JPH04304353A - Production of corrosion resistant hot rolled steel sheet having excellent r value - Google Patents

Abstract

PURPOSE:To produce the hot dip metal coated steel sheet having excellent corrosion resistance by descaling the hot rolled steel sheet which is cast and hot rolled under specific temp. conditions, then spraying the fine powder of plating metals thereto. CONSTITUTION:The melt of a low-carbon steel contg., by weight%, 0.01 to 0.60% Mn and 0.001 to 0.012% S is cast and is cooled at >=5 deg.C/min cooling rate in a 1400 to 1200 deg.C temp. region. The finish hot rolling of the resulted slab is started within 60 minutes from the start of casting of the molten steel and is ended at the temp. above the Ar3 transformation point of this steel. The surface scale is removed by a dry method or a method for injecting high- pressure water, etc., without using acids before the hot rolled steel sheet is coiled to adjust the surface roughness Ra value to >=0.5mum. The powder of Zn, Al, Pb, etc., of >=150 meshes is then sprayed to the steel sheet surfaces of the hot rolled steel sheet heated to the temp. higher by 30 to 200 deg.C than the m.p. of these metals, by which the hot dip coating layers of these metals are produced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to zinc, aluminum,
Highly productive plating of single metals such as lead or their alloys,
The present invention relates to an economical method for producing a corrosion-resistant hot-rolled steel sheet for processing with an excellent ▲r▼ value.

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 electrolyzed with direct current, etc., 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 roughness during the hot rolling process or refining during the spraying process. 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.

On the other hand, regarding the improvement of the ▲r▼ value of hot rolled steel sheets, as described in Japanese Patent Application Laid-Open No. 59-226149,
A method for producing ultra-low carbon steel using Ti by oil-lubricated rolling,
Alternatively, there is a method of manufacturing by adding alloys such as Nb and Ti, as described in JP-A-62-192539. However, regarding the former, the rolling oil used for oil lubrication has a high concentration, and rolling itself is inevitably carried out under conditions at the very edge of the slip limit, and there are restrictions such as rolling temperature, rolling speed, and the size that can be rolled. A significant deterioration in production efficiency cannot be denied. Further, there is also the disadvantage that workability and productivity are poor because it requires time and effort to remove oil adhering to the rolls. On the other hand, regarding the latter, since alloys such as Nb and Ti are used, there is a problem that the alloy cost is high and it is not economical.

[0005]

[Problems to be Solved by the Invention] The present invention does not involve the above-mentioned problems, is economical, has good workability, and has a corrosion-resistant plating layer made of a single metal such as zinc or an alloy thereof and has good plating adhesion. An object of the present invention is to provide a method for producing a hot rolled steel sheet with high corrosion resistance and excellent ▲r▼ value.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides Mn: 0.10 to 0.60% by weight.
, S: 0.001 to 0.012%, and other Fe and other unavoidable components are cast and solidified in the temperature range of 1400°C to 1200°C at a cooling rate of ≧5.0°C/min to obtain a slab. Finish rolling of the slab is started within 60 minutes from the start of casting and completed at the Ar3 point or higher, and then the scale on the surface of the steel plate is removed by dry descaling or high-pressure water descaling until the steel plate is wound. At the same time, the surface roughness is set to 0.5 μm or more in terms of Ra value, and then a metal powder such as a single metal such as zinc, aluminum, or lead or an alloy thereof is applied to the required surface of the steel plate. A first method for producing 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 temperature of 30° C. or higher and 200° C. or lower than the melting point of the powder. Means, weight %, Mn: 0.10 to 0.60
%, S: 0.001 to 0.012%, and other Fe
and 1400°C to 1200°C for steel consisting of unavoidable components.
The slab is cast and solidified at a cooling rate of ≧5.0°C/min, and the slab is finished rolled for 60 minutes from the start of casting.
After starting within minutes and finishing at the Ar3 point or higher, the scale on the surface of the steel plate is removed using dry descaling or high-pressure water descaling, and the surface roughness is reduced to Ra. The value is 0.5 μm or more,
Subsequently, a metal powder such as a single metal such as zinc, aluminum, or lead 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 of 30°C or higher than the melting point of the metal powder.
The second means is a method for manufacturing a corrosion-resistant hot-rolled steel sheet, which is characterized in that a hot-dip coating layer is formed on a required surface of the steel sheet by spraying at a steel sheet temperature of 00° C. or lower.

[0007] Note that the hot-rolled steel sheet for processing in the present invention refers to
In the field of manufacturing and using hot-rolled steel sheets for processing, steels commonly used for such steel sheets, for example, C:
0.01% to 0.10%, Mn: 0.10% to 0.60
%, Si: 0.001-0.06% and P: 0.00
1% ~ 0.050%, S: 0.001% ~ 0.012%
This refers to steel that contains Fe and other unavoidable components.

[0008]

[Operation] In order to achieve the above-mentioned object, the present inventors conducted various experimental studies and obtained the following knowledge.

[0009] Steel having the above components is cast and solidified in the temperature range of 1400°C to 1200°C at a cooling rate of 5°C/min or more to form a slab, and finish rolling of the slab is started within 60 minutes from the start of solidification. However, when the rolling is finished below the Ar3 point, Mn
The amount of S that precipitates as S is ensured in a solid solution state until the rolling, and precipitates as fine MnS during the rolling,
The precipitated fine MnS suppresses austenite recrystallization and forms a fully developed austenite rolling texture, which transforms into ferrite with a high concentration of (112) planes, resulting in a steel sheet with a high ▲r▼ value. I found out what I can get.

[0010] On the other hand, the inventors conducted experiments in which various metal powders such as pure zinc powder, pure aluminum powder, and zinc-aluminum alloy powder were injected after removing scale from hot-rolled steel sheets heated to various temperatures. 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 if this happens, 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 that receives the injection of metal powder is set to 30°C higher than the melting point of the powder.
It has been found that increasing the temperature to a range of ˜200° C. provides the heat of fusion to melt the powder and maintain the molten state for a sufficient period of time to initiate the alloying reaction, while also preventing the development of an oxidized layer.

[0011] Metals forming a plating layer for corrosion-resistant purposes 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 turned out to be a good thing to do.

[0012] In addition, from the viewpoint of productivity and economy, as a pre-treatment 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 plate surface to increase the contact area between the base steel and the plating layer and 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, 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 the water sufficiently using gas.

Regarding the surface roughness of the steel plate formed during descaling, a coarser 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 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 2 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. A score of 1 was obtained in the impact test, and a score of 2 was obtained even at 0.3 to 0.4 μm, indicating that sufficient plating adhesion without any practical problems could be obtained. As for the Bl rating described above, 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 Bl rating of 1.

[0014] In order to prevent the formation of new scale after descaling, it is necessary to inject powder after descaling. It is more preferable to maintain a non-oxidizing or reducing atmosphere between descaling and powder injection, such as an inert gas atmosphere such as argon or 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 influence of the particle size of metal powder 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 adjusted to an Ra value of 0.5 μm or more. An experiment was conducted in which spraying was applied to a prepared steel plate. Figure 1 shows an example of the results, and Z
This shows the experimental results when N powder was injected onto a steel plate whose melting point was 100°C higher than the melting point of the B powder.
It was found that a Bl rating of 1 was obtained and the plating adhesion was good, and even with a Bl rating of 50 or more and less than 150 mesh, a Bl rating of 2 was obtained and adhesion that did not cause any practical problems was obtained.

[0016] By utilizing the above knowledge, the present invention has achieved the object.

[0017]

[Example] Steel having the chemical composition shown in Table 1 was manufactured under the hot rolling conditions shown in Table 2. Regarding metal powder injection, various devices were installed between the finishing mill and the winding machine of the hot rolling line. A powder injection device was installed in the scaling device, and various descaling devices were used to perform scale removal and roughness adjustment on the steel plate after finish rolling, after which metal powder was injected with the powder injection device and the sheet was wound up.

[0018]

[Table 1]

[0019]

[Table 2] (Note) ■ CCS: Casting cooling rate ■ FTO: Finish rolling start temperature ■ FTE: Finish rolling end temperature ■ MST: Time from start of solidification to start of rolling

00
Example 1 As shown in the invention examples in Table 3, a high r value hot rolled steel sheet with good plating adhesion and good corrosion resistance can be produced. but,
Compared to the inventive examples, Steel No. 5 had a cooling rate during solidification that was outside the lower limit of the invention, Steel No. 6 had a finish rolling finish temperature below the Ar3 point, and Steel No. 6 had a time from solidification to start of finish rolling that was outside the upper limit. Comparative examples of Steel No. 7 and Steel No. 8 in which S was outside the lower limit of the present invention had low ▲r▼ values of 0.90 or less.

[0021]

[Table 3] (Note) ■ DD refers to descaling method. S is shot blast. ■ The powder type is Zn. Particle size is 250 mesh. ■ Steel plate temperature is 600℃. Ra value is 5 μm. ■ Corrosion resistance was evaluated by SST, and ◎ means very good.

Example 2 As shown in Tables 4 and 5, the present invention example No. 1-11
In this case, a Bl 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 Bl rating of 2 is obtained and the corrosion resistance is good. We were able to obtain hot-rolled steel sheets. 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. In Comparative Examples 20, 22, and 24, the plating adhesion was poor, and it was not possible to obtain a corrosion-resistant hot-rolled steel sheet having the required corrosion resistance.

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

[Effects of the Invention] According to the present invention explained above, unlike the conventional method, alloys such as Ti and Nb are not used, and
Has a good ▲r▼ value without performing oil lubrication rolling, and
It is possible to apply plating layers of single metals such as zinc, aluminum, lead, etc. or their alloys economically with good adhesion and high productivity using small-scale equipment, which brings industrial benefits to the field. The effect is extremely large.

[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 Bl 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 Bl rating using two levels of surface roughness Ra values.

Claims (2)

[Claims] [Claim 1] Mn: 0.10 to 0.60 in weight%
%, S: 0.001 to 0.012%, and other Fe
and 1400°C to 1200°C for steel consisting of unavoidable components.
The slab is cast and solidified at a cooling rate of ≧5.0°C/min, and the slab is finished rolled for 60 minutes from the start of casting.
Start within minutes and finish at Ar3 point or above, and then remove scale on the surface of the steel plate using dry descaling or high-pressure water descaling before winding the steel plate, and then remove zinc, aluminum, lead, etc. A metal powder such as a single metal or an alloy thereof is injected onto a required surface of the steel plate at a steel plate temperature in a range of 30°C or more and 200°C or less than the melting point of the metal powder to melt it on the required surface of the steel plate. A method for producing a corrosion-resistant hot-rolled steel sheet, characterized by forming a plating layer. [Claim 2] Mn: 0.10 to 0.60 in weight%
%, S: 0.001 to 0.012%, and other Fe
and 1400°C to 1200°C for steel consisting of unavoidable components.
The slab is cast and solidified at a cooling rate of ≧5.0°C/min, and the slab is finished rolled for 60 minutes from the start of casting.
After starting within minutes and finishing at the Ar3 point or higher, the scale on the surface of the steel plate is removed using dry descaling or high-pressure water descaling, and the surface roughness is reduced to Ra. The value is 0.5 μm or more,
Subsequently, a metal powder such as a single metal such as zinc, aluminum, or lead 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 of 30°C or higher than 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 steel sheet temperature of 00° C. or lower.