JPH06108217A - Method and device for manufacturing high corrosion resistant coated steel sheet - Google Patents

Abstract

PURPOSE:To manufacture a high corrosion resistant coated steel sheet without bringing over-load on the equipment by adopting gas reduction to surface activa tion of a steel sheet, at the time of executing hot-dipping aluminizing to the steel sheet vapor-depositing Cr as a substrate. CONSTITUTION:The original sheet 10 for coating is passed through a gas reducing furnace 30 to activate the surface of the steel sheet with the reducing gas. The original sheet 10 for coating with activated surface is fed in a vacuum vessel 50, and after vapor-depositing Cr in a Cr vapor-depositing device 54, this sheet is introduced into the hot-dipping aluminizing bath 61. The vacuum vessel 50 is shut off from the gas reducing furnace 30 with a vacuum seal device 40 on the inlet side and sealed with a vacuum seal part 63 of molten Al in a snout 62 on the outlet side. As the original sheet 10 for coating is introduced into the vacuum vessel under the condition activating the surface and the Cr vapor-deposition is executed, the molten Al is stuck to the original sheet 10 for coating at good coating performance without causing reoxidation of Cr, and the hot-dipping aluminizing layer without any defect, such as non-coating position, low stickiness, is formed.

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 an Al-plated steel sheet having excellent corrosion resistance.

[0002]

2. Description of the Related Art Hot-dip Al-plated steel sheets are used as various electric appliances, outer plate materials for household appliances, automobile parts, etc. by utilizing the excellent corrosion resistance, heat resistance and good surface appearance of Al plated layers. Recently, in order to further improve the corrosion resistance of the Al plating layer, Cr is added between the base steel and the Al plating layer.
Layers have come to intervene. When pre-plating with Cr and then hot-dip Al plating, Japanese Patent Application No. 4-59001
6, Japanese Patent Application No. 4-59017, Japanese Patent Application No. 4-73560
As described in No. 3, a highly corrosion-resistant Al-plated steel sheet characterized by a plated layer structure can be obtained. C as an underlayer
The Al-plated steel sheet provided with the r-plated layer is manufactured in the following process, for example.

After activating the surface of the steel sheet by plasma etching or ion beam etching in a vacuum chamber provided in the preceding stage of the Al plating bath, Cr is deposited and then A
A method of introducing a steel plate into a plating bath. After Cr is plated by a vapor deposition method, an electroplating method, or the like using a facility different from the Al plating facility, the surface of the Cr plating layer is removed by plasma etching or ion beam etching in a vacuum chamber provided in the preceding stage of the Al plating bath. Activate,
Then, a method of introducing a steel plate into the Al plating bath.

[0004]

The Al plating layer formed on Cr, which is the underlayer, is greatly affected by the adhesion state of the Cr plating layer to the undercoat steel and the surface properties of the Cr plating layer itself. In particular, Cr is a material that easily forms a surface oxide film and causes defects such as non-plating and poor adhesion in the Al plating layer formed thereon. Therefore, prior to Al plating, the surface of the Cr plating layer is activated by plasma etching or ion beam etching as described above. However, plasma etching,
Ancillary equipment such as ion beam etching is required.

Further, in the case of using Cr as a base layer, it is possible to perform hot-dip Al plating after activating the surface of a Cr-plated steel sheet by gas cleaning in JP-B-63-44825. Has been introduced. However, in this case, as shown in the examples, after electroplating Cr with separate equipment, gas cleaning and hot-dip Al plating are performed. Therefore, problems caused by the strong oxide film formed on the Cr plating layer are introduced, and defects are likely to occur in the Al plating layer formed.

The present invention has been devised in order to solve such a problem. Gas reduction is adopted instead of plasma etching or ion beam etching, and Cr vapor deposition and hot-dip Al plating are performed in a series of vacuum chambers. By carrying out the above, it is intended to reduce the equipment load caused by the incidental equipment and to manufacture the highly corrosion-resistant plated steel sheet at a lower cost.

[0007]

In order to achieve the object, a method for producing a highly corrosion-resistant plated steel sheet according to the present invention, in which a reducing gas is used to activate the surface of the steel sheet, the steel sheet is introduced into a vacuum chamber. The base metal is vapor-deposited on the surface of the steel plate in a vacuum chamber, and then the steel plate is introduced into a molten Al plating bath maintained in the same vacuum atmosphere. Cr is a typical base metal, but Ni,
Cu, Ti, Co, Zr, etc. can also be used. In the following description, Cr is explained as a typical example,
This does not constrain the invention in any way. The steel sheet plated with the base metal is introduced into a molten Al plating bath having a Si concentration of 1 to 13% by weight and subjected to molten Al plating. This molten Al plating bath is preferably saturated with Fe and Cr.

[0008]

[Function] Al-killed steel, Ti-added steel, rimmed steel, etc., when heated in a reducing gas such as hydrogen or a mixed gas of hydrogen-nitrogen, the oxide film on the surface is easily reduced and removed, and an active metal surface is obtained. Can be Other steel types that can be activated by gas reduction include Cr-containing steel of 5% by weight or less,
There are 2 wt% or less of Si-containing steel, 4 wt% or less of Mn-containing steel, P-added steel, high carbon steel and the like. When this gas reduction treatment is used for surface activation before Cr vapor deposition, a highly corrosion-resistant plated steel sheet can be manufactured with a simple equipment configuration, and non-plating caused by an oxide film formed on the steel sheet surface and the Cr layer surface. , No defects such as poor adhesion are brought into the hot-dip Al plating layer.

In the equipment used in the present invention, a gas reduction furnace is arranged in front of a vacuum tank in which a Cr vapor deposition section and a molten Al plating tank are continuously arranged. The surface of the steel sheet to be plated is activated in a gas reduction furnace. Since the gas reduction furnace and the vacuum chamber are connected by the vacuum sealing device, the activated steel sheet is introduced into the vacuum chamber without being re-oxidized while maintaining the active surface. Therefore, the Cr vapor deposition layer and then the molten Al plating layer are also formed without being affected by the oxide film, and a sound plating layer is formed.

The steel sheet introduced into the gas reduction furnace is activated by the reducing gas. As the reducing gas, a mixed gas of hydrogen and nitrogen is more preferable than hydrogen gas having a purity of 100% in terms of cost. When using a mixed gas, it is necessary to increase the hydrogen concentration in order to perform the activation treatment on the surface of the steel sheet at high speed. For example, when a low carbon steel such as Al-killed steel and Ti-added steel is used as the plating original plate, the hydrogen concentration of the mixed gas is maintained at 2% by volume or more. Further, in order to suppress reoxidation of the original plating plate, it is preferable to use a dry reducing gas having a dew point of −10 ° C. or lower.

When passing through the gas reduction furnace, the steel plate is heated to 300 ° C.
It is heated to the above temperature. This steel plate temperature is not only necessary for high-speed surface activation by gas reduction, but also has a favorable effect on the subsequent Cr vapor deposition. That is, when the steel plate temperature is set to 300 ° C. or higher, surface diffusion of evaporated Cr becomes active and a dense Cr evaporated layer is formed. As a result, the corrosion resistance after hot dip Al plating is improved. When an Al killed steel or a Ti-added steel is used as a plating base plate, the surface of the steel plate can be activated in a short time within 10 seconds by gas reduction at a temperature of 300 ° C or higher.

The activated steel sheet is introduced into a vacuum chamber,
Cr is vapor deposited. As the vapor deposition method, a resistance heating vapor deposition method, an electron beam heating vapor deposition method, an arc vapor deposition method, a sputter vapor deposition method, or the like can be adopted. Among them, the solid cathode type arc vapor deposition method is preferable in consideration of high-speed productivity, stability, cost and the like. The deposited Cr layer is in a very active state and easily reacts with residual gas in a vacuum to become inactive. Therefore, it is preferable to maintain the vacuum atmosphere of the Cr vapor deposition section at a high vacuum of 1 × 10 ⁻² Torr or less to suppress the reaction between Cr and the residual gas.

Since the steel sheet on which the Cr layer in the active state is formed is introduced into the hot-dip Al plating bath, the hot-dip A on the Cr layer is
l The throwing power of the plated layer is very good. That is, the Cr layer exhibits good wettability with molten Al,
It does not cause defects such as non-plating and poor adhesion. The molten Al plating bath preferably contains 1 to 13 Si.
An aluminum alloy containing wt% is used. Si
Due to the inclusion, not only a plated steel sheet with high corrosion resistance can be obtained, but also corrosion of pots, snouts, etc. due to molten Al is suppressed. Further, when a saturated amount of Fe, Cr, or the like is added to the molten Al plating bath and the temperature of the plating bath is set to 680 ° C. or lower, corrosion of the pot, snout, etc. can be further suppressed. For example, if the temperature of the plating bath is 650 ° C,
0.1 to 3 wt% Fe and Cr are added to the hot dip Al plating bath.

The apparatus for producing a plated steel sheet according to the present invention comprises a vacuum chamber and a Cr chamber between the gas reduction furnace and the molten Al plating equipment.
It has a structure with a vapor deposition section. Therefore, the conventional "non-oxidizing furnace + gas reduction furnace" type molten Al plating equipment, "degreasing apparatus + gas reduction furnace" type molten Al plating equipment, etc. are modified between the gas reduction furnace and the molten Al plating bath. Just good. By this simple modification, it becomes possible to manufacture a galvanized steel sheet having high corrosion resistance with very little equipment cost. For example, when a vacuum tank and a Cr vapor deposition section are incorporated in a molten Al plating equipment of a “non-oxidizing furnace + gas reducing furnace” type, the equipment configuration shown in FIG. 1 is adopted.

The original plating plate 10 is unwound from a payoff reel 11 and introduced into a non-oxidizing furnace 20 via a deflector roll 12. In the non-oxidizing furnace 20, fats and oils such as rolling oil adhering to the surface of the steel sheet are decomposed, volatilized and removed.
The original plating plate 10 is sent from the non-oxidizing furnace 20 to the gas reduction furnace 30. The gas reduction furnace 30 includes a heating zone 31 and a cooling zone 32, and circulates hydrogen or a mixed gas of hydrogen and nitrogen. The original plating plate 10 is heated to a temperature of 300 ° C. or higher in the heating zone 31 under a reducing atmosphere, and oxides and the like on the surface are reduced and removed. The plating base plate 10 whose surface is activated by gas reduction is cooled to 200 in the cooling zone 32.
After being cooled to an appropriate temperature of ˜700 ° C., it is sent to the vacuum chamber 50 through the vacuum sealing device 40.

The vacuum chamber 50 is hermetically isolated from the gas reduction furnace 30 by a vacuum sealing device 40. The vacuum tank 50 is, for example, 1 × 1 by the vacuum pumps 21 and 22.
The pressure is reduced to a vacuum of 0 ^-2 torr or less. Inside the vacuum chamber 50, an auxiliary heating device 53 and a Cr vapor deposition device 54 are arranged from the upstream side along the plate passing direction of the plating original plate 10. The temperature of the original plating plate 10 is adjusted by the auxiliary heating device 53 so that the plate temperature when introduced into the molten Al plating bath 64 becomes the same as the bath temperature of the molten Al plating bath 64.
At this time, by controlling the plate temperature of the original plating plate 10 introduced into the vacuum chamber 50, the heating by the auxiliary heating device 53 can be reduced or omitted. Then, Cr vapor deposition is performed on the temperature-controlled original plating plate 10.

A molten Al plating tank 60 is arranged on the outlet side of the vacuum tank 50. The molten Al plating bath 61 accommodated in the molten Al plating tank 60 raises the snout 62 according to the degree of vacuum of the vacuum tank 50, and becomes a vacuum seal portion 63. Between the vacuum seal part 63 and the Cr vapor deposition device 54,
Partition wall 55 having slits through which the plating base plate 10 passes
Is provided. The sink rolls 64 and 65 are immersed in the molten Al plating bath 61. The original plating plate 10 introduced into the molten Al plating bath 61 is a sink roll 6
After going around 4, 65, it is pulled up from the molten Al plating bath 61. The plated steel sheet 15 that has been pulled up is aluminized by the gas wiping device 66 located immediately after the pulling up.
The amount of plating applied is adjusted. Next, plated steel sheet 15
Is taken up by the take-up reel 19 via the deflector rolls 16 to 18.

In this way, the plating original plate 10 whose surface has been activated is introduced into the vacuum chamber without being exposed to the atmosphere, and Cr vapor deposition and hot Al plating are performed in the vacuum chamber 50. Therefore, hot-dip Al plating is formed on the active Cr surface, and a high-quality hot-dip Al-plated steel sheet without defects such as non-plating and poor adhesion is manufactured.

[0019]

EXAMPLE Using the hot dip Al plating equipment shown in FIG.
Al-killed steel plate having a plate thickness of 0.5 mm and a plate width of 100 mm is used as a plating base plate 10 and melted at a line speed of 30 m / min.
Plated. The Al killed steel used was C: 0.02% by weight, Si: 0.04% by weight, Mn: 0.19% by weight,
It contained S: 0.11% by weight and Al: 0.045% by weight. In the non-oxidizing furnace 20, natural gas was burned at an air-fuel ratio of 0.87 to remove oils and fats adhering to the surface of the original plating plate 10 and the original plating plate 10 was heated to 670 ° C. Then, the original plating plate 10 was introduced into the gas reduction furnace 30 in which a mixed gas of H ₂ : N ₂ = 1: 1 (dew point −40 ° C.) was circulated, and after heating to 720 ° C. in the heating zone 31, It cooled to 650 degreeC with the cooling zone 32.

The vacuum chamber 50 was maintained at a vacuum degree of 1 × 10 ^-1 Pa by vacuum pumps 51 and 52. After the temperature of the original plating plate 10 was adjusted by the auxiliary heating device 53 so that the plate temperature became 650 ° C. when immersed in the molten Al plating bath 61, Cr was added.
A solid cathode type arc vapor deposition apparatus as the vapor deposition apparatus 54 is used to deposit Cr having a thickness of 0.1 to 0.5 μm on the surface of the original plating plate 10.
The layers were deposited. The Cr-deposited original plating plate 10 was introduced into a molten Al plating bath 61. This molten Al plating bath 6
1 is Si: 9.1% by weight, Fe: 1.8% by weight, C
r: 0.16% by weight, balance: Al excluding unavoidable impurities
And the temperature was controlled at 650 ° C. Melt A
The coating amount of the plated steel sheet 15 on which the 1-plating was applied was adjusted to 30 g / m ² per side by the gas wiping device 66.

No defects such as non-plating were detected in the obtained plated steel sheet, and the adhesiveness of the molten Al plating layer was good. A test piece was cut out from this plated steel plate and JIS Z
It was subjected to a salt spray test according to 2371. As is clear from Table 1 showing the test results, the obtained plated steel sheet was
It had very good corrosion resistance. In Table 1, S
As a comparative example, a galvanized steel sheet was used in which a molten Al plating bath containing 9.5% by weight of i and saturated with Fe was used to form a molten Al plating layer of 30 g / m ² with one-sided coating amount and without providing a Cr underlayer. Show.

[Table 1]

[0022]

As described above, in the present invention, gas reduction treatment, Cr vapor deposition and hot dip Al plating are performed as a series of treatments, and the steel sheet whose surface is activated by gas reduction is exposed to the atmosphere. Instead, it is installed in a vacuum chamber. Therefore, a good Cr underlayer is formed without being affected by reoxidation, the throwing power of molten Al is improved, and a molten Al plated layer having no defects such as non-plating is formed. The obtained plated steel sheet is used as a material exhibiting extremely excellent corrosion resistance even in a harsh working atmosphere due to the synergistic corrosion resistance of the Al plating layer and the Cr layer. In terms of equipment, it is only necessary to remodel between the gas reduction furnace and the plating bath in the conventional molten Al plating equipment such as the "non-oxidizing furnace + gas reducing furnace" type and the "degreasing device + gas reducing furnace" type. Therefore, the facility burden is also reduced.

[Brief description of drawings]

FIG. 1 is a hot dip Al plating facility used in an example of the present invention.

[Explanation of symbols]

10 Plated original plate 15 Plated steel plate 20
Non-oxidizing furnace 30 Gas reduction furnace 40 Vacuum sealing device 50
Vacuum tank 54 Cr deposition apparatus 60 Hot dip Al plating tank 61 Hot dip Al plating bath

Claims (5)

[Claims] 1. After activating the surface of a steel sheet using a reducing gas, the steel sheet is introduced into a vacuum chamber, a base metal is vapor-deposited on the surface of the steel sheet in the vacuum chamber, and then the same vacuum atmosphere is maintained. A method for producing a highly corrosion-resistant plated steel sheet, which comprises introducing the steel sheet into the molten Al plating bath. 2. The manufacturing method according to claim 1, wherein the base metal is Cr. 3. The molten Al plating bath contains 1 to 13% by weight of S.
The manufacturing method according to claim 1, which contains i. 4. The method according to claim 2, wherein the molten Al plating bath is saturated with Fe and Cr. 5. A gas reducing furnace for activating the surface of a steel sheet to be plated with a reducing gas, a vacuum tank in which a Cr vapor deposition section and a molten Al plating tank are continuously arranged, and an outlet of the gas reducing furnace. An apparatus for manufacturing a highly corrosion-resistant plated steel sheet, characterized in that a vacuum sealing device for air-tightly connecting an inlet side of the vacuum tank is provided on the side, and an outlet side of the vacuum tank is vacuum-sealed with a molten Al plating bath.