JPH06346254A - High corrosion resistant zn/cr series multi-ply plated steel sheet and its production - Google Patents

Abstract

PURPOSE:To obtain a Zn/Cr series multi-ply plated steel sheet excellent in corrosion resistance and workability. CONSTITUTION:The surface of base steel is vapor-deposited with a Cr layer and a Zn layer in a laminating state. This multi-ply plated steel sheet is produced by introducing a plating original sheet into a vacuum chamber to form a Cr layer by a vapor depositing method and successively vapor-depositing Zn. Since there is a Cr layer as a primary layer, the corrosive rate of Zn is reduced, and the sacrificial anticorrosive effect of Zn is maintained over a long time. Since the Cr layer is the one formed by vapor deposition, it has ductility required for securing its workability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used in a wide range of fields such as building materials, home appliances, and automobiles, and exhibits excellent corrosion resistance.
TECHNICAL FIELD The present invention relates to a Cr-based multi-layer plated steel sheet and a method for manufacturing the same.

[0002]

2. Description of the Related Art In order to improve the corrosion resistance of a steel sheet, a Zn plating layer is formed on the surface of the steel sheet by hot dipping, electroplating or the like. The corrosion resistance required for a Zn-plated steel sheet becomes severe as the corrosiveness of the use environment becomes stronger.
In the hot dipping method, the corrosion resistance can be improved by increasing the coating weight. However, increasing the thickness of the Zn plating layer has a limit from the viewpoint of manufacturing, and as a result, there is a limit to improving the corrosion resistance. Further, if the Zn plating layer is made thick, defects such as galling and flaking frequently occur during press molding. In addition, spot weldability is also reduced.

In order to form a thick Zn plating layer by the electroplating method, methods such as increasing the number of plating baths and reducing the plate passing speed of a plating original plate passing through the plating baths are adopted. With these methods, an increase in manufacturing cost and a decrease in continuous productivity cannot be avoided. In addition, even in a plating layer formed by the electroplating method, the problem of quality becomes the same as in the case of hot dipping as the coating weight increases.
Therefore, a method of improving the corrosion resistance by changing the composition of the plating layer has been adopted.

By the electroplating method, a Zn—Ni alloy plated steel sheet or the like can be manufactured as a Zn plated steel sheet having excellent corrosion resistance. However, Zn- produced by electroplating method
The Ni alloy plating layer becomes a hard and brittle plating layer, and easily causes defects such as peeling during press molding. The defective portion of the plated layer becomes a starting point of corrosion, and the original corrosion resistance of the plated steel sheet cannot be expected. The powder separated from the plating layer causes point-like pressure scratches in press molding, that is, pimple defects. Further, when the powder separated from the plating layer is deposited on the mold, the inflow resistance of the plated steel plate into the mold increases, and the plated steel plate may be broken during the forming process.

In the hot dipping method, Zn-Al alloy plated steel sheets and the like are manufactured as plated steel sheets having excellent corrosion resistance. However, an alloy layer is formed between the base steel and the plated layer on the Zn-Al alloy plated steel sheet manufactured by the hot dip coating method. This alloy layer is hard and brittle and similarly promotes peeling of the plating layer during press forming. Vapor deposition plating is being studied as an alternative to conventional electroplating, hot dipping, and the like. In the vapor deposition method, Cr, which has a great effect in improving the corrosion resistance, can be incorporated as a component of the plating layer. For example, when a Zn-Cr alloy plating layer is formed on the surface of a base steel by a vapor deposition method, a plated steel sheet having excellent corrosion resistance can be obtained in JP-A-1-111864 and JP-A-4-9459. Has been done. Further, JP-A-3-170659 discloses that Cr of a plating layer.
By adjusting the content to 1 to 40% by weight, Zn-
It has been reported that the workability of the Cr alloy vapor deposition plating material is improved.

[0006]

The Zn-Cr alloy vapor-deposited plating layer has improved corrosion resistance as the Cr content increases, but it becomes brittle and the workability deteriorates. Therefore, when a Zn-Cr alloy vapor deposition plating material having a high Cr content is press-molded, cracks may occur in the plating layer, or powdering may occur in which the plating layer itself is crushed and peeled off. As a result, the plated layer after processing contains defects. Therefore, a hard plating layer that cannot withstand processing is
Even if it has excellent corrosion resistance, it is not suitable as a practical material. The present invention has been devised to solve such a problem, and is achieved by forming a Zn layer and a Cr layer into multiple layers without alloying which causes hardening, embrittlement, and the like. It is an object of the present invention to provide a plated steel sheet having excellent corrosion resistance and workability.

[0007]

High Corrosion Resistance Zn /
In order to achieve the object of the Cr-based multi-layer plated steel sheet, a Cr layer and a Zn layer are sequentially laminated as a first layer and a second layer on the surface of a base steel. The multi-layer plating layer including the Cr layer and the Zn layer is formed on one side or both sides of the original plating plate.
This multi-layer plated steel sheet, the plating original plate is introduced into the vacuum chamber,
After the Cr layer is formed on the surface of the steel sheet by the vapor deposition method, the Zn layer is subsequently vapor deposited. As the plating base plate, various steel plates such as ordinary steel, alloy steel, ferritic stainless steel, and austenitic stainless steel are used.

Vapor deposition and electroplating are known as industrial methods for forming a Cr plating layer on the surface of a steel sheet. In the present invention, the Cr layer is preferably formed by vapor deposition. In the electroplating method, hydrogen is easily mixed in the plating layer, and the mixed hydrogen may cause the Cr layer to become brittle. Good workability cannot be obtained with a brittle plating layer. Further, the electroplating reaction of Cr not only consumes a large amount of electricity because it is a reduction reaction of Cr ⁺⁶ to Cr.
The current efficiency is as low as about 20%. Therefore, in adopting the high-speed mass production method, the electroplating of Cr is disadvantageous.
Further, since Cr ions have many valences, there is a problem in operation such that it is difficult to control the plating bath. In this respect,
In the vapor deposition method, hydrogen is not mixed in the Cr layer, and there is no risk that the plating layer becomes brittle.

As the vapor deposition method, a vacuum vapor deposition method by electron beam heating or an arc vapor deposition method is adopted because Cr has a high melting point. Among them, in the arc vapor deposition method, metal Cr exhibits sublimation property, and thus it is difficult to control evaporation by other methods.
It is suitable as a method of controlling the evaporation amount of the. The Zn layer is preferably formed by a vacuum vapor deposition device equipped with a Zn vapor guide hood. The Zn vapor vaporized by the Zn evaporator is introduced to the tip of the hood through the vapor guiding hood and is vapor-deposited on the surface of the plating original plate which is continuously running. It is preferable that the tip of the vapor guide hood has an opening that is close to the original plating plate and is slightly wider than the original plating plate.

The vapor guide hood prevents the Zn vapor from flowing out to other than the plating original plate, and improves the utilization efficiency of the evaporated Zn vapor. Further, it is possible to prevent troubles such as a failure of a drive system and a poor electrical insulation caused by vapor deposition of Zn vapor on an internal device other than the plating original plate. Furthermore, the steam guide hood wider than the original plating plate has the effect of making the thickness distribution of the Zn layer uniform in the plate width direction of the original plating plate. When the plating original plate is plated on both sides, when there is a risk of Zn vapor leaking from both ends in the plate width direction of the plating original plate, the guide hoods facing both sides of the plating original plate are opposed to each other. Then, by sealing the side surface of the guide hood, scattering of the leaked Zn vapor is prevented. The adhesion and deposition of Zn vapor on the inside of the guide hood can be suppressed by heating and holding the hood above the evaporation temperature of Zn.

Further, when forming the Cr layer and the Zn layer, the original plating plate is continuously passed through the equipment connected to the respective vapor deposition chambers, so that the Zn / Cr multi-layer plated steel sheet having excellent corrosion resistance can be produced with high productivity. It becomes possible to manufacture efficiently. In particular, the Cr of the first layer is a metal that is easily oxidized, and when the surface of the Cr plating layer is oxidized, the adhesion of the Zn plating layer is significantly reduced.
In order to secure the adhesiveness with the plating layer, it is necessary to deposit Zn after Cr deposition.

As the plating apparatus, for example, the equipment configuration shown in FIG. 1 is adopted. The plating base plate 10 is rewound from the pay-off reel 11, and the deflector rolls 12 and
It is guided by 13 and introduced into the vacuum chamber 20. Vacuum chamber 20
Further, it is guided inside by deflector rolls 14 and 15, is sent out from the vacuum chamber 20, and is then wound around a winding reel 16. An inlet side vacuum seal 21 and an outlet side vacuum seal 22 are provided on the inlet side and the outlet side of the vacuum chamber 20, respectively. The inside of the vacuum chamber 20 between the inlet side vacuum seal 21 and the outlet side vacuum seal 22 is formed by the partition walls 23 to 25 having slits through which the plating base plate 20 passes, by the pretreatment zone 30, the Cr vapor deposition zone 40, and the Zn. Deposition zone 5
It is classified into 0. The inside of the vacuum chamber 20 is set by the vacuum pumps 27 and 28 and a vacuum pump (not shown).
The pressure is reduced to about 10 ⁻³ Pa.

In the pretreatment zone 30, a high frequency heating device 31 and an ion beam etching device 32 are arranged along the running direction of the plating original plate 10. Pretreatment zone 3
The plating base plate 10 sent to 0 is the high frequency heating device 3
After being heated to a predetermined temperature by 1, the ion beam 33 emitted from the ion beam etching device 32 is irradiated. As a result, the surface of the original plating plate 10 is etched, and the active state of the plated metal is adjusted.
In the Cr vapor deposition zone 40, a Cr vapor deposition apparatus 41 such as an arc vapor deposition system is arranged on both sides of the traveling original plate 10. In the Zn vapor deposition zone 50, Zn vapor deposition devices 51 are arranged on both sides along the traveling direction of the original plating plate 10. The Zn vapor deposition device 51 uses the Zn vaporized from the Zn bath 52.
A guide hood 53 that guides steam toward the plating base plate 10.
Is equipped with. The guide hood 53 has an opening 54 wider than the original plating plate 10, and a slit 55 through which the original plating plate 10 passes is formed in the opening 54.

In the equipment configuration shown in FIG. 1, the high frequency heating device 3 is used.
1, ion beam etching device 32, Cr vapor deposition device 4
1, a Zn vapor deposition device 51 and the like are vertically arranged inside the vacuum chamber 20. However, the arrangement form is not limited to this, and can be appropriately determined in consideration of the space of the vacuum chamber 20 and the shapes of various devices. Further, as the Cr vapor deposition apparatus 41, it is preferable to adopt an arc vapor deposition method, but if controllability, stability, etc. are not so required, other methods such as electron beam heating can also be used.

[0015]

The Zn / Cr multi-layer plated steel sheet according to the present invention is continuously manufactured by depositing a Cr layer on the surface of a base steel and then depositing a Zn layer. Corrosion resistance is ensured by the Zn layer, which acts as a sacrificial anode. The sacrificial anticorrosive action is maintained until the Zn is exhausted. In the multi-layer plating layer according to the present invention, the Cr layer existing as the first layer has an action of reducing the corrosion rate of the Zn layer, so that the sacrificial anticorrosion action is maintained for a long period of time. The second Zn layer is a metal layer exhibiting sufficient ductility. The first Cr layer is also rich in ductility, unlike the one formed by electroplating. Therefore, it is possible to perform a high degree of forming on the plated steel sheet without causing a crack penetrating the plating layer. Further, when the arc vapor deposition method is adopted, Cr, which is a sublimable metal, can be vaporized at a high speed while stably controlling it. Therefore, the thickness of the Cr plating layer in the Zn / Cr-based multi-layer plating layer to be formed can be controlled with high accuracy, and a multi-layer plated steel sheet having both required corrosion resistance and workability can be obtained.

[0016]

Example A steel plate having a plate thickness of 0.5 mm and a plate width of 100 mm was used as the plating original plate 10. This plating plate 10
Had the composition shown in Table 1.

[0017]

[Table 1]

After degreasing and pickling the original plating plate 10, FIG.
A Zn / Cr multi-layer plated steel sheet was manufactured using the apparatus shown in FIG. In this example, the original plating plate 10 was subjected to ion beam etching under the conditions shown in Table 2. When the source gas of the ion beam is supplied to the ion beam etching device 32, the degree of vacuum in the pretreatment zone 30 is 0.05 P.
It decreased to about a.

[0019]

[Table 2]

While the activated original plate 10 was continuously passed through the Cr vapor deposition zone 40 and the Zn vapor deposition zone 50, multi-layer plating was performed under the conditions shown in Table 3.

[0021]

[Table 3]

A test piece was cut out from the obtained multi-layer plated steel sheet and subjected to a salt spray test according to JIS Z2371. Then, the time until red rust, which occupies 5% of the surface of the test piece, was measured. The corrosion resistance of the multi-layer plated steel sheet was evaluated based on this 5% red rust occurrence time. The workability was evaluated by subjecting the test piece to a draw bead test and measuring the amount of peeling of the plating. Load 5 for draw bead test
It was carried out under the conditions of 00 g and a pulling speed of 200 mm / min. The test results are shown in FIG. For comparison, a plated steel sheet having a Zn layer directly provided on the surface of the steel sheet (Test No. 4) without vapor deposition of a Cr layer (Test No. 4) and a plated steel sheet alloyed with Zn and Cr (Test No. 5) were manufactured. .

As is apparent from FIG. 2, the test pieces of test Nos. 1 to 3 according to the present invention have significantly improved corrosion resistance as compared with the test piece of Test No. 4 having no Cr layer. I understand. Looking at the workability, the test pieces of test numbers 1 to 3
The workability is almost the same as the test piece of Test No. 4 having no Cr layer. In this respect, the test piece of Test No. 5 on which the Zn—Cr alloy plating layer was formed had an extremely large amount of plating peeling and was inferior in workability. As described above, the multi-layer plated steel sheet in which the Zn layer and the Cr layer are laminated according to the present invention is
Excellent in both corrosion resistance and workability.

[0024]

As described above, in the present invention, the plating layer having a multilayer structure in which Cr and Zn are laminated as the first layer and the second layer, respectively, is formed on the surface of the base steel. The presence of the Cr layer as the first layer reduces the corrosion rate of Zn in the second layer as compared with the plating layer containing only Zn, and the sacrificial anticorrosive action of Zn is maintained for a long period of time.
Further, since the Zn layer of the second layer is originally a metal layer having sufficient ductility, and the Cr layer of the first layer formed by vapor deposition also has ductility, the workability of the entire plating layer is good. Is. Further, by continuously depositing Cr and Zn in the integrated vacuum chamber, Zn can be efficiently and inexpensively produced.
/ Cr-based multi-layer plated steel sheet is manufactured at high speed.

[Brief description of drawings]

FIG. 1 Equipment configuration for producing Zn / Cr multi-layer plated steel sheet

[Fig. 2] Evaluation results of corrosion resistance and workability according to the type of plating layer

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

Claims (2)

[Claims] 1. A highly corrosion-resistant Zn / Zn layer in which a Cr layer and a Zn layer are sequentially laminated as a first layer and a second layer on the surface of a base steel.
Cr-based multi-layer plated steel sheet. 2. A method for producing a highly corrosion-resistant Zn / Cr multi-layer plated steel sheet, which comprises introducing the steel sheet into a vacuum chamber, forming a Cr layer on the surface of the steel sheet by a vapor deposition method, and subsequently depositing Zn.