JPH04314847A - Production of hot rolled plate of corrosion resisting steel - Google Patents

Abstract

PURPOSE:To economically produce a hot rolled plate of corrosion resisting steel having a plating layer composed, e.g. of a single metal, such as zinc, aluminum, and lead, or alloys thereof with superior productivity. CONSTITUTION:In the course between the completion of hot rolling and the coiling of a hot rolled steel plate, the scale on the surface of this steel plate is removed by means of dry descaling or high pressure water descaling and successively a metal powder, e.g. of single metal, such as zinc, aluminum, and lead, or alloys thereof is sprayed on the desired surface of the above steel plate at a steel-plate temp. higher by 30-200 deg.C than the melting point of the above metal powder, by which a hot dipping layer is formed on the desired surface of this steel plate. By this method, productivity and economical efficiency can remarkably be improved as compared with those of the conventional hot dipping and electroplating.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to zinc, aluminum,
The present invention relates to a method for producing a corrosion-resistant hot-rolled steel sheet in which a plating layer of a single metal such as lead or an alloy thereof is applied economically and with good productivity.

0002

[Prior Art] Conventionally, in order to plate hot-rolled steel sheets with metals such as zinc, the pickled sheets were cooled once after the hot-rolling process, and then the pickled sheets were immersed in a molten bath of metals such as zinc or alloys. The hot-dip plating method, in which the pickled plate is immersed in a solution containing the salt of the metal to be plated, and the electroplating method, in which DC electrolysis is performed, have been used. However, these methods require pickling equipment and large-scale plating equipment, requiring large equipment costs and a large installation space.In addition, hot-dip plating requires fuel costs to heat the steel plate, and electroplating However, since electricity costs are required for electrolysis, improvements in economic efficiency have been desired.

[0003] As a metal plating method that compensates for these drawbacks, Japanese Patent Application Laid-Open No. 146230/1983 discloses a method in which molten metal is sprayed onto the outer surface of a rolled steel material running in a hot rolling process or in a finishing line, and the surface layer of the steel material is coated with molten metal. A method of forming a uniform plating layer has been proposed. However, this method does not take into account the influence of scale formed during the hot rolling process, and when this method is implemented, the plating adhesion is poor because molten metal is sprayed over the scale. In the case of thin steel sheets that are subjected to press working or the like after manufacturing, the plating peels off after processing, resulting in poor corrosion resistance. In addition, in order to overcome these problems, the type of sprayed metal, the temperature of the steel plate during spraying, the appropriate roughness of the steel plate surface to improve adhesion, and the processing during the hot rolling process or finishing process during spraying. There is no description of desirable positions on the line, etc., and there is no disclosure or suggestion of specific conditions for obtaining a plating layer that guarantees practical adhesion.

0004

[Problems to be Solved by the Invention] The present invention provides a corrosion-resistant hot-rolled steel sheet with excellent corrosion resistance and having a plating layer with good plating adhesion made of a single metal such as zinc or its alloy.
Our goal is to provide a highly productive and economical manufacturing method using small-scale equipment.

[0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides dry descaling or high-pressure water descaling to remove scale on the surface of a steel plate after hot rolling, before winding up the steel plate. and continue to remove it using
A metal powder such as a single metal such as zinc, aluminum, or lead or an alloy thereof is injected onto a required surface of the steel plate at a steel plate temperature higher than the melting point of the metal powder in a range of 30°C or more and 200°C or less. The first method is to produce a corrosion-resistant hot-rolled steel sheet, which is characterized by forming a hot-dip coating layer on the required surface of the steel sheet. In addition to removing the scale using dry descaling or high pressure water descaling,
The surface roughness is set to 0.5 μm or more in Ra value, and then a metal powder of a single metal such as zinc, aluminum, lead or an alloy thereof or an alloy thereof with a particle size of 150 mesh or more is applied to the required surface of the steel plate at a temperature below the melting point of the metal powder. A second method of manufacturing a corrosion-resistant hot rolled steel sheet is characterized in that a hot-dip coating layer is formed on a required surface of the steel sheet by spraying at a high steel sheet temperature in the range of 30° C. or higher and 200° C. or lower. It is something to do.

[0006]

[Function] In order to achieve the above-mentioned problems, the present inventors focused on the high temperature of the steel sheet during the hot rolling process or after winding, and used the heat to coat the steel sheet with powder metal for plating. The following experiment was conducted on the premise that a plating layer would be formed by spraying and melting and utilizing the alloy reaction observed there.
We obtained the knowledge described below.

[0007] The inventors conducted experiments in which, after removing scale from hot rolled steel sheets heated to various temperatures, various metal powders such as pure zinc powder, pure aluminum powder, and zinc-aluminum alloy powder were injected. It is possible to form a plating layer with good adhesion when the temperature of the steel plate is 30°C or more higher than the melting point of the metal powder to be injected, and when the temperature of the steel plate is 200°C or more higher than the melting point. It was discovered that an oxidized layer develops, impairing the appearance, and making it impossible to control the amount of plating. Based on these findings, the temperature of the steel plate receiving the injection of metal powder should be set at 30℃ to 2℃ higher than the melting point of the powder.
It has been found that increasing the temperature to the 00°C range provides the heat of fusion to melt the powder and the heat to maintain the molten state for a sufficient period of time to cause the alloying reaction, and also prevents the development of an oxidized layer.

[0008] Metals forming a plating layer for corrosion-resistant use include zinc, aluminum, lead, an alloy of zinc and aluminum, and an alloy of zinc and iron with an iron content of about 5% by weight or less. The melting point of these metals is approximately 70°C above 327°C.
It is in the temperature range of about 0°C or less, and is 3° below the melting point of these.
The temperature range from 0℃ to 200℃ higher is the period from the end of finish rolling to the winding in the hot rolling process, and during that time, the injection position is determined based on the melting point of the metal used for injection, and the position that is most productive and economical. It's fine if you do this.

[0009] In addition, from the viewpoint of productivity and economy, as a pretreatment for plating, if there is scale between the plating layer and the base metal, it will easily peel off in that area and the adhesion of the plating will deteriorate. It is better to simultaneously remove scale to prevent this and optimize the roughness of the steel sheet surface to increase the contact area between the base steel and the plating layer to promote the alloying reaction. High-pressure water descaling or dry descaling that does not use a liquid is effective for this purpose, and specifically, shot blasting, grit blasting, brushing roll, vacuum arc discharge methods, etc. have been found to be effective for dry descaling. However, in the case of high-pressure water descaling, surface roughness is actively applied during the final finishing pass or under light pressure immediately after descaling, unless the final finishing pass gives a roughness of 0.5 μm or more. It's fine. In addition, if water remains on the steel plate after descaling, it will promote the generation of new scale and further impede the alloying reaction during powder injection. It is necessary to drain thoroughly.

Regarding the surface roughness of the steel sheet formed during descaling, a rougher surface roughness is preferable for improving plating adhesion, since the surface area becomes larger and alloying reactions are more likely to occur. In order to investigate the effect of the surface roughness of a steel plate on plating adhesion, Zn powder or Al powder with a particle size of 150 mesh or more was heated to a temperature of 30 to 200 °C higher than the melting point of the metal on a roughness-adjusted steel plate. We conducted an experiment to spray the liquid. Figure 1 shows an example of the results, and shows the experimental results when Zn powder was injected onto a steel plate 100°C higher than its melting point. Score of 1 based on impact test)
was obtained, sufficient plating adhesion was obtained, and Ra value was 0.3.
A BI rating of 2 was obtained at ~0.4 μm, and it was found that there was no problem in practical use. As for the above-mentioned BI rating, 1 indicates the best plating adhesion, and the larger the value, the worse the plating adhesion. For a corrosion-resistant hot-rolled steel sheet for processing purposes, it is most desirable to obtain a BI rating of 1.

[0011] In order to prevent the formation of new scale after descaling, it is necessary to inject powder immediately after descaling. Argon between descaling and powder injection.
It is more preferable to maintain it in a non-oxidizing or reducing atmosphere such as an inert gas atmosphere such as nitrogen, a mixed atmosphere of an inert gas and hydrogen, or a hydrogen atmosphere. In this case, it goes without saying that descaling or powder injection may be carried out in a non-oxidizing or reducing atmosphere.

Regarding the particle size of the metal powder to be sprayed, if the powder is too large, heat conduction will be poor and it will be difficult to melt, so it is better to use a small powder as long as it does not scatter and consume and does not require a large amount of pulverization cost. In order to investigate the effect of metal powder particle size on plating adhesion, Zn powder or Al powder was heated to a temperature 30 to 200°C higher than the melting point of the metal, and the surface roughness was roughened to 0.5 μm or more in terms of Ra value. An experiment was conducted in which the water was sprayed onto a steel plate whose temperature had been adjusted. Figure 2 shows an example of the results.
This shows the experimental results when Zn powder was injected onto a steel plate that was 100°C higher than its melting point, and it was found that if the particle size of the powder was 150 mesh or more, it would melt quickly and accurately.
A BI score of 1 was obtained, indicating that the plating adhesion was good, and even when the particle size was 50 or more and less than 150 mesh, a BI score of 2 was obtained, indicating that adhesion that did not cause any practical problems could be obtained.

[0013]

[Example] Various descaling devices and powder injection devices are installed between the finish rolling mill and the winding machine of a hot rolling line, and various descaling devices are used to remove scale and roughen the steel plate after finish rolling. After the temperature was adjusted, metal powder was injected using a powder injection device and the material was wound up. Table 1 shows the chemical composition of the steel type, and Table 2 shows the manufacturing conditions, plating adhesion, and corrosion resistance.

[0014]

[Table 1]

[0015]

[Table 2]

As is clear from Table 2, the present invention example No.
1 to 11, a BI rating of 1 was obtained, and a corrosion-resistant hot-rolled steel sheet with good plating adhesion and good corrosion resistance could be obtained. Moreover, No. 1 of the present invention example. In Nos. 12 to 18, the particle size of the powder or the surface roughness of the steel plate which is the requirement of claim 2 is not met, but all the requirements of claim 1 are satisfied, so a BI rating of 2 is obtained and the corrosion resistance is good. Corrosion-resistant hot-rolled steel sheets could be obtained. On the other hand, in No. 1, the lower limit temperature of the steel plate, which is a requirement of claim 1 of the present invention, was not met. 19, 21, 23, No. 1 where the upper limit temperature of the steel plate was exceeded. Comparative Examples Nos. 20, 22, and 24 all had poor plating adhesion, and it was not possible to obtain corrosion-resistant hot rolled steel sheets having the required corrosion resistance.

[0017]

[Effects of the Invention] According to the present invention as described above, a corrosion-resistant hot rolled steel sheet having a plating layer of a single metal such as zinc, aluminum, or lead or an alloy thereof can be produced with good plating adhesion using small-scale equipment. Since it becomes possible to produce it efficiently and economically, it has an extremely large industrial effect on the field of art.

[Brief explanation of drawings]

[Figure 1] The relationship between the surface roughness Ra value of the steel plate before spraying the plating metal powder and the plating adhesion indicated by the BI rating.
FIG. 2 shows a level of powder particle size.

FIG. 2 is a diagram showing the relationship between the particle size of the plating metal powder and the plating adhesion indicated by the BI rating using two levels of surface roughness Ra values.

Claims (2)

[Claims] [Claim 1] Before winding up a steel plate after hot rolling, scale on the surface of the steel plate is removed using dry descaling or high-pressure water descaling, and then monomers such as zinc, aluminum, and lead are removed. A hot-dip coating layer is formed on the desired surface of the steel sheet by injecting a metal powder such as one metal or an alloy thereof onto a desired surface of the steel sheet at a temperature higher than the melting point of the metal powder in the range of 30°C or more and 200°C or less. A method for producing a corrosion-resistant hot-rolled steel sheet, the method comprising: forming a corrosion-resistant hot-rolled steel sheet; 2. Before winding up the steel plate after hot rolling, scale on the surface of the steel plate is removed using dry descaling or high-pressure water descaling, and
The surface roughness is set to 0.5 μm or more in Ra value, and then a metal powder of a single metal such as zinc, aluminum, lead or an alloy thereof or an alloy thereof with a particle size of 150 mesh or more is applied to the required surface of the steel plate at a temperature below the melting point of the metal powder. A method for producing a corrosion-resistant hot-rolled steel sheet, which comprises forming a hot-dip coating layer on a desired surface of the steel sheet by spraying at a high steel sheet temperature in the range of 30° C. or higher and 200° C. or lower.