JPS61270390A - Steel sheet for fuel vessel - Google Patents

Abstract

PURPOSE:To provide superior resistance to corrosion by fuel to a steel sheet having a specified composition by forming a specified diffusion coating layer and a specified coating layer on one side of the steel sheet corresponding to the inside of a fuel vessel and a coating layer of a specified alloy or a specified diffusion coating layer on the other side corresponding to the outside. CONSTITUTION:The composition of a steel sheet for a fuel vessel is composed of, by weight, <0.002% C, 3-20% Cr, 0.003-0.1% acid-sol. Al, 0.03-0.3% one or more among Ti, Nb, Zr and V <0.003% B and the balance Fe with inevitable impurities. A diffusion coating layer of Ni and/or Co having >=0.01mu thickness and a coating layer of one or more among Sn, Ni and Co having 0.5X10mum thickness are formed on one side of the steel sheet corresponding to the inside of the fuel vessel. A coating layer of a Pb-Sn alloy having 1-10mum thickness or a diffusion coating layer of Ni and/or Co having >=0.01mum thickness is formed on the other side corresponding to the outside of the fuel vessel.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a surface-treated steel sheet for a fuel container used as a container material for containing fuel such as alcohol fuel, alcohol-containing gasoline, and gasoline.

(Prior art) With the recent deterioration of the oil situation (rise in oil costs and decrease in production), alcohol fuels such as methyl alcohol and ethyl alcohol or gasoline have been replaced as automobile fuels. Fuels (so-called gasohol) mixed with alcohols such as methyl alcohol, ethyl alcohol, and methyl tertiary-butyl alcohol (MTBA) are now being used as alternative fuels.

The material for automobile fuel containers for these alcohol fuels or alcohol-added gasoline (gasohol) is
Pb-Sn alloy coated steel sheets, such as those published in many publications such as JP-A-23345 and JP-A-51-115240, are commonly used, but there is a problem in that their 'A provisional side-corrosion properties are significantly deteriorated. Ta. The cause is Pb-
Sn alloy steel sheets are composed of a eutectic alloy of Pb and Sn, with Pb as the main component, and their coating layer is composed of, for example: (a) Since Pb metal is severely corroded by methyl alcohol, the Pb metal layer of the coating layer is parts are susceptible to corrosion.

(b) Acetaldehyde, succinic acid (
oxidation products of ethyl alcohol) or formaldehyde, Git! Pb in R (oxidation product of methyl alcohol)
The metal is severely corroded, and the portion of the Pb metal layer in the coating layer is corroded.

(C) Moisture contained in alcohol or oxidation products of alcohol increase corrosion from pinholes formed in the coating layer.

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

For this reason, as a container steel plate for storing such fuel,
Highly corrosion-resistant materials are required that have fewer pinholes and have excellent corrosion resistance against alcohol and alcohol oxidation products (formaldehyde, acetaldehyde, formic acid, saccharic acid).

Materials that meet these requirements include surface Ni plating, Ni-Co alloy plating, and Ni-So alloy plating.

Steel sheets coated with Nl, Co, 811, or alloys thereof, such as Sn plating, have been developed, and relatively good corrosion resistance has been achieved.

Furthermore, due to the processed shape of the fuel container or high-speed molding process, the pinholes in the coating layer may be enlarged, and the surface may become hard to press.
Due to defects in the coating layer due to this phenomenon, defects that reached the base steel, and defects that reached the base steel during handling, red rust phenomena were observed that occurred from these defects. In particular, corrosion progressed when there was a large amount of CL- ions and water mixed in from gasoline or the outside, or water separated from a mixed fuel of alcohol and gasoline, and pitting corrosion was also observed.

On the other hand, the problem of snowmelt salt corrosion on the outer surface of tanks has become more severe in recent years, and corrosion caused by CL- ions, especially holes, is caused by defects in the coating layer or by the occurrence of scratches that reach the base steel due to collisions with road-sprayed salt (so-called chipping phenomenon). Perforation corrosion, which leads to pitting, was also frowned upon.

(Problems to be Solved by the Invention) The present invention has been made in response to these circumstances, and solves the problem of corrosion resistance of steel plates to 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 fuel containers that has excellent formability, weldability, and the like.

(Means to solve the problem) That is, the gist of the present invention is that C: 0.02% or less, Cr:
3 to 20%, acid-soluble A1: 0.005 to 0.10%, and one or more of Ti, Nb, Zr, and V containing 0.03 to 0.05%, and further B:
A steel plate with a thickness of 0.003% or less and the remainder consisting of iron and unavoidable impurities is coated on the side corresponding to the inner surface of the fuel container.
A diffusion coating layer of one or two types of Ni or Co with a thickness of 0.01μ or more, and a diffusion coating layer of 05 to 10μ with a thickness of 0.05 to 10μ.
A Pb-Sn alloy coating layer with a thickness of 1 to 10μ or a coating layer of one or two types of Ni or Co with a thickness of 001μ or more is applied on the side corresponding to the outer surface of the other fuel container. and a diffusion coating layer with a thickness of 001 to 1μ.
, by applying one or both of the coating layers consisting of one or more of Nt, Co, and Cu,
This is a steel sheet for a fuel container provided with a Pb-Sn alloy coating layer having a thickness of 1 to 10 μm.

The present invention will be explained in detail below.

Steel sheets containing 3% or more of Cr, especially Cr A steel plate containing 5 or more copper exhibits excellent corrosion resistance.

However, if the Cr content exceeds 20 inches, the workability and weldability deteriorate, making it difficult to form or weld the fuel container during manufacturing. Therefore, from the viewpoint of corrosion resistance, workability, and weldability in a corrosive atmosphere targeting the inner surface of the fuel container, the Cr content is 3 to 20%, preferably 5 to 11%.
is within the range of

From the viewpoint of workability, in the transformation region composition of r phase and α phase with Cr of 11% or less, coarsening of crystal grains due to cholera transformation is difficult to occur during steel plate manufacturing, and when subjected to severe forming processing, From the viewpoint of processability, it is particularly preferable that the upper limit of the Cr content is 11 inches or less, since a roughening phenomenon called ridging is unlikely to occur.

From the viewpoint of corrosion resistance of steel sheets, as mentioned above, Cr has the greatest effect, but in the present invention, from the viewpoint of targeting materials for fuel tanks for automobiles and other storage, other steel components such as C, rR and soluble M are also considered. It is necessary to limit the content.

As the C content increases, chromium carbide is precipitated, which deteriorates the mechanical properties and corrosion resistance of steel.

Therefore, the C content is less than O, l O, preferably 0,
0.02% or less.

When the amount of acid-soluble AI (5olA1) remaining in the steel is less than 0.005%, it is difficult to prevent the generation of bubbles due to oxygen gas, and the rate of occurrence of surface defects in the steel is significantly increased. This becomes the starting point for corrosion resistance deterioration of the steel material. In addition, excessive acid-soluble M present in OIO%i causes M-based diride to be scattered on the steel surface, causing deterioration of corrosion resistance or causing non-plating, pinholes, etc. on the plated surface, and inhibiting the plating. Damage the health of the threat.

In addition, in the present invention, in addition to the above-mentioned steel components, 0,03~
Cr contained by containing one or more of 0.50% of Ti, Nb, Zr, and V to combine with C in the steel.
The objective is to further improve moldability and corrosion resistance.

If the total content of steel components such as T1 is less than 0.031%, there is little effect in preventing precipitation of chromium carbide and improving formability and corrosion resistance, and if the content exceeds 0.50%, The effect reaches saturation and becomes uneconomical, and the precipitation of these components tends to harden the material and deteriorate moldability. Particularly preferably, the content of these elements is 0o)5 to 0
．． It is in the range of 20%.

Furthermore, in the present invention, in addition to the above-mentioned steel components, 0003
% or less of B is added. B is added for the purpose of further improving formability and preventing strength deterioration in heat-affected zones during welding and brazing operations.

That is, the reason for adding B to the steel components of the present invention is as follows.

If a fuel container or other item is highly molded and used in a cold region, it may
Cracks called secondary processing cracks may occur.

As mentioned above, since the C content is limited to an extremely small amount, P,
This is thought to be because the precipitation of S and the like at the grain boundaries increases and embrittles the grain boundaries.

Therefore, instead of these impurities, B is an element that precipitates at the grain boundaries, suppresses the precipitation of p, s, etc., strengthens the grain boundaries, and prevents secondary 7JQ cracking. is added. In addition, the addition of B precipitates at grain boundaries, so when welding or brazing is subjected to high-temperature operations, it prevents the growth and coarsening of grains in these heat-affected zones.
Depending on the use of the product of the present invention, B may be added in an amount of 0.3% or less, preferably 0.1% or less.

This B is also O, and if OQ is added in excess of 3%,
Since the steel plate is hardened and the forming processability is deteriorated, it is limited to the above range.

In the present invention, if a steel plate having the above-mentioned composition is used as it is as a fuel container material for alcohol fuel, alcohol-containing fuel, etc., good results cannot necessarily be obtained. The cause of this is that 01- ions or moisture in the atmosphere accumulate on the fuel or the inner surface of the container, or that fluxes used during container manufacturing, such as zinc chloride, moisture, etc., are mixed into the container. The water containing IJ- and IJ- ions is separated into two phases, and the water phase containing 01- ions causes red rust and pitting corrosion.

On the other hand, the outer surface of the fuel container is exposed to CI- ions caused by salt sprayed to prevent roads from freezing in the winter, or in a sea lice atmosphere where C1- ions are present, causing red rust and perforation corrosion from areas where red rust occurs. There is a problem that the corrosion resistance life is significantly deteriorated. Therefore, in the present invention, if a steel plate as described above is used as it is for 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 is coated with a diffusion coating 11- made of one or both of Ni and Co with a thickness of 001μ or more, and the upper layer of the coating 1 is coated with a thickness Q, 5-10μ of one or two of Sn, Ni, Co
A two-layer coating 1 of a coating layer consisting of seeds or more is applied.

On the other hand, the outer surface of the fuel container is made of pb-Sn with a thickness of 1 to 10 μm.
Apply an alloy coating layer. Or a diffusion layer made of one type of Ni, Co, or 22fI with a thickness of 0.01 μ or more, and a diffusion layer of Ni, Co, Sn, Cu with a thickness of 0.01 to 1 μ.
Pb-Sn with a thickness of 1 to 10μ is applied by applying one or both of the coating layers consisting of one or two or more of the following.
Apply an alloy coating layer.

That is, one side of the Cr-containing steel plate corresponding to the inner surface of the fuel container is coated with metals such as Ni and Go that have good corrosion resistance against alcohol, alcohol-containing fuel, alcohol oxidation products, moisture, gasoline, CL-ions, etc. Or a diffusion layer of an alloy and a coating of Sn, Nx, etc. 1. By providing -, it is possible to ensure complete corrosion resistance, and also to ensure corrosion resistance of the steel substrate such as defects (pinholes) in these coating layers and eaves against the base steel during forming processing.

In addition, by using a Cr-containing steel component and a coating layer, the couple corrosion current between the steel base and the coating layer is reduced, so defects in the coating layer, such as pinholes and scratches that occur during forming, can be avoided. However, if the coating layer has a lower potential than the steel base, the amount of corrosion due to the sacrificial corrosion protection of the coating layer will be small, and even if the coating layer has a lower potential than the steel base, The amount of corrosion on the steel base is small, and the risk of drilling corrosion is extremely low.

As a result, the coating amount (plating) of the coating layer of the present invention can be reduced, resulting in extremely excellent effects in terms of adhesion of the coating layer and moldability, which is particularly required for fuel containers. .

In the present invention, the Sn, Ni, Co 2 coating treatment method, coating treatment conditions, etc. are not particularly specified, but surface cleaning of Cr-containing steel sheets such as degreasing and pickling,
After the activation treatment, coating treatment is performed under the following conditions (1) Ni plating plating bath composition: *Nickel acid 2502μ Nickel chloride 70rμ Boric acid 30? /1 Current density 5~l 50 A/dm” (2) S
N plating plating bath composition: Phenol sulfone fil 20
1/1 sulfuric acid 1% J4 60 f/I ENSA (additive) IOP/current density
5 to 50 A/dm' (3) Ni-Sn alloy plated nickel chloride 250 f/ to stannous chloride 509/ to acidic ammonium fluoride 50 r/L Current density 5 to 50 A/ate? (4n Ni-
Co alloy plated nickel sulfate 125 ? / cobalt sulfate 259 / nickel chloride 3 at/L cobalt chloride 30/L boric acid 25 f/L O, 5 to 10μ, particularly preferably 1 to 7μ. This is because if the thickness is less than 0.05 μm, the uniform coverage of the coating layer is extremely insufficient, a large amount of pinholes are generated, and the effect of improving corrosion resistance may not be obtained. Furthermore, if the thickness of the coating layer exceeds 10 μm, the effect of improving corrosion resistance is saturated, and the adhesion and moldability of the coating layer tend to deteriorate, which is not preferable.

The alloy composition of the coating layer is Ni, Sn.

The alloy compositions when combined with Co 2 exhibit almost the same excellent corrosion resistance performance with each metal, and alloy compositions over the entire composition range are used.

Furthermore, in the present invention, the above-mentioned S
A diffusion coating layer made of Ni, Co, or a Ni-Co alloy is applied to the surface of the steel sheet containing .

That is, by applying a diffusion coating layer to the surface of a Cr-containing steel sheet, the corrosion resistance of the Cr-containing steel sheet against alcohol, alcohol-containing fuel, moisture, C1- ions, etc. is further improved, and the coupling corrosion current with the coating layer is reduced. , the effect of further reducing the size can be obtained.

As a result, even if there are defects (pinholes) in the coating layer or defects that reach the steel substrate with these diffusion coating layers, such as eaves during forming, the exposed layer is potentially less noble. In some cases, the amount of corrosion due to sacrificial corrosion protection of the coating layer itself can be reduced,
Further, in the case where the coating layer is electrically sensitive, the amount of corrosion of the steel substrate having the diffusion coating layer is further reduced, so that the corrosion resistance life is further improved. .

Furthermore, by providing these diffusion coating layers, it is expected that the corrosion resistance of the welded portion will be further improved. In other words, in the welded part and the heat-affected zone in the vicinity thereof, the above-mentioned coating layer is generally damaged by the heating tower, so that exposed parts of the steel base often occur. In this case, the presence of a diffusion coating layer on the surface of the steel substrate, which has excellent corrosion resistance against alcohol, alcohol-containing fuel, moisture, C1- ions, etc., is extremely advantageous for its corrosion resistance. Therefore, even if exposure of the steel substrate is generated during welding operations, for example, the corrosion-resistant life can be expected to be extended due to the presence of the diffusion coating layer.

Therefore, the method for obtaining such a diffusion coating layer of Ni, Co, and Ni-Co alloy is not particularly specified, but the method for obtaining this diffusion layer may be, for example, the following method. achieved. That is, after degreasing and pickling the surface of a cold-rolled material (ascold material), a predetermined thickness is obtained by electroplating with Ni, Co, or NL-Co as described above, or by applying an aqueous solution containing salts of these metals. By providing a pre-coating layer of
A diffusion coating layer is provided by heat treatment for 30 to 180 seconds at a temperature range of ~950<0>C.

Of course, a pre-coating layer of Ni, Co, or Ni-Co may be provided using a cold-rolled or annealed material (full-finished material), and then heat diffusion treatment may be performed. Due to the processing strain of the cold rolled material,
Since interdiffusion between the pre-coating layer and the steel sheet is promoted, a short heat treatment can generate the diffusion layer that is the object of the present invention, and the surface oxidation of the Cr-containing steel plate during the annealing process can be reduced to the pre-coating layer. There are advantages such as being able to prevent this, and it is also advantageous in terms of the process.

Next, Ni is used as an intermediate coating layer between the Cr-containing steel sheet and a coating layer of Sn, Ni, Co, or an alloy of two or more of these.

When providing a diffusion layer of Co or Ni-Co alloy, it is necessary to provide a diffusion layer with a thickness of 0.01 μm or more. This is because when the thickness of the diffusion layer is less than 0.01μ, Cr
This is because a diffusion layer made of Nλ, Co, , Ni-Co alloy is not uniformly generated on the surface of the containing steel plate, and the above objective is not achieved, and the thickness is preferably 0.05μ or more. Further, from the viewpoint of processability, the upper limit is preferably limited to 10 μm or less, similar to the above-mentioned coating layer.

Regarding the method of providing a coating layer of Sn, Ni, Co, or an alloy containing two or more of these as a two-layer coating shoulder on the diffusion coating layer thus generated, please refer to the diffusion coating method. A coating layer may be provided on the surface of the layer directly or after activation treatment such as pickling using the electrolytic bath composition and electrolytic conditions as described above.

Next, apply alcohol to the outer surface of the fuel container.

However, its corrosion resistance is inferior to alcohol-containing fuels. □−
Pb-S has extremely excellent corrosion resistance against ions and moisture, and can also impart other important properties required for fuel containers, such as solderability and formability, to Cr-containing steel sheets.
Apply n-alloy '4i coating.

That is, it can provide an excellent effect in improving the corrosion resistance of the outer surface of the fuel container when exposed to a corrosive atmosphere rich in CL''' ions and moisture, such as sprayed salt for preventing road icing or a sea breeze atmosphere. In particular, due to the combined effect of the Cr-containing steel plate used in the present invention, the couple corrosion current between the steel plate and the PB-Sn coating is lower than that of a steel plate without Crf used as a full-wave plating original plate. If the Pb-Sn alloy coating layer becomes extremely small or becomes anodic depending on the Cr content, corrosion of the original plate to be plated may occur from the via holes in the alloy coating layer or from scratched areas during forming. is significantly reduced, resulting in an extremely excellent effect of extending corrosion resistance life.

Furthermore, as an effect of applying a Pb-Sn alloy coating layer to one side corresponding to the outer surface of the fuel container as described above, since the coating layer is composed of a soft and highly lubricating metal, This is extremely advantageous when a precise molding process is required, since the coating layer provides a lubricating effect.

In addition, since the Pb-9m alloy coating layer is a solder alloy,
Since many parts of piping such as fuel containers and fuel feed pipes are soldered, the steel sheet of the present invention has extremely excellent solderability and is particularly advantageous as a steel sheet for fuel containers.

The composition of this Pb-Sn alloy coating layer is not particularly defined, but from the viewpoint of solderability, Sn
A pb-Sn alloy composition with a Sn content of 3% or more, preferably 5% or more is used, and the upper limit of the Sn content is not specified, but from an economical point of view it is less than 50%, preferably 30%.
An alloy of the following composition is used:

The thickness of this coating layer is important for achieving the object of the present invention, and the thickness is defined in the range of 1 to 10 microns.

That is, if the thickness is less than 1 μm, the uniform coating on the surface of the Cr-containing steel sheet will not be sufficient, a large amount of pinholes will be formed, the corrosion resistance will be insufficient, and the coating layer will be too thin. The lubricating effect and solderability improvement effect of the coating layer cannot be obtained.

In addition, if the thickness exceeds 10μ, the effect will be saturated,
Not only is it uneconomical, but the smoothness of the coating layer increases, which increases the contact resistance during molding and deteriorates the formability, and increases the contamination of electrodes by the metal of the coating layer during welding to create fuel containers. This is not preferable because it deteriorates weldability. Therefore, the thickness of the Pb-an alloy coating layer is 1 to 10 microns, preferably 3 to 7 microns.

The pb-sn alloy coating layer may be provided on only one side of the Cr-containing steel plate by any of electroplating, hot-dip plating, and vapor phase plating. After surface cleaning such as degreasing and pickling, and activation treatment, the surface of the Cr-containing steel plate is subjected to Pb-1n alloy coating treatment. For example, in the case of electroplating, a fluoride bath containing Pb ions and Sn ions corresponding to a predetermined alloy composition is used to energize only one side of the steel plate to obtain a predetermined thickness. Obtained by electrolytic treatment.

In addition, in the case of hot-dip plating, a fusking agent, such as a Cr2O3-based compound or a silicate compound, which prevents the reaction with the hot-dip Pb-Sn alloy plating bath, is applied to the non-plated surface of the Cr-containing steel sheet, and then added to the plating bath. By immersion treatment, molten Pb- containing a predetermined amount of Sn is applied to only one side of the plated surface.
A Sn alloy plated coating layer can be obtained. The vapor phase plating method can also be achieved by heating and evaporating a molten Pb-Sn alloy plating bath in a vacuum on only one side of the plated surface, and providing Pb-Sn alloy vapor deposition on only one side of the steel plate. In the present invention, P
Although the b-Sn alloy coating layer may be provided only on one side of the Cr-containing steel plate, it is necessary to provide the coating layer with a thickness of 1 to 10 μm from the viewpoint of performance.

This Pb-So alloy layer exhibits excellent corrosion resistance against moisture, Cj- ions, SO, -2 ions, etc., but extremely low corrosion resistance against alcohol, alcohol oxides, etc. Corrosion resistance is poor, and its dissolution is significant. the result,
If the Pb-Sn alloy coating layer is present on the surface in contact with the alcohol fuel, there is a problem that corrosion products caused by the alcohol fuel may clog the tank piping. Therefore, this Pb
- The Sn alloy coating layer must be limited to only one side corresponding to the outer surface of the fuel container.

Furthermore, in the present invention, Ni and Co each having a thickness of 0.01 μ or more are used as an intermediate layer between the Pb-Sn alloy coating j- on the side corresponding to the outer surface of the fuel container and the Cr-containing steel plate.

Ni-Co alloy diffusion layer and thickness O, Ol ~ l p
Ni.

Intermediate coating layer 7'' consisting of one or both of coating layers consisting of one or more of Co, So, and Cu.
By providing these coating layers in the intermediate coating layer of the gold coating layer,
The following advantages can be obtained. In other words, Cr-containing steel!
Compared to providing a Pb-8n alloy coating layer directly on the surface,
The coating layer is composed of a Pb-8n alloy coating layer and a bottom tt [which improves corrosion resistance by reducing pinholes due to the weight effect of the second layer. C. In both cases, the reactivity of the Sn metal in the Pb-8n alloy coating layer is excellent, so a uniform and dense alloy layer is generated, which reduces pinpoles and reduces the effects of heat during welding or soldering work. In this case, an Sn-containing alloying reaction between the coating layer and these underlying metals easily occurs, which provides advantages such as preventing deterioration of the corrosion resistance of these heat-affected zones and enhancing solder bondability.

In addition, the diffusion layer can bring the potential of the Cr-containing steel sheet in a corrosion atmosphere where Cj''' ions are present to a positive direction, and can reduce the coupled corrosion current with the Pb-8n alloy coating layer.
As a result, due to the combined effect with the Pb-3n alloy coated bottle, it is possible to further improve its corrosion resistance life.

Furthermore, Cr-containing steel sheets are generally easily oxidized during the annealing process to ensure their material quality, so strict atmospheric control of the annealing conditions and severe pickling are required when providing a Pb-8n alloy plating layer after annealing. Pretreatment and activation treatment are required.

Therefore, such as Ni, Co, Ni-Co alloy,
It is difficult to oxidize during the heat annealing process and is relatively easily activated during pretreatment pickling, etc., so the uniform coverage of the subsequent Pb-8n alloy coating layer and the plating adhesion of the coating layer are improved. However, effects such as improving corrosion resistance or reducing peeling of the coating layer during molding (so-called powdering property) can be obtained.

When applying a two-layer coating treatment of a diffusion coating layer and a coating layer,
Due to the above-mentioned combined effects, further performance improvements in corrosion resistance, moldability, and solderability of the outer surface of the fuel container can be obtained. In order to obtain these performance-improving effects, the thickness of the coating layer needs to be 0.01 to 1 μm. The thickness of the coating layer is 0.
If it is less than 0.01μ, the uniformity of the base coating layer on the surface of the Cr-containing steel sheet is insufficient, a large amount of pinholes are formed, and the desired effects of the present invention cannot be obtained. on the other hand,
When the thickness exceeds 1μ, the performance improvement effect is saturated and it becomes uneconomical, and the Pb
This results in drawbacks such as peeling of the -5n alloy coating layer or cracks originating from the base coating layer that easily reach the surface of the Pb-8n alloy coating layer on the surface.

Therefore, the thickness of these base coating layers is 0.01 to 1 μm.
, preferably 0.05 to 0.3μ.

There is no particular restriction on the method of providing these base coating layers, but they may be applied in a conventional manner by electroplating after degreasing and pickling the Cr-containing steel sheet.

Next, when providing a diffusion layer as an intermediate coating layer between the Cr-containing steel plate and the Pb-3n alloy coating layer, the thickness must be 0.01 μm or more. If the thickness of the diffusion layer is less than 0.01μ, Cr
This is because a diffusion layer made of Ni, Co, and Ni-Co alloy is not uniformly generated on the surface of the containing steel plate, and the above object is not achieved.The thickness of the diffusion layer is preferably 0.05μ. In addition, from the viewpoint of processability, the upper limit is preferably 10 μm or less, similar to the above-mentioned diffusion layer.

Although the method for obtaining this diffusion layer is not particularly limited, it can be achieved, for example, by the following method.

After degreasing and pickling the surface of the male, cold-rolled material (ascold), Ni, Co, and Ni-Co alloys are electroplated or coated with a water solution containing these metal salts to form a predetermined surface. A pre-coating layer with a certain thickness is provided, and by utilizing the annealing process of cold-rolled material, the diffusion coating layer is simultaneously annealed in a reducing atmosphere and heat-treated for 30-180 seconds at a temperature range of 700-950°C. is provided.

Of course, a pre-coating layer of Ni, Co, or Ni-Co may be provided using a cold-rolled or annealed material (full-finished material), and then heat diffusion treatment may be performed. Due to the processing strain of the cold rolled material,
Since interdiffusion between the pre-coating layer and the steel sheet is promoted, a short heat treatment can generate the diffusion layer that is the object of the present invention, and the surface oxidation of the Cr-containing steel plate during the annealing process can be reduced to the pre-coating layer. There are advantages such as being able to prevent this, and it is also advantageous in terms of the process.

Furthermore, by providing a two-layer intermediate coating layer of the above-mentioned diffusion layer and base coating layer as an intermediate base coating layer between the pb-sn alloy coating layer and the Cr-containing steel plate, it is possible to further improve the -/I(7) performance. However, in order to obtain the desired effect of the present invention, each coating layer can be provided within the above-mentioned specified thickness range.

As for the method of providing these two intermediate base coating layers, the diffusion coating layer is provided as described above, and then either as it is or after activation treatment by pickling, electroplating or the like is performed.
A base coating layer may be provided.

In addition, when each base coating layer is provided as the intermediate base coating layer of the present invention, Ni, Co, Sn, Cu, and an alloy consisting of two or more of these are selected, and in the case of a diffusion layer, Ni, The reason why Co, Ni--Co alloy was selected is as follows.

That is, Ni, Co, Sn, Cu and these 2
Alloys consisting of more than one species include Sn in the Pb-Sn alloy coating layer.
This is because it has excellent wetting reactivity with carbon dioxide and corrosion resistance against C1- ions, moisture, etc. Therefore, as mentioned above, in heat affected zones such as welds and solder parts, Pb-8
Due to the reaction with So during nn horizontal stacking, an alloy layer is likely to be generated, and it is possible to deteriorate the corrosion resistance of these heat-affected zones and improve the bondability of solder joints.

In addition, since the Pb-Sn alloy coating layer is extremely soft, it is easy to get scratches that reach the base iron during handling or forming processing.
Often causes deterioration of corrosion resistance. However, the presence of such a base coating layer prevents damage from reaching the base metal, and these base coating layers with good corrosion resistance can prevent deterioration of corrosion resistance.

In addition, when providing a diffusion coating layer, Ni, Co.

The reason for limiting the Ni-Co alloy is that Sn, Cu, and alloys containing these have low melting points in the case of buttons, making it difficult for Sn to diffuse uniformly through heat diffusion treatment.
In the case of u, the material of the Cr-containing steel sheet is hardened by the diffusion treatment, which deteriorates the formability and makes cracks more likely to occur during forming of the fuel container, which is not preferable.

In addition, if the Pb-Sn alloy coating layer contains Zn, Bb, etc. from the base metal used for forming the coating layer, it will not have any adverse effect on the performance of the product of the present invention. Even if the content is 5% or less, there will be no adverse effect. Furthermore, Ni, which is an element that improves corrosion resistance, is added to the Cr-containing steel sheet used in the present invention.

Even if Mo, Co, etc. are contained in an amount of about 10% or less, this does not impede the present invention in any way.

Next, the surface of the Pb-an alloy coating layer targeted at the outer surface of the fuel container is further chemically treated to improve its corrosion resistance, or by painting. For the purpose of improving coating performance when used, an aqueous solution containing phosphate ions or C
r+6. A chemical treatment using an aqueous solution containing Cr+3 ions may also be performed.

For example, using an aqueous solution of 0.01 to 5% phosphoric acid,
Chemical treatment for improving corrosion resistance or paint adhesion may be performed by dipping or spraying at a temperature of 0° C. for 1 to 10 seconds.

Although the present invention has been mainly described above with respect to alcohol or a fuel tank containing alcohol, there is no problem in applying or sharing the present invention to a fuel tank intended for ordinary gasoline as its corrosion resistance is good.

Examples of the present invention will be described below.

Table 1 shows that the present invention was applied to each surface of the Cr-containing steel plate after pretreatment such as degreasing and pickling, and activation treatment using steel plates with steel components whose Cr content was mainly changed. The results of performance evaluation targeting the outer and inner surfaces of each fuel container are shown in the second section.
Shown in the table.

Furthermore, the results of performance evaluation of the product of the present invention in terms of moldability, solderability, and weldability assuming the formation of a fuel container are also shown. In addition, for the coating layer, Pb
The surface of the -Sn alloy layer was chemically treated by dipping at 70° C. for 7.5 seconds, ringer roll squeezing, and drying using a 0.5-trine aqueous solution.

The evaluation test was conducted in the following manner.

1. Corrosion resistance evaluation for the outer surface of the fuel container (A) Corrosion resistance by salt spray test External surface of the fuel container after 500 hours of salt spray test (m multilayer surface)
The corrosion resistance was evaluated based on the following criteria.

◎・・・100×300. Number of red rust occurrences in a test piece size of 5 or less O...100 x 300 Number of red rust occurrences in a test piece size of W 6 to 12 Δ...100 x 300. Number of red rust occurrences in a test piece size of 13 to 20 x ... 21 or more red rust occurrences in a test piece size of 100 x 300 y (B) Corrosion resistance cycle corrosion test by C, C, T test ( C, C, T test) ■Salt water spray (5 t NaCj 35℃ x 4 hours) → ■Drying (70C
Humidity 60% 2 hours) → ■ Humidity (49℃ humidity 98%
2 hours)→■Cooling (-20℃ x 2 hours)→■Water spray■～■1 cycle of C, C, T test 6o cycles were performed, and red rust was detected using a test piece with a thickness of 0.8I. Corrosion resistance was evaluated by measuring the amount of plate thickness reduction in the corrosion-initiated/corroded areas.

O... Amount of plate thickness reduction less than 0.25 u or more O... Amount of plate thickness reduction 0.25 to 0.45 less than y Δ・
...Plate thickness reduction 0.45. More than 0.75m×・
...Plate thickness reduction 0.75XJ or more (C) 0.8
Using a test piece of X 100 X i 50 +u, the diameter is 1~2! After colliding and chipping Lm Alundum against the coating layer surface of the test piece for 10 seconds at a pressure of IKP/- at a rate of 1.52 per ml, the above C, C, and T tests were conducted for 4.5 cycles to determine whether red rust occurred. The amount of decrease in plate thickness of each part was measured and evaluated based on the evaluation criteria of CB) above.

2. Test for inner surface of fuel container From a test piece with a blank size of 0.8 x 150 gφ, with a punch diameter of 5 mm and a wrinkle pressing force of 1 t, a test piece with a punch diameter of 5 Uφ and a height of 4
0. A cylindrical container was prepared, filled with 1 OOcc of a corrosion-promoting solution for the following alcohol fuels, and sealed, and an evaluation test was conducted.

(D) Test on gasohol (20 cetanol + 0.03 tsicic acid + 0.15 tl % NaCj water and gasoline) (E) Test on gasohol () 0 thimethanol + 10 Thiisoprobyl alcohol +
o, 03%giff+0.3% of 1.2%N, CL
Evaluation test CF for 3 months using a solution of water and gasoline
) l 0% alcohol target test (99% methanol + 〇, 01 thiformic acid + 0.99% o, s % NyuC
A three-month evaluation test was conducted using each solution consisting of 1 aqueous solution), and the evaluation was performed according to the following evaluation criteria.

O...Number of red rust occurrences inside the cylindrical container (both solution immersed part and steam contact part) 0-3 O...Number of red rust occurrence inside cylindrical container (solution immersion part and steam contact part both) 3-10 Δ...Number of red rust occurrences inside the cylindrical container (both the solution immersion part and the steam contact part) 10 to 20 X°゛The number of red rust occurrences inside the cylindrical container (both the solution immersion part and the steam contact part) 21 or more to many Occurrence 3 Fuel container target/Seam welding target test Inner surface target corresponding to the inner surface of the fuel container The coating layers were superimposed on each other, and using a 08□ test material, a pressure of 4ookF4-r was applied using a trapezoidal electrode with a width of 4u, and a welding speed of 2. sm/Co1n 1
Perform seam welding W for a welding time of 2-20 seconds, create a test piece as shown in Figure 1, fill it with the solution shown below, cover the top with a plastic lid, and observe the external appearance after 3 months. The evaluation was carried out by

O Gasohol target test (80 timethanol + 5 thiene propyl alcohol 10, 10 % formic acid, 1 % NaCl water, 3% 1 % petrol) solution for 3 months evaluation O evaluation standard O... bottom surface and side surface red rust occurrence rate less than 5% O...
Incidence rate of red rust on the bottom and sides: 5 to less than 10% Δ・Incidence of red rust on the bottom and sides: 10 to less than 20% The 5n-Zn alloy used (8 in Sn
0-90%) To evaluate the solder bondability between the plated steel plate and the outer surface of this evaluation material, we used ZnCl2-HCL flux and 60% 5n-40% Pb solder to
The external solder resistance between the alloy plated surface and the coating layer surface and the strength of the solder joint were measured, and a comprehensive relative evaluation of the evaluation materials and comparative materials was performed.

O: Very good O: Relatively good Δ: Slightly poor ×: Very poor Layers were overlapped, using a trapezoidal electrode with a width of 4xJ, a pressure of 400 Kp-f, and a welding speed of 2.5 m1m1n.
The welding current range, nugget formation status, and appearance of the welded part were comprehensively evaluated at welding times of 2 to 200 seconds, and the weldability of each evaluation material was relatively evaluated.

O: Very good O: Relatively good Δ: Fairly poor ×: Very poor Molding workability ○ Evaluation method ■ Blank size 0.8X500X500. After applying lubricating oil, square cylinder drawing was performed using a 150xx square punch under the condition of a wrinkle pressing pressure of 30T, and the limit of the drawing depth and the occurrence of galling on the outer surface of the square cylinder drawing material were evaluated.

O4: No damage due to galling of the coating layer, very good molding processability Q: No damage due to galling of the coating layer, and fairly good molding processability Δ: Damage due to galling of the coating layer depending on the degree of processing Slight occurrence ×...O evaluation method with extremely poor forming processability ■ Using samples with plate thicknesses O and S, the blank diameter is 133.2 m, and the drawing ratio is 1 stage p (2, 2z) → 2 stages drawing. shi(2,
219) → Perform 3-stage aperture (3, 6), -
A conical punch was pressed into the workpiece at 40° C., and the secondary workability of -t was evaluated to see if vertical cracks would occur in the workpiece.

O: No vertical cracks, good secondary workability (Poor properties) (Effects of the Invention) Compared to comparative materials, the product of the present invention has extremely superior properties as a steel plate for alcohol or alcohol-containing fuel containers.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the preparation of seam welded test pieces.

Claims (1)

[Claims] C: 0.02% or less, Cr: 3-20%, acid-soluble Al:
Contains 0.03 to 0.50% of one or more of Ti, Nb, Zr, and V in addition to 0.005 to 0.10%,
Furthermore, a diffusion coating of one or two types of Ni or Co with a thickness of 0.01μ or more is applied to the steel plate containing 0.003% or less of B, with the remainder consisting of iron and unavoidable impurities, on the side corresponding to the inner surface of the fuel container. layer and Sn, Ni, Co with a thickness of 0.5-10μ
A Pb-Sn alloy coating layer with a thickness of 1 to 10 μm or a coating layer of Ni or Co with a thickness of 0.01 μ or more is applied on the other side corresponding to the outer surface of the fuel container.
A diffusion coating layer consisting of one or two species and a thickness of 0.01 to 1
Applying one or both of the coating layers made of one or more of Sn, Ni, Co, and Cu of μ,
A steel sheet for a fuel container, characterized in that it is coated with a Pb-Sn alloy coating layer having a thickness of 1 to 10 μm.