JPH0575839B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] This invention relates to a method for producing a surface-treated steel sheet for use in alcohol-based fuel tanks for automobiles, etc., which has corrosion resistance to withstand corrosion caused by fuel and workability required for tank forming. It is. [Prior Art] Corrosion is an important problem in fuel tanks of automobiles and the like. In addition to tank leakage due to pitting corrosion, corrosion products can obstruct fuel circulation and impede driving, so the materials used to make these tanks must be processable enough to withstand tank formation and corrosion resistant due to fuel. It must also have corrosion resistance. Conventionally, gasoline has been generally used as fuel for automobiles, and the materials used for gasoline tanks have been Zn-plated steel sheets and Pb-Sn alloy-plated steel sheets called turnsheets. These surface-treated steel sheets had good corrosion resistance against gasoline and excellent workability required in the process of forming fuel tanks. However, due to the development of alternative energy after oil shocks and pollution problems, in recent years alcohol has begun to be used instead of gasoline. In other words, alcohol is mixed with gasoline as a fuel, or alcohol itself is used as fuel, and some of these methods have already been put into practical use in South America, Europe, and the United States. The problem here is the corrosive nature of alcohol. Alcohol and mixed fuels of alcohol and gasoline, that is, alcohol-based fuels, are more corrosive than gasoline, and it has become difficult to expect corrosion resistance from conventional surface-treated steel sheets for gasoline tanks. The first reason for this is that Pb and Zn are easily corroded by alcohol itself, but the effects of alcohol's water absorption and deterioration products also promote corrosion. Alcohol easily absorbs water, thereby increasing the electrical conductivity of the solution. The increased conductivity promotes catalytic galvanic corrosion of metals or alloys at different potentials. Furthermore, when water is mixed into the mixed fuel of alcohol and gasoline, the gasoline and the aqueous alcohol solution separate into two phases, causing corrosion due to the aqueous alcohol solution. Furthermore, as alcohol deteriorates,
The oxidation products, aldehydes and organic acids, increase, which increases the electrical conductivity of the fuel and promotes catalytic corrosion, and also promotes the dissolution of metals such as Pb and Zn. Because alcohol acts in this way, conventional surface-treated steel sheets for fuel tanks such as Zn-coated steel sheets and
When Pb-Sn alloy coated steel sheets are used in alcohol-based fuel tanks, holes may form in the tank due to pitting corrosion, or rapid dissolution of the plating layer may occur, resulting in the formation of insoluble white precipitates. This precipitate can clog the fuel circulation system, which can impede driving. Under these circumstances, research has recently been conducted on new surface-treated steel sheets to replace these, and surface-treated steel sheets using metals such as Sn, Ni, and Co that are resistant to alcohol corrosion have been proposed. for example,
In JP-A-61-56297, on the Pb-Sn alloy plating layer,
A surface-treated steel sheet coated with Ni or Ni alloy has been disclosed, and in JP-A-62-33795, Zn
Alternatively, Ni-Ni may be added as a second layer on the Zn-Ni alloy plating layer.
It is disclosed that Fe alloy plating is applied. However, the method of combining these plating layers is to attach a plating layer that is less likely to corrode on top of a plating layer that is more likely to corrode, thereby protecting the underlying plating layer. In this case, in the area where the underlying plating layer has corroded and disappeared,
There is a high risk that the upper plating layer will fall off as a solid and impede fuel circulation. In order to avoid this problem, the above-mentioned JP-A-62-
33795 has good corrosion resistance against pure alcohol.
A single-layer treated steel sheet plated with a Ni-Fe alloy is disclosed. [Problems to be solved by the invention] In pure alcohol, the Ni-Fe alloy exhibits good corrosion resistance, and its electrode potential is also slightly less base than that of steel, so it protects the steel by sacrificial corrosion protection. . However, since this anti-corrosion effect dissolves itself in order to protect the steel, its lifespan becomes a problem. Also, as alcohol deteriorates and formic acid increases, this potential relationship reverses,
The Ni-Fe alloy plating layer only plays the role of separating the steel and alcohol (barrier effect). However, in such an environment, only the Fe in the Ni-Fe alloy is selectively dissolved, and the plating layer tends to collapse and loses its barrier effect in a short period of time. This invention was made to solve these problems, and the plating film does not dissolve easily in alcohol, and even if the alcohol deteriorates,
The purpose is to manufacture surface-treated steel sheets that can maintain the integrity of the plating film. [Means for solving the problems] That is, the present invention provides (1) on at least one side of a steel plate,
A Ni-Fe alloy plating layer with a thickness of 0.5 μm to 10 μm is applied as the first layer, and on top of that a Ni-Fe alloy plating layer with a thickness of 0.5 μm to 10 μm is applied as the second layer.
After applying a 10μm Ni plating layer, the temperature is 400℃~800℃
A method for manufacturing a surface-treated steel sheet for an alcohol-based fuel tank, characterized in that the steel sheet is heat-treated in the range of (2) a first layer having a thickness of 0.5 μm to at least one side of the steel sheet;
A 10μm Ni-Fe alloy plating layer is applied, and a second Ni-P alloy plating layer with a thickness of 0.5μm to 10μm is applied on top of that, followed by heat treatment at a temperature in the range of 400℃ to 800℃. A method for manufacturing a surface-treated steel sheet for an alcohol-based fuel tank, (3) applying a Ni plating layer with a thickness of 0.5 μm to 10 μm as a first layer on at least one side of the steel sheet, and on top of that a Ni plating layer with a thickness of 0.5 μm to 10 μm as a second layer. μm～10μm
After applying the Ni-P alloy plating layer, 400℃~800℃
This is a method for manufacturing a surface-treated steel sheet for an alcohol-based fuel tank, which is characterized by heat treatment in a temperature range of . Ni--Fe alloy plating and Ni plating may be performed by electroplating using an acidic solution of boric acid, or by using a dry process such as ion plating. The N--P alloy plating may be performed by electroplating using an acidic aqueous solution of boric acid/phosphoric acid, or by a dry process. The thickness of plated metal varies
A suitable thickness is 0.5 μm to 10 μm; if it is less than 0.5 μm, coating defects such as pinholes may be unavoidable, and it is not sufficient to exhibit the properties of the plating layer such as sacrificial anticorrosion. The thicker the layer, the better the anti-corrosion performance, but a thickness of 10 μm is sufficient. Heat treatment will be explained in detail later, but the effect can be seen by treating it at 400℃ for a few minutes.
A temperature of °C is sufficient. In pure alcohol, the potential of metals and alloys is
Starting from you, the order is steel, Ni-Fe alloy, Ni, and Ni-P alloy. If there is a second Ni plating layer or Ni-P alloy plating layer on the Ni-Fe alloy plating layer, the second layer acts as a sacrificial anode and protects the Ni-Fe alloy plating layer from corrosion. . The same applies when the first layer has a Ni plating layer and the second layer has a Ni-P plating layer.
The second layer provides sacrificial corrosion protection to the first layer. That is, in the present invention, a more base layer covers the outside according to the potential series. Therefore, the potential difference between the first layer and the second layer is smaller than that between the second layer and the steel;
The amount of sacrificial dissolution of the second layer is smaller than if the second layer were present directly on the steel. Therefore, with such a plating layer configuration, the life of the second layer is long, and the life of the first layer of Ni--Fe alloy plating or Ni plating protected by this is significantly extended. Next, when the alcohol deteriorates and formic acid increases, the potentials between the steel and Ni reverse as shown in FIG. Figure 3 shows the elution current (coupling current) measured by immersing Ni and steel in a corrosion evaluation solution consisting of 90% methanol and 10% water with formic acid added. It is. When the amount of formic acid exceeds 100 ppm, Ni becomes more base, and the coupling current that previously flowed from the steel to the Ni in the connection begins to flow in the opposite direction. Figure 4 shows the amount of Ni and steel measured in the corrosion solution during the above experiment. Initially, as the amount of formic acid increases, the amount of Ni eluted increases; but
When the content exceeds 100 ppm, the amount of Ni leached decreases, indicating that steel leaching begins. In this way, as formic acid increases, the potentials between the Ni-Fe alloy and the steel also reverse. Therefore, in degraded alcohol-based fuel, the Ni-Fe alloy plating layer no longer sacrificially protects the underlying steel from corrosion.
It only serves as a barrier between the steel and the fuel. Moreover, in this situation, Fe in the Ni-Fe alloy plating layer is selectively dissolved. At this time, if a Ni plating layer is present as the second layer, this prevents the elution of Fe. The same applies when there is a Ni-P alloy plating layer as the second layer. Furthermore, when the first layer is Ni plating and the second layer is Ni-P alloy plating, the first and second layers are stable, and the barrier effect prevents the underlying Fe.
suppresses the elution of Therefore, even in degraded alcohol, the corrosion protection life of the plating layer is extended. Next, the effect of heat treatment will be explained in detail. This will simultaneously improve the anticorrosion performance and workability of the plating layer. FIG. 1 shows the results of a corrosion test conducted using a corrosion evaluation solution containing formic acid on a sample that was subjected to the above plating treatment and then heat treated for 3 minutes at varying temperatures.
Compared to those not heat-treated, those treated at 300°C have considerably less corrosion loss, and those heat-treated at temperatures of 400°C or higher have almost no corrosion. Figure 2 shows the results of applying heat treatment at different temperatures after plating, extruding these treated steel sheets to a depth of 7 mm using an Erichsen tester, and performing the above corrosion test on the processed parts. . The effect of heat treatment can be seen at 300°C, but it is not sufficient, and becomes more noticeable at 400°C or higher, resulting in almost no corrosion. The heat treatment temperature is
It may be higher than 800°C, but 800°C is sufficient. As described above, when heat treatment is performed, corrosion resistance and workability are improved, and as a result, post-processing corrosion resistance is further improved. [Example] Using the method according to the present invention, surface-treated steel sheets for alcohol-based fuel tanks were manufactured, and their corrosion resistance was evaluated with and without processing. First, the plating layer was electroplated under the conditions listed in Table 1, and both the first and second layers were each given a thickness of 1.5 μm.

【table】

[Table] Heat treatment was performed using an electric resistance heating furnace.
3 at temperatures of 400℃, 500℃, 600℃, 700℃, 800℃
I went for a minute. For processing, the sample was extruded to 7 mm using an Erichsen testing machine, and the extruded part was subjected to the test. For evaluation of corrosion resistance, formic acid was added to a solution of 90% methanol and 10% water at 100 _ppn , 300 _ppn , 400 _ppn , and
After being immersed in a corrosion evaluation solution containing 600 _ppn for one week, the occurrence of iron rust was observed. Second
The table shows the results in comparison with a conventional surface-treated steel sheet. As shown in Table 2, the surface-treated steel sheets produced by the method of the invention do not show any rust, and have extremely superior corrosion resistance compared to the surface-treated steel sheets produced using the conventional technology. Corrosion resistance is good. [Effects of the Invention] In the surface-treated steel sheet manufactured by the manufacturing method according to the present invention, as described above, each plating layer acts, so not only when the alcohol is new, but also when it deteriorates and attracts ants.

【table】

[Table] ○: No rust occurred, △: Rust occurred partially, ×: Rust occurred all over.
The values in parentheses indicate the thickness of each plating layer, and the thickness of each plating layer in the embodiment of the invention is 1.5 μm.
Even when the amount of acid increases, the double plating layers complement each other and provide long-term corrosion protection.In addition, heat treatment further improves corrosion resistance and workability. Conventionally, it has not been possible to produce a surface-treated steel sheet with corrosion resistance and workability suitable for use in alcohol-based fuel tanks, but the present invention is highly effective in achieving this.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between heat treatment and corrosion resistance for explaining this invention, FIG. 2 is a diagram showing the relationship between heat treatment and post-processing corrosion resistance for explaining this invention, and FIG. The figure is a diagram showing coupling current changes in a corrosion evaluation solution for explaining this invention, and FIG. 4 is a diagram for explaining this invention.
FIG. 3 is a diagram showing the amount of metal eluted in a corrosion evaluation solution.

Claims (1)

[Claims] 1 At least one side of the steel plate has a thickness as a first layer.
After applying a Ni-Fe alloy plating layer with a thickness of 0.5 μm to 10 μm and then applying a second Ni plating layer with a thickness of 0.5 μm to 10 μm, heat treatment is performed at a temperature in the range of 400°C to 800°C. A method for manufacturing surface-treated steel sheets for alcohol tanks. 2 At least one side of the steel plate has a thickness as a first layer.
After applying a Ni-Fe alloy plating layer with a thickness of 0.5 μm to 10 μm and on top of that a Ni-P alloy plating layer with a thickness of 0.5 μm to 10 μm, heat treatment is performed in the range of 400°C to 800°C. A method for manufacturing a surface-treated steel sheet for alcohol-based fuel tanks, characterized by: 3 At least one side of the steel plate has a thickness as a first layer.
After applying a Ni-Fe plating layer with a thickness of 0.5 μm to 10 μm and on top of that a Ni-P alloy plating layer with a thickness of 0.5 μm to 10 μm, heat treatment is performed at a temperature in the range of 400°C to 800°C. A method for manufacturing a surface-treated steel sheet for alcohol-based fuel tanks, characterized in that: