JP3133235B2 - Steel plate for fuel tank with excellent workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, tin-zinc 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. In addition, tin-zinc alloy-plated steel sheets have excellent corrosion resistance and solderability because they contain tin in addition to zinc, 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, in Japanese Patent Application Laid-Open No. 4-214848, 70 to 98% by weight of tin-
A tin alloy plated coating and a method for producing the same are disclosed. Japanese Patent Application Laid-Open No. 5-263208 discloses a zinc-based material in which an iron-based substrate is coated with molten zinc or an alloy layer containing tin as a galvanized zinc alloy plating layer, or an alloy layer containing zinc and aluminum, which is sequentially coated with a chromium plating layer. Plating coatings and manufacturing methods are disclosed. On the other hand, lead-tin plated steel sheets excellent in corrosion resistance, workability, solderability, etc. have been used mainly in Japan and overseas as fuel gasoline tank materials, 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 addition can be increased, but the treatment time can be lengthened or a large amount of current can be passed. Need to be created, which causes major problems in productivity and economy. 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. The thickness is 5 to 35 μm (the outer plating layer is 5 to 40 μm, preferably 10 to 30 μm), which is equal to or more than the thickness of the plating layer. For severe processing such as a tank, the alloy layer is larger than the plating layer. When the hardness is high and the ratio of such an alloy layer to the plating coating layer is high and the thickness is large, cracks easily enter the vicinity of the alloy layer and plating and peeling and cracks easily develop on the inner and outer surfaces, and as a fuel tank Not suitable.

[0004] Further, the iron-based substrate is a zinc or zinc alloy layer,
When sequentially coated with a chromium plating layer, the chromium coating layer is added to further improve the corrosion resistance and the like, but the thickness of the zinc or zinc alloy layer is 5 to 75 μm, preferably 10 to 5 μm.
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 the hardness is increased because the base iron is contained in the alloy layer in the hot-dip plating method, and the workability is greatly increased. And is unsuitable as a fuel tank material. In the use of lead-tin plated steel sheet,
Corrosion resistance that satisfies the service life of the vehicle, processing that can be adapted to the complex structure of the vehicle bottom, solderability that can join fuel tank parts, and weldability are ensured, but lead elution from industrial waste such as shredder dust With respect to environmental regulations such as regulations, it is not preferable because lead-tin plated steel sheets contain lead. Further, the processing degree of the fuel tank tends to become more and more severe due to an increase in four-wheel drive vehicles and the like, and workability equal to or higher than that of a lead-tin plated steel sheet is required.

[0005]

In order to provide a steel plate for a fuel tank containing no lead (excluding unavoidable impurities), the present inventors have proposed an alloy layer composition, a thickness, a coating layer composition, and the like. Various studies on surface lubricity have revealed that the material of this configuration satisfies the required performance as a fuel tank material with excellent workability. The gist is that an alloy layer containing at least one of nickel, iron, zinc and tin is present on the surface of the steel sheet to be plated at a thickness of 1.5 μm or less on one side, and zinc, tin, and zinc- The tin plating layer is present in an amount of 2 to 25 μm per side, and the number of zinc crystals in the plating layer is not more than 20 / 0.25 mm ^{2 when} viewed from the plating surface. It is a steel plate for a fuel tank excellent in workability, characterized by having a Ra of 0.2 to 3.0 µmRa.

Hereinafter, the present invention will be described in detail. Pre-treatment such as removing rolling oil by using an annealed steel sheet or rolled material that has been subjected to heat treatment such as hot rolling, pickling, cold rolling, or rolling from a slab as a non-plated material. After that, plating is performed. The plated steel sheet manufactured in this manner is used. Regarding the composition of the alloy layer in the vicinity of steel, after hot-dip plating or electroplating, heat treatment and sealing
A structure containing both components is formed at the plating layer interface. This structure is hereinafter referred to as an alloy layer. This alloy layer contains nickel, iron, zinc,
Although they contain one or more types of tin, their structure progresses slowly with respect to gasoline fuel, and a thicker alloy layer is advantageous in ensuring long-term corrosion resistance. However, in order to perform severe processing suitable for a complicated shape with a reduction rate of the thickness of the lower part of the vehicle of about 20%, a small amount of the alloy layer having low workability is preferably small enough to secure plating adhesion. It is necessary to regulate the upper limit of the alloy layer thickness in consideration of the lubricity of the plating surface and the workability of the plating layer, which are closely related to the above.
Therefore, the thickness of the alloy layer is set to 1.5 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, a corrosion resistance outside against salt damage environment such as spraying of snow-melting salt, a workability which can be processed into a complicated shape, and a fuel. It is necessary to have a zinc-tin composition range that can secure solderability and resistance weldability required for joining pipes and the like. When the tin content in the plating layer is less than 70%, the corrosion resistance of the inner surface of the tank and the outer surface in a salt damage environment are greatly reduced, and the dissolution roughness of the plating layer is increased and the zinc content is increased. The crack propagation prevention ability and solderability during the processing of the plating layer are also reduced.
When the tin content exceeds 99%, the performance is not significantly reduced, but when a flaw is formed, iron rust is easily generated from the substrate. Therefore, the composition of the plating layer is considered as
Of zinc: 1 to 30%, with the balance being tin and unavoidable impurities.

Further, the workability has a great influence on the deformability and lubricity of the plating layer main body, and it is necessary to set these conditions optimally when forming the fuel tank. Regarding the thickness of the plating layer, if it is too thin, base corrosion will easily occur for long-term use.However, in severely processed parts in the tank, the plating thickness will be reduced or damaged, so the time until base corrosion is the shortest. Short and dominates life. In the present invention, the lubrication and workability of the plating layer are taken into consideration and the wear of the plating layer during processing is minimized, so that the plating layer can be used even if the plating thickness is relatively small. If the plating thickness is too large, corrosion resistance and the like are sufficiently ensured, but plating peeling may occur during severe processing, and it is necessary to set an upper limit. In consideration of the above, the plating thickness was set to 2 to 25 μm per side.

Regarding the form of zinc in the plating layer, when zinc precipitates as a primary crystal in the cooling process, if the size of the zinc crystal is large, the zinc crystal is liable to corrode preferentially, and the plating layer is locally corroded. The layer dissolves non-uniformly, shortening the life until plating penetration. 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 a passage from the outside through the crack through the plating layer to the substrate, thereby accelerating the progress of corrosion to the substrate. Therefore, there is a problem if the size of the zinc crystal in the plating layer is too large.
20 μm or less / 0.25 mm ² .

[0010] The roughness is related to the surface lubricity and has a great influence on the coefficient of friction and the oil retention. At least at the time of actual tank pressing, the steel plate is coated with at least the rust-preventive oil at the time of product shipment, and oil retention is important. The higher the roughness Ra, the better the oil retention, but if too large, the effect is saturated and the plating thickness becomes locally non-uniform after processing, adversely affecting corrosion resistance and the like. Therefore, the upper limit is Ra3.0.
μm. On the other hand, when the thickness is less than 0.2 μm, the oil retention is significantly reduced and the surface lubricity is deteriorated in the present plating composition.
Considering the above, the roughness Ra was set to 0.2 to 3.0 μm.

When the workability is viewed in terms of the coefficient of friction, the post-treatment for improving various properties such as the plating layer composition and corrosion resistance, the type of the surface film including the coating oil, and the surface unevenness are affected. Cracking occurs in the plating layer or cracks occur in the plating layer, causing a problem that the wear of the plating layer increases and affects the corrosion resistance. Considering this, the dynamic friction coefficient in the zinc-tin based composition region is preferably 0.3 or less after oil application.

[0012]

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-carbon steel was degreased and pickled, nickel or iron-nickel pre-plating was performed, or continuous plating was performed by a flux method without pre-plating, and bath temperature, line speed, and flux conditions were adjusted. Various adjustments were made, the amount of adhesion was adjusted, and the mixture was cooled to produce this material. Further, the surface roughness of the manufactured material was adjusted by the roll roughness and the rolling force during pressure regulation. Tables 1 and 2 show the processing characteristics of the obtained material and the inner surface corrosion resistance of the processed material. (1) Working characteristics Press forming was performed under the test conditions shown below, and the workability and the plating adhesion after working were ascertained. As a result, the present invention obtained the same or better results as the current lead-tin plated steel sheet. On the other hand, in comparison, depending on the workability and lubrication performance of the alloy layer and the plating layer, cracking or plating peeling occurred during processing.

[0013]

[Table 1]

After the rust-preventive oil was applied to the flat plate sample, the working depth was changed and crank pressing was performed, and the maximum working depth at which the work was possible without plating peeling was determined. Test conditions: die shoulder radius / 3.5 mm, die corner radius / 10 mm punch shoulder radius / 3 mm, punch size / 70 × 70 m
m, pressing force 110 ton ・ Evaluation of plating peeling: Carefully taping the outside and inside of the corner side wall after processing, and visually observe the presence or absence of plating peeling. Judgment method: Limit processing depth that can be processed and does not cause plating peeling ◎ 30 mm or more, Δless than 30 mm to 25 mm or more, × 2
Less than 5mm

(2) Inner Corrosion Resistance of Worked Material The inner surface corrosion resistance was determined using samples having the following shapes and test conditions. As a result, in the present invention, good results were obtained without corrosion from the substrate. On the other hand, the comparative material was not good in corrosion resistance due to red rust and red discoloration from the substrate and discoloration due to the effect that the plating layer was largely dissolved.

[0016]

[Table 2]

(Evaluation Method of Inner Corrosion Resistance) A cup drawing process was performed, a fuel was sealed therein, and a test was conducted at 45 ° C. for one month to evaluate the appearance of the inner side wall portion of the sample and the state of base corrosion. However, at the time of squeezing the cup, a rust-preventive oil was used, and before the corrosion resistance test was sufficiently degreased with toluene.・ Cup drawing condition: punch diameter 28.5mmφ, blank diameter 60mmφ, drawing depth 22mm ・ Corrosion test solution: 6.3c of 10 times diluted gasoline diluted solution
c + 0.7 cc of distilled water ・ Judgment method: ◎ No significant change in appearance, △ Significant change in appearance, × Rust from base

Example 2 After acid-washed low-carbon steel is degreased and pickled, nickel or iron-nickel pre-plating is performed, or the hot-rolled sheet and the cold-rolled sheet pickled are oxidized in an oxidation furnace or non-oxidized state. Furnace, after performing heat treatment in a furnace having a reduction furnace, etc., hot-dip plating to adjust the amount of adhesion, and after further cooling, the surface roughness was adjusted by the roll roughness and the rolling reduction at the time of pressure adjustment, and further Chromate treatment was performed to produce the material. Tables 3 and 4 show the processing characteristics of the obtained material and the inner surface corrosion resistance of the processed material. (1) Working characteristics Press forming was performed under the test conditions shown below, and the workability and the plating adhesion after working were ascertained. As a result, the present invention obtained the same or better results as the current lead-tin plated steel sheet. On the other hand, in comparison, depending on the workability and lubrication performance of the alloy layer and the plating layer, cracking or plating peeling occurred during processing.

[0019]

[Table 3]

After the rust-preventive oil was applied to the flat sample, crank pressing was performed while changing the processing depth, and the maximum processing depth that could be processed at that time and had no plating peeling was determined. Test conditions: die shoulder radius / 3.5 mm, die corner radius / 10 mm punch shoulder radius / 3 mm, punch size / 70 × 70 m
m, pressing force 110 ton ・ Evaluation of plating peeling: Carefully taping the outside and inside of the corner side wall after processing, and visually observe the presence or absence of plating peeling. Judgment method: Limit processing depth that can be processed and does not cause plating peeling ◎ 30 mm or more, Δless than 30 mm to 25 mm or more, × 2
Less than 5mm

(2) Inner Corrosion Resistance of Worked Material The inner surface corrosion resistance was ascertained by using samples having the following shapes and test conditions. As a result, in the present invention, good results were obtained without corrosion from the substrate. On the other hand, the comparative material was not good in corrosion resistance due to red rust and red discoloration from the substrate and discoloration due to the effect that the plating layer was largely dissolved.

[0022]

[Table 4]

(Evaluation Method of Inner Corrosion Resistance) A cup drawing process was carried out, a fuel was sealed therein, and a test was conducted at 45 ° C. for 1 month to evaluate the appearance of the inner side wall portion of the sample and the state of base corrosion. However, at the time of squeezing the cup, a rust-preventive oil was used, and before the corrosion resistance test was sufficiently degreased with toluene.・ Cup drawing condition: punch diameter 28.5mmφ, blank diameter 60mmφ, drawing depth 22mm ・ Corrosion test solution: 6.3c of 10 times diluted gasoline diluted solution
c + 0.7 cc of distilled water ・ Judgment method: ◎ No significant change in appearance, △ Significant change in appearance, × Rust from base

[0024]

As described above, the steel plate for a fuel tank according to the present invention has excellent workability, and a very good steel plate for a fuel tank can be obtained.

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Nobuyoshi Okada 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Yawata Works (58) Fields surveyed (Int. Cl. ⁷ , DB Name) C23C 28/02 C25D 5/26

Claims (1)

(57) [Claims] 1. An alloy layer containing at least one of nickel, iron, zinc, and tin on a surface of a steel sheet to be plated having a thickness of 1.5 per side.
μm or less, and zinc, tin, and a zinc-tin plating layer composed of unavoidable impurities thereon are 2 to 25 μm per side.
exists, and the major axis of the zinc crystal in the plating layer is 250 μm.
The above are 20 or less / 0.25 when viewed from the plating surface
a mm ^2, the roughness of the plating layer surface 0.2~3.0μ
A steel plate for a fuel tank excellent in workability, characterized by having mRa.