JPH0517865A - Vapor deposition al alloy plated steel sheet - Google Patents

Abstract

PURPOSE:To improve the properties of a vapor deposition Al alloy plated steel sheet by forming an Al alloy plated layer in which Zr content is gradually increased in the depth direction on the surface of the steel sheet. CONSTITUTION:A Zr-contg. Al alloy plated layer in which Zr content is gradually increased in the depth direction of the plated layer is formed on the surface of the steel sheet. At this time, the Zr content in the Zr-contg. Al alloy plated layer is regulated to <=30mass% on the surface side, and that on the boundary side with the basis steel sheet is regulated to >=50mass%. In this way, the corrosion resistance, heat resistance and workability of the Zr-contg. vapor deposition Al alloy plated steel sheet can be improved.

Description

Detailed Description of the Invention

[001]

TECHNICAL FIELD The present invention relates to a Zr-containing vapor-deposited Al alloy-plated steel sheet having excellent corrosion resistance, heat resistance and workability.

[002]

2. Description of the Related Art Conventionally, a large amount of Al-plated steel sheets have been used, but this general one is a single-layer plated steel sheet in which the steel sheet is directly plated with Al by a hot dipping method. Since this Al-plated steel sheet has excellent corrosion resistance and heat resistance as long as the thickness of the plated layer is 8 μm or more, it has been widely used for automobile exhaust gas system components, combustion equipment components, household equipment components, etc. ing. However, recently, depending on the application,
In order to reduce the manufacturing cost of members, thin-plated products are required, and expansion of use to applications that are affected by salt corrosion is being considered.

[003]

However, when an Al-plated steel sheet is used in an environment in which halogen ions exist that are subject to salt corrosion, the oxide film on the surface having corrosion resistance is dissolved, and therefore Al (OH) ₃ White rust, which is mainly composed of, occurs on the surface and pitting corrosion that reaches the base steel sheet occurs.

Therefore, when it is used for the purpose of receiving salt damage, the thickness of the plating layer is increased to about 40 μm so that pitting corrosion does not reach the base steel sheet in a short time. Then, there was a problem that it became expensive. Further, the surface of the plated layer is subjected to chemical conversion treatment such as chromate treatment which is a general post-treatment of the plated steel sheet, but this effect is temporary and does not essentially improve the corrosion resistance. .

In the hot-dip Al-plated steel sheet, Si is usually contained in the plating layer in an amount of 8 to 12 mass% to suppress the development of an Al-Fe intermetallic compound layer having poor workability which is generated at the interface between the base steel sheet and the plating layer. However, in this case, if the base steel sheet is a low carbon rimmed steel or Al killed steel that has been commonly used in the past,
When heated to 00 ° C or higher, the interface between the plated layer and the base steel sheet is preferentially oxidized, and when heated to 700 ° C or higher, the plated layer may be alloyed and peeled off, which is not always sufficient in terms of heat resistance. I can not say. This heat resistance problem is ameliorated by using a low carbon-Ti-added steel or ultra-low carbon-0.2Ti-added steel that can withstand repeated heating at 650 ° C or higher for the base steel sheet. If it is used, the product price will be considerably higher than that of Al-killed steel, which is not preferable. Even if a Ti-added steel is used as the base steel sheet, a brittle Al-Fe-Si intermetallic compound layer is generated at the interface between the base steel sheet and the plating layer, so that satisfactory formability cannot be obtained.

On the other hand, non-aqueous solution electroplating with Al or ordinary vacuum vapor deposition Al plating can produce an Al-plated steel sheet in which an Al-Fe intermetallic compound layer is not formed at the interface between the base steel sheet and the plated layer, so that it is at room temperature. Although it is excellent in workability, when manufactured by such a method, when heated to a high temperature, Al of the plating layer diffuses into the base steel sheet, and the base steel sheet is oxidized, so that the heat resistance is poor, Moreover, since a brittle Al-Fe intermetallic compound is formed at the interface between the base steel sheet and the plating layer, workability deteriorates. In addition, since the plating layer has defects such as pinholes that reach the base steel plate, the base steel plate is corroded even in a relatively soft environment where halogen ions do not exist, and there is a problem in corrosion resistance. .

As described above, the conventional Al-plated steel sheet was not always satisfactory in terms of corrosion resistance, heat resistance and workability. Then, this invention provides the vapor deposition Al alloy plating steel plate which improved these characteristics.

[0085]

The present invention is directed to the surface of a steel sheet.
The vapor-deposited Al alloy-plated steel sheet was formed with a Zr-containing Al alloy plating layer in which the Zr content rate gradually increased in the depth direction of the plating layer.

[0109]

[Function] In order to improve the corrosion resistance, heat resistance and workability of the Al-plated steel sheet, it is possible to suppress the occurrence of pitting corrosion in the plating layer and suppress the occurrence of pinholes in the plating layer. It is an essential condition that the Al-Fe intermetallic compound layer is not formed at the boundary between the plating layer and the base steel sheet.

That is, the corrosion of the Al plating layer is pitting corrosion. When the pitting corrosion reaches the base steel sheet, a local battery is formed between the base steel sheet and the plating layer, and a galvanic current flows between them. , It occurs when the plating layer becomes base electric potential and is preferentially dissolved. This galvanic current is so large that local dissolution rapidly occurs in the plating layer and spreads to the surroundings.
Then, when the dissolution of the plating layer is expanded to the range where the sacrificial anticorrosive action of Al on the base steel sheet is not reached, corrosion of the base steel sheet is started and red rust occurs.

Further, in an environment where halogen ions do not exist, such as in ordinary air, since the passivation film of the Al plating layer is stable, the sacrificial anticorrosion effect of the Al plating layer on the base steel sheet does not work, and the pinhole The base steel sheet will be corroded through. Therefore, in order to improve the corrosion resistance, it is necessary to prevent pitting corrosion from occurring in the plating layer and to suppress the generation of pinholes.

Further, since the Al--Fe intermetallic compound layer is brittle and grows by heating, it is necessary to prevent the intermetallic compound layer from being formed in order to improve heat resistance and workability.

FIG. 1 shows an example of the element content distribution in the cross section of the vapor-deposited Al alloy-plated steel sheet of the present invention. Thus, the Zr content rate gradually increases toward the base steel sheet side. If an Al alloy plating layer is formed, the corrosion resistance, heat resistance and workability are improved as follows.

(1) When the Al alloy plating layer is corroded in a salt-corrosion environment, the potential of the plating layer gradually increases in the depth direction, so that pitting corrosion does not occur and general corrosion occurs. Corrosion progresses in the form of. Therefore, the base steel sheet is not corroded until the Al alloy plated layer disappears, and the base steel sheet is corroded for a long period of time.

(2) A Zr content gradient was provided in the depth direction.
The Al alloy plating layer has the effect of embedding the pinhole generated at the initial stage of forming the plating layer, and since the exposure of the base steel sheet to the outside is suppressed, corrosion of the base steel sheet even in a relatively soft environment such as normal air Is suppressed.

(3) Since the Al alloy-plated steel sheet of the present invention is vapor-deposition plated, an intermetallic compound layer is not formed at the boundary between the plating layer and the base steel sheet as in hot dipping, and the base material of the plating layer is not formed. Since the Zr content is high on the steel plate side,
During heating, Zr has a function of suppressing diffusion of Al into the base steel sheet.

The plated steel sheet according to the present invention has a Zr surface side of the plating layer.
The difference between the content and the Zr content on the boundary side between the base steel sheet, that is,
If the width of the Zr content is small, the effect of preventing pitting corrosion in a salt-corrosion environment and the effect of embedding the pinhole in the plating layer become small. Therefore, in order to improve the corrosion resistance, the plating layer requires a certain range of Zr content, and the range of Zr content is preferably 20 mass% or more. On the other hand, the Zr content in the plating layer is the Zr content on the boundary side with the base steel sheet.
If the content is less than 50 mass%, the effect of suppressing the diffusion of Al into the base steel sheet becomes insufficient. Therefore, the Zr content at the boundary with the base steel sheet is set to 50 mass% or more, and the Zr content on the plating layer surface is 20 mass% lower than that of 30 mass%.
It is preferably ss% or less.

The vapor-deposited Al alloy-plated steel sheet of the present invention can be manufactured as follows. First, one method is a method using a binary simultaneous vapor deposition method. That is, when the Zr evaporation source is arranged in front of the steel plate traveling direction in the vacuum chamber and the Al evaporation source is arranged in the rear direction in order to evaporate Zr and Al from each evaporation source, Zr vapor and Al
Allow steam to overlap at the height of the steel plate surface. In this case, the metal vapor flow density distribution generated from each evaporation source is highest directly above the evaporation source and gradually decreases as it moves away from the evaporation source in the horizontal direction. It becomes a mixed vapor of Al-Zr in which the Al content gradually increases. If a steel sheet whose surface is activated by pretreatment in the presence of such mixed steam is introduced into the vacuum chamber, an Al-Zr alloy in which the Al content gradually increases from the base steel strip side to the surface is obtained. Plated. The thickness of the plating layer and the Al-Zr concentration gradient are the magnitude and ratio of the input power to each evaporation source, the distance between the Zr evaporation source and the Al evaporation source, the distance between the evaporation source and the steel plate, the degree of vacuum, and the vapor deposition time. , The position and area of the mask on the steel plate surface are adjusted.

Another method is to first form a Zr plating layer by a vapor deposition method and then, when depositing Al, utilize the steel plate temperature and the heat of condensation of Al vapor in the Zr plating layer. This is a method in which Al is thermally diffused into Al to form a gradient in the Zr content.
The deposition of Zr and Al by these methods may be any method such as electron beam, arc discharge and sputtering.

[0204]

Example A vapor-deposited Al alloy-plated steel sheet of the present invention was produced on a steel sheet by the following vapor deposition method. (1) Vapor deposition method 1 A water-cooled copper hearth containing Zr was placed on the inlet side of the vacuum chamber, and on the outlet side.
Ceramic crucibles containing Al are arranged,
Al-kild cold rolling with alkaline electrolytic degreasing in a vacuum chamber of a binary vacuum evaporation system in which the distance between the water-cooled copper hearth and the ceramic crucible was adjusted so that Zr vapor and Al vapor were mixed at the position where the steel strip was threaded. After setting a steel strip (plate thickness 0.6 mm) and evacuating to a vacuum degree of 1 × 10 ^-2 to 1 × 10 ^-3 Pa, an ion beam was used.
Beam-shaped Ar ions were made to collide with the steel strip from the aluminum generator at an accelerating voltage of 5 kV to remove impurities such as oxides on the surface of the steel strip and activate the surface. Next, while moving the steel strip at the same degree of vacuum, Zr and Al were dissolved and evaporated by an electron beam to deposit an Al alloy plating layer.

(2) Vapor Deposition Method 2 A water-cooled copper hearth containing Zr and a ceramic crucible containing Al are arranged in a vacuum chamber, and the vacuum vapor deposition is arranged so that Zr vapor deposition and Al vapor deposition can be switched. Set the Al electrolytic degreased Al-killed cold-rolled steel sheet (sheet thickness 0.6 mm) in the vacuum chamber of the equipment and activate the steel sheet surface by the same method as in the case of vapor deposition method 1 and simultaneously raise the steel sheet temperature to 400 ° C. After heating, Zr vapor deposition was performed by electron beam vapor deposition. Next, e-mail
Al is vapor-deposited by vapor deposition, and the condensation heat of the vapor-deposited Al raises the steel plate temperature to 600 ° C. to diffuse Al into the Zr plating layer.
-Zr alloyed.

Al alloy-plated steel sheet and Al or Zr single-layer vapor-deposited steel sheet produced by the above vapor deposition method, vapor-deposited Al-Zr alloy-plated steel sheet of uniform composition with no content gradient in the depth direction of the plating layer, Si9mass% The following tests were carried out for the contained hot dip Al plated steel sheet.

(1) Adhesion test With the plated surface facing outward, the plate was adhered and bent by 180 degrees, and a sero tape was attached to the bent portion and peeled off, and the presence or absence of peeling of the plating layer was indicated according to the following criteria. ○ No peeling of plating layer × Peeling of plating layer

(2) Corrosion resistance test before processing A salt spray test (according to JIS Z 2371) was performed, and the time until the occurrence of red rust was evaluated according to the following criteria.
The test piece used had a size of 70 × 150 mm, and the end face and the back face were sealed. ○ Red rust does not occur within 500 hours △ Red rust occurs within 200 to 500 hours × Red rust occurs within less than 200 hours

(3) Corrosion resistance test after processing With the plated surface facing outward, cylindrical drawing with a diameter of 41.5 mm and a depth of 25 mm was performed, and a salt spray test was conducted under the same conditions as the corrosion resistance test before processing, with the same criteria. The state of occurrence of red rust was evaluated by.

(4) Pinhole test Wet test (according to JIS K 2246) was performed, and the time until the ratio of the red rust occurrence area to the total test area was 5% was classified into the following three levels and evaluated. . A test piece having a size of 70 × 150 mm was used, and the end face and the back face were sealed as in the corrosion resistance test. ○ 5% red rust occurrence time 1000 hours or more △ 5% red rust occurrence time 500 to less than 1000 hours × 5% red rust occurrence time less than 500 hours

(5) Heat resistance test After heating in air at 800 ° C. for 8 hours and then cooling in air for 16 hours, one cycle of heating-cooling test was performed three times, and oxidation was performed before and after the cycle test. The weight gain was measured and evaluated according to the following criteria. ○ oxidized amount 50 g / m ² or less △ oxidation weight gain 50 g / m ² greater, 100 g / m ² or less × oxidation weight gain 100 g / m ² than in Table 1, summarizes the results of these tests in Table 2.

[028]

[Table 1]

[029]

[Table 2]

[030]

As described above, the vapor-deposited Al alloy-plated steel sheet of the present invention is superior to the conventional Al-plated steel sheet in corrosion resistance, heat resistance and workability.

[Brief description of drawings]

FIG. 1 shows an example of a cross-sectional element content distribution of a vapor deposited Al alloy plated steel sheet according to the present invention.

Claims (2)

[Claims] 1. A vapor-deposited Al alloy plated steel sheet, wherein a Zr-containing Al alloy plated layer having a Zr content gradually increasing in the depth direction of the plated layer is formed on the surface of the steel sheet. 2. The Zr content of the Zr-containing Al alloy plating layer is 30 mass% or less on the surface side and 50 on the boundary side with the base steel sheet.
The vapor-deposited Al alloy-plated steel sheet according to claim 1, wherein the mass% or more.