JPH0689475B2 - Steel plate for fuel container - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention requires a fuel container such as an alcohol fuel, a gasoline containing alcohol, a container material for a fuel such as gasoline, which has corrosion resistance, moldability, solderability and the like. The present invention relates to a surface-treated steel sheet for a fuel container, which has excellent properties in terms of performance.

(Prior Art) With the recent deterioration of petroleum circumstances (increased petroleum cost and decrease in production), instead of gasoline as fuel for automobiles, alcohol fuel such as methyl alcohol or ethyl alcohol, or methyl against gasoline Fuels mixed with alcohols (so-called gasohol) such as alcohol, ethyl alcohol, and methyl tert-butyl alcohol (MTBA) are being used as alternative fuels.

These alcohol fuels or alcohol-added gasoline (gasohol) automobile fuel container materials are disclosed in JP-A-50-
Pb-Sn alloy coated steel sheets, which have been widely announced such as Japanese Patent No. 23345 and Japanese Patent Application Laid-Open No. 51-115240, are generally used, but there is a problem that the corrosion resistance of the steel sheet is significantly deteriorated. The cause is that Pb-Sn alloy steel sheet is mainly composed of Pb
Since the coating layer is composed of a eutectic alloy of Pb and Sn, for example, (a) Pb metal is significantly corroded by methyl alcohol, so that the Pb metal layer portion of the coating layer is easily corroded.

(B) Pb metal is significantly corroded by acetaldehyde, succinic acid (oxidation product of ethyl alcohol) or formaldehyde, formic acid (oxidation product of methyl alcohol) produced by oxidation of alcohol fuel or alcohol-added gasoline, and coating layer The Pb metal layer portion inside is easily corroded.

(C) Corrosion increases from the pinhole portion formed in the coating layer due to the water content of the alcohol or the oxidation product of the alcohol.

Due to such reasons, the corrosion resistance of Pb-Sn and alloy plated steel sheets is significantly deteriorated.

Therefore, as a container steel plate containing such fuel,
A material having a high number of pinholes in the coating layer and excellent corrosion resistance to alcohol and oxidation products of alcohol (formaldehyde, acetaldehyde, formic acid, succinic acid) is required.

As a material to meet these requirements, Ni plating, N on the surface
Steel sheets such as i-Co alloy plating, Ni-Sn alloy plating, and Sn plating having Ni, Co, Sn and a coating layer of these alloys have been started, and relatively good corrosion resistance has been obtained.

Furthermore, depending on the shape of the fuel container or the high-speed forming process, pinholes in the coating layer are enlarged, defects that reach the base metal due to flaws in the coating layer due to the press "cag" phenomenon on the surface, and the base metal during handling are reached. A red rust phenomenon caused by these defects was observed due to flaws and the like. Especially when there are a lot of Cl ^- ions and water mixed from gasoline or the outside,
Corrosion progressed due to water separated from the mixed fuel of alcohol and gasoline, and piercing corrosion was also observed.

On the other hand, the problem of snow salt corrosion on the outer surface of the tank has become more severe in recent years. Corrosion due to Cl ^- ions is caused by defects in the coating layer or scratches that reach the ground iron due to collision of road spray salt (so-called chipping phenomenon). There was also concern about piercing corrosion, which leads to piercing.

(Problems to be Solved by the Invention) The present invention has been made in view of these situations, and solves the corrosion resistance problem of Cr-containing steel plate against alcohol fuel, alcohol-containing fuel, gasoline, etc. and the problem of snow-melting salt corrosion on the outer surface of the tank. In addition, the present invention provides a steel sheet for a fuel container, which has excellent formability and weldability.

(Means for Solving Problems) That is, the gist of the present invention is C: 0.1% or less, Cr: 3 to 20%,
Acid-soluble Al: 0.005-0.10%, Ti, Nb, Zr, V, one or more, 0.03-0.50%, B: 0.003% or less, the balance from Fe and unavoidable impurities On the side of the inner surface of the steel sheet that corresponds to the inner surface of the fuel container with a Ni underlayer of 0.01 to 1.0 μm thick and
A two-layer coating layer of 0.5-1.0 μm Sn layer is applied, and on the other fuel container outer surface equivalent side, a Pb-Sn-based alloy coating layer having a thickness of 1-10 μm or Zn or a Zn-based alloy containing Zn as a main component is formed. The coating layers are applied, and if necessary, these coating layers have a thickness of 0.01-1.
This is a steel plate for a fuel container containing 0 μm of Ni-based ground treatment and alcohol or alcohol.

The present invention will be described in detail below.

Alcohol, fuel containing alcohol, gasoline, oxides of alcohol (organic acids such as aldehydes, formic acid, and succinic acid), steel containing 3% or more of Cr, especially 5% of Cr, with respect to moisture contained in these The steel sheet contained above exhibits excellent corrosion resistance.

However, if the Cr content exceeds 20%, the workability and weldability deteriorate, and it becomes difficult to perform the forming process or the contact property when manufacturing the fuel container. Therefore, the Cr content is 3 to 20%, preferably 5 to 11% from the viewpoint of corrosion resistance against the corrosive atmosphere for the inner surface of the fuel container, workability, and weldability.

From the viewpoint of workability, in the transformation region composition of γ phase and α phase of Cr 11% or less, during the steel sheet production, coarsening of crystal grains hardly occurs due to these transformations, and when subjected to severe forming, From the viewpoint of workability, it is particularly preferable that the upper limit of the Cr content be 11% or less from the viewpoint of workability, in which a roughening phenomenon called ridging hardly occurs.

From the viewpoint of the corrosion resistance of the steel sheet, Cr has the greatest effect as described above, but in the present invention, from the viewpoint of targeting fuel tank materials for automobiles and other storage, C, acid-soluble Al and other steel components are also included. It is necessary to limit the amount.

Due to the increase in the content of C, chromium carbide precipitates and deteriorates the mechanical properties and corrosion resistance of the steel. Therefore, the C content is 0.10% or less, preferably 0.02% or less.

The amount of acid-soluble Al (SolAl) remaining in steel is 0.005%.
If the content is less than the lower limit, it is difficult to prevent the generation of bubbles due to the oxidizing gas, the surface defect occurrence rate of the steel is remarkably increased, and the corrosion resistance of the steel material is deteriorated. Further, an excess of acid-soluble Al exceeding 0.10% causes Al-based oxides to be scattered on the surface of the steel, and causes scratches, pinholes, etc. at the starting point of corrosion resistance deterioration or on the plated surface, and Impair soundness.

Further, in the present invention, in addition to the above steel components 0.03 to 0.50
% Ti, Nb, Zr, V is contained in one or more kinds and is combined with C in the steel to measure the effectiveness of Cr contained and further improve the formability and corrosion resistance. It is the one to be confused.

When the total content of steel components such as Ti is less than 0.03%, the effect of preventing the precipitation of chromium carbide and improving the formability and corrosion resistance is small, and the content is 0.50%.
If it exceeds, the effect reaches saturation and becomes uneconomical, and the precipitation of these components causes the material to harden,
Molding processability tends to deteriorate. The content of these elements is preferably in the range of 0.075 to 0.20%.

Furthermore, in the present invention, in addition to the above steel components, 0.003
% Or less B is added. B is added for the purpose of excellent moldability and prevention of strength deterioration in heat affected zones such as welding and brazing work. That is, the addition of B to the steel component of the present invention is for the following reason.

In the case where a fuel container or the like is subjected to a high degree of forming and is used in a cold region, when it is subjected to an impact at a low temperature, cracks called secondary processing cracks may occur. This is because the C content is limited to an extremely small amount as described above, so that precipitation of inevitable impurities such as P and S contained in the steel to the crystal grain boundaries increases, and the crystal grain boundaries are increased. It is thought to be due to embrittlement.

Therefore, instead of these impurities, it precipitates at the crystal grain boundary, suppresses the precipitation of P, S, etc., and it is possible to strengthen the crystal grain boundary.
B is added as an element capable of preventing secondary work cracking.
Further, since the addition of B precipitates at the grain boundaries, it prevents the growth and coarsening of crystal grains in these heat-affected zones when subjected to high heat operations such as welding or brazing work. In the product, 0.003% or less of B is added, preferably 0.001% or less.

If B is also added in an amount of more than 0.003%, the steel sheet is hardened and the formability is deteriorated, so the content is limited to the above range.

In the present invention, good results cannot always be obtained by directly using a steel sheet having the above-described composition as a fuel container material such as alcohol fuel or alcohol-containing fuel. The cause of this is that Cl ^- ions or water in the atmosphere are accumulated in the fuel or the inner surface of the container, or the flux used during the manufacturing of the container, such as zinc chloride or water, is mixed in the container, resulting in alcohol fuel and Cl ^- ion. The water containing water is separated into two phases, and due to the water phase containing Cl ⁻ ions, red rust and perforation corrosion occur.

The fuel container outer surface, Cl by spraying salt for road antifreeze in winter ^- ions, or Cl ^- and raised in sea breeze atmosphere such as in the presence of ions, occurrence of red rust, perforation corrosion from rust generating parts, corrosion resistant life There is a problem that it significantly deteriorates.
Therefore, in the present invention, if the above steel plate is used as it is in a fuel container, the corrosion resistance is insufficient.

In the present invention, the inner surface of the fuel container of the Cr-containing steel plate has a thickness of 0.01 to 1.
A two-layer coating layer consisting of a 0 μm Ni-based undercoating layer and a 0.5 to 10 μm thick Sn metal coating layer is applied.

On the other hand, for the outer surface of the fuel container, (2) the thickness is 1 to 10μ.
Pb-Sn alloy coating layer or Zn or Zn with a thickness of 1-10 μm
A coating layer of Zn-Ni, Zn-Fe, Zn-Co, Zn-Ni-Co alloy, etc. containing as a main component is applied (3) and, if necessary, Pb-
As the Sn-based alloy coating layer or the Zn- or Zn-based alloy coating layer, a Cr-containing steel sheet may be coated with a Ni-based undercoat layer having a thickness of 0.01 to 1.0 μm.

That is, one side of the Cr-containing steel plate on the side corresponding to the inner surface of the fuel container has corrosion resistance against alcohol, oxides of alcohol, alcohol-containing fuel, gasoline, moisture, Cl ^- ions, etc., and is soft and has a lubricating performance. Sn metal, which is rich and improves the formability of the steel sheet and has excellent solderability and weldability, is used as the main film forming metal.

Further, in order to reduce the pinholes of this Sn metal coating layer, a Ni-based undercoating layer is applied. The Ni metal has good corrosion resistance to the corrosion factors on the inner surface of the fuel container as described above, and is highly reactive with Sn metal, and is diffused even at room temperature with Sn metal, and Ni-Sn alloy. Since the layer is uniformly and densely formed and has a great effect of reducing pinholes reaching the steel surface of Sn metal, it is used as an undercoating layer for the Sn coating layer.

In this case, the Ni-based undercoat layer, in addition to the Ni plating layer by the electric plating method, the electric plating or the Ni ion-containing aqueous solution is applied to the steel surface to provide a heating Ni diffusion layer, or further the Ni diffusion layer, The Ni plating layer may be applied by an electric plating method.

In the present invention, in this way, on the corresponding surface of the inner surface of the fuel container,
One of the important reasons for forming a two-layer coating layer consisting of a Ni-based undercoat layer and a Sn metal coating layer is that the diffusion of Sn metal and Ni metal causes the formation of a uniform and dense alloy layer at the boundary between the two layers. This is to improve the corrosion resistance by reducing the pinholes in the Sn coating layer.

That is, when the Sn metal coating layer is provided directly on the steel surface having the Ni diffusion layer, the Ni concentration becomes low, the uniform and dense formation of the Ni-Sn alloy layer becomes insufficient, and the Sn metal comes into contact with the metal. Since it is desirable that the boundary has a high Ni concentration, a Ni metal plating layer is applied to the contact surface with Sn.

Thus, as described above, it is provided on one surface corresponding to the inner surface of the fuel container.
The coating method and the processing conditions of the Ni-based undercoating layer and the Sn metal coating layer are not particularly limited, but their thicknesses need to be specified for the following reasons.

That is, the thickness of the Ni-based undercoat layer of each of the Ni plating layer or the Ni diffusion layer is limited to 0.01 to 1.0 μm. This is N
If the thickness of the i-based undercoating layer is less than 0.01 μ, the uniform coverage of the Ni metal is not sufficient, and the diffusion with the Sn metal provided thereon is not sufficiently performed, resulting in the formation of the Ni-Sn alloy layer. No pinhole reduction effect can be obtained.

On the other hand, when the thickness of the Ni-based undercoat layer exceeds 1 μ, the corrosion resistance improving effect due to the pinhole reduction effect due to the formation of the Ni-Sn alloy layer due to the diffusion with Sn provided in the upper layer is saturated and the Ni- The hardness of the Sn-based alloy layer causes cracks to occur during the molding process, and also causes deterioration of the moldability and corrosion resistance.

Therefore, the thickness of this Ni-based undercoat layer is 0.01-1.0.
μ, preferably 0.05 to 0.5 μ. On the other hand, the thickness of the Sn coating layer is specified to 0.5 ~ 10μ, the thickness of less than 0.5μ, the uniform coverage of Sn metal is not sufficient, corrosion resistance of the object of the present invention, solderability, Sn metal of The effect of improving the formability due to the lubricating effect cannot be obtained. If the thickness exceeds 10μ, the effects on corrosion resistance and solderability will be saturated, and
The adhesiveness and molding processability of the coating layer tend to deteriorate, which is not preferable. Therefore, the thickness of the Sn metal coating layer is 0.5-10 μm.
It is limited to the range of, and preferably 1 to 7 μ.

Then, these Ni-based undercoating and Sn coating layer are applied by the following method, for example.

(1) Ni plating layer by electroplating method Using a plating bath made of nickel sulfate-nickel chloride-boric acid system, and plating at a current density of 5 to 50 A / dm ² (2) Ni diffusion layer and Ni plating layer Steel After the electroplating method or the (nickel oxalic acid-surfactant) type aqueous solution is applied on the surface and dried, a diffusion layer is provided as follows, for example.

That is, the cold-rolled material (as cold material) surface is pretreated with Ni as described above, and by utilizing the annealing step of this cold-rolled material, at the same time as annealing in a reducing atmosphere, for example,
The diffusion layer is provided by heat treatment for 30 to 180 seconds in the temperature range of 700 to 950 ° C.

Of course, cold rolling and annealing material (full-finished material) may be used to provide a preliminary coating layer of Ni and heat diffusion treatment may be performed. However, the cold rolling material described above is more suitable for cold rolling. Due to the processing strain of the material, mutual diffusion between the preliminary coating layer and the steel sheet is promoted, so that a short-time heat treatment produces the diffusion layer intended by the present invention, and in the annealing step.
There is an advantage that the surface oxidation of the Cr-containing steel sheet can be prevented by the preliminary coating layer, which is also advantageous in the process.

Thus, a Ni plating layer is provided on the surface of the diffusion layer formed by such a method, directly or after the activation treatment by pickling, using the Ni electrolytic bath composition and plating conditions as described above.

Incidentally, when a Ni plating layer is provided in these Ni-based undercoat layers, other metals contained as unavoidable impurities in the chemicals used, especially in nickel sulfate, are often about
About 20% of cobalt is contained and is also contained in the Ni coating layer, but the presence of these impurities does not hinder the present invention.

(3) Sn metal coating layer (Phenol sulphonic acid Sn-sulfuric acid-surfactant) type bath and (Softening Sn-borofutic acid-boric acid-surfactant) type bath are used and the current density is 5 to 60A. The Ni-based undercoating layer and the Sn metal coating layer are respectively provided by the method of plating with / dm ² .

Thus, by providing a multi-layer coating layer consisting of a Ni-based undercoating layer and a Sn metal coating layer on one surface of the Cr-containing steel sheet for the inner surface of the fuel container, the following advantages can be obtained. .
That is, in addition to the above-mentioned corrosion factors, Sn, which has good corrosion resistance to Cl ^- ions, can be added to the Cr-containing steel plate having good corrosion resistance to alcohol, alcohol oxides, alcohol-containing fuel, water, and gasoline. By providing the metal as a double coating layer together with the Ni-based undercoat layer in order to reduce pinholes, extremely excellent corrosion resistance to alcohol and alcohol-containing fuel can be secured.

In addition, the Sn coating layer with the Ni-based undercoat layer is
Since it is a steel sheet containing, by the effect of reducing the copper corrosion current between them, even if there is a pinhole, or even if there is a coating layer defect such as a flaw during molding, etc., the coating layer If the Cr content is base-potentially lower than that of the steel base, the amount of corrosion due to sacrificial corrosion of the coating layer is small, and the coating layer is more noble than the steel base. Even in such a case, the corrosion amount of the steel base material becomes small, the risk of piercing corrosion becomes extremely small, and the effect of improving the corrosion resistance and extending the corrosion resistance life can be expected.

Further, since the Sn metal coating layer is used, the lubrication effect provides the effect of improving the formability of the Cr-containing steel sheet for the forming process of the fuel container which is subjected to severe forming process. In addition, the Cr-containing steel sheet tends to have poor solderability and weldability in general, but due to the effect of the Sn coating layer which is a low melting point metal,
Advantages such as the remarkable improvement of these performances can be obtained.

Next, on the other hand, one side of the Cr-containing steel plate corresponding to the outer surface of the fuel container is inferior in corrosion resistance to alcohol, oxides of alcohol, and fuel containing alcohol, but is inferior in corrosion resistance to Cl ^- ions, water, etc. Excellent solderability and molding processability, which are other important properties required for fuel containers,
A Pb-Sn-based alloy coating layer, a Zn coating layer, or a Zn-based alloy coating layer containing Zn as a main component, which can be applied to the contained steel sheet, is applied.

These coating layers have an excellent effect on improving the corrosion resistance of the outer surface of the fuel container when exposed to a spray salt for preventing road freezing and a corrosive atmosphere containing a large amount of Cl ⁻ ions and water such as a sea breeze atmosphere. Can be given.

In particular, due to the combined effect of the Cr-containing steel sheet used in the present invention, the copper corrosion current between the steel sheet and the Pb-Sn alloy coating layer,
Compared to the case of using a steel plate that does not contain Cr as a plating base plate, it becomes extremely small, or the Pb-Sn alloy coating layer becomes an anodic depending on the Cr content, so the pinholes of these alloy coating layers Since the corrosion of the original plate to be scratched from the portion or the scratched portion during the forming process is remarkably reduced, an extremely excellent effect of extending the corrosion resistance life can be obtained.

Furthermore, as an effect of applying a Pb-Sn alloy coating layer on one surface corresponding to the outer surface of the fuel container as described above, since the coating layer is soft and composed of a metal having a high lubricity, such as a steel plate for a fuel container. When severe molding is required, the lubricating effect of the coating layer is imparted, which is extremely advantageous.

Further, since the Pb-Sn alloy coating layer is a solder alloy, the joints of pipes such as the fuel feed pipe, like the fuel container, have many solder joints, so that the steel sheet of the present invention has solderability. Since it is extremely excellent, it is particularly advantageous as a steel sheet for fuel containers.

The composition of the Pb-Sn alloy coating layer is not particularly specified, but the Sn content is 3 from the viewpoint of solderability.
% Or more, preferably 5% or more of a Pb-Sn alloy composition is used, and the upper limit of the Sn content is not specified, but from the economical viewpoint, an alloy having a composition of less than 50%, preferably 30% or less is used. To be done.

As a method for providing the Pb-Sn alloy coating layer only on one surface of the Cr-containing steel plate, any of an electric plating method, a melting plating method, and a vapor deposition plating method may be used. Cr
The surface of the contained steel sheet is subjected to surface cleaning such as degreasing and pickling, and activation treatment, followed by Pb-Sn alloy coating treatment.

For example, in the case of the electric plating method, a bath of fluoride containing Pb ions and Sn ions corresponding to a predetermined alloy composition is used, and only one side of the steel sheet is energized with an electric amount of electricity for obtaining a predetermined thickness. It is obtained by processing.

Further, in the case of molten plating, on the non-plated surface of the Cr-containing steel sheet, a masking agent that prevents the reaction with the molten Pb-Sn alloy plating bath, for example, a Cr ₂ O ₃ compound or a silicic acid compound is applied, By dipping in a plating bath, it is possible to obtain a molten Pb-Sn alloy plating coating layer containing a predetermined content of Sn only on one plating surface.

The vapor phase deposition method can also be achieved by heating and evaporating the molten Pb-Sn alloy plating bath in vacuum only on one side of the plating surface and providing the Pb-Sn alloy deposition layer on only one side of the steel sheet. it can. In the present invention, in any method
The Pb-Sn alloy coating layer may be provided on only one side of the Cr-containing steel plate, but it is necessary to provide the above-mentioned coating layer having a thickness of 1 to 10 µ from the viewpoint of performance.

Thus, the Pb-Sn alloy coating layer contains water, Cl ^- ions, S
It has excellent corrosion resistance to O ₄ ^-2 ions, etc., but has extremely poor corrosion resistance to alcohols and oxides of alcohols, and its dissolution is remarkable. As a result, when the Pb-Sn alloy coating layer is present on the surface in contact with the alcohol fuel, there is a problem that the corrosion product due to the alcohol fuel causes the tank pipe to be clogged. Therefore, this Pb-Sn alloy coating layer,
It must be limited to one side corresponding to the outer surface of the fuel container.

Incidentally, even in the case where Zn, Sb, etc. are contained in the Pb-Sn alloy coating layer from the metal or the like used for forming the coating layer,
Since it does not have any adverse effect on the performance of the product of the present invention, even if the content of these is 5% or less, there is no difference.

Furthermore, in the present invention, for corrosion protection of the Cr-containing steel sheet for the outer surface of the fuel container, in addition to the Pb-Sn alloy,
A Zn coating layer or a Zn-based alloy coating layer containing Zn as a main component may be provided.

That is, it has a sacrificial anticorrosive ability for a Cr-containing steel sheet, and
Cl ^- relative moisture containing ions, relatively good Yotsute these coating layers of corrosion resistance, Cl and Cr-containing steel sheet ^- to prevent corrosion deterioration due to the generation of red rust due to ions, and may improve the corrosion life .

As the Zn-based alloy coating layer, 20% or less of Ni, Co, Fe and an alloy coating layer containing two or more of these with respect to Zn having the above performance are used. When the content of these alloying elements exceeds 20%, the sacrificial anticorrosive ability deteriorates, so the content is limited to 20% or less.

The method of providing the Zn coating layer or the Zn-based alloy coating layer is not particularly specified, and the following method is adopted, for example. That is, using a (zinc sulfate-sodium sulfate) -based bath, a (zinc sulfate-nickel sulfate-conductive salt) -based bath, a (zinc sulfate-iron sulfate) -based bath, etc., a predetermined thickness is obtained on only one side of the steel sheet. It is obtained by a method of energizing and electrolyzing the amount of electricity for the purpose.

Alternatively, in addition to the above electric plating method, a molten zinc plating bath is supplied to only one surface of a steel plate by using an electromagnetic pump or the like, and a single-sided plating method for controlling the thickness of the plating is performed. A Ni-based undercoating layer and a multi-layered coating layer composed of a Sn metal coating layer may be provided on one surface.

Next, a Ni-based undercoat layer may be applied as an intermediate layer between the Pb-Sn alloy coating layer or the Zn, Zn-based alloy coating layer and the Cr-containing steel plate. By providing this undercoat layer, the effect of improving the corrosion resistance by reducing the pinholes due to the superposition effect with the upper coating layer can be obtained.

In particular, when the Ni-based coating layer is provided as the undercoating layer of the Pb-Sn-based alloy coating layer, the following advantages are further obtained. That is, since the Ni-based undercoating layer has excellent reactivity with Sn in the Pb-Sn alloy coating layer, the corrosion resistance improving effect can be obtained by reducing pinholes due to the formation of a uniform and dense alloy layer.

In addition, when a flaw is generated in the Pb-Sn alloy coating layer or the Zn-based coating layer during forming, etc., the presence of this Ni-based undercoat layer suppresses the occurrence of flaws that reach the steel substrate. By doing so, excellent advantages such as prolonging the corrosion resistance life can be obtained. Thus, the method of providing this undercoating layer may be the same as the method described above.

In addition, its thickness is specified in the range of 0.01 to 1 μ. That is, if the thickness is less than 0.01 μm, the uniform coating property on the steel substrate is not sufficient, and the above-described effects of the present invention cannot be obtained. On the other hand, when the thickness of this Ni-based undercoating layer exceeds 1 μ, the above corrosion resistance improving effect is saturated and the crack originated from this undercoating layer is subjected to severe molding. It is not preferable because it tends to occur. Therefore, the thickness is 0.01-1μ
It is limited to the range of, preferably 0.05 to 0.5 μ.

Next, the thickness of the Pb-Sn alloy coating layer, or the Zn coating layer, or the Zn alloy coating layer provided for improving the performance such as the corrosion resistance of the outer surface of the fuel container is specified in the range of 1 to 10 μm, respectively. To be done. That is, if the thickness is less than 1 μm, the uniform coating properties of these coating layers are not sufficient, the amount of pinholes generated is large, the corrosion resistance thereof is not sufficient, and the coating layer is too thin. The effect intended by the present invention cannot be obtained such as the effect of improving the property cannot be obtained. Also,
If the thickness exceeds 10μ, these effects saturate,
Not only is it economical, but also the smoothness of the coating layer increases, which increases the contact resistance during molding, which reduces moldability, and increases the contamination of the electrode by the coating layer metal during welding. Is deteriorated, which is not preferable.
Therefore, the Pb-Sn alloy coating layer, the Zn coating layer, and the Zn alloy coating layer each have a thickness of 1 to 10 [mu], preferably 3 to 7 [mu].

In particular, among these coating layers, the Pb-Sn alloy coating layer is Z
Compared to n, Zn alloy-based coating layers, the coating layer-forming alloy itself has extremely excellent solderability and lubrication effect, so it is possible to perform severe forming work, high-speed soldering work with fuel pipes, etc. as in the present invention. For the purpose of the required fuel container, the use of the Pb-Sn alloy coating layer is excellent.

Thus, the Pb-Sn alloy coating layer, the Zn coating layer, and the Zn alloy coating layer that form the coating layer for the outer surface of these fuel containers have excellent corrosion resistance to Cl ^- ions, moisture, etc. However, the corrosion resistance to alcohol fuel, alcohol oxides, etc. is poor, and the dissolution due to the corrosion is remarkable.

As a result, if these coating layers are present on the surface corresponding to the inner surface of the fuel container that comes into contact with the alcohol fuel, there is a risk that the corrosion product will clog the fuel container piping. Therefore, it is necessary that the coating layer intended for the corrosion protection of the outer surface of the fuel container is limited to only one surface corresponding to the outer surface.

The Cr-containing steel sheet used in the present invention does not hinder the present invention even when the corrosion resistance improving elements such as Ni, Co and Mo are contained in an amount of about 10% or less.

Next, the coating layer of the present invention, in particular, the coating layer intended for the outer surface of the fuel container, by further chemically treating the defective portion of the coating layer, a method or coating for improving the corrosion resistance performance. In order to improve the coating performance, etc., when used as an aqueous solution, an aqueous solution containing phosphate ions, Cr ⁺⁶ ,
Even if chemical treatments such as immersion and electrolysis are performed using an aqueous solution containing Cr ⁺³ ions or a mixed aqueous solution of Cr ⁺⁶ , Cr ⁺³ ions and SO ₄ ^-2 ions, PO ₄ ^-3 ions Good.

For example, the Pb-Sn alloy coating layer is subjected to a dipping treatment for 1 to 10 seconds at a temperature of room temperature to 80 ° C using a 0.1 to 5% phosphoric acid aqueous solution to obtain its corrosion resistance and paint adhesion performance. May be subjected to chemical treatment. Similarly, in the case of a Zn-based coating layer, using an aqueous solution containing Cr ^{+ 6} ions and SO ₄ ^-2 ions, subjected to cathodic electrolytic treatment, its corrosion resistance performance, about the method for improving the coating performance, etc. It is the same.

Although the present invention has been mainly described above with respect to a fuel container for alcohol and a fuel containing alcohol, even if it is applied to or commonly used as a fuel container for ordinary gasoline, its corrosion resistance and performance are good and there is no problem.

Examples of the present invention will be described below.

In Table 1, using steel plates with steel components that are changed mainly in Cr content, after performing pretreatment such as degreasing and pickling and activation treatment,
The product of the present invention in which a predetermined amount of the coating treatment of the present invention is applied to each surface of the Cr-containing steel plate is shown. Table 2 shows the results of performance evaluation for the outer surface and the inner surface of the fuel container. It was

In addition, the results of performance evaluation of the products of the present invention regarding solder jointability, weldability, and moldability assuming formation of a fuel container are also shown.

When the coating layer intended for the outer surface of the fuel container is a Pb-Sn alloy coating layer, including the surface of the Sn coating layer on the inner surface, 0.5%
When phosphoric acid aqueous solution is used, dipping treatment is performed at 70 ° C for 5.7 seconds, Ringer roll squeezing treatment, and phosphoric acid treatment by drying are performed, and when the outer surface coating layer is zinc-based treatment (20 g / lCrO ₃ -20 g / lSi
O ₂ type) aqueous solution was used for roll coater treatment, and only the Zn-based coating layer surface was subjected to single-side chromate treatment and dried.

The evaluation test method was carried out by the following method.

(A) Corrosion Resistance by Salt Spray Test The corrosion resistance of the outer surface (covering layer surface) of the fuel container after 500 hours of the salt spray test was evaluated, and the evaluation criteria were as follows.

◎… The number of red rust occurrences in a 100 × 300 mm test piece size is 5 or less ○: The number of red rust occurrences in a 100 × 300 mm test piece size is 6 to 12
Number △… Number of red rust occurrences in a 100 × 300 mm test piece size 13 to 20
No. of red rust in the size of 100 × 300 mm test piece 21 or more (B) Corrosion resistance by C, C, T test Cycle corrosion test (C, C, T test) Salt spray (5% NaCl 35 ° C × 4) Time) → Dry (70 ℃, humidity 60%, 2 hours) → Wet (49 ℃, humidity 98%, 2 hours) → Cooling (-20 ℃, 2 hours) → Salt spray 60 cycles of C, C, T test The
Using a 0.8 mm thick test piece, the corrosion resistance was evaluated by measuring the amount of red rust generation / thickness reduction in the corroded area.

◎ ... thickness reduction amount less than 0.25 mm or more ○ ... thickness reduction amount 0.25 mm to less than 0.45 mm △ ... thickness reduction amount 0.45 mm to less than 0.75 mm × ... thickness reduction amount 0.75 mm or more (C) 0.8 × 100 Using a 150 mm test piece, an alundum having a diameter of 1 to 2 mm was collided with the coating layer surface of the test piece at a pressure of 1 Kg / cm ² for 10 seconds at a rate of 1.5 g per 1 cm ² and chipped. The T test was performed for 4.5 cycles, the amount of reduction in plate thickness at the red rust occurrence portion was measured, and evaluation was performed according to the evaluation criteria of (B) above.

2. Test for inner surface of fuel container Punch diameter from blank size 0.8 × 150mmφ test piece
A cylindrical container having a diameter of 75 mm and a height of 40 mm was prepared with a pressure of 75 mm and a wrinkle holding force of 1 t. A corrosion promoting solution for alcohol fuel of 100 cc or less was filled and sealed, and an evaluation test was performed.

(D) Gasohol target test (20% ethanol + 0.03% succinic acid + 0.15% 1% NaCl water + residual gasoline) solution for 3 months evaluation test (E) Gasohol target test (70% methanol + 10% isopropyl alcohol +0.03
% Formic acid + 0.3% 1.2% NaCl water + residual gasoline) solution for 3 months evaluation test (F) 100% alcohol target test (99% methanol + 0.01% formic acid + 0.99% 0.5% NaCl) Each of the evaluation tests was carried out for 3 months using a solution consisting of (aqueous solution), and the evaluation was performed according to the following evaluation criteria.

◎… Number of red rust occurrences in cylindrical container (both solution immersion part and steam contact part) 0 to 3 ○… Number of red rust occurrence in cylindrical container (solution immersion part and steam contact part) 3 to 10 △… Cylinder container Number of red rust occurrences inside (both solution immersion part and steam contact part) 10 to 20 × ... Number of red rust occurrences inside cylindrical container (both solution immersion part and steam contact part) from 21 to many occurrence 3. Fuel container target Target test for seam welded parts The inner target coating layers corresponding to the inner surface of the fuel container are overlaid, 0.8 mm test material is used, and a pressure is applied with a 4 mm width trapezoidal electrode.
Seam welding W was carried out at 400 kg / f, welding speed 2.5 m / min, and welding time 2-200 seconds to prepare a test piece as shown in Fig. 1. Fill the solution shown below with the plastic upper part. The lid was put on and the appearance was evaluated after 3 months, and the evaluation was performed.

○ Test solution for gasohol (80% methanol + 5% isopropyl alcohol + 0.01
% Formic acid + 0.1% NaCl water 0.3% + residual gasoline) solution for 3 months Evaluation test ◎ Evaluation criteria ◎… Red rust occurrence rate of lower and side is less than 5% ○… Red rust occurrence rate of lower and side 5 Less than -10% △… Red rust occurrence rate on the bottom and side is 10 to less than 20% ×… Red rust occurrence rate on the bottom and side is 20% or more 4. Solderability Sn-Zn alloy (Sn ≈ 80) used for fuel container piping ~ 90
%) In order to evaluate the solder bondability between the plated steel plate and the outer surface of this evaluation material, ZnCl ₂ -HCl system flux and 60% Sn-40% Pb
Using the solder, the solder rising property between the Sn-Zn alloy plated surface and the coating layer surface and the strength of the solder joint were measured, and the relative evaluation of the evaluation material and the comparative material was performed comprehensively.

◎… Extremely good ○… Relatively good △… Slightly inferior ×… Very inferior 5. Weldability Using a sample with a plate thickness of 0.8 mm, overlaying the coating layers for the inner surface of the fuel container, and making them 4 mm wide With a trapezoidal electrode, a welding force of 400 kg / f, a welding speed of 2.5 m / min, a welding time of 2-200 seconds, a comprehensive evaluation of the welding current range, the state of nugget generation, and the appearance of the welded part, the weldability of each evaluation material Was evaluated relatively.

◎… Very good ○… Relatively good △… Very inferior ×… Very inferior 6.Molding workability ○ Evaluation method Blank size 0.8 × 500 × 500 mm, after applying lubricating oil, wrinkle holding pressure 30T, 150 A rectangular cylinder was drawn with a punch of × 150 mm square, and evaluation was made based on the limit of the drawing depth and the occurrence of galling on the outer surface of the rectangular drawing material.

◎ ... No damage due to scoring of the coating layer and extremely good moldability ○ ... No damage due to scoring of the coating layer and fairly good molding processability △ ... Some damage due to scoring of the coating layer occurs depending on the degree of processing. Molding processability is extremely poor ○ Evaluation method A sample with a plate thickness of 0.8 mm and a plank diameter of 133.2 mm and a drawing ratio of 1 step (2.22) → 2 step (2.89) → 3 step (3.6) Then, the conical punch was pushed into the above-mentioned processed material at -40 ° C, and the secondary workability was evaluated by whether or not vertical cracking occurred in the above-mentioned processed material.

⊚: No vertical cracks, good secondary workability ×: No vertical cracks, poor secondary workability Measurement not possible: Cracking occurred due to three-stage drawing, secondary workability evaluation impossible (poor workability) (Effect of the Invention) As described above, the product of the present invention has extremely excellent characteristics as a steel sheet for alcohol or a fuel container containing alcohol, as compared with the comparative material.

[Brief description of drawings]

 FIG. 1 is a schematic diagram of a seam welding test.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location // C22C 38/28 (72) Inventor Minoru Fujinaga 1-1-Emitsu, Hachimanto-ku, Kitakyushu, Fukuoka 1 Inside Nippon Steel Co., Ltd. Yawata Works (56) References JP-A-61-270388 (JP, A)

Claims (2)

[Claims] 1. C: 0.02% or less, Cr: 3 to 20%, acid-soluble Al: 0.0
In addition to 05 to 0.10%, it is 0 for Ti, Nb, Zr, V, one or more.
A steel sheet containing 03-0.50% and B: 0.003% or less with the balance being Fe and unavoidable impurities on the side corresponding to the inner surface of the fuel container with a Ni-based underlayer with a thickness of 0.01-1.0 μ 0.5 ~ 10μ of the two-layer coating of Sn layer, the other fuel container outer surface equivalent side, 1-10μ thick Pb-Sn alloy coating layer or Zn or Zn-based Zn-based alloy of the main component A steel sheet for a fuel container having a coating layer. 2. C: 0.1% or less, Cr: 3 to 20%, acid-soluble Al: 0.00
In addition to 5 to 0.10%, one or more of Ti, Nb, Zr, V and 0.0
Contains 3 to 0.50%, further contains B: 0.003% or less,
On the side corresponding to the inner surface of the fuel container of the steel sheet with the balance being Fe and unavoidable impurities, a Ni-based underlayer with a thickness of 0.01 to 1.0 μ and a thickness of 0.5 to
A two-layer coating layer of 10 μm Sn layer is applied, and on the other side corresponding to the outer surface of the fuel container, a Ni-based underlayer having a thickness of 0.01 to 1.0 μ and a thickness of 1 to 10 μm.
2. A steel sheet for a fuel container, characterized by being coated with the Pb-Sn alloy coating layer or the Zn or Zn coating alloy containing Zn as a main component.