JP3291111B2 - Method for producing hot-dip Al-coated steel sheet having Zn diffusion layer - Google Patents

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 hot-dip Al-coated steel sheet having a Zn diffusion layer.

[0002]

2. Description of the Related Art At present, Al-based plated steel sheets are made of pure Al.
A steel plate is immersed in a plating bath or an Al-based alloy plating bath added with Si, Mn, Cr, Ti, Mg, Fe, etc., plated, and then manufactured by a hot-dip plating method that adjusts the amount of plating by gas drawing or the like. Most are what is being done. Although this hot-dip Al-plated steel sheet has high corrosion resistance, the sacrificial corrosion protection of the plating layer does not work in the early stage of atmospheric corrosion.
Exposed portions of the steel plate such as scratched portions and end surfaces are corroded, and red rust is generated therefrom. Therefore, in order to impart a sacrificial anticorrosion effect to the plating layer, it has been studied to apply Zn plating on the Al-based plating layer.

[0003] As a method of applying Zn plating on the corrosion-resistant Al-based plating layer without deteriorating its characteristics, an electroplating method, a vapor deposition plating method, and the like can be considered. Is covered by Zn
The adhesion of plating is inferior. In the case of electroplating or the like, this poor adhesion can be improved by performing a pre-treatment of zincate treatment. However, since the additive element in aluminum forms an uneven portion in the plating layer, the adhesion of the plating layer is reduced. There is a problem of non-uniformity. Furthermore, since zincate treatment requires a long time for the treatment, it is difficult to apply it to pretreatment of a continuous electric Zn plating line.

As another method of applying Zn plating to an Al-based plated steel sheet, a method of spraying Zn powder can be considered. For example, JP-A-1-79358, JP-A-2-93
No. 053 proposes a method of spraying various metal powders onto a hot-dip Zn-coated steel sheet immediately after rising from a plating bath to produce a Zn-based alloy-coated steel sheet.
It is also conceivable to apply this to a hot-dip Al-based plated steel sheet. However, a method of diffusing Zn into a hot-dip Al-based plated steel sheet has not been reported in detail.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for producing a hot-dip Al-coated steel sheet having a diffusion layer in which Zn powder is sprayed on a hot-dip Al-coated steel sheet to diffuse Zn into the coating layer. is there.

[0006]

According to the present invention, a steel sheet is made of aluminum.
In the production of a hot-dip Al-coated steel sheet that adjusts the coating weight after plating in a system plating bath, the flow rate when the Zn powder collides with the steel sheet while the plating layer is in an unsolidified state after the coating weight adjustment is 5 to 120 m. It is sprayed together with a carrier gas of / sec to diffuse the Zn powder into the plating layer.

[0007]

FIG. 1 shows a method of manufacturing a hot-dip Al-based steel sheet according to the present invention. After cleaning the surface of a steel sheet 1 in a pre-treatment zone, a snout 2 is used for a synchrochlor 3 in an Al-based plating bath. 4, plating is carried out, and then raised above the Al-based plating bath 4, and the amount of plating applied is adjusted by a gas wiping nozzle 5. Then, after the adjustment of the plating adhesion amount, the Z disposed on both sides in a state where the plating layer is in an unsolidified state.
Zn powder is sprayed from the n-powder spray nozzle 6, and Zn is diffused into the plating layer by the heat of the steel sheet. Here, as the Zn powder spray nozzle 6, a nozzle having a slit-shaped spray port is used to spray Zn powder uniformly over the entire width of the plate. In addition, it is preferable that the Zn powder spray nozzle 6 be movable up and down because the solidification position of the plating layer varies depending on the thickness of the steel sheet 1 and the amount of plating. After the Zn powder is sprayed, it is generally allowed to cool in the air or forced air cooling. However, when it is desired to proceed with diffusion, for example, a heating device 7 is arranged on the Zn powder spray nozzle 6 to continue thermal diffusion. Is also good.

The Zn powder is sprayed by accelerating with a carrier gas having a flow velocity of 5 to 120 m / sec at the time of collision with the plating layer. This is because an oxide film is formed on the surface of the plating layer immediately after hot-dip plating, and it is necessary to break through the oxide film and drive Zn powder into the plating layer to diffuse it. If the flow velocity at the time of collision of the carrier gas with the plating layer is less than 5 m / sec, the oxide powder on the surface cannot be pierced, so that the Zn powder simply adheres to the plating layer surface, and the inside of the plating layer Does not spread. However, the flow rate of the carrier gas at the time of collision with the plating layer is set to 120
If the speed is higher than m / sec, the surface of the plating layer is roughened by the collision of Zn powder, and the appearance is significantly impaired. In the present invention, the spraying speed of the Zn powder is defined by the flow rate of the carrier gas, because the two speeds are considered to be approximately the same.

As the carrier gas, air, N ₂ , Ar
Are preferred. The smaller the particle size of the Zn powder, the better from the viewpoint of facilitating diffusion, but it is preferably 1 to 10 μm in consideration of handleability and economy. There is no particular limitation on the temperature of the carrier gas or the Zn powder, but when the amount of the sprayed Zn powder is large, to facilitate diffusion,
It is desirable to spray after heating in the preheating chamber.

The Zn concentration in the plating layer and the thickness of the Zn diffusion layer are adjusted by the amount of the Z powder sprayed, the carrier gas flow rate, the temperature of the steel sheet at the time of spraying the Zn powder, and the cooling or heating conditions after the spraying. When it is desired to form a Zn diffusion layer only on the plating layer on one side of the steel sheet, Zn powder is sprayed only from the Zn powder spray nozzle 6 on one side of FIG.

[0011]

【Example】

Example 1 At a pilot plant of a continuous hot-dip plating line as shown in FIG. 2, a degreased plate thickness of 0.8 mm and a plate width of 100 m
m-killed low-carbon steel sheet was passed through to produce a hot-dip Al-based plated steel sheet having a Zn diffusion layer. The steel sheet 1 is supplied from a pay-off reel 8 and is subjected to 50% H ₂ -N _{2 in} an annealing furnace 9.
After annealing and reduction at 700 ° C. in an atmosphere, the plate was dipped from Snout 2 into a plating bath 4 (bath temperature: 660 ° C.) having a composition of Al-9.5% Si-1.8% Fe. After plating, plating weight 60g / m with gas wiping nozzle 5
² (one side), Zn powder was sprayed from the Zn powder spray nozzle 6 under the following conditions, and the air jet cooler was used.
After cooling at 10, it was wound up on a tension reel 11. Table 1 shows the presence or absence of a Zn diffusion layer, the Zn content, and the surface state of the plated layer of the manufactured Al-based plated steel sheet. In addition, the steel plate temperature was measured with the radiation thermometer. Steel sheet temperature: 570 to 630 ° C. Zn powder average particle size: 5 μm Carrier gas: N ₂ gas Carrier gas flow rate upon collision with the plating layer: 1 to 125 m
/ sec Carrier gas pressure: 1 kg / cm ² Carrier gas, Zn powder temperature: room temperature

[0012]

[Table 1]

Example 2 In Example 1, the temperature of the steel sheet at the time of spraying the Zn powder and the flow rate of the carrier gas at the time of collision with the plating layer were variously changed to obtain a molten steel.
An l-plated steel sheet was manufactured, and the relationship between the Zn content in the plating layer, the steel sheet temperature, and the carrier gas flow velocity at the time of collision with the plating layer was investigated. The result is shown in FIG.

[0014]

As described above, according to the present invention, a hot-dip Al-based steel sheet having a Zn diffusion layer can be manufactured.

[Brief description of the drawings]

FIG. 1 shows molten Al having a Zn diffusion layer according to the present invention.
1 shows a method for producing a system-plated steel sheet.

FIG. 2 shows a pilot plant of a continuous hot-dip galvanizing line used for manufacturing a hot-dip Al-coated steel sheet having a Zn diffusion layer in Examples.

FIG. 3 is a graph showing the relationship between the Zn content in the plating layer of the hot-dip Al-coated steel sheet having a Zn diffusion layer manufactured in Example 2, the steel sheet temperature, and the carrier gas flow velocity at the time of collision with the plating layer. It is.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steel plate, 2 ... Snout, 3 ... Synchronous, 4 ... Plating bath, 5 ... Gas wiping nozzle, 6 ... Zn powder spray nozzle, 7 ... Heating device, 8 ... Payoff reel, 9 ... Annealing furnace, 10 ... Air jet cooler, 11 ... tension reel,

Continuation of the front page (72) Minoru Saito 5th Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Steel Research Laboratory Surface Treatment Research Department (56) References JP-A-63-143249 (JP, A) JP-A-61-104091 (JP, A) JP-A-58-3956 (JP, A) JP-A-62-253780 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 2 / 00-2/40

Claims (1)

(57) [Claims] Claims: 1. In the production of a hot-dip Al-coated steel sheet in which a steel sheet is plated in an Al-based plating bath and then the amount of plating is adjusted, Zn powder is added to the steel sheet while the plating layer is in an unsolidified state after the adjustment of the amount of plating. Flow velocity at the time of collision is 5-120m
A method for producing a hot-dip Al-plated steel sheet having a Zn diffusion layer, wherein the powder is sprayed together with a carrier gas at a rate of / sec to diffuse Zn powder into the plating layer.