JPH0517881A - Manufacture of corrosion resistant hot rolled steel sheet - Google Patents

Abstract

PURPOSE:To economically manufacture a corrosion resistant hot rolled steel sheet having the plating layer of a zinc-aluminum alloy with good productivity. CONSTITUTION:Scales on the surface of a steel sheet finished with hot rolling are subjected to dry descaling in the process of recoiling, and the surface of the above steel sheet is sprayed with the powder of a zinc-aluminum alloy having 15 to 30% aluminum content in a required range when the temp. of the steel sheet lies in 200 to 300 deg.C to form a hot-dip coating layer in a required range of the steel sheet. In this way, its productivity and economicity are exceedingly improved compared to the case of the conventional hot-dip coating and electroplating.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a corrosion-resistant hot-rolled steel sheet having a zinc-aluminum alloy plating layer having a ball impact rating (hereinafter referred to as BI rating) of 2 or less, which indicates plating adhesion, with high productivity. , About the method of manufacturing economically.

[0002]

2. Description of the Related Art Conventionally, a method for plating a metal on a hot-rolled steel sheet or the like is, after hot-rolling, once cooled, pickled, and then dipped in a molten bath of plated metal for hot dipping, There is a method in which the pickled steel sheet is immersed in a solution containing a salt of a plating metal and electroplated by direct current electrolysis. However, both of these methods require large-scale pickling equipment and plating equipment, which not only requires a vast installation site, but the hot dipping method requires a heating device for steel sheets and its fuel. Since the method requires electric power for electrolysis and requires a large amount of equipment cost and energy cost, it is strongly desired to improve the overall economic efficiency. In order to meet the demand for this improvement, Japanese Patent Laid-Open Publication No. 54-146230 discloses that the thermal energy of the hot rolling process is utilized to spray a molten metal onto the outer surface of a rolled steel sheet that is running in the hot rolling process or the refining process. Then, there is a proposal to form a uniform plating layer on the surface of the steel material and economically perform metal plating with a small-scale facility. However, since this proposal does not remove the scale formed during hot rolling, it means that molten metal is sprayed on the scale,
As a result, the plating adhesion is poor, and if press working or the like is performed after manufacturing, the plating layer peels off and corrosion resistance deteriorates. In addition, in order to overcome these problems, the type of sprayed metal required, the steel plate temperature during spraying, the appropriate roughness of the steel plate surface to improve plating adhesion, and the hot rolling process for spraying Alternatively, there is no specific description about a desired position in the adjusting step, and specific implementation conditions for obtaining a plating layer that guarantees adhesion are neither disclosed nor suggested and are completely unknown.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art and uses an alloy of zinc and aluminum to form a corrosion-resistant hot-rolled steel sheet having a plated layer with good adhesion to the steel sheet. It is an object of the present invention to provide a method for economically manufacturing the product with reasonable equipment.

[0004]

In order to achieve the above-mentioned object, the present invention performs dry descaling on the surface of a hot-rolled steel sheet that has been rolled after rolling and is rewound during rolling back.
% By weight on the surface of the steel sheet in the temperature range of 0 ° C to 300 ° C
A method for producing a corrosion-resistant hot-rolled steel sheet, which comprises spraying an alloy powder of zinc and aluminum containing 15% or more and 30% or less of aluminum to form a plating layer in a required range on the surface of the steel sheet. As the first means,

The first means is characterized in that, after dry descaling, the conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed onto the required area of the steel sheet surface is a non-oxidizing atmosphere. The method for producing the corrosion-resistant hot-rolled steel sheet according to the second aspect,

[0006] The first means is characterized in that, after dry descaling, the conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed onto a required area of the steel sheet surface is a reducing atmosphere. The method for producing a corrosion-resistant hot-rolled steel sheet as

The hot rolled steel sheet wound after hot rolling is rewound through the unwinding and the surface of the steel sheet is dry-descaled to have a surface roughness Ra of 3 μm or more, and then 200 ° C. or more 30
Zinc-aluminum alloy powder having a grain size of 120 mesh or more and containing 15% or more and 30% or less by weight of aluminum is sprayed at a pressure of 0.05 MPa or more on the surface of the steel plate in a temperature range of 0 ° C. or less. A fourth method is a method for producing a corrosion-resistant hot-rolled steel sheet, which is characterized in that a plating layer is formed in a required range on the surface of the steel sheet.

A fourth means characterized in that after dry descaling, the conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed onto a required area of the steel sheet surface is a non-oxidizing atmosphere. The method for producing the corrosion-resistant hot-rolled steel sheet according to the fifth aspect,

A fourth means is characterized in that, after dry descaling, the conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed onto a required area of the steel sheet surface is a reducing atmosphere. The method for producing a corrosion-resistant hot-rolled steel sheet of No. 6 is the sixth means.

[0010]

In order to achieve the above-mentioned object, the present inventors have investigated the plating adhesion of corrosion-resistant hot-rolled steel sheets used in the market, and as a result, have found that the corrosion resistance is satisfactory in each application. Plating adhesion of hot-rolled steel sheet has a BI rating of 2
We have found that: The BI rating of 1 indicates the best plating adhesion, and the larger the value, the lower the plating adhesion. In order to elucidate the controlling factors of this plating adhesion, the present inventors have made a detailed investigation of the boundary between the surface of the base steel and the plating layer of the above-mentioned survey steel sheet, and as a result, the metal powder injected onto the steel sheet is superplastic flow It was found that they dig into the irregularities on the surface and adhere. The present inventors utilized the high temperature of the hot rolled steel sheet based on the above knowledge, and exposed the hot rolled steel sheet rolled after rolling by removing the scale of the hot rolled steel sheet surface during rewinding. The experiment of producing a plated steel sheet by injecting pure zinc and zinc-aluminum alloy powder on the surface of the base metal was repeated, and the findings of Fig. 1 were obtained. From FIG. 1, the present inventors have found that the steel plate temperature is in the range of 200 ° C. to 300 ° C.
It has been found that when a zinc-aluminum alloy powder containing 15% or more and 30% or less by weight of aluminum is sprayed onto the surface of the steel sheet, a plated steel sheet having a BI adhesion of 2 or less is obtained.

Further, it has been found that it is desirable to remove the scale and increase the roughness of the surface of the base metal at the same time as removing the scale. This is because the scale removes the plating layer directly on the base metal to improve the plating adhesion, and the metal powder sprayed on the surface of the base metal, which has a rough surface, bites into the irregularities on the surface of the base iron for an anchoring effect. This is because the adhesion of the plating layer brings about stability for a longer period of time. As a descaling method suitable for this, it was found that there are dry descaling methods such as shot blasting, grit blasting, brushing roll, and arc discharge.

[0012] In order for the metal powder sprayed on the irregularities of the surface of the base metal thus descaled to bite and melt to form a plating layer with good adhesion on the steel plate, it is necessary to collide the powder with a strong spraying pressure. I found out that there is. Therefore, after heating to 250 ° C., the surface roughness, powder particle size, and spraying pressure were changed variously on the surface of the hot-rolled steel sheet subjected to the various dry descaling described above, and the aluminum content was 25% by weight of 25% zinc. The alloy powder of aluminum was sprayed and the adhesion of each plating layer was evaluated by BI rating. The result is shown in FIG. From FIG. 2, the present inventors have found that the surface roughness is 3 μm or more in Ra value, the grain size of the alloy powder is 120 mesh or more, and the spray pressure is 0.05 MPa or more. It turned out that sex can be obtained.

Further, in order to obtain a plated layer having excellent adhesion,
The timing and atmosphere of spraying the plating metal powder are important, and it is desirable that the timing is immediately after descaling, that is, when descaling is completed and a new scale has not yet been generated. It is desirable that the steel sheet conveyance path between the two should be a non-oxidizing atmosphere using an inert gas such as argon or nitrogen, or a reducing atmosphere using hydrogen gas or a mixed gas of an inert gas and hydrogen gas. I got to know. The present invention is based on the above findings.

[0014]

EXAMPLES The present inventors implemented the present invention by installing a dry descaling device, a metal powder injecting device for plating, and an atmosphere gas injecting device between a hot-rolled steel sheet rewinding machine and a skin bath rolling machine. did. First, the coil of the hot-rolled steel sheet is rewound, the scale is removed by a dry descaling device and the roughness is adjusted, and then the metal powder for plating is sprayed on the surface of the steel plate by a spraying device in various atmospheres to make a skin pass. It was rolled. The chemical composition of the sample steel at that time in weight% is shown in Table 1, the hot rolling conditions, the descaling conditions, the distance when the plating metal is sprayed, and the atmospheric conditions are shown in Table 2, and the aluminum content and grain size of the plating metal. Table 3 shows the spray pressure, spray angle, spray time, spray thickness and steel plate temperature at that time, skin pass rolling conditions and plating adhesion.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

As is clear from Tables 2 and 3, the No. of the present invention satisfying all the conditions of the particle size of the powder, the surface roughness of the steel sheet and the powder spraying pressure of the plated metal, which are the requirements of claim 4, are satisfied. ．
1 to 7 show good plating adhesion showing a BI rating of 1,
An excellent corrosion resistant hot rolled steel sheet was obtained. In addition, No. 1 of the present invention example that satisfies all the requirements of claim 1. In Nos. 8 to 12, corrosion-resistant hot-rolled steel sheets having a BI adhesion rating of 2 were obtained.

On the other hand, the alloy powder of the requirement of claim 1 is out of the composition of No. Nos. 13 to 16 and Nos. Nos. 17, 18 and Nos. 1
In each of Comparative Examples 9 and 20, the plating adhesion was poor at 3 to 4, and the required corrosion resistance could not be obtained.

[0020]

As described above, according to the present invention, a hot-rolled steel sheet having a surface with high plating activity is sprayed with a zinc-aluminum alloy having a predetermined ratio for plating, so that good adhesion can be obtained. It becomes possible to economically produce a corrosion-resistant hot-rolled steel sheet having excellent corrosion resistance with good productivity, and not only the effect brought to the field of the art but also the ripple effect to the related fields is extremely large.

[Brief description of drawings]

FIG. 1 shows the relationship between the steel plate temperature before spraying a zinc-aluminum alloy powder for plating and the plating adhesion indicated by BI score.

FIG. 2 shows the relationship between the surface roughness Ra value of the hot steel plate temperature before spraying a zinc-aluminum alloy powder for plating and the plating adhesion shown by BI rating.

Claims (6)

[Claims] 1. A hot-rolled steel sheet rolled after hot rolling is dry-descaled on the surface of the hot-rolled steel sheet during unwinding and then the surface of the steel sheet in a temperature range of 200 ° C. or higher and 300 ° C. or lower is weighted. A method for producing a corrosion-resistant hot-rolled steel sheet, which comprises spraying a zinc-aluminum alloy powder containing 15% or more and 30% or less of aluminum to form a plating layer in a required range on the surface of the steel sheet. 2. The non-oxidizing atmosphere of the steel sheet after the dry descaling until the zinc-aluminum alloy powder is sprayed to a required range on the surface of the steel sheet. A method for producing a corrosion-resistant hot-rolled steel sheet according to. 3. The method according to claim 1, wherein after carrying out dry descaling, a conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed onto a required area of the steel sheet surface is made into a reducing atmosphere. A method for producing the corrosion-resistant hot-rolled steel sheet described. 4. A hot-rolled steel sheet wound after hot rolling is rewound through rewinding to make the surface of the steel sheet dry descale to have a surface roughness Ra of 3 μm or more, and then 200 ° C. or more 3.
Zinc-aluminium alloy powder having a grain size of 120 mesh or more and containing 15% or more and 30% or less by weight of aluminum is sprayed at a pressure of 0.05 MPa or more on the surface of the steel plate in a temperature range of 00 ° C or less. A method for producing a corrosion-resistant hot-rolled steel sheet, which comprises forming a plating layer on a required area of the steel sheet surface. 5. The non-oxidizing atmosphere of the steel sheet after the dry descaling, until the zinc-aluminum alloy powder is sprayed onto the surface of the steel sheet in a required range. A method for producing a corrosion-resistant hot-rolled steel sheet according to. 6. The method according to claim 4, wherein after carrying out dry descaling, the conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed to a required range on the surface of the steel sheet is a reducing atmosphere. A method for producing the corrosion-resistant hot-rolled steel sheet described.