KR19990051982A - Molten steel heating method and apparatus for vacuum circulating degassing equipment - Google Patents

Abstract

The present invention, unlike the conventional molten steel heating method in the RH facility, which is a vacuum circulating degassing facility, by heating by plasma, while preventing the deterioration of the cleanliness of the steel caused by the production of a large amount of alumina inclusions and now adhere to the vacuum chamber An object of the present invention is to provide a method and a device for properly raising the temperature of molten steel.

The molten steel temperature raising method is a molten steel refining method that flows molten steel in the ladle to the vacuum tank of the vacuum circulating degassing equipment, and degassing the molten steel, wherein a plasma torch is installed on the top or sidewall of the vacuum chamber during the degassing process. Characterized by heating molten steel; Also,

The apparatus is provided with a torch on the upper side or sidewall of the vacuum chamber in a vacuum circulating degassing facility which introduces molten steel into a rising tube deposited in the molten steel of the ladle, and vacuum degassing in the vacuum chamber and then refluxing the treated molten steel into a descending tube. And a driving means for moving the plasma torch up and down in the room.

Description

Molten steel heating method and apparatus for vacuum circulating degassing equipment

The present invention relates to a method and apparatus for vacuum degassing of molten steel, and more particularly, while ensuring cleanliness of molten steel in the process of refining molten steel in a vacuum circulating degassing plant, The present invention relates to a method of raising the temperature of molten steel for preventing the temperature drop of molten steel and an apparatus used for the temperature increase.

Generally, in the converter steelmaking process, after decarburization is performed in a converter, casting is performed after vacuum degassing for the purpose of manufacturing ultra low carbon steel, removing molten steel, inclusions in molten steel, and homogenizing components.

As such a vacuum degassing facility, various facilities such as DH, RH, and tank degasser have been developed, but as a typical facility, a vacuum circulating degassing device (hereinafter, referred to as 'RH') as shown in FIG. 1 is generally used. . One of the most important functions of this RH is the decarburization of undeoxidized molten steel.

The decarburization limit in the converter is about 200 ~ 300ppm, and if it is blown at a lower concentration than this, the evaporation of iron is large at the firing point, and the iron loss in the slag is not only increased due to the rapid oxidation of iron, but also the melting loss of the converter refractory. This becomes large. Therefore, RH treatment is effective to lower the carbon concentration to very low carbon concentration of 100 ppm or less.

The decarburization reaction in RH proceeds to the chemical reaction of [C] and [O] in molten steel as in Scheme 1.

[C] + [O] = CO (g)

That is, the carbon in the molten steel is removed by the CO gas generated by reacting with oxygen supplied from various oxygen sources such as oxygen or iron ore, oxygen gas, etc. in the molten steel by the chemical reaction of Scheme 1.

Another important function of the RH treatment for molten steel is to introduce hydrogen, nitrogen in the vacuum vessel 3 while refluxing the molten steel 1 in the ladle 2 into the riser 4a and then refluxing it into the downcomer 4b. In order to manufacture clean steel by removing gas components such as the like and inducing mutual collision and aggregation of inclusions present in the molten steel to rise to the upper portion of the molten steel.

On the other hand, the molten steel temperature during the degassing treatment in the RH drops not only by heat transfer to the ladle refractory and the vacuum chamber refractory in contact with the molten steel, but also by the gas discharged into the vacuum chamber, thereby greatly decreasing. In particular, during the decarburization treatment, the temperature drop is very large due to the large amount of CO gas generated by the decarburization reaction. If the temperature of the molten steel is lower than the temperature required in the post process, that is, the playing process, the playing operation may not be performed smoothly. Therefore, some RH facilities are equipped with an oxygen blowing device into the molten steel and a temperature raising function in order to smoothly flow the process and reduce the temperature load in the converter.

In general, the elevated temperature treatment of molten steel in RH is performed by using heat of oxidation of Al, as shown in FIG. That is, Al is added to the molten steel and oxygen gas is blown into the molten steel from the nozzles 5 and 15 provided on the side wall of the vacuum chamber 103 to oxidize Al in the steel as shown in Equation 2 to increase the temperature using the heat generated at this time. Do the processing.

2 [Al] + 3 [O] = Al ₂ O ₃ (s)

ΔH ^o = 74,148 kcal / kg-Al

In addition, the oxygen blown into the molten steel generates heat as well as the oxidation of Al in Scheme 2 while partially oxidizing elements such as silicon and manganese in the steel. Therefore, a large amount of oxides such as alumina are generated during the temperature raising process in RH. These oxides float to the upper part of the slag due to the difference in specific gravity with the molten steel during the RH treatment, but the oxides remaining in some molten steels have a fatal effect on the quality of the product. Therefore, if the oxide inclusions are not produced and the heat escaped during the RH treatment is compensated, or if the temperature is increased, the cleanliness of the molten steel can be improved, and the product can be further advanced.

As described above, the conventional heating treatment in RH uses the heat of oxidation of aluminum, so that the apparatus and the heating treatment are relatively simple. However, since a large amount of expensive aluminum is used, the processing cost increases. More importantly, the alumina inclusions produced in large quantities deteriorate the cleanliness of molten steel, which can have a detrimental effect on the quality of the product. In addition, it can adversely affect the productivity and operability by providing a cause of nozzle clogging in the production operation.

In addition, the RH treatment now adheres and grows inside the vacuum chamber, preventing the release of the gas during the degassing treatment, thereby reducing the refining efficiency and causing the incorporation of impurities such as carbon in the manufacture of ultra low carbon steel. Therefore, if the current grows to some extent, the attached current must be removed, which lowers the productivity of the RH facility and increases the work load, thereby hampering the production efficiency. Therefore, if the current is prevented from adhering and growing inside the vacuum chamber, the refractory can be kept clean and the refractory life can be improved, and the removal operation can be reduced now, thereby reducing the cost.

Therefore, the present invention, unlike the conventional molten steel heating method in the RH facility, which is a vacuum circulating degassing facility, by heating by plasma, deterioration of the cleanliness of the steel due to the production of a large amount of alumina inclusions and now attached in the vacuum chamber. It is an object of the present invention to provide a method capable of properly raising the temperature of molten steel while preventing it and an apparatus used therefor.

1 is a cross-sectional configuration of a general vacuum circulating degassing equipment

Figure 2 is a cross-sectional configuration of the vacuum circulation degassing equipment equipped with a temperature raising device of the present invention

Figure 3 is a cross-sectional configuration of the vacuum circulating degassing equipment with another heating device of the present invention

Figure 4 is a graph showing the temperature of molten steel according to the treatment time at the time of elevated temperature according to the present invention

Figure 5 is a graph showing the change in the amount of oxygen in the molten steel according to the treatment time at the time of heating the molten steel according to the conventional

Brief description of the drawings

1 ..... molten steel 2 ...... ladle 3 ...... vacuum chamber

4a ..... riser 4b ..... downcomer 5 ..... nozzle

6, 7 ...... Plastic Torch 8 ...... Drive

9 ...... Torch Room

In the present invention for achieving the above object in the refining method of the molten steel for degassing the molten steel by introducing the molten steel in the ladle into the vacuum tank of the vacuum circulation degassing facility,

The present invention relates to a molten steel heating method of a vacuum circulating degassing apparatus for heating a molten steel during a degassing process by installing a plasma torch on the top or sidewall of the vacuum chamber.

In addition, the present invention in the vacuum circulating degassing equipment for introducing the molten steel into the rising pipe deposited in the molten steel of the ladle to vacuum degassing treatment in the vacuum chamber and reflux the treated molten steel into the down pipe,

It relates to a molten steel heating apparatus of a vacuum degassing facility composed of a plasma torch built into the torch chamber and a driving means for moving the plasma torch up and down.

First, the molten steel heating apparatus of the present invention will be described in detail with reference to the drawings.

The molten steel heating apparatus of the present invention is introduced into the rising pipe (4a) deposited in the molten steel (1) of the ladle (2) by vacuum degassing treatment in the vacuum tank (3) As long as the vacuum circulation degassing facility which refluxs molten steel to the downcomer 4b, it can be applied to any facility. 2 shows a case where the plasma torch 6 is attached to the upper portion of the vacuum chamber 3.

In addition, the plasma torch may be installed in the side wall portion of the vacuum chamber 3, and FIG. 3 shows a molten steel heating apparatus provided with the plasma torch 7 provided in the side wall portion of the vacuum chamber 3.

The plasma torch (6) (7) is water-cooled is suitable, and when installed on the upper side is advantageous because the device is simple, the direct current transfer method is preferred. In addition, when installing on the side wall of a vacuum chamber, you may use the DC-type transfer system or the three-phase alternating current system. In the case of Fig. 3, a three-phase AC plasma torch that generates a high output is more preferable.

When installed in the side wall portion of the vacuum chamber, the plasma torch is installed at intervals of about 120 degrees and installed downward toward the molten steel.

The plasma torch of the present invention moves to the upper portion when the temperature increase processing is not performed by the driving means 8 in the torch chamber 9 and descends to generate the plasma when the temperature increase is necessary. At this time, the plasma energy depends on the installation capacity, but in the case of the present invention is about 1 ~ 10MW is suitable.

Hereinafter, the molten steel temperature raising method of the present invention using the temperature raising device will be described in detail.

First, the converter refining is completed and the RH facility, which is a vacuum circulating degassing facility equipped with the temperature raising device, is deposited on the molten steel received on the ladle. In applying the temperature raising method of the present invention, the target steel grade is not particularly limited, and when applied to steels requiring high cleanliness,

desirable.

When the degassing process starts, while injecting an inert gas such as argon, current flows to each plasma torch 6, 7 so as to ignite and heat up the molten steel. The heating degree and the heating time of the torch during the temperature increase process can be determined by looking at the temperature drop of the steel grade and the molten steel.

According to the present invention, the plasma arc heat is directly transmitted to the molten steel to heat the molten steel, which is very advantageous for the production of the clean steel without degrading the cleanliness of the molten steel. In addition, by keeping the sidewall in the vacuum chamber at a high temperature by the radiant heat of the plasma arc, it is possible to prevent the current adhesion and growth thereof.

Hereinafter, the present invention will be described in detail through examples.

Example 1

In a RH facility in which a three-phase alternating current plasma torch was installed in a vacuum chamber side of a 300 ton vacuum circulating degassing facility, the temperature was increased from 5 minutes after the start of treatment using plasma energy during the degassing process. The target molten steel was Al deoxidation ultra low carbon steel and the plasma output was 5.5MW. The result of comparing the molten steel temperature with the case without the temperature increase treatment is shown in FIG. 4.

As shown in FIG. 4, the temperature of the molten steel decreases when the temperature increase is not performed, whereas the temperature of the molten steel gradually increases when the plasma temperature increase process is performed. During the decarburization of the ultra low carbon steel, a temperature increase effect of about 0.5 ° C. per minute and about 0.8 to 1.0 ° C. during refluxing was obtained.

Example 2

Except for using the Al-Si deoxidation molten steel, the molten steel was heated in the same manner as in Example 1, and the transition time according to the treatment time with respect to the total amount of oxygen in the molten steel is shown in FIG. 5 is a comparison between the case of plasma heating in the molten steel and the case of heating up by Al and oxygen blowing.

As shown in FIG. 5, when Al oxygen is blown as in the conventional method, the amount of oxygen in the molten steel is increased and then decreased after 3 to 11 minutes. In other words, after the RH treatment, the oxygen content was somewhat higher than when arriving at the RH facility.

On the other hand, in the case of plasma heating according to the present invention, since oxygen is not supplied at all, the amount of oxygen in the steel is continuously decreased, and thus, after the RH treatment, it can be seen that it contains oxygen lower than the total oxygen at the arrival of the RH facility. .

As described above, in the present invention, when the molten steel in the ladle is introduced into the vacuum chamber to perform the degassing of molten steel to the RH facility, which is a vacuum circulation degassing facility, a plasma torch is installed on the upper side or the sidewall of the vacuum chamber. By heating the molten steel using plasma energy during the gas treatment, the temperature can be raised without the generation of a large amount of alumina inclusions generated during the temperature raising process by normal oxygen injection, that is, without degrading the cleanness of the molten steel. In addition to being very advantageous for steel production, by keeping the side wall in the vacuum chamber at a high temperature by the radiant heat of the plasma arc, it prevents the current adhesion, thereby reducing the cost as well as improving the workability.

Claims (2)

In the refining method of the molten steel in which the molten steel in the ladle flows into the vacuum tank of the vacuum circulation degassing equipment to degas the molten steel, A molten steel heating method of a vacuum circulating degassing apparatus characterized by installing a plasma torch on the top or sidewall of the vacuum chamber to heat molten steel during degassing. In the vacuum circulating degassing equipment for introducing the molten steel into the rising pipe deposited in the molten steel of the ladle, vacuum degassing treatment in the vacuum chamber and then refluxing the treated molten steel into the down pipe, The molten steel heating apparatus of the vacuum degassing facility, characterized in that it comprises a plasma torch built into the torch chamber of the upper or side wall of the vacuum chamber and driving means for moving the plasma torch up and down.