JPH10317125A - Production of vapor deposition zinc plated steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a vapor deposition Zn plated steel strip or a vapor deposi tion Zn-Mg plated steel strip, having a pore-free dense Zn layer and excellent in corrosion resistance. SOLUTION: At the time of producing a vapor deposition Zn plated steel strip by introducing a continuously traveling steel strip into a vacuum chamber, vapor deposition Zn plating is carried out under the condition that a relation of T>=-(2/5)R+215 is valid between the temp. T( deg.C) of the steel strip to be vapor deposition plated and Zn vapor deposition rate R (g/m<2> .sec), by which the dense vapor deposition Zn plating layer free from pores in the inner part is formed. At the time of producing a vapor deposition Zn-Mg plated steel strip by performing vapor deposition plating treatments with Zn, Mg, and Zn in the order named, a relation of T>=-(2/5)R+215 is valid at the time of applying a first vapor deposition Zn plating. It is preferable that respective Zn vapor deposition treatments are carried out in the vacuum chamber held so that it has an atmosphere composed of nonoxidizing gases of 0.005-1.0 Torr pressure. By this method, the dense vapor deposition Zn layer can be formed, and corrosion resistance inherent in vapor deposition plating can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a vapor-deposited Zn-based steel strip or a vapor-deposited Zn-Mg-based steel strip.

[0002]

2. Description of the Related Art Various surface treatments have conventionally been employed to improve the corrosion resistance of steel strips. Among them, an electroplating method and a hot-dip plating method are mainly used for Zn plating, which is a typical surface treatment method. The demand for improvement in corrosion resistance tends to increase year by year, and accordingly, various improvements in hot-dip plating and electroplating have been proposed. In order to improve the corrosion resistance of the Zn-plated steel strip by the hot-dip plating method, firstly, it is conceivable to increase the adhesion amount of the Zn-plated layer, that is, to increase the thickness of the plated layer. However, there is an upper limit to the amount of adhesion due to restrictions from the viewpoint of manufacturing, and there is a limit to improving the corrosion resistance by increasing the amount of adhesion. Further, when the plating layer is thick, it tends to cause defects such as galling and flaking when press-forming the plated steel strip.

On the other hand, it is conceivable that the amount of adhesion is similarly increased by electroplating. However, increasing the amount of adhesion by the electroplating method increases the amount of electricity required for depositing the plated metal, and causes an increase in the cost of the plated steel strip. Therefore, in the electroplating method, the corrosion resistance is improved by applying a Zn alloy plating such as a Zn-Ni alloy plating. However, the Zn—Ni alloy plating layer is hard and brittle, and tends to generate defects such as cracks and chips in the plating layer during molding. When such a defect occurs in the plating layer, the underlying steel is exposed through the defective portion, so that the original performance of the plating layer is not exhibited, and corrosion starting from the defective portion proceeds.

[0004]

From the background described above, attempts have been made to produce a highly corrosion-resistant Zn-based plated steel strip or Zn-Mg-based plated steel strip by a vapor deposition method. Deposition Z
n-plated steel strips, vapor-deposited Zn-Mg-based steel strips, etc., exhibit superior corrosion resistance compared to conventional Zn-plated steel strips, but are used in relatively mild corrosive environments such as outdoors in rural areas. When exposed, the original high corrosion resistance may not be exhibited. The present inventors considered that the cause of the lack of the original excellent corrosion resistance of vapor-deposited Zn plating was due to the structure of the vapor-deposited plating layer, and investigated the relationship between the structure of the plating layer and the corrosion resistance.
As a result, it was found that unless the Zn plating layer formed on the surface of the steel strip had a sufficiently dense and continuous structure, the intrinsic properties of the vapor-deposited Zn-based plated steel strip could not be exhibited.

[0005] In the case of producing a vapor-deposited Zn-Mg-based steel strip by vapor-depositing a steel strip in the order of Zn, Mg, and Zn, a Zn-plated layer formed on the steel sheet surface by the first vapor-deposition Zn plating is formed. If the structure is not sufficiently dense and continuous, the effect is reflected on the Mg layer, and the deposited Zn-
It was found that the high corrosion resistance of the Mg-based plating did not appear. The present invention has been devised to solve such a problem, by adjusting the relationship between the steel strip temperature and the Zn deposition rate, to form a vapor-deposited Zn layer having a dense and continuous structure, Evaporated Zn-based steel strip with excellent corrosion resistance and evaporated Zn-
An object is to provide a Mg-based plated steel strip.

[0006]

According to the manufacturing method of the present invention, in order to achieve the object, when a continuously running steel strip is introduced into a vacuum chamber to manufacture a vapor-deposited Zn-based steel strip, vapor-deposition plating is performed. Steel strip temperature T (° C) and Zn deposition rate R (g / m
² · sec) to form a dense vapor-deposited Zn plating layer containing no voids by applying vapor-deposited Zn plating under the condition that T ≧ − (2/5) R + 215 is satisfied. Features. In the case of producing a vapor-deposited Zn—Mg-based steel strip by vapor-depositing Zn, Mg, and Zn in this order, T ≧ − (2 /
5) The relationship of R + 215 is established. It is preferable that any Zn deposition be performed in a vacuum chamber maintained in an atmosphere composed of a non-oxidizing gas species at a pressure of 0.005 to 1.0 Torr.

[0007]

In the vapor-deposited Zn plating of a steel strip, flying Zn vapor adheres to the surface of the steel strip and grows as crystal grains to form a plating layer. The deposition of Zn vapor, the growth of crystal grains, and the formation of a plating layer are affected by the deposition rate and the temperature of the steel strip. The present inventors,
As a result of investigating and studying the structure of the deposited Zn layer, it was presumed that voids were formed in the deposited Zn layer for the following reasons. When Zn vapor is supplied to the plating surface, Z
n is a crystal grain. Further, when the Zn vapor continuously comes, the flying Zn adheres to the crystal grains, and the deposited Zn layer gradually grows in the direction in which the Zn vapor comes. If the deposition rate is low, there are few crystal grains generated on the plating surface, so that the Zn vapor grows in the flying direction.
If the vapor is small, it is difficult to grow in the in-plane direction. Therefore, the crystal grains do not become continuous in the in-plane direction of the steel strip, and voids are generated in the Zn plating layer as shown in FIG.

On the other hand, when the deposition rate is high, the number of Zn crystal grains formed on the plating surface increases, so that discontinuity is less likely to occur. At a high deposition rate, a large amount of Zn vapor is supplied to the plating surface, so that the Zn vapor collides with each other, and the flying directions of the Zn vapor become uneven when viewed from the plating surface, so that the Zn vapor comes from different directions. Become. As a result, the growth of crystal grains in the in-plane direction is promoted, and a continuous Zn layer without voids is formed. Zn attached to the plated surface moves in the plated surface, and the movement of Zn is promoted as the temperature of the plated surface increases. Therefore, even when the deposition rate is small and the crystal grains are difficult to grow in the in-plane direction, if the temperature of the plating surface is increased, the growth of the deposited Zn is promoted in the in-plane direction by the movement of the attached Zn, and as a result, the deposition rate is small. Also, a continuous deposited Zn layer is easily formed.

[0009] Such a deposition rate and a steel strip temperature are determined by the deposition Z
As a result of quantitative analysis of the effects on the formation and growth of the n-layer from a number of experiments, the temperature T (° C.)
T ≧ − between Zn and the deposition rate R of Zn (g / m ² · second).
It has been clarified that when the relationship of (2/5) R + 215 is established, a deposited Zn layer having a dense and sound structure without voids therein is formed. In addition, M
When further depositing g and Zn, the finally formed Zn
It was found that the Mg-based plating layer stably exhibited the original high corrosion resistance. On the other hand, T <− (2/5) R + 21
When Zn is deposited under the condition of 5, the deposited Zn layer having voids is easily formed as shown in FIG. Further, when Mg and Zn are further vapor-deposited and diffused on the vapor-deposited Zn layer to form a Zn—Mg-based plating layer, as shown in FIG. 2, the underlying Zn layer contains voids. Does not exhibit high corrosion resistance.

The growth of the deposited Zn layer is easily affected by the atmospheric pressure when the pressure of the gas component contained in the atmosphere is high.
Oxidizing gas components such as water vapor (H ₂ O) unavoidably present in the atmosphere oxidize and contaminate the plating surface, hindering the growth of a dense and continuous deposited Zn layer. After that, the exhaust gas is exhausted to suppress the adverse effect of the oxidizing gas component. If the atmospheric pressure is high,
The gas component reaching the plating surface increases, which hinders the movement of Zn attached to the plating surface. When a vapor-deposited Zn layer grows, the ratio of the number of molecules of the ambient gas / the number of Zn vapor reaching to the surface per unit time is suppressed to 1.0 or less. A deposited Zn layer having a texture is formed. For example, when the deposition rate of Zn is 300 g / m ² · sec, the pressure of the atmosphere gas is 1.
If the pressure is 0 Torr, the number of molecules of the atmospheric gas to be reached / Z
The ratio of the number of n vapors becomes 1.0.

The inside of the evaporation chamber is evacuated by a vacuum pump. For example, the vapor deposition Zn plating equipment shown in FIG.
It operates in a vacuum pressure range of 0.005 to 1.0 Torr. Pressures up to about 0.005 Torr can be obtained relatively easily with a Roots pump or the like. It is possible to realize a low pressure (high vacuum) of 0.005 Torr or less, but it is necessary to take countermeasures against the backflow of oil from the vacuum pump, and the piping of the exhaust system becomes large in diameter. It is not realistic as a simple manufacturing facility. Further, when Zn is deposited at a high pressure (low vacuum) exceeding 1.0 Torr, the Zn vapors tend to aggregate with each other to form a powder, and the Zn powder tends to adhere to the steel strip. Therefore, it is preferable to set the atmospheric pressure at the time of Zn deposition to 1.0 Torr or less.
In addition, if the steel strip surface is clean, sufficient adhesion can be obtained even by vapor deposition Zn plating on a steel strip at a temperature around room temperature. That is, the temperature of the steel strip introduced into the vacuum chamber is set to at least 20
By maintaining the temperature at not less than ° C., vapor deposition Zn plating can be performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows a vapor deposition plating line for producing a vapor-deposited Zn-Mg-based steel strip having a plating layer having a three-layer structure, without restricting the present invention. Deposition Z
The n-plated steel strip is manufactured by a vapor deposition plating line having no Mg vapor deposition system or a line in which the Mg vapor deposition system of FIG. 3 is stopped. The plating base plate 10 is unwound from the payoff reel 11, surface-activated and annealed in a non-oxidizing furnace 20 and a reduction annealing furnace 25, and then passed through a steel strip temperature control device 26 to form a vacuum chamber 3.
It is led to 0. The steel strip temperature control device 26 is a device that cools the plating base plate 10 by blowing a mixed gas of nitrogen and hydrogen, and the temperature of the plating base plate 10 is adjusted by the amount of the blown gas.

The vacuum chamber 30 has an airtight structure having an inlet-side vacuum seal portion 31 and an outlet-side vacuum seal portion 32, and is maintained in a reduced pressure atmosphere of about 0.05 Torr by an appropriate vacuum pump. Inside the vapor deposition chamber 33 disposed in the vacuum chamber 30, a pre-Zn vapor deposition unit 34, a Mg vapor deposition unit 35, and a post Zn vapor deposition unit 36 are sequentially disposed along the transport direction of the plating original plate 10. Pre-Zn deposition unit 34, Mg deposition unit 35
In the post-Zn vapor deposition section 36, a pre-Zn duct 37, a Mg duct 38, and a post-Zn duct 39 connected to an evaporation source (not shown) are open toward the running plating original plate 10. When the plating original plate 10 introduced into the vacuum chamber 30 is used to produce a vapor-deposited Zn-Mg-based plated steel strip,
In the pre-Zn deposition section 34, pre-Zn is first deposited, and then M
The Mg deposition section 35 deposits Mg, and the post Zn deposition section 3
6, Zn is deposited. When producing a vapor-deposited Zn-based plated steel strip, only the pre-Zn vapor deposition unit 34 or the Mg vapor deposition unit 35
Is stopped and the pre-Zn deposition unit 34 and the post Zn
Zn is vapor-deposited in the vapor deposition section 37. The vapor deposition plating is performed on one side or both sides of the original plating plate 10 as necessary.

The plated steel strip 15 after the vapor deposition is sent out of the vacuum chamber 30 through the outlet side vacuum seal section 32 and is cooled.
0, and finally wound up on a take-up reel 16 as a plated steel strip 15. The plated steel strip 15 has a cooling device 40.
Is cooled by blowing nitrogen gas. Cooling device 4
The cooling capacity of 0 is adjusted by the temperature and flow rate of the blown nitrogen gas or air. When vapor deposition plating is performed while the plating base plate is continuously running, the manufacturing conditions include the adhesion amount G of the plated steel strip to be manufactured, the traveling speed V of the plating base plate, the length L of the portion to be subjected to vapor deposition plating, and the like. Length L
Is predetermined as the equipment specification. The following relationship is established between these operating conditions and the deposition rate R of the pre-plated Zn.

[0015] For example, in the case of performing Zn plating with a deposition amount G of 30 g / m ² at a running speed V of a plating original plate of 0.83 m / sec (50 m / min) on a production line having a pre-Zn deposition length L = 0.5 m. , 50 g / m ² so as to satisfy the above equation.
It is necessary to supply Zn vapor to the plating base plate at a deposition rate of seconds. That is, the deposition rate R of Zn is determined by the specifications of the plated steel strip to be manufactured (adhesion amount G), the manufacturing conditions (running speed V of the steel strip), and the specifications of the manufacturing line (deposition length L). According to the deposition rate R determined in this way, the temperature of the plating base plate 10 is changed by the steel strip temperature controller 26.
Adjust properly.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Using the vapor deposition plating line shown in FIG.
An n-Mg-based plated steel strip was manufactured. In the production conditions of Tables 1 and 2, the coating weight G and the steel strip traveling speed V are fixed stepwise, in other words, the Zn deposition rate R is set stepwise at a constant stepwise rate. The steel strip temperature was changed. The atmosphere pressure in the vapor deposition chamber 33 was set to 0.05 Torr. When manufacturing a vapor-deposited Zn-based plated steel strip,
Only the pre-Zn deposition unit 34 was operated. Evaporated Zn-Mg
When manufacturing a system-plated steel strip, pre-Zn deposition is performed in the pre-Zn deposition section 34 under the same conditions, and then Mg is deposited in the Mg deposition section 35.
It was vapor-deposited and post-Zn-plated in a post-Zn vapor deposition unit 36. The relationship between the deposition conditions of the pre-Zn layer and the structure of the plating layer during the production of the vapor-deposited Zn-Mg-plated steel strip is the same as in the case of producing the vapor-deposited Zn-plated steel strip. Will be described.

Table 3 shows the results obtained by changing the steel strip temperature while maintaining the atmospheric pressure of the vapor deposition chamber 33 at a constant value of 0.05 Torr, and examining the effect of the steel strip temperature on the structure of the plating layer. Table 4 shows the influence of the atmospheric pressure on the structure of the plating layer by changing the atmospheric pressure while fixing the deposition conditions.
The steel strip temperature was controlled by the steel strip temperature control device 26.
The steel strip temperature control device 26 is a device that cools the steel strip by spraying a mixed gas of nitrogen and hydrogen onto the steel strip surface, and the steel strip temperature is adjusted by increasing or decreasing the amount of the blowing gas. The atmospheric pressure of the vapor deposition chamber 33 is controlled by the input side vacuum sealing device 3
1. The control is performed by adjusting the sealing state of the outlet side vacuum sealing device 32, adjusting the opening of an exhaust valve connected to a vacuum pump attached to the vapor deposition chamber 33, and the like. The cross-sectional structures of the manufactured vapor-deposited Zn-based plated steel strip and vapor-deposited Zn-Mg-based plated steel strip were observed with an electron microscope, and the structures of the vapor-deposited Zn plating layer and the pre-Zn layer were investigated. When no voids were detected inside the pre-Zn layer as shown in FIG. 1, the structure of the pre-Zn layer was good (○), and when the voids were detected, the texture of the pre-Zn layer was poor (×). ) And the results are shown in Tables 1 to 4. In addition, when the quality of the plating layer structure was determined based on the relationship between the deposition rate R and the steel strip temperature T, as shown in FIG. 4, a plating layer having a dense structure without voids was formed at T ≧ − (2/5) R + 215 as shown in FIG. It turned out to be.

[0018]

[0019]

[0020]

[0021]

From the results shown in Tables 1 to 4, it can be seen from the results that the deposition Z having a good structure was obtained.
It can be seen that in order to form the n-layer, Zn vapor should be adhered to the plating surface at a high temperature and the temperature of the original plating plate should be kept high. In addition, when the quality of the plating layer structure was determined based on the relationship between the deposition rate R and the steel strip temperature T, as shown in FIG. 4, a plating layer having a dense structure without voids was formed at T ≧ − (2/5) R + 215 as shown in FIG. It turned out to be. Specifically, Zn
The temperature of the plating base plate 10 to be deposited is 100 ° C. or higher and 150
When the temperature is lower than 150 ° C., the temperature of the original plating plate 10 is set at 15 ° C. so that Zn is deposited at a deposition rate of 300 g / m ² second or less.
200 to 300 g / m when 0 ° C or higher and lower than 200 ° C
^When the temperature of the plating base plate 10 is 200 ° C. or more and less than 220 ° C., Zn is reduced to 50 to 3 so that Zn is deposited in ² seconds.
Deposited at 00 g / m ² · sec.
When the temperature is 20 ° C. or more and less than 370 ° C., 5-300 g of Zn
/ M ² · sec, by selecting the combination of the temperature of the steel strip to be plated and the deposition rate of Zn so as to confirm that a dense and continuous deposited Zn layer without voids is formed inside did. The temperature of the original plating plate 10 was 370 ° C.
The reason for defining the lower limit is that even if the Zn plating is performed at a temperature exceeding this temperature, alloying occurs due to the diffusion of Fe and Zn between the base steel and the Zn plating layer, and the cross section as shown in FIG. 1 or FIG. Zn-plated steel strip or Z with a plating structure of
This is because an n-Mg-based plated steel strip cannot be obtained. Through the deposited Zn-based plated steel strip having the deposited Zn plating layer formed in this way and the similarly dense pre-Zn layer, the Zn-
Deposition Z of three-layer structure with Mg layer and post Zn layer formed
The n-Mg plated steel strip exhibited extremely good corrosion resistance in various corrosion tests. On the other hand, a vapor-deposited Zn-based steel strip having a vapor-deposited Zn-plated layer and a vapor-deposited Zn-Mg-plated steel strip having a voided pre-Zn layer are milder in a countryside far from the coastal region and in a warm climate. Corrosion occurred in a corrosion test exposed outdoors in a corrosive environment.

[0023]

As described above, when producing a vapor-deposited Zn-based plated steel strip according to the present invention, dense vapor deposition without voids is controlled by correlating the vapor deposition rate of Zn vapor and the steel strip temperature. A Zn layer is formed on the surface of the steel strip. The vapor-deposited Zn-plated steel strip produced in this manner exhibits excellent corrosion resistance unique to vapor-deposition plating. In addition, evaporation Zn
-In the production of a Mg-based plated steel strip, a dense pre-Zn layer having no voids formed in the same manner is used as the first layer, and Z
An n-Mg layer and a post Zn layer are formed. The deposited Zn—Mg-based plating layer having a three-layer structure formed as described above has no defect inside the plating layer, and has a conventional deposition Zn—Mg-based plating layer.
It exhibits the high corrosion resistance inherent in a system-plated steel strip and is used as a building material with excellent durability especially in a mild corrosive environment such as a rural area.

[Brief description of the drawings]

FIG. 1 shows a vapor-deposited Zn on which a vapor-deposited Zn layer is formed.
Sectional structure of galvanized steel strip

FIG. 2 Evaporated Zn-Mg with pre-Zn layer with voids
Section structure of system-coated steel strip

FIG. 3 A vapor deposition plating line for producing a vapor-deposited Zn—Mg-based steel strip

Fig. 4 Effect of deposition rate and steel strip temperature on microstructure of plated layer

[Explanation of symbols]

10: Plated steel plate (steel strip) 11: Payoff reel
15: Plated steel strip 16: Take-up reel 20: Non-oxidizing furnace 25: Reduction annealing furnace 26: Steel strip temperature control device 30: Vacuum chamber 31: Inlet vacuum seal part 32: Outlet vacuum seal part 33: Evaporation chamber 34 : Pre-Zn deposition unit 35: Mg
Deposition section 36: Post Zn deposition section 37: Pre-Zn
Duct 38: Mg duct 39: Post Zn duct 40: Cooling device

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[Procedure amendment]

[Submission date] July 15, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005] In the case of producing a vapor-deposited Zn-Mg-based steel strip by vapor-depositing a steel strip in the order of Zn, Mg, and Zn, a Zn-plated layer formed on the steel sheet surface by the first vapor-deposition Zn plating is formed. It was found that if the structure was not sufficiently dense and continuous, high corrosion resistance of the deposited Zn-Mg based plating would not be exhibited. The present invention has been devised to solve such a problem, by adjusting the relationship between the steel strip temperature and the Zn deposition rate, to form a vapor-deposited Zn layer having a dense and continuous structure, An object is to provide a vapor-deposited Zn-based plated steel strip and a vapor-deposited Zn-Mg-based plated steel strip having excellent corrosion resistance.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Minoru Saito 5th Ishizu Nishimachi, Sakai-shi, Osaka Nisshin Steel Co., Ltd.

Claims (4)

[Claims] When a continuously traveling steel strip is introduced into a vacuum chamber to produce a vapor-deposited Zn-based steel strip, the temperature T (° C.) of the steel strip to be vapor-deposited and the Zn deposition rate R (g / m 2). ² seconds)
A dense vapor-deposited Zn plating layer containing no voids therein by applying vapor-deposited Zn plating under a condition that a relationship of T ≧ − (2/5) R + 215 is established between the two. A method for producing a Zn-based plated steel strip. 2. A method for producing a vapor-deposited Zn-based plated steel strip according to claim 1, wherein a vacuum chamber in which vapor-deposited Zn plating is performed is held in an atmosphere composed of a non-oxidizing gas species at a pressure of 0.005 to 1.0 Torr. . 3. A continuously running steel strip is introduced into a vacuum chamber.
vapor deposition Z by vapor deposition plating in the order of n, Mg, Zn
When producing an n-Mg-based steel strip, the temperature T (° C.) of the steel strip to be vapor-deposited and the Zn deposition rate R (g / m ^2.
The second deposition Zn plating is performed under the condition that the relationship of T ≧ − (2/5) R + 215 is established between the first deposition Zn plating layer and the second deposition plating layer.
A method for producing a vapor-deposited Zn-Mg-based steel strip, which is formed by a second vapor-deposited Zn plating. 4. The vapor-deposited Zn—Mg-based steel strip according to claim 3, wherein a vacuum chamber in which vapor-deposition Zn plating is performed is held in an atmosphere composed of a non-oxidizing gas species at a pressure of 0.005 to 1.0 Torr. Production method.