JPH06272031A - Production of high corrosion resistant plated steel - Google Patents

Abstract

PURPOSE:To establish a means for stably producing a thin coating surface density aluminum plated steel capable of keeping excellent corrosion resistant function over a long period and excellent in workability by vapor phase plating method. CONSTITUTION:The surface of the steel is vapor phase-plated with Cr or Ti having 0.01-2.0mum thickness as a 1st layer and, after that, plasma is generated in a vacuum treating vessel as it is or plasma is generated while introducing an oxidizing gas containing H2O or O2 into the vacuum treating vessel, and the plated surface is plasma-treated by impressing -200 to -10V bias voltage to the steel for 0.1-1000 seconds, and then, vapor phase-plated with Al or Al alloy having 0.2-30mum thickness as a 2nd layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plated steel material having excellent corrosion resistance by a vapor phase plating method.

[0002]

2. Description of the Related Art In general, "aluminum-plated steel sheet" having a steel sheet surface coated with Al or an Al alloy has not only excellent corrosion resistance but also excellent heat resistance. It has been used for a wide range of applications such as, and therefore, a large amount of aluminum-plated steel sheets have been produced by the hot dipping method.

However, when an aluminum-plated steel sheet is produced by the hot dip coating method, a diffusion reaction occurs between Al and the steel sheet due to the temperature rise of the steel sheet during the plating treatment, and the brittle Al- It was unavoidable that the Fe alloy layer was formed. Therefore, it has been considered that the aluminum-plated steel sheet manufactured by the hot dip coating method has remarkably poor workability.

However, in order to prevent the formation of this brittle Al-Fe alloy layer, Si is added to the aluminum plating bath in ordinary hot-dip aluminum plating, whereby the diffusion reaction of Al and Fe during the plating process. Although it is trying to suppress, it is still impossible to completely prevent the diffusion between the plating layer and the base material, and the workability of the plated material is not sufficient.

Therefore, it is possible to obtain an aluminum-plated steel sheet which is excellent in workability and film adhesion without formation of an alloy layer unlike the hot-dip plating method. Methods for manufacturing steel sheets are being studied. However, the plated film produced by the vapor-phase plating method usually has many pinhole defects due to the surface roughness of the vapor deposition substrate, the growth direction of the vapor deposition material, and fine dust in the vacuum chamber. There is a problem that the base material is exposed at this defective portion.

That is, since Al is a material that is electrically baser than steel, if it is placed in a corrosive environment while Al and steel are in contact with each other, dissimilar metal contact corrosion (galvanic corrosion) occurs.
Is known to accelerate the dissolution of Therefore, in the steel material where the aluminum film is vapor-deposited, the steel material exposed at the pinhole defect becomes a cathode, and Al near the pinhole defect becomes an anode, and the aluminum plating film is short-term. It had the drawback of disappearing.

Therefore, as a means for improving the above-mentioned drawbacks, when an aluminum-plated steel sheet is manufactured by a vapor-phase plating method, the cathode overvoltage is higher than that of the steel sheet as a base material.
A method of interposing a Ti or Cr plating film between a steel material and an aluminum plating film, thereby suppressing the cathodic reaction at the pinhole defect portion and reducing the dissolution rate of the aluminum film due to the corrosion of dissimilar metals. Have been proposed (for example, JP-A-62-80261, JP-A-62-109967,
"Surface Technology" Vol.43, No.7, 1992, P.78 ■ 83 etc.).

Certainly, when aluminum is plated on the surface of a steel material by the vapor phase plating method, if a Ti or Cr base is provided as described above to form two layers, the aluminum plating film disappears until the aluminum plating film disappears. It is considerably improved compared to wood. However, even with such a plated material, dissimilar metal contact corrosion still occurs between "Al and Ti" or "Al and Cr", and the "metal Al material" in the pinhole portion of the upper aluminum plating film. Its own corrosion rate "
The problem that the elution of the aluminum film proceeds at a very high speed was not sufficiently solved as compared with the above.

According to Japanese Patent Application Laid-Open No. 62-80262, after the steel plate surface is vapor-deposited with Ti, a) a titanium oxide film is formed by spraying oxygen gas or oxygen-containing gas on the Ti film. B) In the latter half of the step of forming the Ti layer, oxygen gas or oxygen-containing gas is blown into the atmosphere to form a titanium oxide film, c) ion plating is performed in an oxygen atmosphere to form a titanium oxide film, There is disclosed a plated steel sheet obtained by forming an intermediate layer of a titanium oxide film by any one of the above means, and thereafter vapor-plating an aluminum upper layer. In this plated steel sheet, no Al-Fe alloy layer was formed, and even if a pinhole was present on the upper layer of aluminum, the insulating titanium oxide film was present, resulting in corrosion between the aluminum film and the base steel sheet. It is said that the current is prevented from flowing and the elution of the aluminum film can be suppressed.

However, when actually examined, as disclosed in JP-A-62-80262, even if oxygen gas or oxygen-containing gas is blown to the Ti vapor phase plating film, the oxidation rate is slow and the substantial insulation Getting the layers was difficult. Further, in the latter half of the Ti vapor phase plating step, when an oxygen gas or an oxygen-containing gas is blown into the atmosphere or a titanium oxide film is formed on the Ti film by ion plating in an oxygen atmosphere, after the aluminum plating, Although its corrosion resistance was good, the adhesion at the interface between the titanium oxide film and the aluminum upper layer was poor, and it was difficult to secure good workability.

In view of the above, the object of the present invention is to stably produce a light-weighted aluminum-plated steel material which maintains an excellent anticorrosion function for a long period of time and is excellent in workability by a vapor phase plating method. It is to establish means.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted studies to achieve the above-mentioned object, and have stated that "aluminum (Al or Al alloy) is formed by vapor phase plating for the purpose of cathodic protection of steel materials.
In the case of thin plating, as a matter of course, the plating film defects (pinholes) are eliminated to suppress the plating film disappearance rate due to corrosion of dissimilar metal contacts, and the aluminum plating film completely shields the base steel from the corrosive environment. It is most desirable to do so, but with the current plating technology, it is necessary to add a thick weight in order to eliminate the pinholes in the formed plating film, which is not practical. ” As a result of further research, we were able to obtain the following findings.

That is, when an aluminum (Al or Al alloy) -plated steel material is manufactured by a vapor phase plating method, first Cr or Ti is plated as a first layer (underlayer), and then the surface is subjected to plasma treatment and then aluminum. If the vapor phase plating is performed, the elution rate of the aluminum plating film becomes very slow and long-term corrosion resistance can be secured even if the upper layer aluminum plating film is thin and many pinhole defects are present in the thin plating. It has been found that an aluminum-plated steel material can be obtained which has excellent adhesion of the plated film and is sufficiently satisfactory in terms of workability.

The present invention has been made on the basis of the above-mentioned findings and the like. "Cr or Ti is used as the first layer on the surface of a steel material.
After vapor-phase plating with a thickness of 0.01 to 2.0 μm, plasma is generated in the vacuum processing tank as it is, or an oxidizing gas containing H ₂ O or O ₂ gas is introduced into the vacuum processing tank and plasma is generated. Generated, and -200 to steel
By applying a bias voltage of -10V for 0.1 to 1000 seconds, the plating surface is plasma-treated, and then Al or Al alloy is vapor-phase plated with a thickness of 0.2 to 30 μm as the second layer to obtain excellent corrosion resistance. , The point that we were able to stably manufacture thin plated materials exhibiting workability ”.

The present invention will be described in detail below along with its operation.

In the method of the present invention, first, the vapor-phase plating film of Cr or Ti is provided as the underlayer (first layer) on the surface of the steel material which is the base material because the cathode overvoltage is higher than that of the steel material and By interposing a Cr or Ti film with good adhesion with the steel material and the aluminum (Al or Al alloy) plating film, the cathode reaction at the pinhole defect part of the aluminum plating film is suppressed. This is to reduce the dissolution rate of the aluminum film due to the corrosion of dissimilar metals, and in this respect, JP-A-62-80261 and JP-A-62-10996.
The aim is the same as the technique disclosed in Japanese Patent Publication No. 7 or the like. In this case, the thickness of the first layer Cr or Ti film is 0.01
If it is more than μm, it covers the surface of the steel material, but even if it exceeds 2.0 μm, the effect of improving corrosion resistance hardly changes, so 0.01 to 2.
It was set to 0 μm.

Next, as a second step, the formed Cr or
Plasma treatment of the Ti vapor phase plating film surface is performed.
It is carried out in order to suppress the corrosion of dissimilar metal contact between the Cr or Ti film of the first layer and the aluminum plating film (second layer) to be applied thereafter without adversely affecting the adhesion of the plating film.

That is, although vapor phase plating is carried out in a vacuum chamber, the composition of the residual gas in the vacuum chamber varies greatly depending on the exhaust system used, but an oil diffusion pump or roots pump used in general vapor phase plating is used. In the vacuum system produced, most of the residual gas in the tank is H ₂ O. Therefore, a small amount of oxidation reaction occurs in Cr, Ti, etc., which have a strong oxygen affinity, even in a vacuum. However, if it is left as it is, the oxidation is insignificant, but if plasma is generated by a well-known means in the vacuum chamber and a negative bias voltage is applied to the Cr or Ti film surface through the steel material as the base material, Cr Or Ti
Plasma particles given kinetic energy by the applied bias collide with the surface of the film. For this reason,
Sputtering of the Cr or Ti film surface occurs, but since H ₂ O and the like exist in the vacuum chamber as described above, surface oxidation of the Ti or Cr film also occurs rapidly.

The applied bias voltage is -200.
When it is set to V or less, the oxidation rate is faster than the sputtering rate on the surface, so that an oxide film is formed on the surface of the Cr or Ti film. Therefore, the Cr or Ti film of the first layer and the second layer
Electric resistance is generated between the Al film and the Al alloy film, and galvanic corrosion is suppressed. At this time, when the applied bias voltage becomes -10 V or less, not only the surface oxidation rate decreases but also surface sputtering does not occur, and conversely, when the applied bias voltage exceeds -200 V, sputtering becomes remarkable and an oxide film does not form. Therefore, the applied bias voltage was set to -200 to -10V.

Further, in the above plasma treatment, the effect is not observed when the plasma treatment time is 0.1 seconds or less, while when the treatment is performed for more than 1000 seconds, the Cr or Ti film by sputtering and the base material (steel material). Therefore, the plasma processing time was limited to 0.1 to 1000 seconds.

When the above plasma treatment is applied, a slight amount of Cr or Ti film surface sputtering occurs simultaneously with oxidation. Therefore, micro-roughness is generated on the oxidized surface, and the adhesion with the aluminum plating film to be applied thereafter is improved, and as a result, the plated steel material has good workability. Is also one of the major features of the method of the present invention.

By the way, in a vacuum system in which the oxidation potential in the vacuum chamber is low and sufficient oxidation cannot be obtained in the plasma treatment, it is necessary to introduce an oxidizing gas containing H ₂ O or O ₂ gas into the vacuum chamber. Good. Further, when the degree of vacuum in the vacuum chamber is low and plasma is not generated, Ar, N ₂ or the like may be appropriately introduced into the vacuum chamber.

As described above, the oxidation of the surface of the Cr or Ti film occurs even if it is left in an oxidizing atmosphere, but the oxidation rate is slow and it does not substantially become an electric resistance layer. In addition, a Ti oxide film or
When a Cr oxide film is formed, the corrosion resistance after aluminum plating is good, but the adhesion at the interface between the oxide film and the aluminum plating film becomes poor, and the workability does not improve compared to the hot dip aluminum plated steel material. .

In the method of the present invention, the second layer (upper layer) is formed after the plasma treatment is performed on the surface of the vapor deposition film of Cr or Ti.
Vapor plating of aluminum (Al or Al alloy) is performed as. Here, the thickness of the aluminum plating film is 0.2μ
If the thickness is less than m, the number of pinhole defects increases, and the desired corrosion resistance cannot be obtained even by the treatment of the present invention. On the other hand, when the thickness of the aluminum plating film is 0.2 μm or more, pinhole defects hardly occur. The thicker the film thickness, the better the corrosion resistance. However, if the thickness of the aluminum plating film exceeds 30 μm, the workability of the plated steel material deteriorates, so the film thickness was set to 0.2 to 30 μm.

Next, the present invention will be described with reference to examples.

[Example] A commercially available SUS410L steel plate was used as a base material, and the surface thereof was degreased and washed with an organic solvent before being inserted into a vacuum treatment tank, and a vapor phase plating test under each condition shown in Table 1 was conducted. It was

[0025]

[Table 1]

Vapor plating (both the first layer and the second layer)
Then, the degree of vacuum in the vacuum chamber was set to 1 × 10 ^-5 torr by using an oil diffusion pump as an exhaust system, and then ion bombarding of the substrate surface was performed as a pretreatment, followed by an electron beam method. The plating material was deposited by.

In the plasma processing, the vacuum processing tank is
The degree of vacuum was adjusted to 1 × 10 ⁻⁴ torr by introducing Ar gas (in some cases, a slight amount of water vapor or O ₂ gas was mixed in).
Ar gas was introduced into the vacuum processing tank to adjust the vacuum to 1 × 10 ^-4 torr.
Then, a bias voltage was applied to the base steel sheet, and plasma was generated by the RF coil for treatment.

Then, for comparison, an oxygen plating gas was introduced into the vacuum treatment tank during vapor deposition of Ti, whereby a vapor deposition plating material in which the first layer plating was titanium oxide plating was also prepared.

The performance of each vapor-deposited plated material thus obtained was evaluated under the following conditions. A) Corrosion resistance evaluation A salt spray test using a 5% NaCl aqueous solution was performed to measure the time until red rust was generated on the plated steel sheet, and the corrosion resistance was evaluated by the time. B) Coating Adhesion A test piece (width 70 mm) of plated steel sheet was subjected to a 180 ° 1t bending process with the plating surface facing outward, and the adhesion of the plating film was evaluated by the film peeling condition by cellophane tape at the bent portion. did. The evaluation criteria for adhesion were as follows. ⊚: No crack peeling, ○: Partial cracking occurred, Δ: Cracking and peeling occurred, ×: Full surface peeling occurred.

The results of these evaluations are also shown in Table 1.
As is clear from the results shown in Table 1, the thin plated steel sheet produced according to the method of the present invention exhibits excellent corrosion resistance over a long period of time, and at the same time, is excellent in the adhesion of the plated film. It can be confirmed that it has workability.

[0031]

[Summary of Effects] As described above, according to the present invention, it is possible to stably produce an aluminum thin-plated steel sheet having a very long anticorrosion life and excellent workability by the vapor phase plating method. This will bring about extremely useful effects in the industry such as possible.

Claims (2)

[Claims] 1. A steel material having 0.01% Cr or Ti as a first layer on the surface thereof.
After vapor-phase plating with a thickness of ~ 2.0 μm, plasma is generated in the vacuum treatment tank, and the plating surface is plasma-treated by applying a bias voltage of -200 to -10 V to the steel material for 0.1 to 1000 seconds, Next, vapor-phase plating of Al or Al alloy with a thickness of 0.2 to 30 μm as a second layer is provided, and a method for producing a highly corrosion-resistant plated steel material. 2. Cr or Ti as a first layer on the surface of a steel material is 0.01
After vapor-phase plating to a thickness of ˜2.0 μm, an oxidizing gas containing H ₂ O or O ₂ gas is introduced into the vacuum treatment tank and plasma is generated, and the steel material has a temperature of −200 to −10.
The plating surface is plasma-treated by applying a bias voltage of V for 0.1 to 1000 seconds, and then as a second layer.
A method for producing a highly corrosion-resistant plated steel material, which comprises vapor-depositing Al or an Al alloy to a thickness of 0.2 to 30 μm.