JP3126622B2 - Rustproof steel plate for fuel tank - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rustproof steel plate for a fuel tank.

[0002]

2. Description of the Related Art Conventionally, zinc-tin alloy plated steel sheets have been mainly produced by an electroplating method in which electrolysis is carried out in a solution containing zinc and tin ions as disclosed in Japanese Patent Application Laid-Open No. 52-130438. Zinc-tin alloy-plated steel sheets, which contain tin in addition to zinc, have excellent corrosion resistance and solderability, and have been widely used for electronic parts and the like. In the hot-dip plating method, the coating weight can be relatively easily increased.
Products manufactured by the hot-dip plating method are used in harsh environments such as outdoor applications. For example, Japanese Patent Application Laid-Open No. Hei 4-214848 discloses a coating obtained by plating an iron-based material with a zinc-tin alloy of 70 to 98% by weight of tin and a method for producing the same.
In JP-A-5-263208, an alloy layer containing tin as a hot-dip zinc or hot-dip zinc alloy plating layer on an iron-based substrate,
Alternatively, there is disclosed a zinc-based plating coating which is sequentially coated with a chromium plating layer on an alloy layer containing zinc and aluminum, and a production method. On the other hand, Pb- has been used as a fuel tank material, which has excellent corrosion resistance, workability, solderability, weldability, etc.
Sn-plated steel sheets and the like are mainly used in Japan and overseas and have been used as actual fuel tanks.

[0003]

Although the use of the tin-zinc coated steel sheet by the electroplating method has improved the solderability and corrosion resistance, it is not suitable for an environment requiring long-term corrosion resistance such as a fuel tank. Although a coated steel sheet with a large amount of adhesion is required, the control of the amount of adhesion in the electroplating method depends on the time and the magnitude of the current, so the amount of adhesion can be increased, but the processing time can be lengthened and a large amount of current can be applied. Need to do so, which raises major productivity and economic problems. In addition, the use of tin-zinc plated steel sheet by hot-dip coating method shows considerable corrosion resistance even in salt spray, but the structure of the plating layer is usually an iron-zinc alloy layer with a characteristic such as a shelf-like layer and a columnar layer. 5 to 35 μm (the outer coating layer is 5 to 40 μm, preferably 10 to 30 μm), which is equal to or more than the thickness of the coating layer. For harsh processing such as the above, since the alloy layer is higher in hardness than the plating coating layer, when the ratio of such an alloy layer to the plating coating layer is high and the thickness is large, cracks etc. are likely to occur and corrosion of the inner and outer surfaces of the fuel tank Progress is much more likely to occur, making it unsuitable as a fuel tank material.

Further, when the iron-based substrate is sequentially coated with a zinc or zinc alloy layer and a chromium plating layer, a chromium coating layer is added to further improve the corrosion resistance and the like. 75 μm, preferably 10-5
0 μm, more preferably 10 to 30 μm, which is very thick. As described above, the corrosion resistance is secured by the alloy layer, and in the hot-dip plating method, since the base iron is contained in the alloy layer, the hardness increases and the workability is greatly increased. Therefore, it is not suitable as a fuel tank material. In addition, the use of Pb-Sn plated steel sheets ensures corrosion resistance that satisfies the life of the vehicle, workability that can be processed according to the complicated structure of the vehicle bottom, solderability that can join fuel tank parts, and weldability. The use of Pb-Sn plated steel sheets is not preferable for environmental regulations such as Pb elution from industrial waste such as shredder dust because Pb is contained in the Pb-Sn plated steel sheets.

[0005]

Means for Solving the Problems Accordingly, the present inventors have proposed P
In order to provide a rustproof steel plate for a fuel tank containing no b (excluding unavoidable impurities), the coating layer structure was examined in various ways, and the structure of this configuration satisfies the required performance as a fuel tank material. This is what we have learned. The gist is as follows: (1) An alloy layer containing at least one of Ni, Fe, Zn, and Sn on the surface of a steel sheet has a thickness of 2 μm or less per side, and tin: 40 to 99 wt%, the remaining zinc and unavoidable impurities. The major axis of the zinc crystal contained therein is 250 μm
A rust-preventive steel plate for a fuel tank, characterized in that there are 20 or less / 0.25 mm ² and a tin-zinc alloy plating layer having a thickness per side of 4 to 50 μm.

(2) Ni, Fe, Zn, S
An alloy layer containing at least one kind of n has a thickness of 2 μm or less per side, and further contains tin: 40 to 99 wt%, the balance being zinc and unavoidable impurities, and having a major axis of zinc crystal of 250 μm or more. 20 or less / 0.25 mm ² , there is a tin-zinc alloy plating layer with a thickness of 4 to 50 μm per side, and further a chromate-treated coating of 0.2 to 25 mg / m ² per side in terms of Cr on the outside. A rustproof steel plate for a fuel tank characterized by having:

Hereinafter, the present invention will be described in detail. After using an annealed steel plate or rolled material as a material to be plated, which has been subjected to heat treatment such as hot rolling, pickling, cold rolling, or the like from a slab, and after performing a pretreatment such as removal of rolling oil. Perform plating. The plated steel sheet manufactured in this manner is used.
With respect to the alloy structure near the steel, when hot-dip or electroplating is performed and then heat treatment is performed to perform a sealing treatment, a structure including a steel component and a plating component is generated at the interface with the steel. This structure is hereinafter referred to as an alloy layer. This alloy layer contains Ni, Fe, Zn,
Although they contain one or more types of Sn, these structures are less likely to corrode with fuels such as gasoline, and a thicker alloy layer is advantageous in that long-term corrosion resistance is ensured. However, from the point of ensuring strict workability suitable for the complicated shape of the lower part of the car, the hardness of this structure is high, so cracks occur in the alloy layer during processing, and when the alloy layer thickness is larger than a certain thickness, the upper part of the alloy layer Cracks propagate in the plating layer to cause cracks in the plating layer, and there is a concern that corrosion resistance may be degraded due to plating peeling or damage to the plating layer. Therefore, the thickness of the present alloy layer is set to 2 μm or less.

The plating layer is composed of a composition containing tin and zinc, and has a corrosion resistance inside the tank against fuel such as gasoline, an outside corrosion resistance against a salt damage environment generated when running in a snow-melting salt spray area, and furthermore, a structure according to the structure of the lower part of the automobile. It is necessary to ensure the workability that can be processed by soldering and the solderability necessary for joining parts such as fuel pipes. When the tin content in the plating layer is less than 40%, the corrosion resistance of the inner surface of the tank is greatly reduced, the dissolution rate of the plating layer is increased, and the dissolution rate of the plating layer in a salt damage environment is also increased, so that the corrosion resistance is significantly reduced. . In addition, the workability of the plating layer also decreases as the zinc content increases. Furthermore, the zinc content increases and the solderability is greatly reduced. When the tin content in the plating layer is more than 99%, the performance is not particularly deteriorated, but the sacrificial corrosion protection effect of the plating layer in a salt damage environment is reduced, and when a flaw or the like is formed, iron rust is easily generated from the substrate. Therefore, tin: 40 to 99 wt% as a plating layer composition,
The balance consisted of zinc and unavoidable impurities.

Regarding the form of zinc in the plating layer, when zinc precipitates as a primary crystal during the cooling process, if the size of the zinc crystal is large, the zinc crystal is likely to preferentially corrode, and the plating layer is locally corroded. The life until the plating layer penetrates is shortened.
In the case of processing, the large zinc crystal becomes a crack propagation path, and the crack propagates through the plating layer to cause plating exfoliation or accelerate the progress of corrosion to the steel. Therefore, there is a problem that the size of the zinc crystal in the plating layer is too large, so that the number of the zinc crystals having a major axis of 250 μm or more is set to 20 or less / 0.25 mm ² .

[0010] The thickness of the plating layer affects the corrosion resistance, but if it is too thin, the corrosion tends to progress to the substrate in a relatively short period of time, and the fine pinholes generated during plating cover the material for a long time as a fuel tank material. Since the substrate is exposed without being exposed, substrate corrosion occurs earlier than the life estimated from the plating thickness. If the plating thickness is too thick, the corrosion resistance is sufficiently ensured, but the performance becomes excessive. Note that the soldering property also depends on the amount of adhesion, and when the amount of adhesion is extremely small, it is easily affected by the base and the soldering property is reduced. Therefore, the plating thickness was 4 to 50 μm per side. Further, a chromate treatment film is provided on the plating layer. This treated film is very familiar with the plating layer of the present composition, and has an effect of covering a defective portion such as a minute pinball or the like and dissolving the plating layer to repair a pinhole, and greatly improves corrosion resistance. Therefore, the lower limit for improving the corrosion resistance was 0.2 mg / m ^{2 in} terms of Cr. In addition, when the amount of adhesion in this treatment increases, the solderability is greatly reduced. Therefore, the upper limit was set to 25 mg / m ^{2 in} terms of Cr. Therefore, the amount of this treatment is 0.2 to 25 mg / m ^{2 in} terms of Cr.
And

[0011]

EXAMPLES The quality characteristics of the rustproof steel plate for a fuel tank according to the present invention will be shown in examples. Example 1 After annealed low C steel was degreased and pickled, Ni pre-plating was performed.
The Fe-Ni pre-plating was performed or the pre-plating was not performed, but the continuous hot-dip plating was performed by a flux method to adjust the adhesion amount, and further cooled to produce the present material. Tables 1 to 9 show the inner corrosion resistance, outer corrosion resistance, and solderability of the obtained material. (1) Inner Surface Corrosion Resistance (Tables 1 to 3) The inner surface corrosion resistance was determined using samples having the following shapes and test conditions. As a result, the material of the present invention was good without corrosion from the substrate. On the other hand, in the comparative material, red rust and red discoloration from the base material and large discoloration due to the effect of the dissolution of the plating layer were large, and the corrosion resistance was not good.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

[Table 3]

(Inner surface evaluation method)-A cup drawing process is performed, and fuel is sealed therein.
A monthly test was performed to evaluate the appearance of the inner surface of the sample and the state of substrate corrosion.・ Cup drawing condition: punch diameter 30mmφ, blank diameter 60
mmφ, drawing depth 15mm ・ Corrosion test solution: Degraded gasoline 100 times diluted solution 4.5
cc + 0.5 cc of distilled water ・ Judgment method: ◎ No significant change in appearance, あ り Significant change in appearance, × Rust from substrate (signs in Tables 1 to 3) * 1: Ni or Fe-Ni Ni content of plating (g /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area.

(2) Corrosion resistance on the outer surface (Tables 4 to 6) The corrosion resistance on the inner surface was determined by using samples having the following shapes and test conditions. As a result, the material of the present invention was good without corrosion from the substrate. On the other hand, in the comparative material, red rust and red discoloration from the base material and large discoloration due to the effect of the dissolution of the plating layer were large, and the corrosion resistance was not good.

[0017]

[Table 4]

[0018]

[Table 5]

[0019]

[Table 6]

(External Surface Evaluation Method) The sample was placed horizontally so that the outer surface was exposed to salt spray, and the appearance after one month test and the state of substrate corrosion were evaluated.・ Cup drawing condition: punch diameter 30mmφ, blank diameter 60
mmφ, drawing depth 15 mm ・ Salt water spray condition: 5% sodium chloride solution, 50 ° C. ・ Judgment method: ◎ No significant change in appearance, △ Significant change in appearance, × Red rust generated (symbols in Tables 4 to 6) * 1: Ni content of Ni or Fe-Ni plating (g /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area.

(3) Solderability (Tables 7 to 9) The solder spreadability was determined based on the following test conditions.
As a result, the material of the present invention showed the same or better results as the current Pb-Sn plated steel sheet. On the other hand, the comparative material, such as a sample having a large Zn content, had poor solderability.

[0022]

[Table 7]

[0023]

[Table 8]

[0024]

[Table 9]

(Evaluation method for solderability) After degreased a flat plate sample with toluene, apply a small amount of flux, apply a certain amount of solder, and then float in a lead bath for a certain period of time, pull up, and measure the spread area did. Test conditions: solder / Pb-40% Sn (250 mg)
Flux / 13% rosin-isopropyl alcohol,
Float in a lead bath / 280 ° C for 30 seconds, then lift. -Judgment method: Compared with Pb-8% Sn-plated steel sheet, ◎ Equal or greater spread area, Δ 50 to 80% spread area, × less than 50% spread area (Table 7 to Table 9 * 1: Ni content of Ni or Fe-Ni plating (g / g)
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area.

Example 2 Annealed low C steel was degreased and pickled, and then Ni pre-plated.
The material was manufactured by performing continuous hot-dip plating by a flux method without or with pre-plating of Fe—Ni to adjust the amount of adhesion, and after cooling, chromate treatment. Tables 10 to 12 show the inner corrosion resistance, outer corrosion resistance, and solderability of the obtained material. (1) Inner Surface Corrosion Resistance (Table 10) The inner surface corrosion resistance was determined using samples having the following shapes and test conditions. As a result, the material of the present invention was good without corrosion from the substrate. On the other hand, in the comparative material, there was red rust and red discoloration from the substrate, and large discoloration due to the effect of the significant dissolution of the plating layer, and the corrosion resistance was not good.

[0027]

[Table 10]

(Inner surface evaluation method)-A cup drawing process is performed, a fuel is sealed therein, and the temperature is reduced to 1 at 45 ° C.
A monthly test was performed to evaluate the appearance of the inner surface of the sample and the state of substrate corrosion.・ Cup drawing condition: punch diameter 30mmφ, blank diameter 60
mmφ, drawing depth 15mm ・ Corrosion test solution: Degraded gasoline 100 times diluted solution 4.5
cc + 0.5 cc of distilled water ・ Judgment method: ◎ No significant change in appearance, あ り Significant change in appearance, × Rust from substrate (meaning in Table 10) * 1: Ni content of Ni or Fe-Ni plating (G /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

(2) Outer surface corrosion resistance (Table 11) The inner surface corrosion resistance was determined by using samples having the following shapes and test conditions. As a result, the material of the present invention was good without corrosion from the substrate. On the other hand, in the comparative material, there was red rust and red discoloration from the substrate, and large discoloration due to the effect of the significant dissolution of the plating layer, and the corrosion resistance was not good.

[0030]

[Table 11]

(External Surface Evaluation Method) The sample was placed horizontally so that the outer surface was exposed to salt spray, and the appearance and the state of corrosion of the substrate after one month were evaluated.・ Cup drawing condition: punch diameter 30mmφ, blank diameter 60
mmφ, drawing depth 15mm ・ Salt water spray condition: 5% sodium chloride solution, 50 ° C ・ Judgment method: ◎ No significant change in appearance, △ Significant change in appearance, × Red rust generated (meaning in Table 11) * 1 : Ni content of Ni or Fe-Ni plating (g /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

(3) Solderability (Table 12) The solder spreadability was determined based on the following test conditions.
As a result, the material of the present invention showed the same or better results as the current Pb-Sn plated steel sheet. On the other hand, the comparative material was a sample having a large Zn content, a sample having a large amount of chromate film, and the like, and had poor solderability.

[0033]

[Table 12]

(Evaluation method of solderability) A flat plate sample was degreased with toluene, coated with a small amount of flux, soldered in a fixed amount, then floated in a lead bath for a certain period of time, lifted up, and the spread area was measured. Test conditions: Solder / Pb-40% Sn (with 250 mg), flux / 13% rosin-isopropyl alcohol, lead bath / floating in 280 ° C. for 30 seconds, then pull up. -Judgment method: Compared with Pb-8% Sn-plated steel sheet, ◎ Equal or greater spread area, Δ 50 to 80% spread area, × less than 50% spread area (meaning in Table 12) * 1: Ni content of Ni or Fe-Ni plating (g /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

Example 3 A hot-rolled sheet or cold-rolled sheet having been pickled is degreased and pickled, and then Ni pre-plating or Fe-Ni pre-plating is performed. After performing a heat treatment in a furnace having an oxidation furnace, a non-oxidation furnace, a reduction furnace, or the like as it is, hot-dip plating was performed, the amount of adhesion was adjusted, and the material was further cooled to produce the present material.
Tables 13 to 15 show the inner surface corrosion resistance, outer surface corrosion resistance, and solderability of the obtained material. (1) Inner Surface Corrosion Resistance (Table 13) Inner surface corrosion resistance was evaluated using samples having the following shapes and test conditions. As a result, the material of the present invention was good without corrosion from the substrate. On the other hand, in the comparative material, red rust and red discoloration from the base material and large discoloration due to the effect of the dissolution of the plating layer were large, and the corrosion resistance was not good.

[0036]

[Table 13]

(Inner surface evaluation method)-A cup drawing process is performed, a fuel is filled therein, and a
A monthly test was performed to evaluate the appearance of the inner surface of the sample and the state of base corrosion.・ Cup drawing condition: punch diameter 30mmφ, blank diameter 60
mmφ, drawing depth 15mm ・ Corrosion test solution: Degraded gasoline 100 times diluted solution 4.5
cc + 0.5 cc of distilled water ・ Judgment method: ◎ No significant change in appearance, あ り Large change in appearance, × Rust from substrate (meaning in Table 13) * 1: Ni content of Ni or Fe-Ni plating (G /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

(2) Outer Surface Corrosion Resistance (Table 14) The outer surface corrosion resistance was determined by using samples having the following shapes and test conditions. As a result, the material of the present invention was good without corrosion from the substrate. On the other hand, in the comparative material, there was red rust and red discoloration from the substrate, and large discoloration due to the effect of the significant dissolution of the plating layer, and the corrosion resistance was not good.

[0039]

[Table 14]

(External Surface Evaluation Method) The sample was placed horizontally so that the outer surface was exposed to salt spray, and the appearance and the state of corrosion of the substrate after one month were evaluated.・ Cup drawing condition: punch diameter 30mmφ, blank diameter 60
mmφ, drawing depth 15mm ・ Salt water spray condition: 5% sodium chloride solution, 50 ° C ・ Judgment method: ◎ No significant change in appearance, △ Significant change in appearance, × Red rust generated (meaning in Table 14) * 1 : Ni content of Ni or Fe-Ni plating (g /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

(3) Solderability (Table 15) The solder spreadability was determined based on the test conditions shown below.
As a result, the material of the present invention showed the same or better results as the current Pb-Sn plated steel sheet. On the other hand, the comparative material was a sample having a high Zn content and the solderability was not good.

[0042]

[Table 15]

(Evaluation method of solderability) A sample of a flat plate was degreased with toluene and coated with a small amount of flux. Then, a fixed amount of solder was applied. Test conditions: Solder / Pb-40% Sn (with 250 mg), flux / 13% rosin-isopropyl alcohol, lead bath / floating in 280 ° C. for 30 seconds, then pull up. -Judgment method: Compared with Pb-8% Sn plated steel sheet, ◎ Equal or greater spread area, Δ 50 to 80% spread area, × less than 50% spread area (meaning in Table 15) * 1: Ni content of Ni or Fe-Ni plating (g /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

Example 4 A hot-rolled sheet or a cold-rolled sheet which has been pickled is degreased and pickled, and then Ni pre-plating or Fe-Ni pre-plating is performed. Heat treatment was performed in a furnace having an oxidation furnace, a non-oxidation furnace, a reduction furnace, or the like as it was, hot-dip plating was performed to adjust the amount of adhesion, and after cooling, chromate treatment was performed to produce the present material. (1) Inner Corrosion Resistance (Table 16) The inner surface corrosion resistance was determined by using samples having the following shapes and test conditions. As a result, the material of the present invention was good without corrosion from the substrate. On the other hand, in the comparative material, there was red rust and red discoloration from the substrate, and large discoloration due to the effect of the significant dissolution of the plating layer, and the corrosion resistance was not good.

[0045]

[Table 16]

(Inner surface evaluation method)-A cup drawing process is performed, and fuel is sealed therein.
A monthly test was performed to evaluate the appearance of the inner surface of the sample and the state of base corrosion.・ Cup drawing condition: punch diameter 30mmφ, blank diameter 60
mmφ, drawing depth 15mm ・ Corrosion test solution: Degraded gasoline 100 times diluted solution 4.5
cc + 0.5 cc of distilled water ・ Judgment method: ◎ No significant change in appearance, △ Large change in appearance, × Rust from substrate (meaning in Table 16) * 1: Ni content in Ni or Fe-Ni plating (G /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

(2) Outer Surface Corrosion Resistance (Table 17) The outer surface corrosion resistance was determined using samples having the following shapes and test conditions. As a result, the material of the present invention was good without corrosion from the substrate. On the other hand, in the comparative material, there was red rust and red discoloration from the substrate, and large discoloration due to the effect of the significant dissolution of the plating layer, and the corrosion resistance was not good.

[0048]

[Table 17]

(External Surface Evaluation Method) The sample was placed horizontally so that the outer surface was exposed to salt water spray during the cup drawing process, and the appearance and the state of body corrosion one month later were evaluated.・ Cup drawing condition: punch diameter 30mmφ, blank diameter 60
mmφ, drawing depth 15mm ・ Salt water spray condition: 5% sodium chloride solution, 50 ° C ・ Judgment method: ◎ No significant change in appearance, △ Significant change in appearance, × Red rust generated (meaning in Table 17) * 1 : Ni content of Ni or Fe-Ni plating (g /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

(3) Solderability (Table 18) The solder spreadability was determined based on the test conditions shown below.
As a result, the material of the present invention showed the same or better results as the current Pb-Sn plated steel sheet. On the other hand, the comparative material was a sample having a large Zn content and a material having a large amount of chromate film, and the solderability was not good.

[0051]

[Table 18]

(Evaluation method of solderability) A sample of a flat plate was degreased with toluene, coated with a small amount of flux, soldered in a fixed amount, then floated in a lead bath for a certain period of time, pulled up, and measured the spread area. Test conditions: Solder / Pb-40% Sn (250 mg attached), flux / 13% rosin-isopropyl alcohol, lead bath / floating in 280 ° C. for 30 seconds, then lift. -Judgment method: Compared with Pb-8% Sn-plated steel sheet ◎ Spread area equal or greater △ Spread area of 50 to 80% × Spread area of less than 50% (meaning in Table 18) * 1: Ni Alternatively, the Ni content of the Fe—Ni plating (g /
m ² ) * 2: Number of zinc crystals with a major axis of 250 μm or more contained in the plating layer per 0.25 mm ² surface area

[0053]

As described above, the present invention has an extremely excellent effect of obtaining a rustproof steel plate for a fuel tank having excellent characteristics as a fuel tank material.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Satoru Sawada 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Yawata Works (56) References JP-A-63-69631 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 2/06-2/08 C23C 28/00-28/02 C23C 30/00

Claims (2)

(57) [Claims] 1. An alloy layer containing at least one of Ni, Fe, Zn and Sn on the surface of a steel sheet having a thickness of 2 μm or less on one side, and further comprising tin: 40 to 99 wt%, balance zinc and unavoidable impurities. A fuel tank characterized by having a tin-zinc alloy plating layer having a zinc crystal having a major axis of 250 μm or more and having a major axis of not more than 20 / 0.25 mm ² , and having a thickness per side of 4 to 50 μm. Rust-proof steel plate. 2. An alloy layer containing at least one of Ni, Fe, Zn, and Sn on the surface of a steel sheet having a thickness of 2 μm or less on one side, and further comprising tin: 40 to 99 wt%, balance zinc and unavoidable impurities. Among them, there are 20 or less zinc crystals having a major axis of 250 μm or more and 0.25 mm ² or less, and there is a tin-zinc alloy plating layer having a thickness per side of 4 to 50 μm. in fuel tank for anticorrosive steel sheet characterized by having a chromate conversion coating in per side 0.2~25mg / m ^2.