chemical conversion salt and coating adhesion during chemical conversion treatment, but brittle Fe-Zn alloy layer precipitates in the plating layer Therefore, workability is poor. In addition, since the plating film is alloyed within the above-mentioned range, the plating thickness cannot be made too large due to restrictions on the equipment of the alloying furnace and the necessity of securing the minimum workability. High corrosion resistance cannot be obtained as compared with.

On the other hand, the GI steel sheet can have a sufficiently large plating thickness as compared with the GA steel sheet, has high corrosion resistance, and has excellent workability as compared with the GA steel sheet. However, since the GI steel sheet solidifies the hot-dip galvanized coating with the amount of plating being adjusted by gas wiping, the surface of the plating film has irregularities caused by vibrations during gas wiping and the like in the plating bath. Adhered dross (Fe-Zn-based alloy grains) remains and is inferior to GA steel sheet in surface appearance. for that reason,
Until now, GI steel sheets could not be used without coating on visible parts of automobile exterior panel materials and home appliances, which are strict against irregularities on the surface of the plating film.

[0005] The method disclosed in Japanese Patent Application Laid-Open No. 52-6340 is a method for solving the above-mentioned problem.
In order to make the concentration higher than that of a normal GI steel sheet plating bath,
It is necessary to replace the plating bath and prepare two types of plating pots, and a large number of man-hours are required to change the plating bath, resulting in a very high cost and poor productivity. Further, since the Al concentration in the plating bath is high, the Al concentration in the plating film also increases with the increase, and the weldability deteriorates.

The method disclosed in Japanese Patent Application Laid-Open No. 62-4858 is a multi-method for controlling the thickness of the alloy layer at the interface between the plating film and the steel sheet to improve the workability.
Since the concentration is low and only the brittle Fe-Zn alloy layer grows as the alloy layer at the interface between the plating film and the steel sheet, the workability is not inferior to the GA steel sheet, but the workability is lower than that of the GI steel sheet. Is clearly inferior.

When a steel sheet is processed by press forming or the like, a press oil is generally applied in order to prevent the steel sheet or the press die from being damaged due to insufficient lubrication. The applied press oil is degreased in a degreasing step after processing. Conventionally, an organic solvent such as 1,1,1-trichloroethane, which is a specific freon, has been used for the degreasing. However, the use of certain CFCs has been totally abolished by the domestic law enacted in 1988. In addition, the use of other organic solvents, due to work environment and drainage problems,
It is a direction that is not used as much as possible.

Therefore, in recent years, lubricated steel sheets which can be processed without applying press oil have come to be used especially in manufacturers of home electric appliances and automobiles. By using this lubricated steel sheet, the press oil application step and the degreasing step can be omitted, the problem of organic solvents such as chlorofluorocarbons during degreasing can be avoided, and the cost reduction by improving the environment of the press workplace and eliminating steps. However, because of its effectiveness, the need for lubricated steel sheets is increasing.

Generally, a lubricated steel sheet is formed by using a zinc-plated steel sheet which is relatively inexpensive and has excellent corrosion resistance as a base material, and on which a lubricating organic resin film having excellent lubricity is formed.
It has been practiced to add a solid lubricant to a resin film as a lubrication function-imparting agent to impart lubricity to the film. Solid lubricants include waxes, inorganic layered materials (eg, graphite,
Molybdenum disulfide, boron nitride, etc.), organic plastics having a low coefficient of friction (eg, fluororesin, polyethylene), metal soap and the like are used.

[0010] The lubricated steel sheets proposed so far include, for example, the following. An organic composite steel sheet having excellent cationic electrodeposition coating properties obtained by applying an organic solvent type coating composition containing a urethane-containing epoxy ester resin, silica powder, a hydrophilic polyamide resin and polyethylene wax to a thickness of 0.3 to 5 μm (JP-A-63-3579)
No. 8).

A resin-coated steel sheet having excellent press workability, in which a resin film containing a fluorine resin and silica fine particles is formed in an acrylated epoxy resin (Japanese Patent Laid-Open No. 3-96)
No. 337).

A surface-treated steel sheet having excellent lubricity and corrosion resistance in which an emulsion of montan wax oxide containing fluororesin particles and silica fine particles is coated on a chromate film (Japanese Patent Application Laid-Open No. 17190/1991).

[0013]

As described above, the conventional lubricated steel sheet having a lubricating resin film containing a solid lubricant as described above has a low surface friction coefficient, and is not coated with press oil. It can be processed without. However, in more severe processing, the lubricating film was peeled off, which sometimes caused a problem in the corrosion resistance.

In view of such circumstances, the present invention has lubricating properties that can be processed without applying press oil, so that a degreasing step is not required, and at the same time, the surface appearance is excellent.
An object of the present invention is to provide a lubricated steel sheet having excellent corrosion resistance after working and a method for producing the same.

More specifically, an object of the present invention is to provide a high workability and high corrosion resistance which cannot be obtained from a GA steel sheet,
I The steel sheet not only achieves beautiful surface quality without unevenness defects that cannot be obtained with steel sheet, but also has corrosion resistance after processing,
An object of the present invention is to provide a lubricated steel sheet having an adhesive property and a method of manufacturing the same.

[0016]

Means for Solving the Problems The inventors of the present invention have conducted various studies to secure corrosion resistance after processing when applying a lubricating film, and as a result, the surface of a hot-dip galvanized steel sheet is re-melted and solidified. By adjusting the oxidation state of the galvanized surface of the hot dip galvanized film, the adhesion between the chromate film and the lubricating resin film and the plated film was unexpectedly improved, and the present invention was achieved.

Here, the present invention relates to a composite coated steel sheet in which a hot-dip galvanized film, a chromate film, and an organic resin composite film are sequentially coated on a steel sheet, wherein the plated film has an Al content of 0.20 to 1.0% by mass. And Fe: 0.5 to 6.0% by mass, wherein the chromate film is provided on the plating film, and the organic resin composite film is a silica-containing lubricating organic resin film. Is a lubricated steel sheet with excellent post-process corrosion resistance.

From another aspect, the present invention relates to a composite coated steel sheet comprising a steel sheet coated with a hot-dip galvanized film, a chromate film, and an organic resin composite film, wherein the plating film has an Al: 0.20 ~ 1.0 mass%, and Fe: 0.5 ~ 6.0
The chromate film contains 5 to 80 mg / m ² in terms of Cr, the lubricating organic resin film contains 5 to 30% by mass of silica particles as SiO _{2 in} the base resin, and A lubricated steel sheet containing a lubricating function-imparting agent in an amount of 3 to 30% by mass, and having an adhesion amount of the lubricating organic resin film of 0.1 to 5 g / m ² in terms of dry film weight.

Further, the present invention relates to a method for manufacturing a steel sheet comprising:
Immersed in a hot-dip galvanizing bath containing 0.30% by mass, lifted, and then heated the coated steel sheet obtained by adjusting the coating weight by gas wiping at a steel sheet temperature in the range of 420 to 600 ° C.
Cr equivalent coating weight on the surface of the obtained plated steel sheet is 5 to 80 mg / m
² of chromate film formed, and then lubrication surface and providing a silica-containing lubricating organic resin coating thereon at a coverage of dry film weight at 0.1 to 5 g / m ² and excellent beautiful processing corrosion resistance after This is a method for producing a treated steel sheet.

The lubricating organic resin film may further contain 0.3 to 7% of alkali metal silicic acid.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the reasons for defining the composition of a plating film in the present invention as described above will be specifically described. In this specification, unless otherwise specified, a plating bath, a plating bath, “%” Which defines the composition of the film, the chromate film, the lubricating resin film and the like means “% by mass”.

The steel sheet used in the steel sheet present invention, i.e. steel sheet may be either hot-rolled sheet, any of Hiyanobeban. A steel sheet for processing, which has been conventionally hot-dip galvanized, is exemplified. However, as long as hot-dip galvanizing is performed and required press forming can be performed, for example, a high-tensile steel sheet or the like is not limited.

[0023] For the Al concentration contained in the plating film plating film, if less than 0.20%, Fe ₂ Al ₅ phase alloy layer which formed at the interface between the plated coating and the steel sheet is less likely to grow at the time of plating, brittle The Fe-Zn-based alloy layer is likely to precipitate, and the adhesion of the plating film to the base steel sheet is impaired.

However, if the Al concentration in the plating film is too high, an FeAl ₃ phase precipitates at the interface between the plating film and the steel sheet in addition to the Fe ₂ Al ₅ phase, and this FeAl ₃ phase is formed of the Fe—Zn alloy layer. In order to promote growth, the adhesion of the plating film to the base steel sheet is impaired. Also, in a commonly used plating bath for GI steel sheets, the Al concentration in the plating film cannot exceed 1.0%.

Therefore, in the present invention, Al in the plating film
The content is defined as 0.20 to 1.0%. Preferably, 0.2 to
0.4%. 0.5% for Fe% in plating film
If it is less than 3, when the plated steel sheet is heated after gas wiping, the temperature cannot be raised to a temperature at which the plating film surface dissolves, and unevenness defects on the plating film surface cannot be eliminated.
On the other hand, if Fe% in the plating film exceeds 6.0%, brittle Fe-Zn
A large number of alloy layers are deposited, and the adhesion of the plating film to the base steel sheet is impaired. Preferably it is less than 2.5%.

As described above, according to the present invention, when the Al concentration in the plating film is in the range of 0.2 to 1.0% and the Fe ₂ Al ₅ phase having good adhesion exists in the plating film, the Zn
Alloying of Fe and steel sheet and precipitating the Fe phase of the Fe-Zn alloy layer in a certain range has a beautiful surface without unevenness of the plating film surface while maintaining the adhesion of the plating film to the steel sheet. A hot-dip galvanized steel sheet can be obtained.

The unevenness of the plating film surface is caused by the magnitude of the plating adhesion amount in the same plane. However, by alloying Zn in the plating film with Fe of the steel sheet, the plating adhesion amount is higher than that of the portion having a larger plating adhesion amount. The smaller the number, the greater the heat input to the interface between the plating film and the steel sheet, and the faster the alloying, the more the ζ phase precipitates, and the variation in plating thickness, that is, the surface unevenness can be reduced.

Therefore, in a preferred embodiment of the present invention, when the η phase in the plating film exceeds 95 at%, alloying of the plating film does not proceed, and the effect of reducing unevenness on the plating surface is poor, and the plating surface is beautiful. Can not. On the other hand, the Fe-Zn alloy layer such as the ζ phase in the plating film grows thickly, and the η phase becomes 50 at%.
If it is less than this, the plating film becomes too brittle, and the adhesion of the plating film decreases.

Regarding the unevenness of the surface of the plated steel sheet, JIS B061
As specified by 0, reference length 30mm, cut-off 0.8m
It was evaluated by the value of the measured W _CM in m, as long as this value is 10μm or less, even in rigorous application to the surface irregular defect such as automotive exterior panels, is good because no appearance manifested. Thus, in the preferred embodiment of the present invention, the surface roughness of the plating film with at W _CM defined by JIS B0610 specified in 10μm or less.

By the way, as a production technique for suppressing the surface unevenness of the plating film and securing the adhesion of the plating film, the Al content in the hot-dip galvanizing bath is set to 0.20%. 0.15 ~ 0.3 to be ~ 1.0%
% Range. Al has higher reactivity with Fe than Zn,
Since the Fe ₂ Al ₅ phase precipitates at the interface between the plating film and the steel sheet,
Al is concentrated in the plating film to a concentration higher than that of the plating bath.

The Al concentration in the plating bath is the same as that of a normal GI
It is a plating bath for steel sheets, and in carrying out the present invention,
Since there is no need to replace the bath, products can be supplied at low cost.

The base steel sheet is immersed in a hot-dip galvanizing bath having a specified Al content as described above, pulled up, and then the amount of plating applied is adjusted by gas wiping. After adjusting the adhesion amount, the plated steel sheet is heated.

The purpose of ripening the plated steel sheet is to redissolve the surface of the plated film. In the conventional GI steel sheet,
Since the galvanized film is solidified in the state of gas wiping, irregularities (wavelike irregularities) due to vibration during gas wiping and dross adhered in the plating bath are present on the surface of the plated film. All of these impair the appearance. In the present invention, the surface of the plating is redissolved, and the plating is solidified in a state free of vibration during wiping, thereby eliminating irregularities on the plating film surface,
At the same time, dross adhering in the plating bath is moved to the interface between the plating film and the steel sheet by reheating and alloying the plating film, thereby making the surface beautiful.

In order to re-dissolve the surface of the galvanized film, the temperature must be higher than the melting point of zinc, and it is heated to 420 ° C. or higher. However, when heated to over 600 ° C,
A brittle Fe-Zn-based alloy layer precipitates at the interface between the plating film and the steel sheet, thereby deteriorating the adhesion of the plating film and causing uneven color tone due to alloying unevenness on the surface of the plating film.
The preferred heating temperature has a lower limit of 450 ° C and an upper limit of 550 ° C.

Further, by performing such a re-dissolution treatment, the state of the surface of the plating film is changed, and the adhesion with the subsequent chromate film and the lubrication treatment film is remarkably improved, and the corrosion resistance after the processing is improved.

The mechanism by which the adhesion between the chromate film and the lubricating film is improved is not clear, but is considered as follows. First, the surface of the solidified zinc plating film after gas wiping has irregularities due to the vibration during gas wiping and dross adhered in the plating bath as described above. By solidifying the plating film in a state free from vibration during wiping, the unevenness on the plating film surface is eliminated, and at the same time, the dross adhering in the plating bath is obtained by reheating and alloying the plating film. Is transferred to the interface between the plating film and the steel sheet.At this time, the A1 concentrated layer in the plating surface layer is diffused into the plating film, so that the Al-concentrated layer on the plating film surface is reduced. Reactivity when chromate treatment is applied on top improves,
It is considered that the adhesion of the chromate film and the lubricating resin film layer to the plating film is improved.

That is, it is considered that the film formation mechanism in the chromate treatment basically includes the following three steps. Emission of electrons due to dissolution of metals such as zinc Reduction of Cr ₂ O ₇ ^2- and CrO ₄ ^{2- in} the treatment solution by electrons Precipitation of film due to increase in pH near metal surface due to dissolution and reduction reaction According to the present invention, since the reheat treatment reduces the Al-concentrated layer on the surface of the plating film as described above, it is promoted, and strong adhesion with the chromate film is realized.

Chromate film The chromate film can be formed by any method such as a coating type, a reaction type and an electrolytic type. The chromate treatment solution to be used is not particularly limited, but a preferred chromate treatment solution is a coating type chromate treatment solution containing colloidal silica, which is excellent in both corrosion resistance and resin film adhesion. The coating type chromate treatment liquid may be a two-stage reduction type liquid that has been partially reduced in advance in order to promote film formation. In addition, the chromate treatment solution may be a conventional one or two.
A small amount of at least one or more kinds of additives (eg, fluorinated acid such as hydrofluoric acid, citric acid, phosphoric acid, aqueous resin, etc.) may be contained.

In the case of a coating type chromate treatment liquid, after applying this on a plating film, it is dried to form a chromate film. The heating temperature at this time is 30 to 10
The range of 0 ° C is common.

It is sufficient that the amount of the chromate film adhered is substantially 5 to 80 mg / m ² in terms of Cr. This amount is 5mg / m
^If it is less than ² , the effect of the above-mentioned chromate film is insufficient, and if it exceeds 80 mg / m ² , further improvement in corrosion resistance cannot be obtained, which is uneconomical and also reduces workability. The more preferred amount of the chromate film is 10
6060 mg / m ² .

A lubricating resin film is preferably formed on the chromate film thus formed. This resin film is
In the base resin (A),. 5 to silica particles (B) as a SiO ₂
It contains 30% by weight, 3 to 30% of a lubricating function-imparting agent (C), and 0.3 to 7% of a basic alkali metal salt (D), and has a coating weight of 0.1 to 5 g / m ² in terms of dry film weight. Each of the components (A) to (D) can be used alone or in combination.

(A) Base resin: The base resin of the resin film is not particularly limited as long as it has sufficient strength to withstand processing and can form a transparent film. Suitable resins include polyurethane resins, epoxy resins,
An acrylic resin, a phenol resin, a polyolefin resin, an alkyd resin, a melamine resin, a polyvinyl butyral resin, and the like can be given.

(B) Siliceous component: The siliceous component is blended, for example, as silica particles in a resin film in order to improve the corrosion resistance of the lubricated steel sheet. This siliceous component
Colloidal silicide (aqueous silica), for example, Snowtex C-N (all manufactured by Nissan Chemical Industries, Ltd.), and gas-phase silica powder, for example, hydrophobic silica AEROSIL R-811, hydrophilic silica AEROSIL 200V (both manufactured by Nippon Aerosil Co., Ltd.) ) Etc. can be used. Further, an organic silicate (eg, ethyl silicate) which produces silica by hydrolysis is also a precursor of silica particles, but can be used in the present invention as silica particles. Are described as silica particles.

The average primary particle size of the silica particles is 5 to 5.
Suitably 100 nm, preferably in the range of 10 to 50 nm. The amount of silica particles in the resin film in as SiO ₂ 5 to 30
%, Preferably in the range of 15 to 25%. Silica is SiO ₂
If it is less than 5%, the corrosion resistance is not sufficient, and it is difficult to apply it for exterior use. On the other hand, when it exceeds 30%, the hardness of the resin film is increased, and the mold is formed at the time of molding, and the press formability is reduced. In order to improve the adhesion between the resin and the silica particles, a small amount of a silane coupling agent may be used in combination with the silica particles.

(C) Lubricating function-imparting agent: As a lubricating function-imparting agent, a solid that exerts a lubricating (reducing friction coefficient) function (ie, is generally known as a solid lubricant) and does not hinder the transparency of a resin film. Use powder. For example, graphite blackens the coating and is not used in the present invention unless a blackened surface is specifically intended.

The lubricating function-imparting agent suitable for use in the present invention is a powder of a polyolefin wax and a fluororesin, and these are preferably in the form of fine powder having an average particle diameter of 5 μm or less. Since the mold temperature can reach nearly 90 ° C during continuous processing, it is preferable to use a polyolefin wax with a softening point of 90 ° C or higher, especially 100 ° C or higher so that it does not soften even during continuous processing. .
Particularly preferred polyolefin wax powder has an average particle size of 0.6 to 1.1 μm, a small particle size distribution width, and a specific gravity (25%).
C) of 0.95 to 0.98 and a softening point of 100 to 150 ° C., which is a fine powder of a polyolefin-based polymer or copolymer such as polyethylene or polypropylene.

Examples of the fluorine resin include ethylene tetrafluoride resin (PTFE), ethylene trifluoride chloride resin, vinylidene fluoride resin, vinyl fluoride resin ethylene / tetrafluoroethylene copolymer resin, ethylene tetrafluoride / ethylene Hexafluoropropylene copolymer resin and the like. The average particle size of the fluororesin powder is preferably in the range of 0.1 to 5 μm, particularly preferably 0.5 to 2 μm.

The lubricating function-imparting agent is contained in the resin film in an amount of 3 to 30%.
To be present in the proportion of If this amount is less than 3%,
This is because when the lubricity is little improved and exceeds 30%, the adhesion to the substrate is reduced, the resin film strength is reduced, and the appearance is also deteriorated. The preferred compounding amount of the lubricating function-imparting agent is 8 to
It is within the range of 20%.

(D) Basic alkali metal salt: When a basic alkali metal salt is present in the resin film, the corrosion resistance of the lubricated steel sheet, particularly the corrosion resistance after the end face and after processing, is further improved.
That is, when severe processing or continuous processing is performed, sufficient corrosion resistance cannot be obtained only with the silica particle (B) component,
Although corrosion resistance cannot be ensured on the end face where the resin film is not formed, such a problem can be solved by blending a basic alkali metal salt.

As the basic alkali metal salt, various basic alkali metal salts such as hydroxides, carbonates, silicates, phosphates, borates and organic acid salts of alkali metals can be used. For example, hydroxide and NaOH, KOH, LiOH, CsOH, RbOH
However, as carbonates, NaHCO ₃ , Na ₂ CO ₃ , KHCO ₃ , K ₂ CO ₃ ,
LiHCO ₃ etc. are sodium silicate (Na ₂ O
iO ₂ ), potassium silicate (K ₂ O.xSiO ₂ ), lithium silicate (Li ₂ O
XSiO ₂ ) and the like, and phosphates such as Na ₂ HPO ₄ and K ₂ HPO ₄
Examples of the borate include NaBO ₂ , KBO _{2 and the} like. As the alkali metal silicate, for example, Na salt (sodium silicate)
X values are 2 (No. 1), 2.5 (No. 2) and 3 (No. 3). For Li salts, the x value is 3.5 (lithium silicate 35), 4.5 (lithium silicate 45), 7.5 (lithium silicate) 5) is available.

The reason why addition of a basic alkali metal salt improves the corrosion resistance particularly at the end face and the corrosion resistance after processing is as follows.
Although it is not clear, this alkali metal salt exerts a function as an inhibitor, particularly at a site where corrosion factors such as end faces and fine flaws generated by processing easily enter, and blocks corrosion factors such as Cl-. It is guessed. The pH of the coating composition used for forming the resin film is generally 7.5 to 12 by adding the basic alkali metal salt.

The basic alkali metal salt is contained in the resin film in an amount of 0.3%.
７7% by weight. If the amount is less than 0.3% by weight, the above-mentioned effect as an inhibitor is small, and sufficient corrosion resistance particularly at the end face cannot be obtained. On the other hand, if it exceeds 7% by weight, the resin film is apt to gel and becomes uneven at the time of coating, not only the appearance quality is deteriorated, but also the coating film becomes non-uniform, so that lubricity and flatness are obtained. Corrosion resistance is deteriorated. The preferred compounding amount of the basic alkali metal salt is 0.5 to 2% by weight.

In the base resin (A), the above components (B) to
The lubricating resin film containing each of the components (C) is formed in an amount of 0.1 to 5 g / m ² as a dry film weight per one surface. If the amount is less than 0.1 g / m ² , the effect of improving lubricity and corrosion resistance is small. If it exceeds 5 g / m ² , the corrosion resistance is improved, but the breathability is reduced and the cost is increased. In particular, to obtain a good appearance even after processing, the adhesion amount should be 1.0 g / m ²
It is preferable to make the above.

The resin coating composition used for forming the resin film comprises, in addition to the base resin (A), the components (B) to (D) in an amount within the above-mentioned predetermined range based on the total amount of non-volatile components. contains. If necessary, the coating composition may contain a crosslinking agent,
An additive caroten such as an antifoaming agent may be added. The type of solvent is
It may be any of water, alcohol, and organic solvent, and is selected according to the type of resin used.

The coating method may be selected from various coating methods such as roll coating and curtain flow coating depending on the situation. The drying temperature of the coated film is selected according to the type of resin and solvent.

[0056]

Examples Table 1 shows examples of the present invention and comparative examples.
In this example, a cold-rolled steel sheet obtained by heating, hot-rolling, pickling and cold-rolling a continuously cast slab was used as the material of the galvanized steel sheet. As the material of the steel plate, a low-carbon steel having the following composition and a thickness of 0.8 mm was used.

[C] ≦ 0.02%, [Si] ≦ 0.20%, [Mn] ≦ 0.
10%, [P] ≦ 0.05%, [S] ≦ 0.05%
iron. Use of these steel sheets in a continuous hot-dip galvanizing line
The Al concentration in the hot-dip galvanizing bath is 0.15 to 0.32%.
After immersion in a bath, the plating weight on one side is 30 to 150 g / m ^Two
After plating in the range of 400-620 ° C
Was reheated in the range.

The contents of Fe and Al in the plating film were determined by quantitatively analyzing a solution obtained by dissolving the plating film with hydrochloric acid by ICP. The volume ratio of η phase in the plating film was determined by using an electrolytic potential method.

[0059] In other _{words, ZnSO 4 · 7H 2 O:} 100g / l, NaCl:
In a 200 g / l electrolytic solution, constant current electrolysis was performed at a current density of 20 mA / cm ^{2 using} the sample as an anode, and the potential was measured using Ag as a reference electrode. At this time, electrolysis is promoted starting from the outermost layer,
The range showing a potential of less than -750 mV with respect to the Ag electrode was defined as the η phase. The plating layer was subjected to electrolysis starting from the outermost layer, and a range showing a potential of -290 mV with respect to the Ag electrode was defined as a plating layer constituting the plating film.

Here, after starting the electrolysis of the outermost layer. Ag
The time required to show a potential of -750 mV with respect to the electrode is A second,
After starting the outermost layer electrolysis, -290 mV with respect to the Ag electrode
Is assumed to be T seconds, the ratio of the η phase in the plating film can be obtained by η phase at% = A × 100 / T.

For the chromate film to be applied on such a plating film, a coating type chromate treatment solution (containing a colloidal sily force) was used to form a chromate film in which the amount of metal Cr was changed within the range shown in Table 1. did.

Next, on the chromate film, a resin containing silica particles (colloidal silica having an average particle diameter of 20 nm), polyethylene wax (average particle diameter of 1 μm), and sodium silicate No. 2 (Na ₂ O · 2SiO ₂ ) The coating composition is applied so as to have a predetermined adhesion amount after drying with a bar coater,
After drying at 120 ° C. for 30 seconds, a resin film was formed to obtain a lubricated steel sheet.

Table 1 shows the composition of the coating film and the amount of the chromate film deposited on the base material hot-dip galvanized steel sheet used, the resin which is the main component of the organic resin composite film, that is, the base resin, The content of the silica particles and the polyethylene wax, the content of the basic alkali metal salt, and the adhesion amount of the organic resin composite film are collectively shown.

Next, the characteristics of the lubricated steel sheet obtained in this example were evaluated in the following manner. Lubricity test, using the measuring apparatus shown in FIG. 1, at the specimen on the slide table, while applying a predetermined load to the slide bar fitted with a steel ball on the tip, sliding the specimen.
At this time, load 1kg, sliding speed 4mm / sec, sliding distance 20mm
The Bowden friction coefficient was measured under the following conditions. This measurement is 0.
If it is 1 or less, it can be determined that the lubricity is good.

The above test results are also shown in Table 1. Hat forming test with bead Using a crank press with a bead having the dimensions (mm) and shape shown in FIG. 2, a 250 × 50 mm test piece was deep drawn into a hat shape. The bead height was 7 mm, the forming height was 43 mm, and the forming speed was 70 mm / sec.

Observing the appearance of the ironed portion of the molded product,
(Good, no change in appearance) → ○ → △ → × (Not good, large occurrence of galling, large powdering). Corrosion resistance after processing Cylindrical deep drawing was performed without using press oil under the following conditions, and then a salt spray test (according to JIS Z2371) was performed for 240 hours.

[Cylinder deep drawing conditions] Blank diameter: diameter of 60 mm Punch diameter: diameter of 33 mm Dice diameter: diameter of 36 mm [Evaluation] ：: no change: less than 5% white rust △: less than 25% white rust ×: whole surface White Rust Surface Unevenness
Standard length, 30mm cut-off as specified in B0610
The value of W _CM at 0.8 mm was measured, and W _CM value obtained at that time, the value of W _CM from the evaluation results after painting was considered good 10μm or less.

As can be seen from the results shown in Table 1, by performing the plating in the range of the Al concentration in the zinc plating bath specified in the present invention, the Al content in the plating film was reduced to 0.20 to 0.20.
1.0%, and by setting the recalorizing temperature after plating to 420-600 ° C,
Fe content can be reduced to 0.5-6.0%.
Phase W _CM plating film surface in 95～50At% is not less 10μm or less, it was possible to obtain a beautiful steel sheet surface irregularities and excellent less workability.

On the other hand, as shown in the comparative example, when the reheating temperature after plating is too low, 400 ° C., the Fe content in the plating film is less than 0.5%, and the volume ratio of the Δ phase is, for example, less than 5 at%. And the unevenness of the surface of the plating film remains.

When the reheating temperature is higher than 600 ° C., the growth of the Fe—Zn alloy in the plating film proceeds, and the Fe content in the plating film exceeds 6.0%.
The volume ratio of the ζ phase is large, for example, more than 50 at%, and the adhesion of the plating is deteriorated and the workability is poor.

When the Al concentration in the galvanizing bath is less than 0.15%, when the recaloric heat is applied after the plating, the Fe content in the plating film is reduced.
Since the content sharply increases, the Fe content in the plating film specified in the present invention cannot be obtained, and the adhesion of the plating film to the base steel sheet is poor.

When the Al concentration in the zinc plating bath exceeds 0.30%,
The Fe content in the plating film increases at all, the predetermined Fe content in the plating film defined in the present invention cannot be obtained, and no effect is observed in reducing the unevenness of the plating film surface.

Further, it was found that a lubricated steel sheet having good corrosion resistance after working can be obtained by applying the chromate film and the lubricating resin film specified in the present invention.

[0074]

[Table 1]

[0075]

According to the present invention, a lubricated steel sheet having a beautiful surface and excellent post-work corrosion resistance and lubricity can be obtained. Since the lubricated steel sheet has good fingerprint resistance and good paintability, it is useful for various applications including automobiles, home appliances, building materials, and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of a Bowden friction test in Examples.

FIG. 2 is a schematic view showing a state of hat forming with a bead (crank press).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 2/26 C23C 2/26 2/40 2/40 (72) Inventor Tatsumi Tatsumi Minato, Wakayama, Wakayama 1850 Address Sumitomo Metal Industries, Ltd. Wakayama Works F-term (reference) AB31B AJ11 AJ11H AK01D AK51 BA04 BA07 BA10A BA10D CA19D DE01D EH462 EH71B EH712 EJ422 EJ482 EJ69C EJ692 GB07 GB32 JB02 JK16D JL01 JL11 JM02D 4K027 AA02 AA22 AB02 AB05 AB15 AB26 AB02 AB05 AB15 AB26 BC05 BC09 CA11 CA16 CA53 CA62

Claims (10)

[Claims] 1. A composite coated steel sheet in which a hot-dip galvanized film, a chromate film, and an organic resin composite film are sequentially coated on a steel sheet, wherein the plating film has an Al: 0.20 to 1.0
% By mass, and Fe: 0.5 to 6.0% by mass, wherein the chromate film is provided on the plating film, and the organic resin composite film is a silica-containing lubricating organic resin film. Lubricated steel sheet with beautiful surface and excellent corrosion resistance after processing. 2. The chromate film according to claim 1, wherein said conversion amount of Cr is 5 or less.
Characterized in that it is a to 80 mg / m ^2, lubricated steel sheet according to claim 1, wherein. 3. The lubricating organic resin film according to claim 1, wherein the lubricating organic resin film contains 5 to 30% by mass of a siliceous component as SiO ₂ and 3 to 30% by mass of a lubricating function-imparting agent in the base resin. wherein the amount of adhesion of the coating is 0.1 to 5 g / m ² on a dry film weight, lubricated steel sheet according to claim 1 or 2 wherein. 4. The lubricated steel sheet according to claim 1, wherein an η phase is present in the plating film in an amount of 95 to 50 at%. 5. The lubricated steel sheet according to any one of claims 1 to 4, characterized in that W _CM of the surface of the plated film is 10μm or less. 6. The lubricated steel sheet according to claim 1, wherein the organic resin composite coating further contains 0.3 to 7% by weight of an alkali metal silicate. 7. A composite coated steel sheet in which a steel sheet is coated with a hot-dip galvanized film, a chromate film, and an organic resin composite film, wherein the plating film has an Al content of 0.20 to 1.0% by mass and an Fe content of 0.5 to 1.0%. 6.0 mass%, the chromate film has a Cr equivalent adhesion of 5 to 80 mg / m ² , and the lubricating organic resin film has a siliceous component of SiO _{2 in the} base resin.
A lubricating treatment, characterized in that the lubricating organic resin film contains 0.1 to 5 g / m ² in terms of dry film weight. steel sheet. 8. A plated steel sheet obtained by immersing a base steel sheet in a hot-dip galvanizing bath containing 0.15 to 0.30% by mass of Al, pulling it up, adjusting the amount of coating by gas wiping, and removing
600 was heated at a steel sheet temperature in the range of ° C., Cr equivalent coating amount on the surface of the resulting plated steel sheet is provided with a chromate film of 5-80 mg / m ^2, then dried silica containing lubricating organic resin coating thereon A method for producing a lubricated steel sheet having a beautiful surface and excellent corrosion resistance after processing, characterized in that the coating weight is 0.1 to 5 g / m ² . 9. The lubricating organic resin film according to claim 1, wherein the base resin contains 5 to 30% by weight of a siliceous component as SiO ₂ and 3 to 30% by weight of a lubricating function-imparting agent. 9. The method for producing a lubricated steel sheet according to item 8. 10. The lubricating organic resin film further contains 0.3 to 7% of alkali metal silicic acid.
A method for producing the lubricated steel sheet according to the above.