JPS61246346A - Surface treated steel sheet for fuel vessel - Google Patents

Abstract

PURPOSE:To improve corrosion resistance and forming workability by forming a Pb-Sn alloy coating layer of prescribed thickness onto the outside surface alone of a fuel vessel made of steel sheet containing prescribed percentage of C, SolAl, Cr, Ti, Nb, etc. CONSTITUTION:The surface treated steel sheet for fuel vessel is made by forming the Pb-Sn alloy coating layer of 1-10mu thickness only on one side, corresponding to the outside surface of vessel, of the steel sheet which contains <=0.1% C, 0.005-0.1% SolAl, 3-20% Cr, or further, besides the above, 0.03-0.5% of >=1 element among Ti, Nb, Zr and V.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides surface treatment for fuel containers that has excellent corrosion resistance and moldability as a container material for alcohol fuel, alcohol-containing gasoline, and fuels such as gasoline. This relates to steel plates.

(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 methyl alcohol and methyl alcohol in gasoline, have been replaced with gasoline as automobile fuel. Ethyl alcohol, methyl tert-butyl alcohol (MT
It is being proposed to use fuels mixed with alcohol (so-called gasohol), such as BA), inpropyl alcohol, and the like.

Automotive fuel container materials for these alcohol fuels or alcohol-added gasoline (gasohol) are disclosed in Japanese Patent Application Laid-Open No. 1986-
Pb-Sn alloy coated steel sheets disclosed in many patent publications such as No. 23345 and JP-A No. 51-115240 have been used, but there has been a problem in that the corrosion resistance of the steel sheets is significantly deteriorated.

This is because the Pb-Sn alloy coated steel sheet is composed mainly of pb.
For example, (a) Pb metal is severely corroded by methyl alcohol, so the Pb metal layer portion of the coating layer is easily corroded. (b) PB gold metal is significantly corroded by acetaldehyde, succinic acid (oxidation product of ethyl alcohol) or formaldehyde, formic acid (oxidation product of methyl alcohol) produced when alcohol fuel or alcohol-added gasoline is oxidized; The part of the PB metal layer in the coating layer is corroded t14. (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 coated steel sheets is significantly deteriorated.

For this reason, as a container steel plate for storing such fuel,
A highly corrosion-resistant material is required that has fewer pinholes in the coating layer and has 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, Ni-8n alloy plating, and S
Steel sheets coated with Ni, Co, Sn, or their alloys, such as n-plating, have been developed and have relatively good corrosion resistance.

Furthermore, due to the processed shape of the fuel container or high-speed molding process, the pinholes in the coating layer may expand, and the surface may become press-coated.
Due to defects that reached the base steel due to scratches in the coating layer caused by this phenomenon, and scratches that reached the base steel during handling, red rust phenomena were observed that occurred from these defects.

In addition, the problem of snowmelt salt corrosion, especially on the outer surface of tanks, has become more severe in recent years.
Due to the occurrence of flaws that reach the base metal due to the so-called chipping phenomenon, there was a concern that corrosion due to Ct'''' ions, especially perforation corrosion that would lead to perforation, would occur.

(Problems to be Solved by the Invention) The present invention has been made in response to these circumstances, and is made by adding 3 to 20% Cr to ultra-low carbon steel to produce gasoline, alcohol, or alcohol-containing gunlin. Improves corrosion resistance against fuels such as Ti, Nb, Z
One or more types of r, V, 0.03 to 0.50
% to improve workability, and a Pb-Sn alloy coating layer is applied to the outer surface of the fuel container to combine the Cr-containing steel plate and the Pb-Sn alloy.
Corrosion resistance is improved by the combined effect of the -Sn alloy coating layer, and if necessary, one or more coating layers of Ni, Co, Sn, and Cu are applied, and a Pb -Sn alloy coating layer is applied. The object of the present invention is to provide a surface-treated steel sheet for containers that solves the problem of corrosion resistance to fuel, alcohol-containing gasoline fuel, etc., and the problem of snow melting salt corrosion on the outer surface of the tank, and has excellent formability and weldability.

The present invention will be explained in detail below.

Steel sheets containing 3% or more of Cr, especially Cr Steel plates containing 5% or more of C exhibit excellent corrosion resistance. However, C
When the r content exceeds 20%, workability and weldability deteriorate, making it difficult to form or weld the fuel container. Therefore, from the viewpoint of corrosion resistance, workability, and weldability in the above-mentioned corrosive atmosphere, the Cr content was set to 3 to 20%.

Preferably it is 5 to 11%. In particular, when the Cr content is 11 or less, the Cr content is in the two-phase component region of γ phase and α phase.
During heat treatment during the manufacturing process of containing steel sheets, coarsening of crystal grains is less likely to occur, and the "hardening roughness 1" phenomenon called ridging during forming is prevented.

As mentioned above, Cr has the greatest effect in terms of corrosion resistance, but in this invention, from the viewpoint of targeting fuel tank materials for automobiles and other storage, the content of C, acid-soluble At, and other steel components is also determined. limit.

Increased carbon content deteriorates the workability of steel sheets, and the large amount of cementite precipitated scattered on the steel sheet surface causes many pinholes to occur after base coating treatment or coating treatment (painting treatment). Become. Therefore, the C component is a harmful element that deteriorates corrosion resistance, so it is preferable to have a small amount, and its upper limit is 0.10%, and preferably 0.02% or less.

With AA, if the amount of acid-soluble At (5otAt) remaining in the steel is less than 0.005%, it is difficult to prevent the generation of bubbles due to oxidizing gas, and the incidence of surface defects in the steel increases. This significantly increases the corrosion resistance of steel materials, and becomes the starting point for deterioration of the corrosion resistance of steel materials. In addition, excess acid-soluble At exceeding 0.10% causes At-based oxides to be scattered on the steel surface, which may be the starting point for deterioration of corrosion resistance, or the plated surface of the steel sheet may become unplated.
This causes pinholes, etc., which impairs the integrity of the plating layer.

Further, the present invention further includes Ti, teeth, and Z in addition to the above-mentioned steel components.
One or more types of r and V are contained in an amount of 0.03 to 0.50% to combine with C in the steel, thereby reducing the amount of Cr contained in the steel.
The objective is to further improve moldability and corrosion resistance.

The total content of steel components such as Ti and Nb is 0.03
If the temperature is less than 100g, it will have little effect in preventing the precipitation of chromium carbide and improving formability and corrosion resistance.
Furthermore, if the content exceeds 0.50%, the effect described in item 7 reaches saturation and becomes uneconomical, and the precipitation of these components tends to cause the material to become hard and deteriorate moldability. The preferred content is 0.075-0.20%.

When a steel plate having the above-mentioned composition is used as it is as a material for alcohol or an alcohol-containing fuel container, the corrosion resistance against alcohol-containing fuel is good, but the corrosion resistance against the outer surface of the fuel container is insufficient. In particular, in a sea breeze atmosphere where Ct- ions are caused by salt sprayed on the road or where Ct- ions are present, red rust develops on the outer surface of the fuel container, and furthermore, the red rust develops into pitting corrosion, resulting in a significant deterioration of the corrosion resistance life.

Therefore, in the present invention, an alloy coating layer having a thickness of 1 to 10 μm and containing Pb and Sn as main components is provided only on one side of the steel plate corresponding to the outer surface of the fuel container. This has extremely excellent corrosion resistance against Ct- ions, moisture, etc., and can provide an excellent effect of improving the corrosion resistance of the outer surface of the fuel container even when exposed to the above-mentioned corrosive atmosphere.

In particular, the couple corrosion current between the Cr-containing steel plate and the Pb-Sn alloy coating layer becomes extremely small compared to when a Cr-free steel plate is used as the plated base plate, or depending on the Cr content, Since the Pb-Sn alloy coating layer is anodic, corrosion of the plated original plate from pinholes in the alloy coating layer or flawed areas during forming is significantly reduced, resulting in extremely excellent corrosion resistance and extended service life. Effects can be obtained.

Further, since the Pb-Sn alloy coating layer is a soft metal with high lubricity, when it is formed into a fuel container, the coating layer has a lubricating effect.

Furthermore, since the Pb-Sn alloy coating layer is a solder alloy, many parts of piping such as the fuel feed pipe of a fuel container are soldered, so the steel sheet of the present invention has extremely excellent solderability. It is particularly advantageous as a steel plate for fuel containers.

The composition of this Pb-Sn alloy coating layer is not particularly specified, but from the viewpoint of solderability, a pb-Sn alloy composition with a Sn content of 3% or more, preferably 5% or more is preferred. There is no upper limit to the Sn content, but from an economical point of view, an alloy with a composition of less than 50%, preferably 30% or less is used.

The thickness of this coating layer is important for achieving the objectives of the invention, and its thickness ranges from 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 plate is insufficient, a large amount of pinholes are generated, the corrosion resistance is insufficient, and the coating layer is too thin. The lubricating effect and solderability improvement effect of the coating layer cannot be obtained.

Moreover, when the thickness exceeds lOμ, the effect is saturated,
It is not economical (at the same time, since the smoothness of the coating layer increases, the contact resistance during molding increases, deteriorating the moldability, and the electrodes are contaminated by the metal of the coating layer during welding to create a fuel container). This is undesirable because weldability deteriorates, such as an increase in

Therefore, the thickness of the Pb-Sn alloy coating layer is 1-10μ, preferably 3-7μ.

The method of providing the Pb-Sn alloy coating layer only on one side of the Cr-containing steel plate may be any of electroplating, hot-dip plating, and vapor deposition plating. Cr
The surface of the containing steel plate 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 electroplating, p corresponding to a given alloy composition
Using a fluoride bath containing B ions and Sn ions, the amount of electricity to obtain a specified thickness on only one side of the steel plate is
Obtained by applying electricity and electrolyzing.

In addition, in the case of hot-dip plating, a masking agent, such as a CrzOs 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 the masking agent is applied to the non-plated surface of the Cr-containing steel sheet. By immersing it in
Molten Pb containing a predetermined content of Sn only on one plated surface
-A Sn alloy plating coating layer can be obtained.

The vapor phase deposition 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 to provide a Pb-Sn alloy vapor deposition layer on only one side of the steel plate. In the present invention, the Pb-Sn alloy coating layer may be provided on only one side of the Cr-containing steel sheet using either method, but it is necessary to provide the coating layer with a thickness of 1 to 10 μm from the viewpoint of performance. be.

This Pb-Sn alloy coating layer exhibits excellent corrosion resistance against moisture, Ct- ions, SO4 ions, etc., but has extremely poor corrosion resistance against alcohol, alcohol oxides, etc. Its dissolution is significant. As a result, if the Pb-Sn alloy coating layer is present on the surface in contact with alcohol fuel, there is a problem in that corrosion products caused by the alcohol fuel cause clogging of tank piping. Therefore, this Pb-S
The n-alloy coating layer must be limited to only one side corresponding to the outer surface of the fuel container.

Furthermore, in the present invention, as an intermediate layer between the Pb-Sn alloy coating layer on one side corresponding to the outer surface of the fuel container and the Cr-containing steel plate, Ni, Co, Sn, C with a thickness of 0.01 to 1 μm is used.
A base coat layer made of a base coat layer of u or an alloy of two or more of these is provided. When these coating layers are provided as an intermediate coating layer between the Cr-containing steel sheet and the Pb-Sn alloy coating layer, the following advantages can be obtained.

That is, compared to providing a Pb-Sn alloy coating layer directly on the surface of a Cr-containing steel sheet, Ni, Co, 5n
When a base coat layer of SCu or a base coat layer made of an alloy of two or more of these is provided, corrosion resistance is improved by reducing pinholes due to the superposition effect of the Pb-Sn alloy coat layer and these base coat layers.

Furthermore, the metals or alloys constituting these base coating layers have a fast diffusion rate with the Sn metal in the Pb-Sn alloy coating layer and have excellent wetting reactivity. A uniform and dense alloy layer with Sn is generated, which reduces pinholes reaching the base metal in the Pb-Sn alloy coating layer.At the same time, when affected by heat such as welding or soldering, the coating layer and these The Sn-containing alloying reaction with the underlying metal can easily occur, thereby providing advantages such as preventing deterioration of the corrosion resistance of these heat-affected zones and enhancing solder bondability.

In order to obtain the effect of improving the performance of the base coating of Ni, Co, 5nSCu, and alloys containing two or more of these,
A thickness of 0.01 to 1 μm is required. If the thickness of the base coating layer is less than 0.01μ, the uniformity of the base coating layer over the Cr-containing steel plate surface is insufficient, a large amount of pinholes are generated, and the desired effect of the present invention cannot be obtained. .

On the other hand, when the thickness exceeds 1μ, the performance improvement effect is saturated,
In addition to being uneconomical, due to the influence of the base coating layer during processing, peeling of the Pb-Sn alloy coating layer or cracks originating from the base coating layer are likely to reach the surface of the Pb-Sn alloy coating layer on the surface. Therefore, the thickness of these base coating layers ranges from 0.01 to 1 micron, preferably from 0.05 to 0.3 micron.

The method of providing these base coating layers is not particularly limited, but it may be applied by a normal electroplating method after degreasing and pickling the Cr-containing steel sheet.

In addition, in the present invention, the intermediate base coating layer contains Ni, Co, and Sn.
, Cu, and an alloy consisting of two or more of these are selected for the following reasons. Ni, Co, Sn%Cu, and alloys consisting of two or more of these have excellent diffusion reactivity and wetting reactivity with Sn in the Pb-Sn alloy coating layer, and corrosion resistance against Ct- ions, moisture, etc. Are better.

Therefore, as mentioned above, in heat-affected zones such as welds and solder zones, an alloy layer is likely to be formed due to the reaction with Sn in the Pb-Sn coating layer. It is possible to improve bonding properties.

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 molding.
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 Zn, Sb, etc. are contained in the Pb-Sn alloy coating layer, they do not have any adverse effect on the performance of the present invention, so even if they are contained in an amount of about 5% or less. good.

Furthermore, even if the Cr-containing steel sheet used in the present invention contains 10% or less of corrosion resistance improving elements such as Ni, Mo, Co, etc., this does not impede the purpose of the present invention.

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

For example, using a 0.1 to 5% phosphoric acid aqueous solution,
It is possible to improve the corrosion resistance or paint adhesion by performing immersion or spray treatment at a temperature of 80° 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.

(Example) After performing pre-treatment such as degreasing and pickling, and activation treatment using steel sheets with steel components whose Cr content was changed as shown in Table 1,
The results of performance evaluations of the outer and inner surfaces (non-plated surfaces) of fuel containers of the products of the present invention, in which a predetermined amount of coating treatment is applied to one side of a Cr-containing steel plate, are shown.

Furthermore, the results of performance evaluation of the product of the present invention in terms of moldability and solderability assuming the formation of a fuel container are also shown. In addition, the surface of the Pb-Sn alloy layer is 065
% phosphoric acid aqueous solution at 70° C. for 7.5 seconds, ringer roll squeezing, and drying. As a result, the product of the present invention has extremely superior properties as a steel plate for alcohol or alcohol-containing fuel containers compared to comparative materials.

The evaluation test was conducted in the following manner.

1. Corrosion resistance evaluation for the outer surface of the fuel container (2) Corrosion resistance by salt spray test External surface of the fuel container (coating layer surface) after 500 hours of salt spray test
The corrosion resistance was evaluated using the following criteria.

◎... Number of red rust occurrences in a test piece size of 1100 x 300 10 or less ○... 11 to 20 pieces △ ... 21 to 30 pieces × ... 31 or more (B) Based on C, C, T test Corrosion resistant cycle roller
John test (C, C, T test M) ■ Salt spray (5% NaC
L35℃ x 4 hours) → ■ Drying (70℃ humidity 60% 2 hours) → ■ Humidity (49℃ humidity 98% 2 hours) → ■ Cooling (
-20°C x 2 hours) → ■Salt water spray ■~■ is carried out for 60 cycles of C, C, T test, using test pieces with thicknesses in order of 0 and 8. Corrosion resistance was evaluated by measuring the amount of thickness reduction.

◎・・・Plate thickness reduction less than 0.25mm ○"°゛More than 0.25~less than 0.45 △-0,45
m or more - less than 0.75rrm×...0
, 754 or more (C) Using a test piece of 0.8 x 100
y/atx" for 10 seconds to impact and chip the coating layer surface of the test piece with 1.52 particles per 2 pieces, and then apply the above C and C.
, T test was carried out for 45 cycles, the amount of plate thickness reduction in the area where red rust occurred was measured, and evaluation was performed according to the evaluation criteria in (B) above.

2. Test for the inner surface of a fuel container From a test piece with a blank size of 0.8 x 15 orrtxl, a punch diameter of 75 mm and a wrinkle pressing force of 1 t were used to measure 75 m.
Create a cylindrical container of g×height 40tIx, fill it with corrosion accelerating solution for alcohol fuel of 100cc or less,
It was sealed and an evaluation test was conducted.

0 Gasohol target test (10% methanol + 3% isopropyl alcohol + 〇, 01 formic acid + 0.25% distilled water + residual gasoline) A three-month evaluation test was conducted.

(9 Gasohol target test (20% ethanol + 0.03% succinic acid + 0.50% distilled water + residual gasoline) solution was used to conduct an evaluation test for 3 months.

(3) 100% alcohol test (99% methanol + 0.2 thiformic acid + 0.8% distilled water)
A three-month evaluation test was conducted using the solution.

(G) Evaluation test for gasoline (99% gasoline + 1% distilled water) A 3-month evaluation test was conducted using a solution.

The evaluation was carried out using the following evaluation criteria.

◎...Number of red rust occurrences inside the cylindrical container (both the solution immersion part and the steam contact part) 0 to 3, 10 to 20, 21 or more to many occurrences 3, 5H-Zn used for solderable fuel container piping Alloy (8 in Sn
0 to 90%) In order to evaluate the solder bondability between the plated steel plate and the outer surface of this evaluation material, 5n-Zn
The solder climbing property between the alloy plated surface and the coating layer surface and the strength of the solder joint were measured, and a relative evaluation of the evaluation materials and comparative materials was performed comprehensively.

◎...Extremely good○...Comparatively goodΔ...Slightly poor ×...Very poor4, Formability Blank size 0.8 x 500 x 500, after applying lubricating oil, under the condition of wrinkle pressing pressure of 30t Square tube drawing was performed using a 150x150 simple square punch, and evaluation was made based on the limit of the drawing depth and the occurrence of galling on the outer surface of the square tube drawing material.

◎・・・Damage due to galling of the coating layer or the outer surface of the steel plate (
, extremely good moldability.

○...No damage due to galling of the coating layer or the outer surface of the steel plate, and the formability is quite good.

△: Depending on the degree of processing, some damage may occur due to galling of the coating layer or the outer surface of the steel plate.

×...Moldability is extremely poor.

Claims (4)

[Claims] (1) On the relevant side of the outer surface of the fuel container of a steel plate containing C: 0.1% or less, solAl: 0.005 to 0.1%, and Cr: 3 to 20%, with the remainder being iron and unavoidable impurities. Thickness 1~1
A surface-treated steel sheet for a fuel container, characterized in that it is coated with a 0μ Pb-Sn alloy coating layer. (2) Contains C: 0.1% or less, solAl: 0.005-0.1%, Cr: 3-20%, and further contains Ti, Nb, Zr,
A Pb-Sn alloy with a thickness of 1 to 10 μm is applied to the outer surface of the fuel container of a steel plate containing 0.03 to 0.50% of one or more types of V, with the remainder consisting of iron and unavoidable impurities. A surface-treated steel sheet for fuel containers characterized by being coated with a coating layer. (3) On the relevant side of the outer surface of the fuel container of a steel plate containing C: 0.1% or less, solAl: 0.005 to 0.1%, and Cr: 3 to 20%, with the remainder consisting of iron and unavoidable impurities. , thickness 0.
A coating layer of one or more types of Ni, Co, Sn, and Cu with a thickness of 01 to 1 μm is applied, and a coating layer of 1 to 10 μm in thickness is applied thereon.
A surface-treated steel sheet for a fuel container, characterized in that it is coated with a Pb-Sn alloy coating layer. (4) Contains C: 0.1% or less, solAl: 0.005 to 0.1%, Cr: 3 to 20%, and further contains Ti, Nb, Zr,
Ni with a thickness of 0.01 to 1 μm is applied to the outer surface of the fuel container of a steel plate containing 0.03 to 0.5% of one or more of V and the remainder consisting of iron and inevitable impurities. Co,
A surface-treated steel sheet for a fuel container, characterized in that a coating layer of one or more of Sn and Cu is applied, and a Pb-Sn alloy coating layer with a thickness of 1 to 10 μm is further applied thereon.