JPH08134632A - Production of zinc-magnesium alloy plated steel sheet - Google Patents

Abstract

PURPOSE: To inhibit the diffusion of Mg causing the formation of a brittle intermediate layer and to produce a dense and highly corrosion resistant Zn-Mg alloy plated steel sheet excellent in adhesion by a vapor deposition method. CONSTITUTION: Preliminary Zn vapor deposition is applied to the surface of a steel sheet so that the coating weight of Zn per unit area becomes >=1.5 times the coating weight of Mg, and then, Mg vapor deposition and Zn vapor deposition are applied to the steel sheet held at >=180 deg.C. A starting sheet 1 for plating is surface-activated by reducing heating 12, passed through a reducing atmosphere zone 13, a nitrogen substitution chamber 19, a nitrogen atmosphere duct 20, and a vacuum sealing device 31, and introduced into a vacuum vapor deposition chamber 30. In this vacuum vapor deposition chamber 30, preliminary Zn vapor deposition 40, Mg vapor deposition 50, and Zn vapor deposition 60, 70 are successively clone. At this time, the steel sheet is passed through the nitrogen atmosphere duct 20 under the conditions satisfying X×Z<=1.2 and Y×Z<=35 when X, Y, and Z(sec) represent theO2 , concentration (vol.%) of the nitrogen atmosphere duct 20, H2 O concentration (vol.%), and sheet passing time, respectively. Further, H2 can be added to the nitrogen atmosphere duct 20.

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 Zn-Mg alloy plated steel sheet which surely forms a Zn-Mg alloy plated layer having excellent adhesiveness and structure on the surface of the steel sheet.

[0002]

2. Description of the Related Art Conventionally, various surface treatments have been performed to improve the corrosion resistance of steel materials. Above all, the Zn-plated steel sheet is mainly manufactured by hot dipping, electroplating, or the like. Also, in some cases, Zn is deposited by vapor deposition.
Manufactures plated steel sheets. The demand for improved corrosion resistance tends to increase year by year. Along with this, various improvements have been attempted by a hot dipping method, an electroplating method, and the like. When attempting to improve the corrosion resistance of a Zn-plated steel sheet by the hot dip coating method, it is first thought that the amount of the Zn-plated layer deposited is increased. However, since the upper limit of the adhesion amount is restricted from the manufacturing aspect, there is a limit to thickening the plating layer to improve the corrosion resistance. Further, an increase in the amount of adhesion, that is, an increase in the thickness of the plated layer, tends to cause defects such as galling and flaking when press-forming a Zn-plated steel sheet. If an attempt is made to similarly form a thick plating layer by electroplating, the line speed must be slowed down, resulting in a marked loss of productivity. Therefore, in the electroplating method, Zn-Ni-based Zn alloy plating is applied to improve the corrosion resistance. However, since the Zn-Ni alloy plating layer is likely to be a hard and brittle plating layer, defects such as cracks and chips are likely to occur in the plating layer during press molding. When such a defect occurs in the plated layer, the underlying steel exposes the plated layer through the defective portion, so that the original performance of the plated layer is not exhibited and corrosion starting from the defective portion proceeds.

From the above background, it has been attempted to manufacture a Zn-based alloy plated steel sheet having high corrosion resistance by a vapor deposition method. Among them, Zn-Mg alloy plating exhibits an excellent anticorrosion effect. For example, in Japanese Patent Laid-Open No. 64-17853, Zn-Mg containing 0.5 to 40% by weight of Mg.
Forming an alloy plating layer is disclosed. Also,
Between the Zn-Mg alloy plating layer and the base steel, Zn, Ni,
JP-A-2-141588 discloses that when an intermediate layer of Cu, Mg, Al, Fe, Co, Ti or the like is interposed, the adhesion and workability of the plating layer are improved.
When the Zn-Mg alloy plating layer is composed mainly of Zn-Mg based intermetallic compound and does not contain Mg phase, the coating film peeling resistance after coating is improved.
-17853. Furthermore, JP-A-6
In Japanese Patent Publication No. 4-25990, a Zn-Ti alloy plating layer is provided on a Zn-Mg alloy plating layer to improve the corrosion resistance after coating. The vapor-deposited Zn-plated steel sheet is continuously produced by heating and reducing the steel sheet surface in a non-oxidizing furnace and a reduction treatment furnace similar to the hot-dip galvanized steel sheet to activate the steel sheet surface, and then performing vapor deposition [Nisshin Steel Engineering Co., Ltd. Report No. 5
6 (1987), page 41]. Burning off and heated steel sheet of oil adhering to the surface in non-oxidizing furnace, H ₂ -N
It is annealed in a reduction annealing furnace maintained in an atmosphere of ₂ , H _2, etc., and the oxide film on the surface is removed and activated. After that, the steel sheet is cooled in a reducing atmosphere, and H
_It passes through a nitrogen atmosphere duct provided to prevent explosion caused by the entry of _{2, and} is introduced into the vacuum deposition chamber through a vacuum sealing device. In the vacuum vapor deposition chamber, Zn is vapor-deposited on the fed steel plate and is delivered to the atmosphere through the vacuum sealing device on the delivery side. Since this vapor-deposited Zn-plated steel sheet manufacturing method employs the same pretreatment as the hot dipping method, some of the existing equipment can be used. In addition, a degreasing cleaning device may be used instead of the non-oxidizing furnace.
Such a vapor deposition Zn plating method has a production efficiency equal to or higher than that of the electric Zn plating method.

[0004]

In the method of vapor-depositing Mg and Zn in this order and manufacturing the Zn-Mg alloy plated steel sheet by the subsequent diffusion treatment, the surface oxide film is formed by heating the steel sheet in a reducing atmosphere. To be removed. However, since the steel sheet passes through the nitrogen atmosphere duct even after the surface has been activated, good plating adhesion may not be obtained in some cases. This is due to the small amount of O ₂ and H _{2 in} the nitrogen atmosphere.
The surface of the steel sheet is oxidized by O, and the produced oxide film is Mg, F
It is considered that the cause is that it reacts with e and Zn that has diffused to form a brittle reaction product. Further, when the steel plate temperature is low, voids start to appear in the plating layer. As a result, the obtained plating layer is not dense and the base steel is exposed to a corrosive atmosphere through the plating layer,
The original corrosion resistance is not exhibited. The present invention has been devised to solve such a problem, and Zn deposition excellent in corrosion resistance is achieved by performing Zn deposition prior to Mg deposition to achieve plating adhesion and densification of the plating layer. The purpose is to obtain a Mg alloy plated steel sheet.

[0005]

The method for producing a Zn-Mg alloy vapor-deposited plated steel sheet according to the present invention, in order to achieve the object,
Pre-Zn vapor deposition is performed on the surface of the steel sheet at a Zn deposition amount per unit area of 1.5 times or more the Mg deposition amount, and then Mg vapor deposition and Zn vapor deposition are performed. During Mg vapor deposition and Zn vapor deposition, it is preferable to maintain the steel plate temperature at 180 ° C. or higher. The steel sheet to be plated is introduced into the vacuum deposition chamber through a reducing atmosphere zone which activates the surface of the steel sheet by reduction heating, a nitrogen substitution chamber, a nitrogen atmosphere duct and a vacuum sealing device. In the vapor deposition chamber, pre-Zn vapor deposition, Mg vapor deposition, and Zn vapor deposition are sequentially performed, and a Zn-Mg alloy plating layer is formed by mutual diffusion. At this time, when the O ₂ concentration (volume%) of the nitrogen atmosphere duct is X, the H ₂ O concentration (volume%) is Y, and the strip running time is Z (seconds), X × Z ≦ 1.2 and Y × Z ≦ 3
Pass the nitrogen atmosphere duct under the condition satisfying the condition 5.
The nitrogen atmosphere duct is preferably 0.05 to 4% by volume
Of H ₂ is added. In this case, X × Z ≦ 3.8 and Y ×
A nitrogen atmosphere duct is passed under the condition of satisfying Z ≦ 80.

[0006]

In the present invention, the pre-Z is performed before the Mg vapor deposition.
n Steel plate is vapor-deposited. Even if there is a thin oxide film on the surface of the steel sheet, Zn can be vapor-deposited with good adhesiveness, so that the adhesiveness of the Mg vapor deposition layer and the Zn vapor deposition layer formed thereon is improved.
However, it takes several seconds or more from Mg vapor deposition to Zn vapor deposition, and 180 ° C. is required to improve the adhesion of the plating layer.
In the case of vapor deposition at the above steel plate temperatures, if the pre-Zn layer is thin, a large amount of Mg diffuses to the steel plate interface, and a brittle intermediate layer is likely to be formed. In addition, Mg diffuses into the pre-Zn layer during the diffusion treatment of the plating layer, and similarly a fragile intermediate layer is formed. The formation of a brittle intermediate layer can be prevented by forming a pre-Zn layer having a weight ratio of 1.5 times or more the amount of the deposited Mg layer. This amount of pre-Zn layer has a steel plate temperature of 1
It suppresses the diffusion of Mg to the steel sheet interface at the time of vapor deposition at 80 ° C. or higher or at the time of diffusion heat treatment, and limits the diffusion amount to a small amount. As a result, a brittle intermediate layer is not formed, and the adhesion of the Zn-Mg alloy plating layer to the base steel is improved.

When the steel sheet to be plated is passed through the nitrogen atmosphere duct, the O ₂ concentration in the N ₂ gas atmosphere is X (volume%),
When the H ₂ O concentration is Y (volume%) and the strip running time is Z (seconds), if the conditions of X × Z ≦ 1.2 and Y × Z ≦ 35 are satisfied, it is generated on the steel sheet surface by reoxidation. The oxide film is prevented from becoming thicker. As a result, the adhesion when pre-Zn vapor deposition is secured. Further, when a small amount of H ₂ is added to the nitrogen atmosphere duct, restrictions on the atmosphere of the nitrogen atmosphere duct and the passage time are alleviated, and the production of the Zn—Mg alloy plated steel sheet becomes easy. Zn-Mg according to the invention
The alloy vapor deposition plated steel sheet is produced, for example, by a plating facility whose outline is shown in FIG. The plating base plate 1 is rewound from the pay-off reel 2, and is transferred from the pretreatment zone 10 including the non-oxidizing furnace 11, the reduction annealing furnace 12 and the reducing atmosphere cooling zone 13 to the vacuum chamber 30 through the nitrogen substitution chamber 19 and the nitrogen atmosphere duct 20. Be led to. In the reduction annealing furnace 12, for example, 50
The original plating plate 1 is subjected to oxide film removal and annealing by heating in a reducing atmosphere having a composition of% H ₂ —N ₂ .

The inside of the vacuum deposition chamber 30 is kept airtight by the inlet vacuum roll 31 and the outlet vacuum roll 32, and the pressure is reduced to about 1 × 10 ^-2 Torr by a vacuum pump (not shown). Inside the vacuum deposition chamber 30, the pre-Zn deposition chamber 40, the Mg deposition chamber 50, the first Zn deposition chamber 60, and the second Zn deposition chamber 70 are arranged along the transport path of the plating original plate 1.
Are arranged. If necessary, an auxiliary Zn vapor deposition chamber 65 may be provided between the first Zn vapor deposition chamber 60 and the second Zn vapor deposition chamber 70. The vapor deposition of Mg is performed by electric resistance heating evaporation,
High frequency heating evaporation, electron beam heating evaporation, arc evaporation, etc. can be adopted. In the illustrated equipment, the Mg evaporation source 51 and the Mg vapor guide hood 52 are arranged opposite to each other on both sides of the original plating plate. The Mg evaporation source 51 operates either one or both in accordance with single-sided plating or double-sided plating.

The Zn vapor deposition chambers 40, 60, 70 include Zn vapor generators 41, 61, 71 and a Zn vapor guide hood 42.
62 and 72 are opposed to the plating original plate 1 and the Mg-deposited original plate 3. In the pre-Zn vapor deposition chamber 40, the vapor guide hoods 42 are opposed to both sides of the original plating plate 1 so that Zn vapor deposition can be performed on both sides simultaneously. In the first Zn vapor deposition chamber 60 and the second Zn vapor deposition chamber 70, the original plating plate 3 is wound around the winding rolls 63 and 73, and Zn is vapor-deposited on each side. The plated steel sheet 4 after Zn vapor deposition is guided to the heating furnace 80 via the exit side vacuum roll 32. Plated steel plate 4
Is subjected to heat treatment in the heating furnace 80 as needed by appropriate heating means such as high frequency heating. When passing through the post-treatment zone 90, the plated steel sheet 5 after heating is subjected to necessary chemical conversion treatment and the like. Finally, the Zn-Mg alloy vapor-deposited steel plate 6 is taken up by the take-up reel 7. When the heating process is not performed in the heating furnace 80, the plated steel sheet 4 can be batch-heated in a separate heating furnace. The plated steel sheet thus manufactured has a Zn—Mg alloy plating layer formed on one side or both sides as necessary. For example, when forming a Zn-Mg alloy vapor deposition plating layer on one side, either one of the Mg evaporation sources 51 or 51 and Zn
The steam generator 61 or 71 is operated.

[0010]

[Example] An unannealed cold-rolled steel sheet having a composition shown in Table 1 and a thickness of 1.0 mm and a width of 918 mm was used as a plating original sheet. The original plating plate 1 was passed through the plating equipment shown in FIG. 1 to produce a Zn—Mg alloy vapor deposition plated steel plate.

[0011]

[Table 1]

Example 1: The atmosphere in the nitrogen atmosphere duct 20 is an N ₂ atmosphere having an O ₂ concentration of 0.001% by volume and an H ₂ O concentration of 0.06% by volume, and the plating base plate 1 passes through the nitrogen atmosphere duct 20. The time was set to 70 seconds. The steel plate temperature was adjusted so that the temperature when the plating original plate 1 enters the pre-Zn vapor deposition chamber 40 and the first Zn vapor deposition chamber 60 has a predetermined value. Although the steel plate temperature slightly rises due to vapor deposition or the like, the temperature rise amount at this time was adjusted to be less than 10 ° C. with respect to the predetermined temperature. Under these conditions, the amount of Zn deposited in the first Zn vapor deposition chamber 60 and the second Zn vapor deposition chamber 70 was set to 10 g / m ² on each side. Then, the plated steel plate 4 was introduced into the high-frequency heating furnace 80, and the plated steel plate 4 was heated to 310 ° C. for 5 seconds in an N ₂ atmosphere. Pre Zn
By changing the amount of deposition, the amount of Mg deposition, and the steel plate temperature during vapor deposition,
The effect of the plated layer on the adhesion and structure was investigated. Regarding the adhesiveness, the presence or absence of peeling was examined by the 180-degree tightly folded tape peeling test, and when no peeling was observed at all, it was evaluated as good. The structure of the plating layer, the cross section is observed by SEM,
We investigated its precision.

As can be seen from Table 2 showing the results of the investigation, when the pre-Zn deposition amount is 1.5 times or more the Mg deposition amount and the steel sheet temperature during vapor deposition is kept at 180 ° C. or higher, the adhesion is good. A Zn-Mg alloy plating layer having a dense structure was formed. On the other hand, if the pre-Zn adhesion amount is less than 1.5 times the Mg adhesion amount, peeling occurs in part or all of the plating layer, and a Zn-Mg alloy plated steel sheet with good adhesion cannot be obtained. It was Further, when the pre-Zn adhesion amount was less than 1.5 times the Mg adhesion amount without heat treatment, peeling occurred in a part of the plating layer. Furthermore, when the steel sheet temperature is less than 180 ° C. during vapor deposition, even if the adhesion is good, there are voids in the plating layer and a dense Zn-M
The g alloy plating layer could not be obtained.

[0014]

[Table 2]

Example 2: O ₂ in the nitrogen atmosphere duct 20
The effects on the plating adhesion were investigated by changing the concentration X (volume%), the H ₂ O concentration Y (volume%), the strip running time Z (seconds) and the H ₂ addition amount. The amount of pre-Zn deposited is 5 g /
The amount of m ² and Mg deposited was set to 1.2 g / m ² , and the temperature of the steel sheet during vapor deposition was set to 250 ° C. Then, the plated steel sheet 4 is heated in a high frequency heating furnace 80 kept in an N ₂ atmosphere for 30
Heat treatment was performed at 0 ° C. As can be seen in Table 3 showing the survey results, X × Z ≦ 1.2 and Y without addition of H ₂
Good adhesion is obtained when xZ ≦ 35. But X
If any of the conditions of × Z ≦ 1.2 and Y × Z ≦ 35 was not satisfied, the adhesiveness was lowered as shown in Table 4. Also, when H ₂ is added to the nitrogen atmosphere duct, X
Good adhesiveness is obtained with xZ ≦ 3.8 and Y × Z ≦ 80. However, if any of the conditions of X × Z ≦ 3.8 and Y × Z ≦ 80 was not satisfied, the adhesiveness was lowered.
As described above, the effect of H ₂ for alleviating the atmospheric conditions became remarkable when the added amount was 0.05% by volume or more.

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

As described above, in the present invention, when a Zn-Mg alloy vapor deposition plated steel sheet is manufactured by the vapor deposition method, 1.5 times or more of the amount of Mg deposited is deposited prior to the Mg vapor deposition. This improves the adhesion of the plating tank and prevents the formation of a brittle intermediate layer between the base steel and the plating layer. Further, by controlling the atmosphere before being introduced into the vacuum deposition chamber, reoxidation of the steel sheet surface activated by reduction annealing is suppressed, and plating adhesion is improved. The Zn-Mg alloy vapor-deposited steel sheet thus obtained exhibits good adhesion of the plating layer,
Used for applications that take advantage of the high corrosion resistance inherent in the n-Mg alloy plating layer.

[Brief description of drawings]

FIG. 1 is a plating facility for producing a Zn-Mg alloy vapor-deposited steel sheet according to the present invention.

[Explanation of symbols]

1: Plating base plate 3: Mg-deposited plating base plate
4: Zn plated steel sheet after vapor deposition 5: Plated steel sheet after heating 6: Zn-Mg alloy vapor deposited steel sheet 10: Pretreatment zone 11: Non-oxidizing furnace 12: Reduction annealing furnace
13: Cooling zone for reducing atmosphere 19: Nitrogen replacement chamber 2
0: Nitrogen atmosphere duct 30: Vacuum deposition chamber 40:
Pre-Zn vapor deposition chamber 50: Mg vapor deposition chamber 60: 1st Z
n vapor deposition chamber 70: second Zn vapor deposition chamber 80: heating furnace 90: post-treatment zone

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Saito 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd.

Claims (5)

[Claims] 1. A Zn-M characterized in that a Zn deposition amount per unit area is 1.5 times or more the Mg deposition amount, pre-Zn vapor deposition is performed on the surface of a steel sheet, and then Mg vapor deposition and Zn vapor deposition are performed.
Method for producing g-alloy plated steel sheet. 2. A method for producing a Zn—Mg alloy plated steel sheet, wherein Mg vapor deposition and Zn vapor deposition according to claim 1 are performed on a steel sheet kept at a temperature of 180 ° C. or higher. 3. A steel sheet whose surface has been activated by reduction heating is introduced into a vacuum deposition chamber through a reducing atmosphere zone, a nitrogen substitution chamber, a nitrogen atmosphere duct and a vacuum sealing device to perform pre-Zn vapor deposition, Mg vapor deposition and Zn vapor deposition. When performing sequentially, change the O ₂ concentration (volume%) of the nitrogen atmosphere duct to the X, H ₂ O concentration (volume%).
Is Y and the strip running time is Z (seconds), X × Z ≦ 1.2
And a method of manufacturing a Zn-Mg alloy-plated steel sheet according to claim 1 or 2, wherein a nitrogen atmosphere duct is passed under a condition satisfying Y x Z ≤ 35. 4. The nitrogen atmosphere duct according to claim 3, wherein H _{2 is} added to the nitrogen atmosphere duct.
The manufacturing method of the Zn-Mg alloy plating steel plate which adds. 5. The nitrogen atmosphere duct according to claim 3 or 4, to which 0.05 to 4% by volume of H ₂ is added, and X × Z ≦ 3.8.
And a method for producing a Zn-Mg alloy-plated steel sheet in which a nitrogen atmosphere duct is passed under conditions satisfying Y × Z ≦ 80.