JPH05222550A - Multiple layer alloy plated steel sheet and its manufacture - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and heat resistance of a plated steel sheet without using a hot dip Al-Si plating bath contg. Cr by forming a multiple layer alloy plated layer in which a secondary layer contains a relatively large amount of Cr. CONSTITUTION:The space between an Al-Si-Fe series primary layer L1 formed on base steel S by hot dip Al-Si allay plating and an Al-Si series third layer L3 is provided with an Al-CrSi-Fe series secondary layer L2 excellent in corrosion resistance by which the objective multiple layer alloy plated steel sheet excellent in corrosion resistance and heat resistance can be obtd. The Cr concn. of the secondary layer L2 is preferably regulated to >=0.7wt.%. Cr in the secondary layer L2 is fed from a Cr coated layer formed on a plating original sheet before immersion in a hot dip plating bath by electroplating, vacuum evaporation or the like. The corrosion resistance and heat resistance of the plated steel sheet are remarkably improved by the secondary layer L2 and third layer L3 and the corrosion resistance equal to that of stainless steel even in the case inexpensive common steel is used as a plating original sheet can be obtd. at 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 multi-layer alloy 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 having sufficient durability even in a harsh atmosphere, 0.01 to 2% by weight of C is used.
Al-Si alloy plated steel sheet containing r
It is introduced in Japanese Patent No. 8754. As a plating original plate on which Al-Si alloy plating is applied, not only ordinary steel but also
Cr-containing low alloy steels, stainless steels, etc., which have excellent corrosion resistance by themselves, are also being used.

The molten Al-Si alloy-plated steel sheet is annealed in a pretreatment zone under a reducing atmosphere to reduce and remove an oxide film on the surface of the steel sheet and activate the surface of the steel sheet. It is usually manufactured by using an in-line reduction annealing type continuous hot dip plating equipment for plating. However, like low alloy steel and stainless steel, C
When a steel sheet containing an easily oxidizable element such as r, Si, or Al is used as a plating original sheet, it is difficult to remove the oxide film on the surface of the steel sheet with a reducing gas.

Therefore, in order to improve the adhesion of the Al-Si alloy plating layer to the base steel, the steel sheet is previously made of Fe or F.
After electroplating e-B, it is melted by passing through a normal in-line reduction annealing type continuous hot dip coating equipment.
An l-Si alloy plating layer is formed. In addition, JP-A-6
In JP-A-3-176482, Co, Ni, Mn, M
It has been proposed to improve the adhesion between the base steel and the Al plating layer by plating with o, Cu, Cr, W, etc. and further forming an Fe plating layer.

[0006]

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. For example, in the case where stainless steel containing 16% by weight or more of Cr is used as a plating base plate, the product price is lower than that when ordinary steel such as Al killed steel or low carbon steel plate is used as a plating base plate. Is more than doubled.

Therefore, as seen in Japanese Patent Publication No. 2-88754, the molten Al-Si containing Cr is added.
It is conceivable to produce an Al-Si alloy plated steel sheet in which Cr is added to the plating layer by using the plating bath. 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 of using the Al-Si plating bath containing Cr cannot significantly improve the corrosion resistance of the obtained Al-Si alloy-plated steel sheet.

On the other hand, a steel sheet coated with Cr, which is easily oxidized and easily forms an oxide film on the surface, cannot be hot-dipped by the usual in-line reduction annealing method for hot-diping ordinary steel. That is, the Cr formed on the surface
The oxide film is strong, and the reduction removal reaction of the oxide film does not proceed under normal conditions in which the surface is heated in a reducing gas for activation. For example, N ₂ -75% H at dew point -60 ° C
Even if heated at 700 ° C for 5 minutes in ₂ atmosphere, the oxide film on the surface is not completely removed. As a result, defects such as non-plating occur when hot dip plating is performed on the steel sheet after reduction annealing.

High-temperature heating is necessary for rapid reduction and removal of the oxide film. For example, if an attempt is made to reduce and remove an oxide film in a short time within 10 seconds using the same reducing atmosphere, the oxide film is removed only at an ambient temperature exceeding 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. In addition, some steel types cannot be heated at high temperature because mechanical properties such as elongation and strength deteriorate.

In this regard, 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.

The present invention has been devised to solve such a problem. By removing Cr oxide by etching using plasma or an ion beam,
An object of the present invention is to provide an inexpensive multilayer alloy-plated steel sheet which is excellent in corrosion resistance while improving the adhesion of the 1-Si alloy plating layer.

[0013]

The multi-layer alloy-plated steel sheet of the present invention achieves the object thereof by applying Al-on the base steel sheet.
It is characterized in that a first layer of a Si—Fe alloy, a second layer of an Al—Cr—Si—Fe alloy, and a third layer of an Al—Si alloy are sequentially laminated.

Further, in the multilayer alloy-plated steel sheet of the present invention, after the steel sheet is Cr-plated, the surface of the Cr-plated layer is activated by plasma etching or ion beam etching in a vacuum atmosphere, and then immersed in a molten Al-Si plating bath. It is manufactured by The Cr plating layer can be formed by either electroplating or vacuum deposition.

When Cr plating is performed in a vacuum atmosphere, it is also possible to perform plasma etching or ion beam etching in the same vacuum atmosphere. Alternatively, it is also possible to store the plating original plate on which the Cr plating layer is formed in advance by electroplating or vacuum deposition in the air atmosphere and perform the molten Al-Si plating according to the production plan.

The present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, the multilayer alloy-plated steel sheet of the present invention has a structure in which a first layer L ₁ , a second layer L _2, and a third layer L ₃ are laminated on a base steel S. 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 order to reduce the product cost. The first layer L ₁ is a Al-Si-Fe alloy layer, the Al-Cr-Si-Fe second layer L ₂ of the alloy layer is formed thereon. Then, on the outermost layer, Al-Si
A third layer L ₃ of the system is formed.

The Cr concentration in the second layer L ₂ is preferably 0.7% by weight or more in order to secure the corrosion resistance of the multilayer alloy-plated steel sheet. The second layer L ₂ is formed by immersing the steel plate after being coated with Cr in a molten Al-Si plating bath. At this time, the Cr concentration of the second layer L ₂ can be adjusted according to the amount of Cr deposited on the steel plate. Target Al—Cr—Si—Fe-based second layer L ₂
In order to form Cr, the thickness of the Cr coating layer is preferably 1.5 μm or less.

The composition and temperature of the molten Al-Si plating bath are not particularly limited, but since they extend the life of the plating bath pot and impart a good surface appearance to the multi-layer alloy plated steel sheet, It is preferable to maintain the concentration in the range of 1 to 12% by weight and the bath temperature at a temperature of 680 ° C. or lower. In particular, when forming a thin Al-Si-Fe alloy layer, the plating bath has a Si concentration of 6 to 12% by weight and a bath temperature of 68.
It is desirable to set it to 0 ° C. or lower. In the molten Al-Si plating bath, the constituent elements dissolved from the heat resistant steel in the plating bath pot are present as impurities. 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 vapor deposition, and a high-purity Cr coating layer can be formed at low cost with high productivity. After the Cr coating layer is formed, 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. An apparatus for continuously hot-plating a steel plate whose surface has been activated by plasma etching or ion beam etching is disclosed in, for example, Japanese Patent Laid-Open No. Hei 3
-86170.

Plasma etching activated hot dip plating equipment, ion beam etching activated hot dip plating equipment, etc.
The inside is kept in a vacuum atmosphere. Therefore, by utilizing the vacuum and depositing Cr prior to the plasma etching activation treatment or the ion beam etching activation treatment, the Al—Cr—Si alloy plated steel sheet can be manufactured at a lower cost. In this case, if the surface of the steel sheet is cleaned by pickling or the like and heated to 600 ° C. or higher in vacuum,
Adhesion of evaporated Cr is improved.

[0021]

[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
The Cr-Si-Fe layer and Al-Si layer of the third layer L _3, the corrosion of the first layer L ₁ of Al-Si-Fe layer and the substrate steel S is suppressed. Compared with this, ordinary molten Al-S
The i alloy plated steel sheet, since the second layer L ₂ is not present, the anticorrosion against the substrate steel depending on the Al-Si layer of the surface layer portion, the corrosion resistance is insufficient.

Further, molten Al is applied to the steel sheet after being coated with Cr.
Since the -Si plating is performed, the Cr concentration in the second layer L ₂ does not decrease due to the limitation of the amount of Cr dissolved in the plating bath. In other words, depending on the Cr deposition amount, the Cr of the second layer L ₂
The concentration can be increased, and the corrosion resistance and heat resistance can be greatly improved. Moreover, the adhesion of each layer to the base steel is good, and a plated steel sheet excellent in workability without flaking, powdering, etc. can be obtained.

The obtained multi-layer alloy-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 original sheet. Further, although the raw material cost becomes high, when a low-alloy steel, stainless steel, or the like is used as the plated raw plate, the corrosion resistance and heat resistance are further improved, and the corrosion resistance and heat resistance superior to those of high Ni high Cr stainless steel can be 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, when Cr vapor deposition is performed in the same vacuum atmosphere in a line where hot-dip plating is performed after activation by plasma etching, ion beam etching, etc. in a vacuum, it is possible to continuously produce a multilayer alloy-plated steel sheet. Can be further reduced.

[0025]

[Example] 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 dipping apparatus shown in FIGS. 2 and 3.

FIG. 2 shows a hot-dip plating facility in which a plasma etching apparatus is incorporated. The original plating plate 10 is fed from a pay-off reel 11 and is deflected by a deflector roll 1.
Guided by 2 and 13, it is sent to the vacuum chamber 20. A vacuum sealing device 21 is provided on the inlet side of the vacuum tank 20, and the high-frequency heating device 3 is provided along the running direction of the plating original plate.
0, Cr vapor deposition apparatus 40 and plasma etching apparatus 50
Are arranged.

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.

The vacuum chamber 20 is evacuated by vacuum pumps 22 and 23. The original plating plate 1 introduced into the vacuum chamber 20
0 is heated to a predetermined temperature by the high-frequency heating device 30, coated with Cr by the Cr vapor deposition device 40, and then the surface is activated by the plasma etching 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.

FIG. 3 shows a hot-dip plating equipment incorporating an ion beam etching apparatus. Instead of the plasma etching apparatus 50 shown in FIG. 2, a pair of ions are provided so as to face both sides of the original plating plate 10 running in the vacuum chamber 20. Beam etching devices 70, 70 are arranged. Ion beam 71 emitted from the ion beam etching apparatus 70, 70,
71 collides with the surface of the original plating plate 10 and etches away the oxide film, the surface-altered layer, etc. on the surface of the Cr coating layer formed by the Cr vapor deposition device 40.

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 reaches a predetermined vacuum degree, the high frequency heating device 30 and the plasma etching device 50 or the ion beam etching device 7
0 was activated. By introducing the raw material gas at this time, the vacuum degree of the vacuum chamber 20 was lowered to 0.05 to 5 Pa.

The original plating plate 10 is formed by the Cr vapor deposition device 40.
When the Cr coating is applied to the substrate, the high-frequency heating device 30 heats the plating base plate 10 prior to vapor deposition, so that a Cr vapor deposition layer having excellent adhesion was formed. Plasma etching is performed under the conditions shown in Table 1, and ion beam etching is performed in Table 2.
It carried out on the conditions shown in.

[0033]

[Table 1]

[0034]

[Table 2]

[Table 3]
The molten Al-Si alloy plating was performed under the conditions shown in.

[Table 3]

In the obtained multi-layer alloy-plated steel sheet, the third layer L ₃ was formed as a mixed layer of a primary crystal Al—Si alloy having a low Si content and a eutectic Al—Si alloy. Also, the third
Below the layer L _3, a second layer L of Al-Cr-Si-Fe system is formed.
₂ and the first layer L ₁ of Al-Si-Fe system was formed.

The Cr concentration of the second layer L ₂ was changed by adjusting the thickness of the Cr coating layer provided by vapor deposition. Then, the relationship between the Cr concentration and the corrosion resistance was investigated.
The survey results are shown in FIG. The corrosion resistance was evaluated by performing a salt spray test specified in JIS and measuring the time until 5% of area rust was generated on the surface of the test piece. Figure 4
As is clear from the above, the thickness of the deposited Cr film is 0.03 μm.
When the above is set, the Cr concentration of the second layer L ₂ is 0.7% by weight.
From the above, it can be seen that the corrosion resistance is significantly improved.

On the other hand, 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. Was there. Also, in a comparative example in which molten Al—Si alloy plating was performed after vapor deposition Cr coating,
When the thickness of the deposited Cr film was less than 0.03 μm, the Cr concentration in the second layer L ₂ was insufficient, and sufficient corrosion resistance could not be obtained.

The fact that the excellent corrosion resistance is ensured by ensuring the Cr concentration of the second layer L ₂ was the same when the test piece coated with Cr by ion beam etching was activated. Further, after the Cr coating is formed on the surface of the plating original plate by electroplating in advance, the Cr coating is introduced into the vacuum tank 20 of the hot dip plating equipment shown in FIGS. 2 and 3 and subjected to etching and hot dipping Al-Si alloy plating. Similarly, as long as the Cr concentration of the second layer L ₂ was 0.7% by weight or more, the multilayer alloy-plated steel sheet exhibited significantly better corrosion resistance than the conventional Al-Si alloy-plated steel sheet.

[0040]

As described above, in the present invention, the Al-Si-Fe-based intermediate layer is used as the first layer L ₁ on the base steel, and the Al-Cr- which has excellent corrosion resistance is formed on the intermediate layer. Si
Forming a second layer L ₂ and Al-Si-based third layer L ₃ of -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 multilayer alloy-plated steel sheet of the present invention.

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

[Fig. 3] Hot dip plating facility with ion beam etching

FIG. 4 is a graph showing the corrosion resistance of the multilayer alloy-plated steel sheets obtained in the examples of the present invention in comparison with reference examples and comparative examples.

[Explanation of reference numerals] 10 plating original plate 20 vacuum tank 30
High-frequency heating device 40 Cr vapor deposition device 50 Plasma etching device 60 Hot dip plating device 70 Ion beam etching device

Claims (4)

[Claims] 1. A first layer of an Al--Si--Fe based alloy, a second layer of an Al--Cr--Si--Fe based alloy and A on a base steel.
A multi-layer alloy-plated steel sheet, wherein a third layer of an l-Si alloy is sequentially laminated. 2. 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.
A method for producing a multi-layer alloy-plated steel sheet, which comprises immersing in an i plating bath. 3. A method for producing a multilayer alloy-plated steel sheet, wherein the Cr plating according to claim 2 is performed in a vacuum atmosphere, and plasma etching or ion beam etching is performed in the same vacuum atmosphere. 4. The method for producing a multi-layer alloy plated steel sheet according to claim 2, wherein the Cr plating layer is formed by electroplating or vacuum deposition.