JPH093658A - Anti-rust steel plate for fuel tanks with excellent workability, corrosion resistance and weldability - Google Patents

Abstract

(57) [Summary] [Object] The present invention is an organic-metal alloy coating, in which the composition and the amount of adhesion are specified as a post-treatment film in tin-zinc based hot-dip alloy plating.
By applying an inorganic composite film, a corrosion-resistant steel sheet for fuel tanks having excellent corrosion resistance, workability, and weldability is provided. [Structure] (1) An alloy layer having a thickness of 0.05 to 1.5 μ, in which 50% or more of the composition is (Fe + Sn), and a thickness of 2.0 to 1 in which 80% or more of the composition is tin, on the surface of the steel sheet.
Cr, S on the metal plating of 5.0μ tin-based alloy
Deposition amount of 0.01 to 2.0 including at least one of i, P and Mn
An anti-rust steel sheet for fuel tanks that has excellent workability, corrosion resistance, and weldability, characterized by having an organic-inorganic composite coating of g / m ² . (2) The tin-based alloy contains 80% or more of tin and the balance is Zn, Mn,
A rust preventive steel plate for a fuel tank having excellent workability, corrosion resistance, and weldability according to (1), which is composed of Cd, Al, Cr, Ti, and Mg. (3) A rust preventive steel plate for fuel tank having excellent workability, corrosion resistance, and weldability according to (1), characterized in that the main component of the organic resin is acrylic, polyester, and epoxy resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rust preventive steel sheet mainly used for a fuel tank for automobiles or a member for wiring electric (electronic) equipment.

[0002]

2. Description of the Related Art Conventionally, lead-tin alloy-plated steel sheets having excellent corrosion resistance, workability, solderability, etc. have been widely used as fuel tank materials or electric (electronic) device wiring members. On the other hand, tin-zinc alloy-plated steel sheets have been mainly produced by electroplating in an aqueous solution containing zinc and tin ions, as disclosed in, for example, JP-A No. 52-130438. The tin-zinc alloy plated steel sheet mainly composed of tin is
It has excellent corrosion resistance and solderability and has been widely used for electronic parts.

[0003]

Lead-tin alloy-plated steel sheet is used as a fuel tank material for automobiles because it has various excellent properties (for example, workability, tank inner surface corrosion resistance, solderability, seam weldability, etc.). However, it has been regarded as a problem with the recent increase in awareness of the global environment. In other words, the regulation of lead elution from industrial waste such as automobile shredder dust is being screamed severely, and since lead-tin alloy plated steel sheet contains a large amount of lead, there is a movement to limit its use. It is a thing. On the other hand, tin-zinc electroplated steel sheets have been used mainly for electronic parts requiring solderability etc. in applications where the corrosive environment is not so severe, but tin-zinc alloy plated steel sheets by the hot dipping method were used. There are few examples, and in particular, a plated steel sheet containing a large amount of corrosion-promoting components such as deteriorated gasoline and capable of withstanding a harsh and special environment for a long time has not been put into practical use.

[0004]

The present inventors have found that lead-containing
No (excluding inevitable impurities) Anti-corrosion steel plate for fuel tank
Plating composition, coating structure, composition, etc. for the purpose of providing
Various investigations have been made to arrive at the present invention. The present invention includes (1) Fe and Sn in a total amount of 5 on the surface of the steel sheet to be plated.
Alloy layer containing 0% or more and having a thickness of 0.05 to 1.5 μm
Sn having a thickness of 2.0 to 15.0 μm on its surface
It has a base alloy plating layer, and the amount of adhesion on the surface is 0.0
1 to 2.0 g / m ^Two Having an organic-inorganic composite film
Fuel tank with excellent workability, corrosion resistance, and weldability
Corrosion-proof steel plate.

(2) The Sn-based alloy plating layer is Zn: 20
% Or less, Cr: 5% or less, Mn: 5% or less, Ti: 5%
Hereinafter, one or more of Al: 5% or less, Cd: 5% or less, and Mg: 5% or less is contained in a total of 20% or less, and the balance is Sn and inevitable impurities. (1) A rust-proof steel plate for fuel tanks that has excellent workability, corrosion resistance, and weldability. (3) The above-mentioned (1) or (2), wherein the organic-inorganic composite coating contains 20% or more in total of one or more Cr, Si, P and Mn-based compounds. Rust-proof steel plate for fuel tanks with excellent workability, corrosion resistance, and weldability. (4) The processability according to (1), (2) or (3) above, wherein the organic resin of the organic-inorganic composite film is one or more of acrylic, polyester and epoxy resins. -Fuel tank anti-corrosion steel plate with excellent corrosion resistance and weldability.

Hereinafter, the present invention will be described in detail. Pre-treatment such as removal of rolling oil or oxide film is performed by using an annealed steel sheet that has undergone a series of processes such as hot rolling, pickling, cold rolling, annealing, pressure adjustment or a cold rolled material as a non-plating material. After that, plating is performed. Regarding steel components, it is a component system that can be processed into a complicated shape of a fuel tank, the thickness of the alloy layer at the steel-plating layer interface is thin, and it is possible to prevent plating delamination, and the development of corrosion in the fuel tank and in the external environment. It must be a constitutive ingredient system.

The present invention is characterized in that the components constituting the film and the thickness thereof are specified, and the manufacturing method is not specified, but the hot dipping method is suitable. The electroplating method can also be manufactured by combining appropriate heat treatment conditions. The main reason for recommending the hot dip plating method is to secure the coating weight. Even in the electroplating method, if the electrolysis is carried out for a long period of time, the amount of plating adhered can be secured, but there is a problem in economic efficiency. In the present invention, the range of coating weight is 2.0 to
15.0μ (one side), about 2.0 if alloy layer thickness is taken into consideration
The area is relatively thick with ˜16.5 μ, and the hot dipping method is most suitable.

Corrosion on the inner surface of the tank is not a problem when only normal gasoline is used, but a considerably severe corrosive environment appears due to mixing of water and chlorine ions and generation of organic carboxylic acid due to oxidative deterioration of gasoline. . If gasoline leaks out of the tank due to piercing corrosion, it can lead to serious accidents and these corrosions must be completely prevented. When deteriorated gasoline containing the above corrosion-promoting component was prepared and the performance under various conditions was investigated, tin 8
It was confirmed that the tin-based alloy plating containing more than 0.0% exhibits extremely excellent corrosion resistance. In the case of a tin-only film, since the plating metal does not have a sacrificial anticorrosion function, corrosion in the pinhole portion of the plating layer that is always present industrially becomes a problem. The presence of stable pure tin results in the corrosion of dissimilar metals and promotes the dissolution of iron in the pinholes.

In the case of a 100% tin film, the tin film has a more noble potential in the corrosive liquid than the iron, so that the iron is preferentially dissolved in the plating pinholes, and the plating corros
cause ion. In order to prevent this, the electric potential of tin may be set to be baser than that of iron. It is possible to make the potential of tin less base than iron by adding zinc in an amount of 1% or more, but if a large amount of zinc is added in an amount of 20% or more, only zinc will be preferentially dissolved, which may cause engine clogging. There is. Therefore, zinc is added as the remaining 20%, to be exact 1 to 20%, as a component. On the other hand, the outer surface of the tank is often painted after the tank is molded because perfect rust prevention is required. Therefore, the rust preventive ability as a whole depends on the coating thickness, but a sacrificial anticorrosive effect by metal plating is required at a defective portion of the coating film caused by the local flying or collision of stones or the like.

Zn ≦ 20%, Cr ≦ 5.0%, Mn ≦
5.0%, Ti ≦ 5.0%, Al ≦ 5.0%, Cd ≦
One kind or two or more kinds of 5.0% and Mg ≦ 5.0% are contained in total of 20% or less. The main component of addition is zinc, which imparts sacrificial anticorrosive ability. When zinc alone is used, white rust tends to occur when the amount is increased. Additive elements other than zinc have the effect of modifying the white rust of zinc, and improve the corrosion resistance by stabilizing and stabilizing the corrosion product. Therefore, a smaller amount than zinc may be added as an addition aid. Metal tin itself is a metal that is relatively stable in the atmosphere, but its sacrificial anticorrosive ability to protect iron is weak, so Zn, M
An effective means is to add n, Cd, Al, Cr, Ti, Mg or the like to improve the sacrificial anticorrosion ability. In particular, the greater the amount of zinc deposited, the higher the sacrificial anticorrosion ability, and the greater the effect of preventing red rust of iron or preventing the elution of iron on the inner surface of the tank.

As described above, having a sacrificial anticorrosive action is an important factor, but when zinc is packaged in a large amount exceeding 20%, the preferential dissolution of zinc becomes strong, and the corrosion product becomes short-term. Since a large amount is generated, there is a problem that the engine is likely to be clogged. In addition, the workability of the plated layer also decreases due to the increase in the zinc content. Furthermore, the solder content is significantly reduced by increasing the zinc content. Therefore, in the present invention, a tin-based alloy containing tin in an amount of more than 80% is basically used, and zinc is added as a main component to impart a sacrificial anticorrosion property to the alloy.
r, Mn, Ti, Al, Cd, Mg, etc. are added as auxiliary additives. 5% or less of each of these auxiliary additives is sufficient.

Next, as to the reason for limiting the thickness of the metal plating layer, if it is less than 2.0 μm, many micro defects are locally (where the iron base is exposed) due to severe processing during tank molding.
Occurs and the corrosion resistance is greatly deteriorated. Corrosion resistance improves as the amount of adhesion increases, but problems such as weldability occur due to the low melting point metal, and tin is a relatively expensive metal,
Excessive adhesion is economically disadvantageous. Therefore, the upper limit thickness of the metal plating layer is set to 15.0 μ.

In the present invention, an alloy layer is required under these tin-based alloys to obtain strong adhesion to the iron substrate and good corrosion resistance. In order to prevent the occurrence of plated pinholes and obtain a uniform plated film having good corrosion resistance, it is important that the surface to be plated and the plated metal are well wetted (alloyed). In order to process a complicated shape such as a fuel tank, it is necessary to secure a high degree of workability.

The alloy layer must be formed in a small amount in order to get wet well, but it is hard and brittle, so cracks are likely to occur during processing. If the thickness exceeds a certain thickness, cracks propagate to the plating layer outside the alloy layer and the plating layer This will cause cracks in the interior, which will cause deterioration of corrosion resistance due to plating peeling and damage to the plating layer. Such plating peeling is very closely related to the plating type, thickness, and steel type, and in the case of the present invention, the alloy layer thickness needs to be in the range of 0.05 to 1.5 µ.

In order to improve the wettability, it is effective to change the surface of the steel sheet. In the manufacturing process of a steel sheet, some oxides formed on the surface of the steel sheet are difficult to remove, which hinders the plating property. In order to eliminate this effect, Ni, Co, C that easily reacts with tin on the surface of the steel sheet immediately before plating
u, etc. are plated to improve wettability. Ni, Co, Cu
Etc. may be plated alone, an alloy with iron, or an alloy of these metals. The amount of plating is such that the surface of the steel sheet is uniformly covered, for example, 0.1 to 2.0 g.
/ M ² is sufficient. The product after plating is N
0.5% or more of one or more of i, Co, Cu is contained in the alloy layer, but the main component is iron, which reacts with tin, zinc, and other auxiliary additives constituting the metal plating layer. 50% or more of the composition of the alloy layer is (Fe
+ Sn).

Further, in order to improve the wettability with the plating metal (tin-based alloy), the surface of the steel sheet is underplated with Ni, Co, Cu or the like. These components are relatively noble metals, and as the amount of these components increases, the alloy layer formed naturally also has noble potential. When this alloy layer is exposed due to processing, the effect of promoting the dissolution of the tin-based plating metal becomes stronger, so Fe + S
The composition was limited to n ≧ 50.0%.

In the present invention, the outermost layer plays an important role in controlling corrosion resistance, weldability, solderability and brazing property. In the case of a tin-based alloy, particularly a tin-based alloy in which tin accounts for more than 80%, the solderability and brazing property are basically excellent, but the weldability is difficult. Spot welding and seam welding are often used as the manufacturing method for gasoline tanks, and they are not considered to be useful materials because of their poor weldability. Spot welding / seam welding is electric resistance welding using a copper-based alloy as an electrode, and the tin-based alloy that is the plating metal of the present invention easily reacts with the copper-based alloy of the electrode due to heat during welding,
Deterioration of the electrode life is regarded as a problem. If this problem can be solved, the plated steel sheet of the present invention can be regarded as a tank material having excellent workability, corrosion resistance, and weldability.

In the present invention, C is formed on the above-mentioned metal plating.
Adhesion amount 0.01-containing at least one of r, Si, P and Mn
The presence of an organic-inorganic composite coating of 2.0 g / m ² is intended to improve spot welding / seam weldability. As the organic resin film, an acrylic resin, a polyester resin, or an epoxy resin, which has excellent adhesion to a metal, is used as a desirable base resin. These resins are
It is used as an organic-inorganic composite resin containing one or more compounds of Cr, Si, P, Mn as a solvent type or water-soluble type.

The chromium compound is added in the form of chromic acid or chromate salt in order to improve the rust preventive action. The silicon compound is added as an oxide / fluoride to improve the film characteristics. The phosphorus compound is added as an organic / inorganic phosphoric acid or a phosphoric acid compound for improving the adhesion, corrosion resistance and weldability of the film. Like the chromium compound, the manganese compound is added mainly for the purpose of improving the rust preventive action. The mixing ratio of these compounds and the resin is not particularly limited, but when improving the weldability, the mixing ratio of the organic resin is 80% or less (by weight ratio), preferably 50% or less. It is better to say

The adhesion amount is 0.01 in total weight.
~ 2.0g / m^Two Range, more preferably 0.02
0.50 g / m^Two The range is good. Lower limit value 0.01
g / m ^Two Is the limit at which improvement in corrosion resistance and weldability is recognized.
Yes, upper limit value 2.0 g / m^Two Is a local abnormality during welding
This is the limit of spatter generation due to heat generation. Hereinafter, the present invention
For fuel tanks with excellent workability and corrosion resistance
An example of a rustproof steel plate will be shown.

In each of the present invention and the comparative example, the steel sheet to be plated was a flux for plating containing zinc chloride and hydrochloric acid after the annealed and pressure-controlled steel sheet having a thickness of 0.8 mm was subjected to the undercoating shown in Table 1. Was applied and introduced into the Sn-based alloy plating bath in Table 1. After the plating bath and the surface of the steel sheet were sufficiently reacted, the steel sheet was drawn out, the coating amount was adjusted by the gas wiping method, and the steel sheet was rapidly cooled. The thickness of the alloy layer was adjusted by the reaction time between the plating bath and the steel plate surface. After plating, an organic-inorganic composite film was formed under the conditions shown in Table 1. As a result, the alloy layer, the plating layer and the organic-inorganic composite film shown in Table 2 were formed. Fe and Sn in the alloy layer were mainly FeSn ₂ .

[0022]

[Table 1]

[0023]

[Table 2]

The steel plate obtained as described above was left in a pressure vessel at 100 ° C. for one day and night, and 10 vol% of water was added to forcedly deteriorated gasoline to prepare a corrosive solution simulating internal corrosion of the tank. 45 ℃ x 3 in this corrosive liquid
A corrosion test was conducted for a week, and the metal ion elution results shown in Table 3 were obtained. The metal ion elution amount of the present invention was small and excellent. The processing method and bondability were judged by making an actual tank by trial, and the results shown in Table 3 were obtained. Here, the workability was evaluated by the press workability. A cylindrical deep drawing test was performed as a method of determining press workability. A 200 mmφ blank was squeezed out with a punch having a diameter of 100 mmφ, and the state of plating removal on the side wall of the cup was observed. In order to make a rigorous determination of workability, the shoulder radius of the die was set to 2.5 mm, and stricter processing conditions than usual were adopted.

[0025]

[Table 3]

The bondability was evaluated by seam weldability and spot weldability. -Seam weldability: Continuous seam welding was performed by a constant current control method of 60 Hz single layer alternating current (disc diameter 300 mmφ, electrode diameter 6R), and weldability was determined by observing the cross section and surface of the welded portion.・ Spot weldability: Tip diameter 6 with stationary spot welder
A continuous dot test was conducted using a constant current control system of a single-layer alternating current of 60 Hz using an electrode of mm. The cross section was observed at every 20 spots, the number of spots until the nugget diameter fell below a certain value was determined, and the weldability was determined. The evaluation symbols are ⊚: excellent, ◯: good, and x: poor.

[0027]

Industrial Applicability According to the present invention, a lead-free rust preventive steel sheet for a fuel tank, which is excellent in corrosion resistance, workability and weldability and can withstand deteriorated gasoline for a long time, can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuyoshi Okada 1-1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works

Claims (4)

[Claims] 1. The surface of a steel sheet to be plated contains Fe and Sn in a total amount of 50% or more and has a thickness of 0.05 to 1.5 μm.
Has an alloy layer of and the thickness is 2.0-15.0μ on the surface.
It has an Sn-based alloy plating layer of m, and further has an organic-inorganic composite coating of 0.01 to 2.0 g / m ^{2 on} its surface, and has excellent workability, corrosion resistance, and weldability. Anti-rust steel plate for fuel tank. 2. A Sn-based alloy plating layer comprising: Zn: 20% or less, Cr: 5% or less, Mn: 5% or less, Ti: 5% or less, Al: 5% or less, Cd: 5% or less, Mg: The fuel tank excellent in workability, corrosion resistance, and weldability according to claim 1, characterized in that it contains 5% or less of one kind or two or more kinds in total of 20% or less, and the balance is Sn and unavoidable impurities. Anti-rust steel plate for use. 3. The organic-inorganic composite coating comprises Cr, Si,
1 or 2 or more of each of P and Mn-based compounds in total is 2
The rust preventive steel sheet for a fuel tank having excellent workability, corrosion resistance, and weldability according to claim 1 or 2, characterized by containing 0% or more. 4. The processability / corrosion resistance according to claim 1, wherein the organic resin of the organic-inorganic composite coating is one or more of acrylic, polyester and epoxy resins. Anti-rust steel plate for fuel tanks with excellent weldability.