JPH06228725A - Hot-dip al-si-cr base plated steel sheet and its production - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and heat resistance of a plated steel sheet by forming a multilayer alloy plating layers where relatively large amounts of Cr are contained in a second layer. CONSTITUTION:A second layer L2 of Al-Cr-Si-Fe base, excellent in corrosion resistance, is provided between a first layer L1 of Al-Si-Fe-Cr type, formed on a substrate steel S by means of hot-dip Al-Si alloy coating, and a third layer L3 of Al-Si-Cr type, by which a hot-dip Al-Si-Cr base plated steel sheet excellent in corrosion resistance and heat resistance is obtained. The Cr in the second layer L2 is supplied from a Cr coating layer formed by means of electroplating, vacuum vapor deposition, etc., on the starting sheet for plating before immersion in hot-dipping bath. By this method, the corrosion resistance and heat resistance of the plated steel sheet can be remarkably improved by means of the second layer L2 and the third layer L3, and, even if an inexpensive plain steel is used as a starting sheet for plating, corrosion resistance equal to that of stainless steel can be obtained at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inexpensive hot-dip Al-Si-Cr based plated steel sheet having excellent corrosion resistance and a method for producing the same.

[0002]

2. Description of the Related Art Al-Si alloy plated steel sheets are
It is manufactured by a hot dip plating method in which a steel sheet is immersed in a hot dip bath containing Si and Si. The Al-Si alloy plating layer formed on the surface of the steel sheet is excellent in corrosion resistance, heat resistance, etc., and has a beautiful surface appearance, so that it is used in a wide range of fields as automobile exhaust system materials, building materials, etc. There is. In order to further improve the corrosion resistance and heat resistance of the Al-Si alloy plated steel sheet and to obtain a structural material that exhibits sufficient durability even in a harsh atmosphere, an Al-Si alloy plating containing 0.01 to 2% by weight of Cr Steel plate is Japanese Patent Laid-Open No. 2-887
No. 54 publication. As a plating original plate on which Al-Si alloy plating is applied, not only ordinary steel but also Cr-containing low alloy steel, stainless steel, and the like, which have excellent corrosion resistance by themselves, have come to be used. In addition, Japanese public Sho6
Japanese Patent Laid-Open No. 3-44825 introduces that an Al-plated steel sheet excellent in corrosion resistance can be obtained by plating Ni, Cu, Co, Cr or the like and then performing hot-dip Al plating by a gas cleaning method.

The hot dip Al-Si alloy plated steel sheet is annealed in the pretreatment zone in a reducing atmosphere to reduce and remove the oxide film on the steel sheet surface and activate the steel sheet surface by gas cleaning. After that, it is usually manufactured using an in-line reduction annealing type continuous hot dip coating equipment for hot dip plating. However, when a steel sheet containing an easily oxidizable element such as Cr, Si, or Al or a steel sheet coated with an easily oxidizable element such as low alloy steel or stainless steel is used as a plating original sheet, the surface of the steel sheet is reduced by a reducing gas. It is difficult to remove a certain oxide film. Therefore, in order to improve the adhesion of the Al-Si alloy plating layer to the base steel, after electroplating Fe or Fe-B on the steel sheet in advance,
A hot-dip Al-Si alloy plating layer is formed by passing through a continuous hot-dip galvanizing equipment of a normal in-line reduction annealing system. Further, in Japanese Patent Laid-Open No. 63-176482, the adhesion between the base steel and the Al plating layer is obtained by plating Co, Ni, Mn, Mo, Cu, Cr, W, etc. and further forming an Fe plating layer. Is proposed to be improved.

[0004]

When low alloy steel or stainless steel is used as a plating base plate, the corrosion resistance of the Al-Si alloy plated steel plate is improved. However, since the raw material cost and the manufacturing cost of the plated original plate are increased, the product cost of the entire Al-Si alloy plated steel sheet is increased. Therefore, use of steel containing no Cr or low grade stainless steel having a low Cr content is unavoidable, and as a result, the corrosion resistance of the base steel cannot be expected, and a significant improvement in corrosion resistance cannot be expected. Therefore, as disclosed in Japanese Patent Publication No. 2-88754, the molten Al-Si plating bath containing Cr is used to manufacture an Al-Si alloy-plated steel sheet with Cr added to the plating layer. It is possible. However, when Cr is added to the plating bath, the melting point of the Al-Si alloy forming the plating bath rises. As a result, it is necessary to keep the plating bath at a high temperature, the pot of the plating bath is severely eroded by the molten Al-Si alloy, and the life of the pot is significantly reduced.

At this point, the amount of Cr that can be added is restricted. For example, a bath temperature of 68 used in normal production
In an Al-Si plating bath (Si concentration <18% by weight) at 0 ° C or lower, the upper limit of the Cr addition amount is 0.5% by weight. As a result, the method using the Al-Si plating bath containing Cr cannot significantly improve the corrosion resistance of the obtained Al-Si alloy-plated steel sheet. The in-line gas reduction method adopting the ordinary gas cleaning method is designed for hot dip plating of ordinary steel, and is a steel sheet coated with Cr that is easily oxidized and easily forms an oxide film on the surface. Is not suitable for use as a plating original plate. The Cr oxide film formed on the surface is strong, and the surface is covered with H ₂ , H
Under ordinary conditions of heating to a temperature of 500 to 850 ° C. in a reducing gas atmosphere such as ₂ + N _2, the reduction removal reaction of the oxide film does not proceed thermodynamically. For example, even if the Cr-coated steel sheet is heated at 700 ° C. for 5 minutes in an atmosphere of H ₂ + 25% N _{2 having} a dew point of −60 ° C., the oxide film on the surface is not removed.

As a result, even if the steel sheet after reduction annealing is hot-dipped, the reaction between the base steel and the molten Al-Si alloy plating bath is hindered by the oxide film on the surface, and the entire surface of the steel sheet is not plated. And other defects occur. According to the experiments conducted by the present inventors, when the Cr-coated steel sheet was subjected to hot-dip Al—Si alloy plating in a hot-dip coating system of a continuous in-line reduction annealing system, 60% or more of the area ratio was unplated.
A plated steel sheet having unplated distribution cannot be used as a practical material. Even in the part where the plating is adhered, the reaction between the base steel and the plating layer is only partial, and most of the plating layer is simply put on the Cr-coated steel plate by physical force. Not too much. Therefore, the formed plating layer has extremely poor adhesion and is easily peeled off from the surface of the steel sheet by light processing. Therefore, even the portion where the plating layer is attached cannot withstand actual use.

In Japanese Patent Publication No. 63-44825, Si is disclosed.
Is used, and the temperature of the normal Al-Si alloy plating bath is 620-67.
The temperature of the plating bath is kept at 700 ° C higher than 0 ° C. Limiting the Si content and raising the temperature of the plating bath increase the reactivity of the plating bath, and thus effectively work to reduce the area ratio of non-plating. However, even in this case, the occurrence of non-plating cannot be completely avoided. When observing the cross section of the plated adhesion portion of the plated steel sheet obtained by this method, it is considered that a reaction occurs between the plated layer and the Cr-coated steel sheet at the portion where the oxide film of Cr is broken. However, since the reactivity of the Al plating bath containing no Si is too high, the brittle alloy layer grows thick in the reaction portion. Therefore, although the reaction portion is increased, the adhesion of the plating layer is not improved. On the other hand, Ni, Co or Cu
When a steel sheet coated with Cr is used as a plating original plate, the oxide film is removed from the surface of the steel sheet by the gas reduction method.
Problems such as coatings due to the surface oxide film do not occur. The effect of the type of coating layer is as follows.
It can be seen from the data listed in the examples of Japanese Patent No. 4825.

In order to remove the Cr oxide film by the gas reduction method, high temperature heating is thermodynamically required. For example, when an oxide film is to be reduced and removed in an N ₂ -75% H ₂ atmosphere with a dew point of −60 ° C., the oxide film is removed only at an ambient temperature of over 1000 ° C. However, due to the high temperature heating, not only a large amount of heat energy is consumed, but also the reduction annealing equipment itself is required to be made of an expensive material having excellent heat resistance. Also, since high temperature heating deteriorates mechanical properties such as elongation and strength, most steel types to which high temperature heating cannot be applied. Therefore, high temperature heating is C
It cannot be practically used as a method for removing the oxide film of r.

In this respect, the above-mentioned Japanese Patent Laid-Open No. 63-17648.
Pre-plating of Fe, Fe alloys, etc., as introduced in Japanese Patent Publication No. 2 suppresses the adverse effect caused by the oxide film of Cr. However, since an extra step is required for pre-plating and the cost of electroplating Fe, Fe alloy, etc. is high, the total manufacturing cost is increased. Also, pre-plated F
An alloy layer having a high Fe concentration is generated due to the e, Fe alloy or the like, and the improvement in corrosion resistance is suppressed. The present invention has been devised to solve such a problem, and by introducing a Cr-coated steel sheet without an oxide film into a molten Al-Si alloy plating bath, Al-Si-Cr system plating is performed. Inexpensive molten A that improves the adhesion of layers and has excellent corrosion resistance
An object is to provide an l-Si-Cr-based plated steel sheet.

[0010]

Means for Solving the Problems Molten Al-Si of the present invention
In order to achieve the object, the --Cr-based plated steel sheet has a first layer of Al--Si--Fe--Cr based alloy, Al, on the base steel.
-Cr-Si-Fe alloy second layer and Al-Si-C
The third layer of the r-based alloy is sequentially laminated. As the base steel, it is possible to use any of ordinary steel or alloy steel not containing Cr, or ordinary steel, alloy steel or stainless steel containing Cr. The hot-dip Al-Si-Cr-based plated steel sheet of the present invention is produced by immersing a Cr-coated steel sheet in a hot-dip Al-Si alloy plating bath. The Cr coating is formed by electroplating, vacuum deposition or the like. The molten Al-Si alloy plating bath may be either a Cr-free bath or a Cr-added bath. When using the Al-Si alloy plating bath to which Cr is added, the content of Cr contained in the first layer and the second layer increases. When Cr is added to the plating bath, the addition amount is not particularly limited, but practically the limit is 0.5% by weight.

When Cr coating and hot-dip Al-Si alloy plating are performed in separate manufacturing apparatuses, Cr coating is performed in the first manufacturing apparatus, and then plasma etching or ion beam etching is performed in the second manufacturing apparatus in a vacuum atmosphere. Then, the Cr coating layer is activated by removing the oxide film on the surface. Then, Cr in the molten Al-Si alloy plating bath
Immerse the coated steel sheet. Since the oxide film is removed from the surface of the immersed Cr-coated steel sheet by plasma etching or ion beam etching, it is hot-dipped with high reactivity with the hot-dip Al-Si alloy plating bath. In addition, the first manufacturing apparatus can be arranged continuously to the second manufacturing apparatus. When manufacturing with a single manufacturing apparatus, after vapor-depositing Cr on the steel plate surface in a vacuum atmosphere,
The Cr-coated steel sheet is immersed in a molten Al-Si alloy plating bath in the same vacuum atmosphere. In this case, since the Cr vapor deposition and the immersion in the hot dip plating bath are performed in the same vacuum atmosphere, the Cr coated steel sheet is immersed in the plating bath without oxidizing the surface of the Cr coating layer. Therefore, the Cr-coated steel sheet is
-Hot dip plating is performed in a state where the surface reactivity to the Si alloy plating bath is good.

The present invention will be specifically described below with reference to the drawings. As shown in FIG. 1, the hot-dip Al—Si—Cr-based plated steel sheet of the present invention has a first layer L on a base steel S.
_It has a structure in which _1st , 2nd layer L ₂ and 3rd layer L ₃ are laminated. The material of the plating base plate to be the base steel S is not particularly limited, but it is preferable to use ordinary steel in consideration of the product cost. The first layer L ₁ is made of Al−
It is a Si-Fe-Cr alloy layer. Since the first layer L ₁ has a high Al concentration and contains Cr, it has high corrosion resistance. The Cr concentration is 0.7% by weight or less when a steel plate such as a plain steel containing no Cr is used as a plating original plate. Further, when an alloy steel, a stainless steel, or the like containing Cr is used as the plating original plate, the Cr concentration in the first layer L ₁ becomes high due to the Cr diffusion from the base steel S. The higher the concentration of Cr contained in the first layer L ₁ , the higher the corrosion resistance.
However, even when high Cr steel containing 40% by weight or more of Cr is used as a plating original plate, the Cr concentration of the first layer L ₁ is 5% by weight or less.

The second layer L ₂ is an Al—Cr—Si—Fe based alloy layer, in which Cr is preferentially concentrated. Since the Al concentration is high in addition to the Cr concentration, it is the layer having the best corrosion resistance among the three layers L _{1 to} L ₃ . The Cr concentration of the second layer L ₂ can be adjusted by the amount of Cr deposited on the original plating plate. For example, in the case where the Cr coating layer is provided with an adhesion amount of 0.1 μm, the Cr concentration of the second layer L ₂ is about 3% by weight. Therefore, for applications requiring high corrosion resistance, the Cr deposition amount is set high. Third layer L ₃
Is Al-Si-C produced by solidification of the plating bath metal.
It is an r layer and has a composition almost the same as the composition of the plating bath except that it contains Cr. Cr is also diffused in the third layer L ₃ and contains a small amount of Cr of 0.1 wt% or less. The third layer L ₃ contains Cr, although in a small amount, so that the corrosion resistance is improved.

The composition and temperature of the molten Al-Si plating bath are not particularly limited, but the life of the plating bath pot is extended and a good surface appearance is obtained with the molten Al-Si-Cr.
Since it is applied to the system-based plated steel sheet, the Si concentration should be 1 to 1
It is preferable to maintain the bath temperature at 680 ° C. or lower in the range of 3% by weight. In particular, when forming a thin Al-Si-Fe alloy layer, the plating bath should have a Si concentration of 6 to 12% by weight.
And it is desirable to keep the bath temperature at 680 ° C. or lower. Molten Al
In the -Si plating bath, the constituent element dissolved from the heat-resistant steel in the plating bath pot is present as an impurity. Among the impurities, Fe is the element containing the largest amount, but the Fe concentration is usually regulated to 3% by weight or less.

The Cr coating can be performed by either electroplating or vacuum deposition, and a high-purity Cr coating layer can be formed at low cost with high productivity. When the Cr coating layer is formed by a separate manufacturing apparatus, the surface of the steel sheet is activated by plasma etching or ion beam etching, and the steel sheet is immersed in a molten Al-Si plating bath to form the plating layer. Equipment for continuous hot-dip plating of steel sheet whose surface has been activated by plasma etching or ion beam etching
For example, it is introduced in JP-A-3-86170. The inside of the plasma etching activated hot-dip galvanizing apparatus, the ion beam etching activated hot-dip galvanizing apparatus and the like are kept in a vacuum atmosphere. Therefore, using the vacuum, C
When vapor-depositing r, an Al-Si-Cr alloy-plated steel sheet can be manufactured more inexpensively.

[0016]

[Operation] Since the second layer L ₂ contains a large amount of Cr, it has excellent corrosion resistance. Al− of this second layer L ₂
Al-S of the first layer L ₁ including the Cr-Si-Fe layer
the i-Fe-Cr layer and Al-Si-Cr layer of the third layer L _3, the corrosion of the steel substrate S is suppressed. In comparison, in the conventional melt Al-Si alloy-plated steel sheet, the second layer L ₂ without, because corrosion resistance of the Al-Si-Fe layer corresponding to the first layer L ₁ is low, the surface layer portion of the corrosion protection for the substrate steel Al
-Depending on the Si layer, the corrosion resistance is insufficient. Al-Si
The corrosion resistance of the layer itself is also inferior to that of the Al-Si-Cr based plating layer according to the present invention. Since the hot-dip Al-Si plating is applied to the steel sheet after being coated with Cr, the Cr concentration in the second layer L ₂ does not decrease due to the limited amount of Cr dissolved in the plating bath. In other words, the Cr concentration in the second layer L ₂ can be increased by adjusting the Cr deposition amount,
Corrosion resistance and heat resistance can be greatly improved.

In both cases of plasma-etching or ion-beam etching a Cr-coated steel sheet and then performing hot-dip Al-Si alloy plating, or when carrying out Cr vapor deposition and hot-dip Al-Si alloy plating in the same vacuum, C
The steel sheet coated with r is immersed in a molten Al-Si alloy plating bath without any oxide film on the surface. Therefore, the reactivity between the surface of the steel sheet and the molten Al—Si alloy is high, and defects such as non-plating do not occur, and the first layer L ₁ to the third layer L
A plating layer formed uniformly up to ₃ is provided on the surface of the base steel S with good adhesion. Therefore, the obtained plated steel sheet has very excellent corrosion resistance.

The obtained hot-dip Al-Si-Cr-based plated steel sheet exhibits corrosion resistance comparable to that of a high-grade steel sheet such as stainless steel due to the above-mentioned layer structure even when an inexpensive ordinary steel is used as a plating base sheet. Also, although the raw material cost will increase,
When a low-alloy steel, stainless steel, or the like is used as the plating base plate, the corrosion resistance of the base steel S and the first layer L ₁ in addition to the second layer L ₂ is high, and therefore the corrosion resistance and heat resistance are further improved, and high Cr high Ni
Corrosion resistance and heat resistance superior to stainless steel are also obtained. The surface of the steel sheet coated with Cr by vacuum vapor deposition or electroplating is activated by plasma etching, ion beam etching or the like without the need for pre-plating Fe, Fe alloy or the like. By omitting the pre-plating, the manufacturing process is simplified and the manufacturing cost is reduced. Moreover,
In a line for hot-dip plating after activation by plasma etching, ion beam etching, etc. in vacuum,
When Cr vapor deposition is performed in the same vacuum atmosphere, molten Al-Si
It is possible to continuously produce a Cr-plated steel sheet with a single facility, and it is possible to further reduce the production cost.

[0019]

【Example】

Example 1: As a plating original plate, C: 0.02% by weight, S
i: 0.04% by weight, Mn: 0.19% by weight, P: 0.
011% by weight, S: 0.011% by weight, Al: 0.04
An Al-killed steel plate having a composition of 5% by weight and the balance of Fe and impurities and having a plate thickness of 0.5 mm and a plate width of 100 mm was used. After degreasing and pickling the original plating plate, hot dip Al-Si plating was performed using the hot dip coating apparatus shown in FIG. FIG. 2 shows a hot-dip plating facility incorporating a plasma etching apparatus. The original plating plate 10 is fed from a payoff reel 11, guided by deflector rolls 12 and 13, and fed into a vacuum tank 20. A vacuum sealing device 21 is provided on the inlet side of the vacuum chamber 20, and a high-frequency heating device 30, a plasma etching device 40, and a Cr vapor deposition device 50 are arranged along the running direction of the original plating plate.

The outlet side of the vacuum chamber 20 is a hot dip coating device 60.
It is vacuum-sealed by being immersed in the hot dip plating bath 61. At this time, the hot-dip galvanizing bath 61 is sucked up from the hot-dip galvanizing bath 62 to form the snout portion 63 according to the degree of vacuum in the vacuum tank 20, so that the hot-dip galvanizing bath 61 completes the vacuum seal. Vacuum tank 20
Is evacuated by the vacuum pumps 22 and 23. Vacuum tank 2
The plating base plate 10 introduced into the 0 is a high frequency heating device 3
After being heated to a predetermined temperature by 0, the surface is activated by the plasma etching device 40, and Cr coating is performed by the Cr vapor deposition device 50.

Next, the plating base plate 10 is provided with a snout portion 6
It is immersed in the plating bath 61 after passing through 3. Plate 10
Is transported through the sink rolls 64 and 65 in the plating bath 61, pulled up from the plating bath 61, and the coating amount of the plating is adjusted by the gas wiping device 66. The plated steel sheet is taken up by the take-up reel 17 via the deflector rolls 14 to 16. The vacuum chamber 20 was evacuated to 1 × 10 ⁻³ Pa by vacuum pumps 22 and 23. After the inside of the vacuum chamber 20 reached a predetermined degree of vacuum, the high frequency heating device 30 and the plasma etching device 40 were operated. By introducing the raw material gas at this time, the vacuum degree of the vacuum chamber 20 becomes 3
It decreased to Pa. The plasma etching conditions are shown in Table 1. Hot-dip Al-Si alloy plating was performed on the etched plated original plate under the conditions shown in Table 2.

[Table 1]

[Table 2]

In the obtained hot-dip Al-Si-Cr-based plated steel sheet, the third layer L ₃ was formed as a mixed layer of an alloy having a high Al content and an alloy having a high Si content precipitated by eutectic. . Further, under the third layer L ₃ , Al-Cr-Si-F is formed.
e-based second layer L ₂ and Al-Si-Fe-Cr-based first layer
Layer L ₁ had been formed. A cross section of the plated steel sheet obtained by hot-dip Al-Si alloy plating of the steel sheet on which the Cr coating layer had a thickness of 0.3 μm was subjected to line analysis by EPMA. The analysis result is shown in FIG. 3 (b), which was compared with the cross-sectional structure of FIG. 3 (a). By adjusting the thickness of the Cr coating layer provided by vapor deposition, the Cr concentration of the second layer L ₂ was changed. Then, the relationship between the Cr film thickness and the corrosion resistance was investigated. The survey results are shown in FIG. The corrosion resistance is JI
The salt spray test based on SZ2371 was performed, and the time required until 5% of area ratio of red rust was generated on the surface of the test piece was evaluated. As is clear from FIG. 4, when the thickness of the deposited Cr film is 0.02 μm or more, the corrosion resistance is improved. At this time, the Cr concentration of the second layer L ₂ becomes 0.7% by weight or more,
It can be seen that the corrosion resistance is greatly improved. In contrast,
In the reference example in which only Cr was vapor-deposited, even when the thickness of the vapor-deposited Cr coating was increased to 1.5 μm, the 5% red rust generation time was as short as 50 hours or less, and the corrosion resistance was poor.

Example 2: As a plating original plate, C: 0.0
1% by weight, Si: 0.48% by weight, Mn: 0.23% by weight, P: 0.026% by weight, S: 0.003% by weight, C
r: 11.96% by weight, SUS410L stainless steel having a composition of Fe excluding residual impurities, and C: 0.06% by weight, Si: 0.45% by weight, Mn: 0.28% by weight,
P: 0.025% by weight, S: 0.007% by weight, Cr:
SUS430 stainless steel having a composition of Fe with 16.44% by weight and balance of impurities was used. The plate thickness and the plate width were 0.5 mm and 100 mm, which were the same as in Example 1.

These stainless steels were subjected to hot-dip Al-Si plating under the same conditions as in Example 1 except for the plating equipment, plating conditions, plating bath composition, plasma etching conditions and the like. A test piece was cut out from the obtained hot dip plated stainless steel sheet and subjected to a salt spray test. When the effect of the Cr film thickness on the 5% red rust generation time in the salt spray test was investigated, there was a relationship shown in FIG. 5 between them.
From FIG. 5, it can be seen that even in the case where the stainless steel is used as the plating original plate, the corrosion resistance is significantly improved as compared with the case where no Cr vapor deposition (Cr film thickness is 0 μm) of the comparative example and the original plate of the reference example.

Example 3: The effect of a combination of Cr coating and hot dip coating processes on corrosion resistance was investigated. The same Al killed steel as in Example 1 was used as the plating base plate, and the plating bath composition, the amount of Al-Si alloy deposited, and the like were set to the same conditions as in Example 1. When the original plating plate is immersed in the molten Al-Si alloy plating bath after being preliminarily coated with Cr using other equipment, the Cr coating steel plate is passed through the apparatus shown in FIG. 2 and the Cr vapor deposition apparatus 50 is operated. After activating the plasma etching apparatus 40 without activating the surface of the Cr coating layer, the Cr coated steel plate was introduced into the molten Al-Si alloy plating bath. It can be seen from Table 3 that a plated steel sheet having excellent corrosion resistance can be obtained as in the case of Example 1 even when the molten Al-Si plating is applied to the steel sheet previously coated with Cr by the vapor deposition method or the electroplating method. .

[Table 3]

[0026]

As described above, according to the present invention, in the present invention, as Al-Si-Fe-Cr-based first layer L ₁ and intermediate layer on the base steel, excellent in corrosion resistance thereon Al- Cr
Forming a second layer L ₂ and Al-Si-Cr-based third layer L ₃ of the -Si-Fe system. Due to this multi-layered structure, even if an inexpensive plating base plate such as ordinary steel is used, it is possible to obtain a material that is excellent in corrosion resistance and heat resistance and is suitable as a material for automobile exhaust systems, building materials, etc. To be Further, when the vacuum deposition of Cr is also performed in a vacuum for performing plasma etching or ion beam etching and hot dip plating, the plating process and the plating equipment itself are simplified, and a low cost and highly corrosion resistant product is obtained.

[Brief description of drawings]

FIG. 1 shows a layer structure of a molten Al—Si—Cr type plated steel sheet according to the present invention.

[Fig. 2] Hot dip plating facility with plasma etching

FIG. 3 is a sectional structure (a) of the molten Al—Si—Cr-based plated steel sheet obtained in Example 1 and a line analysis by EPMA (b).

FIG. 4 is a graph showing the corrosion resistance of the molten Al—Si—Cr-based plated steel sheet obtained in Example 1 in comparison with Reference Example and Comparative Example.

FIG. 5 is a graph showing the corrosion resistance of the molten Al—Si—Cr system plated stainless steel sheet obtained in Example 2 in comparison with Reference Example and Comparative Example.

[Explanation of symbols]

10: Plate original plate 20: Vacuum tank 30: High frequency heating device 40: Plasma etching device 50: C
r Vapor deposition equipment 60: Hot dip coating equipment

[Procedure amendment]

[Submission date] July 26, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

Claims (8)

[Claims] 1. A first layer of an Al--Si--Fe--Cr alloy, a second layer of an Al--Cr--Si--Fe alloy, and a third layer of an Al--Si--Cr alloy are provided on a base steel. A hot-dip Al-Si-Cr-based plated steel sheet, which is sequentially laminated. 2. Molten Al, characterized in that the base steel according to claim 1 is ordinary steel or alloy steel containing no Cr.
-Si-Cr type plated steel sheet. 3. The hot dip Al—Si—Cr system plated steel sheet, wherein the base steel according to claim 2 is ordinary steel, alloy steel or stainless steel containing Cr. 4. A steel sheet is plated with Cr, the surface of the Cr plated layer is activated by plasma etching or ion beam etching in a vacuum atmosphere, and then molten Al—S is formed.
Molten Al- characterized by being immersed in an i alloy plating bath
Manufacturing method of Si-Cr type plated steel sheet. 5. After vapor-depositing Cr plating on the surface of a steel sheet in a vacuum atmosphere, the steel sheet is melted A in the same vacuum atmosphere.
A method for producing a molten Al-Si-Cr-based plated steel sheet, which comprises immersing in a 1-Si alloy plating bath. 6. A method for manufacturing a molten Al—Si—Cr based plated steel sheet, wherein the molten Al—Si alloy plating bath according to claim 4 or 5 contains Cr. 7. The method for producing a hot dip Al—Si—Cr-based plated steel sheet, wherein the steel sheet according to claim 4 or 5 is a normal steel or an alloy steel containing no Cr. 8. A method for producing a hot dip Al—Si—Cr based plated steel sheet, wherein the steel sheet according to claim 4 or 5 is a normal steel, an alloy steel or a stainless steel containing Cr.