JPH06240432A - Production of ti-containing hot dipped steel sheet - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and heat resistance of a plated steel sheet by forming a multilayer plating layer containing relatively large amounts of Ti in a second layer. CONSTITUTION:A course of stages, consisting of activation treatment by plasma etching or ion beam etching, vacuum deposition of Ti, and hot dip Al-Si alloy coating, is done in the same vacuum tank. On a substrate steel S, a second layer L2 of Al-Ti-Si-Fe type, excellent in corrosion resistance, is formed between a first layer L1 of Al-Si-Fe-Ti type and a third layer L3 of Al-Si-Ti type. It is preferable to regulate Ti concentration in the second layer L to >=0.5wt.%. Further, Ti in the second layer L2 is supplied from a Ti coating layer formed by means of vacuum deposition on a starting sheet for plating prior to immersion in a hot dipping bath. By this method, the corrosion resistance and heat resistance of the plated steel sheet can remarkably be improved by means of the second layer L2 and the third layer L3, and corrosion resistance equal to that of stainless steel can be obtained at a low cost even in the case where inexpensive plain steel is used as a starting sheet for plating.

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 hot dip plated steel sheet in which the corrosion resistance of a plated layer is improved by containing Ti.

[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.

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 using in-line reduction annealing continuous hot dip plating equipment. 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 base sheet, it is difficult to remove the oxide film on the surface of the steel sheet with a reducing gas. Then, in order to improve the adhesion of the Al-Si alloy plating layer to the base steel, after the steel plate is electroplated with Fe, Fe-B, etc. 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. 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 can be seen in Japanese Patent Publication No. 2-88754 mentioned above,
It is conceivable to produce an Al-Si alloy-plated steel sheet with Cr added to the plating layer by using a molten Al-Si plating bath containing Cr. However, when Cr is added to the plating bath, Al-S that forms the plating bath
The melting point of the i-based alloy increases. 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. On the other hand, a steel sheet coated with Ti, which is easily oxidized and easily forms an oxide film on its surface, cannot be hot-dipped by a normal in-line reduction annealing method for hot-diping ordinary steel. That is, the Cr oxide film formed on the surface is strong, and the reduction removal reaction of the oxide film does not occur under normal conditions in which the surface is heated in a reducing gas and activated.

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 No. 2 cannot be formed on the Ti surface with good adhesion.
This is because it is difficult to remove the Ti oxide film. The present invention has been devised to solve such a problem, and etching using a plasma or an ion beam in a vacuum atmosphere, vapor deposition of Ti, and molten Al-Si.
By performing plating as a series of steps, a predetermined amount of T
It is an object of the present invention to improve the adhesion of an Al-Si alloy plating layer containing i and to provide an inexpensive hot-dip galvanized steel sheet excellent in corrosion resistance.

[0007]

In order to achieve the object, the method for producing a hot-dip plated steel sheet according to the present invention is such that the plating original plate introduced into a vacuum chamber is subjected to plasma etching or ion beam etching to obtain a surface of the plating original plate. Is activated, then a Ti coating is formed by vacuum vapor deposition, and then introduced into a molten Al-Si plating bath.

The present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, the hot dip plated steel sheet produced according to the present invention has a first layer L ₁ ,
It has a structure in which the second layer L ₂ and the third 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 order to reduce the product cost. The first layer L ₁ is Al-Si
-Fe-Ti alloy layer on which Al-Ti-Si
The second layer L ₂ of the —Fe alloy layer is formed. And
An Al—Si—Ti-based third layer L ₃ is formed on the outermost layer.

The Ti concentration in the second layer L ₂ is 0.5% by weight in order to secure the corrosion resistance of the multi-layer Al-based alloy plated steel sheet.
The above is preferable. The second layer L ₂ is formed by immersing the steel plate coated with Ti in a molten Al-Si plating bath. At this time, the Ti concentration of the second layer L ₂ can be adjusted according to the amount of Ti deposited on the steel sheet. On the other hand, the first and third layers contain Ti in the solid solution range.
Is contained. Further, when an alloy steel such as stainless steel is used for the plating original plate, alloy components such as Cr and Ni diffuse from the original plate to the first to third layers of the plating layer. However, the first to third
Since Ti is present in any of the layers, the corrosion resistance hardly deteriorates. When ferritic stainless steel or the like is used as a plating original plate, since Cr is contained in each layer, the corrosion resistance is rather improved.

The composition and temperature of the hot-dip Al-Si plating bath are not particularly limited, but the Si concentration is determined in order to prolong the life of the hot-dip pot and impart a good surface appearance to the hot-dipped steel sheet. In the range of 1 to 13% by weight,
It is preferable to maintain the bath temperature at a temperature of 680 ° C. or lower.
In particular, when forming a thin Al-Si-Fe-Ti alloy layer, the plating bath has a Si concentration of 6 to 13% by weight and a bath temperature of 67.
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. Fe from molten Al-Si plating bath
Is transferred to the plating layer, so that impurities such as Fe are inevitably mixed in the third layer L ₃ of the plating layer.

The Ti coating is applied to the active plating original plate from which the oxide film has been removed by plasma etching or ion beam etching, and the Ti coating layer is formed at low cost and with high productivity. After the Ti coating layer is formed, molten Al-
A plating layer is formed by immersing a steel plate in a Si plating bath. An apparatus for continuously hot-diping a steel sheet whose surface has been activated by plasma etching or ion beam etching is introduced, for example, in Japanese Patent Laid-Open No. 3-86170.

Plasma etching activated hot dip coating equipment, ion beam etching activated hot dipping equipment, etc.
The inside is kept in a vacuum atmosphere. Therefore, when the vacuum is used to deposit Ti on a plating original plate that has been subjected to plasma etching activation treatment or ion beam etching activation treatment, it is possible to produce an Al-Ti-Si-based hot-dip steel sheet at a lower cost. You can 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, the surface activation reaction due to plasma etching, ion beam etching or the like will proceed rapidly.

[0013]

Since the second layer L ₂ contains a large amount of Ti, it has excellent corrosion resistance. The second layer L ₂ Al-Ti-
Si-Fe layer, Al of the third layer L ₃ that solid solution of Ti
-Si-Ti layer and the first layer _{L 1 Al-Si-Fe-} T
In combination with the i layer, it suppresses corrosion of the base steel S. In comparison, in the conventional melt Al-Si alloy-plated steel sheet, that no second layer L ₂ is, of course, because it does not contain Ti in layers, Al-Si layer of the surface layer portion of the corrosion protection for the substrate steel Corrosion resistance is insufficient. In addition, since the hot-dip Al-Si plating is applied to the steel sheet after being coated with Ti, the Ti concentration of the second layer L ₂ does not decrease due to the limited amount of dissolved Ti in the plating bath. In other words, the Ti concentration of the second layer L ₂ can be increased by the Ti adhesion amount, and the corrosion resistance,
It is possible to greatly improve the heat resistance. Moreover, the adhesion of each layer to the base steel is good, and a plated steel sheet having excellent workability without flaking or powdering can be obtained.

The obtained hot-dip galvanized 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.
In addition, although the raw material cost is high, when low alloy steel, stainless steel, etc. are used as the plating base plate, the corrosion resistance and heat resistance are further improved, and the corrosion resistance is superior to that of high Cr high Ni stainless steel.
It also has heat resistance. Since Ti is vacuum-deposited on the plating original plate activated by plasma etching, ion beam etching, or the like, the adhesion of the formed vapor-deposited Ti film to the plating original plate is good. In addition, a large number of active points are formed on the surface of the original plating plate by the activation treatment. The vapor-deposited Ti film grown starting from the active point has a uniform thickness over the front surface of the original plating plate. The vapor-deposited Ti film formed in this manner serves as a Ti supply source for the second layer L ₂ , and thus the _second Ti layer accurately corresponding to the desired target concentration can be obtained.
Layer L ₂ , and thus a multi-layer plating layer, can be formed.

Further, activation treatment by etching, Ti
The vacuum evaporation and the molten Al-Si plating are sequentially performed in a vacuum chamber. Therefore, molten Al-Si
It is possible to suppress the formation of an oxide film on the surface of the vapor-deposited Ti film, which causes a decrease in the adhesion of the plating layer and the occurrence of defects such as non-plating. From the viewpoint of completely suppressing the formation of an oxide film, the atmosphere to which the original plating plate is exposed during the period from the vacuum deposition of Ti to the introduction into the molten Al-Si plating bath has an oxygen partial pressure of 5 × 10 ⁻⁴ Pa or less, It is preferable to maintain a vacuum atmosphere having a degree of vacuum of 2 × 10 ⁻³ Pa or less. The original plating plate has a vapor-deposited Ti film with substantially no oxide film,
It is introduced into a molten Al-Si plating bath. Therefore, the bonding reaction proceeds at the interface between the plated original plate and the molten Al-Si plated alloy without causing a decrease in wettability due to the oxide film. Therefore, defects such as poor adhesion and non-plating do not occur in the formed hot-dip plated layer. Moreover, since the bonding reaction is carried out uniformly over the entire surface of the plated original plate, the thickness of the hot-dip layer and the Ti concentration are also made uniform.

[0016]

[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 device is incorporated, in which a plating base plate 10 is fed from a payoff reel 11, deflector rolls 12,
It is guided by 13 and sent to the vacuum chamber 20. Vacuum tank 2
A vacuum seal device 21 is provided on the entry side of 0, and a high-frequency heating device 30, a plasma etching device 40, and a Ti 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 Ti is coated by the Ti 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. FIG. 3 shows a hot dip plating facility incorporating an ion beam etching apparatus.
In place of the plasma etching apparatus 40, the pair of ion beam etching apparatuses 70, 70 are arranged so as to face both sides of the original plating plate 10 running in the vacuum chamber 20. The ion beams 71, 71 emitted from the ion beam etching devices 70, 70 collide with the surface of the plating original plate 10 to etch away the oxide film, surface-altered layer, etc. on the surface. For the surface-activated plating original plate 10, T
A Ti coating layer is formed by the i vapor deposition device 50.

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 degree of vacuum, the high frequency heating device 30 and the plasma etching device 40 or the ion beam etching device 7
0 was activated to activate the surface of the original plating plate 10.
By introducing the source gas at this time, the vacuum degree of the vacuum chamber 20 was lowered to 0.05 to 5 Pa. When the original Ti plate 10 is coated with Ti by the Ti vapor deposition device 50, the original plating plate 10 is heated by the high-frequency heating device 30 prior to vapor deposition,
Moreover, since the surface is activated by the plasma etching device 40 or the ion beam etching device 70, Ti having a uniform thickness on the surface of the original plating plate 10 and excellent in adhesion is formed.
A vapor deposition layer was formed. The plasma etching is shown in Table 1.
Ion beam etching was performed under the conditions shown in Table 2 under the conditions shown in Table 2.

[Table 1]

[Table 2]

For the plating original plate on which the Ti coating is formed,
Hot dip Al-Si alloy plating was performed under the conditions shown in Table 3.

[Table 3]

In the obtained hot dip plated steel sheet, the third layer L ₃ is formed by a mixed layer of an Al-Si-Ti alloy having a high Al content and an Al-Si-Ti alloy having a high Si content precipitated by eutectic. It had been. Also, under the third layer L ₃ , Al-Ti
-Si-Fe-based second layer L ₂ and Al-Si-Fe-T of
The i-type first layer L ₁ was formed. By adjusting the thickness of the Ti coating layer provided by vapor deposition, the second
The Ti concentration of the layer L ₂ was changed. Then, the relationship between the Ti concentration and the corrosion resistance was investigated. The survey results are shown in FIG. In addition,
The corrosion resistance was evaluated by performing a salt spray test specified in JIS and measuring the time until red rust of 5% in area ratio was generated on the surface of the test piece. As is clear from FIG. 4, when the thickness of the vapor-deposited Ti coating is 0.02 μm or more, the Ti concentration of the second layer L ₂ is 0.5% by weight or more, and the corrosion resistance is significantly improved. .

On the other hand, in the reference example in which only Ti was vapor-deposited, even when the thickness of the vapor-deposited Ti 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. Further, also in the comparative example in which the molten Al—Si alloy plating was performed after the vapor deposition Ti coating was applied, when the thickness of the vapor deposition Ti coating was less than 0.02 μm, the Ti concentration of the second layer L ₂ was insufficient. However, sufficient corrosion resistance was not obtained. The fact that excellent corrosion resistance is ensured by ensuring the Ti concentration of the second layer L ₂ is the same as when hot activation is performed by ion beam etching and vacuum vapor deposition of Ti is performed on the original plating plate to perform hot dipping. . For example,
0.3μ thickness on the original plating after ion beam etching
Al-S is used to melt the original plating plate on which the m vapor-deposited Ti film is formed.
With i alloy plating, 5% red rust generation time is 390
It was 0 hours. On the other hand, a plated original plate on which a vapor-deposited Ti film having a thickness of 0.01 μm was formed was similarly melted with Al—Si
The alloy-plated product had a short 5% red rust generation time of 400 hours.

[0023]

As described above, the hot dip plated steel sheet produced according to the present invention has Al-Si-on the base steel.
The Fe-Ti-based intermediate layer is used as the first layer, and the Al-Ti-Si-Fe-based second layer and Al- having excellent corrosion resistance are formed on the first layer.
It has a multilayer structure in which a third layer of Si-Ti system is laminated. With this multi-layered plating layer, corrosion resistance, even when using an inexpensive original plate such as ordinary steel,
It has excellent heat resistance and can be used as a material suitable for automobile exhaust system components and building materials. Further, since a series of processes of plasma etching or ion beam etching, vacuum deposition of Ti and hot dip plating are performed in the same vacuum tank, the plating process and the plating equipment itself are simplified, and a low cost and highly corrosion resistant product is obtained. can get.

[Brief description of drawings]

FIG. 1 shows a layer structure of a hot dip plated steel sheet manufactured according to 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 hot dip plated steel sheets obtained in the examples of the present invention, in comparison with the reference examples and the comparative examples.

[Explanation of symbols]

10: Original plating plate 20: Vacuum tank 30: High frequency heating device 40: Plasma etching device 50: T
i Vapor deposition apparatus 60: Hot dip plating apparatus 70: Ion beam etching apparatus

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C23F 4/00 C 8414-4K

Claims (2)

[Claims] 1. A plating base plate introduced into a vacuum chamber is subjected to plasma etching or ion beam etching to activate the surface of the plating base plate, and then T is deposited by vacuum deposition.
A method for producing a hot dip plated steel sheet, which comprises forming an i coating and then introducing it into a hot dip Al-Si plating bath. 2. The Ti coating according to claim 1, the Ti of the Al—Ti—Si—Fe based alloy layer formed after hot dip plating.
A method for producing a hot dip plated steel sheet, wherein the concentration is adjusted to 0.5% by weight or more.