JPH04356313A - Hot rolling method excellent in oxidation restraint effect - Google Patents

Abstract

PURPOSE:To restrain the oxidation of a rolled stock during hot rolling and to improve the yield by forming a bubble aggregate area composed of an aggregate of bubbles containing inert gas in the inner part and passing the rolled stock through that area in the hot rolling. CONSTITUTION:The bubbles aggregate area 12 composed of an aggregates of bubbles 10 in which inert gas obtained from interfacial active agent or interfacial active agent water solution is contained is formed in advance and when the rolled stock 14 is passed through the area 12 the cells in contact with the rolled stock 14 are broken. At this time, since the broken bubbles 10 contain the inert gas in their inner parts, the inner part of the aggregate forms an inert gas atmosphere and the rolled stock can be restrained from being oxidized.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a hot rolling method that has a great effect of suppressing oxidation of metal materials. Specifically, the present invention relates to a method of hot rolling that has a large oxidation suppressing effect on metal materials. Hot rolling has a large oxidation suppressing effect, preventing surface oxidation of metal materials (referred to as metal materials), suppressing yield loss due to surface oxidation during hot rolling, and making it possible to manufacture products with thin surface oxide films. Regarding the method.

0002

2. Description of the Related Art It is known that at high temperatures, metals such as Fe and Ti, other than metals that form protective oxide films such as Al, grow oxide films on their surfaces over time. For example, in the hot rolling process of steel materials, rolling is 800
Since the process was carried out at a high temperature of ~1100°C, the surface could not avoid being covered with an oxide film called scale. This scale is iron oxide (Fe20
It is known that the formation rate is extremely high at high temperatures.

[0003] If scale is present on the surface of the steel material during hot rolling, it may cause flaws, so first, before rough rolling, the scale generated in the heating furnace is removed before rolling. However, since the steel material is at a high temperature, it reoxidizes immediately after rolling, and the surface is covered with scale again. If left as is, this secondary scale will become stuck in the next rolling process and cause defects, so the scale must be removed before rolling. Therefore, in hot rolling, the phenomenon of descaling → scale formation → descaling → scale formation is repeated, and the iron matrix is oxidized and peeled off each time, resulting in poor product yield.

[0004]Furthermore, scales generated after finish rolling (during cooling) are removed during the next cold rolling process, etc.
Because it causes problems such as deterioration of surface quality and contamination of rolling oil, it is removed prior to cold rolling in a pickling process using hydrochloric acid or sulfuric acid, or in a mechanical descaling process such as shot blasting. However, this pickling process not only requires a large amount of equipment, but also requires a large amount of money for the acid used, waste acid treatment, and power, and there are also problems in that the yield of steel strips decreases due to overpickling. there were. Therefore, in order to deal with these problems, it is desired to reduce the scale generated during hot rolling as much as possible.

Conventionally, as seen in Japanese Patent Application Laid-Open No. 55-136502, a technique has been proposed in which a hot rolling material is covered with foam to prevent temperature drop and oxidation during the hot rolling process. FIG. 5 is a schematic explanatory diagram showing the technique proposed in this publication. In the figure, a situation is shown in which foam 44 is ejected from the foam ejectors 42, 42 onto the surface of the rolled material 40 being conveyed to cover the rolled material 40 with the foam 44. Furthermore, Japanese Patent Application Laid-open No. 63-256215 proposes a method in which hot steel material is brought into contact with foam formed from an aqueous solution containing a surfactant in order to cool it between rolling stands or after a final finishing mill. . To form bubbles, air or an inert gas such as nitrogen gas, or even a reducing gas may be blown into the aqueous solution, and in the case of an inert gas or reducing gas, an antioxidant effect is also exhibited. See the lower left column of page 5 of the above publication.

[0006]

[Problem to be solved by the invention] JP-A-55-1365
The technology disclosed in the No. 02 publication is as shown in FIG.
Foam 4 is applied to the slab 40, which is a material to be rolled at a high temperature of 00 to 1100°C, by a nozzle provided in a foam jetter 42.
4 is directly sprayed to cover the rolled material 40 with foam 44. In the illustrated example, air bubbles are sprayed from both the front and back surfaces of the slab 40 by the nozzle 42 . It can be thought of as a kind of coating with foam. However, in this method, when using bubbles that are stable at high temperatures, that is, bubbles formed by a surfactant, the bubbles coming out of the nozzle disappear as soon as they come into contact with the material to be rolled, and as a result, the material to be rolled becomes bubbles. It is impossible to wrap it up.

On the other hand, when using air bubbles that are stable at high temperatures, such as air bubbles for fire extinguishers, it is possible to cover the rolled material with the bubbles, but the air bubbles adhere to the rolled material and remains on the surface of the final product, so it is necessary to remove the foam residue in the next step before pickling. In addition, bubbles that are stable at such high temperatures are generally expensive, which poses an economic problem. Furthermore, this method has a problem in that when the bubbles are destroyed, the material to be rolled is oxidized by the oxygen contained in the gas inside the bubbles. Therefore, such means have never been put into practical use. That is, the methods that have been proposed so far cannot perform hot rolling continuously while effectively suppressing scale formation, and are currently not in practical use.

The first object of the present invention is to improve the yield of rolled materials in the hot rolling process, and to omit the oxide removal process by pickling or the like or to simplify it much more than before. It is an object of the present invention to provide a hot rolling method that can suppress oxidation of a rolled material in a rolling process and has a large oxidation suppressing effect. A second object of the present invention is to provide a hot rolling method that has a large oxidation suppressing effect, which can minimize oxidation of rolled materials by inexpensive and simple means in the continuous rolling process of metal or alloy materials. The purpose is to provide a method.

[0009]

[Means for Solving the Problems] As a result of various studies aimed at solving these problems, the present inventors found that foam can easily enter even complicated and narrow parts of the mechanism.
Focusing on the characteristic that there is no need to set up a special device to partition the bubble area since the substance remains a gas even after it disappears, we continued to experiment with its application and obtained the knowledge described in ■ and ■ below. , completed the invention.

[0010] By using bubbles that are rather unstable at high temperatures, such as surfactant foam, it is possible to prevent bubbles from adhering to the surface of the rolled material and remaining on the surface of the final product. ■ When such thermally unstable bubbles are directly sprayed onto the surface of a hot rolled material and brought into contact, the bubbles disappear immediately. However, instead of blowing directly, when an aggregate of the bubbles is formed and the material to be rolled passes through the aggregate, and the bubbles are not brought into direct contact with the material to be rolled, Although the bubbles disappear to some extent due to the radiant heat, the rate of their disappearance is extremely slow.

[0011] As mentioned above, instead of covering the hot rolled material with foam, for example, a high-temperature material is coated within a foam aggregate that has been prepared in advance by blowing an inert gas into an aqueous surfactant solution. By allowing the rolled material to pass through, the foam aggregate becomes a kind of tunnel-shaped sealing material and can effectively and reliably prevent oxidation of the rolled material. ■ N2 in this bubble
If an inert gas such as gas or Ar gas is introduced, an inert gas atmosphere will be created in the tunnel formed by the bubbles, thereby preventing oxidation of the material to be rolled. ■ Air bubbles that do not come into contact with the rolled material are slightly destroyed by the radiant heat from the rolled material. However, since this destruction speed is low, the bubble tunnel can be maintained by replenishing bubbles from the outside in the same amount as the destroyed bubbles.

[0012] The gist of the present invention is a hot rolling method for hot rolling a metal material in a hot rolling line equipped with a finishing rolling mill group and a cooling bed following it, which A cell aggregate region consisting of an aggregate of bubbles containing an inert gas inside obtained from an aqueous solution of a surfactant or surfactant is formed in advance, and during hot rolling, a metal or alloy material is coated in the cell aggregate region. This hot rolling method is characterized by passing the rolled material through the hot rolling method, which is highly effective in suppressing oxidation. In the present invention, the surfactant includes not only anionic surfactants and nonionic surfactants but also cationic surfactants. Anionic surfactants and nonionic surfactants are suitable for the present invention because they are resistant to heat, easily generate bubbles, and are difficult to eliminate. Further, the inert gas includes nitrogen gas, carbon dioxide gas, argon gas, and the like.

[0013]

[Operation] Next, the operation of the present invention will be explained in more detail with reference to the accompanying drawings. 1 and 2 are schematic explanatory diagrams conceptually showing the implementation status of the hot rolling method according to the present invention. 1 and 2 respectively show the conditions when the material to be rolled enters and passes through the bubble aggregate region. In both figures, a rolled material 14, which is a metal material, is passing through a cell aggregate region 12 consisting of an aggregate of bubbles 10 containing an inert gas inside, obtained using a surfactant.

According to the present invention, a region consisting of an aggregate of bubbles 10 as shown in FIG. Although the air bubbles 10 around the material 14 are destroyed, the air bubbles 10 in the area away from the material 14 to be rolled are not destroyed, and as shown in FIG.
A tunnel 20 of bubbles 10 as shown in FIG. That is, according to the present invention, the internal N2, A
Bubbles containing an inert gas such as r are generated, and a bubble aggregate region consisting of an aggregate of the bubbles is installed at a predetermined location on a hot rolling line.

As shown in FIG. 2, when the material to be rolled 14 is passed through the bubble aggregate region 12 made up of the aggregate of bubbles 10, the bubbles 10 in contact with the material to be rolled 14 are destroyed, and the bubbles 10 are destroyed. A tunnel 20 is formed. Since the destroyed bubble 10 contained an inert gas inside, the inside of the formed tunnel 20 becomes an inert gas atmosphere. Bubbles around the tunnel 20 are caused by radiant heat from the rolled material 14,
Alternatively, the bubbles are destroyed by contact with the rolled material 14, but once the tunnel 20 is formed, the bubbles burst at a sufficiently slow rate, so it is easy to replenish more bubbles than the amount destroyed. Therefore, while the material to be rolled passes through, a tunnel of bubbles whose interior is made of inert gas is formed and maintained, and it is possible to suppress oxidation of the material to be rolled.

According to a preferred embodiment of the present invention, the oxygen concentration inside the bubbles is set to 1% by volume or less, since if the oxygen concentration is higher than this, the oxidation suppressing effect on the rolled material will be insufficient. This is because there is a risk. FIG. 4 is a graph showing the relationship between the oxygen concentration in the inert gas atmosphere in the heating furnace and the thickness of the scale produced when a steel plate is oxidized for 30 seconds at various temperatures in the heating furnace. From this, it is recognized that the scale decreases rapidly when the oxygen concentration is 1% by volume or less, and it is clear that reducing the oxygen concentration to 1% by volume or less is effective in achieving the goal of thinning the scale. .

Next, according to the present invention, the locations where the bubble aggregation regions as described above are provided are not limited in any way; for example, between the exit side of the rough rolling mill group and the entry side of the finishing mill group, It may be within the rolling mill group, or further between the outlet side of the finishing rolling mill group and the water cooling device. In particular, it is desirable to provide the cooling bed in both sections between finishing rolling mill groups and in cooling beds after the finishing rolling mill group. This is because the inventors found that the areas where oxide scale is most likely to form are the finishing rolling mill group of the hot rolling mill group and the subsequent cooling stage. This is also because the temperature of the material is considerably lower, making it easier to form and maintain tunnels of air bubbles. Further, the area in which the bubble aggregate is formed in advance may be installed by simply blowing out bubbles into such area, or by providing a covering material to partition such a space, but the above-mentioned method may be used. Since the area in which the bubble aggregate is provided according to the present invention is originally a narrow area with a complicated mechanism, it is rather advantageous to be able to define such an area simply by blowing out the bubbles.

FIGS. 3(a) and 3(b) are a schematic sectional view and a schematic perspective view, respectively, showing the structure of an example of an apparatus capable of forming the bubble aggregate region 12 according to the present invention. In the apparatus shown in the figure, the material to be rolled 14 is passed through a water tank 30, and is placed at an appropriate position where the bubbles 10 generated in the water tank 30 can cover the upper and lower surfaces of the material to be rolled 14. Surfactant aqueous solution reservoirs 32, 34, and 36 (in the example shown in FIG. 3, the rolled material 14
) and the jet hole 38a
A plurality of pipes 38 (in the storage section) are provided in the longitudinal direction so that N2 gas can be blown into the surfactant aqueous solution. This device 30 is constructed by blowing an inert gas into the surfactant from the pipe 38 before use, so that a bubble aggregate region consisting of an aggregate of bubbles 10 made of the surfactant and containing an inert gas inside is produced. 12 may be formed in advance, and the material to be rolled 14 may be passed through the bubble aggregate region 12. According to this device, most of the inert gas used can be utilized as bubbles, which is efficient.

From the viewpoint of preventing oxidation, it is best to install this device in a high temperature range. However, since the degree of oxidation decreases quadratically as the temperature decreases, it is desirable to install it so that it can cover the entire material to be rolled as much as possible. Note that this figure 3(a) and figure 3
As an apparatus other than the apparatus shown in (b), for example, in the conventional apparatus shown in FIG. 5, it is also possible to provide a mesh at the tip of the nozzle and flow a mixed liquid of an inert gas and a surfactant aqueous solution. Incidentally, it is preferable that the material other than the cooling bed has a heat retention effect, but in the present invention, when the material to be rolled in a high temperature state passes through the bubble aggregate region, the surfactant does not come into direct contact with the material to be rolled. The material to be rolled is difficult to cool, and since the material to be rolled is surrounded by bubbles, the cooling effect due to convection of the surrounding air is also small. Therefore, it is desirable to cool the material to be rolled by appropriate means after passing through the bubble aggregate region. Next, the present invention will be explained in more detail with reference to examples thereof.

[0020]

[Example 1] In a steel plate hot rolling line, between a rough rolling mill and a finishing rolling mill (length 100 m, width 2500 m)
m) was filled with bubbles to form a bubble aggregate region, and a steel plate was passed through the bubble aggregate region to suppress oxidation of the steel plate during hot rolling. In this example, the bubbles were created using N2 gas (oxygen concentration 0.02%) in an aqueous solution (concentration 1%) of an anionic surfactant (Sunol LM1140T manufactured by Lion Corporation).
) was generated by supplying.

[0021] If the oxidation of the steel sheet is not suppressed during this period without generating bubbles, an oxide of about 70 μm will be formed on the surface, and this oxide scale will cause surface flaws, so finishing rolling is not necessary. had to be removed before. Descaling was performed by injecting high pressure water. In this case, the temperature of the steel plate was significantly lowered, resulting in a large energy loss. On the other hand, when bubbles are generated, the amount of oxide produced during this time can be suppressed to a thickness of 6 μm, and this thickness will not cause surface flaws, so finish rolling can be performed without removing oxides. was completed. therefore,
This eliminates the need for descaling, which saves energy. Furthermore, by suppressing oxidation in this part, the yield could be improved by about 0.5%.

[0022]

[Example 2] In a hot rolling line for steel plates, the area between the exit side of the finishing rolling mill and the water cooling device (length 10 m, thickness 2500 mm) is filled with bubbles to form a bubble aggregate area, and the steel plate was passed through to suppress oxidation of the steel sheet after hot rolling. In this example, bubbles were generated by supplying N2 gas (oxygen concentration 0.02%) to an aqueous surfactant solution of Sunol LM1140T (concentration 1%) as in Example 1.

If the oxidation of the steel sheet is not suppressed during this time without generating bubbles, an oxide of approximately 10 μm will be formed on the surface of the steel sheet after winding, and this oxidation will be removed in the pickling line of the next process. It took 2 minutes to remove the material. If bubbles are generated and oxidation is suppressed during this time, an oxide of approximately 6 μm will be generated on the surface of the steel sheet after winding, and in the pickling line of the next process, the oxide will be removed for 1 minute. That's good. Furthermore, the yield was improved by about 0.3% due to the reduction in oxide production.

[0024]

[Example 3] In a steel plate hot rolling line, air bubbles are filled between the mills of the finishing continuous rolling mill and between the mill outlet side and the water cooling device to form a bubble aggregate area, and the steel plate is passed through the air bubbles. This suppressed oxidation of the steel sheet during and after hot rolling. In this example, the bubbles are also Sunnor LM11
In a 40T surfactant aqueous solution (concentration 1%), N
It was generated by supplying two gases (oxygen concentration 0.02%). Conventionally, between mills, loopers etc. were installed in narrow spaces, resulting in a complicated structure, and it was impossible to provide a hard seal due to problems such as the rolled material being bitten incorrectly. Ta.

However, if bubbles are used as in the method of the present invention, the bubbles can enter even in places with complex structures, making it easy to seal, and even if troubles occur, the main body of the bubbles will remain intact. There were no problems because it was essentially gas and there were no facilities or structures. If the oxidation of the steel sheet is not suppressed during this time without generating bubbles, an oxide of approximately 10 μm will be formed on the surface of the steel sheet after winding, and this oxide will be removed in the pickling line in the next process. It took 2 minutes to do this. On the other hand, when bubbles are generated according to the present invention and oxidation is suppressed during this time, an oxide of about 3 μm is generated on the surface of the steel sheet after winding, and this oxide is removed in the pickling line in the next process. In order to do so, 0.
It was good for 5 minutes. Additionally, the yield was improved by about 0.5% due to the reduction in oxide production.

The above results are shown in Table 1 along with those of comparative examples.
are summarized in Further, according to the present invention, scale formation between mills is almost eliminated, so roll wear due to scale during rolling is reduced, and roll life is improved by 20%. In this example, only the results of the anionic type Sunnol LM1140T manufactured by Lion Corporation were shown as the surfactant, but even the nonionic type Livonocux NC120 manufactured by Lion Corporation was used.
It was confirmed that -W also has a scale generation inhibiting effect. It was also found that the household detergent Mummy Lemon (trade name) manufactured by Marufuku Cleanser Co., Ltd. was sufficiently effective.

[0027]

[Table 1]

[0028]

As described above, according to the present invention, it is possible to significantly improve the yield by suppressing oxidation during hot rolling, and also to omit or simplify the oxide film removal work in the next process. can be converted into

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing how a rolled material passes through a cooling bed after finish hot rolling provided with a bubble gathering region according to the present invention.

FIG. 2 is a schematic explanatory view showing how a rolled material passes through a cooling bed after finish hot rolling provided with a bubble gathering region according to the present invention.

FIG. 3 is a schematic explanatory diagram showing the configuration of an example of a device capable of forming a bubble aggregate region in the present invention, FIG. 3(a) is a schematic cross-sectional view, and FIG. 3(b) is a schematic perspective view. are shown respectively.

FIG. 4 is a graph showing the relationship between oxygen concentration in an inert gas atmosphere and scale thickness.

FIG. 5 is a schematic explanatory diagram of a conventional bubble blowing method.

[Explanation of symbols]

10: Bubbles 12:
Cell aggregate area 14: Rolled material
20: Tunnel 30: Water tank
32, 34, 36: Storage part 38: Pipe 38a: Spout hole 40:
Slab 42: Foam squirt device 4
4: Foam

Claims (1)

[Claims] Claim 1: A hot rolling method for hot rolling a metal material in a hot rolling line equipped with a group of finishing mills and a subsequent cooling bed, the method comprising: A bubble aggregate region consisting of an aggregate of bubbles containing an inert gas is formed in advance, and a metal or alloy material to be rolled is passed through the bubble aggregate region during hot rolling. , a hot rolling method with a large oxidation suppressing effect.