JP2000256879A - Surface treated steel sheet for fuel tank excellent in press formability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a rust preventive steel sheet in which galling caused at the time of press forming is suppressed and combining excellent resistance weldability and corrosion resistance as the stock for an automotive fuel tank. SOLUTION: The surface of a metallic sheet is provided with a film removing type organic resin film. Moreover, the surface of the metallic sheet having a coating layer composed of Al or Al and at least one kind among Si, Zn and Mg or a coating layer composed of Sn and Zn is provided with an alkali soluble type or hot water soluble type organic resin film. Moreover, it contains 1 to 40 wt.% solid lubricant and contains metallic oxide of >=0.1 μm grain size, in which the thickness is >=2.5 times that of the organic resin film, and its amt. to be added is 1 to 30 wt.%. The surface treated steel sheet has good press formability and resistance weldability and is optimum as a fuel tank stock.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a fuel tank of an automobile, which is capable of performing a stable press working and a stable welding work with no flaw at the time of manufacturing, and in addition, a rust preventive which can withstand long-term use. The present invention relates to a rust-proof steel plate for a fuel tank having power.

[0002]

2. Description of the Related Art Since fuel tanks for automobiles often have complicated shapes, excellent workability (deep drawing characteristics) is required. In addition, since it is an important safety component for automobiles, the material used is free from corrosion products that could lead to filter clogging, free from concerns about perforated corrosion, and a material that can be easily and stably welded. It is important that there is.

[0003] Materials having these various properties include P
A b-Sn alloy plated steel sheet (Japanese Patent Publication No. 57-61833) has been widely used as a fuel tank material for automobiles. This material has stable chemical properties with respect to gasoline, and is excellent in press formability due to excellent plating lubricity, and also excellent in resistance weldability such as spot welding and seam welding. However, in recent years, materials that do not use Pb have been demanded from the viewpoint of load on the environment.

One of the materials which does not use such Pb and has good corrosion resistance and workability is an Al-based plated steel sheet and a Sn-based plated steel sheet. Since a stable oxide film is formed on the surface of Al,
Shows good corrosion resistance to alcohol and organic acids generated when gasoline deteriorates. Similarly, Sn is promising as a fuel tank material because it forms a stable film on the surface and shows good corrosion resistance.

[0005] However, these steel sheets can be formed by deep drawing and can withstand use. However, in rare cases, linear or planar shapes due to mold galling due to running out of oil or mold temperature rise during press forming. There is a problem that a processing scratch is formed and the corrosion resistance is reduced. Therefore, Japanese Patent Application Laid-Open No. 9-14
As disclosed in, for example, Japanese Patent Application Laid-Open No. 2466 and Japanese Patent Application Laid-Open No. H10-95436, various measures have been taken such as applying an organic resin film containing a solid lubricant to the surface. However, the application of an organic film has a problem that it is not desirable for resistance weldability because it increases the contact resistance of the surface and narrows the appropriate welding range.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and provides a rust-preventive steel plate having good press-formability and corrosion resistance as a rust-preventive steel plate for a fuel tank and capable of being stably manufactured. .

[0007]

Means for Solving the Problems The present inventors have conducted various studies in order to ensure good press-formability and attain good weldability. As a result, the present inventors have found that organic compounds desorbed in the degreasing step after press-forming. The present inventors have found that these properties are satisfied by applying a resin film, and have completed the present invention. Furthermore, they have found that an organic resin film contains a solid lubricant and a metal oxide, and that by controlling the metal oxide to a specific particle size, it effectively acts on mold seizure suppression. Furthermore, by coloring these resin films, the state of desorption of the films can be seen at a glance, and a fuel tank surface-treated steel sheet that facilitates degreasing work has been achieved.

[0008] The gist of the present invention is as follows: (1) A surface-treated steel sheet for a fuel tank excellent in press formability, characterized in that a metal sheet has a film-forming type organic resin film. (2) The surface-treated steel sheet for a fuel tank according to the above (1), wherein the organic resin film contains a solid lubricant and is of an alkali-soluble type or a hot-water-soluble type.

(3) The organic resin film according to (1) or (1), wherein the organic resin film comprises a system obtained by polymerizing a hydrocarbon compound having an unsaturated bond to an acrylic resin and a monomer having a carboxyl group and / or a hydroxyl group. 2) A surface-treated steel sheet for a fuel tank excellent in press formability as described in 2). (4) Metal plate is made of Al or Al and Si, Z on steel plate
(1) to (3), wherein the surface-treated steel sheet has a coating layer of at least one alloy of n and Mg, or a surface-treated steel sheet having a coating layer of an alloy of Sn and Zn on the steel sheet. A surface-treated steel sheet for a fuel tank having excellent press formability as described in).

(5) The content of the above (1) to (4), wherein the content of the solid lubricant is 1% by weight or more and 40% by weight or less.
(4) A surface-treated steel sheet for a fuel tank having excellent press formability according to (4). (6) The above (1) to (1), wherein the organic resin film contains a solid lubricant and further contains a metal oxide.
(5) A surface-treated steel sheet for a fuel tank having excellent press formability according to (5).

(7) The particle size of the metal oxide is 0.1 μm or more, 2.5 times or less the thickness of the organic resin film, and the addition amount is 1% by weight or more and 30% by weight or less. (1) A surface-treated steel sheet for a fuel tank excellent in press formability according to (6). (8) The surface-treated steel sheet for a fuel tank according to the above (1) to (7), wherein the organic resin film contains a coloring pigment.

Hereinafter, the present invention will be described in detail. During press forming of plated steel sheets, even if lubricating oil is applied to the surface, in rare cases, contact between the mold and the metal plate of the workpiece occurs due to oil shortage or mold temperature rise during processing. In addition, processing flaws occur due to the occurrence of mold flaws, metal adhesion to the mold, and the like. In order to suppress this, it is important to suppress the contact between the metal mold and the metal plate. For this purpose, it is effective to apply an organic resin film to the surface of the metal plate to prevent the contact. It is more effective to include a solid lubricant in order to enhance the surface slidability.

However, as described above, if the film flows into the tank seam welding process with the film remaining, there is a tendency that the proper current range of welding is adversely affected.
Then, the present inventors have solved these problems by making this film into a film removal type film. The de-coating type coating means a coating which is present on the surface of a metal plate during press forming to prevent contact with a metal mold and is removed in a subsequent degreasing step so as not to affect the welding operation at all.

As a result of various examinations of the film-removal type film, it was found that the film satisfies the most desired performance as a resin film containing a solid lubricant and soluble in alkali or hot water. It has been found that the intended performance can be satisfied most by polymerizing a hydrocarbon compound having an unsaturated bond and a monomer having a carboxyl group and / or a hydroxyl group. Acrylic resin contains carboxyl groups in its skeleton, so OH in alkaline solution
It has high affinity for groups and water, and tends to be water-soluble. By polymerizing this resin and at least one of the above-mentioned carboxyl group-containing monomer and hydroxyl group-containing monomer, detachment of the film in the alkali degreasing step after press molding can be facilitated. However, depending on the compounding ratio, the solubility in alkali becomes too high, and the film may have tackiness due to atmospheric moisture.

Therefore, it is possible to obtain a good degreasing property while suppressing the polymerization by further polymerizing the hydrocarbon compound having an unsaturated bond. The acrylic resin used is styrene, vinyl acetate as a hydrocarbon compound having an unsaturated bond, such as polyacrylic acid having a carboxyl group, methacrylic acid, an acrylate ester, and a methacrylic acid ester, and maleic as a monomer having a carboxyl group. As a monomer having a hydroxyl group such as an acid and phthalic acid, glycol and the like are preferable. The purpose can be achieved by using a water-soluble polyethylene resin, epoxy resin, or the like instead of the acrylic resin.

In the present invention, good mold resistance is obtained by including a solid lubricant in the organic resin film. The type of the solid lubricant is not particularly limited, and for example, an appropriate amount of a water-dispersible polyethylene resin, a tetrafluoroethylene resin, a stearic acid compound, a natural paraffin wax, or the like may be added. The added amount of the solid lubricant is 1 to 4
0% by weight. If it is less than 1% by weight, the effect of addition is small,
If it exceeds 40% by weight, the degreasing property is reduced. In the present invention, the thickness of the organic resin film is not particularly limited. The larger the thickness of the film, the better the mold seizure by pressing, but the load on the degreasing solution increases. As a film thickness that achieves these in a well-balanced manner to match productivity, 5 μm or less is preferable.

In some steps, spot welding may be performed before the degreasing step. In such a case, a thinner film is desirable, and the thickness is preferably 2 μm or less. As a result of various studies on methods of exhibiting good mold galling resistance even in this thin film, it was found that it is very effective to include a solid lubricant in the film and a metal oxide as a filler. I found it. This is because the metal oxide is harder than the resin and acts in a direction to suppress the contact between the mold and the metal plate even in a portion where high pressure is applied.

This effect is further improved by reducing the frictional resistance during sliding by making the metal oxide particle size 0.1 μm or more and 2.5 times or less the thickness of the organic resin film. Mold seizure can be ensured. As the metal oxide, for example, spherical ones such as silica, alumina and titanium oxide can obtain more preferable results. Further, the content is preferably 1% by weight or more and 30% by weight or less. If less than 1% by weight, the effect of addition is small, and 30% by weight.
Above, the retention by the organic resin film is reduced, and the contribution to the anti-galling property is reduced.

The ordinary organic resin film is colorless or slightly white, but it is difficult to immediately determine whether or not the film has detached after the degreasing step in the actual operation with these colors. Therefore, the present inventors have conceived of including a coloring pigment in the organic resin film. The color pigment may be added in such an amount that the color can be visually identified, and the addition thereof does not have any influence on the characteristics. The color type may be any color other than the colorless or slightly white color described above, and it is assumed that it can be used properly according to the user's preference.

The components of the steel sheet used are not particularly limited, and may be ordinary steel or Cr-containing steel.
However, only for fuel tank materials for automobiles, high workability and strength are required for severe machining adapted to the lower part of automobiles. Therefore, it is desirable to use IF steel. C: 0.01% or less, Si: 0.2% or less, Mn: 0.
6% or less, P: 0.04% or less, acid-soluble Al: 0.1%
N: 0.01% or less, one or two of Ti: Nb
It is desirable to contain at least the atomic equivalent of the (C + N) amount and 0.2% or less, and B: 0.0001 to 0.0030%, of the total of the species or more. Al or Al
And alloys of at least one of Si, Zn, and Mg, such as Al-Si alloys, Al-Zn alloys, and Al-Si
-A Mg alloy or an alloy of Sn and Zn is suitable because it exhibits excellent corrosion resistance as a fuel tank material.

In the case of an Al—Si alloy plated steel sheet, Si
Is preferably 3 to 13%. F is less than 3%
The e-Al alloy layer rapidly grows thick, promotes cracking of the plating layer during processing, and adversely affects the corrosion resistance. On the other hand, 13%
If it is excessive, the workability of the plating layer is reduced, so that the Si content is preferably 3 to 13%. Further, the Fe—Al—Si alloy layer existing at the interface between the steel sheet and the plating layer is very hard as compared with the plating layer, and thus easily cracks during processing. If this alloy layer thickness is too thick, cracks will propagate to the plating layer above the alloy layer, causing cracks in the plating layer,
There is a concern that corrosion resistance may deteriorate. Therefore, the thinner the alloy layer is, the better it is, and preferably 5 μm or less. The thickness of the coating layer should be selected according to the application to be used. However, only for the fuel tank application, the thickness including the alloy layer is 8 μm.
It is preferably at least 3 μm and at most 3. If the thickness is less than 8 μm, the corrosion resistance is insufficient.

In the case of an Al-Zn alloy, the content of Zn is 20-99%. If it is less than 20%, the effect of sacrificial corrosion protection by adding Zn is not sufficient, and if it exceeds 99%, the effect of inhibiting corrosion due to the formation of a stable Al-based film is not sufficiently exhibited. The thickness of the coating layer is 6
It is preferable that it is not less than μm and not more than 30 μm. If it is less than 6 μm, the corrosion resistance is insufficient, and if it exceeds 30 μm, the reaction between the electrodes Cu and Al is promoted during resistance welding to promote electrode wear and reduce continuous workability.

In the case of an Al-Si-Mg alloy, the content of Si is preferably 3 to 13%, and the content of Mg is preferably 3 to 15%. The reason for limiting the Si content is the same as in the Al-Si alloy plating described above. If the Mg content is less than 3%, M
The effect of the anticorrosive action due to the addition of g is not sufficient. If it exceeds 15%, the effect of adding Mg is saturated and the appearance is reduced.
The thickness of the coating layer is preferably 8 μm or more and 30 μm or less, including the alloy layer, as in the case of the Al—Si system. 8μ
If it is less than m, the corrosion resistance is insufficient, and if it exceeds 30 µm, the reaction between the electrodes Cu and Al is promoted during resistance welding, electrode wear is promoted, and continuous workability is reduced.

In the case of a Sn—Zn alloy, the content of Zn is desirably 1% or more and 80% or less. If it is less than 1%, the effect of sacrificial corrosion protection by adding Zn is not sufficient, and if it exceeds 80%, the effect of inhibiting corrosion of Sn is not sufficiently exhibited. Regarding the thickness of the coating layer, including the alloy layer, the thickness is 2 μm or more and 20 μm or more.
The following is preferred. If it is less than 2 μm, the corrosion resistance is insufficient, and if it exceeds 30 μm, the reaction between the electrodes Cu and Al is promoted during resistance welding to promote electrode wear and reduce continuous workability.

Further, in the present invention, it is possible to obtain a necessary improvement in corrosion resistance by adding a chemical conversion coating such as a chromate coating or a phosphate coating after plating. In addition, as a treatment after plating, before the chemical conversion treatment, a zero spangle treatment which is an appearance uniform treatment after hot-dip plating, an annealing treatment which is a modification treatment of a plating layer, a surface state,
Although temper rolling and the like for adjusting the material can be performed, the present invention is not particularly limited thereto, and can be applied.

[0026]

(Example 1) Hot-dip Al-10% Si-plated steel sheet (sheet thickness 0.8 mm, plating thickness 15 μm), hot-dip Al
-45% Zn-plated steel sheet (sheet thickness 0.8mm, plating thickness 17μm), hot-dip Al-95% Zn-plated steel sheet (sheet thickness 0.8mm, plating thickness 15μm), hot-dip Al-10%
The chromate treatment shown in Table 1 was performed on a Si-5% Mg plated steel sheet (sheet thickness 0.8 mm, plating thickness 18 μm) and a molten Sn-10% Zn plated steel sheet (sheet thickness 0.8 mm, plating thickness 8 μm). Further, a treatment liquid in which a solid lubricant is added to a system in which a hydrocarbon compound having an unsaturated bond and a monomer having a carboxyl group and / or a hydroxyl group are polymerized in addition to an acrylic resin as shown in Table 2 above. Then, the performance was evaluated. In addition, a liquid in which a filler having variously controlled particle diameters was added to the resin film was applied, and the same evaluation was performed. Table 1 shows compositions of various chromate treatments, Table 2 shows treatment liquids, and Table 3 shows performance evaluation results.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

The performance evaluation method was as follows. (1) Evaluation of mold galling A molding test was performed using a cylindrical punch hydraulic molding machine under the following conditions to evaluate mold galling.・ Punch diameter: 75mmφ ・ Blank diameter: 150mm ・ Pressing load: 5kgf / cm ²・ Molding speed: 3.3 × 10 ^-2 m / s ・ Mold material: FCD-500 I depended. ◎: Formable, no defect on plating layer surface ○: Formable, no defect on plating layer surface, slight discoloration on sliding surface △: Formable, slight galling on plating layer surface ×: Formable Causes many linear scratches on the plating layer surface

(2) Degreasing evaluation FC-301 degreasing solution (manufactured by Nippon Parkerizing Co., Ltd., pH =
The temperature was adjusted to 11 and the temperature was 50 ° C.). The test piece was immersed for 20 s, and the residual ratio of the film was measured and evaluated by infrared spectroscopy. ：: No film residue ：: Film residue 5% or less △: Film residue more than 5% 10% or less ×: Film residue more than 10%

(3) Evaluation of Weldability Spot Weldability Spot welding was performed under the following welding conditions, and an appropriate welding current of the dust generation current value minus the minimum welding current value (nugget diameter was 4√t (t is plate thickness)) The evaluation was based on the size of the range. (Welding conditions) Pressing force: 220 kg, welding time: 15 cycles, electrode tip diameter: 6 mmφ, electrode shape: dome type (Evaluation criteria) ◎: Appropriate welding current range 2.0 kA or more ○: Appropriate welding current range 1.5 kA or more Less than 2.0 kA △: Suitable welding current range 1.0 kA or more and less than 1.5 kA ×: Suitable welding current range less than 1.0 kA

(4) Evaluation of corrosion resistance The corrosion resistance was evaluated for the material after alkali degreasing. 70x
After cutting out a test piece to 150 mm, degreased with FC-301 degreasing solution for 20 s, applied 20 μm of alkyd paint, put a cross cut reaching the ground iron, and performed a salt spray test for 500 h. The maximum swelling width on both sides was evaluated. (Evaluation criteria) ：: Maximum swelling width on both sides 3 mm or less ：: Maximum swelling width on both sides more than 3 mm and 5 mm or less ：: Maximum swelling width on both sides more than 5 mm and 10 mm or less ×: Maximum swelling width on both sides 10 mm or more

(Example 2) Chromate treatment B shown in Table 1 was applied to a hot-dip Al-10% Si-plated steel sheet (sheet thickness 0.8 mm, plating thickness 15 μm). A treatment liquid obtained by adding 0.001% by weight of dioxazine violet as a color pigment to the liquid was applied, and the degreasing test shown in Example 1 was performed. As a result, in the material to which the liquid A was applied, the colored film was dissolved after degreasing and the surface became metallic gloss, whereas in the case of the liquid I, it was easy for the film to remain without decoloring even after degreasing. Could be determined.

[0035]

As described above, an alkali-soluble or hot water-soluble organic resin film containing an appropriate amount of the solid lubricant of the present invention suppresses the occurrence of mold seizure during processing and is excellent in quality. Suitable for a wide range of welding because of its excellent degreasing properties. Further, by adding an appropriate amount of a filler having a controlled particle size, good mold seizure can be obtained even in a thin film, and the residual state of the film can be easily determined by a coloring treatment, which greatly contributes to work efficiency.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoichiro Mori 20-1 Shintomi, Futtsu-shi, Chiba F-term in the Technology Development Division of Nippon Steel Corporation (Reference) 3E061 AA15 AB05 AB13 AD01 DB04 3E062 AA06 AB03 AC03 JA01 JA07 JA08 JB22 JC02 JD03 4D075 CA33 DB02 DC13 EA06 EA37 EB11 EB31 EC02 4K044 AA02 AB02 BA10 BA12 BA15 BA19 BA21 BB03 BB04 BB11 BB16 BC05 CA11

Claims (8)

[Claims] 1. A surface-treated steel sheet for a fuel tank having excellent press-formability, comprising a metal plate having a film-forming type organic resin film. 2. The surface treatment for a fuel tank excellent in press moldability according to claim 1, wherein the organic resin film contains a solid lubricant and is of an alkali-soluble type or a hot-water-soluble type. steel sheet. 3. An organic resin film wherein the organic resin film has a hydrocarbon compound having an unsaturated bond to an acrylic resin, and a carboxyl group and / or
The surface-treated steel sheet for a fuel tank excellent in press formability according to claim 1 or 2, comprising a system obtained by polymerizing a monomer having a hydroxyl group. 4. A surface-treated steel sheet in which a metal sheet has a coating layer of Al or an alloy of at least one of Al, Si, Zn and Mg on a steel sheet, or Sn and Zn on a steel sheet.
The surface-treated steel sheet for a fuel tank having excellent press formability according to any one of claims 1 to 3, which is a surface-treated steel sheet having a coating layer of the alloy of (1). 5. A solid lubricant content of 1% by weight or more and 40% or more.
The surface-treated steel sheet for a fuel tank excellent in press formability according to any one of claims 1 to 4, which is not more than weight%. 6. An organic resin film containing a solid lubricant,
2. The method according to claim 1, further comprising a metal oxide.
6. A surface-treated steel sheet for a fuel tank excellent in press formability according to any one of items 1 to 5. 7. The method according to claim 1, wherein the particle size of the metal oxide is 0.1 μm or more, 2.5 times or less the thickness of the organic resin film, and the addition amount is 1% by weight or more and 30% by weight or less. 1
7. A surface-treated steel sheet for a fuel tank excellent in press formability according to any one of items 1 to 6. 8. The surface-treated steel sheet for a fuel tank excellent in press formability according to claim 1, wherein the organic resin film contains a coloring pigment.