JPH0971879A - Steel sheet for fuel tank excellent in workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel sheet for a fuel tank excellent in working characteristics by specifying the thickness of a zinc-tin plating layer formed on a substrate palating layer on the surface of a steel sheet and the shape of zinc crystals in the plating layer and the roughness of the surface of the plating layer. SOLUTION: On the surface the steel sheet to be applied with plating, an allay layer contg. one or more kinds among nickel, iron, zinc and tin is made present by a thickness of 1.5μm per side. On the surface of the above substrate plating layer, a zinc-tin plating layer composed of zinc and tin with inevitable impurities is formed by a thickness of 2 to 25μm per side. As for zinc crystals in the above zinc-tin plating layer, the ones having >=250Mm major axis are present by <=20 pieces/0.25mm<2> from the viewpoint of the plated surface. Moreover, the roughness of the surface of the plating layer is regulated to 0.2 to 3.0Ra. Thus, its workability improves, and the corrosion resistance at the inside face even in the case of being into fuel tank parts improves.

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 of electrolyzing in a solution containing zinc and tin ions, as disclosed in JP-A-52-130438. Further, the tin-zinc alloy-plated steel sheet has excellent corrosion resistance and solderability because it contains tin in addition to zinc, and has been widely used for electronic parts and the like. With the hot dip coating method, the amount of plating applied can be increased relatively easily.
Products manufactured by the hot dip plating method are used in severe environments such as outdoor applications. For example, in Japanese Unexamined Patent Publication (Kokai) No. 4-214848, 70 to 98% by weight of tin is added to an iron-based object to be plated.
A tin alloy plated coating and a method for producing the same are disclosed. In Japanese Patent Laid-Open No. 5-263208, a zinc-based alloy is formed by sequentially coating a ferrous base with an alloy layer containing tin as a molten zinc or molten zinc alloy plating layer, or an alloy layer containing zinc and aluminum with a chromium plating layer. Plated coatings and methods of manufacture are disclosed. On the other hand, lead-tin plated steel sheets, which are excellent in corrosion resistance, workability, and solderability, have been used mainly as fuel gasoline tank materials both in Japan and overseas, and have been used as actual fuel tanks.

[0003]

Although the solderability and corrosion resistance have been improved by the use of the tin-zinc plated steel sheet by the electroplating method as described above, it is suitable for an environment such as a fuel tank where long-term corrosion resistance is required. Although it is necessary to use a coated steel sheet with a thicker coating amount, the control of the coating amount in the electroplating method depends on the time and the magnitude of the current, so the added amount can be thickened but the processing time is lengthened and a large amount of current is passed. It is necessary and causes a big problem in productivity and economical efficiency. Further, the use of tin-zinc plated steel sheet by the 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 having a characteristic of a shelf-like layer and a columnar layer. The thickness is 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, and the alloy layer is more important than the plating layer in the case of severe processing such as a tank. When the hardness is high and the ratio of the alloy layer to the plating coating layer is high and the thickness is thick, cracks easily enter the vicinity of the alloy layer, and plating peeling and corrosion progress on the inner and outer surfaces due to cracks easily occur, making it a fuel tank. Not suitable.

Further, the iron-based substrate is a zinc or zinc alloy layer,
When sequentially coated with a chromium plating layer, a chromium coating layer is also added to further improve corrosion resistance, etc., but the thickness of the zinc or zinc alloy layer is 5 to 75 μm, preferably 10 to 5 μm.
It is very thick, 0 μm, more preferably 10 to 30 μm, and similarly to the above, the corrosion resistance is secured by the alloy layer, and in the hot dipping method, since the base iron is contained in the alloy layer, the hardness is increased and the workability is greatly improved. And is unsuitable as a fuel tank material. In using lead-tin plated steel sheet,
Corrosion resistance that satisfies the life of the car, that it can be processed according to the complicated structure of the car bottom, solderability that can join fuel tank parts, and weldability are secured, but lead elution from industrial waste such as shredder dust Lead-tin plated steel sheet contains lead because it is not preferable for environmental regulations such as regulations. Further, the workability of the fuel tank is becoming more and more severe as the number of four-wheel drive vehicles increases, and workability equal to or better than that of lead-tin plated steel sheet is required.

[0005]

Therefore, the present inventors have aimed to provide a steel sheet for a fuel tank that does not contain lead (excluding inevitable impurities), alloy layer composition, thickness, coating layer composition, Through various studies on surface lubricity, it was discovered that the material of this composition satisfies the performance required as a fuel tank material with excellent workability. The gist is that an alloy layer containing one or more of nickel, iron, zinc, and tin is present on the surface of a steel sheet to be plated with a thickness of 1.5 μm or less per one surface, and zinc containing zinc, tin, and unavoidable impurities There is a tin plating layer of 2 to 25 μm on each side, and the number of zinc crystals in the plating layer having a major axis of 250 μm or more is 20 or less / 0.25 mm ^{2 when} viewed from the plating surface, and the roughness of the plating layer surface is It is a steel plate for a fuel tank excellent in workability, which is characterized in that it is 0.2 to 3.0 μmRa.

Hereinafter, the present invention will be described in detail. Heat treatment such as hot rolling, pickling, cold rolling, etc. from a slab, annealed steel sheet that has undergone treatment such as rolling, or rolled material is used as a non-plated material, and pretreatment such as removal of rolling oil is performed. After that, plating is performed. The plated steel sheet manufactured in this way is used. Regarding the composition of the alloy layer in the vicinity of the steel, if hot sealing treatment is performed after hot dipping or electroplating
A structure containing both components is generated at the plating layer interface. This structure is hereinafter referred to as an alloy layer. This alloy layer contains nickel, iron, zinc, due to the reaction between the pre-plated metal or the base and the plating bath.
Although one or more types of tin are contained, these structures have a slower progress of corrosion against gasoline fuel, and a thicker alloy layer is advantageous in that long-term corrosion resistance is secured. However, in order to perform rigorous processing suitable for a complicated shape with a plate thickness reduction rate of about 20% in the lower part of an automobile, it is preferable that the alloy layer with low workability has a small amount to secure plating adhesion, but the actual pressability It is necessary to control the upper limit of the alloy layer thickness in consideration of the lubricity of the plated surface and the workability of the plated layer, which are closely related to.
Therefore, the thickness of the alloy layer is set to 1.5 μm or less.

The plating layer is made of a composition containing tin and zinc and has corrosion resistance on the inner surface of the tank against fuel such as gasoline and outer surface against salt damage environment such as spraying of snow-melting salt. The composition range of zinc-tin must be such that the solderability and resistance weldability required for joining pipes and the like can be secured. When the tin content in the plating layer is less than 70%, the corrosion resistance on the inner surface of the tank and the outer surface in a salt-damaged environment are significantly reduced, the dissolution roughness of the plating layer is increased, and the zinc content is increased. The crack propagation prevention capability and solderability during processing of the plated layer are also reduced.
If the tin content exceeds 99%, the performance is not particularly deteriorated, but if the tin content is flawed, iron rust is easily generated from the base material. Therefore, the plating layer composition is weight% considering these factors.
Zinc: 1 to 30%, balance tin and unavoidable impurities are desirable.

Further, the workability is greatly affected by the deformation performance and lubricity of the plating layer body, and it is necessary to optimally set these conditions when molding the fuel tank. Regarding the thickness of the plating layer, if it is too thin, base corrosion will easily occur during long-term use, but the plating thickness will be reduced or damaged at the severely processed part in the tank, so the period until base corrosion is the most Dominate short life. In the present invention, attention is paid to lubricity and workability of the plating layer, and wear of the plating layer during processing is minimized, so that it can be used even if the plating thickness is relatively thin. If the plating thickness is too thick, the corrosion resistance and the like will be sufficiently secured, 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 is set to 2 to 25 μm per surface.

Regarding the form of zinc in the plating layer, when zinc is precipitated as a primary crystal in the cooling process, if the size of the zinc crystal is large, the zinc crystal is likely to be preferentially corroded, and the plating layer is locally corroded and plated. The layers dissolve non-uniformly and the life to penetration of the plating is shortened. Further, when processed, a large zinc crystal becomes a crack propagation path, and the crack propagates through the plating layer to cause plating separation, or a path from the outside to the substrate is formed through the crack in the plating layer to accelerate the progress of corrosion to the substrate. Therefore, if the size of the zinc crystals in the plating layer is too large, there is a problem.
The number of particles having a size of μm or more was 20 or less / 0.25 mm ² .

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

Looking at the workability in terms of friction coefficient, post-treatment for improving various properties such as plating layer composition and corrosion resistance, the type of surface film including oil coating, and surface irregularities influence, and depending on the friction coefficient, The plating layer may be cracked, or the plating layer may be cracked to cause great wear of the plating layer, which causes a problem of affecting corrosion resistance. Considering this, in the zinc-tin system composition range, the dynamic friction coefficient is preferably 0.3 or less after oiling.

[0012]

EXAMPLES The quality characteristics of the rustproof steel sheet for fuel tank of 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 carried out, or continuous plating was carried out by the flux method without pre-plating, and the bath temperature, line speed and flux conditions were set. This material was manufactured by various adjustments, further adjustment of the adhesion amount, and cooling. Further, the surface roughness of the manufactured material was adjusted by the roll roughness and the rolling force during pressure regulation. The processing characteristics of the obtained material and the internal corrosion resistance of the processed material are shown in Tables 1 and 2. (1) Processing characteristics Press forming was performed based on the test conditions shown below, and the workability and the plating adhesion after processing were grasped. As a result, the present invention obtained the same or good results as the current lead-tin plated steel sheet. On the other hand, in the comparison, the alloy layer and the plating layer were cracked or peeled off during processing depending on the workability and lubrication performance.

[0013]

[Table 1]

After applying a rust preventive oil to the flat plate sample, cranking was performed while changing the working depth, and the maximum working depth which was capable of working 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 x 70 m
m, press force 110 tons-Plating removal evaluation: Carefully taping the outside and inside of the corner side wall after processing and visually observing the presence or absence of plating removal. -Judgment method: limit processing depth that can be processed and does not cause plating peeling ◎ 30 mm or more, less than △ 30 mm to 25 mm or more, x 2
Less than 5 mm

(2) Corrosion resistance of inner surface of processed material The inner surface corrosion resistance was grasped by using a sample having the following shape and test conditions. As a result, the present invention was a good result without any corrosion from the base material. On the other hand, the comparative material was not good in corrosion resistance because of red rust from the substrate, red discoloration, and discoloration due to the influence of the significant dissolution of the plating layer.

[0016]

[Table 2]

(Internal Corrosion Resistance Evaluation Method) -A cup drawing process was performed, a fuel was sealed in the cup, and a test was performed at 45 ° C for 1 month to evaluate the external appearance of the inner wall of the sample and the state of base corrosion. However, rust preventive oil was used when squeezing the cup, and it was thoroughly degreased with toluene before the corrosion resistance test.・ Cup drawing conditions: punch diameter 28.5 mmφ, blank diameter 60 mmφ, drawing depth 22 mm ・ Corrosion test solution: degraded gasoline 10 times diluted solution 6.3c
c + distilled water 0.7 cc ・ Judgment method: ◎ No major change in appearance, △ Major change in appearance, × Rust from the substrate

Example 2 Acid-washed low-carbon steel is degreased and pickled, and then nickel or iron-nickel pre-plating is performed, or the pickled hot-rolled sheet or cold-rolled sheet is left as it is in an oxidation furnace or non-oxidation. After performing heat treatment in a furnace having a furnace, a reduction furnace, etc., hot dip plating is performed to adjust the amount of adhesion, and after cooling, the surface roughness is adjusted by the roll roughness and the rolling reduction during pressure adjustment, and This material was manufactured by performing chromate treatment. The processing characteristics of the obtained material and the inner surface corrosion resistance of the processed material are shown in Tables 3 and 4. (1) Processing characteristics Press forming was performed based on the test conditions shown below, and the workability and the plating adhesion after processing were grasped. As a result, the present invention obtained the same or good results as the current lead-tin plated steel sheet. On the other hand, in the comparison, the alloy layer and the plating layer were cracked or peeled off during processing depending on the workability and lubrication performance.

[0019]

[Table 3]

After the rust preventive oil was applied to the flat plate sample, the working depth was changed to perform crank press, and the maximum working depth at which machining was possible and no plating peeling occurred was determined. -Test conditions: die shoulder radius / 3.5 mm, die corner radius / 10 mm punch shoulder radius / 3 mm, punch size / 70 x 70 m
m, press force 110 tons-Plating removal evaluation: Carefully taping the outside and inside of the corner side wall after processing and visually observing the presence or absence of plating removal. -Judgment method: limit processing depth that can be processed and does not cause plating peeling ◎ 30 mm or more, less than △ 30 mm to 25 mm or more, x 2
Less than 5 mm

(2) Internal Corrosion Resistance of Worked Material The internal corrosion resistance was grasped by using the samples having the following shapes and the test conditions. As a result, the present invention was a good result without any corrosion from the base material. On the other hand, the comparative material was not good in corrosion resistance because of red rust from the substrate, red discoloration, and discoloration due to the large dissolution of the plating layer.

[0022]

[Table 4]

(Internal Corrosion Resistance Evaluation Method) -A cup drawing process was performed, a fuel was sealed in the cup, and a test was performed at 45 ° C for 1 month to evaluate the appearance of the inner wall of the sample and the state of base corrosion. However, rust preventive oil was used when squeezing the cup, and it was thoroughly degreased with toluene before the corrosion resistance test.・ Cup drawing conditions: punch diameter 28.5 mmφ, blank diameter 60 mmφ, drawing depth 22 mm ・ Corrosion test solution: degraded gasoline 10 times diluted solution 6.3c
c + distilled water 0.7 cc ・ Judgment method: ◎ No major change in appearance, △ Major change in appearance, × Rust from the substrate

[0024]

As described above, the steel sheet for a fuel tank according to the present invention has excellent workability, and an extremely good steel sheet for a fuel tank 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 (1)

[Claims] 1. An alloy layer containing at least one of nickel, iron, zinc, and tin on the surface of a steel sheet to be plated has a thickness of 1.5 per surface.
2 μm to 25 μm per one surface on which a zinc-tin plating layer consisting of zinc, tin, and unavoidable impurities is present.
m, and the major axis of the zinc crystal in the plating layer is 250 μm
20 or less / 0.25 when viewed from the plating surface
mm ² and the roughness of the plating layer surface is 0.2 to 3.0 μ.
A steel plate for a fuel tank having excellent workability, which is characterized by being mRa.