JP2001098387A - Surface treated steel sheet for fuel tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated steel sheet which allows a stable stamping and welding and has excellent rust preventing property. SOLUTION: In a treated steel sheet having a coating layer of Al or an alloy of Al and at least one kind among Si, Zn and a Mg or a surface treated steel sheet having a coating layer of an alloy of Sn and Zn, either side is provided with a non-film removal type organic resin film, and the other side is provided with a fuel-melting type organic resin film. Desirably, the non-film removal type organic resin film is the one having a glass transition point of <=150 deg.C from the point of weldability and contains a solid lubricant, and it is desirable that the fuel melting type organic resin film is formed of emulsion, and in which a solid lubricant is contained in 1 to 50 wt.%. For the use of resistance welding, the thickness of the organic resin film is desirably controlled to <=2.0 μm.

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 characteristics 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, simply applying an organic coating has a problem that it is not desirable for resistance weldability because it tends to increase the surface contact resistance value and narrow the appropriate welding range. In addition, in the case of a product with a resin coating applied to the inside of the tank, if condensed water accumulates inside the tank, there is a problem that corrosion factors may concentrate on slight coating defects and local corrosion may occur. Have.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a rust-preventive steel plate having good press-formability as a rust-preventive steel plate for a fuel tank and having high corrosion resistance inside the tank. is there.

[0007]

The present inventors have conducted various studies to ensure good press formability and good corrosion resistance on the inner surface of the tank. As a result, the outer surface has good lubrication during press forming. By applying a non-demolding resin film that exhibits good pressability and disposing a film that dissolves in fuel such as gasoline at the stage of actual use after welding on the inner surface side, at the same time as good pressability and weldability The inventors have found that internal corrosion resistance can be obtained, and have completed the present invention.

The gist of the present invention is that (1) a metal plate has a non-removable organic resin film on one surface and an organic resin film soluble in fuel on the other surface;
(2) Metal plate is made of Al or Al and Si, Z on steel plate
a surface-treated steel sheet having a coating layer of an alloy comprising at least one 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; Has a glass transition point of 150 ° C. or lower and contains a solid lubricant; (4) a fuel-soluble organic resin film is formed by an emulsion;

(5) The fuel-soluble organic resin film is solid
(6) The non-demolded organic resin skin
The film or the fuel-soluble organic resin film forms 5 metal oxides.
(7) the metal-coated plate and
5-100mg / m in Cr amount at interface with machine resin film ^Two 
(8) The organic resin skin
The thickness of the film is 2.0 μm or less.

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, if the organic resin film is simply applied as described above, there is a possibility that the appropriate current range in spot or seam welding is narrowed, and that rust is generated on the inner surface, which may cause adverse effects. Therefore, the present inventors have solved these problems by disposing a non-demolding resin film having high lubricity on the outer surface side and applying a film soluble in fuel on the inner surface side. A non-demolded resin film means a film that does not easily fall off in the degreasing process after press molding or in the use environment.A film that dissolves in fuel means a gasoline, light oil, etc. Assumed temperature rise 45
It means a film in which a resin component dissolves and drops off more than half at a temperature of ° C.

As a result of various examinations of the film disposed on the outer surface side, it was found that the film satisfies the most desired performance when it is a non-demolding organic resin film, and further, has a glass transition point (hereinafter, Tg).
Of 150 ° C. or lower was suitable.
The non-removable organic resin film forms a continuous film having excellent toughness and has good mold resistance. In addition, Tg is 15
A resin system having a temperature of 0 ° C. or lower has a feature that the film hardness is low, the electrode is appropriately crushed when the electrode pressure is reduced during welding to form a uniform distribution of energization points, and the appropriate current range is widened.

As these organic resin films, epoxy resins, acrylic resins, urethane resins, polyester resins, polyethylene resins and the like are suitable. Further, by adding a solid lubricant to this organic resin film, a better mold galling resistance can be obtained and a better welding current range can be obtained. It is considered that this is because the uniform distribution of the solid lubricant in the base resin makes it possible to form a more uniform current-carrying point. The type of solid lubricant to be added is not particularly limited, but is preferably an organic substance. For example, an appropriate amount of a water-dispersible polyethylene resin, ethylene tetrafluoride resin, stearic acid compound, natural paraffin wax, or the like may be added. The added amount of the solid lubricant is 1 to 50% by weight. If it is less than 1% by weight, the effect of addition is small, and if it exceeds 50% by weight, the effect is saturated and the coating adhesion is reduced.

On the other hand, it is a feature of the present invention that the resin film on the inner surface side is of a fuel melting type. This resin film is more preferably a film that dissolves in gasoline on the inner surface and has lubricity. As these resins, for example,
A film composed of emulsion particles such as an acrylic resin, a polyolefin resin, and a polyester resin is suitable. This is because the fuel penetrates between the emulsion particles in the coating to weaken the bond, has the effect of decomposing and dissolving in the fuel, and thus very well matches the purpose in this case. is there. Conversely, a resin system in which the resins are crosslinked with each other is not preferable. In order to further improve the galling resistance, it is possible to mix the resin film with the solid lubricant as described above.

In the present invention, the thickness of the organic resin film is desirably 2 μm or less. The larger the film thickness, the better the mold galling by pressing, but if it exceeds 2 μm, spot welding,
Seam weldability tends to decrease. In addition, as a result of various studies on a method of exhibiting good mold galling resistance in the film of this thin film, it is very effective to include a solid lubricant in the film and further contain a metal oxide as a filler. I found that. 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 setting the particle size of the metal oxide to 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 components of the steel sheet used are not particularly limited, and may be ordinary steel or Cr-containing steel.
However, in the case of fuel tank materials for automobiles, high workability and strength are required for severe processing adapted to the lower part of the automobile. Therefore, the use of IF steel is desirable, and C:
0.01% or less, Si: 0.2% or less, Mn: 0.6%
Hereinafter, P: 0.04% or less, acid-soluble Al: 0.1% or less, N: 0.01% or less, and at least one or more of Ti and Nb in total (C + N) atomic equivalent or more It is desirable to contain 0.2% or less and B: 0.0001 to 0.0030%.

As the coating layer of the steel sheet, 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, the content of Si is
3-13% is preferred. If it is less than 3%, the Fe-Al alloy layer grows rapidly and thickly, which promotes cracking of the plating layer during processing and adversely affects the corrosion resistance. On the other hand, if the content exceeds 13%, the workability of the plating layer deteriorates, so the Si content is preferably 3 to 13%.

Further, F existing at the interface between the steel sheet and the plating layer
The e-Al-Si alloy layer is very hard as compared with the plating layer, and thus easily cracks during processing. If the thickness of the alloy layer is too large, cracks propagate in the plating layer above the alloy layer, causing cracks in the plating layer, and there is a concern that the corrosion resistance may deteriorate. Therefore, the thinner the alloy layer is, the more desirable it is, 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 not less than 8 μm
μm or less is preferred. If it is less than 8 μm, the corrosion resistance is insufficient, and if it is more than 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 an Al-Zn alloy, the content of Zn is preferably 20 to 99%. If it is less than 20%, the effect of the sacrificial anticorrosion effect due to the addition of Zn is not sufficient.
Corrosion inhibitory action due to stable base film formation is not sufficiently exhibited. The thickness of the coating layer including the alloy layer is preferably 6 μm or more and 30 μm or less. 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 anti-corrosion effect of 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 not less than 8 μm and not more than 30 μm 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.

The above-mentioned plated steel sheet is usually used after being subjected to post treatment such as chromate. In the present invention, it is possible to further improve the performance by performing a silica-based treatment or an organic resin coating treatment in particular. For example,
As the silica-based treatment, chromic acid-silica-based chromate treatment, white chromate-based treatment with addition of phosphoric acid, silica-resin-based treatment, silica-phosphoric acid-based treatment, and the like can be performed. 5-100 mg / m in conversion
² or 5 to 500 mg / m ^{2 in} terms of Si amount
And

The purpose of these processes, paint adhesion, weldability, is a corrosion resistance, 5 mg / m ² at 5 mg / m ² or Si Lowest Cr to exhibit these effects are required, On the other hand, since the effect is saturated and the uniform processing property is deteriorated, the upper limit is 100 mg / m ^{2 in} Cr.
Alternatively, it is set to 500 mg / m ² with Si. Inhibitors that do not use chromium have recently been studied as post-treatments, but these treatments are naturally applicable. In addition, as the post-plating treatment, before the chemical conversion treatment, there is 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 condition, a temper rolling for adjusting the material quality, and the like. However, in the present invention, these are not particularly limited and can be applied.

[0025]

[Example] Hot-dip Al-10% Si-plated steel sheet
8mm, plating thickness 15μm), molten 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% Si-5% Mg
Plated steel sheet (sheet thickness 0.8mm, plating thickness 18μm),
And hot-dip Sn-10% Zn-plated steel sheet (sheet thickness 0.8m
m, plating thickness of 8 μm) were subjected to the treatments shown in Table 1, and organic resin films were further applied in various combinations as shown in Table 2 to evaluate the performance.

[0026]

[Table 1]

[0027]

[Table 2]

[Conditions for Various Treatments in Table 1] 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 15mm ・ Pressing load: 5kgf / cm ²・ Molding speed: 3.3 × 10 ^-2 m / s ・ Mold material: FCD-500 The evaluation of mold galling depends on the following index. Was. ：: Formable, no defect on plating layer surface 〇: 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) Evaluation of weldability Spot weldability The spot welding was performed under the following welding conditions, and the proper welding current of the dust generation current value minus the minimum welding current value (nugget diameter 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 〇: Appropriate welding current range 1.5 KA or more 2 0.0 KA or less △: Appropriate welding current range of 1.0 KA or more and less than 1.5 KA ×: Appropriate welding current range of less than 1.0 KA

Seam Weldability Using an electrode ring of R6 mm-φ250 mm, welding current 13
KA, pressure 400kg, energization 2on-2off, 10
After performing seam welding of m, a test piece shown in JIS-Z-3141 was prepared, and a leak test was performed. In addition, as in the case of the leak test, the state of cross section penetration and the state of contamination of the electrode surface were observed, and the following evaluation was performed. ：: No leakage (good penetration, almost no electrode surface dirt) 〇: No leakage (good penetration, small electrode surface dirt) △: No leakage (good penetration, large electrode surface dirt) ×: Leakage (Many holes or poor penetration, large stain on electrode surface)

(3) Evaluation of corrosion resistance Flange width 20 mm, diameter 50 m by hydraulic molding tester
m, a 25 mm deep flat-bottomed cylindrical sample was immersed in gasoline at 40 ° C. for 5 days to dissolve the inner coating, then the test solution was added, and the lid was covered with glass via a silicone rubber ring. did. The corrosion state after this test was visually observed. (Test conditions) After test: Gasoline + distilled water 10% + formic acid 200 ppm Test period: Leave at 40 ° C for 3 months (Evaluation criteria) ◎: No change 〇: 0.1% or less of white rust △: 5% or less of red rust Or white rust occurrence 0.1 to 50% ×: red rust occurrence more than 5% or white rust remarkable Table 3 shows the results.

[0032]

[Table 3]

[0033]

As described above, the outer surface is provided with a film exhibiting good lubricity during press molding, and the inner surface is provided with a film which dissolves in fuel. Can be suppressed, and good weldability and corrosion resistance can be ensured. In particular, the Tg of the organic resin film is 150
When the solid lubricant is contained at a temperature of not more than ℃, the weldability is good. Further, by adding an appropriate amount of a filler having a controlled particle diameter, good mold seizure can be obtained even in a thin film, which greatly contributes to work efficiency.

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[Procedure amendment]

[Submission date] October 5, 1999 (1999.10.
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

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[Procedure amendment 2]

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[Correction target item name] Claim 3

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[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] Claim 6

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[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

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[0007]

The present inventors have conducted various studies to ensure good press formability and good corrosion resistance on the inner surface of the tank. As a result, the outer surface has good lubrication during press forming. subjected to non-de-membrane of the resin film that exhibits the gender, it is the inner surface of placing a coating film in the stage of actual use after the welding is soluble in the fuel, such as gasoline, good press formability, and weldability At the same time, they found that internal corrosion resistance was obtained, and completed the present invention.

[Procedure amendment 5]

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[Correction target item name] 0008

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[0008] It is an aspect of the present invention, (1) on one surface of the metal plate having an organic resin film of Hida' membrane, having an organic resin film which is soluble in the fuel on the other surface,
(2) Metal plate is made of Al or Al and Si, Z on steel plate
n, it is surface-treated steel sheet having at least one surface-treated steel sheet having a coating layer of an alloy consisting of, or coated layer of an alloy of Sn and Zn on a steel sheet Mg, (3) non-film removal <br/> The glass transition point of the organic resin film of the mold type is 150 ° C. or lower and contains a solid lubricant; and (4) the organic resin film of the fuel dissolution type is formed of an emulsion;

[Procedure amendment 6]

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[Correction target item name] 0009

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(5) The fuel-soluble organic resin film is solid
(6) the non-demolding agent;filmMold organic resin skin
The film or the fuel-soluble organic resin film forms 5 metal oxides.
(7) the metal-coated plate and
5-100mg / m in Cr amount at interface with machine resin film ^Two 
(8) The organic resin skin
The thickness of the film is 2.0 μm or less.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

However, if the organic resin film is simply applied as described above, there is a possibility that the appropriate current range in spot or seam welding is narrowed, and that rust is generated on the inner surface, which may cause adverse effects. The present inventors, the resin film of the lubricating highly non removal membrane is disposed on the outer surface side, leading to solve these problems by applying a coating that dissolves in the fuel on the inner surface side. The non-coating removal type of the resin film means a film that does not readily fall off in the degreasing step and the use environment after press molding, the film dissolves in fuel, gasoline, to fuel such as light oil, during driving of the automobile Assumed temperature rise of 45
It means a film in which a resin component dissolves and drops off more than half at a temperature of ° C.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

[0012] As a result of the film to be disposed on the outer surface of various studies, the coating satisfies the most objective performance be organic resin film of non-removal membrane, further, the glass transition point (hereinafter Tg)
Of 150 ° C. or lower was suitable.
The organic resin film of non-removal membrane forms a good continuous film on robustness, with good耐型galling resistance. In addition, Tg is 15
A resin system having a temperature of 0 ° C. or lower has a feature that the film hardness is low, the electrode is appropriately crushed when the electrode pressure is reduced during welding to form a uniform distribution of energization points, and the appropriate current range is widened.

Continuing from the front page (72) Inventor Yoichiro Mori 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division (72) Inventor Tatsuya Sakiyama 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation F-term in the Technology Development Division (reference) YY00D 4K026 AA07 AA09 AA10 AA13 BA06 BA07 BB06 BB08 BB10 CA19 CA20 CA22 CA26 CA41 EB11 4K044 AA02 AB02 BA02 BA10 BA21 BB04 BB11 BC02 BC05 CA16 CA18 CA53

Claims (8)

[Claims] 1. A surface-treated steel sheet for a fuel tank, comprising a non-demolded organic resin film on one surface of a metal plate and an organic resin film soluble in fuel on the other surface. 2. A surface-treated steel sheet having 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 according to claim 1, which is a surface-treated steel sheet having a coating layer of the alloy of (1). 3. The surface-treated steel sheet for a fuel tank according to claim 1, wherein the non-demolded organic resin film has a glass transition point of 150 ° C. or less and contains a solid lubricant. . 4. The surface-treated steel sheet for a fuel tank according to claim 1, wherein the fuel-soluble organic resin film is formed using an emulsion as a raw material. 5. The fuel-soluble organic resin film contains 1 to 50% by weight of a solid lubricant.
5. The surface-treated steel sheet for a fuel tank according to 4. 6. The non-demolded organic resin film or the fuel-soluble organic resin film contains 1 to 30% by weight of metal oxide.
The surface-treated steel sheet for a fuel tank according to claim 1, wherein the steel sheet is contained. 7. The surface-treated steel sheet for a fuel tank according to claim 1, wherein a chromate film having a Cr content of 5 to 100 mg / m ² is provided at an interface between the metal-coated plate and the organic resin film. . 8. The surface-treated steel sheet for a fuel tank according to claim 1, wherein the thickness of the organic resin film is 2.0 μm or less.